Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session A37: Focus Session: Semiconductor Qubits - Single Donors |
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Sponsoring Units: GQI Chair: Bruce Kane, Laboratory for Physical Sciences Room: 212A |
Monday, March 2, 2015 8:00AM - 8:36AM |
A37.00001: Entanglement of an Electron-Nuclear Spin Pair in $^{28}$Si Invited Speaker: Stephanie Simmons Single-shot, single spin readout allows for strong projective quantum measurements which are used for Bell inequality violations, teleportation, error correction, and many other quantum codes. Very recently, strong projective measurements have become available using a long-lived electron-nuclear donor spin pair in silicon-28. Here we demonstrate Bell/CHSH inequality violations, a proven entanglement witness, using this two spin system. A Bell inequality violation of 2.7(1) conclusively demonstrates on-demand two-spin entanglement, and the $>99\%$ detection efficiency simultaneously closes the detection loophole for this system. Furthermore, we improve upon the destructive electron measurement approach by mapping all Bell inequality observables onto the nuclear spin for high-fidelity quantum non-demolition (QND) measurement. Lastly, we complement the Bell inequality entanglement witness with full two-qubit state tomography complete with QND measurement. Preliminary results con firm a highly entangled state, yielding a fidelity of $98(3)\%$, concurrence of 0.88(8), and a partial transpose negativity result of -0.46(4). Together these results demonstrate, within a single experiment, the very high initialisation ($>97\%$), estimated control ($>98\%$) and measurement ($>99.9\%$) fidelities in this two-qubit system. [Preview Abstract] |
Monday, March 2, 2015 8:36AM - 8:48AM |
A37.00002: Local electrical control of a single-atom spin qubit in a continuous microwave field Andrea Morello, Arne Laucht, Juha Muhonen, Fahd Mohiyaddin, Rachpon Kalra, Juan Dehollain, Solomon Freer, Fay Hudson, Menno Veldhorst, Andrew Dzurak, Kohei Itoh, Raijb Rahman, Gerhard Klimeck, Jeffrey McCallum, David Jamieson An ideal physical system to encode quantum information should be well isolated from its environment, but locally addressable and readable. Kane's proposal for a silicon spin-based quantum computer suggested tuning the qubit in/out of resonance with a global oscillating magnetic field by applying a local electric field and exploiting the Stark shift of the electron-nuclear hyperfine interaction (``$A$-gate''). We demonstrate universal single-qubit logic gates on both the electron and $^{31}$P nuclear spin of a single phosphorus atom in silicon, subject to an always-on microwave field, and operated via an $A$-gate controlled by nanometre-scale electrodes. The experiment is facilitated by the exceptionally sharp spin resonance frequencies in the nuclear-spin-free $^{28}$Si host material. Randomized benchmarking yields quantum gate fidelities $\geq 99$ $\%$, and the millisecond-long spin coherence times remain identical to those obtained by pulsed spin resonance. This method provides a natural pathway to address arbitrarily many qubits in large-scale quantum computers. [Preview Abstract] |
Monday, March 2, 2015 8:48AM - 9:00AM |
A37.00003: Quantum memory in a single nucleus in silicon Solomon Freer, Stephanie Simmons, Arne Laucht, Juha Muhonen, Juan Pablo Dehollain, Rachpon Kalra, Fay Hudson, Andrew Dzurak, Kohei Itoh, Jeffrey McCallum, David Jamieson, Andrea Morello Long coherence times and fast manipulation are two desirable qualities of a qubit that for many systems are mutually incompatible. Storing quantum information in an ancillary qubit, i.e. a `quantum memory', is a strategy to address this issue. It is a advantageous property of donor impurities in silicon to have qubits of both qualities in a single lattice site. Here we demonstrate storage and retrieval of quantum information from a single donor electron spin to its host phosphorus nucleus in isotopically-enriched $^{28}$Si. We demonstrate a high fidelity memory process characterised via both state and process tomography. We use dynamical decoupling sequences during the nuclear storage to extend the memory time, and demonstrate storage and retrieval of a single qubit of information multiple times before decay. These results underline the inherent versatility and high fidelity of our two qubit system. [Preview Abstract] |
Monday, March 2, 2015 9:00AM - 9:12AM |
