-
Realization of a Synthetic Hall Torus with a Spinor Bose-Einstein Condensate
Authors:
T. -H. Chien,
S. -C. Wu,
Y. -H. Su,
L. -R. Liu,
N. -C. Chiu,
M. Sarkar,
Q. Zhou,
Y. -J. Lin
Abstract:
We report the first experimental realization of a synthetic Hall torus using a spinor Bose-Einstein condensate confined in a ring-shaped trap with in situ imaging. By cyclically coupling three hyperfine spin states via Raman and microwave fields, we impose a periodic boundary condition in the synthetic dimension, which together with a real-space ring trap, realizes a toroidal geometry with a synth…
▽ More
We report the first experimental realization of a synthetic Hall torus using a spinor Bose-Einstein condensate confined in a ring-shaped trap with in situ imaging. By cyclically coupling three hyperfine spin states via Raman and microwave fields, we impose a periodic boundary condition in the synthetic dimension, which together with a real-space ring trap, realizes a toroidal geometry with a synthetic magnetic flux. This flux induces azimuthal density modulations in the condensate, whose periodicity is uniquely determined by the quantized toroidal magnetic flux-a hallmark of the Hall torus geometry. By varying the relative phase between the couplings across repeated experimental runs, we control the location of the density extrema, emulating the behavior of Thouless charge pump in a toroidal geometry. We further investigate the onset of these modulations as the system transitions from a cylindrical to a toroidal topology. Our results establish a versatile platform for investigating quantum Hall physics and topological phenomena in synthetic curved spaces.
△ Less
Submitted 16 February, 2026;
originally announced February 2026.
-
Distinct Lifetimes for $X$ and $Z$ Loop Measurements in a Majorana Tetron Device
Authors:
Morteza Aghaee,
Zulfi Alam,
Rikke Andersen,
Mariusz Andrzejczuk,
Andrey Antipov,
Mikhail Astafev,
Lukas Avilovas,
Ahmad Azizimanesh,
Eric Banek,
Bela Bauer,
Jonathan Becker,
Umesh Kumar Bhaskar,
Andrea G. Boa,
Srini Boddapati,
Nichlaus Bohac,
Jouri D. S. Bommer,
Jan Borovsky,
Léo Bourdet,
Samuel Boutin,
Lucas Casparis,
Srivatsa Chakravarthi,
Hamidreza Chalabi,
Benjamin J. Chapman,
Nikolaos Chatzaras,
Tzu-Chiao Chien
, et al. (142 additional authors not shown)
Abstract:
We present a hardware realization and measurements of a tetron qubit device in a superconductor-semiconductor heterostructure. The device architecture contains two parallel superconducting nanowires, which support four Majorana zero modes (MZMs) when tuned into the topological phase, and a trivial superconducting backbone. Two distinct readout interferometers are formed by connecting the supercond…
▽ More
We present a hardware realization and measurements of a tetron qubit device in a superconductor-semiconductor heterostructure. The device architecture contains two parallel superconducting nanowires, which support four Majorana zero modes (MZMs) when tuned into the topological phase, and a trivial superconducting backbone. Two distinct readout interferometers are formed by connecting the superconducting structure to a series of quantum dots. We perform single-shot interferometric measurements of the fermion parity for the two loops, designed to implement Pauli-$X$ and $Z$ measurements of the tetron. Performing repeated single-shot measurements yields two widely separated time scales $τ_X = 14.5\pm 0.3 \, \mathrm{μs}$ and $τ_Z = 12.4\pm 0.4\, \mathrm{ms}$ for parity switches observed in the $X$ and $Z$ measurement loops, which we attribute to intra-wire parity switches and external quasiparticle poisoning, respectively. We estimate assignment errors of $\mathrm{err}^X_a=16\%$ and $\mathrm{err}^Z_a=0.5\%$ for $X$ and $Z$ measurement-based operations, respectively.
△ Less
Submitted 4 September, 2025; v1 submitted 11 July, 2025;
originally announced July 2025.
