Showing 1–50 of 87 results for author: Ito, T

Beam experiments for reactive ion etching of silicon (Si)-based materials by silicon halide ions

Authors: Kazuhiro Karahashi, Tomoko Ito, Satoshi Hamaguchi

Abstract: Etching yields of Si, SiO2, and Si3N4 have been determined for silicon ion (Si+), halogen ions (F+, Cl+, and Br+) and silicon halide ions (SiF+, SiF3+, SiCl+, SiCl3+, SiBr+, and SiBr3+) irradiation in 300 to 1000 eV using a mass-selected ion beam apparatus that can irradiate a single species ion to sample surfaces under an ultra-high vacuum condition. Si+ irradiation below 1000eV deposits silicon… ▽ More Etching yields of Si, SiO2, and Si3N4 have been determined for silicon ion (Si+), halogen ions (F+, Cl+, and Br+) and silicon halide ions (SiF+, SiF3+, SiCl+, SiCl3+, SiBr+, and SiBr3+) irradiation in 300 to 1000 eV using a mass-selected ion beam apparatus that can irradiate a single species ion to sample surfaces under an ultra-high vacuum condition. Si+ irradiation below 1000eV deposits silicon atoms on Si, SiO2, and Si3N4 surfaces. The etching yields of silicon tri-halide ions (SiF3+, SiCl3+, and SiBr3+) above 1000 eV are larger than those of halogen ions, respectively, and these etching yields depend on the incident ion energy and the etching material (especially Si3N4). At low incident energy, silicon mono-halide ions (SiF+, SiCl+, and SiBr+) deposit silicon on substrates, and the etching threshold energy depends on the halogen species. This information contributes to a database of experimental values needed to increase the precision of an etching process and a profile simulator. △ Less

Submitted 8 August, 2026; originally announced August 2026.

Demonstration of 255-kV high-voltage generation with a Cavallo multiplier system

Authors: S. M. Clayton, T. M. Ito, A. Jacobs, A-T. Le, M. F. Makela, C. M. O'Shaughnessy, N. S. Phan, E. Renner, T. A. Sandborn, T. J. Schaub, I. L. Smythe, J. Surbrook, M. A. Blatnik, B. W. Filippone

Abstract: Many cryogenic precision measurements require large electric fields in environments where conventional high-voltage feedthroughs are impractical. To address this, we developed a Cavallo electrostatic multiplier designed for in situ high-voltage generation under such conditions. Here, we report a room-temperature demonstration of this device. Using a mechanically translated transfer electrode and a… ▽ More Many cryogenic precision measurements require large electric fields in environments where conventional high-voltage feedthroughs are impractical. To address this, we developed a Cavallo electrostatic multiplier designed for in situ high-voltage generation under such conditions. Here, we report a room-temperature demonstration of this device. Using a mechanically translated transfer electrode and a custom rotary field mill for noncontact voltage measurement, the system reached output voltages up to approximately $255~\mathrm{kV}$ from a $25~\mathrm{kV}$ DC-biased input voltage in approximately $600~\mathrm{Torr}$ of SF$_6$. The charging curves are quantitatively described by a capacitance-based model once realistic electrode misalignment is included. Voltage-hold measurements show picoampere-scale leakage currents on long time scales, whereas operation near the maximum voltage is limited by transient discharge processes associated with electrode surface condition and local field enhancement, rather than by the intrinsic dielectric strength of the gas. These results demonstrate the Cavallo multiplier as a viable low-current, in situ high-voltage source and indicate that electrode surface preparation, alignment tolerances, and insulation performance are the principal requirements for reliable operation in future cryogenic implementations. △ Less

Submitted 13 July, 2026; originally announced July 2026.

Comments: 17 pages, 12 figures

Report number: LA-UR-26-24570

Approximate reservoir computing with a semiconductor laser for reducing energy consumption

Authors: Tatsuki Ito, Kazutaka Kanno, Satoshi Kawakami, Atsushi Uchida

Abstract: Photonic reservoir computing is a promising physical machine-learning technique for predicting time-series data. The quantization of the response signal from the reservoir is required for the implementation of photonic reservoir computing, and the number of quantization bits and sampling frequency need to be optimized to achieve high performance and low energy consumption. However, few studies hav… ▽ More Photonic reservoir computing is a promising physical machine-learning technique for predicting time-series data. The quantization of the response signal from the reservoir is required for the implementation of photonic reservoir computing, and the number of quantization bits and sampling frequency need to be optimized to achieve high performance and low energy consumption. However, few studies have been reported to investigate the effect of bit quantization and sampling frequency. In this study, we introduce a concept of approximate reservoir computing with a semiconductor laser by quantizing the amplitude of node states in the reservoir and output weights. We evaluate the performance of a chaotic time-series prediction task and energy consumption per sample. We achieve significant reduction of energy consumption by optimizing the number of quantization bits, the sampling frequency, and the injection current of the semiconductor laser, while maintaining the prediction performance. △ Less

Submitted 25 July, 2026; originally announced July 2026.

Comments: 9 pages, 10 figures, 3 tables

Electrode Design for a Cavallo High Voltage Multiplier in a Cryogenic nEDM Experiment

Authors: Marie A. Blatnik, Steven M. Clayton, Bradley W. Filippone, Takeyasu M. Ito, Nguyen S. Phan, Christopher M. O'Shaughnessy, John C. Ramsey

Abstract: The Cavallo multiplier [http://archive.org/details/b28771035_0003] is an electrostatic inductance machine that can generate low-noise high voltages electrically isolated from its voltage input, making it ideally suited for precision experiments. Its in-situ production makes it especially useful in cryogenic experiments, where the use of traditional feedthroughs is challenging due to thermal, elect… ▽ More The Cavallo multiplier [http://archive.org/details/b28771035_0003] is an electrostatic inductance machine that can generate low-noise high voltages electrically isolated from its voltage input, making it ideally suited for precision experiments. Its in-situ production makes it especially useful in cryogenic experiments, where the use of traditional feedthroughs is challenging due to thermal, electrical, magnetic, and physical size considerations. One such experiment is a cryogenic measurement of the neutron electric dipole moment (nEDM) [arXiv:1908.09937,arXiv:2512.14975], which requires several hundred kilovolts on a measurement cell electrode in 0.4 K liquid helium (LHe). A Cavallo multiplier can generate this voltage by stepping up a smaller input (e.g., 50 kV) from a feedthrough. We designed Cavallo electrodes using finite element analysis to provide high voltage gain and low probability of electrical breakdown in the experimental apparatus. The final geometry achieves a gain of 18, providing a target of 650 kV with peak electric fields of 116 kV/cm distributed over small areas to limit breakdown risk. △ Less

Submitted 11 April, 2026; originally announced April 2026.

Few-picosecond pulse generation featuring ultrafast spectral dynamics in gain-switched surface-grating DFB lasers via impulsive optical pumping

Authors: Yihan Qi, Fuyi Cao, Hidekazu Nakamae, Changsu Kim, Masataka Kobayashi, Cong Wang, To-Fan Pan, Shaoqiang Chen, Takashi Ito, Hidefumi Akiyama

Abstract: To investigate the physics of picosecond gain-switching dynamics in single-mode lasers under femtosecond optical pumping at room temperature, we designed and fabricated first-order surface-grating GaAs distributed-feedback (DFB) lasers with five systematically varied grating periods (120-124 nm), corresponding to lasing wavelengths of 825.7-849.5 nm (1.502-1.459 eV). The 124-nm-period device, clos… ▽ More To investigate the physics of picosecond gain-switching dynamics in single-mode lasers under femtosecond optical pumping at room temperature, we designed and fabricated first-order surface-grating GaAs distributed-feedback (DFB) lasers with five systematically varied grating periods (120-124 nm), corresponding to lasing wavelengths of 825.7-849.5 nm (1.502-1.459 eV). The 124-nm-period device, closest to the quantum-well gain peak among the investigated devices, exhibited the highest output power and spectral bandwidth. Among all devices, the 122-nm-period DFB laser (838.2 nm, 1.480 eV) generated the shortest pulses, despite lasing at a higher photon energy and lower output power than the device closest to the gain peak. All devices exhibited characteristic down-chirp behavior that increased with excitation power. The shortest pulses had a chirped pulse width of 6.6 ps and a chirp rate of 0.13 meV/ps, whereas spectrally resolved measurements revealed a minimum pulse width of 3.8 ps (2.3 ps after deconvolution of the detection time resolution) near the central photon energy of the pulse spectrum. Numerical simulations revealed temporally and spatially resolved dynamics of photons, carriers, gain, and refractive index, reproducing the experimental results qualitatively and quantitatively. Furthermore, a mechanism for generating the shortest pulses at photon energies above the gain peak was identified and attributed to higher differential gain, saturation gain, and a higher transparency carrier density in the high-energy region of the gain spectrum. These experimental and theoretical results elucidate the intrinsic dynamics of picosecond pulse generation in gain-switched DFB lasers and provide design guidance for short-pulse generation and computational tools applicable to both optical and electrical pumping. △ Less

Submitted 2 April, 2026; originally announced April 2026.

Comments: 15 pages, 10 figures, Submitted to Photonics Research

High voltage and electrode system for a cryogenic experiment to search for the neutron electric dipole moment

Authors: M. A. Blatnik, S. M. Clayton, S. A. Currie, B. W. Filippone, M. Makela, C. M. O'Shaughnessy, N. S. Phan, J. C. Ramsey, G. V. Riley, A. Roberts, T. Sandborn, T. J Schaub, G. M. Seidel, E. Smith, I. L. Smythe, J. Surbrook, W. Wei, W. Yao, T. M. Ito

Abstract: The cryogenic approach to the search for the neutron electric dipole moment--performing the experiment in superfluid liquid helium--holds promise for a substantial increase in sensitivity, potentially enabling a sensitivity level of $10^{-28}$ e-cm. A crucial component in realizing such an experiment is the high voltage and electrode system capable of providing an electric field of 75 kV/cm. This,… ▽ More The cryogenic approach to the search for the neutron electric dipole moment--performing the experiment in superfluid liquid helium--holds promise for a substantial increase in sensitivity, potentially enabling a sensitivity level of $10^{-28}$ e-cm. A crucial component in realizing such an experiment is the high voltage and electrode system capable of providing an electric field of 75 kV/cm. This, in turn, requires an electric potential of 635 kV to be applied to the high voltage electrode, while simultaneously satisfying other experimental constraints, such as those on heat load and magnetic noise requirements. This paper describes the outcome of a comprehensive development program addressing these challenges. It outlines the system requirements, discusses new insights into relevant physical phenomena, and details selected technical solutions with their corresponding experimental demonstrations and expected performance. The results collectively demonstrate the successful development of the necessary technology for the high-voltage and electrode system for this approach. △ Less

Submitted 16 December, 2025; originally announced December 2025.

