Showing 1–50 of 56 results for author: Beck, M

Quantum viscosity mechanism of the dissipative dynamics in the Dicke model expressed via Lindblad equation of motion

Authors: M. E. S. Beck, S. S. Seidov, S. I. Muhkin

Abstract: Quantum dissipation is studied in the superradiant phase of the Extended Dicke model. It is demonstrated analytically by quantum mechanical derivation of the Lindblad equation for the Dicke model in the superradiant state coupled to Caldeira-Leggett thermal bath, that the effective viscosity appearing in the semiclassical equations of motion of polaritonic condensate survives in the zero temperatu… ▽ More Quantum dissipation is studied in the superradiant phase of the Extended Dicke model. It is demonstrated analytically by quantum mechanical derivation of the Lindblad equation for the Dicke model in the superradiant state coupled to Caldeira-Leggett thermal bath, that the effective viscosity appearing in the semiclassical equations of motion of polaritonic condensate survives in the zero temperature limit T -> 0. The nonzero contribution to viscosity contains prefactor nB (ω, T ) + 1 with the Bose-Einstein function nB of harmonic oscillators in the thermal bath, indicating that virtual excitations of harmonic oscillators in the thermal bath coupled to the polaritons of Dicke model give rise to effective viscosity in the T -> 0 limit. Besides, it is demonstrated analytically, that correct expression for Lindbladian in the superradiant phase should be built using condensate-shifted creation and annihilation operators of the photons and pseudospin operators in Holstein-Primakoff representation of the coupled to photons two-level systems in order the system could relax to its minimum energy in T -> 0 limit due to thermal bath provided effective viscosity. △ Less

Submitted 22 May, 2026; originally announced May 2026.

Comments: 14 pages, 6 figures

Profiling THz Beams With Off-Label Use of Infrared Microbolometric Cameras

Authors: Gabriel Nagamine, Carlo Vicario, Tariq Leinen, Guy Matmon, Marco Raffa, Mattias Beck, Giacomo Scalari, Adrian L. Cavalieri, Flavio Giorgianni

Abstract: Visualizing the spatial profile of light beams is essential for evaluating irradiance, characterizing beam quality, and achieving precise alignment. In the optical spectral range, this is readily performed using silicon-based CCD and CMOS cameras. In the terahertz (THz) range, however, it typically requires specialized detectors with prohibitive costs. Here, we show that an infrared (IR) camera ca… ▽ More Visualizing the spatial profile of light beams is essential for evaluating irradiance, characterizing beam quality, and achieving precise alignment. In the optical spectral range, this is readily performed using silicon-based CCD and CMOS cameras. In the terahertz (THz) range, however, it typically requires specialized detectors with prohibitive costs. Here, we show that an infrared (IR) camera can be used outside of its labeled specifications to achieve similar performance as a dedicated microbolometric THz camera, at under 1% of the THz camera's cost. We compared the cameras by characterizing THz beam profiles from two sources: a pulsed broadband THz beam produced through optical rectification in organic crystals, and a narrowband quasi-continuous-wave (quasi-CW) THz beam emitted by a quantum cascade laser. For the broadband THz radiation, the beam width measured by the two cameras differed by only ~ 6%, well within the pixel resolution limit, and in the narrowband quasi-CW case by just ~ 1.3%. Additionally, the IR camera exhibits a lower minimum detectable power (down to 1.5 THz) than the THz camera, while also maintaining a linear and polarization-independent responsivity. These results expand the applicability of conventional IR cameras to the THz range, suggesting that they will become routine tools for high-fidelity THz beam diagnostics and imaging in scientific and industrial applications. △ Less

Submitted 30 June, 2026; v1 submitted 23 February, 2026; originally announced February 2026.

Superconducting qubit decoherence correlated with detected radiation events

Authors: A. R. Castelli, K. M. Beck, L. D. H. Alegria, L. A. Martinez, K. R. Chaves, S. R. O'Kelley, N. Materise, J. L DuBois, Y. J. Rosen

Abstract: Most quantum error correction (QEC) protocols for superconducting qubits assume spatially and temporally uncorrelated decoherence events; however, recent evidence suggests that cosmic radiation induces spatially correlated errors. We present a platform that sandwiches a superconducting transmon qubit between two microwave kinetic inductance detector (MKID) arrays, enabling real-time detection of r… ▽ More Most quantum error correction (QEC) protocols for superconducting qubits assume spatially and temporally uncorrelated decoherence events; however, recent evidence suggests that cosmic radiation induces spatially correlated errors. We present a platform that sandwiches a superconducting transmon qubit between two microwave kinetic inductance detector (MKID) arrays, enabling real-time detection of radiation-induced phonon bursts. By synchronizing MKID event detection with single-shot measurements of qubit energy relaxation ($T_1$) and phase coherence ($T_2$), we observe statistically significant reductions in both $T_1$ and $T_2$-up to 30.5%-immediately following dual MKID events attributed to penetrating muons. Our findings directly link radiating events to correlated qubit decoherence. Furthermore, our experimental platform provides a foundation for systematic studies of radiation effects, the development of shielding and mitigation techniques, and the refinement of error-correction algorithms tailored to correlated noise sources. △ Less

Submitted 19 December, 2025; originally announced December 2025.

Comments: 10 pages, 9 figures

Report number: LLNL-JRNL-2008718

Gate-tunable single terahertz meta-atom ultrastrong light-matter coupling

Authors: Elsa Jöchl, Anna-Lydia Vieli, Lucy Hale, Felix Helmrich, Deniz Turan, Mona Jarrahi, Mattias Beck, Jérôme Faist, Giacomo Scalari

Abstract: We study the electrical tunability of ultrastrong light-matter interactions between a single terahertz circuit-based complementary split ring resonator (cSRR) and a two-dimensional electron gas. For this purpose, transmission spectroscopy measurements are performed under the influence of a strong magnetic field at different set points for the electric gate bias. The resulting Landau polariton disp… ▽ More We study the electrical tunability of ultrastrong light-matter interactions between a single terahertz circuit-based complementary split ring resonator (cSRR) and a two-dimensional electron gas. For this purpose, transmission spectroscopy measurements are performed under the influence of a strong magnetic field at different set points for the electric gate bias. The resulting Landau polariton dispersion depends on the applied electric bias, as the gating technique confines the electrons in-plane down to extremely sub-wavelength dimensions as small as d = 410 nm. This confinement allows for the excitation of standing plasma waves at zero magnetic field and an effective tunability of the electron number coupled to the THz resonator. This allows the normalized coupling strength to be tuned in-situ from $η$ = 0.46 down to $η$ = 0.18. This is the first demonstration of terahertz far-field spectroscopy of an electrically tunable interaction between a single terahertz resonator and electrons in a GaAs quantum well heterostructure. △ Less

Submitted 5 November, 2025; originally announced November 2025.

PyPAS -- Python package for Positron Annihilation Spectroscopy Doppler Broadening Analysis

Authors: Achiya Yosef Amrusi, Sharon May-Tal Beck, Hadar Steinberg, Guy Ron

Abstract: Doppler Broadening (DB) of annihilation radiation is a well-established technique within Positron Annihilation Spectroscopy (PAS), used for probing the electronic structure of materials. The analysis of DB experimental data relies on gamma spectroscopy analysis tools, while depth profiling using variable-energy slow positron beams depends on solving the positron diffusion equation. Traditional Var… ▽ More Doppler Broadening (DB) of annihilation radiation is a well-established technique within Positron Annihilation Spectroscopy (PAS), used for probing the electronic structure of materials. The analysis of DB experimental data relies on gamma spectroscopy analysis tools, while depth profiling using variable-energy slow positron beams depends on solving the positron diffusion equation. Traditional Variable Energy Doppler Broadening (VEDB) analysis tools, such as VEPFIT and ROYPROF, often present limitations due to outdated interfaces and lack of integration with comprehensive spectroscopy analysis platforms. Addressing these challenges, an open-source Python package for PAS analysis, PyPAS, is introduced. PyPAS offers functionalities including Coincidence Doppler Broadening (CDB) filtering, two-dimensional CDB analysis with DB and resolution extraction, and computation of lineshape parameters (S and W). Furthermore, it integrates modules for generating thermal positron implantation profiles based on established models, solving positron diffusion equations using finite-difference methods and optimizing diffusion length. This work presents the architecture of the PyPAS package and the validation results and demonstrates the application of the package through case studies. △ Less

Submitted 15 September, 2025; v1 submitted 9 September, 2025; originally announced September 2025.

Comments: 21 pages, 7 figures, 2 table

Multi-mode Deep Strong Coupling in a Multi Quantum Well Fabry-Perot Cavity

Authors: Lucy Hale, Johan Andberger, Ethan Koskas, Frieder Lindel, Mattias Beck, Giacomo Scalari, Jérôme Faist

Abstract: We present multi-mode deep-strong coupling in a multi-quantum well (N=166) heterostructure. The heterostructure itself acts as a Fabry-Perot cavity, for which the even cavity modes strongly couple to the cyclotron resonance to form Landau polaritons. The experimentally observed vacuum Rabi splitting is larger than the mode spacing and well into the deep-strong coupling regime ($η>1$) resulting in… ▽ More We present multi-mode deep-strong coupling in a multi-quantum well (N=166) heterostructure. The heterostructure itself acts as a Fabry-Perot cavity, for which the even cavity modes strongly couple to the cyclotron resonance to form Landau polaritons. The experimentally observed vacuum Rabi splitting is larger than the mode spacing and well into the deep-strong coupling regime ($η>1$) resulting in a rich multi-mode polaritonic spectrum which is accurately reproduced by an all-to-all multi-photonic, multi-electronic Hopfield coupling model. Remarkably, light-matter decoupling is observed across the whole measurable spectrum, including in the low frequency limit ($λ>>L_{cav}$) where the normalized coupling strength reaches $η=8.1$. The system demonstrates a robust platform for exploring extreme coupling regimes and its chiral nature holds potential for chiral cavity and chiral mirror applications. △ Less

Submitted 2 December, 2025; v1 submitted 27 August, 2025; originally announced August 2025.