-
Tunneling current-controlled spin states in few-layer van der Waals magnets
Authors:
ZhuangEn Fu,
Piumi I. Samarawickrama,
John Ackerman,
Yanglin Zhu,
Zhiqiang Mao,
Kenji Watanabe,
Takashi Taniguchi,
Wenyong Wang,
Yuri Dahnovsky,
Mingzhong Wu,
TeYu Chien,
Jinke Tang,
Allan H. MacDonald,
Hua Chen,
Jifa Tian
Abstract:
Effective control of magnetic phases in two-dimensional magnets would constitute crucial progress in spintronics, holding great potential for future computing technologies. Here, we report a new approach of leveraging tunneling current as a tool for controlling spin states in CrI3. We reveal that a tunneling current can deterministically switch between spin-parallel and spin-antiparallel states in…
▽ More
Effective control of magnetic phases in two-dimensional magnets would constitute crucial progress in spintronics, holding great potential for future computing technologies. Here, we report a new approach of leveraging tunneling current as a tool for controlling spin states in CrI3. We reveal that a tunneling current can deterministically switch between spin-parallel and spin-antiparallel states in few-layer CrI3, depending on the polarity and amplitude of the current. We propose a mechanism involving nonequilibrium spin accumulation in the graphene electrodes in contact with the CrI3 layers. We further demonstrate tunneling current-tunable stochastic switching between multiple spin states of the CrI3 tunnel devices, which goes beyond conventional bi-stable stochastic magnetic tunnel junctions and has not been documented in two-dimensional magnets. Our findings not only address the existing knowledge gap concerning the influence of tunneling currents in controlling the magnetism in two-dimensional magnets, but also unlock possibilities for energy-efficient probabilistic and neuromorphic computing.
△ Less
Submitted 24 October, 2024;
originally announced October 2024.
-
Quantum-limited amplification without instability
Authors:
A. Metelmann,
O. Lanes,
T-Z. Chien,
A. McDonald,
I. Tsiamis,
M. Hatridge,
A. A. Clerk
Abstract:
Quantum parametric amplifiers typically generate by operating in proximity to a point of dynamical instability. We consider an alternate general strategy where quantum-limited, large-gain amplification is achieved without any proximity to a dynamical instability. Our basic mechanism (involving dynamics that conserves the number of squeezed photons) enables the design of a variety of one and two mo…
▽ More
Quantum parametric amplifiers typically generate by operating in proximity to a point of dynamical instability. We consider an alternate general strategy where quantum-limited, large-gain amplification is achieved without any proximity to a dynamical instability. Our basic mechanism (involving dynamics that conserves the number of squeezed photons) enables the design of a variety of one and two mode amplifiers that are not limited by any fundamental gain-bandwidth constraint. We focus on a particular realization that allows us to realize an ideal single-mode squeezing operation in transmission, and which has zero reflection. We present both a thorough theoretical analysis of this system (including pump-depletion effects), and also discuss results of an experimental superconducting quantum circuit implementation.
△ Less
Submitted 5 March, 2025; v1 submitted 29 July, 2022;
originally announced August 2022.
-
Small Energy Gap Revealed in CrBr3 by Scanning Tunneling Spectroscopy
Authors:
Dinesh Baral,
Zhuangen Fu,
Andrei S. Zadorozhnyi,
Rabindra Dulal,
Aaron Wang,
Narendra Shrestha,
Uppalaiah Erugu,
Jinke Tang,
Yuri Dahnovsky,
Jifa Tian,
TeYu Chien
Abstract:
CrBr$_{3}$ is a layered van der Waals material with magnetic ordering down to the 2D limit. For decades, based on optical measurements, it is believed that the energy gap of CrBr$_{3}$ is in the range of 1.68-2.1 eV. However, controversial results have indicated that the band gap of CrBr$_{3}$ is possibly smaller than that. An unambiguous determination of the energy gap is critical to the correct…
▽ More
CrBr$_{3}$ is a layered van der Waals material with magnetic ordering down to the 2D limit. For decades, based on optical measurements, it is believed that the energy gap of CrBr$_{3}$ is in the range of 1.68-2.1 eV. However, controversial results have indicated that the band gap of CrBr$_{3}$ is possibly smaller than that. An unambiguous determination of the energy gap is critical to the correct interpretations of the experimental results of CrBr$_{3}$. Here, we present the scanning tunneling microscopy and spectroscopy (STM/S) results of CrBr$_{3}$ thin and thick flakes exfoliated onto pyropytic graphite (HOPG) surfaces and density functional theory (DFT) calculations to reveal the small energy gap (peak-to-peak energy gap to be 0.57 eV $\pm$ 0.04 eV; or the onset signal energy gap to be 0.29 $\pm$ 0.05 eV from dI/dV spectra). Atomic resolution topography images show the defect-free crystal structure and the dI/dV spectra exhibit multiple peak features measured at 77 K. The conduction band - valence band peak pairs in the multi-peak dI/dV spectrum agree very well with all reported optical transitions. STM topography images of mono- and bi-layer CrBr$_{3}$ flakes exhibit edge degradation due to short air exposure (~15 min) during sample transfer. The unambiguously determined small energy gap settles the controversy and is the key in better understanding CrBr$_{3}$ and similar materials.