Comments: 20 pages, 17 figures, 1 table

Report number: LA-UR-25-31563

Journal ref: Phys. Rev. C 113, 045503 (2026)

BIC slow light waveguides based on interband coupling

Authors: Sae R. Endo, Yuta Tanimura, Takahiro Ito, Kenta Takata, Takahiro Uemura, Masaya Notomi, Satoshi Iwamoto, Yasutomo Ota

Abstract: Harnessing bound states in the continuum (BICs) for guiding light in leaky environments has unlocked new possibilities in photonic integrated circuits. BIC confinement enables low-loss waveguiding of leaky transverse-magnetic (TM) modes in etchless waveguides based on dielectric wires loaded on plane slabs. We have recently reported BIC slow light waveguides by introducing one-dimensional photonic… ▽ More Harnessing bound states in the continuum (BICs) for guiding light in leaky environments has unlocked new possibilities in photonic integrated circuits. BIC confinement enables low-loss waveguiding of leaky transverse-magnetic (TM) modes in etchless waveguides based on dielectric wires loaded on plane slabs. We have recently reported BIC slow light waveguides by introducing one-dimensional photonic crystals into such etchless waveguides. However, they were restricted to a high-symmetry point ($X$ point), limiting their applicability. In this Letter, we propose and numerically demonstrate BIC slow light waveguides at off-high-symmetry points by exploiting Friedrich-Wintgen BICs, arising from the interband coupling of two guided modes sharing a radiation continuum. We identified a systematic approach for tuning the loss minimum position in momentum space and simultaneously achieved a high group index over $100$ and a low propagation loss of less than $5 \times 10^{-2}~\mathrm{dB/cm}$ at an off-high-symmetry point. Our findings pave the way for advanced control of light-matter interactions in non-Hermitian photonic systems. △ Less

Submitted 25 September, 2025; originally announced September 2025.

Comments: 4 pages, 4 figures

Detection of ultracold neutrons with powdered scintillator screens

Authors: M. Krivos, N. C. Floyd, C. L. Morris, Z. Tang, M. Blatnik, S. M. Clayton, C. B. Cude-Woods, A. Fratangelo, A. T. Holley, D. E. Hooks, T. M. Ito, C. -Y. Liu, M. Makela, M. R. Martinez, A. S. C. Navazo, C., M. O'Shaughnessy, R. W. Pattie, E. L. Renner, T. A. Sandborn, T. J. Schaub, M. Singh, I. L. Smythe, F. W. Uhrich, N. K. Washecheck , et al. (2 additional authors not shown)

Abstract: Zinc sulfide (ZnS:Ag) scintillators coated with a thin 10B layer are widely used for ultracold neutron (UCN) detection, but their application is limited by long decay times and significant phosphorescence. We investigated two possible replacement scintillators: yttrium aluminum perovskite (YAP:Ce) and lutetium ttrium orthosilicate (LYSO:Ce). Both exhibit decay times on the order of 30-40 ns, which… ▽ More Zinc sulfide (ZnS:Ag) scintillators coated with a thin 10B layer are widely used for ultracold neutron (UCN) detection, but their application is limited by long decay times and significant phosphorescence. We investigated two possible replacement scintillators: yttrium aluminum perovskite (YAP:Ce) and lutetium ttrium orthosilicate (LYSO:Ce). Both exhibit decay times on the order of 30-40 ns, which can help reduce dead time in high-count-rate experiments. YAP:Ce showed approximately 60% lower phosphorescence than ZnS:Ag after 2 days and detected about 20% more UCN. In contrast, LYSO:Ce exhibited higher phosphorescence and produced fewer UCN counts compared to both ZnS:Ag and YAP:Ce. While both tested scintillators are capable UCN detectors, YAP:Ce consistently outperformed LYSO:Ce across all measured performance metrics. △ Less

Submitted 14 January, 2026; v1 submitted 4 September, 2025; originally announced September 2025.

High-harmonic generation during ultrafast melting of a Mott insulating state

Authors: Ryohei Ikeda, Yuta Murakami, Daiki Sakai, Tatsuya Miyamoto, Toshimitsu Ito, Hiroshi Okamoto

Abstract: Solids in an intense laser field show high-harmonic generation (HHG), which can provide information on carrier dynamics and band structures in weakly correlated systems. In strongly correlated systems, a laser field can induce a transition between the various electronic phases formed by the entanglement of charge, spin, and orbital degrees of freedom via carrier generation. The HHG accompanying th… ▽ More Solids in an intense laser field show high-harmonic generation (HHG), which can provide information on carrier dynamics and band structures in weakly correlated systems. In strongly correlated systems, a laser field can induce a transition between the various electronic phases formed by the entanglement of charge, spin, and orbital degrees of freedom via carrier generation. The HHG accompanying this process can reflect information on the nonequilibrium electronic-state dynamics along the oscillating field-an aspect that remains unresolved to date. Here, we show that an intense mid-infrared (MIR) pulse induces melting of a Mott-insulator state in a one-dimensional cuprate, Sr2CuO3, the evolution of which leaves a trace in the HH spectra. When the electric-field amplitude exceeds 6 MV/cm, carriers are efficiently generated and each harmonic frequency decreases from odd multiples of the MIR frequency. Dynamical mean-field theory (DMFT) presents a possibility that these redshifts originate from a series of electronic-structure reconstructions in each electric-field cycle during the melting of the Mott-insulator state, which modifies the radiation phase from carrier recombination cycle-by-cycle. This phenomenon is negligible in rigid-band systems. This experimental-theoretical study suggests that HH spectroscopy has the potential to obtain information on the cycle-by-cycle dynamics of nonequilibrium transitions in correlated materials. △ Less

Submitted 13 August, 2026; v1 submitted 31 July, 2025; originally announced August 2025.

Three-dimensional crustal deformation analysis using physics-informed deep learning

Authors: Tomohisa Okazaki, Takeo Ito, Kazuro Hirahara, Ryoichiro Agata, Masayuki Kano, Naonori Ueda

Abstract: Earthquake-related phenomena such as seismic waves and crustal deformation impact broad regions, requiring large-scale modeling with careful treatment of artificial outer boundaries. Physics-informed neural networks (PINNs) have been applied to analyze wavefront propagation, acoustic and elastic waveform propagations, and crustal deformation in semi-infinite domains. In this study, we investigated… ▽ More Earthquake-related phenomena such as seismic waves and crustal deformation impact broad regions, requiring large-scale modeling with careful treatment of artificial outer boundaries. Physics-informed neural networks (PINNs) have been applied to analyze wavefront propagation, acoustic and elastic waveform propagations, and crustal deformation in semi-infinite domains. In this study, we investigated the capability of PINNs for modeling earthquake crustal deformation in 3-D structures. To improve modeling accuracy, four neural networks were constructed to represent the displacement and stress fields in two subdomains divided by a fault surface and its extension. Forward simulations exhibited high accuracy for internal deformation but yielded errors for rigid motions, underscoring the inherent difficulty in constraining static deformation at an infinite distance. In the inversion analysis, fault slip distributions were estimated using surface observational data. Application to real data from the 2008 Iwate-Miyagi inland earthquake showed a fault slip consistent with previous studies, despite underestimation of the magnitude. This study demonstrates the capability of PINNs to analyze 3-D crustal deformation, thereby offering a flexible approach for large-scale earthquake modeling using real-world observations and crustal structures. △ Less

Submitted 2 July, 2025; originally announced July 2025.

SILVIA: Ultra-precision formation flying demonstration for space-based interferometry

Authors: Takahiro Ito, Kiwamu Izumi, Isao Kawano, Ikkoh Funaki, Shuichi Sato, Tomotada Akutsu, Kentaro Komori, Mitsuru Musha, Yuta Michimura, Satoshi Satoh, Takuya Iwaki, Kentaro Yokota, Kenta Goto, Katsumi Furukawa, Taro Matsuo, Toshihiro Tsuzuki, Katsuhiko Yamada, Takahiro Sasaki, Taisei Nishishita, Yuki Matsumoto, Chikako Hirose, Wataru Torii, Satoshi Ikari, Koji Nagano, Masaki Ando , et al. (4 additional authors not shown)

Abstract: We propose SILVIA (Space Interferometer Laboratory Voyaging towards Innovative Applications), a mission concept designed to demonstrate ultra-precision formation flying between three spacecraft separated by 100 m. SILVIA aims to achieve sub-micrometer precision in relative distance control by integrating spacecraft sensors, laser interferometry, low-thrust and low-noise micro-propulsion for real-t… ▽ More We propose SILVIA (Space Interferometer Laboratory Voyaging towards Innovative Applications), a mission concept designed to demonstrate ultra-precision formation flying between three spacecraft separated by 100 m. SILVIA aims to achieve sub-micrometer precision in relative distance control by integrating spacecraft sensors, laser interferometry, low-thrust and low-noise micro-propulsion for real-time measurement and control of distances and relative orientations between spacecraft. A 100-meter-scale mission in a near-circular low Earth orbit has been identified as an ideal, cost-effective setting for demonstrating SILVIA, as this configuration maintains a good balance between small relative perturbations and low risk for collision. This mission will fill the current technology gap towards future missions, including gravitational wave observatories such as DECIGO (DECihertz Interferometer Gravitational wave Observatory), designed to detect the primordial gravitational wave background, and high-contrast nulling infrared interferometers like LIFE (Large Interferometer for Exoplanets), designed for direct imaging of thermal emissions from nearby terrestrial planet candidates. The mission concept and its key technologies are outlined, paving the way for the next generation of high-precision space-based observatories. △ Less

Submitted 3 September, 2025; v1 submitted 7 April, 2025; originally announced April 2025.

Comments: 10 pages, 6 figures, accepted for publication in Publications of the Astronomical Society of Japan

Initial acquisition requirements for optical cavities in the space gravitational wave antennae DECIGO and B-DECIGO

Authors: Yuta Michimura, Koji Nagano, Kentaro Komori, Kiwamu Izumi, Takahiro Ito, Satoshi Ikari, Tomotada Akutsu, Masaki Ando, Isao Kawano, Mitsuru Musha, Shuichi Sato

Abstract: DECIGO (DECi-hertz Interferometer Gravitational Wave Observatory) is a space-based gravitational wave antenna concept targeting the 0.1-10 Hz band. It consists of three spacecraft arranged in an equilateral triangle with 1,000 km sides, forming Fabry-Pérot cavities between them. A precursor mission, B-DECIGO, is also planned, featuring a smaller 100 km triangle. Operating these cavities requires u… ▽ More DECIGO (DECi-hertz Interferometer Gravitational Wave Observatory) is a space-based gravitational wave antenna concept targeting the 0.1-10 Hz band. It consists of three spacecraft arranged in an equilateral triangle with 1,000 km sides, forming Fabry-Pérot cavities between them. A precursor mission, B-DECIGO, is also planned, featuring a smaller 100 km triangle. Operating these cavities requires ultra-precise formation flying, where inter-mirror distance and alignment must be precisely controlled. Achieving this necessitates a sequential improvement in precision using various sensors and actuators, from the deployment of the spacecraft to laser link acquisition and ultimately to the control of the Fabry-Pérot cavities to maintain resonance. In this paper, we derive the precision requirements at each stage and discuss the feasibility of achieving them. We show that the relative speed between cavity mirrors must be controlled at the sub-micrometer-per-second level and that relative alignment must be maintained at the sub-microradian level to obtain control signals from the Fabry-Pérot cavities of DECIGO and B-DECIGO. △ Less

Submitted 10 December, 2025; v1 submitted 17 March, 2025; originally announced March 2025.

