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Coherent control of a triangular exchange-only spin qubit
Authors:
Edwin Acuna,
Joseph D. Broz,
Kaushal Shyamsundar,
Antonio B. Mei,
Colin P. Feeney,
Valerie Smetanka,
Tiffany Davis,
Kangmu Lee,
Maxwell D. Choi,
Brydon Boyd,
June Suh,
Wonill D. Ha,
Cameron Jennings,
Andrew S. Pan,
Daniel S. Sanchez,
Matthew D. Reed,
Jason R. Petta
Abstract:
We demonstrate coherent control of a three-electron exchange-only spin qubit with the quantum dots arranged in a close-packed triangular geometry. The device is tuned to confine one electron in each quantum dot, as evidenced by pairwise charge stability diagrams. Time-domain control of the exchange coupling is demonstrated and qubit performance is characterized using blind randomized benchmarking,…
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We demonstrate coherent control of a three-electron exchange-only spin qubit with the quantum dots arranged in a close-packed triangular geometry. The device is tuned to confine one electron in each quantum dot, as evidenced by pairwise charge stability diagrams. Time-domain control of the exchange coupling is demonstrated and qubit performance is characterized using blind randomized benchmarking, with an average single-qubit gate fidelity F = 99.84%. The compact triangular device geometry can be readily scaled to larger two-dimensional quantum dot arrays with high connectivity.
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Submitted 5 June, 2024;
originally announced June 2024.
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Interferometric Single-Shot Parity Measurement in an InAs-Al Hybrid Device
Authors:
Morteza Aghaee,
Alejandro Alcaraz Ramirez,
Zulfi Alam,
Rizwan Ali,
Mariusz Andrzejczuk,
Andrey Antipov,
Mikhail Astafev,
Amin Barzegar,
Bela Bauer,
Jonathan Becker,
Umesh Kumar Bhaskar,
Alex Bocharov,
Srini Boddapati,
David Bohn,
Jouri Bommer,
Leo Bourdet,
Arnaud Bousquet,
Samuel Boutin,
Lucas Casparis,
Benjamin James Chapman,
Sohail Chatoor,
Anna Wulff Christensen,
Cassandra Chua,
Patrick Codd,
William Cole
, et al. (137 additional authors not shown)
Abstract:
The fusion of non-Abelian anyons or topological defects is a fundamental operation in measurement-only topological quantum computation. In topological superconductors, this operation amounts to a determination of the shared fermion parity of Majorana zero modes. As a step towards this, we implement a single-shot interferometric measurement of fermion parity in indium arsenide-aluminum heterostruct…
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The fusion of non-Abelian anyons or topological defects is a fundamental operation in measurement-only topological quantum computation. In topological superconductors, this operation amounts to a determination of the shared fermion parity of Majorana zero modes. As a step towards this, we implement a single-shot interferometric measurement of fermion parity in indium arsenide-aluminum heterostructures with a gate-defined nanowire. The interferometer is formed by tunnel-coupling the proximitized nanowire to quantum dots. The nanowire causes a state-dependent shift of these quantum dots' quantum capacitance of up to 1 fF. Our quantum capacitance measurements show flux h/2e-periodic bimodality with a signal-to-noise ratio of 1 in 3.7 $μ$s at optimal flux values. From the time traces of the quantum capacitance measurements, we extract a dwell time in the two associated states that is longer than 1 ms at in-plane magnetic fields of approximately 2 T. These results are consistent with a measurement of the fermion parity encoded in a pair of Majorana zero modes that are separated by approximately 3 $μ$m and subjected to a low rate of poisoning by non-equilibrium quasiparticles. The large capacitance shift and long poisoning time enable a parity measurement error probability of 1%.
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Submitted 2 April, 2024; v1 submitted 17 January, 2024;
originally announced January 2024.
