Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session R52: Semiconducting QC: Donor and Dot-Donor Qubits, Rolf Landauer and Charles Bennett Award SessionFocus Prize/Award
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Sponsoring Units: GQI Chair: Michelle Simmons Room: 399 |
Thursday, March 16, 2017 8:00AM - 8:12AM |
R52.00001: Two-axis control of a coupled quantum dot - donor qubit in Si-MOS Martin Rudolph, Patrick Harvey-Collard, Tobias Jacobson, Joel Wendt, Tammy Pluym, Jason Dominguez, Greg Ten-Eyck, Mike Lilly, Malcolm Carroll Si-MOS based QD qubits are attractive due to their similarity to the current semiconductor industry. We introduce a highly tunable MOS foundry compatible qubit design that couples an electrostatic quantum dot (QD) with an implanted donor. We show for the first time coherent two-axis control of a two-electron spin logical qubit that evolves under the QD-donor exchange interaction and the hyperfine interaction with the donor nucleus. The two interactions are tuned electrically with surface gate voltages to provide control of both qubit axes. Qubit decoherence is influenced by charge noise, which is of similar strength as epitaxial systems like GaAs and Si/SiGe. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. DOE, Office of Basic Energy Sciences user facility. The work was supported by the Sandia National Laboratories Directed Research and Development Program. 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] |
Thursday, March 16, 2017 8:12AM - 8:24AM |
R52.00002: Tunnel coupling tuning of a QD-donor S-T qubit R. M. Jock, M. Rudolph, P. Harvey-Collard, T. Jacobson, J. Wendt, T. Pluym, J. Dominguez, R. Manginell, M.P. Lilly, M.S. Carroll Coherent coupling between an electrostatic quantum dot (QD) and an implanted 31P donor has been recently demonstrated in a singlet-triplet qubit design [arXiv1512.01606]. Controlling the tunnel coupling between the QD and donor is a key design challenge. We demonstrate the ability to voltage-tune the tunnel coupling between a QD and a donor in a new, implanted, MOS-QD design. The tunnel coupling is extracted from the frequency dependence of coherent singlet-triplet oscillations on detuning. By tailoring the electrostatic tuning of the QD, we observe a near-order-of-magnitude change in QD-donor tunnel coupling. Independent control of the QD-lead tunnel rates is also demonstrated. This new MOS foundry compatible QD-donor design shows promise for substantially relaxing fabrication requirements for donor based qubits. 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 (DOE) 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. DOE's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Thursday, March 16, 2017 8:24AM - 8:36AM |
R52.00003: Magnetic field and angular dependent spin rotations in a donor-MOS quantum-dot qubit Andrew Mounce, Martin Rudolph, N. Tobias Jacobson, Patrick Harvey-Collard, Joel Wendt, Tammy Pluym, Jason Dominguez, M. S. Carroll Recently, coherent spin coupling between a MOS QD and a $31$P donor has been shown with effective two electron-singlet-triplet (ST) rotations driven by an effective gradient field formed by the donor's nuclear spin measured as $A/2 \sim$ 57 MHz, [1] consistent with Stark shifted observations from ESR quits [2]. However, a complex dependence of ST rotation-frequency on B-field angular dependence has been observed in a recent, more tunable design [3]. This includes a substantially reduced zero external-magnetic-field rotation-frequency of approximately 12 MHz and, with increasing magnetic field, the frequency splits into multiple magnetic field and angular dependent modes. We show that the key features of the field and angular dependent singlet-triplet rotation frequencies are reproduced with a donor-QD system that has both asymmetric g-factor and anisotropic hyperfine terms that are physically reasonable. [1] P. Harvey-Collard, \textit{et al} arXiv:1512.01606 (2015). [2] J. J. Pla, \textit{et al}, Nature 489, 541 (2012). [3] M. Rudolph \textit{et al}, International Electron Device Meeting, San Francisco, Dec. 2016. [Preview Abstract] |
Thursday, March 16, 2017 8:36AM - 8:48AM |