A37.00004: Optical quantum memory made from single nuclear spin in nitrogen vacancy in diamond Sen Yang, Ya Wang, Thai Hien Tran, S. Ali Momenzadeh, Rainer Stoehr, Philipp Neumann, Hideo Kosaka, Joerg Wrachtrup Quantum repeater is one of the key elements to realize long distance quantum communication. In the heart of a quantum repeater is quantum memory. There are a few requirements for this memory: it needs to couple to flying qubits: photon; it needs to have long coherence time, so quantum error correction algorithm can be performed in the quantum repeater nods; it needs to be stable under optical illuminations. Nitrogen nuclear spin is available for every nitrogen vacancy center(NV) in diamond. Besides it can be a robust quantum memory for spin qubit operations, nitrogen nuclear spin can couple to photon by taking advantage of optically resonant excitation of spin-selective transitions in low temperature. Here we demonstrate the coherent storage of quantum information from photon into nuclear spin. We show this quantum memory fulfils requirements as quantum memory for quantum repeater. Coherent time beyond 5 seconds is measured in $^{13}C$ natural abundant sample. Under resonant laser excitations, the excited state quadruple and hyperfine interaction could lead to decoherence of nuclear spin. We show those interactions are low and nuclear spin can keep its coherence over 1000 times resonant laser excitation of electron spin. [Preview Abstract] |
Monday, March 2, 2015 9:12AM - 9:24AM |
A37.00005: Electron Spin Resonance Experiments on a Single Electron in Silicon Implanted with Phosphorous Dwight R. Luhman, K. Nguyen, L.A. Tracy, S. Carr, J. Borchardt, N. Bishop, G. Ten Eyck, T. Pluym, J. Wendt, M.P. Lilly, M.S. Carroll In this talk we will discuss the results of our ongoing experiments involving electron spin resonance (ESR) on a single electron in a natural silicon sample. The sample consists of an SET, defined by lithographic polysilicon gates, coupled to nearby phosphorous donors. The SET is used to detect charge transitions and readout the spin of the electron being investigated with ESR. The measurements were done with the sample at dilution refrigerator temperatures in the presence of a 1.3 T magnetic field. We will present data demonstrating Rabi oscillations of a single electron in this system as well as measurements of the coherence time, T$_{\mathrm{2}}$. We will also discuss our results using these and various other pulsing schemes in the context of a donor-SET system. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. DOE Office of Basic Energy Sciences user facility. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the U. S. Department of Energy under Contract No. DE-AC04-94AL85000. [Preview Abstract] |
Monday, March 2, 2015 9:24AM - 9:36AM |
A37.00006: Evaluation of strained silicon on insulator for SET based single donor spin read-out Peter Sharma, Greg Ten Eyck, Daniel Ward, Jason Dominguez, Kenton Childs, Joel Wendt, Michael Lilly, Malcolm Carroll Recent successes in realizing single donor control and achieving very high fidelity gate operations has driven interest in silicon-based donor qubits. A number of proposals for donor to donor coupling rely on vertical field for Stark shift and ionization to a nearby interface. Back gating silicon on insulator is one approach to achieving sufficient field strengths. We present low temperature measurements of back gated FET structures and donor implanted SETs fabricated from strained silicon on insulator substrates with a low doped handle. This strained silicon system is useful for studying the effects of strain on both single donor physics and may provide insight into the behavior of strained silicon channels for quantum dots. We use FET thresholds to characterize the oxide/Si defect density. Back gating influences the transient time response, mobility, and FET threshold. These parameters are also modified by above band gap light illumination. Two transport channels are observed, which also strongly depend on back gate voltage and illumination. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy Office of Science. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Monday, March 2, 2015 9:36AM - 9:48AM |
