Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session P28: Spin Qubit ReadoutFocus
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Sponsoring Units: DQI Chair: Michel Pioro-Ladrière, Université de Sherbrooke Room: LACC 405 |
Wednesday, March 7, 2018 2:30PM - 3:06PM |
P28.00001: Quantum Dot Circuit Quantum Electrodynamics Invited Speaker: Jason Petta In the context of superconducting devices, circuit QED provides elegant solutions for qubit control, readout, and coupling.$^{\mathrm{1}}$ I will describe our efforts to develop hybrid ``super-semi'' quantum systems that combine some of the most promising elements of superconducting and long coherence time spin-based quantum computing technologies. In the charge sector, we electric-dipole couple semiconductor double quantum dots (DQDs) to superconducting cavities and demonstrate dispersive readout of DQD charge stability diagrams.$^{\mathrm{2}}$ In the two-electron regime, the Pauli exclusion principle enables dispersive readout of singlet and triplet spin states.$^{\mathrm{3}}$ Overlapping gate electrodes fabricated on Si heterostructures have greatly improved charge coherence, ushering in a new era of strong-coupling quantum dot cQED.$^{\mathrm{4}}$ By placing a Si DQD in a large magnetic field gradient, we have recently achieved strong coupling between a single spin and a single microwave photon.$^{\mathrm{5}}$ These developments in quantum dot cQED, combined with recent demonstrations of high-fidelity two-qubit gates in Si,$^{\mathrm{\thinspace }}$firmly anchor Si as a leading material system in the worldwide race to develop a scalable quantum computer.$^{\mathrm{6}}$\\ \\ $[1.]$ X. Gu \textit{et al}., Phys. Rep. \textbf{718}, 1 (2017).\newline $[2.]$ J. Stehlik \textit{et al.}, Phys. Rev. Appl. \textbf{4}, 014018 (2015).\newline $[3.]$ K. D. Petersson \textit{et al.}, Nature \textbf{490}, 380 (2012).\newline $[4.]$ X. Mi \textit{et al.}, Science \textbf{355}, 156 (2017).\newline $[5.]$ X. Mi \textit{et al.}, Nature (submitted).\newline $[6.]$ D. M. Zajac \textit{et al.}, Science aao5965 (2017). |
Wednesday, March 7, 2018 3:06PM - 3:18PM |
P28.00002: Current-Biased SET-HBT Cryogenic Preamplifier for High-Fidelity Single-Shot Spin Readout Matthew Curry, Andrew Mounce, Troy England, Ron Manginell, Joel Wendt, Tammy Pluym, Stephen Carr, Malcolm Carroll A technique known as “enhanced latching readout” (ELR) produced single-shot readout fidelities of singlet and triplet states as high as 99.86% [Harvey-Collard et al., arXiv:1703.02651 (2017)]. In this case, the readout fidelity was limited by the circuit response time, which was ~100 μs. We present single-shot ELR with an improved circuit response time of microseconds. This is close to a factor of 100 times faster than the previous result and should enable higher fidelity readout. The faster response time is accomplished with a heterojunction-bipolar-transistor (HBT) as a cryogenic preamplifier, which is located at the mixing-chamber stage of a dilution refrigerator. A single-electron-transistor (SET), used to detect the charge state of the qubit, is connected directly to the base junction of the HBT. The SET-HBT current-biased configuration is very low power (e.g., ~0.1 to 1 μW) and combines high gain with potentially lower noise and electron temperature than other AC-coupled configurations. |
Wednesday, March 7, 2018 3:18PM - 3:30PM |
P28.00003: Single-Shot Readout of a S/T Qubit with a Cryogenic AC-Coupled HBT Amplifier in a Lithographic MOS Double Quantum Dot Martin Rudolph, Troy England, Ryan Jock, Peter Sharma, Andrew Mounce, Noah Jacobson, Dan Ward, Tammy Pluym, Beverly Silva, John Anderson, Joel Wendt, Michael Lilly, Malcolm Carroll Existing silicon fabrication capabilities can be exploited to form qubits in MOS nanostructures. However, it has been challenging to produce few-electron lithographically defined MOS double quantum dots (DQD) with tunable tunnel coupling (demonstrated in GaAs and Si-SiGe). We introduce a Si-MOS DQD device utilizing a foundry-compatible single poly-Si gate layer design. We demonstrate a well-defined few-electron DQD and tune the inter-dot tunnel coupling over several orders of magnitude. We demonstrate Pauli spin blockade readout of a two-electron S/T system and analyze the DQD properties via coherent S/T manipulations. The qubit state is read out in single shot with a SiGe HBT cryogenic amplification circuit, with a noise floor of 25 fA/Hz1/2 and readout sensitivity of 360x10-6 Hz-1/2. 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-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. |
Wednesday, March 7, 2018 3:30PM - 3:42PM |
P28.00004: Single-Shot Spin-to-Charge Conversion in Si/SiGe Quantum Dots Using Latched Readout and Cryogenic Amplification Laura De Lorenzo Achieving high signal-to-noise readout of multi-electron Si/SiGe spin qubits is critical for the rapid development of this technology for quantum applications. We report on single-shot spin-to-charge readout of a triple dot using an enhanced readout protocol where the spin states are pulsed to the (1,1,1)/(2,0,1) charge boundary and then into the (1,0,1) charge state. In this scheme, spin singlets decay from (1,1,1) -> (2,0,1) -> (1,0,1), whereas spin triplets are prevented from decaying to (2,0,1) by Pauli spin blockade. The resulting singlet-triplet differential signal is between states with differing numbers of electrons rather than just a spatial re-distribution of a fixed number of electrons. Using enhanced readout in conjunction with a low noise cryogenic HEMT amplifier, we achieve a measurement fidelity of <1e-2 in 600 ns of integration time. At these integration times, our measurement noise is dominated by broadband sources including the HEMT and the Johnson noise of our readout circuitry which together limit fidelity to ~1e-6. Decay mechanisms bound fidelity more severely; we arrive at 1e-2 by including triplet to singlet relaxation (T1) during measurement. Errors arising from T1 decrease linearly with integration time, incentivizing faster measurement. |