Comments: 16 pages, 4 figures

Report number: RESCEU-3/25

Journal ref: Classical and Quantum Gravity 42, 225027 (2025)

Picosecond imaging of dynamics of solvated electrons during femtosecond laser-induced plasma generation in water

Authors: Noritaka Sakakibara, Tsuyohito Ito, Yukiya Hakuta, Yoshiki Shimizu, Kazuo Terashima, Eisuke Miura

Abstract: The dynamics of solvated electrons were visualized using absorption imaging with sub-picosecond time resolution based on a pump-probe measurement during the early stages of femtosecond laser-induced plasma generation in water. The solvated electrons were generated by the propagation of a femtosecond laser pump pulse. In the area with a pump laser intensity over 2x10^13 W/cm2, where a high density… ▽ More The dynamics of solvated electrons were visualized using absorption imaging with sub-picosecond time resolution based on a pump-probe measurement during the early stages of femtosecond laser-induced plasma generation in water. The solvated electrons were generated by the propagation of a femtosecond laser pump pulse. In the area with a pump laser intensity over 2x10^13 W/cm2, where a high density of free electrons was produced, solvated electrons exhibited an additional rapid increase in optical density (OD) at 800 nm, 7-9 ps after the pump pulse excitation. In contrast, no two-step increase in OD was observed when probed at 400 nm, suggesting that the absorption coefficient of the solvated electrons rapidly changed around 800 nm after femtosecond laser excitation for a few picoseconds. This observation might indicate the structural and electronic modulation of solvated electrons owing to the high density of free electrons in water, accompanied by femtosecond-laser-induced plasma generation. △ Less

Submitted 25 February, 2025; originally announced February 2025.

Comments: 25 pages, 7 figures

Journal ref: J. Chem. Phys. 162, 084302 (2025)

Distinguishing Ion Dynamics from Muon Diffusion in Muon Spin Relaxation II -- Extension to Paramagnetic Muons

Authors: Ryosuke Kadono, Takashi U. Ito

Abstract: We extend the previously published model that distinguishes between the diffusive motion of diamagnetic muons and the dynamics of ions around the muon in matter, and propose a generalized model for {\sl paramagnetic muons} (Mu$^0$s, bound states of a muon and an unpaired electron) observed in non-metallic host materials. The new model distinguishes among the independent motion of unpaired electron… ▽ More We extend the previously published model that distinguishes between the diffusive motion of diamagnetic muons and the dynamics of ions around the muon in matter, and propose a generalized model for {\sl paramagnetic muons} (Mu$^0$s, bound states of a muon and an unpaired electron) observed in non-metallic host materials. The new model distinguishes among the independent motion of unpaired electron associated with Mu$^0$, the self-diffusive motion of Mu$^0$ as single atomic entity, and that of the ions surrounding Mu$^0$, where the muon spin relaxation is induced by dynamical fluctuations of the hyperfine (HF) field exerted from the unpaired electron (e.g., due to spin/charge exchange reaction) and/or that of the nuclear hyperfine (NHF) interactions between the unpaired electron and the surrounding ions. We have applied this model to the muonated radicals (Mu$^0$s in a polaron state) in conducting polymers, and examined the validity of the interpretations claimed in the earlier literature that the spin relaxation is induced by quasi-one dimensional motion of the unpaired electron. The result suggests that experimental support for such a claim is still inadequate and needs to be reexamined, including the possibility of other origins for the fluctuations. It is expected that our model will prove a useful guide for $μ$SR studies of various local dynamics involving paramagnetic muon states. △ Less

Submitted 1 May, 2025; v1 submitted 30 October, 2024; originally announced October 2024.

Comments: 10 pages, 13 figures

Journal ref: J. Phys. Soc. Jpn. 94, 064601 (2025)

A practical approach to calculating magnetic Johnson noise for precision measurements

Authors: N. S. Phan, S. M. Clayton, Y. J. Kim, T. M. Ito

Abstract: Magnetic Johnson noise is an important consideration for many applications involving precision magnetometry, and its significance will only increase in the future with improvements in measurement sensitivity. The fluctuation-dissipation theorem can be utilized to derive analytic expressions for magnetic Johnson noise in certain situations. But when used in conjunction with finite element analysis… ▽ More Magnetic Johnson noise is an important consideration for many applications involving precision magnetometry, and its significance will only increase in the future with improvements in measurement sensitivity. The fluctuation-dissipation theorem can be utilized to derive analytic expressions for magnetic Johnson noise in certain situations. But when used in conjunction with finite element analysis tools, the combined approach is particularly powerful as it provides a practical means to calculate the magnetic Johnson noise arising from conductors of arbitrary geometry and permeability. In this paper, we demonstrate this method to be one of the most comprehensive approaches presently available to calculate thermal magnetic noise. In particular, its applicability is shown to not be limited to cases where the noise is evaluated at a point in space but also can be expanded to include cases where the magnetic field detector has a more general shape, such as a finite size loop, a gradiometer, or a detector that consists of a polarized atomic species trapped in a volume. Furthermore, some physics insights gained through studies made using this method are discussed △ Less

Submitted 13 September, 2024; v1 submitted 15 July, 2024; originally announced July 2024.

Report number: LA-UR-24-27277

Journal ref: J. Appl. Phys. 136, 124901 (2024)

Current-readout technique for ultra-high-rate experiments

Authors: Maki Wakata, Shoei Akamatsu, Takuhiro Fujiie, Taisei Furuyama, Lisa Hara, Yumi Ishikawa, Tadashi Ito, Takahiro Kikuchi, Tsutomu Mibe, Sachi Ozaki, Mitsuhiko Yokomizo, Jiro Murata

Abstract: This study developed a new current-readout technique capable of handling measurements with high count rates reaching 1 Gcps. By directly capturing the output current of a photomultiplier as a digitized waveform, we estimated event rates, overcoming the limitations imposed by pulse pileup constraints and deadtimes. This innovative method was applied to a muon spin rotation/relaxation/resonance expe… ▽ More This study developed a new current-readout technique capable of handling measurements with high count rates reaching 1 Gcps. By directly capturing the output current of a photomultiplier as a digitized waveform, we estimated event rates, overcoming the limitations imposed by pulse pileup constraints and deadtimes. This innovative method was applied to a muon spin rotation/relaxation/resonance experiment at the Japan Proton Accelerator Research Complex, demonstrating its anticipated performance. Furthermore, we explored methods for estimating statistical uncertainty and investigated potential applications in analog-logic OR/AND gates. Overall, our findings reveal that the developed technique opens up avenues for the development of future non-binary logic circuits operating based on n-adic numbers. △ Less

Submitted 17 January, 2025; v1 submitted 10 June, 2024; originally announced June 2024.

YAP:Ce scintillator as an absolute ultracold neutron detector

Authors: M. Krivoš, Z. Tang, N. Floyd, C. L. Morris, M. Blatnik, C. Cude-Woods, S. M. Clayton, A. T. Holley, T. M. Ito, C. -Y. Liu, M. Makela, I. F. Martinez, A. S. C. Navazo, C. M. O'Shaughnessy, E. L. Renner, R. W. Pattie, A. R. Young

Abstract: The upcoming UCNProBe experiment at Los Alamos National Laboratory will measure the $β$-decay rate of free neutrons with different systematic uncertainties than previous beam-based neutron lifetime experiments. We have developed a new $^{10}$B-coated YAP:Ce scintillator whose properties are presented. The advantage of the YAP:Ce scintillator is its high Fermi potential, which reduces the probabili… ▽ More The upcoming UCNProBe experiment at Los Alamos National Laboratory will measure the $β$-decay rate of free neutrons with different systematic uncertainties than previous beam-based neutron lifetime experiments. We have developed a new $^{10}$B-coated YAP:Ce scintillator whose properties are presented. The advantage of the YAP:Ce scintillator is its high Fermi potential, which reduces the probability for upscattering of ultracold neutrons, and its short decay time, which is important at high counting rates. Birks' coefficient of YAP:Ce was measured to be ($5.56^{+0.05}_{-0.30})\times 10^{-4}$ cm/MeV and light losses due to 120 nm of $^{10}$B-coating to be about 60%. The loss of light from YAP:Ce due to transmission through deuterated polystyrene scintillator was about 50%. The efficiency for counting neutrons that are captured on the $^{10}$B coating is (86.82 $\pm$ 2.61)%. Measurement with ultracold neutrons showed that YAP:Ce crystal counted 8% to 28% more UCNs compared to ZnS screen. This may be due to an uneven coating of $^{10}$B on the rough surface. △ Less

Submitted 27 March, 2024; originally announced May 2024.

Thermoelectric transport properties of the quasi-one-dimensional dimer-Mott insulator $β'$-(BEDT-TTF)$_2$ICl$_2$

Authors: Kyohei Eguchi, Takeru Ito, Yoshiki J. Sato, Ryuji Okazaki, Hiromi Taniguchi

Abstract: Low-dimensional materials, in which the electronic and transport properties are drastically modified in comparison to those of three-dimensional bulk materials, yield a key class of thermoelectric materials with high conversion efficiency. Among such materials, the organic compounds may serve peculiar properties owing to their unique molecular-based low-dimensional structures with highly anisotrop… ▽ More Low-dimensional materials, in which the electronic and transport properties are drastically modified in comparison to those of three-dimensional bulk materials, yield a key class of thermoelectric materials with high conversion efficiency. Among such materials, the organic compounds may serve peculiar properties owing to their unique molecular-based low-dimensional structures with highly anisotropic molecular orbitals. Here we present the thermoelectric transport properties of the quasi-one-dimensional dimer-Mott insulator $β'$-(BEDT-TTF)$_2$ICl$_2$, where BEDT-TTF stands for bis(ethylenedithio)-tetrathiafulvalene. We find that the thermopower exhibits typical activation-type temperature variation expected for insulators but its absolute value is anomalously large compared to the expected value from the activation-type temperature dependence of the electrical resistivity. Successively, the Jonker-plot analysis, in which the thermopower is usually scaled by the logarithm of the resistivity, shows an unusual relation among such transport quantities. We discuss a role of the low dimensionality for the enhanced thermopower along with recent observations of such a large thermopower in several low-dimensional materials. △ Less

Submitted 29 April, 2024; originally announced April 2024.

Comments: 7 pages, 5 figures. Accepted for publication in Phys. Rev. Materials

Journal ref: Phys. Rev. Materials 8, 055402 (2024)

Development of Two-Dimensional Neutron Imager with a Sandwich Configuration

Authors: Y. Kamiya, R. Nishimura, S. Mitsui, Z. Wang, C. L. Morris, M. Makela, S. M. Clayton, J. K. Baldwin, T. M. Ito, S. Akamatsu, H. Iwase, Y. Arai, J. Murata, S. Asai

Abstract: We have developed a two-dimensional neutron imager based on a semiconductor pixelated sensor, especially designed for experiments measuring of a spatial and a temporal behavior of quantum bound states of ultra-cold neutrons. Through these measurements, we expect to measure the ratio between the inertial and gravitational masses of neutrons and to test the equivalence principle in the quantum regim… ▽ More We have developed a two-dimensional neutron imager based on a semiconductor pixelated sensor, especially designed for experiments measuring of a spatial and a temporal behavior of quantum bound states of ultra-cold neutrons. Through these measurements, we expect to measure the ratio between the inertial and gravitational masses of neutrons and to test the equivalence principle in the quantum regime. As one of the principal neutron imagers, we fabricated a sensor with a sandwich configuration, named 10B-INTPIX4-sw, and tested its response to ultra-cold neutrons at the Los Alamos Neutron Science Center (LANSCE). We observed simultaneous events on both sandwiching sensors without significant loss of detection efficiency. The efficiency was evaluated to be about 16%, relative to the 10B/ZnS reference detector. The coincidence condition reduces its efficiency by a factor of about 3. △ Less

Submitted 19 April, 2024; originally announced April 2024.