A37.00007: Electric field control of donor pair \textit{diatomic molecules} in silicon Alejandra Baena, Andre Saraiva, Mar\'Ia J. Calder\'on, Belita Koiller Single donors are well-established building blocks for engineering electronic properties of semiconductors, acting effectively as giant hydrogen atoms [1]. Donor pairs, analogous to effective hydrogen molecules, were recently investigated [2,3] in the strongly interacting regime in silicon. In this regime, electric field control renders timid results. Pairs that are more distant are more susceptible to external fields, and may harbour single electron charge control. Theoretically, the molecular quantum mechanics analogy between a donor pair and the H$_2$ molecule in vacuum is not as straightforward as it may seem. A detailed understanding of the electronic structure of these molecular systems is a current challenge. We analyze the lowest energy states within effective mass theory, including central cell corrected donor potential effects and the conduction band multiplicity in Si. The spectrum of ionized donor pairs and its response to an external electric field will be presented. We contemplate possible advantages of heteropolar diatomic molecules, e.g, Sb$-$As pairs, as more efficient elements for such devices and applications.\\[4pt] [1] Zwanenburg et al., RMP,85,961 (2013).\\[0pt] [2] M. F. Gonzalez-Zalba et al., Nano. Lett.14,5672 (2014).\\[0pt] [3] Dehollain et al., PRL,112,236801 (2014). [Preview Abstract] |
Monday, March 2, 2015 9:48AM - 10:00AM |
A37.00008: Sifting Through Data from a Two Donor Simulation in Silicon Andre Saraiva, M. Fernando Gonzalez-Zalba, Dominik Heiss, Maria Calder\'on, Belita Koiller, Andrew Ferguson, Juan Dehollain, Juha Muhonen, Kuan Tan, David Jamieson, Andrew Dzurak, Andrea Morello, Alejandra Baena Recently, two independent demonstrations of exchange-coupled donor pairs [1,2] have provided an early step towards two spin entanglement. Even though these systems are not yet suitable for quantum computation, they make blatant the need for more thorough theoretical investigation and, more importantly, more efficient surveying of the large dataset generated by the numerical investigations. We will discuss how useful information can be extracted from large datasets obtained with full configuration interaction, multivalley, central-cell corrected effective mass calculations [3]. As examples, we will study the successful cases of theory-experiment comparison in Refs. [1] and [2], as well as provide early predictions for other systems, such as singlet-triplet donor-based qubits. [1] M. F. Gonzalez-Zalba, A. Saraiva, D. Heiss, M. J. Calder\'{o}n, B. Koiller, and A. J. Ferguson, arXiv:1312.4589 (2013) [2] J. P. Dehollain, J. T. Muhonen, K. Y. Tan, A. Saraiva, D. N. Jamieson, A. S. Dzurak, and A. Morello, Phys. Rev. Lett. 112, 236801 (2014). [3] A. L. Saraiva, A. Baena, M. J. Calder\'{o}n, and B. Koiller, arXiv:1407.8224 (2014) [Preview Abstract] |
Monday, March 2, 2015 10:00AM - 10:12AM |
A37.00009: Robust Two-Qubit Gates for Donors in Silicon Controlled by Hyperfine Interactions Rachpon Kalra, Arne Laucht, Charles D. Hill, Andrea Morello The electron spin of a single atom in silicon is an excellent candidate for the building-block of a quantum computer. Recent breakthrough experiments have shown an individual phosphorus impurity atom can be used to store and elaborate one bit of quantum information. To continue along this exciting path, it is necessary to couple multiple phosphorus atoms in a controllable way and demonstrate quantum logic operations between pairs of qubits. This was thought to require exquisite control of their mutual interaction, and atomically-precise placement of the spins. Our work shows that the nuclei, to which the electrons are bound, can be exploited to enable a logic operation based on selective resonant excitation. This operation has the enormous advantage that the inter-qubit interaction does not require any modification. Our calculations show that high-fidelity operations can be performed while tolerating a rather wide range of distances between atoms. This drastically reduces the demands posed on device fabrication, paving the way forward for large-scale quantum-information processing in silicon. [Preview Abstract] |
Monday, March 2, 2015 10:12AM - 10:24AM |
