Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session P45: Semiconductor Qubits: Quantum Dot / Donor Devices and ReadoutFocus
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Sponsoring Units: GQI Chair: John Gamble, Sandia National Laboratory Room: 348 |
Wednesday, March 16, 2016 2:30PM - 2:42PM |
P45.00001: Nuclear-driven electron spin rotations in a coupled silicon quantum dot and single donor system Patrick Harvey-Collard, Noah Tobias Jacobson, Martin Rudolph, Gregory A. Ten Eyck, Joel R. Wendt, Tammy Pluym, Michael P. Lilly, Michel Pioro-Ladrière, Malcolm S. Carroll Single donors in silicon are very good qubits. However, a central challenge is to couple them to one another. To achieve this, many proposals rely on using a nearby quantum dot (QD) to mediate an interaction. In this work, we demonstrate the coherent coupling of electron spins between a single $^{31}$P donor and an enriched $^{28}$Si metal-oxide-semiconductor few-electron QD. We show that the electron-nuclear spin interaction can drive coherent rotations between singlet and triplet electron spin states. Moreover, we are able to tune electrically the exchange interaction between the QD and donor electrons. The combination of single-nucleus-driven rotations and voltage-tunable exchange provides all elements for future all-electrical control of a spin qubit, and requires only a single dot and no additional magnetic field gradients. 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] |
Wednesday, March 16, 2016 2:42PM - 2:54PM |
P45.00002: All-electrical control of a singlet-triplet qubit coupled to a single nuclear spin N. Tobias Jacobson, Patrick Harvey-Collard, Andrew Baczewski, John Gamble, Martin Rudolph, Erik Nielsen, Richard Muller, Malcolm Carroll Donor nuclear spins in isotopically purified silicon have very long coherence times, suggesting that they may form high-quality quantum memories. We propose that coupling these nuclear spins to few-electron quantum dots could enable nuclear spin readout and two-qubit operations of the joint quantum dot and nuclear spin system without the need for electron spin resonance. As a step towards this goal, our group recently demonstrated coherent singlet/triplet electron spin rotations induced by the hyperfine interaction between electronic spin degrees of freedom and a single nuclear spin in isotopically purified silicon. In this talk, I will discuss the feasibility of universal all-electrical control of such a singlet/triplet electron spin qubit and explore the decoherence mechanisms that we expect to dominate. Finally, I will examine the relative merits of AC and pulsed DC gating schemes. [Preview Abstract] |
Wednesday, March 16, 2016 2:54PM - 3:06PM |
P45.00003: Full Controllability of a Singlet-Triplet Qubit Coupled to a Nuclear Spin Qubit Andrew D. Baczewski, John King Gamble, N. Tobias Jacobson, Richard P. Muller, Erik Nielsen, Stephen M. Carr, Malcolm S. Carroll, Matthew Curry, Patrick Harvey-Collard, Ryan M. Jock, Martin Rudolph Recent experimental developments indicate that it is possible to drive coherent singlet-triplet rotations in a MOS quantum dot coupled to a single nearby phosphorus donor through the electron-nucleus hyperfine interaction. With the addition of NMR, we propose that it is possible to achieve universal 2-qubit control spanning i.) an electronic singlet-triplet subspace of the dot, ii.) the spin-1/2 donor nucleus, and iii.) entangling operations between them. We will assess the practicality of such an approach given realistic experimental conditions and constraints, including a comparison of pulsed and RF control of the detuning between the donor and dot. 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 Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Wednesday, March 16, 2016 3:06PM - 3:18PM |
P45.00004: Transport through an impurity tunnel coupled to a Si/SiGe quantum dot Ryan H. Foote, Daniel R. Ward, J.R. Prance, John King Gamble, Erik Nielsen, Brandur Thorgrimsson, D.E. Savage, A.L. Saraiva, Mark Friesen, S.N. Coppersmith, M.A. Eriksson Here we present measurements of transport through a gate-defined quantum dot formed in a Si/SiGe heterostructure, demonstrating controllable tunnel coupling between the quantum dot and a localized electronic state.$^{1}$ Combining experimental stability diagram measurements with 3D capacitive modeling based on the expected electron density profiles, we determine the most likely location of the localized state in the quantum well. This work is supported in part by NSF (DMR-1206915, IIA-1132804), ARO (W911NF-12-1-0607) and the William F. Vilas Estate Trust. Development and maintenance of the growth facilities used for fabricating samples supported by DOE (DE-FG02-03ER46028). This research utilized facilities supported by the NSF (DMR-0832760, DMR-1121288). The work of J.K.G. and E.N. was supported in part by the Laboratory Directed Research and Development program at Sandia National Laboratories. 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. \\ $^{1}$Ryan H. Foote \textit{et al., Appl. Phys. Lett.} {\bf 107}, 103112 (2015) [Preview Abstract] |
