Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session F36: Focus Session: Semiconductor Qubits: Impurities & Quantum Devices |
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Sponsoring Units: GQI Chair: Sven Rogge, University of New South Wales Room: 703 |
Tuesday, March 4, 2014 8:00AM - 8:12AM |
F36.00001: Single-spin quantum coherence beyond 10 seconds in an isotopically engineered silicon nanostructure Andrea Morello, Juha Muhonen, Juan Pablo Dehollain, Arne Laucht, Fay Hudson, Kohei Itoh, David Jamieson, Jeffrey McCallum, Andrew Dzurak The single-shot readout and coherent control of both the electron and the nuclear spin of a single P atom in silicon has been recently demonstrated, using ion-implanted donors in MOS nanostructures. It is known from bulk experiments that P donors in isotopically purified $^{28}$Si exhibit record coherences, but it is also suspected that the proximity to a Si/SiO$_2$ interface will deteriorate the coherence time. Here we present the first experiment on single electron and nuclear spin qubits in an isotopically engineered $^{28}$Si nanostructure. We measured exceptionally sharp electron spin resonance lines ($< 2$ kHz wide), and we obtained single-qubit control fidelities in excess of $99 \%$. We performed noise spectroscopy experiments to extract the power spectral density of the decoherence sources acting on the electron and the nucleus. Contrary to widespread belief, our data show that the ultimate limit for single-spin coherence in our nanostructure is not set by charge noise and interface effects, but simply by broadband thermal radiation coupled to the qubit through a high-bandwidth transmission line. Using dynamical decoupling, we measured coherence times up to $T_{2e} = 0.5$ s for the electron, and $T_{2n} = 18$ s for the $^{31}$P nucleus. [Preview Abstract] |
Tuesday, March 4, 2014 8:12AM - 8:24AM |
F36.00002: Nuclear spin coherence of neutral $^{31}$P donors in isotopically enriched $^{28}$Si E.S. Petersen, A.M. Tyryshkin, S.A. Lyon, S. Tojo, K.M. Itoh, M.L.W. Thewalt, H. Riemann, N.V. Abrosimov, P. Becker, H.-J. Pohl In natural silicon the nuclear spin coherence of neutral $^{31}$P donors is limited to about 1 second by flip-flopping $^{29}$Si nuclear spins. Here we eliminate this process by using isotopically enriched $^{28}$Si with 50 ppm of $^{29}$Si. This allows us to examine other processes which may decohere the $^{31}$P nuclear spins. We use X-band pulsed ENDOR at 1.7 K to examine isotopically enriched Si crystals with donor concentrations from 10$^{14}$ to 4x10$^{15}$ P/cm$^{3}$ and find a dependence of $^{31}$P nuclear spin coherence time on donor concentration. The measured nuclear spin echo decays are fit by a stretched exponential function, exp(-(t/T$_{2})^{\mathrm{n}})$, with n ranging from 0.7 to 1. This differs from n of about 2 commonly seen for spectral diffusion due to indirect spin flip-flops. The measured T$_{2}$ times decrease significantly when the donor concentration increases, changing from 8 s at 10$^{14}$ to 0.2 s at 4x10$^{15}$ P/cm$^{3}$. From the observed donor concentration dependence at higher densities, we conclude that direct electron spin flip-flops are responsible for $^{31}$P donor nuclear spin decoherence. [Preview Abstract] |
Tuesday, March 4, 2014 8:24AM - 8:36AM |
F36.00003: Spin Measurements of an Electron Bound to a Single Phosphorous Donor in Silicon D.R. Luhman, K. Nguyen, L.A. Tracy, S.M. Carr, J. Borchardt, N.C. Bishop, G.A. Ten Eyck, T. Pluym, J. Wendt, M.S. Carroll, M.P. Lilly The spin of an electron bound to a single donor implanted in silicon is potentially useful for quantum information processing. We report on our efforts to measure and manipulate the spin of an electron bound to a single P donor in silicon. A low number of P donors are implanted using a self-aligned process into a silicon substrate in close proximity to a single-electron-transistor (SET) defined by lithographically patterned polysilicon gates. The SET is used to sense the occupancy of the electron on the donor and for spin read-out. An adjacent transmission line allows the application of microwave pulses to rotate the spin of the electron. We will present data from various experiments designed to exploit these capabilities. 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 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] |