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Nonvolatile Electric-Field Control of Inversion Symmetry
Authors:
Lucas Caretta,
Yu-Tsun Shao,
Jia Yu,
Antonio B. Mei,
Bastien F. Grosso,
Cheng Dai,
Piush Behera,
Daehun Lee,
Margaret McCarter,
Eric Parsonnet,
Harikrishnan K. P.,
Fei Xue,
Ed Barnard,
Steffen Ganschow,
Archana Raja,
Lane W. Martin,
Long-Qing Chen,
Manfred Fiebig,
Keji Lai,
Nicola A. Spaldin,
David A. Muller,
Darrell G. Schlom,
Ramamoorthy Ramesh
Abstract:
In condensed-matter systems, competition between ground states at phase boundaries can lead to significant changes in material properties under external stimuli, particularly when these ground states have different crystal symmetries. A key scientific and technological challenge is to stabilize and control coexistence of symmetry-distinct phases with external stimuli. Using BiFeO3 (BFO) layers con…
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In condensed-matter systems, competition between ground states at phase boundaries can lead to significant changes in material properties under external stimuli, particularly when these ground states have different crystal symmetries. A key scientific and technological challenge is to stabilize and control coexistence of symmetry-distinct phases with external stimuli. Using BiFeO3 (BFO) layers confined between layers of the dielectric TbScO3 as a model system, we stabilize the mixed-phase coexistence of centrosymmetric and non-centrosymmetric BFO phases with antipolar, insulating and polar, semiconducting behavior, respectively at room temperature. Application of in-plane electric (polar) fields can both remove and introduce centrosymmetry from the system resulting in reversible, nonvolatile interconversion between the two phases. This interconversion between the centrosymmetric insulating and non-centrosymmetric semiconducting phases coincides with simultaneous changes in the non-linear optical response of over three orders of magnitude, a change in resistivity of over five orders of magnitude, and a change in the polar order. Our work establishes a materials platform allowing for novel cross-functional devices which take advantage of changes in optical, electrical, and ferroic responses.
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Submitted 2 January, 2022;
originally announced January 2022.
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Optimization of Quantum-dot Qubit Fabrication via Machine Learning
Authors:
Antonio B. Mei,
Ivan Milosavljevic,
Amanda L. Simpson,
Valerie A. Smetanka,
Colin P. Feeney,
Shay M. Seguin,
Sieu D. Ha,
Wonill Ha,
Matthew D. Reed
Abstract:
Precise nanofabrication represents a critical challenge to developing semiconductor quantum-dot qubits for practical quantum computation. Here, we design and train a convolutional neural network to interpret in-line scanning electron micrographs and quantify qualitative features affecting device functionality. The high-throughput strategy is exemplified by optimizing a model lithographic process w…
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Precise nanofabrication represents a critical challenge to developing semiconductor quantum-dot qubits for practical quantum computation. Here, we design and train a convolutional neural network to interpret in-line scanning electron micrographs and quantify qualitative features affecting device functionality. The high-throughput strategy is exemplified by optimizing a model lithographic process within a five-dimensional design space and by demonstrating a new approach to address lithographic proximity effects. The present results emphasize the benefits of machine learning for developing robust processes, shortening development cycles, and enforcing quality control during qubit fabrication.
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Submitted 15 December, 2020;
originally announced December 2020.