Comments: 34 pages, 7 figures

Nesting-driven ferromagnetism of itinerant electrons

Authors: Ya. I. Rodionov, A. V. Rozhkov, M. E. S. Beck, A. O. Sboychakov, K. I. Kugel, A. L. Rakhmanov

Abstract: We theoretically investigate a model with electrons and holes whose Fermi surfaces are perfectly nested. The fermions are assumed to be interacting, both with each other and with the lattice. To suppress inhomogeneous states, a sufficiently strong long-range Coulomb repulsion is included into the model. Using the mean field approximation, one can demonstrate that in the absence of doping, the grou… ▽ More We theoretically investigate a model with electrons and holes whose Fermi surfaces are perfectly nested. The fermions are assumed to be interacting, both with each other and with the lattice. To suppress inhomogeneous states, a sufficiently strong long-range Coulomb repulsion is included into the model. Using the mean field approximation, one can demonstrate that in the absence of doping, the ground state of such a model is insulating and possesses a density-wave order, either SDW, or CDW. Upon doping, a finite ferromagnetic polarization emerges. It is argued that the mechanism driving the ferromagnetism is not of the Stoner type. A phase diagram of the model is constructed, and various properties of the ordered phases, such as half-metallicity and cone magnetic structure, are studied. △ Less

Submitted 22 November, 2025; v1 submitted 15 July, 2025; originally announced July 2025.

Comments: 15 pages, 8 figures

Journal ref: Phys.Rev.B 112,(2025) 205129

Ultrafast Non-Hermitian Skin Effect

Authors: Barbara Schneider, Alexander Dikopoltsev, Markus Bestler, Philipp Täschler, Mattias Beck, David Burghoff, Oded Zilberberg, Jérome Faist

Abstract: Topological phases of matter commonly feature protected states at their boundaries. Transferring this protection to time-metamaterials is extremely challenging, as it requires the generation of an abrupt interface between two topologically distinct bulks. Here, we realize and measure an ultrafast topological non-Hermitian skin mode bound to an interface circulating within the cavity of a fast-gain… ▽ More Topological phases of matter commonly feature protected states at their boundaries. Transferring this protection to time-metamaterials is extremely challenging, as it requires the generation of an abrupt interface between two topologically distinct bulks. Here, we realize and measure an ultrafast topological non-Hermitian skin mode bound to an interface circulating within the cavity of a fast-gain semiconductor laser. The nonlinear stationary state generated in such devices features a jump in the instantaneous frequency. We show that this discontinuity gives rise to a topological interface for the field fluctuations in the system. Using direct intensity sampling, we experimentally measure the skin modes and their positioning at the frequency jump of the stationary state. Analysis of these isolated modes reveals an ultrashort full-width at half-maximum of 583 $\pm$ 16 fs. Furthermore, we show that we can tune the shape and relative timing shift of the skin modes via external bias modulation. Finally, both numerical and experimental analysis of the noise in the system reveal that field fluctuations are funneled into the topological interface. Our findings reveal a new way to generate topologically protected states of light in time, which paves the way for novel time-varying physics as well as metrological applications. △ Less

Submitted 6 May, 2025; originally announced May 2025.

Terahertz chiral sub-wavelength cavities breaking time-reversal symmetry via ultra-strong light-matter interaction

Authors: Johan Andberger, Lorenzo Graziotto, Luca Sacchi, Mattias Beck, Giacomo Scalari, Jérôme Faist

Abstract: We demonstrate terahertz chiral sub-wavelength cavities that break time-reversal symmetry by coupling the degenerate linearly polarized modes of two orthogonal sets of nano-antenna arrays using the inter-Landau level transition of a two-dimensional electron gas in a perpendicular magnetic field, realizing normalized light-matter coupling rates up to $Ω_R/ω_{\mathrm{cav}} = 0.78$ with a dispersion… ▽ More We demonstrate terahertz chiral sub-wavelength cavities that break time-reversal symmetry by coupling the degenerate linearly polarized modes of two orthogonal sets of nano-antenna arrays using the inter-Landau level transition of a two-dimensional electron gas in a perpendicular magnetic field, realizing normalized light-matter coupling rates up to $Ω_R/ω_{\mathrm{cav}} = 0.78$ with a dispersion that is modified by the parasitic capacitive coupling between the orthogonal antennas. The deep sub-wavelength confinement of the nano-antennas means that the ultra-strong coupling regime can be reached even with a small number of carriers compared to Fabry-Perot cavities, making it viable to be used with a variety of 2D materials. The non-degenerate circularly polarized ground state was only obtained after carefully optimizing the optical design to minimize the parasitic coupling to linearly polarized light. △ Less

Submitted 27 April, 2025; v1 submitted 6 August, 2023; originally announced August 2023.

Comments: 17 pages, 8 figures

Stochastic mechanical modeling of metallic foams to determine onset of mesoscale behavior

Authors: Mujan N. Seif, Jake Puppo, Metodi Zlatinov, Denver Schaffarzick, Alexandre Martin, Matthew J. Beck

Abstract: Metallic foams are crucial to many emerging applications, among them shielding against hypervelocity impacts caused by micrometeoroids and orbital debris. The variability of properties at feature-scale and mesoscale lengths originating from the foam's inherently random microstructure makes predictive models of their properties challenging. It also hinders the optimization of components fabricated… ▽ More Metallic foams are crucial to many emerging applications, among them shielding against hypervelocity impacts caused by micrometeoroids and orbital debris. The variability of properties at feature-scale and mesoscale lengths originating from the foam's inherently random microstructure makes predictive models of their properties challenging. It also hinders the optimization of components fabricated with such foams, an especially serious problem for spacecraft design where the balance between cost and mass must also be balanced against the catastrophic results of component failure. To address this problem, we compute the critical transition length between the feature-scale, where mechanical properties are determined by individual features, and the mesoscale, where behavior is determined by ensembles of features. At the mesoscale, distributions of properties -- with respect to both expectation value and standard variability -- are consistent and predictable. The Kentucky Random Structure Toolkit (KRaSTk) is applied to determine the transition from feature-scale to mesoscale for computational volumes representing metallic foams at a range of reduced densities. The transition is found to occur when the side length of a cubic sample volume is ~10x greater than the characteristic length. Comparing KRaSTk-computed converged stiffness distributions with experimental measurements of a commercial metallic foam found excellent agreement for both expectation value and standard variability at all reduced densities. Lastly, we observe that the diameter of a representative MMOD strike is ~30x shorter than the feature-scale to mesoscale transition for the foam at any reduced density. Therefore, features will determine response to hypervelocity impacts, rather than bulk (or even mesoscale) structure. △ Less

Submitted 28 February, 2023; originally announced February 2023.

An engineered planar plasmonic reflector for polaritonic mode confinement

Authors: Shima Rajabali, Josefine Enkner, Erika Cortese, Mattias Beck, Simone De Liberato, Jérôme Faist, Giacomo Scalari

Abstract: It was recently demonstrated that, in deep subwavelength gap resonators coupled to two-dimensional electron gases, coupling to propagating plasmons can lead to energy leakage and prevent the formation of polaritonic resonances. This process, akin to Landau damping, limits the achievable field confinement and thus the value of light-matter coupling strength. In this work, we show how plasmonic subw… ▽ More It was recently demonstrated that, in deep subwavelength gap resonators coupled to two-dimensional electron gases, coupling to propagating plasmons can lead to energy leakage and prevent the formation of polaritonic resonances. This process, akin to Landau damping, limits the achievable field confinement and thus the value of light-matter coupling strength. In this work, we show how plasmonic subwavelength reflectors can be used to create an artificial energy stopband in the plasmon dispersion, confining them and enabling the recovery of the polaritonic resonances. Using this approach we demonstrate a normalized light-matter coupling ratio of Ω/ω = 0.35 employing a single quantum well with a gap size of λ/2400 in vacuum. △ Less

Submitted 27 December, 2022; originally announced December 2022.