IceCube -- Neutrinos in Deep Ice The Top 3 Solutions from the Public Kaggle Competition

Authors: Habib Bukhari, Dipam Chakraborty, Philipp Eller, Takuya Ito, Maxim V. Shugaev, Rasmus Ørsøe

Abstract: During the public Kaggle competition "IceCube -- Neutrinos in Deep Ice", thousands of reconstruction algorithms were created and submitted, aiming to estimate the direction of neutrino events recorded by the IceCube detector. Here we describe in detail the three ultimate best, award-winning solutions. The data handling, architecture, and training process of each of these machine learning models is… ▽ More During the public Kaggle competition "IceCube -- Neutrinos in Deep Ice", thousands of reconstruction algorithms were created and submitted, aiming to estimate the direction of neutrino events recorded by the IceCube detector. Here we describe in detail the three ultimate best, award-winning solutions. The data handling, architecture, and training process of each of these machine learning models is laid out, followed up by an in-depth comparison of the performance on the kaggle datatset. We show that on cascade events in IceCube above 10 TeV, the best kaggle solution is able to achieve an angular resolution of better than 5 degrees, and for tracks correspondingly better than 0.5 degrees. These performance measures compare favourably to the current state-of-the-art in the field. △ Less

Submitted 24 October, 2023; originally announced October 2023.

Scintillation characteristics of the EJ-299-02H scintillator

Authors: N. Floyd, Md. T. Hassan, Z. Tang, M. Krivos, M. Blatnik, S. M. Clayton, C. Cude-Woods, A. T. Holley, T. M. Ito, B. A. Johnson, C. -Y. Liu, M. Makela, C. L. Morris, A. S. C. Navazo, C. M. O'Shaughnessy, E. L. Renner, R. W. Pattie, A. R. Young

Abstract: A study of the dead layer thickness and quenching factor of a plastic scintillator for use in ultracold neutron (UCN) experiments is described. Alpha spectroscopy was used to determine the thickness of a thin surface dead layer, and the relative light outputs from the decay of $^{241}$Am and Compton scattering of electrons were used to extract the quenching parameter. With these characteristics of… ▽ More A study of the dead layer thickness and quenching factor of a plastic scintillator for use in ultracold neutron (UCN) experiments is described. Alpha spectroscopy was used to determine the thickness of a thin surface dead layer, and the relative light outputs from the decay of $^{241}$Am and Compton scattering of electrons were used to extract the quenching parameter. With these characteristics of the material known, the light yield of the scintillator can be calculated. The ability to make these scintillators deuterated, accompanied by its relatively thin dead layer, make it ideal for use in UCN experiment, where the light yield of decay electrons and alphas from neutron capture are critical for counting events. △ Less

Submitted 27 March, 2024; v1 submitted 29 September, 2023; originally announced October 2023.

Melting of excitonic insulator phase by an intense terahertz pulse in Ta$_2$NiSe$_5$

Authors: Naoki Takamura, Tatsuya Miyamoto, Ryohei Ikeda, Tetsushi Kubo, Masaki Yamamoto, Hiroki Sato, Yang Han, Takayuki Ito, Tetsu Sato, Akitoshi Nakano, Hiroshi Sawa, Hiroshi Okamoto

Abstract: In this study, the optical response to a terahertz pulse was investigated in the transition metal chalcogenide Ta$_2$NiSe$_5$, a candidate excitonic insulator. First, by irradiating a terahertz pulse with a relatively weak electric field (0.3 MV/cm), the spectral changes in reflectivity near the absorption edge due to third-order optical nonlinearity were measured and the absorption peak character… ▽ More In this study, the optical response to a terahertz pulse was investigated in the transition metal chalcogenide Ta$_2$NiSe$_5$, a candidate excitonic insulator. First, by irradiating a terahertz pulse with a relatively weak electric field (0.3 MV/cm), the spectral changes in reflectivity near the absorption edge due to third-order optical nonlinearity were measured and the absorption peak characteristic of the excitonic phase just below the interband transition was identified. Next, by irradiating a strong terahertz pulse with a strong electric field of 1.65 MV/cm, the absorption of the excitonic phase was found to be reduced, and a Drude-like response appeared in the mid-infrared region. These responses can be interpreted as carrier generation by exciton dissociation induced by the electric field, resulting in the partial melting of the excitonic phase and metallization. The presence of a distinct threshold electric field for carrier generation indicates exciton dissociation via quantum-tunnelling processes. The spectral change due to metallization by the electric field is significantly different from that due to the strong optical excitation across the gap, which can be explained by the different melting mechanisms of the excitonic phase in the two types of excitations. △ Less

Submitted 11 September, 2023; originally announced September 2023.

Comments: 66 pages, 11 figures, 2 tables

Dynamic complex opto-magnetic holography

Authors: Michal Makowski, Jaroslaw Bomba, Antoni Frej, Mateusz Kolodziejczyk, Maciej Sypek, Tomoyoshi Shimobaba, Tomoyoshi Ito, Andrei Kirilyuk, Andrzej Stupakiewicz

Abstract: Computer-generated holograms with their animated, three-dimensional appearance have long appealed to our imagination as the path towards truly immersive displays with bi-directional natural parallax. Impressive progress in updateable 3-D imagery has been achieved with liquid crystal modulators and high-resolution, but quasi-static holograms are being recorded in photosensitive materials. However,… ▽ More Computer-generated holograms with their animated, three-dimensional appearance have long appealed to our imagination as the path towards truly immersive displays with bi-directional natural parallax. Impressive progress in updateable 3-D imagery has been achieved with liquid crystal modulators and high-resolution, but quasi-static holograms are being recorded in photosensitive materials. However, the memory requirements and computational loads of real-time, large-area holography will be hard to tackle for several decades to come with the current paradigm based on a matrix calculations and bit-plane writing. Here, we experimentally demonstrate a conceptually novel, holistic approach to serial computation and repeatable writing of computer-generated dynamic holograms without Fourier transform, using minimal amounts of computer memory. We use the ultrafast opto-magnetic recording of holographic patterns in a ferrimagnetic film with femtosecond laser pulses, driven by on-the-fly hardware computation of a single holographic point. The intensity-threshold nature of the magnetic medium allows sub-diffraction-limited, point-by-point toggling of arbitrarily localized magnetic spots on the sample, according to the proposed circular detour-phase encoding, providing complex modulation and symmetrical suppression of upper diffractive orders and conjugated terms in holographically reconstructed 3-D images. △ Less

Submitted 4 November, 2022; originally announced November 2022.

Characterization of the new Ultracold Neutron beamline at the LANL UCN facility

Authors: D. K. -T. Wong, M. T. Hassan, J. F. Burdine, T. E. Chupp, S. M. Clayton, C. Cude-Woods, S. A. Currie, T. M. Ito, C. -Y. Liu, M. Makela, C. L. Morris, C. M. O'Shaughnessy, A. Reid, N. Sachdeva, W. Uhrich

Abstract: The neutron electric dipole moment (nEDM) experiment that is currently being developed at Los Alamos National Laboratory (LANL) will use ultracold neutrons (UCN) and Ramsey's method of separated oscillatory fields to search for a nEDM. In this paper, we present measurements of UCN storage and UCN transport performed during the commissioning of a new beamline at the LANL UCN source and demonstrate… ▽ More The neutron electric dipole moment (nEDM) experiment that is currently being developed at Los Alamos National Laboratory (LANL) will use ultracold neutrons (UCN) and Ramsey's method of separated oscillatory fields to search for a nEDM. In this paper, we present measurements of UCN storage and UCN transport performed during the commissioning of a new beamline at the LANL UCN source and demonstrate a sufficient number of stored polarized UCN to achieve a statistical uncertainty of $δd_n = 2\times 10^{-27}$~$e\cdot\text{cm}$ in 5 calendar years of running. We also present an analytical model describing data that provides a simple parameterization of the input UCN energy spectrum on the new beamline. △ Less

Submitted 17 January, 2023; v1 submitted 30 August, 2022; originally announced September 2022.

Comments: 12 pages, 13 figures

Report number: LA-UR-22-28534

Journal ref: Nucl. Instrum. Methods Phys. Res. A (2023) 168105

Fill and dump measurement of the neutron lifetime using an asymmetric magneto-gravitational trap

Authors: C. Cude-Woods, F. M. Gonzalez, E. M. Fries, T. Bailey, M. Blatnik, N. B. Callahan, J. H. Choi, S. M. Clayton, S. A. Currie, M. Dawid, B. W. Filippone, W. Fox, P. Geltenbort, E. George, L. Hayen, K. P. Hickerson, M. A. Hoffbauer, K. Hoffman, A. T. Holley, T. M. Ito, A. Komives, C. -Y. Liu, M. Makela, C. L. Morris, R. Musedinovic , et al. (17 additional authors not shown)

Abstract: The past two decades have yielded several new measurements and reanalyses of older measurements of the neutron lifetime. These have led to a 4.4 standard deviation discrepancy between the most precise measurements of the neutron decay rate producing protons in cold neutron beams and the lifetime measured in neutron storage experiments. Measurements using different techniques are important for inve… ▽ More The past two decades have yielded several new measurements and reanalyses of older measurements of the neutron lifetime. These have led to a 4.4 standard deviation discrepancy between the most precise measurements of the neutron decay rate producing protons in cold neutron beams and the lifetime measured in neutron storage experiments. Measurements using different techniques are important for investigating whether there are unidentified systematic effects in any of the measurements. In this paper we report a new measurement using the Los Alamos asymmetric magneto-gravitational trap where the surviving neutrons are counted external to the trap using the fill and dump method. The new measurement gives a free neutron lifetime of . Although this measurement is not as precise, it is in statistical agreement with previous results using in situ counting in the same apparatus. △ Less

Submitted 4 May, 2022; originally announced May 2022.

Report number: LA-UR-22-23486

Controllable energy angular spectrum method

Authors: Fan Wang, Tomoyoshi Shimobaba, Takashi Kakue, Tomoyoshi Ito

Abstract: A controllable energy method, which considers the undersampling issue of the transfer function and valid spectral energy of a source signal, is proposed to implement angular spectrum diffraction calculation in near and far fields. The proposed method provides an optimized frequency boundary $f_{CE}$ within which it always keeps controllable energy to be diffracted. The controllable energy angular… ▽ More A controllable energy method, which considers the undersampling issue of the transfer function and valid spectral energy of a source signal, is proposed to implement angular spectrum diffraction calculation in near and far fields. The proposed method provides an optimized frequency boundary $f_{CE}$ within which it always keeps controllable energy to be diffracted. The controllable energy angular spectrum method significantly reduces the number of samples while having the same accuracy as previous angular spectrum methods, implying a higher calculation efficiency. The new perspective of analyzing spectral energy is shown to improve the performance of relevant diffraction calculations. △ Less

Submitted 18 March, 2022; originally announced March 2022.

