Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B46: Experimental Advances in Semiconducting QCFocus
|
Hide Abstracts |
Sponsoring Units: GQI Chair: Thaddeus Ladd, HRL Laboratories Room: 393 |
Monday, March 13, 2017 11:15AM - 11:51AM |
B46.00001: High-fidelity entangling gate for double-quantum-dot spin qubits Invited Speaker: John Nichol Electron spins in semiconductors are promising qubits, because their long coherence times enable nearly a billion coherent quantum gate operations. However, developing a scalable high-fidelity two-qubit gate remains challenging. We discuss a new entangling gate between two double-quantum-dot spin qubits in GaAs, which uses a magnetic field gradient between the two dots in each qubit to suppress decoherence due to charge noise. When the magnetic gradient dominates the voltage-controlled exchange interaction between electrons, qubit coherence times increase by an order of magnitude. Using randomized benchmarking, we measure single-qubit gate fidelities of approximately 99{\%}, and through self-consistent quantum measurement, state, and process tomography, we measure an entangling gate fidelity of 90{\%}. In the future, operating double quantum dot spin qubits with large gradients in nuclear-spin-free materials, such as Si, should enable a two-qubit gate fidelity surpassing the threshold for fault tolerant quantum information processing. [Preview Abstract] |
Monday, March 13, 2017 11:51AM - 12:03PM |
B46.00002: Randomized Benchmarking in a Si/SiGe Triple-Dot Decoherence-Free Subsystem Reed Andrews We demonstrate single-qubit randomized benchmarking of an exchange-only quantum-dot qubit. The qubit is implemented using an array of three electron spins in three undoped accumulation-mode quantum dots fabricated from an isotopically enhanced Si/SiGe heterostructure [1]. The three spins form a decoherence-free subsystem with encoded universal control using the exchange interaction [2], for which Clifford operators are composed of 1 to 4 sequential, voltage-controlled exchange evolutions of calibrated strength. Symmetric pulsing using an inter-dot exchange gate reduces sensitivity to charge noise [3]. We find that at zero magnetic field, charge noise nevertheless contributes significantly to gate errors, with additional errors due to pulse imperfections and spurious magnetic field gradients. Errors as low as 1\% have been obtained for single qubit randomized benchmarking using only the exchange interaction for qubit rotations. \newline [1] M.G. Borselli et al., Nanotechnology 26, 375202 (2015)\newline [2] K. Eng et al., Sci. Adv. 1, e1500214 (2015)\newline [3] M.D. Reed et al., Phys. Rev. Lett. 116B, 110402 (2016) [Preview Abstract] |
Monday, March 13, 2017 12:03PM - 12:15PM |
B46.00003: All-electrical universal control of two electron spin qubits in Si/SiGe Thomas Watson, E. Kawakami, D. R. Ward, Z. Ramlakhan, P. Scarlino, M. Veldhorst, D. E. Savage, M. G. Lagally, Mark Friesen, S. N. Coppersmith, M. A. Eriksson, L. M. K. Vandersypen Electron spins confined to quantum dots in silicon are promising qubits for quantum information as they have long coherence times due to the low abundance of nuclear spins in the silicon substrate which cause decoherence. Here, we demonstrate the initialisation, readout, and universal control of two coupled single electron spin qubits confined to a Si/SiGe double quantum dot. In contrast to previous work on Si-MOS double dots [1], single qubit gates are achieved by performing electric dipole spin resonance (EDSR) in the presence of a magnetic field gradient produced by micromagnets [2]. This allows for faster qubit manipulation and facilitates selective addressing of individual qubits. Here the resonance frequencies of the two qubits are separated by $\sim$1GHz due to the magnetic field gradient. In addition, we demonstrate two-qubit gates by controlling the exchange interaction between the two electron spins achieving both a controlled-rotation gate and a controlled-phase gate, both of which are locally equivalent to the CNOT gate. [1] M. Veldhorst et al., Nature 526, 410 (2015) [2] E. Kawakami et al., Nature Nanotechnology 9, 666 (2014) [Preview Abstract] |
Monday, March 13, 2017 12:15PM - 12:27PM |