Comments: 13 pages, 3 figures

Journal ref: Optical Materials Express, Vol. 13, Issue 10, pp. 2944-2952 (2023)

Wideband Josephson Parametric Isolator

Authors: M. A. Beck, M. Selvanayagam, A. Carniol, S. Cairns, C. P. Mancini

Abstract: The cryogenic hardware required to build a superconducting qubit based quantum computer demands a variety of microwave components. These elements include microwave couplers, filters, amplifiers, and circulators/isolators. Traditionally implemented as discrete components, integration of this peripheral hardware, in an effort to reduce overall footprint, thermal load, and added noise, is a key chall… ▽ More The cryogenic hardware required to build a superconducting qubit based quantum computer demands a variety of microwave components. These elements include microwave couplers, filters, amplifiers, and circulators/isolators. Traditionally implemented as discrete components, integration of this peripheral hardware, in an effort to reduce overall footprint, thermal load, and added noise, is a key challenge to scaling modern quantum processors with qubit counts climbing over the 100+ mark. Ferrite--based microwave isolators, generally employed in the readout chain to decouple qubits and resonators from readout electronics, persist as one of the volumetrically largest devices still utilized as discrete components. Here we present an alternative two--port isolating integrated circuit derived from the DC Superconducting Quantum Interference Device (DC-SQUID). Non-reciprocal transmission is achieved using the three-wave microwave mixing properties of a flux-modulated DC--SQUID. We show that when multiple DC-SQUIDs are embedded in a multi--pole admittance inverting filter structure, the three-wave mixing derived from the flux pumping of the DC-SQUIDs can provide directional microwave power flow. For a three--pole filter device, we experimentally demonstrate a directionality greater than 15 dB over a 600 MHz bandwidth. △ Less

Submitted 23 June, 2023; v1 submitted 16 December, 2022; originally announced December 2022.

Comments: 16 pages, 10 figures

Journal ref: Phys. Rev. Applied 20, 034054 (2023)

A Review of Sc-containing "Scandate" Thermionic Cathodes

Authors: Mujan N. Seif, Qunfei Zhou, Xiaotao Liu, T. John Balk, Matthew J. Beck

Abstract: Although thermionic emission has been studied for more than 100 years, recent interest in novel electron devices for military and civilian use has led to a surge in demand for cathodes with enhanced emission properties (e.g. higher current density, more uniform emission, lower operating temperatures, or extended in-service longevity). Sc-containing "scandate" cathodes have been widely reported to… ▽ More Although thermionic emission has been studied for more than 100 years, recent interest in novel electron devices for military and civilian use has led to a surge in demand for cathodes with enhanced emission properties (e.g. higher current density, more uniform emission, lower operating temperatures, or extended in-service longevity). Sc-containing "scandate" cathodes have been widely reported to exhibit superior emission properties compared to previous-generation thermionic cathodes, including oxide, B-, and M-type cathodes. Despite extensive study spanning several decades, the mechanism by which the addition of Sc enhances cathode emission remains ambiguous, and certain limitations -- non-uniform emission, low reproducibility, inconsistent longevity -- continue to prevent widespread commercial integration of scandate cathodes into electron devices. This review attempts to survey the literature to-date addressing the fabrication, structure, and properties of scandate cathodes, with particular attention to studies addressing the role of Sc in enhancing emission. △ Less

Submitted 9 February, 2022; originally announced February 2022.

A Kapitza Pendulum for Ultracold Atoms

Authors: Jian Jiang, Erik Bernhart, Marvin Röhrle, Jens Benary, Marvin Beck, Christian Baals, Herwig Ott

Abstract: We report on the experimental realization of a Kapitza pendulum for ultracold atoms. Using time-periodic attractive and repulsive Gaussian potentials, we create an effective trap for ultracold neutral atoms in a regime where the time average of the potential is equal to zero. We analyze the role of experimental imperfections, the stability of the trapped atomic cloud, and the magnitude of the effe… ▽ More We report on the experimental realization of a Kapitza pendulum for ultracold atoms. Using time-periodic attractive and repulsive Gaussian potentials, we create an effective trap for ultracold neutral atoms in a regime where the time average of the potential is equal to zero. We analyze the role of experimental imperfections, the stability of the trapped atomic cloud, and the magnitude of the effective potential. We find good agreement with the high-frequency expansion of the underlying system dynamics. Our experimental approach opens up new possibilities to study Floquet systems of neutral atoms. △ Less

Submitted 29 June, 2023; v1 submitted 20 December, 2021; originally announced December 2021.

Comments: 5 pages, 4 figures

Journal ref: PhysRevLett.131.033401 (2023)

An ultrastrongly coupled single THz meta-atom

Authors: Shima Rajabali, Sergej Markmann, Elsa Jöchl, Mattias Beck, Christian A. Lehner, Werner Wegscheider, Jérôme Faist, Giacomo Scalari

Abstract: Free-space coupling to strongly subwavelength individual optical elements is a central theme in quantum optics, as it allows to control and manipulate the properties of quantum systems. In this work, we show that by combining an asymmetric immersion lens setup and complementary design of metasurfaces we are able to perform THz time-domain spectroscopy of an individual, strongly subwavelength (d/λ0… ▽ More Free-space coupling to strongly subwavelength individual optical elements is a central theme in quantum optics, as it allows to control and manipulate the properties of quantum systems. In this work, we show that by combining an asymmetric immersion lens setup and complementary design of metasurfaces we are able to perform THz time-domain spectroscopy of an individual, strongly subwavelength (d/λ0=1/20) meta-atom. We unravel the linewidth dependence of planar metamaterials as a function of the meta-atom number indicating quenching of the Dicke superradiance. On these grounds, we investigate ultrastrongly coupled Landau polaritons at the single resonator level, measuring a normalized coupling ratio of Ω/ω=0.60 resulting from coupling of the fundamental mode to a few thousand electrons. Similar measurements on a low loss, less doped two dimensional electron gas yield a coupling ratio Ω/ω=0.33 with a cooperativity C=4g^2/κγ= 94. Interestingly, the coupling strength of a coupled single resonator is the same as of a coupled array. Our findings pave the way towards the control of light-matter interaction in the ultrastrong coupling regime at the single electron/single resonator level. The proposed technique is way more general and can be useful to characterize the complex conductivity of micron-sized samples in the THz and sub-THz domain. △ Less

Submitted 19 October, 2021; originally announced October 2021.

Comments: 28 pages, 5 figures

Balls and Walls: A Compact Unary Coding for Bosonic States

Authors: Hatem Barghathi, Caleb Usadi, Micah Beck, Adrian Del Maestro

Abstract: We introduce a unary coding of bosonic occupation states based on the famous "balls and walls" counting for the number of configurations of $N$ indistinguishable particles on $L$ distinguishable sites. Each state is represented by an integer with a human readable bit string that has a compositional structure allowing for the efficient application of operators that locally modify the number of boso… ▽ More We introduce a unary coding of bosonic occupation states based on the famous "balls and walls" counting for the number of configurations of $N$ indistinguishable particles on $L$ distinguishable sites. Each state is represented by an integer with a human readable bit string that has a compositional structure allowing for the efficient application of operators that locally modify the number of bosons. By exploiting translational and inversion symmetries, we identify a speedup factor of order $L$ over current methods when generating the basis states of bosonic lattice models. The unary coding is applied to a one-dimensional Bose-Hubbard Hamiltonian with up to $L=N=20$, and the time needed to generate the ground state block is reduced to a fraction of the diagonalization time. For the ground state symmetry resolved entanglement, we demonstrate that variational approaches restricting the local bosonic Hilbert space could result in an error that scales with system size. △ Less

Submitted 15 September, 2021; originally announced September 2021.

Comments: Main text: 7 pages, 3 figures + Supplementary material: 3 pages 1 figure. For associated data and code repository see: https://github.com/DelMaestroGroup/papers-code-UnaryBosonicBasis

Journal ref: Phys. Rev. B 105, L121116 (2022)

Breakdown of the topological protection by cavity vacuum fields in the integer quantum Hall effect

Authors: Felice Appugliese, Josefine Enkner, Gian Lorenzo Paravicini-Bagliani, Mattias Beck, Christian Reichl, Werner Wegscheider, Giacomo Scalari, Cristiano Ciuti, Jérôme Faist

Abstract: The control of the electronic properties of materials via the vacuum fields of cavity electromagnetic resonators is one of the emerging frontiers of condensed matter physics. We show here that the enhancement of vacuum field fluctuations in subwavelength split-ring resonators dramatically affects arguably one of the most paradigmatic quantum protectorates, namely the quantum Hall electron transpor… ▽ More The control of the electronic properties of materials via the vacuum fields of cavity electromagnetic resonators is one of the emerging frontiers of condensed matter physics. We show here that the enhancement of vacuum field fluctuations in subwavelength split-ring resonators dramatically affects arguably one of the most paradigmatic quantum protectorates, namely the quantum Hall electron transport in high-mobility 2D electron gases. The observed breakdown of the topological protection of the integer quantum Hall effect is interpreted in terms of a long-range cavity-mediated electron hopping where the anti-resonant terms of the light-matter coupling finally result into a finite resistivity induced by the vacuum fluctuations. The present experimental platform can be used for any 2D material and provides new ways to manipulate electron phases in matter thanks to vacuum-field engineering △ Less

Submitted 29 July, 2021; originally announced July 2021.

Journal ref: Science 375, 6584 (2022)

Low frequency correlated charge noise measurements across multiple energy transitions in a tantalum transmon

Authors: Daniel M. Tennant, Luis A. Martinez, Kristin M. Beck, Sean R. O'Kelley, Christopher D. Wilen, R. McDermott, Jonathan L DuBois, Yaniv J. Rosen

Abstract: Transmon qubits fabricated with tantalum metal have been shown to possess energy relaxation times greater than 300 $μ$s and, as such, present an attractive platform for high precision, correlated noise studies across multiple higher energy transitions. Tracking the multi-level fluctuating qudit frequencies with a precision enabled by the high coherence of the device allows us to extract the charge… ▽ More Transmon qubits fabricated with tantalum metal have been shown to possess energy relaxation times greater than 300 $μ$s and, as such, present an attractive platform for high precision, correlated noise studies across multiple higher energy transitions. Tracking the multi-level fluctuating qudit frequencies with a precision enabled by the high coherence of the device allows us to extract the charge offset and quasi-particle dynamics. We observe qualitatively different charge offset behavior in the tantalum device than those measured in previous low frequency charge noise studies. In particular, we find the charge offset dynamics are dominated by rare, discrete jumps between a finite number of quasi-stationary charge configurations, a previously unobserved charge noise process in superconducting qubits. △ Less

Submitted 29 November, 2021; v1 submitted 15 June, 2021; originally announced June 2021.