R52.00004: Atomically precise control of a coupled donor-quantum dot system in silicon Joseph Salfi, Ben Voisin, Archana Tankasala, Juanita Bocquel, Muhammad Usman, Michelle Simmons, Lloyd Hollenberg, Rajib Rahman, Sven Rogge Single donors in silicon have long spin coherence times of interest for quantum computing. While quantum dots are promising candidates to couple donor spin qubits[1,2], the experimental tunability of the interactions and the influence of valley degrees of freedom (recently measured in donors[3]) in donor-quantum dot coupling remain open questions. We have directly measured the spectrum and wavefunctions of a donor interacting with a single-electron quantum dot that follows a movable scanned probe tip with sub-nm accuracy. Analysis of the two-electron energy as a function of the quantum dot position reveals no detectable lattice-incommensurate ``exchange oscillations'', even though donor state and its valley population is robust to quantum dot potential. This contrasts direct donor-donor exchange, which is predicted to depend sensitively on donor position due to valley interference. This result has important implications for obtaining robust interactions among donors in a surface code quantum computer. [1] G Pica et al, Phys. Rev. B. 93, 035306 (2016). [2] Gonzalez-Zalba, Phys. Rev. X 5 031024 (2015). [3] Salfi et al, Nature Materials, 13, 606 (2014). [4] B. Koiller et al, Phys. Rev. Lett. 88, 027903 (2001). [Preview Abstract] |
Thursday, March 16, 2017 8:48AM - 9:00AM |
R52.00005: Electrical control of spin qubit shuttling between a donor and a quantum dot Peihao Huang, Garnett Bryant Shuttling an electron spin qubit through coherent tunneling adiabatic passage is a promising way to transfer quantum information and achieve two-qubit gate among spatially separated qubits. The controllability of tunneling rate is essential for the shuttling of an electron while preserving quantum information that the electron spin carries. We study the tunneling between a donor atom and a gate-defined, near-surface quantum dot in silicon by using atomistic tight-binding simulation. We show the role that valley degrees of freedom, quantum-dot size and dot-donor separation play in the tunneling rate and how electric field can be employed to tune the tunneling rate and increase the spin transfer fidelity. [Preview Abstract] |
Thursday, March 16, 2017 9:00AM - 9:36AM |
R52.00006: Rolf Landauer and Charles H. Bennett Award Talk: Experimental development of spin qubits in silicon Invited Speaker: Andrea Morello The modern information era is built on silicon nanoelectronic devices. The future quantum information era might be built on silicon too, if we succeed in controlling the interactions between individual spins hosted in silicon nanostructures.\\ Spins in silicon constitute excellent solid-state qubits, because of the weak spin-orbit coupling and the possibility to remove nuclear spins from the environment through $^{28}$Si isotopic enrichment. Substitutional $^{31}$P atoms in silicon behave approximately like hydrogen in vacuum, providing two spin 1/2 qubits -- the donor-bound electron and the $^{31}$P nucleus -- that can be coherently controlled [1,2], read out in single-shot [2,3], and are naturally coupled through the hyperfine interaction.\\ In isotopically-enriched $^{28}$Si, these single-atom qubits have demonstrated outstanding coherence times, up to 35 seconds for the nuclear spin [4], and 1-qubit gate fidelities well above 99.9\% for both the electron and the nucleus [5]. The hyperfine coupling provides a built-in interaction to entangle the two qubits within one atom. The combined initialization, control and readout fidelities result in a violation of Bell’s inequality with $S = 2.70$, a record value for solid-state qubits [6].\\ Despite being identical atomic systems, $^{31}$P atoms can be addressed individually by locally modifying the hyperfine interaction through electrostatic gating [7]. Multi-qubit logic gates can be mediated either by the exchange interaction [8] or by electric dipole coupling [9].\\ Scaling up beyond a single atom presents formidable challenges, but provides a pathway to building quantum processors that are compatible with standard semiconductor fabrication, and retain a nanometric footprint, important for truly large-scale quantum computers.\\ \ \\ {[1]} J.J. Pla et al., Nature 489, 541 (2012)\\ {[2]} J.J. Pla et al., Nature 496, 334 (2013)\\ {[3]} A. Morello et al., Nature 467, 687 (2010)\\ {[4]} J.T. Muhonen et al., Nature Nanotech. 9, 986 (2014)\\ {[5]} J.T. Muhonen et al., J. Phys.: Condens. Matt. 27, 154205 (2015)\\ {[6]} J.P. Dehollain et al., Nature Nanotech. 11, 242 (2016)\\ {[7]} A. Laucht et al., Science Advances 1, e1500022 (2015)\\ {[8]} R. Kalra et al., Phys. Rev. X 4, 021044 (2014)\\ {[9]} G. Tosi et al., arXiv:1509.08538 (2015) [Preview Abstract] |