△ Less
Submitted 2 December, 2020; v1 submitted 30 August, 2019;
originally announced September 2019.
-
Designing Anisotropic Microstructures with Spectral Density Function
Authors:
Akshay Iyer,
Rabindra Dulal,
Yichi Zhang,
Umar Farooq Ghumman,
TeYu Chien,
Ganesh Balasubramanian,
Wei Chen
Abstract:
Materials' microstructure strongly influences its performance and is thus a critical aspect in design of functional materials. Previous efforts on microstructure mediated design mostly assume isotropy, which is not ideal when material performance is dependent on an underlying transport phenomenon. In this article, we propose an anisotropic microstructure design strategy that leverages Spectral Den…
▽ More
Materials' microstructure strongly influences its performance and is thus a critical aspect in design of functional materials. Previous efforts on microstructure mediated design mostly assume isotropy, which is not ideal when material performance is dependent on an underlying transport phenomenon. In this article, we propose an anisotropic microstructure design strategy that leverages Spectral Density Function (SDF) for rapid reconstruction of high resolution, two phase, isotropic or anisotropic microstructures in 2D and 3D. We demonstrate that SDF microstructure representation provides an intuitive method for quantifying anisotropy through a dimensionless scalar variable termed anisotropy index. The computational efficiency and low dimensional microstructure representation enabled by our method is demonstrated through an active layer design case study for Bulk Heterojunction Organic Photovoltaic Cells (OPVCs). Results indicate that optimized design, exhibiting strong anisotropy, outperforms isotropic active layer designs. Further, we show that Cross-sectional Scanning Tunneling Microscopy and Spectroscopy (XSTM/S) is as an effective tool for characterization of anisotropic microstructures.
△ Less
Submitted 20 August, 2019;
originally announced August 2019.
-
Elongated Nano Domains and Molecular Intermixing induced Doping in Organic Photovoltaic Active Layers with Electric Field Treatment
Authors:
Rabindra Dulal,
Akshay Iyer,
Umar Farooq Ghumman,
Joydeep Munshi,
Aaron Wang,
Ganesh Balasubramanian,
Wei Chen,
TeYu Chien
Abstract:
The effects of the electric-field-assisted annealing on the bulk heterojunction nano-morphology in the P3HT/PCBM active layer of the organic photovoltaic cells (OPVCs) are presented here. It was widely accepted that the electric-field-assisted annealing will facilitate the P3HT, the polar polymer, to be better crystalline to enhance the charge mobility, hence the improvement of the OPVC performanc…
▽ More
The effects of the electric-field-assisted annealing on the bulk heterojunction nano-morphology in the P3HT/PCBM active layer of the organic photovoltaic cells (OPVCs) are presented here. It was widely accepted that the electric-field-assisted annealing will facilitate the P3HT, the polar polymer, to be better crystalline to enhance the charge mobility, hence the improvement of the OPVC performance. The influences on the nano-morphology of the electron donor and accepter domains are not well understood. Here, using the cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/S), the electric-field-assisted annealing treatment is found to influence the molecular domains to be elongated with the orientation near the direction of the external electric field. The elongation of the molecular domains is believed to facilitate the domain percolation, which causes higher charge mobility, hence the higher short-circuit current density (Jsc). On the other hand, it was also observed that the electronic properties of the P3HT-rich and PCBM-rich domains in the electric-field-assisted annealed samples showed smaller energy band gaps and smaller molecular orbital offset between the two domains, which is argued to decrease the open circuit voltage (Voc) and negatively impact the OPVC performance. Based on the X-ray diffraction (XRD) and small angle X-ray scattering (SAXS) results, the altered electronic properties are argued to be due to the molecular intermixing induced doping effects. These results point out competing factors affecting the OPVC performance with the electric-field-assisted annealing treatment.