Wednesday, March 16, 2016 3:18PM - 3:30PM |
P45.00005: Silicon quantum dots with counted antimony donor implants Meenakshi Singh, Jose Pacheco, Daniel Perry, Joel Wendt, Ronald Manginell, Jason Dominguez, Tammy Pluym, Dwight Luhman, Edward Bielejec, Michael Lilly, Malcolm Carroll Antimony donor implants next to silicon quantum dots have been detected with integrated solid-state diode detectors with single ion precision. Devices with counted number of donors have been fabricated and low temperature transport measurements have been performed. Charge offsets, indicative of donor ionization and coupling to the quantum dot, have been detected in these devices. The number of offsets corresponds to 10-50{\%} of the number of donors counted. We will report on tunneling time measurements and spin readout measurements on the donor offsets. 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] |
Wednesday, March 16, 2016 3:30PM - 3:42PM |
P45.00006: Detection of ion implanted patterns in silicon using STM Hyun-Soo Kim, A.N. Ramanayaka, K.J. Dwyer, M.D. Stewart Jr., J.M. Pomeroy Ion implanted regions in silicon are scanned using STM to detect features which will facilitate in-situ overlay and alignment of STM hydrogen patterned nano-devices. STM hydrogen lithography is used to make atomically precise devices such as single electron transistors and single atom qubits. However, with currently available imaging techniques, we are limited to make devices on a single plane using STM lithography. In-situ detection of high local doping concentrations using STM will allow precise alignment between the multiple layers of buried nano-devices and metal electrodes. [Preview Abstract] |
Wednesday, March 16, 2016 3:42PM - 3:54PM |
P45.00007: Atomistic simulations of negatively charged donor states probed in STM experiments Archana Tankasala, Joe Salfi, Sven Rogge, Gerhard Klimeck, Rajib Rahman A single donor in silicon binding two electrons ($D^-$) is important for electron spin readout and two-qubit operations in a donor based silicon (Si) quantum computer, and has recently been probed in Scanning Tunneling Microscope (STM) experiments for sub-surface dopants. In this work, atomistic configuration interaction technique is used to compute the two-electron states of the donor taking into account the geometry of the STM-vacuum-silicon-reservoir device. While 45 meV charging energy is obtained for $D^-$ in bulk Si, the electrostatics of the device reduces the charging energy to ~30 meVs. It is also shown that the reduced charging energy enables spin triplet states to be bound to the donor. The exchange splitting between the singlet and triplet states can be tuned by an external electric field. The computed wavefunctions of the $D^-$ state helps to understand how the contribution of the momentum space valley states change with donor depth and electric field. [Preview Abstract] |
Wednesday, March 16, 2016 3:54PM - 4:06PM |
P45.00008: Atomic Precision Donor Devices Fabricated on Strained Silicon on Insulator (sSOI) with SiGe E. Yitamben, E. Bussmann, D.A. Scrymgeour, M. Rudolph, S.M. Carr, D.R. Ward, M.S. Carroll Recently, Si:P donor spin qubits have achieved coherence times (nuclear {\&} e-) that underscore their quantum computing potential. One next major challenge is to integrate donors into a gated structure where electrons can be moved between P, or drawn off of the P to interact, e.g. to an interface as in Kane's proposal. A key constraint is limited thermal budget, to limit P thermal segregation, which precludes typical gate oxidation of Si. We are developing an alternative materials stack utilizing an interfacial barrier layer of relaxed epitaxial SiGe, with donors placed in a strained Si-on-insulator (sSOI) substrate. We fabricate atomic precision donor structures in sSOI via STM hydrogen lithography. Utilizing Si microfabrication and STM in tandem with our Si and Ge molecular beam epitaxy (MBE), we fabricated devices to test our SiGe/sSOI stack concept and atomic-precision fab techniques. To establish our donor-doping capability, we made Hall and Van der Pauw devices in P:sSOI delta-doped layers exhibiting n$_{\mathrm{e}}$ \textgreater 10$^{\mathrm{14}}$/cm$^{\mathrm{2}}$ and mobilities of \textasciitilde 100 cm$^{\mathrm{2}}$/Vs (T$=$4K) similar to results reported relaxed Si reported elsewhere. Second, we have grown our concept epitaxial SiGe/sSOI stack, evaluated the morphology using STM, and fabricated Hall devices to evaluate low-T transport in our first SiGe/sSOI. Here, we report on these advances in atomic precision donor fab, along with STM analysis our MBE SiGe/sSOI. This work extends STM-based atom precision fab on strained Si toward a vertically gated architecture. [Preview Abstract] |