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Adaptive hard and tough mechanical response in single-crystal B1 VNx ceramics via control of anion vacancies
Authors:
A. B. Mei,
H. Kindlund,
E. Broitman,
L. Hultman,
I. Petrov,
J. E. Greene,
D. G. Sangiovanni
Abstract:
High hardness and toughness are generally considered mutually exclusive properties for single-crystal ceramics. Combining experiments and ab initio molecular dynamics (AIMD) atomistic simulations at room temperature, we demonstrate that both the hardness and toughness of single-crystal NaCl-structure VNx/MgO(001) thin films are simultaneously enhanced through the incorporation of anion vacancies.…
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High hardness and toughness are generally considered mutually exclusive properties for single-crystal ceramics. Combining experiments and ab initio molecular dynamics (AIMD) atomistic simulations at room temperature, we demonstrate that both the hardness and toughness of single-crystal NaCl-structure VNx/MgO(001) thin films are simultaneously enhanced through the incorporation of anion vacancies. Nanoindentation results show that VN0.8, here considered as representative understoichiometric VNx system, is ~20% harder, as well as more resistant to fracture than stoichiometric VN samples. AIMD modeling of VN and VN0.8 supercells subjected to [001] and [110] elongation reveal that the tensile strengths of the two materials are similar. Nevertheless, while the stoichiometric VN phase systematically cleaves in a brittle manner at tensile yield points, the understoichiometric compound activates transformation-toughening mechanisms that dissipate accumulated stresses. AIMD simulations also show that VN0.8 exhibits an initially greater resistance to both {110}<1-10> and {111}<1-10> shear deformation than VN. However, for progressively increasing shear strains, the VN0.8 mechanical behavior gradually evolves from harder to more ductile than VN. The transition is mediated by anion vacancies, which facilitate {110}<1-10> and {111}<1-10> lattice slip by reducing activation shear stresses by as much as 35%. Electronic-structure analyses show that the two-regime hard/tough mechanical response of VN0.8 primarily stems from its intrinsic ability to transfer d electrons between 2nd-neighbor and 4th-neighbor (i.e., across vacancy sites) V-V metallic states. Our work offers a route for electronic-structure design of hard materials in which a plastic mechanical response is triggered with loading.
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Submitted 21 March, 2020; v1 submitted 24 January, 2020;
originally announced January 2020.
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Imaging uncompensated moments and exchange-biased emergent ferromagnetism in FeRh thin films
Authors:
Isaiah Gray,
Gregory M. Stiehl,
John T. Heron,
Antonio B. Mei,
Darrell G. Schlom,
Ramamoorthy Ramesh,
Daniel C. Ralph,
Gregory D. Fuchs
Abstract:
Uncompensated moments in antiferromagnets are responsible for exchange bias in antiferromagnet/ferromagnet heterostructures; however, they are difficult to directly detect because any signal they contribute is typically overwhelmed by the ferromagnetic layer. We use magneto-thermal microscopy to image uncompensated moments in thin films of FeRh, a room-temperature antiferromagnet that exhibits a 1…
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Uncompensated moments in antiferromagnets are responsible for exchange bias in antiferromagnet/ferromagnet heterostructures; however, they are difficult to directly detect because any signal they contribute is typically overwhelmed by the ferromagnetic layer. We use magneto-thermal microscopy to image uncompensated moments in thin films of FeRh, a room-temperature antiferromagnet that exhibits a 1st-order phase transition to a ferromagnetic state near 100~$^\circ$C. FeRh provides the unique opportunity to study both uncompensated moments in the antiferromagnetic phase and the interaction of uncompensated moments with emergent ferromagnetism within a relatively broad (10-15~$^\circ$C) temperature range near $T_C$. In the AF phase below $T_C$, we image both pinned UMs, which cause local vertical exchange bias, and unpinned UMs, which exhibit an enhanced coercive field that reflects exchange-coupling to the AF bulk. Near $T_C$, where AF and FM order coexist, we find that the emergent FM order is exchange-coupled to the bulk Néel order. This exchange coupling leads to the nucleation of unusual configurations in which different FM domains are pinned parallel, antiparallel, and perpendicular to the applied magnetic field before suddenly collapsing into a state uniformly parallel to the field.
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Submitted 17 June, 2019;
originally announced June 2019.
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Local Photothermal Control of Phase Transitions for On-demand Room-temperature Rewritable Magnetic Patterning
Authors:
Antonio B. Mei,
Isaiah Gray,
Yongjian Tang,
Jurgen Schubert,
Don Werder,
Jason Bartell,
Daniel C. Ralph,
Gregory D. Fuchs,
Darrell G. Schlom
Abstract:
The ability to make controlled patterns of magnetic structures within a nonmagnetic background is essential for several types of existing and proposed technologies. Such patterns provide the foundation of magnetic memory and logic devices, allow the creation of artificial spin-ice lattices and enable the study of magnon propagation. Here, we report a novel approach for magnetic patterning that all…
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The ability to make controlled patterns of magnetic structures within a nonmagnetic background is essential for several types of existing and proposed technologies. Such patterns provide the foundation of magnetic memory and logic devices, allow the creation of artificial spin-ice lattices and enable the study of magnon propagation. Here, we report a novel approach for magnetic patterning that allows repeated creation and erasure of arbitrary shapes of thin-film ferromagnetic structures. This strategy is enabled by epitaxial Fe$_{0.52}$Rh$_{0.48}$ thin films designed so that both ferromagnetic and antiferromagnetic phases are bistable at room temperature. Starting with the film in a uniform antiferromagnetic state, we demonstrate the ability to write arbitrary patterns of the ferromagnetic phase by local heating with a focused laser. If desired, the results can then be erased by cooling with a thermoelectric cooler and the material repeatedly re-patterned.