Hyperparameter tuning of optical neural network classifiers for high-order gaussian beams

Authors: Shunsuke Watanabe, Tomoyoshi Shimobaba, Takashi Kakue, Tomoyoshi Ito

Abstract: High-order Gaussian beams with multiple propagation modes have been studied for free-space optical communications. Fast classification of beams using a diffractive deep neural network, D2NN, has been proposed. D2NN optimization is important because it has numerous hyperparameters, such as interlayer distances and mode combinations. In this study, we classify Hermite-Gaussian beams, which are high-… ▽ More High-order Gaussian beams with multiple propagation modes have been studied for free-space optical communications. Fast classification of beams using a diffractive deep neural network, D2NN, has been proposed. D2NN optimization is important because it has numerous hyperparameters, such as interlayer distances and mode combinations. In this study, we classify Hermite-Gaussian beams, which are high-order Gaussian beams, using a D2NN, and automatically tune one of its hyperparameters known as the interlayer distance. We used the tree-structured Parzen estimator, a hyperparameter auto-tuning algorithm, to search for the best model. Results indicated that classification accuracy obtained by auto-tuning hyperparameters was higher than that obtained by manually setting interlayer distances at equal intervals. In addition, we confirmed that accuracy by auto-tuning improves as the number of classification modes increases. △ Less

Submitted 18 December, 2021; originally announced December 2021.

Optimization of phase-only holograms calculated with scaled diffraction calculation through deep neural networks

Authors: Yoshiyuki Ishii, Tomoyoshi Shimobaba, David Blinder, Tobias Birnbaum, Peter Schelkens, Takashi Kakue, Tomoyoshi Ito

Abstract: Computer-generated holograms (CGHs) are used in holographic three-dimensional (3D) displays and holographic projections. The quality of the reconstructed images using phase-only CGHs is degraded because the amplitude of the reconstructed image is difficult to control. Iterative optimization methods such as the Gerchberg-Saxton (GS) algorithm are one option for improving image quality. They optimiz… ▽ More Computer-generated holograms (CGHs) are used in holographic three-dimensional (3D) displays and holographic projections. The quality of the reconstructed images using phase-only CGHs is degraded because the amplitude of the reconstructed image is difficult to control. Iterative optimization methods such as the Gerchberg-Saxton (GS) algorithm are one option for improving image quality. They optimize CGHs in an iterative fashion to obtain a higher image quality. However, such iterative computation is time consuming, and the improvement in image quality is often stagnant. Recently, deep learning-based hologram computation has been proposed. Deep neural networks directly infer CGHs from input image data. However, it is limited to reconstructing images that are the same size as the hologram. In this study, we use deep learning to optimize phase-only CGHs generated using scaled diffraction computations and the random phase-free method. By combining the random phase-free method with the scaled diffraction computation, it is possible to handle a zoomable reconstructed image larger than the hologram. In comparison to the GS algorithm, the proposed method optimizes both high quality and speed. △ Less

Submitted 1 December, 2021; originally announced December 2021.

Deep learning models for predicting RNA degradation via dual crowdsourcing

Authors: Hannah K. Wayment-Steele, Wipapat Kladwang, Andrew M. Watkins, Do Soon Kim, Bojan Tunguz, Walter Reade, Maggie Demkin, Jonathan Romano, Roger Wellington-Oguri, John J. Nicol, Jiayang Gao, Kazuki Onodera, Kazuki Fujikawa, Hanfei Mao, Gilles Vandewiele, Michele Tinti, Bram Steenwinckel, Takuya Ito, Taiga Noumi, Shujun He, Keiichiro Ishi, Youhan Lee, Fatih Öztürk, Anthony Chiu, Emin Öztürk , et al. (4 additional authors not shown)

Abstract: Messenger RNA-based medicines hold immense potential, as evidenced by their rapid deployment as COVID-19 vaccines. However, worldwide distribution of mRNA molecules has been limited by their thermostability, which is fundamentally limited by the intrinsic instability of RNA molecules to a chemical degradation reaction called in-line hydrolysis. Predicting the degradation of an RNA molecule is a ke… ▽ More Messenger RNA-based medicines hold immense potential, as evidenced by their rapid deployment as COVID-19 vaccines. However, worldwide distribution of mRNA molecules has been limited by their thermostability, which is fundamentally limited by the intrinsic instability of RNA molecules to a chemical degradation reaction called in-line hydrolysis. Predicting the degradation of an RNA molecule is a key task in designing more stable RNA-based therapeutics. Here, we describe a crowdsourced machine learning competition ("Stanford OpenVaccine") on Kaggle, involving single-nucleotide resolution measurements on 6043 102-130-nucleotide diverse RNA constructs that were themselves solicited through crowdsourcing on the RNA design platform Eterna. The entire experiment was completed in less than 6 months, and 41% of nucleotide-level predictions from the winning model were within experimental error of the ground truth measurement. Furthermore, these models generalized to blindly predicting orthogonal degradation data on much longer mRNA molecules (504-1588 nucleotides) with improved accuracy compared to previously published models. Top teams integrated natural language processing architectures and data augmentation techniques with predictions from previous dynamic programming models for RNA secondary structure. These results indicate that such models are capable of representing in-line hydrolysis with excellent accuracy, supporting their use for designing stabilized messenger RNAs. The integration of two crowdsourcing platforms, one for data set creation and another for machine learning, may be fruitful for other urgent problems that demand scientific discovery on rapid timescales. △ Less

Submitted 22 April, 2022; v1 submitted 14 October, 2021; originally announced October 2021.

Dynamics of solvated electrons during femtosecond laser-induced plasma generation in water

Authors: Noritaka Sakakibara, Tsuyohito Ito, Kazuo Terashima, Yukiya Hakuta, Eisuke Miura

Abstract: We studied the dynamics of solvated electrons in the early stage of plasma generation in water induced with an intense femtosecond laser pulse. According to the decay kinetics of solvated electrons, fast recombination process of solvated electrons (geminate recombination) occurred with a more prolonged lifetime (500 ps to 1 ns) than that observed in previous pulse photolysis studies (10-100 ps). T… ▽ More We studied the dynamics of solvated electrons in the early stage of plasma generation in water induced with an intense femtosecond laser pulse. According to the decay kinetics of solvated electrons, fast recombination process of solvated electrons (geminate recombination) occurred with a more prolonged lifetime (500 ps to 1 ns) than that observed in previous pulse photolysis studies (10-100 ps). This unusually longer lifetime is attributed to additional production of solvated electrons due to abundant free electrons generated with the laser-induced plasma, implying significant influence of free electrons on the dynamics of solvated electrons. △ Less

Submitted 29 November, 2020; originally announced November 2020.

Comments: 24 pages, 5 figures

Journal ref: Physical Review E 102, 053207 (2020)

A study of DC electrical breakdown in liquid helium through analysis of the empirical breakdown field distributions

Authors: N. S. Phan, W. Wei, B. Beaumont, N. Bouman, S. M. Clayton, S. A. Currie, T. M. Ito, J. C. Ramsey, G. M. Seidel

Abstract: We report results from a study on electrical breakdown in liquid helium using near-uniform-field stainless steel electrodes with a stressed area of $\sim$0.725 cm$^2$. The distribution of the breakdown field is obtained for temperatures between 1.7 K and 4.0 K, pressures between the saturated vapor pressure and 626 Torr, and with electrodes of different surface polishes. A data-based approach for… ▽ More We report results from a study on electrical breakdown in liquid helium using near-uniform-field stainless steel electrodes with a stressed area of $\sim$0.725 cm$^2$. The distribution of the breakdown field is obtained for temperatures between 1.7 K and 4.0 K, pressures between the saturated vapor pressure and 626 Torr, and with electrodes of different surface polishes. A data-based approach for determining the electrode-surface-area scaling of the breakdown field is presented. The dependence of the breakdown probability on the field strength as extracted from the breakdown field distribution data is used to show that breakdown is a surface phenomenon closely correlated with Fowler-Nordheim field emission from asperities on the cathode. We show that the results from this analysis provides an explanation for the supposed electrode gap-size effect and also allows for a determination of the breakdown-field distribution for arbitrary shaped electrodes. Most importantly, the analysis method presented in this work can be extended to other noble liquids to explore the dependencies for electrical breakdown in those media. △ Less

Submitted 16 November, 2020; originally announced November 2020.

Report number: LA-UR-20-29356

Journal ref: J. Appl. Phys. 129 (2021) 8, 083301

Ultracold Neutron Properties of the Eljen-299-02D deuterated scintillator

Authors: Z. Tang, E. B. Watkins, S. M. Clayton, S. A. Currie, D. E. Fellers, Md. T. Hassan, D. E. Hooks, T. M. Ito, S. K. Lawrence, S. W. T. MacDonald, M. Makela, C. L. Morris, L. P. Neukirch, A. Saunders, C. M. O'Shaughnessy, C. Cude-Woods, J. H. Choi, A. R. Young, B. A. Zeck, F. Gonzalez, C. Y. Liu, N. C. Floyd, K. P. Hickerson, A. T. Holley, B. A. Johnson , et al. (2 additional authors not shown)

Abstract: In this paper we report studies of the Fermi potential and loss per bounce of ultracold neutron (UCN) on a deuterated scintillator (Eljen-299-02D). These UCN properties of the scintillator enables a wide variety of applications in fundamental neutron research. In this paper we report studies of the Fermi potential and loss per bounce of ultracold neutron (UCN) on a deuterated scintillator (Eljen-299-02D). These UCN properties of the scintillator enables a wide variety of applications in fundamental neutron research. △ Less

Submitted 25 September, 2020; originally announced September 2020.

Comments: 6 pages, 6 figures

Rabi-Oscillation Spectroscopy of the Hyperfine Structure of Muonium Atoms

Authors: S. Nishimura, H. A. Torii, Y. Fukao, T. U. Ito, M. Iwasaki, S. Kanda, K. Kawagoe, D. Kawall, N. Kawamura, N. Kurosawa, Y. Matsuda, T. Mibe, Y. Miyake, N. Saito, K. Sasaki, Y. Sato, S. Seo, P. Strasser, T. Suehara, K. S. Tanaka, T. Tanaka, J. Tojo, A. Toyoda, Y. Ueno, T. Yamanaka , et al. (4 additional authors not shown)

Abstract: As a new method to determine the resonance frequency, Rabi-oscillation spectroscopy has been developed. In contrast to the conventional spectroscopy which draws the resonance curve, Rabi-oscillation spectroscopy fits the time evolution of the Rabi oscillation. By selecting the optimized frequency, it is shown that the precision is twice as good as the conventional spectroscopy with a frequency swe… ▽ More As a new method to determine the resonance frequency, Rabi-oscillation spectroscopy has been developed. In contrast to the conventional spectroscopy which draws the resonance curve, Rabi-oscillation spectroscopy fits the time evolution of the Rabi oscillation. By selecting the optimized frequency, it is shown that the precision is twice as good as the conventional spectroscopy with a frequency sweep. Furthermore, the data under different conditions can be treated in a unified manner, allowing more efficient measurements for systems consisting of a limited number of short-lived particles produced by accelerators such as muons. We have developed a fitting function that takes into account the spatial distribution of muonium and the spatial distribution of the microwave intensity to apply the new method to ground-state muonium hyperfine structure measurements at zero field. This was applied to the actual measurement data and the resonance frequencies were determined under various conditions. The result of our analysis gives $ν_{\rm HFS}=4\ 463\ 301.61 \pm 0.71\ {\rm kHz}$, which is the world's highest precision under zero field conditions. △ Less

Submitted 12 February, 2021; v1 submitted 24 July, 2020; originally announced July 2020.