Tuesday, March 4, 2014 8:36AM - 9:12AM |
F36.00004: Bottom-up superconducting and Josephson junction devices and qubits inside a Group-IV semiconductor Invited Speaker: Yun-Pil Shim The Nb/AlOx/Nb (or Al/AlOx/Al) Josephson junction (JJ) has become ubiquitous for superconducting (SC) applications such as magnetometers, voltage standards, logic, and qubits. But heterogeneous devices such as these can pose problems, especially for low-power or quantum applications, where losses in or at the interfaces of the various materials can limit device quality dramatically. Possible solutions include better materials, weak-link junctions, symmetry protection, or 3D cavity qubits. Here we consider another alternative: atomically-precise, hole-doped SC silicon (or germanium) JJ devices and qubits made entirely out of the same crystal [1]. Like the Si spin qubit, our super-semi JJ devices exist inside the ``vacuum'' of ultra-pure silicon, far away from any dirty interfaces. We predict the possibility of SC wires, JJs, and qubits, calculate their critical parameters, and find that most known SC qubits should be realizable. This approach could enable better devices, hybrid superconducting-spin qubit systems, and exotic SC circuits, as well as a new physical testbed for superconductivity. \\[4pt] [1] Yun-Pil Shim and Charles Tahan, arXiv:1309.0015. [Preview Abstract] |
Tuesday, March 4, 2014 9:12AM - 9:24AM |
F36.00005: Electron shuttling in phosphorus donor qubit systems N. Tobias Jacobson, John King Gamble, Erik Nielsen, Richard P. Muller, Wayne M. Witzel, Ines Montano, Malcolm S. Carroll Phosphorus donors in silicon are a promising qubit architecture, due in large part to their long nuclear coherence times and the recent development of atomically precise fabrication methods. Here, we investigate issues related to implementing qubits with phosphorus donors in silicon, employing an effective mass theory that non-phenomenologically takes into account inter-valley coupling. We estimate the significant sources of decoherence and control errors in this system to compute the fidelity of primitive gates and gate timescales. We include the effects of valley repopulation during the process of shuttling an electron between a donor and nearby interface or between neighboring donors, evaluating the control requirements for ensuring adiabaticity with respect to the valley sector. [Preview Abstract] |
Tuesday, March 4, 2014 9:24AM - 9:36AM |
F36.00006: Transport Measurements on Si Nanostructures with Counted Sb Donors Meenakshi Singh, Edward Bielejec, Elias Garratt, Gregory Ten Eyck, Nathaniel Bishop, Joel Wendt, Dwight Luhman, Malcolm Carroll, Michael Lilly Donor based spin qubits are a promising platform for quantum computing. Single qubits using timed implant of donors have been demonstrated.$^{\mathrm{1}}$ Extending this to multiple qubits requires precise control over the placement and number of donors. Such control can be achieved by using a combination of low-energy heavy-ion implants (to reduce depth straggle), electron-beam lithography (to define position), focused ion beam (to localize implants to one lithographic site) and counting the number of implants with a single ion detector.$^{\mathrm{2}}$ We report transport measurements on MOS quantum dots implanted with 5, 10 and 20 Sb donors using the approach described above. A donor charge transition is identified by a charge offset in the transport characteristics. Correlation between the number of donors and the charge offsets is studied. These results are necessary first steps towards fabricating donor nanostructures for two qubit interactions. 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 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. $^{\mathrm{1}}$J. J. Pla et al., Nature \textbf{496}, 334 (2013) $^{\mathrm{2}}$J. A. Seamons et al., APL \textbf{93}, 043124 (2008). [Preview Abstract] |
Tuesday, March 4, 2014 9:36AM - 9:48AM |