Comments: 19 pages, 11 figures

Polaritonic non-locality in ultrastrong light-matter coupling

Authors: Shima Rajabali, Erika Cortese, Mattias Beck, Simone De Liberato, Jérôme Faist, Giacomo Scalari

Abstract: Sub-wavelength electromagnetic field localization has been central in photonic research in the last decade, allowing to enhance sensing capabilities as well as increasing the coupling between photons and material excitations. The ultrastrong light-matter coupling regime in the THz range with split-ring resonators coupled to magnetoplasmons has been widely investigated, achieving successive world-r… ▽ More Sub-wavelength electromagnetic field localization has been central in photonic research in the last decade, allowing to enhance sensing capabilities as well as increasing the coupling between photons and material excitations. The ultrastrong light-matter coupling regime in the THz range with split-ring resonators coupled to magnetoplasmons has been widely investigated, achieving successive world-records for the largest light-matter coupling ever achieved. Ever shrinking resonators have allowed to approach the regime of few electrons strong coupling, in which single-dipole properties can be modified by the vacuum field. Here we demonstrate, theoretically and experimentally, the existence of a limit to the possibility of arbitrarily increasing electromagnetic confinement in polaritonic systems. Strongly sub-wavelength fields can excite a continuum of high-momenta propagative magnetoplasmons. This leads to peculiar nonlocal polaritonic effects, as certain polaritonic features disappear and the system enters in the regime of bound-to-continuum strong coupling. Emerging nonlinearities due to the local breaking of Kohn's theorem are also reported. △ Less

Submitted 21 January, 2021; originally announced January 2021.

Comments: 24 pages, 4 figures

The SPOT-IL Positron Beam Construction and Its Use for Doppler Broadening Measurement of Titanium Thin Films

Authors: P. Or, G. Erlichman, D. Cohen, I. Sabo-Napadesky, E. Gordon, S. Cohen, O. Presler, E. O. Cohen, E. Piasetzky, H. Steinberg, S. May-Tal Beck, Guy Ron

Abstract: The construction and first operation of the slow positron beam built at the Hebrew University is reported here. The beam follows a traditional design, using a 22Na source, a Tungsten moderator, and a target cell equipped with a load-lock system for easy sample insertion. The beam energy varies between 0.03 keV and 30 keV. The detection system consists of two high purity Germanium detectors, facing… ▽ More The construction and first operation of the slow positron beam built at the Hebrew University is reported here. The beam follows a traditional design, using a 22Na source, a Tungsten moderator, and a target cell equipped with a load-lock system for easy sample insertion. The beam energy varies between 0.03 keV and 30 keV. The detection system consists of two high purity Germanium detectors, facing each other, allowing low-background Doppler-Broadening (DB) measurements. Event readout is done using a state-of-the-art compact desktop system. The target cell is designed to allow a combined measurement of DB and sample conductivity, with the flexibility to add more detection options in the future. The beam has been successfully tested by using it to charecterize Titanium (Ti) films. Two 1.2 μm Ti films -- as produced, and after annealing, were measured at various energies (2 keV - 25 keV), and the results show consistent behavior with previous measurements. △ Less

Submitted 12 July, 2020; originally announced July 2020.

Digital coherent control of a superconducting qubit

Authors: Edward Leonard Jr., Matthew A. Beck, JJ Nelson, Brad G. Christensen, Ted Thorbeck, Caleb Howington, Alexander Opremcak, Ivan V. Pechenezhskiy, Kenneth Dodge, Nicholas P. Dupuis, Jaseung Ku, Francisco Schlenker, Joseph Suttle, Christopher Wilen, Shaojiang Zhu, Maxim G. Vavilov, Britton L. T. Plourde, Robert McDermott

Abstract: High-fidelity gate operations are essential to the realization of a fault-tolerant quantum computer. In addition, the physical resources required to implement gates must scale efficiently with system size. A longstanding goal of the superconducting qubit community is the tight integration of a superconducting quantum circuit with a proximal classical cryogenic control system. Here we implement coh… ▽ More High-fidelity gate operations are essential to the realization of a fault-tolerant quantum computer. In addition, the physical resources required to implement gates must scale efficiently with system size. A longstanding goal of the superconducting qubit community is the tight integration of a superconducting quantum circuit with a proximal classical cryogenic control system. Here we implement coherent control of a superconducting transmon qubit using a Single Flux Quantum (SFQ) pulse driver cofabricated on the qubit chip. The pulse driver delivers trains of quantized flux pulses to the qubit through a weak capacitive coupling; coherent rotations of the qubit state are realized when the pulse-to-pulse timing is matched to a multiple of the qubit oscillation period. We measure the fidelity of SFQ-based gates to be ~95% using interleaved randomized benchmarking. Gate fidelities are limited by quasiparticle generation in the dissipative SFQ driver. We characterize the dissipative and dispersive contributions of the quasiparticle admittance and discuss mitigation strategies to suppress quasiparticle poisoning. These results open the door to integration of large-scale superconducting qubit arrays with SFQ control elements for low-latency feedback and stabilization. △ Less

Submitted 20 June, 2018; originally announced June 2018.

Comments: 13 pages, 9 figures, 1 table

Journal ref: Phys. Rev. Applied 11, 014009 (2019)

Magneto-transport controlled by Landau polariton states

Authors: Gian L. Paravicini-Bagliani, Felice Appugliese, Eli Richter, Federico Valmorra, Janine Keller, Mattias Beck, Nicola Bartolo, Clemens Rössler, Thomas Ihn, Klaus Ensslin, Cristiano Ciuti, Giacomo Scalari, Jerome Faist

Abstract: Hybrid excitations, called polaritons, emerge in systems with strong light-matter coupling. Usually, they dominate the linear and nonlinear optical properties with applications in quantum optics. Here, we show the crucial role of the electronic component of polaritons in the magneto-transport of a cavity-embedded 2D electron gas in the ultrastrong coupling regime. We show that the linear dc resist… ▽ More Hybrid excitations, called polaritons, emerge in systems with strong light-matter coupling. Usually, they dominate the linear and nonlinear optical properties with applications in quantum optics. Here, we show the crucial role of the electronic component of polaritons in the magneto-transport of a cavity-embedded 2D electron gas in the ultrastrong coupling regime. We show that the linear dc resistivity is significantly modified by the coupling to the cavity even without external irradiation. Our observations confirm recent predictions of vacuum-induced modification of the resistivity. Furthermore, photo-assisted transport in presence of a weak irradiation field at sub-THz frequencies highlights the different roles of localized and delocalized states. △ Less

Submitted 17 October, 2018; v1 submitted 2 May, 2018; originally announced May 2018.

Comments: Accepted for Nature Physics

Journal ref: Nat. Phys. 15, 186-190 (2019)

Multi-Terminal Memtransistors from Polycrystalline Monolayer MoS2

Authors: Vinod K. Sangwan, Hong-Sub Lee, Hadallia Bergeron, Itamar Balla, Megan E. Beck, Kan-Sheng Chen, Mark C. Hersam

Abstract: In the last decade, a 2-terminal passive circuit element called a memristor has been developed for non-volatile resistive random access memory and has more recently shown promise for neuromorphic computing. Compared to flash memory, memristors have higher endurance, multi-bit data storage, and faster read/write times. However, although 2-terminal memristors have demonstrated basic neural functions… ▽ More In the last decade, a 2-terminal passive circuit element called a memristor has been developed for non-volatile resistive random access memory and has more recently shown promise for neuromorphic computing. Compared to flash memory, memristors have higher endurance, multi-bit data storage, and faster read/write times. However, although 2-terminal memristors have demonstrated basic neural functions, synapses in the human brain outnumber neurons by more than a factor of 1000, which implies that multiterminal memristors are needed to perform complex functions such as heterosynaptic plasticity. Previous attempts to move beyond 2-terminal memristors include the 3-terminal Widrow-Hoff memistor and field-effect transistors with nanoionic gates or floating gates, albeit without memristive switching in the transistor. Here, we report the scalable experimental realization of a multi-terminal hybrid memristor and transistor (i.e., memtransistor) using polycrystalline monolayer MoS2. Two-dimensional (2D) MoS2 memtransistors show gate tunability in individual states by 4 orders of magnitude in addition to large switching ratios with high cycling endurance and long-term retention of states. In addition to conventional neural learning behavior of long-term potentiation/depression, 6-terminal MoS2 memtransistors possess gate-tunable heterosynaptic functionality that is not achievable using 2-terminal memristors. For example, the conductance between a pair of two floating electrodes (pre-synaptic and post-synaptic neurons) is varied by 10X by applying voltage pulses to modulatory terminals. In situ scanning probe microscopy, cryogenic charge transport measurements, and device modeling reveal that bias-induced MoS2 defect motion drives resistive switching by dynamically varying Schottky barrier heights. △ Less

Submitted 21 February, 2018; originally announced February 2018.