Comments: 6 pages, 5 figures

Journal ref: Phys. Rev. A 104, 020801 (2021)

New high-sensitivity searches for neutrons converting into antineutrons and/or sterile neutrons at the European Spallation Source

Authors: A. Addazi, K. Anderson, S. Ansell, K. Babu, J. Barrow, D. V. Baxter, P. M. Bentley, Z. Berezhiani, R. Bevilacqua, C. Bohm, G. Brooijmans, J. Broussard, R. Biondi, B. Dev, C. Crawford, A. Dolgov, K. Dunne, P. Fierlinger, M. R. Fitzsimmons, A. Fomin, M. Frost, S. Gardner, A. Galindo-Uribarri, E. Golubeva, S. Girmohanta , et al. (70 additional authors not shown)

Abstract: The violation of Baryon Number, $\mathcal{B}$, is an essential ingredient for the preferential creation of matter over antimatter needed to account for the observed baryon asymmetry in the universe. However, such a process has yet to be experimentally observed. The HIBEAM/NNBAR %experiment program is a proposed two-stage experiment at the European Spallation Source (ESS) to search for baryon numbe… ▽ More The violation of Baryon Number, $\mathcal{B}$, is an essential ingredient for the preferential creation of matter over antimatter needed to account for the observed baryon asymmetry in the universe. However, such a process has yet to be experimentally observed. The HIBEAM/NNBAR %experiment program is a proposed two-stage experiment at the European Spallation Source (ESS) to search for baryon number violation. The program will include high-sensitivity searches for processes that violate baryon number by one or two units: free neutron-antineutron oscillation ($n\rightarrow \bar{n}$) via mixing, neutron-antineutron oscillation via regeneration from a sterile neutron state ($n\rightarrow [n',\bar{n}'] \rightarrow \bar{n}$), and neutron disappearance ($n\rightarrow n'$); the effective $Δ\mathcal{B}=0$ process of neutron regeneration ($n\rightarrow [n',\bar{n}'] \rightarrow n$) is also possible. The program can be used to discover and characterise mixing in the neutron, antineutron, and sterile neutron sectors. The experiment addresses topical open questions such as the origins of baryogenesis, the nature of dark matter, and is sensitive to scales of new physics substantially in excess of those available at colliders. A goal of the program is to open a discovery window to neutron conversion probabilities (sensitivities) by up to three orders of magnitude compared with previous searches. The opportunity to make such a leap in sensitivity tests should not be squandered. The experiment pulls together a diverse international team of physicists from the particle (collider and low energy) and nuclear physics communities, while also including specialists in neutronics and magnetics. △ Less

Submitted 8 June, 2020; originally announced June 2020.

Injection induced seismicity size distribution dependent on shear stress

Authors: Yusuke Mukuhira, Michael C. Fehler, Takatoshi Ito, Hiroshi Asanuma, Markus O. Häring

Abstract: Like natural seismicity, induced seismicity caused by fluid injection also shows a power law size distribution, and its gradient b-value (ratio of small to large earthquakes) is often used for seismic hazard analysis. Despite well-known relationship that b-value is negatively correlated with differential stress for natural earthquakes, there is no understanding of the physical causes for b-value v… ▽ More Like natural seismicity, induced seismicity caused by fluid injection also shows a power law size distribution, and its gradient b-value (ratio of small to large earthquakes) is often used for seismic hazard analysis. Despite well-known relationship that b-value is negatively correlated with differential stress for natural earthquakes, there is no understanding of the physical causes for b-value variations in injection-induced seismicity in the scale where the differential is nearly constant. We investigate a b-value dependence on the relative shear stress acting on existing fractures and show that the seismicity occurring along existing fractures with high shear stress have significantly lower b-values than does that associated with lower shear stress fractures. The b-value for injection induced seismicity is dependent on relative shear stress on faults. Our results provide a novel physical explanation for the b-value variations of induced seismicity. △ Less

Submitted 30 May, 2020; originally announced June 2020.

Comments: 15 pages, 8 figures, Supplementary information

Femtosecond X-ray emission study of the spin cross-over dynamics in haem proteins

Authors: Dominik Kinschel, Camila Bacellar, Oliviero Cannelli, Boris Sorokin, Tetsuo Katayama, Giulia F. Mancini, Jeremy R. Rouxel, Yuki Obara, Junichi Nishitani, Hironori Ito, Terumasa Ito, Naoya Kurahashi, Chika Higashimura, Shotaro Kudo, Theo Keane, Frederico A. Lima, Wojciech Gawelda, Peter Zalden, Sebastian Schulz, James Budarz, Dmitry Khakhulin, Andreas Galler, Christian Bressler, Christopher J. Milne, Thomas Penfold , et al. (4 additional authors not shown)

Abstract: In haemoglobin (consisting of four globular myoglobin-like subunits), the change from the low-spin (LS) hexacoordinated haem to the high spin (HS) pentacoordinated domed form upon ligand detachment and the reverse process upon ligand binding, represent the transition states that ultimately drive the respiratory function. Visible-ultraviolet light has long been used to mimic the ligand release from… ▽ More In haemoglobin (consisting of four globular myoglobin-like subunits), the change from the low-spin (LS) hexacoordinated haem to the high spin (HS) pentacoordinated domed form upon ligand detachment and the reverse process upon ligand binding, represent the transition states that ultimately drive the respiratory function. Visible-ultraviolet light has long been used to mimic the ligand release from the haem by photodissociation, while its recombination was monitored using time-resolved infrared to ultraviolet spectroscopic tools. However, these are neither element- nor spin-sensitive. Here we investigate the transition state in the case of Myoglobin-NO (MbNO) using femtosecond Fe Kalpha and Kbeta non-resonant X-ray emission spectroscopy (XES) at an X-ray free-electron laser upon photolysis of the Fe-NO bond. We find that the photoinduced change from the LS (S = 1/2) MbNO to the HS (S = 2) deoxy-myoglobin (deoxyMb) haem occurs in ca. 800 fs, and that it proceeds via an intermediate (S = 1) spin state. The XES observables also show that upon NO recombination to deoxyMb, the return to the planar MbNO ground state is an electronic relaxation from HS to LS taking place in ca. 30 ps. Thus, the entire ligand dissociation-recombination cycle in MbNO is a spin cross-over followed by a reverse spin cross-over process. △ Less

Submitted 12 May, 2020; originally announced May 2020.

Effect of an electric field on liquid helium scintillation produced by fast electrons

Authors: N. S. Phan, V. Cianciolo, S. M. Clayton, S. A. Currie, R. Dipert, T. M. Ito, S. W. T. MacDonald, C. M. O'Shaughnessy, J. C. Ramsey, G. M. Seidel, E. Smith, E. Tang, Z. Tang, W. Yao

Abstract: The dependence on applied electric field ($0 - 40$ kV/cm) of the scintillation light produced by fast electrons and $α$ particles stopped in liquid helium in the temperature range of 0.44 K to 3.12 K is reported. For both types of particles, the reduction in the intensity of the scintillation signal due to the applied field exhibits an apparent temperature dependence. Using an approximate solution… ▽ More The dependence on applied electric field ($0 - 40$ kV/cm) of the scintillation light produced by fast electrons and $α$ particles stopped in liquid helium in the temperature range of 0.44 K to 3.12 K is reported. For both types of particles, the reduction in the intensity of the scintillation signal due to the applied field exhibits an apparent temperature dependence. Using an approximate solution of the Debye-Smoluchowski equation, we show that the apparent temperature dependence for electrons can be explained by the time required for geminate pairs to recombine relative to the detector signal integration time. This finding indicates that the spatial distribution of secondary electrons with respect to their geminate partners possesses a heavy, non-Gaussian tail at larger separations, and has a dependence on the energy of the primary ionization electron. We discuss the potential application of this result to pulse shape analysis for particle detection and discrimination. △ Less

Submitted 14 September, 2020; v1 submitted 6 May, 2020; originally announced May 2020.

Journal ref: Phys. Rev. C 102, 035503 (2020)

Ultrafast Light-driven Simultaneous Excitation of Coherent Terahertz Magnons and Phonons in Multiferroic BiFeO$_3$

Authors: Pritam Khan, Masataka Kanamaru, Keita Matsumoto, Toshimitsu Ito, Takuya Satoh

Abstract: The ultrafast switching of magnetization in multiferroic materials by a femtosecond laser could provide various advantages in photonics and magnonics. An efficient approach to control the light matter interaction is the modulation of ultrafast coherent magnons and phonons in the high frequency range. Spontaneous Raman and infrared spectra reveal the excitation of magnons and optical phonons in mul… ▽ More The ultrafast switching of magnetization in multiferroic materials by a femtosecond laser could provide various advantages in photonics and magnonics. An efficient approach to control the light matter interaction is the modulation of ultrafast coherent magnons and phonons in the high frequency range. Spontaneous Raman and infrared spectra reveal the excitation of magnons and optical phonons in multiferroic BiFeO3 in the sub few terahertz range. However, coherent control of such quasiparticles has not been achieved yet. In this study, we demonstrate that linearly polarized laser pulses simultaneously excite coherent magnons out of plane and in plane cyclone modes and optical phonon E mode in BiFeO3. Experimental results in conjugation with phenomenological theory, by considering three uniformly distributed magnetic domains reveal that impulsive stimulated Raman scattering is responsible for the generation of coherent magnons and phonons in BiFeO3. The observation of these terahertz magnon and optical phonon modes paves the way for the development of ultrafast magneto electro optical devices. △ Less

Submitted 13 April, 2020; v1 submitted 18 February, 2020; originally announced February 2020.

Comments: 36 pages, 11 fihures, 7 tables

Journal ref: Phys. Rev. B 101, 134413 (2020)

Simple complex amplitude encoding of a phase-only hologram using binarized amplitude

Authors: Tomoyoshi Shimobaba, Takayuki Takahashi, Yota Yamamoto, Ikuo Hoshi, Atsushi Shiraki, Takashi Kakue, Tomoyoshi Ito

Abstract: For this work, we introduced the use of binary amplitude for our proposed complex amplitude encoding of a phase-only hologram. By principle, a complex amplitude in a hologram plane can be represented by the amplitude and its phase. However, a phase-only hologram contains only phase information of the complex amplitude, which results in degradation of reconstruction quality from the hologram. In ou… ▽ More For this work, we introduced the use of binary amplitude for our proposed complex amplitude encoding of a phase-only hologram. By principle, a complex amplitude in a hologram plane can be represented by the amplitude and its phase. However, a phase-only hologram contains only phase information of the complex amplitude, which results in degradation of reconstruction quality from the hologram. In our method, by approximating the amplitude in the hologram plane using a binary amplitude, we can finally record the complex amplitude of an original light in the phase-only hologram. We validated the effectiveness of our method with two examples, hologram reconstruction and generation of Hermite-Gaussian beams. △ Less

Submitted 17 September, 2019; originally announced September 2019.