△ Less
Submitted 8 August, 2019;
originally announced August 2019.
-
Josephson parametric converter saturation and higher order effects
Authors:
G. Liu,
T. -C. Chien,
X. Cao,
O. Lanes,
E. Alpern,
D. Pekker,
M. Hatridge
Abstract:
Microwave parametric amplifiers based on Josephson junctions have become a key component of many quantum information experiments. One key limitation which has not been well predicted by theory is the gain saturation behavior which determines its ability to process large amplitude signals. The typical explanation for this behavior in phase-preserving amplifiers based on three-wave mixing is pump de…
▽ More
Microwave parametric amplifiers based on Josephson junctions have become a key component of many quantum information experiments. One key limitation which has not been well predicted by theory is the gain saturation behavior which determines its ability to process large amplitude signals. The typical explanation for this behavior in phase-preserving amplifiers based on three-wave mixing is pump depletion, in which the consumption of pump photons to produce amplification results in a reduction in gain. However, in this work we present experimental data and theoretical calculations showing that the fourth-order Kerr nonlinearities inherent in the Josephson junctions are the dominant factor in the Josephson Parametric Converter (JPC). The Kerr-based theory has the unusual property of causing saturation to both lower and higher gains, depending on bias conditions. This work presents a new methodology for optimizing device performance in the presence of Kerr nonlinearities while retaining device tunability, and points to the necessity of controlling higher-order Hamiltonian terms to make further improvements in parametric devices.
△ Less
Submitted 4 September, 2017; v1 submitted 13 March, 2017;
originally announced March 2017.
-
Correlation between surface rumpling and structural phase transformation of SrTiO3
Authors:
S. Singh,
Te-Yu Chien,
J. R. Guest,
M. R. Fitzsimmons
Abstract:
We present x-ray reflectivity, x-ray diffraction and atomic force microscopy measurements of single crystal SrTiO3 taken as a function of temperature. We found a rumpling transformation of the SrTiO3 surface after cooling the sample below ~105 K. The rumpling transformation is correlated with the cubic to tetragonal phase transformation that occurs at the same temperature. The rumpling transformat…
▽ More
We present x-ray reflectivity, x-ray diffraction and atomic force microscopy measurements of single crystal SrTiO3 taken as a function of temperature. We found a rumpling transformation of the SrTiO3 surface after cooling the sample below ~105 K. The rumpling transformation is correlated with the cubic to tetragonal phase transformation that occurs at the same temperature. The rumpling transformation is reversible.
△ Less
Submitted 29 November, 2011;
originally announced November 2011.
-
Visualizing nanoscale electronic band alignment at the La$_{2/3}$Ca$_{1/3}$MnO$_{3}$/Nb:SrTiO$_{3}$ interface
Authors:
TeYu Chien,
Jian Liu,
Jacques Chakhalian,
Nathan P. Guisinger,
John W. Freeland
Abstract:
Cross-sectional scanning tunnelling microscopy and spectroscopy (XSTM/S) were used to map out the band alignment across the complex oxide interface of La$_{2/3}$Ca$_{1/3}$MnO$_{3}$/Nb-doped SrTiO$_{3}$. By a controlled cross-sectional fracturing procedure, unit-cell high steps persist near the interface between the thin film and the substrate in the non-cleavable perovskite materials. The abrupt c…
▽ More
Cross-sectional scanning tunnelling microscopy and spectroscopy (XSTM/S) were used to map out the band alignment across the complex oxide interface of La$_{2/3}$Ca$_{1/3}$MnO$_{3}$/Nb-doped SrTiO$_{3}$. By a controlled cross-sectional fracturing procedure, unit-cell high steps persist near the interface between the thin film and the substrate in the non-cleavable perovskite materials. The abrupt changes of the mechanical and electronic properties were visualized directly by XSTM/S. Using changes in the DOS as probe by STM, the electronic band alignment across the heterointerface was mapped out providing a new approach to directly measure the electronic properties at complex oxide interfaces.
△ Less
Submitted 2 July, 2010; v1 submitted 24 June, 2010;
originally announced June 2010.