Thursday, March 16, 2017 9:36AM - 9:48AM |
R52.00007: Low magnetic field anomalies of spin relaxation in silicon in the low temperature limit Stefanie Tenberg, Serwan Asaad, Arne Laucht, Rachpon Kalra, Fay E. Hudson, Kohei M. Itoh, David N. Jamieson, Jeffrey C. McCallum, Andrew S. Dzurak, Andrea Morello The electron spin relaxation rate of donors in silicon is predicted to follow a magnetic field dependence of $1/T_{1}\propto B^{5}$ at low temperatures, where only spontaneous emission of phonons is relevant [1]. This behaviour has been observed in experiments on individual P donors [2,3]. However, these measurements also showed a deviation from the theoretical prediction at low fields (\textless 2 T). Here we present an extensive analysis of single donor relaxation rates at low magnetic fields, down to 0.3 T. To maintain a high spin readout contrast at low field we use steered initialisation, where a real-time feedback loop corrects for spin loading errors. Using a vector magnet, we investigate the dependence of the relaxation rate on the magnetic field direction. This allows us to disentangle valley-repopulation and single-valley contributions [1], and to study the potential impact of extrinsic relaxation mechanisms, such as evanescent-wave Johnson noise [4]. \newline [1] F.A. Zwanenburg et al., Rev. Mod. Phys. 85, 961 (2013). [2] A. Morello et al., Nature(London) 467, 687 (2010). [3] Y.-L. Hsueh et al., Phys. Rev. Lett. 113, 245406 (2014). [4] L. S. Langsjoen et al., Phys. Rev. B 89, 115401 (2014). [Preview Abstract] |
Thursday, March 16, 2017 9:48AM - 10:00AM |
R52.00008: Accurate donor electron wave functions from a multivalley effective mass theory. Luke Pendo, Xuedong Hu Multivalley effective mass (MEM) theories combine physical intuition with a marginal need for computational resources, but they tend to be insensitive to variations in the wavefunction. However, recent papers suggest full Bloch functions and suitable central cell donor potential corrections are essential to replicating qualitative and quantitative features of the wavefunction [1,2]. In this talk, we consider a variational MEM method that can accurately predict both spectrum and wavefunction of isolated phosphorus donors. As per Gamble et. al [1], we employ a truncated series representation of the Bloch function with a tetrahedrally symmetric central cell correction. We use a dynamic dielectric constant, a feature commonly seen in tight-binding methods. Uniquely, we use a freely extensible basis of either all Slater- or all Gaussian-type functions. With a large basis able to capture the influence of higher energy eigenstates, this method is well positioned to consider the influence of external perturbations, such as electric field or applied strain, on the charge density. [1] JK Gamble, et al., Phys. Rev. B \textbf{91}, 235318 (2015) [2] AL Saraiva, et al., Phys. Rev. B \textbf{93}, 045303 (2016) [Preview Abstract] |
Thursday, March 16, 2017 10:00AM - 10:12AM |
R52.00009: The emergence of chaos in a single nuclear spin of a donor in silicon Serwan Asaad, Vincent Mourik, Hannes Firgau, Jeffrey McCallum, Gerard Milburn, Cathy Holmes, Andrea Morello Classical conservative systems usually exhibit rapid dispersion of initial conditions – chaos – while the corresponding quantum equivalent system exhibits quasi-periodicity, localization, and tunneling through classically forbidden regions in phase space. How to reconcile these strikingly different behaviours has been the topic of active theoretical debate, but accompanied by few experimental results. We propose an experiment aimed at realizing the