A New Cryogenic Apparatus to Search for the Neutron Electric Dipole Moment

Authors: M. W. Ahmed, R. Alarcon, A. Aleksandrova, S. Baessler, L. Barron-Palos, L. M. Bartoszek, D. H. Beck, M. Behzadipour, I. Berkutov, J. Bessuille, M. Blatnik, M. Broering, L. J. Broussard, M. Busch, R. Carr, V. Cianciolo, S. M. Clayton, M. D. Cooper, C. Crawford, S. A. Currie, C. Daurer, R. Dipert, K. Dow, D. Dutta, Y. Efremenko , et al. (69 additional authors not shown)

Abstract: A cryogenic apparatus is described that enables a new experiment, nEDM@SNS, with a major improvement in sensitivity compared to the existing limit in the search for a neutron Electric Dipole Moment (EDM). It uses superfluid $^4$He to produce a high density of Ultra-Cold Neutrons (UCN) which are contained in a suitably coated pair of measurement cells. The experiment, to be operated at the Spallati… ▽ More A cryogenic apparatus is described that enables a new experiment, nEDM@SNS, with a major improvement in sensitivity compared to the existing limit in the search for a neutron Electric Dipole Moment (EDM). It uses superfluid $^4$He to produce a high density of Ultra-Cold Neutrons (UCN) which are contained in a suitably coated pair of measurement cells. The experiment, to be operated at the Spallation Neutron Source at Oak Ridge National Laboratory, uses polarized $^3$He from an Atomic Beam Source injected into the superfluid $^4$He and transported to the measurement cells as a co-magnetometer. The superfluid $^4$He is also used as an insulating medium allowing significantly higher electric fields, compared to previous experiments, to be maintained across the measurement cells. These features provide an ultimate statistical uncertainty for the EDM of $2-3\times 10^{-28}$ e-cm, with anticipated systematic uncertainties below this level. △ Less

Submitted 20 November, 2019; v1 submitted 26 August, 2019; originally announced August 2019.

Journal ref: Journal of Instrumentation, Vol 14, P11017, 2019

A next-generation inverse-geometry spallation-driven ultracold neutron source

Authors: K. K. H. Leung, G. Muhrer, T. Hügle, T. M. Ito, E. M. Lutz, M. Makela, C. L. Morris, R. W. Pattie, Jr., A. Saunders, A. R. Young

Abstract: The physics model of a next-generation spallation-driven high-current ultracold neutron (UCN) source capable of delivering an extracted UCN rate of around an-order-of-magnitude higher than the strongest proposed sources, and around three-orders-of-magnitude higher than existing sources, is presented. This UCN-current-optimized source would dramatically improve cutting-edge UCN measurements that ar… ▽ More The physics model of a next-generation spallation-driven high-current ultracold neutron (UCN) source capable of delivering an extracted UCN rate of around an-order-of-magnitude higher than the strongest proposed sources, and around three-orders-of-magnitude higher than existing sources, is presented. This UCN-current-optimized source would dramatically improve cutting-edge UCN measurements that are currently statistically limited. A novel "Inverse Geometry" design is used with 40 L of superfluid $^4$He (He-II), which acts as a converter of cold neutrons (CNs) to UCNs, cooled with state-of-the-art sub-cooled cryogenic technology to $\sim$1.6 K. Our design is optimized for a 100 W maximum heat load constraint on the He-II and its vessel. In our geometry, the spallation target is wrapped symmetrically around the UCN converter to permit raster scanning the proton beam over a relatively large volume of tungsten spallation target to reduce the demand on the cooling requirements, which makes it reasonable to assume that water edge-cooling only is sufficient. Our design is refined in several steps to reach $P_{UCN}=2.1\times10^9\,/$s under our other restriction of 1 MW maximum available proton beam power. We then study effects of the He-II scattering kernel as well as reductions in $P_{UCN}$ due to pressurization to reach $P_{UCN}=1.8\times10^9\,/$s. Finally, we provide a design for the UCN extraction system that takes into account the required He-II heat transport properties and implementation of a He-II containment foil that allows UCN transmission. We estimate a total useful UCN current from our source of $R_{use}=5\times10^8\,/$s from a 18 cm diameter guide 5 m from the source. Under a conservative "no return" approximation, this rate can produce an extracted density of $>1\times10^4\,/$cm$^3$ in $<$1000~L external experimental volumes with a $^{58}$Ni (335 neV) cut-off potential. △ Less

Submitted 24 October, 2019; v1 submitted 23 May, 2019; originally announced May 2019.

Comments: Submitted to Journal of Applied Physics

Final results for the neutron $β$-asymmetry parameter $A_0$ from the UCNA experiment

Authors: B. Plaster, E. Adamek, B. Allgeier, J. Anaya, H. O. Back, Y. Bagdasarova, D. B. Berguno, M. Blatnik, J. G. Boissevain, T. J. Bowles, L. J. Broussard, M. A. -P. Brown, R. Carr, D. J. Clark, S. Clayton, C. Cude-Woods, S. Currie, E. B. Dees, X. Ding, S. Du, B. W. Filippone, A. Garcia, P. Geltenbort, S. Hasan, A. Hawari , et al. (69 additional authors not shown)

Abstract: The UCNA experiment was designed to measure the neutron $β$-asymmetry parameter $A_0$ using polarized ultracold neutrons (UCN). UCN produced via downscattering in solid deuterium were polarized via transport through a 7 T magnetic field, and then directed to a 1 T solenoidal electron spectrometer, where the decay electrons were detected in electron detector packages located on the two ends of the… ▽ More The UCNA experiment was designed to measure the neutron $β$-asymmetry parameter $A_0$ using polarized ultracold neutrons (UCN). UCN produced via downscattering in solid deuterium were polarized via transport through a 7 T magnetic field, and then directed to a 1 T solenoidal electron spectrometer, where the decay electrons were detected in electron detector packages located on the two ends of the spectrometer. A value for $A_0$ was then extracted from the asymmetry in the numbers of counts in the two detector packages. We summarize all of the results from the UCNA experiment, obtained during run periods in 2007, 2008--2009, 2010, and 2011--2013, which ultimately culminated in a 0.67\% precision result for $A_0$. △ Less

Submitted 10 April, 2019; originally announced April 2019.

Comments: 6 pages, 7 figures, to appear in proceedings of the International Workshop on Particle Physics at Neutron Sources 2018

The neutron electric dipole moment experiment at the Spallation Neutron Source

Authors: K. K. H. Leung, M. Ahmed, R. Alarcon, A. Aleksandrova, S. Baeßler, L. Barrón-Palos, L. Bartoszek, D. H. Beck, M. Behzadipour, J. Bessuille, M. A. Blatnik, M. Broering, L. J. Broussard, M. Busch, R. Carr, P. -H. Chu, V. Cianciolo, S. M. Clayton, M. D. Cooper, C. Crawford, S. A. Currie, C. Daurer, R. Dipert, K. Dow, D. Dutta , et al. (68 additional authors not shown)

Abstract: Novel experimental techniques are required to make the next big leap in neutron electric dipole moment experimental sensitivity, both in terms of statistics and systematic error control. The nEDM experiment at the Spallation Neutron Source (nEDM@SNS) will implement the scheme of Golub & Lamoreaux [Phys. Rep., 237, 1 (1994)]. The unique properties of combining polarized ultracold neutrons, polarize… ▽ More Novel experimental techniques are required to make the next big leap in neutron electric dipole moment experimental sensitivity, both in terms of statistics and systematic error control. The nEDM experiment at the Spallation Neutron Source (nEDM@SNS) will implement the scheme of Golub & Lamoreaux [Phys. Rep., 237, 1 (1994)]. The unique properties of combining polarized ultracold neutrons, polarized $^3$He, and superfluid $^4$He will be exploited to provide a sensitivity to $\sim 10^{-28}\,e{\rm \,\cdot\, cm}$. Our cryogenic apparatus will deploy two small ($3\,{\rm L}$) measurement cells with a high density of ultracold neutrons produced and spin analyzed in situ. The electric field strength, precession time, magnetic shielding, and detected UCN number will all be enhanced compared to previous room temperature Ramsey measurements. Our $^3$He co-magnetometer offers unique control of systematic effects, in particular the Bloch-Siegert induced false EDM. Furthermore, there will be two distinct measurement modes: free precession and dressed spin. This will provide an important self-check of our results. Following five years of "critical component demonstration," our collaboration transitioned to a "large scale integration" phase in 2018. An overview of our measurement techniques, experimental design, and brief updates are described in these proceedings. △ Less

Submitted 4 October, 2019; v1 submitted 6 March, 2019; originally announced March 2019.

Comments: Submitted to proceedings of PPNS 2018 - International Workshop on Particle physics at Neutron Sources (https://www.webofconferences.org/epj-web-of-conferences-forthcoming-conferences/1148-ppns-2018)

A boron-coated CCD camera for direct detection of Ultracold Neutrons (UCN)

Authors: K. Kuk, C. Cude-Woods, C. R. Chavez, J. H. Choi, J. Estrada, M. Hoffbauer, M. Makela, P. Merkel, C. L. Morris, E. Ramberg, Z. Wang, T. Bailey, M. Blatnik, E. R. Adamek, L. J. Broussard, M. A. -P. Brown, N. B. Callahan, S. M. Clayton, S. A. Currie, X. Ding, D. Dinger, B. Filippone, E. M. Fries, P. Geltenbort, E. George , et al. (26 additional authors not shown)

Abstract: A new boron-coated CCD camera is described for direct detection of ultracold neutrons (UCN) through the capture reactions $^{10}$B (n,$α$0$γ$)$^7$Li (6%) and $^{10}$B(n,$α$1$γ$)$^7$Li (94%). The experiments, which extend earlier works using a boron-coated ZnS:Ag scintillator, are based on direct detections of the neutron-capture byproducts in silicon. The high position resolution, energy resolutio… ▽ More A new boron-coated CCD camera is described for direct detection of ultracold neutrons (UCN) through the capture reactions $^{10}$B (n,$α$0$γ$)$^7$Li (6%) and $^{10}$B(n,$α$1$γ$)$^7$Li (94%). The experiments, which extend earlier works using a boron-coated ZnS:Ag scintillator, are based on direct detections of the neutron-capture byproducts in silicon. The high position resolution, energy resolution and particle ID performance of a scientific CCD allows for observation and identification of all the byproducts $α$, $^7$Li and $γ$ (electron recoils). A signal-to-noise improvement on the order of 10$^4$ over the indirect method has been achieved. Sub-pixel position resolution of a few microns is demonstrated. The technology can also be used to build UCN detectors with an area on the order of 1 m$^2$. The combination of micrometer scale spatial resolution, few electrons ionization thresholds and large area paves the way to new research avenues including quantum physics of UCN and high-resolution neutron imaging and spectroscopy. △ Less

Submitted 28 February, 2019; originally announced March 2019.