F36.00007: Phonon induced spin relaxation times of single donors and donor clusters in silicon Yuling Hsueh, Holger Buch, Lloyd Hollenberg, Michelle Simmons, Gerhard Klimeck, Rajib Rahman The phonon induced relaxation times (T1) of electron spins bound to single phosphorous (P) donors and P donor clusters in silicon is computed using the atomistic tight-binding method. The electron-phonon Hamiltonian is directly computed from the strain dependent tight-binding Hamiltonian, and the relaxation time is computed from Fermi's Golden Rule using the donor states and the electron-phonon Hamiltonian. The self-consistent Hartree method is used to compute the multi-electron wavefunctions in donor clusters. The method takes into account the full band structure of silicon including the spin-orbit interaction, and captures both valley repopulation and single valley g-factor shifts in a unified framework. The single donor relaxation rate varies proportionally to B$^{5}$, and is of the order of seconds at B$=$2T, both in good agreement with experimental single donor data (A. Morello et. al., Nature 467, 687 (2010)). T1 calculations in donor clusters show variations for different electron numbers and donor numbers and locations. The computed T1 in a 4P:5e donor cluster match well with a scanning tunneling microscope patterned P donor cluster (H. Buch et. al., Nature Communications 4, 2017 (2013)). [Preview Abstract] |
Tuesday, March 4, 2014 9:48AM - 10:00AM |
F36.00008: Electronic Structure of donor pairs in Si Belita Koiller, Andre Saraiva, Maria Jose Calderon, Fernando Gonzalez-Zalba, Dominik Heiss, Andrew J. Ferguson We develop an effective mass theory for a pair of substitutional group-V donors in Si. An empirical central cell correction for a single donor, applied to energies and wavefunctions, leads to an accurate description of the $D_2$ ``molecular'' spectrum. No configuration averages simulating an ensemble of pairs are taken: our formalism applies to the single pair regime, including the A1, T and E single donor states in the hydrogenic S-like manifold and a Configuration Interaction approach to account for electron-electron correlations. We also obtain the inter donor distance dependence of experimentally accessible quantities: first ionization $(D_2^0 \to D_2^+)$, second ionization $(D_2^+ \to D_2^{++})$ energies, charging energy and singlet-triplet splitting. All results are consistent with recently performed experiments on As doped Si, suggesting that our approach is reliable down to distances $\sim$ 2 nm, and possibly smaller. [Preview Abstract] |
Tuesday, March 4, 2014 10:00AM - 10:12AM |
F36.00009: Quantum information processing using acceptors in silicon and phonon entanglement Susan Clark, Charles Reinke, Hayden McGuinness, Ihab El-Kady Quantum computing with large numbers of qubits remains challenging due to the decoherence and complexity that arise as more qubits are added to a system. Here I propose a new platform for semiconductor quantum computing which may be robust to common sources of decoherence and may not be difficult to fabricate repeatedly. This system consists of a hole bound to an acceptor in silicon which has been implanted in the center of a mechanical cavity (similar to a photonic crystal cavity) and connected to other cavities by a system of waveguides. I will outline a basic entangling gate and calculations showing the promise of this platform as the ideal qubit. 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] |
Tuesday, March 4, 2014 10:12AM - 10:24AM |
F36.00010: A donor molecule in silicon M. Fernando Gonzalez Zalba, Dominik Heiss, Andrew J. Ferguson, Andre Saraiva, Maria J. Calderon, Belita Koiller In 1954 Kohn and Luttinger introduced the description for a single donor in silicon as a hydrogen atom analogue in a semiconductor environment. Generalizing the concept, a donor pair may behave as a hydrogen molecule. However, a detailed understanding of the electronic structure of these molecular systems is a challenge to be overcome. Here we present an experimental demonstration of the energy spectrum of a strongly interacting donor pair in the channel of a silicon nanotransistor. We show the first evidence of a simultaneous enhancement of the binding and charging energies with respect to the single donor spectrum as well as a measurable exchange coupling. The measured data can be accurately matched by an effective mass theory incorporating the Bloch states multiplicity in Si, a central cell donor corrected potential and a full configuration interaction. These results suggest a novel physical mechanism to increase the operation temperature of conventional single-atom transistors and improve their robustness against interfacial electric fields. Furthermore, the data describes the Kane basic quantum processing element in the range of molecular hybridization. [Preview Abstract] |