B46.00004: Progress towards two double-dot qubits in Si/SiGe: quadruple quantum dots Ryan H. Foote, Daniel R. Ward, Dohun Kim, Brandur Thorgrimsson, Luke Smith, D. E. Savage, M. G. Lagally, Mark Friesen, S. N. Coppersmith, M. A. Eriksson We present the fabrication and electrical characterization of two types of gate-defined quadruple quantum dot devices formed in Si/SiGe heterostructures. We compare two designs, one which uses three layers of tightly overlapping gates and is similar to the work found in [1], and one which uses only two layers of gates and has significantly more open space between neighboring gates [2]. We demonstrate charge-state conditional quantum oscillations in the more open device, we compare the tunability of both devices with each other, and we discuss the implications of these measurements on a path towards larger numbers of coupled quantum dot qubits. This work is supported in part by ARO (W911NF-12-1-0607), NSF (DMR-1206915, PHY-1104660), ONR (N00014-15-1-0029) and the Department of Defense. Development and maintenance of the growth facilities used for fabricating samples supported by DOE (DE-FG02-03ER46028). DK acknowledges support from the Korea Institute of Science and Technology Institutional Program (Project No. 2E26681). This research utilized facilities supported by the NSF (DMR-0832760, DMR-1121288). [1] D. M. Zajac \textit{et al}., \textit{Appl. Phys. Lett. }\textbf{106}, 223507 (2015). [2] D. R. Ward \textit{et al.}, \textit{npj Quant. Inf.} \textbf{2}, 16032 (2016). [Preview Abstract] |
Monday, March 13, 2017 12:27PM - 12:39PM |
B46.00005: Scalable gate architecture for a one-dimensional array of semiconductor spin qubits David Zajac, Thomas Hazard, Xiao Mi, Jason Petta Electron spins in quantum dots have become one of the most intensely researched candidates for quantum computation due to their long lifetimes and their ability to be fabricated using standard semiconductor fabrication techniques. However realizing entanglement between large numbers of spins will require the fabrication of large, robust arrays of quantum dots. We demonstrate an array of nine quantum dots with three single dot sensors as a proof-of-concept device for a scalable, one-dimensional gate architecture*. We measure average single dot charging and orbital energies of 6.9 meV and 3.0 meV respectively, with standard deviations less than 20\% across the array. We achieve a charge sensitivity of 8.2 x 10$^{-4}$ e/√Hz with our single dot charge sensors, which allows for the detection of real-time tunneling events in the array. Using real-time charge detection we perform single shot spin readout and measure a spin relaxation time of T$_1$ = 170 ms at a magnetic field of B = 1 T. We also measure the capacitive coupling of two adjacent double quantum dots to be 200 µeV, suggesting that 50 GHz two-qubit gates may be possible. *D. M. Zajac et al., Phys. Rev. Appl. (in press). [Preview Abstract] |
Monday, March 13, 2017 12:39PM - 12:51PM |
B46.00006: Single spin relaxation measurements in Si/SiGe quantum dots T. M. Hazard, D. M. Zajac, X. Mi, J. R. Petta Spin qubits fabricated in silicon hold great promise for quantum computing due to their long relaxation and coherence times. We measure the spin relaxation time, $T_1$, as a function of in-plane magnetic field, $B$, in undoped accumulation-mode Si/SiGe quantum dots. Using single shot measurements\footnote{J. M. Elzerman \textit{et al.}, Nature, \textbf{435}, 431 (2004).}, we measure $T_1=$ 170 ms at $B=$ 1 T. In the limit where the Zeeman energy is much greater than the valley splitting, $E_z \gg E_v$, we find that $T_1$ scales as $B^3$. Using a large linear array of dots\footnote{D. M. Zajac \textit{et al.}, Phys. Rev. Appl. (in press).}, we are able to measure differences in the relaxation rates for adjacent dots in the same device and find a similar power law scaling in 4 dots. By changing the size of the dots, we find no substantial difference in the relaxation rate when the orbital energy of the dot is changed by an order of magnitude. Spin relaxation hot spots\footnote{C. H. Yang \textit{et al.}, Nat. Comm., \textbf{4}, 2069 (2013).} are observed at small magnetic fields in 2 of the 4 measured dots, giving further evidence that the valley splitting is small in these devices. [Preview Abstract] |
Monday, March 13, 2017 12:51PM - 1:03PM |