Comments: 22 pages, 4 figures

Journal ref: Nature 2018

Self-Aligned van der Waals Heterojunction Diodes and Transistors

Authors: Vinod K. Sangwan, Megan E. Beck, Alex Henning, Jiajia Luo, Hadallia Bergeron, Junmo Kang, Itamar Balla, Hadass Inbar, Lincoln J. Lauhon, Mark C. Hersam

Abstract: A general self-aligned fabrication scheme is reported here for a diverse class of electronic devices based on van der Waals materials and heterojunctions. In particular, self-alignment enables the fabrication of source-gated transistors in monolayer MoS2 with near-ideal current saturation characteristics and channel lengths down to 135 nm. Furthermore, self-alignment of van der Waals p-n heterojun… ▽ More A general self-aligned fabrication scheme is reported here for a diverse class of electronic devices based on van der Waals materials and heterojunctions. In particular, self-alignment enables the fabrication of source-gated transistors in monolayer MoS2 with near-ideal current saturation characteristics and channel lengths down to 135 nm. Furthermore, self-alignment of van der Waals p-n heterojunction diodes achieves complete electrostatic control of both the p-type and n-type constituent semiconductors in a dual-gated geometry, resulting in gate-tunable mean and variance of anti-ambipolar Gaussian characteristics. Through finite-element device simulations, the operating principles of source-gated transistors and dual-gated anti-ambipolar devices are elucidated, thus providing design rules for additional devices that employ self-aligned geometries. For example, the versatility of this scheme is demonstrated via contact-doped MoS2 homojunction diodes and mixed-dimensional heterojunctions based on organic semiconductors. The scalability of this approach is also shown by fabricating self-aligned short-channel transistors with sub-diffraction channel lengths in the range of 150 nm to 800 nm using photolithography on large-area MoS2 films grown by chemical vapor deposition. Overall, this self-aligned fabrication method represents an important step towards the scalable integration of van der Waals heterojunction devices into more sophisticated circuits and systems. △ Less

Submitted 3 February, 2018; originally announced February 2018.

Landau polaritons in highly non-parabolic 2D gases in the ultra-strong coupling regime

Authors: Janine Keller, Giacomo Scalari, Felice Appugliese, Shima Rajabali, Mattias Beck, Johannes Haase, Christian A. Lehner, Werner Wegscheider, Michele Failla, Maksym Myronov, David R. Leadley, James Lloyd-Hughes, Pierre Nataf, Jerome Faist

Abstract: We probe ultra-strong light matter coupling between metallic terahertz metasurfaces and Landau-level transitions in high mobility 2D electron and hole gases. We utilize heavy-hole cyclotron resonances in strained Ge and electron cyclotron resonances in InSb quantum wells, both within highly non-parabolic bands, and compare our results to well known parabolic AlGaAs/GaAs quantum well (QW) systems.… ▽ More We probe ultra-strong light matter coupling between metallic terahertz metasurfaces and Landau-level transitions in high mobility 2D electron and hole gases. We utilize heavy-hole cyclotron resonances in strained Ge and electron cyclotron resonances in InSb quantum wells, both within highly non-parabolic bands, and compare our results to well known parabolic AlGaAs/GaAs quantum well (QW) systems. Tuning the coupling strength of the system by two methods, lithographically and by optical pumping, we observe a novel behavior clearly deviating from the standard Hopfield model previously verified in cavity quantum electrodynamics: an opening of a lower polaritonic gap. △ Less

Submitted 30 December, 2019; v1 submitted 25 August, 2017; originally announced August 2017.

Journal ref: Phys. Rev. B 101, 075301 (2020)

Molecular Packing Motifs Determine Charge-Transfer and Carrier Dynamics in Molecular Heterosystems: the Case of Pentacene - Perfluoropentacene

Authors: Andre Rinn, Tobias Breuer, Julia Wiegand, Michael Beck, Jens Hübner, Michael Oestreich, Wolfram Heimbrodt, Gregor Witte, Sangam Chatterjee

Abstract: The great majority of electronic and optoelectronic devices depends on interfaces between n-type and p-type semiconductors. Finding such matching donor-acceptor systems in molecular crystals remains a challenging endeavor. Structurally compatible molecules may not necessarily be suitable with respect to their optical and electronic properties: large exciton binding energies may favor bound electro… ▽ More The great majority of electronic and optoelectronic devices depends on interfaces between n-type and p-type semiconductors. Finding such matching donor-acceptor systems in molecular crystals remains a challenging endeavor. Structurally compatible molecules may not necessarily be suitable with respect to their optical and electronic properties: large exciton binding energies may favor bound electron-hole pairs rather than charge separation by exciton dissociation, and free, band-like transport is challenging to achieve as hopping commonly dominates charge motion. Structurally well-defined pentacene-perfluoropentacene heterostructures in different polymorphs and molecular orientations are model systems to study the relation of packing motif and optical properties. These heterosystems feature two characteristic interface-specific luminescence channels at around 1.4 and 1.5 eV. Their relative emission strength strongly depends on the molecular alignment of the respective donor and acceptor molecules. Evaluating their dynamics in comparison with the corresponding unitary films reveals the role of singlet-triplet intersystem crossing and different channels for carrier injection into the interface-specific resonances. △ Less

Submitted 11 December, 2016; originally announced December 2016.

Negative free carrier absorption in terahertz quantum cascade lasers

Authors: C. Ndebeka-Bandou, M. Rösch, K. Ohtani, M. Beck, J. Faist

Abstract: We analyze the peculiar case where the free carrier absorption arising from LO phonon absorption-assisted transitions becomes negative and therefore turns into a gain source for quantum cascade lasers. Such an additional source of gain exists when the ratio between the electronic and the lattice temperatures is larger than one, a condition that is usually fulfilled in quantum cascade lasers. We fi… ▽ More We analyze the peculiar case where the free carrier absorption arising from LO phonon absorption-assisted transitions becomes negative and therefore turns into a gain source for quantum cascade lasers. Such an additional source of gain exists when the ratio between the electronic and the lattice temperatures is larger than one, a condition that is usually fulfilled in quantum cascade lasers. We find a gain of few cm$^{-1}$'s at 200K. We report the development of a terahertz quantum cascade laser operating in the negative free carrier absorption regime. △ Less

Submitted 28 November, 2016; originally announced November 2016.

Journal ref: Appl. Phys. Lett. 108, 091102 (2016)

THz ultrastrong light-matter coupling

Authors: Giacomo Scalari, Curdin Maissen, Sara Cibella, Roberto Leoni, Christian Reichl, Werner Wegscheider, Mattias Beck, Jérôme Faist

Abstract: Cavity photon resonators with ultrastrong light-matter interactions are attracting interest both in semiconductor and superconducting systems displaying the capability to manipulate the cavity quantum electrodynamic ground state with controllable physical properties. Here we review a series of experiments aimed at probing the ultrastrong light-matter coupling regime, where the vacuum Rabi splittin… ▽ More Cavity photon resonators with ultrastrong light-matter interactions are attracting interest both in semiconductor and superconducting systems displaying the capability to manipulate the cavity quantum electrodynamic ground state with controllable physical properties. Here we review a series of experiments aimed at probing the ultrastrong light-matter coupling regime, where the vacuum Rabi splitting $Ω$ is comparable to the bare transition frequency $ω$ . We present a new platform where the inter-Landau level transition of a two-dimensional electron gas (2DEG) is strongly coupled to the fundamental mode of deeply subwavelength split-ring resonators operating in the mm-wave range. Record-high values of the normalized light-matter coupling ratio $\fracΩω= 0.89$ are reached and the system appears highly scalable far into the microwave range. △ Less

Submitted 28 November, 2016; originally announced November 2016.

Journal ref: Il Nuovo Saggiatore, Vol 31, 3-4, pag.4-14, 2015

Optimized Coplanar Waveguide Resonators for a Superconductor-Atom Interface

Authors: M. A. Beck, J. A. Isaacs, D. Booth, J. D. Pritchard, M. Saffman, R. McDermott

Abstract: We describe the design and characterization of superconducting coplanar waveguide cavities tailored to facilitate strong coupling between superconducting quantum circuits and single trapped Rydberg atoms. For initial superconductor-atom experiments at 4.2 K, we show that resonator quality factors above $10^4$ can be readily achieved. Furthermore, we demonstrate that the incorporation of thick-film… ▽ More We describe the design and characterization of superconducting coplanar waveguide cavities tailored to facilitate strong coupling between superconducting quantum circuits and single trapped Rydberg atoms. For initial superconductor-atom experiments at 4.2 K, we show that resonator quality factors above $10^4$ can be readily achieved. Furthermore, we demonstrate that the incorporation of thick-film copper electrodes at a voltage antinode of the resonator provides a route to enhance the zero-point electric fields of the resonator in a trapping region that is 40 $μ$m above the chip surface, thereby minimizing chip heating from scattered trap light. The combination of high resonator quality factor and strong electric dipole coupling between the resonator and the atom should make it possible to achieve the strong coupling limit of cavity quantum electrodynamics with this system. △ Less

Submitted 17 August, 2016; v1 submitted 6 May, 2016; originally announced May 2016.