A37.00010: Triangulating the Position of Antimony Donors Implanted in Silicon Chloe Bureau-Oxton, Erik Nielsen, Dwight Luhman, Gregory Ten Eyck, Tammy Pluym, Joel Wendt, Michel Pioro-Ladri\`ere, Michael Lilly, Malcolm Carroll A potential candidate for a quantum bit is a single Sb atom implanted in silicon. A single-electron-transistor (SET) situated close to an Sb donor can be used to measure the occupancy and spin of the electron on the donor while the lithographically patterned poly-silicon gates defining the SET can be used to control donor occupancy. In our samples two clusters of Sb donors have been implanted adjacent to opposite sides of the SET through a self-aligned process. In this talk, we will present experimental results that allow us to determine the approximate position of different donors by determining their relative capacitance to pairs of the SET's poly-silicon gates. We will present the results of capacitive-based modeling calculations that allow us to further locate the position of the donors. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. DOE Office of Basic Energy Sciences user facility. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the U. S. Department of Energy under Contract No. DE-AC04-94AL85000. [Preview Abstract] |
Monday, March 2, 2015 10:24AM - 10:36AM |
A37.00011: Atomistic configuration interaction simulations of two-electron states of donors in silicon Archana Tankasala, Yu Wang, Gerhard Klimeck, Rajib Rahman Two-electron states bound to donors in silicon are important for both two qubit gates and spin readout. We present a full configuration interaction technique in the atomistic tight-binding basis to capture multi-electron exchange and correlation effects taking into account the full bandstructure of silicon and the atomic scale inhomogeneity of a nanoscale device. The negatively charged two-electron D$^-$ state of a single donor is solved as a function of a vertical field and depth from the silicon surface. Excited $s$-like states are found to strongly influence the charging energy. The same technique is used to solve the two-electron states of two donors as a function of separation, showing the transition from a Heitler-London like regime to a molecular regime. Excited valley states are found to affect the exchange energy for small donor separations. [Preview Abstract] |
Monday, March 2, 2015 10:36AM - 10:48AM |
A37.00012: Electronic structure of Si vacancy centers in SiC Oney Soykal, Pratibha Dev, Sophia Economou The spin state of silicon vacancies in SiC is a promising candidate for applications in solid state quantum information technologies due to its long coherence time at room temperature, its technological availability and wide range of polytypism. Until recently, the electronic structure of this vacancy was not well understood. We have developed a group theoretical model that correctly predicts the spin 3/2 structure seen in recent experiments for the 4H-SiC defect. We have included several different mechanisms involved in the mixing of its spin states, such as crystal field splitting, spin-orbit coupling, spin-spin coupling, strain and Jahn-Teller interactions. We have also carried out DFT calculations that support and complement our analytical results. [Preview Abstract] |
Monday, March 2, 2015 10:48AM - 11:00AM |
A37.00013: First-principles theory of defect spins in w-AlN for quantum information and sensing technologies Hosung Seo, Marco Govoni, Giulia Galli The detection and coherent manipulations of the single nitrogen-vacancy defect spin in diamond [1] attracted a tremendous amount of attention for possible applications in quantum computing and metrology. In addition, these results stimulated an active search for other materials, which may exhibit defect spins with similar properties. We present a systematic study aimed at searching for localized triplet spin states in $n-$type $w-$AlN. We use a combination of \textit{ab-initio} calculations based on density functional and many-body perturbation theory and model calculations with an extended Hubbard Hamiltonian whose parameters were derived from first-principles. We consider five native defects: V$_{\mathrm{N}}$, V$_{\mathrm{Al}}$, O$_{\mathrm{N}}$, V$_{\mathrm{Al}}$O$_{\mathrm{N}}$, and V$_{\mathrm{Al}}$V$_{\mathrm{N}}$. We investigated the defect charge and spin-state energetics and we discuss the effect of strain fields on the defect stability. We also discuss possible initialization schemes utilizing spin-dependent optical transitions and possible decoherence dynamics for qubits in $w-$AlN, which is most likely dominated by Al nuclear spin bath. \\[4pt] [1] A. Gruber et al., Science 276, 2012 (1997); F. Jelezko et al., Phys. Rev. Lett 93, 130501 (2004). [Preview Abstract] |
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