Wednesday, March 16, 2016 4:06PM - 4:18PM |
P45.00009: Low-frequency conductance fluctuations in Si:P and Ge:P $\delta$-layers Saquib Shamim, Suddhasatta Mahapatra, Giordano Scappucci, W. M. Klesse, Michelle Y. Simmons, Arindam Ghosh Delta doped Si:P and Ge:P devices offer a formidable platform for application towards quantum computation. The fabrication of single donor devices by STM-lithography takes us forward to address the solid state quantum bits. The atomic scale control however makes the devices extremely sensitive to fluctuations and disorder which affect their long term stability. Hence, a study of low frequency 1/f noise for these devices is desirable. We measure 1/f noise in Si:P and Ge:P $\delta$-layers of varying doping density. Fluctuations in conductivity arise due to fluctuations in mobility and the Hooge parameter scales inversely with mobility as $1/\mu^3$ for all devices. For highly doped Ge:P $\delta$-layer, the noise magnitude in a perpendicular magnetic field ($B_\perp$) reduces by factors of two at the phase breaking breaking field and the Zeeman field indicating universal conductance fluctuations (UCF). The phase breaking length $l_\phi^{UCF}$ extracted by fitting the $B_\perp$ dependence of noise to the crossover function matches well with $l_\phi^{WL}$ extracted from weak localization (WL) fits to magnetoconductivity indicating that both UCF and WL are governed by same scattering rates. [Preview Abstract] |
Wednesday, March 16, 2016 4:18PM - 4:30PM |
P45.00010: Weak measurement and quantum steering of spin qubits in silicon Andrea Morello, Juha Muhonen, Stephanie Simmons, Solomon Freer, Juan Dehollain, Jeffrey McCallum, David Jamieson, Kohei Itoh, Andrew Dzurak Single-shot, projective measurements have been demonstrated with very high fidelities on both the electron [1] and the nuclear [2] spin of single implanted phosphorus ($^{31}$P) donors in silicon. Here we present a series of experiments where the measurement strength is continousuly reduced, giving access to the regime of weak measurement of single spins.\\ For the electron qubit, the measurement strength is set by the measurement time compared to the spin-dependent tunneling time between the $^{31}$P donor and a charge reservoir. For the nuclear qubit, the measurement strength is set by the rotation angle of an ESR pulse.\\ We have demonstrated quantum steering of the spin states, with curious and useful applications. We can improve the fidelity of electron qubit initialization by steering it towards the ground state, thus bypassing thermal effects on the initialization process. We can also accurately measure the electron-reservoir tunnel coupling, without the electron ever tunneling away from the $^{31}$P atom. Finally, these techniques allow the study of weak values and Leggett-Garg inequalities.\\ {[1]} A. Morello et al., Nature 467, 687 (2010)\\ {[2]} J.J. Pla et al., Nature 496, 334 (2013) [Preview Abstract] |
Wednesday, March 16, 2016 4:30PM - 4:42PM |
P45.00011: Single-Shot Charge Readout Using a Cryogenic Heterojunction Bipolar Transistor Preamplifier Inline with a Silicon Single Electron Transistor at Millikelvin Temperatures Matthew Curry, Troy England, Joel Wendt, Tammy Pluym, Michael Lilly, Stephen Carr, Malcolm Carroll Single-shot readout is a requirement for many implementations of quantum information processing. The single-shot readout fidelity is dependent on the signal-to-noise-ratio (SNR) and bandwidth of the readout detection technique. Several different approaches are being pursued to enhance read-out including RF-reflectometry, RF-transmission, parametric amplification, and transistor-based cryogenic preamplification. The transistor-based cryogenic preamplifier is attractive in part because of the reduced experimental complexity compared with the RF techniques. Here we present single-shot charge readout using a cryogenic Heterojunction-Bipolar-Transistor (HBT) inline with a silicon SET charge-sensor at millikelvin temperatures. For the relevant range of HBT DC-biasing, the current gain is 100 to 2000 and the power dissipation is 50 nW to 5 $\mu $W, with the microfabricated SET and discrete HBT in an integrated package mounted to the mixing chamber stage of a dilution refrigerator. We experimentally demonstrate a SNR of up to 10 with a bandwidth of 1 MHz, corresponding to a single-shot time-domain charge-sensitivity of approximately 10$^{\mathrm{-4}} \quad e$/$\surd $Hz. This measured charge-sensitivity is comparable to the values reported using the RF techniques. [Preview Abstract] |
Wednesday, March 16, 2016 4:42PM - 4:54PM |