Comments: 4 pages, 4 figures

Journal ref: Appl. Phys. Lett. 109, 092602 (2016)

Origin and Suppression of $1/f$ Magnetic Flux Noise

Authors: P. Kumar, S. Sendelbach, M. A. Beck, J. W. Freeland, Zhe Wang, Hui Wang, C. C. Yu, R. Q. Wu, D. P. Pappas, R. McDermott

Abstract: Magnetic flux noise is a dominant source of dephasing and energy relaxation in superconducting qubits. The noise power spectral density varies with frequency as $1/f^α$ with $α\sim 1$ and spans 13 orders of magnitude. Recent work indicates that the noise is from unpaired magnetic defects on the surfaces of the superconducting devices. Here, we demonstrate that adsorbed molecular O$_2$ is the domin… ▽ More Magnetic flux noise is a dominant source of dephasing and energy relaxation in superconducting qubits. The noise power spectral density varies with frequency as $1/f^α$ with $α\sim 1$ and spans 13 orders of magnitude. Recent work indicates that the noise is from unpaired magnetic defects on the surfaces of the superconducting devices. Here, we demonstrate that adsorbed molecular O$_2$ is the dominant contributor to magnetism in superconducting thin films. We show that this magnetism can be suppressed by appropriate surface treatment or improvement in the sample vacuum environment. We observe a suppression of static spin susceptibility by more than an order of magnitude and a suppression of $1/f$ magnetic flux noise power spectral density by more than a factor of 5. These advances open the door to realization of superconducting qubits with improved quantum coherence. △ Less

Submitted 4 April, 2016; originally announced April 2016.

Comments: Main text: 5 pages, 4 figures. Supplement: 8 pages, 6 figures

Journal ref: Phys. Rev. Applied 6, 041001 (2016)

Melting the Superconducting State in the Electron Doped Cuprate Pr$_{1.85}% $Ce$_{0.15}$CuO$_{4-δ}$ with Intense near-infrared and Terahertz Pulses

Authors: M. Beck, M. Klammer, I. Rousseau, M. Obergfell, P. Leiderer, M. Helm, V. V. Kabanov, I. Diamant, A. Rabinowicz, Y. Dagan, J. Demsar

Abstract: We studied the superconducting (SC) state depletion process in an electron doped cuprate Pr$_{1.85}$Ce$_{0.15}$CuO$_{4-δ}$ by pumping with near-infrared (NIR) and narrow-band THz pulses. When pumping with THz pulses tuned just above the SC gap, we find the absorbed energy density required to deplete superconductivity, $A_{dep}$, matches the thermodynamic condensation energy. Contrary, by NIR pumpi… ▽ More We studied the superconducting (SC) state depletion process in an electron doped cuprate Pr$_{1.85}$Ce$_{0.15}$CuO$_{4-δ}$ by pumping with near-infrared (NIR) and narrow-band THz pulses. When pumping with THz pulses tuned just above the SC gap, we find the absorbed energy density required to deplete superconductivity, $A_{dep}$, matches the thermodynamic condensation energy. Contrary, by NIR pumping $A_{dep}$ is an order of magnitude higher, despite the fact that the SC gap is much smaller than the energy of relevant bosonic excitations. The result implies that only a small subset of bosons contribute to pairing. △ Less

Submitted 14 March, 2016; originally announced March 2016.

Journal ref: Phys. Rev. B 95, 085106 (2017)

Sub-cycle measurement of intensity correlations in the Terahertz range

Authors: Ileana-Cristina Benea-Chelmus, Curdin Maissen, Giacomo Scalari, Mattias Beck, Jérôme Faist

Abstract: The Terahertz frequency range bears intriguing opportunities, beyond very advanced applications in spectroscopy and matter control. Peculiar quantum phenomena are predicted to lead to light emission by non-trivial mechanisms. Typically, such emission mechanisms are unraveled by temporal correlation measurements of photon arrival times, as demonstrated in their pioneering work by Hanbury Brown and… ▽ More The Terahertz frequency range bears intriguing opportunities, beyond very advanced applications in spectroscopy and matter control. Peculiar quantum phenomena are predicted to lead to light emission by non-trivial mechanisms. Typically, such emission mechanisms are unraveled by temporal correlation measurements of photon arrival times, as demonstrated in their pioneering work by Hanbury Brown and Twiss. So far, the Terahertz range misses an experimental implementation of such technique with very good temporal properties and high sensitivity. In this paper, we propose a room-temperature scheme to measure photon correlations at THz frequencies based on electro-optic sampling. The temporal resolution of 146 fs is faster than one cycle of oscillation and the sensitivity is so far limited to ~1500 photons. With this technique, we measure the photon statistics of a THz quantum cascade laser. The proposed measurement scheme allows, in principle, the measurement of ultrahigh bandwidth photons and paves the way towards THz quantum optics. △ Less

Submitted 16 December, 2015; v1 submitted 7 December, 2015; originally announced December 2015.

Journal ref: Phys. Rev. A 93, 043812 (2016)

Spin pairs in a weakly coupled many-electron quantum dot

Authors: S. Hellmüller, D. Bischoff, T. Müller, M. Beck, K. Ensslin, T. Ihn

Abstract: We report the observation of an unusually large number of consecutive spin pairs in a weakly coupled many-electron GaAs/AlGaAs quantum dot. The pairs are identified due to pairwise parallel shifts of Coulomb resonances in a perpendicular magnetic field. Using a nearby quantum point contact for time-resolved charge detection, the tunneling rates are investigated as a function of gate voltage and ma… ▽ More We report the observation of an unusually large number of consecutive spin pairs in a weakly coupled many-electron GaAs/AlGaAs quantum dot. The pairs are identified due to pairwise parallel shifts of Coulomb resonances in a perpendicular magnetic field. Using a nearby quantum point contact for time-resolved charge detection, the tunneling rates are investigated as a function of gate voltage and magnetic field. We compare our experimental data to a single-level transport model and discuss possible reasons for deviations. △ Less

Submitted 27 September, 2015; originally announced September 2015.

Comments: 7 pages, 4 figures

Journal ref: Phys. Rev. B 92, 115401 (2015)

Momentum sharing in imbalanced Fermi systems

Authors: O. Hen, M. Sargsian, L. B. Weinstein, E. Piasetzky, H. Hakobyan, D. W. Higinbotham, M. Braverman, W. K. Brooks, S. Gilad, K. P. Adhikari, J. Arrington, G. Asryan, H. Avakian, J. Ball, N. A. Baltzell, M. Battaglieri, A. Beck, S. May-Tal Beck, I. Bedlinskiy, W. Bertozzi, A. Biselli, V. D. Burkert, T. Cao, D. S. Carman, A. Celentano , et al. (116 additional authors not shown)

Abstract: The atomic nucleus is composed of two different kinds of fermions, protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority fermions (usually neutrons) to have a higher average momentum. Our high-energy electron scattering measurements using 12C, 27Al, 56Fe and 208Pb targets show that, even in heavy neutron-rich nuclei, short-range… ▽ More The atomic nucleus is composed of two different kinds of fermions, protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority fermions (usually neutrons) to have a higher average momentum. Our high-energy electron scattering measurements using 12C, 27Al, 56Fe and 208Pb targets show that, even in heavy neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few body systems to neutron stars and may also be observable experimentally in two-spin state, ultra-cold atomic gas systems. △ Less

Submitted 29 November, 2014; originally announced December 2014.

Comments: Published in Science. 10 pages, 3 figures

Journal ref: Science 346, 614 (2014)

InGaAs/AlInGaAs THz Quantum Cascade Lasers operating up to 195 K in strong magnetic field

Authors: Federico Valmorra, Giacomo Scalari, Keita Ohtani, Mattias Beck, Jerome Faist

Abstract: Terahertz quantum cascade lasers based on InGaAs wells and quaternary AlInGaAs barriers were measured in magnetic field. This study was carried out on a four quantum well active region design with photon energy of 14.3 meV processed both with Au and Cu waveguides. The heterostructure operates up to 148 K at B=0 T and in a Cu waveguide. The complete magneto-spectroscopic study allowed the compariso… ▽ More Terahertz quantum cascade lasers based on InGaAs wells and quaternary AlInGaAs barriers were measured in magnetic field. This study was carried out on a four quantum well active region design with photon energy of 14.3 meV processed both with Au and Cu waveguides. The heterostructure operates up to 148 K at B=0 T and in a Cu waveguide. The complete magneto-spectroscopic study allowed the comparison of emission and transport data. Increasing the magnetic field, the low effective mass of the InGaAs wells allowed us to reach the very strong confinement regime. At B=12 T, where the cyclotron transition is almost resonant with the LO-phonon, we recorded a maximum operating temperature of 195 K for the devices with Cu waveguide. Additional lasing at 5.9 meV was detected for magnetic fields between 7.3 and 7.7 T. △ Less

Submitted 20 February, 2015; v1 submitted 6 November, 2014; originally announced November 2014.

Journal ref: New J. Phys. 17 (2015) 023050

Ultrastrong Coupling in the Near-field of Complementary Split Ring Resonators

Authors: Curdin Maissen, Giacomo Scalari, Federico Valmorra, Sara Cibella, Roberto Leoni, Christian Reichl, Christohpe Charpentier, Werner Wegscheider, Mattias Beck, Jérôme Faist

Abstract: The ultrastrong light-matter interaction regime was investigated in metallic and superconducting complementary split ring resonators coupled to the cyclotron transition of two dimensional electron gases. The sub-wavelength light confinement and the large optical dipole moment of the cyclotron transition yield record high normalized coupling rates of up to $\frac{Ω_R}{ω_c}=$ 0.87. We observed a blu… ▽ More The ultrastrong light-matter interaction regime was investigated in metallic and superconducting complementary split ring resonators coupled to the cyclotron transition of two dimensional electron gases. The sub-wavelength light confinement and the large optical dipole moment of the cyclotron transition yield record high normalized coupling rates of up to $\frac{Ω_R}{ω_c}=$ 0.87. We observed a blue-shift of both polaritons due to the diamagnetic term of the interaction Hamiltonian. △ Less

Submitted 15 August, 2014; originally announced August 2014.