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Submitted 17 June, 2019;
originally announced June 2019.
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Discovery of Ordered Vortex Phase in Multiferroic Oxide Superlattices
Authors:
Antonio B. Mei,
Ramamoorthy Ramesh,
Darrell G. Schlom
Abstract:
Ferroics, characterized by a broken symmetry state with nonzero elastic, polar, or magnetic order parameters $\vec{u}$, are recognized platforms for staging and manipulating topologically-protected structures as well as for detecting unconventional topological phenomena. The unrealized possibility of producing ordered topological phases in magnetoelectric multiferroics, exhibiting coupled magnetic…
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Ferroics, characterized by a broken symmetry state with nonzero elastic, polar, or magnetic order parameters $\vec{u}$, are recognized platforms for staging and manipulating topologically-protected structures as well as for detecting unconventional topological phenomena. The unrealized possibility of producing ordered topological phases in magnetoelectric multiferroics, exhibiting coupled magnetic and polar order parameters, is anticipated to engender novel functionality and open avenues for manipulating topological features. Here, we report the discovery of an ordered $π_1$-$S_\infty$ vortex phase within single-phase magnetoelectric multiferroic BiFeO$_3$. The phase, characterized by positive topological charge and chiral staggering, is realized in coherent TbScO$_3$ and BiFeO$_3$ superlattices and established via the combination of direct- and Fourier-space analyses. Observed order-parameter morphologies are reproduced with a field model describing the local order-parameter stiffness and competing non-local dipole-dipole interactions. Anisotropies canting the order parameter towards $\left<100\right>$ suppress chiral staggering and produced a competing $π_1$-$C_{\infty v}$ vortex phase in which cores are centered.
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Submitted 30 October, 2018;
originally announced October 2018.
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Effects of surface vibrations on interlayer mass-transport: ab initio molecular dynamics investigation of Ti adatom descent pathways and rates from TiN/TiN(001) islands
Authors:
D. G. Sangiovanni,
A. B. Mei,
D. Edström,
L. Hultman,
V. Chirita,
I. Petrov,
J. E. Greene
Abstract:
We carry out density-functional ab initio molecular dynamics (AIMD) simulations of Ti adatom (Tiad) migration on, and descent from, TiN <100>-faceted epitaxial islands on TiN(001) at temperatures T ranging from 1200 to 2400 K. Adatom-descent energy-barriers determined via ab initio nudged-elastic-band calculations at 0 Kelvin suggest that Ti interlayer transport on TiN(001) occurs essentially excl…
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We carry out density-functional ab initio molecular dynamics (AIMD) simulations of Ti adatom (Tiad) migration on, and descent from, TiN <100>-faceted epitaxial islands on TiN(001) at temperatures T ranging from 1200 to 2400 K. Adatom-descent energy-barriers determined via ab initio nudged-elastic-band calculations at 0 Kelvin suggest that Ti interlayer transport on TiN(001) occurs essentially exclusively via direct hopping onto a lower layer. However, AIMD simulations reveal comparable rates for Tiad descent via direct-hopping vs. push-out/exchange with a Ti island edge atom for T >= 1500 K. We demonstrate that the effect is due to surface vibrations, which yield considerably lower activation energies at finite temperatures by significantly modifying the adatom push/out-exchange reaction pathway.
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Submitted 27 November, 2017; v1 submitted 20 June, 2017;
originally announced June 2017.