P45.00012: Flexible Low-power SiGe HBT Amplifier Circuits for Fast Single-shot Spin Readout Troy England, Michael Lilly, Matthew Curry, Stephen Carr, Malcolm Carroll Fast, low-power quantum state readout is one of many challenges facing quantum information processing. Single electron transistors (SETs) are potentially fast, sensitive detectors for performing spin readout of electrons bound to Si:P donors. From a circuit perspective, however, their output impedance and nonlinear conductance are ill suited to drive the parasitic capacitance of coaxial conductors used in cryogenic environments, necessitating a cryogenic amplification stage. We will introduce two new amplifier topologies that provide excellent gain versus power tradeoffs using silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs). The AC HBT allows in-situ adjustment of power dissipation during an experiment and can provide gain in the millikelvin temperature regime while dissipating less than 500 nW. The AC Current Amplifier maximizes gain at nearly 800 A/A. We will also show results of using these amplifiers with SETs at 4 K. 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] |
Wednesday, March 16, 2016 4:54PM - 5:06PM |
P45.00013: Dispersively Detected Pauli Spin-Blockade in a Silicon Nanowire Field-Effect Transistor Andreas Betz, R Wacquez, M. Vinet, X. Jehl, A.L. Saraiva, M. Sanquer, A.J. Ferguson, M.F. Gonzalez-Zalba We report the dispersive readout of the spin state of a double quantum dot (DQD) formed at the corner states of a silicon nanowire FET. Two face-to-face topgate electrodes allow us to independently tune the charge occupation of the quantum dot system down to the few-electron limit. We measure the charge stability of the DQD in DC transport as well as dispersively via in situ gate-based radio frequency (rf) reflectometry, where one top-gate electrode is connected to a resonator. The latter removes the need for external charge sensors in quantum computing architectures and provides a compact way to readout the dispersive shift caused by changes in the quantum capacitance during inter-dot charge transitions. Here, we observe Pauli spin-blockade in the rf response of the circuit at finite magnetic fields between singlet and triplet states. The blockade is lifted at higher magnetic fields when intra-dot triplet states become the ground state configuration. A line shape analysis of the dispersive signal reveals furthermore an intra-dot valley-orbit splitting $\Delta_{vo}\simeq 145 \mu$eV. Our results open up the possibility to operate compact CMOS technology as a singlet-triplet qubit and make split-gate silicon nanowire architectures an ideal candidate for the study of spin dynamics. [Preview Abstract] |
Wednesday, March 16, 2016 5:06PM - 5:18PM |
P45.00014: Characterization and Monte Carlo simulation of single ion Geiger mode avalanche diodes integrated with a quantum dot nanostructure Peter Sharma, J. B. S. Abraham, G. Ten Eyck, K. D. Childs, E. Bielejec, M. S. Carroll Detection of single ion implantation within a nanostructure is necessary for the high yield fabrication of implanted donor-based quantum computing architectures. Single ion Geiger mode avalanche (SIGMA) diodes with a laterally integrated nanostructure capable of forming a quantum dot were fabricated and characterized using photon pulses. The detection efficiency of this design was measured as a function of wavelength, lateral position, and for varying delay times between the photon pulse and the overbias detection window. Monte Carlo simulations based only on the random diffusion of photo-generated carriers and the geometrical placement of the avalanche region agrees qualitatively with device characterization. Based on these results, SIGMA detection efficiency appears to be determined solely by the diffusion of photo-generated electron-hole pairs into a buried avalanche region. Device performance is then highly dependent on the uniformity of the underlying silicon substrate and the proximity of photo-generated carriers to the silicon-silicon dioxide interface, which are the most important limiting factors for reaching the single ion detection limit with SIGMA detectors. 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] |
Wednesday, March 16, 2016 5:18PM - 5:30PM |
P45.00015: Joint measurement of electron spin qubits via proximal conductance Jason Kestner We propose a method to carry out joint measurements on spin qubits that are separated by several microns. Joint measurements, which reveal multi-qubit properties without determining anything about the individual qubits, are a key ingredient to performing quantum error correction and to producing measurement-based entanglement of non-interacting qubits. We presume that the qubits are capacitively coupled to a common conductance channel and are separated by a distance less than the phase coherence length of the semiconductor, and we calculate the tolerance of the procedure to various experimental imperfections. Conditions for carrying out $N$-qubit syndrome measurements are discussed. [Preview Abstract] |
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