Octave-spanning semiconductor laser

Authors: Markus Rösch, Giacomo Scalari, Mattias Beck, Jérôme Faist

Abstract: We present here a semiconductor injection laser operating in continuous wave with an emission covering more than one octave in frequency, and displaying homogeneous power distribution among the lasing modes. The gain medium is based on a heterogeneous quantum cascade structure operating in the THz range. Laser emission in continuous wave takes place from 1.64 THz to 3.35 THz with optical powers in… ▽ More We present here a semiconductor injection laser operating in continuous wave with an emission covering more than one octave in frequency, and displaying homogeneous power distribution among the lasing modes. The gain medium is based on a heterogeneous quantum cascade structure operating in the THz range. Laser emission in continuous wave takes place from 1.64 THz to 3.35 THz with optical powers in the mW range and more than 80 modes above threshold. Free-running beatnote investigations on narrow waveguides with linewidths of 980 Hz limited by jitter indicate frequency comb operation on a spectral bandwidth as wide as 624 GHz, making such devices ideal candidates for octave-spanning semiconductor-laser-based THz frequency combs. △ Less

Submitted 11 July, 2014; originally announced July 2014.

Superconducting complementary metasurfaces for THz ultrastrong light-matter coupling

Authors: G. Scalari, C. Maissen, S. Cibella, R. Leoni, P. Carelli, F. Valmorra, M. Beck, J. Faist

Abstract: A superconducting metasurface operating in the THz range and based on the complementary metamaterial approach is discussed. Experimental measurements as a function of temperature and magnetic field display a modulation of the metasurface with a change in transmission amplitude and frequency of the resonant features. Such a metasurface is successively used as a resonator for a cavity quantum electr… ▽ More A superconducting metasurface operating in the THz range and based on the complementary metamaterial approach is discussed. Experimental measurements as a function of temperature and magnetic field display a modulation of the metasurface with a change in transmission amplitude and frequency of the resonant features. Such a metasurface is successively used as a resonator for a cavity quantum electrodynamic experiment displaying ultrastrong coupling to the cyclotron transition of a 2DEG. A finite element modeling is developed and its results are in good agreement with the experimental data. In this system a normalized coupling ratio of $\fracΩ{ω_c}=0.27$ is measured and a clear modulation of the polaritonic states as a function of the temperature is observed. △ Less

Submitted 1 November, 2013; originally announced November 2013.

Journal ref: New J. Phys. 16 033005 (2014)

Suppression of the radiative decay of atomic coherence in squeezed vacuum

Authors: K. W. Murch, S. J. Weber, K. M. Beck, Eran Ginossar, I. Siddiqi

Abstract: Quantum fluctuations of the electromagnetic vacuum are responsible for physical effects such as the Casimir force and the radiative decay of atoms, and set fundamental limits on the sensitivity of measurements. Entanglement between photons can produce correlations that result in a reduction of these fluctuations below the vacuum level allowing measurements that surpass the standard quantum limit i… ▽ More Quantum fluctuations of the electromagnetic vacuum are responsible for physical effects such as the Casimir force and the radiative decay of atoms, and set fundamental limits on the sensitivity of measurements. Entanglement between photons can produce correlations that result in a reduction of these fluctuations below the vacuum level allowing measurements that surpass the standard quantum limit in sensitivity. Here we demonstrate that the radiative decay rate of an atom that is coupled to quadrature squeezed electromagnetic vacuum can be reduced below its natural linewidth. We observe a two-fold reduction of the transverse radiative decay rate of a superconducting artificial atom coupled to continuum squeezed vacuum generated by a Josephson parametric amplifier, allowing the transverse coherence time T_2 to exceed the vacuum decay limit of 2T_1. We demonstrate that the measured radiative decay dynamics can be used to tomographically reconstruct the Wigner distribution of the the itinerant squeezed state. Our results are the first confirmation of a canonical prediction of quantum optics and open the door to new studies of the quantum light-matter interaction. △ Less

Submitted 22 April, 2013; v1 submitted 26 January, 2013; originally announced January 2013.

Comments: 9 pages, 5 figures

Journal ref: Nature 499, 62-65 (04 July 2013)

Room-temperature transverse-electric polarized intersubband electroluminescence from InAs/AlInAs quantum dashes

Authors: V. Liverini, L. Nevou, F. Castellano, A. Bismuto, M. Beck, Fabian Gramm, J. Faist

Abstract: We report the observation of transverse electric polarized electroluminescence from InAs/AlInAs quantum dash quantum cascade structures up to room temperature. The emission is attributed to the electric field confined along the shortest lateral dimension of the dashes, as confirmed by its dependence on crystallographic orientation both in absorption measurements on a dedicated sample and from elec… ▽ More We report the observation of transverse electric polarized electroluminescence from InAs/AlInAs quantum dash quantum cascade structures up to room temperature. The emission is attributed to the electric field confined along the shortest lateral dimension of the dashes, as confirmed by its dependence on crystallographic orientation both in absorption measurements on a dedicated sample and from electroluminescence itself. From the absorption we estimate a dipole moment for the observed transition of <x>=1.7 nm. The electroluminescence is peaked at around 110 meV and increases with applied bias. Its temperature dependence shows a decrease at higher temperatures limited by optical phonon emission. △ Less

Submitted 1 September, 2012; originally announced September 2012.

Comments: 15 pages, 4 figures, submitted to Applied Physics Letters

Quantum dot admittance probed at microwave frequencies with an on-chip resonator

Authors: T. Frey, P. J. Leek, M. Beck, J. Faist, A. Wallraff, K. Ensslin, T. Ihn, M. Büttiker

Abstract: We present microwave frequency measurements of the dynamic admittance of a quantum dot tunnel coupled to a two-dimensional electron gas. The measurements are made via a high-quality 6.75 GHz on-chip resonator capacitively coupled to the dot. The resonator frequency is found to shift both down and up close to conductance resonance of the dot corresponding to a change of sign of the reactance of the… ▽ More We present microwave frequency measurements of the dynamic admittance of a quantum dot tunnel coupled to a two-dimensional electron gas. The measurements are made via a high-quality 6.75 GHz on-chip resonator capacitively coupled to the dot. The resonator frequency is found to shift both down and up close to conductance resonance of the dot corresponding to a change of sign of the reactance of the system from capacitive to inductive. The observations are consistent with a scattering matrix model. The sign of the reactance depends on the detuning of the dot from conductance resonance and on the magnitude of the tunnel rate to the lead with respect to the resonator frequency. Inductive response is observed on a conductance resonance, when tunnel coupling and temperature are sufficiently small compared to the resonator frequency. △ Less

Submitted 3 October, 2012; v1 submitted 4 July, 2012; originally announced July 2012.

Comments: 8 pages, 4 figures

Journal ref: Phys. Rev. B 86, 115303 (2012)

Optimization of sample-chip design for stub-matched radio-frequency reflectometry measurements

Authors: S. Hellmüller, M. Pikulski, T. Müller, B. Küng, G. Puebla-Hellmann, A. Wallraff, M. Beck, K. Ensslin, T. Ihn

Abstract: A radio-frequency (rf) matching circuit with an in situ tunable varactor diode used for rf reflectometry measurements in semiconductor nanostructures is investigated and used to optimize the sample-specific chip design. The samples are integrated in a 2-4 GHz stub-matching circuit consisting of a waveguide stub shunted to the terminated coplanar waveguide. Several quantum point contacts fabricated… ▽ More A radio-frequency (rf) matching circuit with an in situ tunable varactor diode used for rf reflectometry measurements in semiconductor nanostructures is investigated and used to optimize the sample-specific chip design. The samples are integrated in a 2-4 GHz stub-matching circuit consisting of a waveguide stub shunted to the terminated coplanar waveguide. Several quantum point contacts fabricated on a GaAs/AlGaAs heterostructure with different chip designs are compared. We show that the change of the reflection coefficient for a fixed change in the quantum point contact conductance can be enhanced by a factor of 3 compared to conventional designs by a suitable electrode geometry. △ Less

Submitted 8 June, 2012; originally announced June 2012.

Journal ref: Appl. Phys. Lett. 101, 042112 (2012);

Quantum dot occupation and electron dwell time in the cotunneling regime

Authors: B. Küng, C. Rössler, M. Beck, J. Faist, T. Ihn, K. Ensslin

Abstract: We present comparative measurements of the charge occupation and conductance of a GaAs/AlGaAs quantum dot. The dot charge is measured with a capacitively coupled quantum point contact sensor. In the single-level Coulomb blockade regime near equilibrium, charge and conductance signals are found to be proportional to each other. We conclude that in this regime, the two signals give equivalent inform… ▽ More We present comparative measurements of the charge occupation and conductance of a GaAs/AlGaAs quantum dot. The dot charge is measured with a capacitively coupled quantum point contact sensor. In the single-level Coulomb blockade regime near equilibrium, charge and conductance signals are found to be proportional to each other. We conclude that in this regime, the two signals give equivalent information about the quantum dot system. Out of equilibrium, we study the inelastic-cotunneling regime. We compare the measured differential dot charge with an estimate assuming a dwell time of transmitted carriers on the dot given by h/E, where E is the blockade energy of first-order tunneling. The measured signal is of a similar magnitude as the estimate, compatible with a picture of cotunneling as transmission through a virtual intermediate state with a short lifetime. △ Less

Submitted 28 August, 2012; v1 submitted 20 April, 2012; originally announced April 2012.