-
A survey of fractured SrTiO$_3$ surfaces: from the micro-meter to nano-meter scale
Authors:
TeYu Chien,
Nathan P. Guisinger,
John W. Freeland
Abstract:
Cross-sectional scanning tunneling microscopy was utilized to study fractured perovskie oxide surfaces. It was found for the non-cleavable perovskite oxide, SrTiO$_{3}$, that atomically flat terraces could be routinely created with a controlled fracturing procedure. Optical and scanning electron microscopy as well as a profilometer were used to obtain the information from sub-millimeter to sub-m…
▽ More
Cross-sectional scanning tunneling microscopy was utilized to study fractured perovskie oxide surfaces. It was found for the non-cleavable perovskite oxide, SrTiO$_{3}$, that atomically flat terraces could be routinely created with a controlled fracturing procedure. Optical and scanning electron microscopy as well as a profilometer were used to obtain the information from sub-millimeter to sub-micrometer scales of the fractured surface topography.
△ Less
Submitted 5 February, 2010;
originally announced February 2010.
-
Nanometer-scale striped surface terminations on fractured SrTiO$_{3}$ surfaces
Authors:
Nathan P. Guisinger,
Tiffany S. Santos,
Jeffrey R. Guest,
Te-Yu Chien,
Anand Bhattacharya,
John W. Freeland,
Matthias Bode
Abstract:
Using cross-sectional scanning tunneling microscopy on in situ fractured SrTiO$_{3}$, one of the most commonly used substrates for the growth of complex oxide thin films and superlattices, atomically smooth terraces have been observed on (001) surfaces. Furthermore, it was discovered that fracturing this material at room temperature results in the formation of stripe patterned domains having cha…
▽ More
Using cross-sectional scanning tunneling microscopy on in situ fractured SrTiO$_{3}$, one of the most commonly used substrates for the growth of complex oxide thin films and superlattices, atomically smooth terraces have been observed on (001) surfaces. Furthermore, it was discovered that fracturing this material at room temperature results in the formation of stripe patterned domains having characteristic widths (~10 nm to ~20 nm) of alternating surface terminations that extend over a long-range. Spatial characterization utilizing spectroscopy techniques revealed a strong contrast in the electronic structure of the two domains. Combining these results with topographic data, we are able to assign both TiO$_{2}$ and SrO terminations to their respective domains. The results of this proof-of-principle experiment reveal that fracturing this material leads to reproducibly flat surfaces that can be characterized at the atomic-scale and suggests that this technique can be utilized for the study of technologically relevant complex oxide interfaces.
△ Less
Submitted 10 August, 2009;
originally announced August 2009.
-
Surface Geometric and Electronic Structure of BaFe2As2(001)
Authors:
V. B. Nascimento,
Ang Li,
Dilushan R. Jayasundara,
Yi Xuan,
Jared O'Neal,
Shuheng Pan,
T. Y. Chien,
Biao Hu,
X. B. He,
Guorong Li,
A. S. Sefat,
M. A. McGuire,
B. C. Sales,
D. Mandrus,
M. H. Pan,
Jiandi Zhang,
R. Jin,
E. W. Plummer
Abstract:
BaFe2As2 exhibits properties characteristic of the parent compounds of the newly discovered iron (Fe)-based high-TC superconductors. By combining the real space imaging of scanning tunneling microscopy/spectroscopy (STM/S) with momentum space quantitative Low Energy Electron Diffraction (LEED) we have identified the surface plane of cleaved BaFe2As2 crystals as the As terminated Fe-As layer - th…
▽ More
BaFe2As2 exhibits properties characteristic of the parent compounds of the newly discovered iron (Fe)-based high-TC superconductors. By combining the real space imaging of scanning tunneling microscopy/spectroscopy (STM/S) with momentum space quantitative Low Energy Electron Diffraction (LEED) we have identified the surface plane of cleaved BaFe2As2 crystals as the As terminated Fe-As layer - the plane where superconductivity occurs. LEED and STM/S data on the BaFe2As2(001) surface indicate an ordered arsenic (As) - terminated metallic surface without reconstruction or lattice distortion. It is surprising that the STM images the different Fe-As orbitals associated with the orthorhombic structure, not the As atoms in the surface plane.
△ Less
Submitted 19 May, 2009;
originally announced May 2009.