B46.00007: Strong coupling of a single electron in silicon to a microwave photon Xiao Mi, Jeffrey Cady, David Zajac, Jason Petta We demonstrate a hybrid circuit quantum electrodynamics (cQED) architecture in which a single electron in a Si/SiGe double quantum dot is dipole-coupled to the electric field of microwave photons in a superconducting cavity. Vacuum Rabi splitting is observed in the cavity transmission when the transition energy of the single-electron charge qubit matches that of a cavity photon, demonstrating that our device is in the strong coupling regime. The achievement of strong coupling is largely facilitated by an exceptionally low charge decoherence rate of 5 MHz and paves the way toward a wide range of cQED experiments with quantum dots, such as non-local qubit interactions \footnote{J. Majer \textit{et al.}, \textit{Nature} \textbf{449}, 443 (2007).}, strong spin-cavity coupling \footnote{J. J. Viennot \textit{et al.}, \textit{Science} \textbf{349}, 408 (2015).} and single photon generation \footnote{A. A. Houck \textit{et al.}, \textit{Nature} \textbf{449}, 328 (2007).}. [Preview Abstract] |
Monday, March 13, 2017 1:03PM - 1:15PM |
B46.00008: Characterization of enhancement-mode two-channel triple quantum dot device fabricated from an undoped Si/Si$_{\mathrm{0.8}}$Ge$_{\mathrm{0.2}}$ quantum well hetero-structure. Sergei Studenikin, D. G. Austing, T. M. Lu, E. R. Luhman, D. Bethke, M. C. Wanke, M. P. Lilly, M. S. Carroll, A. S. Sachrajda Recently, single- and double-dot characteristics of an enhancement-mode quantum dot device fabricated from an undoped Si/Si$_{\mathrm{0.8}}$Ge$_{\mathrm{0.2}}$ hetero-structure were reported in [1]. As compared to Si/SiGe hetero-structures with a Ge concentration of 30{\%} typically encountered, a 20{\%} Ge concentration offers high electron mobility, and the fabrication process flow is simplified to incorporate a single accumulation metal-gate layer. We report a number of new results for the device which consists of two channels (upper and lower) formed with two separate accumulation gates. With other gates, a double-dot (in upper channel) and single-dot (in lower channel) can be formed under the accumulation gates energized positively. We demonstrate charge sensing of the upper double-dot with the lower single-dot. We also discuss the formation of a triple-dot formed by coupling the single-dot in the lower channel when made non-conducting to the double-dot in the upper conducting channel. We will discuss technological issues, and describe an intriguing and reproducible phenomenon in the quantum dot behavior that occurs at a temperature \textasciitilde 1 K during the $^{\mathrm{3}}$He cryostat refresh cycle. [1] T. M. Lu \textit{et al}., Appl. Phys. Lett. \textbf{109}, 093102 (2016). [Preview Abstract] |
Monday, March 13, 2017 1:15PM - 1:27PM |
B46.00009: Spin-orbit and hyperfine interaction mediated spin relaxation in a single electron GaAs quantum dot Liuqi Yu, L. C. Camenzind, D. M. Zumbuehl, P. Stano, J. Zimmerman, A. C. Gossard Understanding and controlling spin relaxation is of great importance for spin qubit. The spin-orbit interaction (SOI) and hyperfine interaction are two most important ones that can couple the electron spin states to its orbital states so that spins can relax. In a magnetic field, it has been shown that spin relaxation is primarily caused by spin-phonon coupling mediated by SOI [1, 2]. Here we present measurements of the spin relaxation rate in a gate defined single-electron GaAs quantum dot. The spin relaxation rate W is measured in a magnetic field up to 14 T in the plane of the 2D electron gas. The shape of the quantum dot can be well controlled. Due to the interplay of Rashba and Dresselhaus SOIs, W shows strong anisotropy with varying directions of applied in-plane magnetic fields. Along crystal axis [1-10] where the overall SOI coupling is weak, spin relaxation time T1 of more than 30 s has been obtained at a magnetic field of 0.6 T. However, this long T1 time is still much shorter than the expected value within the scope of SOI mediated spin relaxation. Given the field dependence of W, particularly in low field regime, the shorter T1 times are attributed to the hyperfine interaction mediated spin relaxation via phonons [3], which is observed for the first time. [1] S. Amasha \textit{et al.}, PRL. \textbf{100}, 046803 (2008). [2] V. N. Golovach et al., PRL \textbf{93}, 016601 (2004). [3] S. Erlingsson \textit{et al}., PRB. \textbf{66}, 155327 (2002). [Preview Abstract] |