Journal ref: New Journal of Physics vol. 14, p. 083003 (2012)

Direct surface cyclotron resonance terahertz emission from a quantum cascade structure

Authors: François-Régis Jasnot, Louis-Anne De Vaulchier, Yves Guldner, Gérald Bastard, Angela Vasanelli, Christophe Manquest, Carlo Sirtori, Mattias Beck, Jérôme Faist

Abstract: A strong magnetic field applied along the growth direction of a semiconductor quantum well gives rise to a spectrum of discrete energy states, the Landau levels. By combining quantum engineering of a quantum cascade structure with a static magnetic field, we can selectively inject electrons into the excited Landau level of a quantum well and realize a tunable surface emitting device based on cyclo… ▽ More A strong magnetic field applied along the growth direction of a semiconductor quantum well gives rise to a spectrum of discrete energy states, the Landau levels. By combining quantum engineering of a quantum cascade structure with a static magnetic field, we can selectively inject electrons into the excited Landau level of a quantum well and realize a tunable surface emitting device based on cyclotron emission. By applying the appropriate magnetic field between 0 and 12 T, we demonstrate emission from a single device over a wide range of frequencies (1-2 THz and 3-5 THz). △ Less

Submitted 23 March, 2012; originally announced March 2012.

Journal ref: Applied Physics Letters 100 (2012) 102103

Room temperature terahertz polariton emitter

Authors: Markus Geiser, Giacomo Scalari, Fabrizio Castellano, Mattias Beck, Jérôme Faist

Abstract: The strong-coupling regime between an electronic transition and the photonic mode of a optical resonator manifests itself in the lifting of the degeneracy between the two modes and the creation of two polariton states with mixed optical and electronic character. This phenomenon has been studied in atoms, excitons in semiconductors and quantum electrodynamics circuits based on Josephson junctions.… ▽ More The strong-coupling regime between an electronic transition and the photonic mode of a optical resonator manifests itself in the lifting of the degeneracy between the two modes and the creation of two polariton states with mixed optical and electronic character. This phenomenon has been studied in atoms, excitons in semiconductors and quantum electrodynamics circuits based on Josephson junctions. Recently, there is also strong interest to study similar effects using intersubband transitions in quantum wells in the terahertz, where the ultra strong coupling regime can be reached and new physical effects have been predicted. An other interesting feature of this system is that, in contrast to systems based on superconductors, the ultra strong coupling regime can be maintained up to room temperature. In this work, we demonstrate that parabolic quantum wells coupled to LC circuit resonators in the ultra strong coupling regime can achieve terahertz emission up to room temperature. △ Less

Submitted 9 January, 2012; originally announced January 2012.

Ultra strong coupling regime and plasmon-polaritons in parabolic semiconductor quantum wells

Authors: Markus Geiser, Fabrizio Castellano, Giacomo Scalari, Mattias Beck, Laurent Nevou, Jérôme Faist

Abstract: Ultra strong coupling is studied in a modulation-doped parabolic potential well coupled to an inductance-capacitance resonant circuit. In this system, in accordance to Kohn's theorem, strong reduction of the energy level separation caused by the electron-electron interaction compensates the depolarization shift. As a result, a very large ratio of 27% of the Rabi frequency to the center resonance f… ▽ More Ultra strong coupling is studied in a modulation-doped parabolic potential well coupled to an inductance-capacitance resonant circuit. In this system, in accordance to Kohn's theorem, strong reduction of the energy level separation caused by the electron-electron interaction compensates the depolarization shift. As a result, a very large ratio of 27% of the Rabi frequency to the center resonance frequency as well as a polariton gap of width 2? ? 670GHz are observed, suggesting parabolic quantum wells as the system of choice in order to explore the ultra-strong coupling regime. △ Less

Submitted 13 December, 2011; v1 submitted 30 November, 2011; originally announced November 2011.

Ultrastrong coupling of the cyclotron transition of a two-dimensional electron gas to a THz metamaterial

Authors: Giacomo Scalari, Curdin Maissen, Dana Turcinková, David Hagenmüller, Simone De Liberato, Cristiano Ciuti, Dieter Schuh, Christian Reichl, Werner Wegscheider, Mattias Beck, Jérôme Faist

Abstract: Artificial cavity photon resonators with ultrastrong light-matter interactions are attracting interest both in semiconductor and superconducting systems, due to the possibility of manipulating the cavity quantum electrodynamic ground state with controllable physical properties. We report here experiments showing ultrastrong light-matter coupling in a terahertz metamaterial where the cyclotron tran… ▽ More Artificial cavity photon resonators with ultrastrong light-matter interactions are attracting interest both in semiconductor and superconducting systems, due to the possibility of manipulating the cavity quantum electrodynamic ground state with controllable physical properties. We report here experiments showing ultrastrong light-matter coupling in a terahertz metamaterial where the cyclotron transition of a high mobility two-dimensional electron gas is coupled to the photonic modes of an array of electronic split-ring resonators. We observe a normalized coupling ratio $\fracΩ{ω_c}=0.58$ between the vacuum Rabi frequency $Ω$ and the cyclotron frequency $ω_c$. Our system appears to be scalable in frequency and could be brought to the microwave spectral range with the potential of strongly controlling the magnetotransport properties of a high-mobility 2DEG. △ Less

Submitted 4 May, 2012; v1 submitted 10 November, 2011; originally announced November 2011.

Journal ref: Science. 2012 Mar 16;335(6074):1323-6

Dipole coupling of a double quantum dot to a microwave resonator

Authors: T. Frey, P. J. Leek, M. Beck, A. Blais, T. Ihn, K. Ensslin, A. Wallraff

Abstract: Quantum coherence in solid-state systems has been demonstrated in superconducting circuits and in semiconductor quantum dots. This has paved the way to investigate solid-state systems for quantum information processing with the potential benefit of scalability compared to other systems based on atoms, ions and photons. Coherent coupling of superconducting circuits to microwave photons, circuit qua… ▽ More Quantum coherence in solid-state systems has been demonstrated in superconducting circuits and in semiconductor quantum dots. This has paved the way to investigate solid-state systems for quantum information processing with the potential benefit of scalability compared to other systems based on atoms, ions and photons. Coherent coupling of superconducting circuits to microwave photons, circuit quantum electrodynamics (QED), has opened up new research directions and enabled long distance coupling of qubits. Here we demonstrate how the electromagnetic field of a superconducting microwave resonator can be coupled to a semiconductor double quantum dot. The charge stability diagram of the double dot, typically measured by direct current (DC) transport techniques, is investigated via dispersive frequency shifts of the coupled resonator. This hybrid all-solid-state approach offers the potential to coherently couple multiple quantum dot and superconducting qubits together on one chip, and offers a method for high resolution spectroscopy of semiconductor quantum structures. △ Less

Submitted 26 August, 2011; originally announced August 2011.

Comments: 5 pages, 4 figures

Journal ref: Phys. Rev. Lett. 108, 046807 (2012)

Irreversibility on the Level of Single-Electron Tunneling

Authors: B. Küng, C. Rössler, M. Beck, M. Marthaler, D. S. Golubev, Y. Utsumi, T. Ihn, K. Ensslin

Abstract: We present a low-temperature experimental test of the fluctuation theorem for electron transport through a double quantum dot. The rare entropy-consuming system trajectories are detected in the form of single charges flowing against the source-drain bias by using time-resolved charge detection with a quantum point contact. We find that these trajectories appear with a frequency that agrees with th… ▽ More We present a low-temperature experimental test of the fluctuation theorem for electron transport through a double quantum dot. The rare entropy-consuming system trajectories are detected in the form of single charges flowing against the source-drain bias by using time-resolved charge detection with a quantum point contact. We find that these trajectories appear with a frequency that agrees with the theoretical predictions even under strong nonequilibrium conditions, when the finite bandwidth of the charge detection is taken into account. △ Less

Submitted 19 January, 2012; v1 submitted 21 July, 2011; originally announced July 2011.

Journal ref: Physical Review X 2, 011001 (2012)

Characterization of a microwave frequency resonator via a nearby quantum dot

Authors: T. Frey, P. J. Leek, M. Beck, K. Ensslin, A. Wallraff, T. Ihn

Abstract: We present measurements of a hybrid system consisting of a microwave transmission-line resonator and a lateral quantum dot defined on a GaAs heterostructure. The two subsystems are separately characterized and their interaction is studied by monitoring the electrical conductance through the quantum dot. The presence of a strong microwave field in the resonator is found to reduce the resonant condu… ▽ More We present measurements of a hybrid system consisting of a microwave transmission-line resonator and a lateral quantum dot defined on a GaAs heterostructure. The two subsystems are separately characterized and their interaction is studied by monitoring the electrical conductance through the quantum dot. The presence of a strong microwave field in the resonator is found to reduce the resonant conductance through the quantum dot, and is attributed to electron heating and modulation of the dot potential. We use this interaction to demonstrate a measurement of the resonator transmission spectrum using the quantum dot. △ Less

Submitted 18 April, 2011; originally announced April 2011.

Comments: 3 pages, 3 figures

Journal ref: Appl. Phys. Lett. 98, 262105 (2011)