Comments: 10 pages, 8 figures

Report number: Los Alamos National Laboratory Report number LA-UR-19-21706

Journal ref: Nuclear Instruments and Methods in Physics Research Section A, Volume 1003, 1 July 2021, 165306

Solid deuterium surface degradation at ultracold neutron sources

Authors: A. Anghel, T. L. Bailey, G. Bison, B. Blau, L. J. Broussard, S. M. Clayton, C. Cude-Woods, M. Daum, A. Hawari, N. Hild, P. Huffman, T. M. Ito, K. Kirch, E. Korobkina, B. Lauss, K. Leung, E. M. Lutz, M. Makela, G. Medlin, C. L. Morris, R. W. Pattie, D. Ries, A. Saunders, P. Schmidt-Wellenburg, V. Talanov , et al. (5 additional authors not shown)

Abstract: Solid deuterium (sD_2) is used as an efficient converter to produce ultracold neutrons (UCN). It is known that the sD_2 must be sufficiently cold, of high purity and mostly in its ortho-state in order to guarantee long lifetimes of UCN in the solid from which they are extracted into vacuum. Also the UCN transparency of the bulk sD_2 material must be high because crystal inhomogeneities limit the m… ▽ More Solid deuterium (sD_2) is used as an efficient converter to produce ultracold neutrons (UCN). It is known that the sD_2 must be sufficiently cold, of high purity and mostly in its ortho-state in order to guarantee long lifetimes of UCN in the solid from which they are extracted into vacuum. Also the UCN transparency of the bulk sD_2 material must be high because crystal inhomogeneities limit the mean free path for elastic scattering and reduce the extraction efficiency. Observations at the UCN sources at Paul Scherrer Institute and at Los Alamos National Laboratory consistently show a decrease of the UCN yield with time of operation after initial preparation or later treatment (`conditioning') of the sD_2. We show that, in addition to the quality of the bulk sD_2, the quality of its surface is essential. Our observations and simulations support the view that the surface is deteriorating due to a build-up of D_2 frost-layers under pulsed operation which leads to strong albedo reflections of UCN and subsequent loss. We report results of UCN yield measurements, temperature and pressure behavior of deuterium during source operation and conditioning, and UCN transport simulations. This, together with optical observations of sD_2 frost formation on initially transparent sD_2 in offline studies with pulsed heat input at the North Carolina State University UCN source results in a consistent description of the UCN yield decrease. △ Less

Submitted 28 August, 2018; v1 submitted 23 April, 2018; originally announced April 2018.

Comments: 15 pages, 22 figures, accepted by EPJ-A

Search for dark matter decay of the free neutron from the UCNA experiment: n $\rightarrow χ+ e^+e^-$

Authors: X. Sun, E. Adamek, B. Allgeier, M. Blatnik, T. J. Bowles, L. J. Broussard, M. A. -P. Brown, R. Carr, S. Clayton, C. Cude-Woods, S. Currie, E. B. Dees, X. Ding, B. W. Filippone, A. García, P. Geltenbort, S. Hasan, K. P. Hickerson, J. Hoagland, R. Hong, G. E. Hogan, A. T. Holley, T. M. Ito, A. Knecht, C. -Y. Liu , et al. (35 additional authors not shown)

Abstract: It has been proposed recently that a previously unobserved neutron decay branch to a dark matter particle ($χ$) could account for the discrepancy in the neutron lifetime observed in experiments that use two different measurement techniques. One of the possible final states discussed includes a single $χ$ along with an $e^{+}e^{-}$ pair. We use data from the UCNA (Ultracold Neutron Asymmetry) exper… ▽ More It has been proposed recently that a previously unobserved neutron decay branch to a dark matter particle ($χ$) could account for the discrepancy in the neutron lifetime observed in experiments that use two different measurement techniques. One of the possible final states discussed includes a single $χ$ along with an $e^{+}e^{-}$ pair. We use data from the UCNA (Ultracold Neutron Asymmetry) experiment to set limits on this decay channel. Coincident electron-like events are detected with $\sim 4π$ acceptance using a pair of detectors that observe a volume of stored Ultracold Neutrons (UCNs). The summed kinetic energy ($E_{e^{+}e^{-}}$) from such events is used to set limits, as a function of the $χ$ mass, on the branching fraction for this decay channel. For $χ$ masses consistent with resolving the neutron lifetime discrepancy, we exclude this as the dominant dark matter decay channel at $\gg~5σ$ level for $100~\text{keV} < E_{e^{+}e^{-}} < 644~\text{keV}$. If the $χ+e^{+}e^{-}$ final state is not the only one, we set limits on its branching fraction of $< 10^{-4}$ for the above $E_{e^{+}e^{-}}$ range at $> 90\%$ confidence level. △ Less

Submitted 28 March, 2018; originally announced March 2018.

Comments: 5 pages, 5 figures

Journal ref: Phys. Rev. C 97, 052501 (2018)

Cavallo's Multiplier for in situ Generation of High Voltage

Authors: Steven M. Clayton, Takeyasu M. Ito, John C. Ramsey, Wanchun Wei, Marie A. Blatnik, Bradley W. Filippone, George M. Seidel

Abstract: A classic electrostatic induction machine, Cavallo's multiplier, is suggested for in situ production of very high voltage in cryogenic environments. The device is suitable for generating a large electrostatic field under conditions of very small load current. Operation of the Cavallo multiplier is analyzed, with quantitative description in terms of mutual capacitances between electrodes in the sys… ▽ More A classic electrostatic induction machine, Cavallo's multiplier, is suggested for in situ production of very high voltage in cryogenic environments. The device is suitable for generating a large electrostatic field under conditions of very small load current. Operation of the Cavallo multiplier is analyzed, with quantitative description in terms of mutual capacitances between electrodes in the system. A demonstration apparatus was constructed, and measured voltages are compared to predictions based on measured capacitances in the system. The simplicity of the Cavallo multiplier makes it amenable to electrostatic analysis using finite element software, and electrode shapes can be optimized to take advantage of a high dielectric strength medium such as liquid helium. A design study is presented for a Cavallo multiplier in a large-scale, cryogenic experiment to measure the neutron electric dipole moment. △ Less

Submitted 9 April, 2018; v1 submitted 20 March, 2018; originally announced March 2018.

Comments: 9 pages, 10 figures

Report number: LA-UR-18-22384

Journal ref: S.M. Clayton et al 2018 JINST 13 P05017

Computational ghost imaging using deep learning

Authors: Tomoyoshi Shimobaba, Yutaka Endo, Takashi Nishitsuji, Takayuki Takahashi, Yuki Nagahama, Satoki Hasegawa, Marie Sano, Ryuji Hirayama, Takashi Kakue, Atsushi Shiraki, Tomoyoshi Ito

Abstract: Computational ghost imaging (CGI) is a single-pixel imaging technique that exploits the correlation between known random patterns and the measured intensity of light transmitted (or reflected) by an object. Although CGI can obtain two- or three- dimensional images with a single or a few bucket detectors, the quality of the reconstructed images is reduced by noise due to the reconstruction of image… ▽ More Computational ghost imaging (CGI) is a single-pixel imaging technique that exploits the correlation between known random patterns and the measured intensity of light transmitted (or reflected) by an object. Although CGI can obtain two- or three- dimensional images with a single or a few bucket detectors, the quality of the reconstructed images is reduced by noise due to the reconstruction of images from random patterns. In this study, we improve the quality of CGI images using deep learning. A deep neural network is used to automatically learn the features of noise-contaminated CGI images. After training, the network is able to predict low-noise images from new noise-contaminated CGI images. △ Less

Submitted 18 October, 2017; originally announced October 2017.

Performance of the upgraded ultracold neutron source at Los Alamos National Laboratory and its implication for a possible neutron electric dipole moment experiment

Authors: T. M. Ito, E. R. Adamek, N. B. Callahan, J. H. Choi, S. M. Clayton, C. Cude-Woods, S. Currie, X. Ding, D. E. Fellers, P. Geltenbort, S. K. Lamoreaux, C. Y. Liu, S. MacDonald, M. Makela, C. L. Morris, R. W. Pattie Jr., J. C. Ramsey, D. J. Salvat, A. Saunders, E. I. Sharapov, S. Sjue, A. P. Sprow, Z. Tang, H. L. Weaver, W. Wei , et al. (1 additional authors not shown)

Abstract: The ultracold neutron (UCN) source at Los Alamos National Laboratory (LANL), which uses solid deuterium as the UCN converter and is driven by accelerator spallation neutrons, has been successfully operated for over 10 years, providing UCN to various experiments, as the first production UCN source based on the superthermal process. It has recently undergone a major upgrade. This paper describes the… ▽ More The ultracold neutron (UCN) source at Los Alamos National Laboratory (LANL), which uses solid deuterium as the UCN converter and is driven by accelerator spallation neutrons, has been successfully operated for over 10 years, providing UCN to various experiments, as the first production UCN source based on the superthermal process. It has recently undergone a major upgrade. This paper describes the design and performance of the upgraded LANL UCN source. Measurements of the cold neutron spectrum and UCN density are presented and compared to Monte Carlo predictions. The source is shown to perform as modeled. The UCN density measured at the exit of the biological shield was $184(32)$ UCN/cm$^3$, a four-fold increase from the highest previously reported. The polarized UCN density stored in an external chamber was measured to be $39(7)$ UCN/cm$^3$, which is sufficient to perform an experiment to search for the nonzero neutron electric dipole moment with a one-standard-deviation sensitivity of $σ(d_n) = 3\times 10^{-27}$ $e\cdot$cm. △ Less

Submitted 16 January, 2018; v1 submitted 14 October, 2017; originally announced October 2017.

Comments: 6 pages, 6 figures

Report number: LA-UR-17-29313

Journal ref: Phys. Rev. C 97, 012501 (2018)

Fast, large-scale hologram calculation in wavelet domain

Authors: Tomoyoshi Shimobaba, Kyoji Matsushima, Takayuki Takahashi, Yuki Nagahama, Satoki Hasegawa, Marie Sano, Ryuji Hirayama, Takashi Kakue, Tomoyoshi Ito

Abstract: We propose a large-scale hologram calculation using WAvelet ShrinkAge-Based superpositIon (WASABI), a wavelet transform-based algorithm. An image-type hologram calculated using the WASABI method is printed on a glass substrate with the resolution of $65,536 \times 65,536$ pixels and a pixel pitch of $1 μ$m. The hologram calculation time amounts to approximately 354 s on a commercial CPU, which is… ▽ More We propose a large-scale hologram calculation using WAvelet ShrinkAge-Based superpositIon (WASABI), a wavelet transform-based algorithm. An image-type hologram calculated using the WASABI method is printed on a glass substrate with the resolution of $65,536 \times 65,536$ pixels and a pixel pitch of $1 μ$m. The hologram calculation time amounts to approximately 354 s on a commercial CPU, which is approximately 30 times faster than conventional methods. △ Less

Submitted 13 August, 2017; originally announced August 2017.