Monday, March 13, 2017 1:27PM - 1:39PM |
B46.00010: Negative spin exchange in a multielectron GaAs quantum dot Ferdinand Kuemmeth, F. Martins, F. K. Malinowski, P. D. Nissen, C. M. Marcus, G. C. Gardner, S. Fallahi, M. J. Manfra, T. Smith, A. C. Doherty, S. D. Bartlett We use a singlet-triplet qubit implemented in a GaAs double dot to probe the exchange interaction between one of its dots and a nearby multielectron dot. By applying fast gate voltage pulses, we first initialize the double dot in the singlet state, then allow tunneling between one of its dots and the multielectron dot for a short time, followed by singlet-triplet readout of the double dot. We find that the spin-exchange energy can have opposite sign compared to exchange between singly-occupied dots. This behavior occurs already at zero magnetic field and is not affected by in-plane magnetic fields. The exchange profile can, however, be changed by applying out-of-plane magnetic fields or by changing the occupancy of the multielectron dot. By coupling a second singlet-triplet qubit to the multielectron dot, we can map out different configurations that are relevant for non-nearest-neighbor coupling of semiconducting spin qubits. [Preview Abstract] |
Monday, March 13, 2017 1:39PM - 1:51PM |
B46.00011: Exchange interaction between distant spins mediated by a multielectron quantum dot F. K. Malinowski, F. Martins, P. D. Nissen, C. M. Marcus, F. Kuemmeth, G. C. Gardner, S. Fallahi, M. J. Manfra, T. Smith, A. C. Doherty, S. D. Bartlett We demonstrate coherent exchange interactions between two separated electron spins in a GaAs heterostructure, mediated by a central multielectron quantum dot. We observe three different regimes of spin exchange. First, long-range superexchange, mediated my virtual occupations of the multielectron dot. Second, direct exchange, induced by moving one of the electrons onto the multielectron dot. Finally, on-site exchange, with both electrons transferred to the multielectron dot. Using independent readout of both spins, we further show that this interaction mechanism can be used for a fast and high-fidelity square-root-SWAP entangling gate for single electronic spins. [Preview Abstract] |
Monday, March 13, 2017 1:51PM - 2:03PM |
B46.00012: Towards Jellybean-Coupled Spin Qubits Sebastian Pauka, Xanthe Croot, David Reilly, John Watson, Michael Manfra Semiconductor-based spin qubits are interesting platforms for investigating the scalability of elementary quantum computers. Here, we present results taken on a GaAs five-quantum dot device in which an intermediary, multi-electron ‘jellybean’ dot is used as a coherent, exchange-based spin coupler. Our geometry, together with the use of positively biased accumulation gates, allows for the routine loading and charge sensing of all dots in the 5-dot array. Control of the jellybean dot and capacitive coupling of two singlet-triplet qubits is demonstrated. [Preview Abstract] |
Monday, March 13, 2017 2:03PM - 2:15PM |
B46.00013: A split accumulation gate architecture for silicon MOS quantum dots Sophie Rochette, Martin Rudolph, Anne-Marie Roy, Matthew Curry, Gregory Ten Eyck, Jason Dominguez, Ronald Manginell, Tammy Pluym, John King Gamble, Michael Lilly, Chlo\'{e} Bureau-Oxton, Malcolm S. Carroll, Michel Pioro-Ladri\`{e}re We investigate tunnel barrier modulation without barrier electrodes in a split accumulation gate architecture for silicon metal-oxide-semiconductor quantum dots (QD). The layout consists of two independent accumulation gates, one gate forming a reservoir and the other the QD. The devices are fabricated with a foundry-compatible, etched, poly-silicon gate stack. We demonstrate 4 orders of magnitude of tunnel-rate control between the QD and the reservoir by modulating the reservoir gate voltage. Last electron charging energies of app. 10 meV and tuning of the ST splitting in the range 100-200 ueV are observed in two different split gate layouts and labs. 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 operated by Sandia Corporation, a Lockheed-Martin Company, for the U. S. Department of Energy under Contract No. DE-AC04-94AL85000. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700