real-time experimental observation of a single quantum system whose dynamics is classically chaotic – a periodically-driven nonlinear top. Our experimental proposal builds upon the existing infrastructure of the 31-P donor qubit in purified 28-Si, which shows record-long coherence times and high-fidelity single-shot readout. Replacing the 31-P donor with 123-Sb, which has a larger nuclear spin of 7/2, its nuclear quadrupole interaction adds the necessary nonlinearity to implement the periodically-driven nonlinear top. We show how the resulting enlarged nuclear Hilbert space is sufficient to observe signatures of classical chaos, allowing us to study the quantum-classical crossover in the nuclear spin’s dynamics. [Preview Abstract] |
Thursday, March 16, 2017 10:12AM - 10:24AM |
R52.00010: Silicon Donor Array One-Dimensional Electron Gas Chao Lei, Allan H. MacDonald One strategy for establishing robust solid state quantum information processing hardware is to take exploit the relatively simple bound states that surround donors or acceptors in the most well understood semiconductor material, silicon. It is now possible to place donor atoms in a silicon crystal host with an spatial accuracy of close to one lattice constant. Because of the valley degree of freedom possessed by donor levels in silicon, this level of accuracy is not sufficient to avoid important disorder. With this motivation we present a theoretical study of a one-dimensional electron gas derived from the silicon conduction band and formed by electrons bound to a line of approximately equally spaced donors. We present a simple model for the central cell valley-dependent interactions that are responsible for valley splitting of donor levels in bulk silicon, explain how they are important source of disorder even for inaccuracies in donor placement that are only on the lattice constant scale, and explore the competition between interactions and disorder that ensues. Our emphasis is on exploring some of the interesting interacting electron physics that has been enabled by advances in controlling semiconductor donor and acceptor defects made with a quantum information motivation [Preview Abstract] |
Thursday, March 16, 2017 10:24AM - 10:36AM |
R52.00011: Strongly correlated transport and edge states in dopant arrays in silicon Nguyen Le, Andrew Fisher, Eran Ginossar Advanced experimental techniques such as single-ion implantation and STM lithography have enabled the fabrication of deterministically placed dopants in silicon. We have studied theoretically the strongly correlated coherent transport in small arrays of Si:P. The array is described by an effective Hubbard model whose eigenstates are obtained by exact diagonalization, coupled by hopping to non-interacting leads. We study the tunnel coupling disorder caused by multi-valley interference and the dopants’ positional fluctuation. This disorder results in Lifshitz localization of the many-body wavefunction, which suppresses the charge transport through the array. The effect of long range inter-dopant Coulomb interactions in the system is also investigated. Finally, we show that topological edge states can be realised, and discuss the characteristics of the topological phase transition in a one-dimensional superlattice of Si:P. [Preview Abstract] |
Thursday, March 16, 2017 10:36AM - 10:48AM |
R52.00012: Zero field optical study of phosphorus donor spin resonance in enriched silicon K J Morse, J Huber, P Dluhy, J Z Salvail, K Saeedi, N V Abrosimov, S Simmons, M L W Thewalt Donor spins in silicon are some of the most promising qubits for upcoming solid-state quantum technologies. The nuclear spins of phosphorus donors in enriched silicon have among the longest coherence times of any solid-state system as well as simultaneous qubit initialization, manipulation and readout fidelities near ~99.9\%. Here we characterize the phosphorus in silicon system in the regime of “zero” magnetic field, close to a singlet-triplet spin “clock transition”, using laser spectroscopy and magnetic resonance. We show the system can be optically hyperpolarized and has ∼10 s Hahn echo coherence times. [Preview Abstract] |
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