Tuesday, March 4, 2014 10:24AM - 10:36AM |
F36.00011: Qubits Based on Shallow Donor Spins in Ge Phononic Crystals Vadim Smelyanskiy, Vasyl Hafiychuck, Mark Dykman, Andre Petukhov We propose qubits based on shallow donor electron spins in germanium. Spin-orbit interaction for donor spins in germanium is in many orders of magnitude stronger than in silicon. In a uniform bulk material it leads to very short spin lifetimes. However the lifetime increases dramatically when the donor is placed into a quasi-2D phononic crystal (PHC) and the energy of the Zeeman splitting is tuned to lie within a phonon bandgap. In this situation single phonon processes are suppressed by energy conservations. The remaining two-phonon decay channel is very slow. The Zeeman splitting within the gap can be fine tuned to induce a strong coupling between the spins of remote donors via exchange of virtual phonons. The analysis immediately extends to the interaction between nuclear spins. We also show that the long-range longitudinal interaction (z-z) between localized electron spins in PHC is similar to that mediated by Lamb waves in elastic plates. We explore various shapes of PHC cells in order to maximize the coherent effects of the spin-spin coupling while keeping the decay rate minimal. We find that phononic crystals with unit cell sizes ~ 100-150 nm are viable candidates for quantum computing applications. [Preview Abstract] |
Tuesday, March 4, 2014 10:36AM - 10:48AM |
F36.00012: Using bound exciton transitions to optically resolve neutral donor hyperfine states of various donor species in Silicon-28 Jeff Salvail, Phillip Dluhy, Kamyar Saeedi, Michael Szech, Helge Riemann, Nikolai Abromisov, Peter Becker, Hans-Joachim Pohl, Michael Thewalt Phosphorus in silicon is established as a promising resource for use in quantum information processing tasks. The neutral donor hyperfine states have been shown to have record long coherence times, high fidelity gates via RF pulses, and projective readout via optical bound exciton transitions. As Shannon's theory of information tells us, we can process more information in an alphabet of more symbols, so there is motivation to look at donors with higher nuclear spin than the $I=1/2$ of $^{31}$P, which provide access to Hilbert spaces of dimension greater than two. In this talk I will describe optical studies of the donors $^{75}$As ($I=3/2$), $^{121}$Sb ($I=5/2$), and $^{209}$Bi ($I=9/2$) in $^{28}$Si. [Preview Abstract] |
Tuesday, March 4, 2014 10:48AM - 11:00AM |
F36.00013: Experimental quantum simulation using 1D LaAlO$_3$/SrTiO$_3$ nanostructures Megan Kirkendall, Patrick Irvin, Jeremy Levy, Sangwoo Ryu, Chang-Beom Eom Quantum simulation of important Hamiltonians could lead to new insights into quantum matter, for example, high-temperature superconductors. The 2DEG at the LaAlO$_3$/SrTiO$_3$ interface\footnote{A. Ohtomo and H.Y. Hwang, Nature \textbf{427}, 423 (2004)} exhibits a wide variety of phenomena including a tunable metal-insulator transition, magnetism, strong spin-orbit coupling, and superconductivity. These properties can be controlled at extreme nanoscale dimensions using a conductive-AFM writing technique\footnote{C. Cen \textit{et al.}, Nat. Mater. \textbf{7}, 298 (2008)}. Here we describe experiments in which 1D lattice structures are created at the LaAlO$_3$/SrTiO$_3$ interface and investigated using low temperature magnetotransport. These devices will allow us to modify the effective interactions between Cooper pairs and quasiparticles in the superconducting lattice, and represent an early demonstration of the potential of this solid-state quantum simulation platform. [Preview Abstract] |
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