Wednesday, March 7, 2018 3:42PM - 3:54PM |
P28.00005: Tuning of Two-Stage HEMT Cryogenic Amplifier to Reduce Electron Temperature in a Nearby Quantum Dot Trevor Knapp, J. P. Dodson, Brandur Thorgrimsson, D. E. Savage, Max Lagally, Susan Coppersmith, M. A. Eriksson Cryogenic amplification using the two-stage HEMT amplifier [L. A. Tracy, et al., APL 108, 063101 (2016)] is one of several competing techniques for boosting the bandwidth of low-current high-impedance measurements in a dilution refrigerator. While it has previously been shown that the heat dissipation of the amplifier can be tuned below the typical cooling power of a mixing chamber in a dilution refrigerator, we show that the amplifier may still create a local heating effect that could substantially raise the electron temperature in a nearby sample (e.g., a quantum dot qubit). Fortunately the amplifier can be tuned to mitigate heat dissipation while preserving bandwidth. We present evidence that operation of the amplifier can be consistent with quantum dot electron temperatures of ~100 mK and single shot measurement. |
Wednesday, March 7, 2018 3:54PM - 4:06PM |
P28.00006: On-chip HEMT amplifiers for semiconductor spin qubit readout Lisa Tracy, John Reno, Terry Hargett Recent experiments have demonstrated improvements in spin qubit readout using semiconductor-based (HEMT or HBT) amplifiers located adjacent to the qubit chip, at the mixing chamber of a dilution refrigerator. Based on these results, a natural next step is to integrate the amplifier and spin qubit on the same semiconductor chip. For semiconductor spin qubits fabricated using heterostructures supporting high-mobility 2D electron layers (e.g. s-Si/SiGe, GaAs/AlGaAs), fabrication of on-chip HEMTs should be possible. We will discuss progress towards integration of HEMT amplifiers on-chip with quantum dots in GaAs/AlGaAs heterostructures, including design, fabrication, and expected gain and noise performance based on preliminary characterization of HEMT devices. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. DOE, Office of Basic Energy Sciences user facility, and was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. |
Wednesday, March 7, 2018 4:06PM - 4:18PM |
P28.00007: Non-linear dispersive response of a strongly driven quantum dot at gigahertz frequencies Mark Hogg, Matthew House, Michelle Simmons Minimizing the number of physical gates required for control of semiconductor spin qubits is an important consideration for scale-up to multi-qubit devices. A promising strategy is to use rf reflectometry with “gate-based” charge sensing for qubit readout. Studies to date have focused on charge sensing performance in the regime of weak rf driving where the response is linear, but when driven strongly the admittance of a quantum dot saturates to a constant ac current due to Coulomb blockade. Here we present the results of an rf reflectometry experiment on a quantum dot patterned in silicon by scanning tunneling microscope lithography. The quantum dot is addressed by only one gate and one reservoir lead, specifically designed to maximize the nonlinearity of the admittance. We observe saturation of the response at high driving amplitudes and verify the response predicted by a simple rate equation model. We study the performance of this quantum dot as a microwave mixer, demonstrating wide bandwidth down-conversion of signals 0-5 GHz with minimal losses. The quantum dot as an on-chip, lowloss microwave mixer may be a useful tool for modulating qubit control signals in future solid-state quantum computing applications. |
Wednesday, March 7, 2018 4:18PM - 4:30PM |
P28.00008: Conditional dispersive readout of a CMOS single-electron memory cell Simon Schaal, Sylvain Barraud, John Morton, M Fernando Gonzalez-Zalba Quantum computers require interfaces with classical electronics for efficient qubit control, measurement and fast data processing. Fabricating the qubit and the classical control layer using the same technology is appealing to facilitate the integration process, improve feedback speeds and offer potential solutions to wiring and layout challenges. By using CMOS processes the processor can benefit from the most mature industrial technology for the fabrication of large scale circuits. In this talk I’d like to present the integration of a single-electron charge storage CMOS quantum dot with a CMOS transistor (FET) for control of the readout via gate-based dispersive sensing. A charge sensitivity of δq=95 μe/√Hz is obtained when the quantum dot readout is enabled by the control FET combined with a single-electron retention time of the order of one second when the FET is switched off, opening the path towards time-based multiplexing of gate-based radio-frequency readout in CMOS quantum devices. |
Wednesday, March 7, 2018 4:30PM - 4:42PM |
P28.00009: A silicon-based single-electron interferometer coupled to a fermionic sea Anasua Chatterjee, Sergey Shevchenko, Sylvain Barraud, Ruben Otxoa, Franco Nori, John Morton, M Fernando Gonzalez-Zalba We study Landau-Zener-Stueckelberg-Majorana (LZSM) interferometry under the influence of projective readout using a charge qubit tunnel-coupled to a fermionic sea. The device is realised within a silicon complementary metal-oxide-semiconductor (CMOS) transistor. We first read out the charge state of the system in a continuous non-demolition manner by measuring the dispersive response of a high-frequency electrical resonator coupled to the quantum system via the gate. By performing multiple fast passages around the qubit avoided crossing, we observe a multi-passage LZSM interferometry pattern. At larger driving amplitudes, a projective measurement to an even-parity charge state is realised, showing a strong enhancement of the dispersive readout signal. At even larger driving amplitudes, two projective measurements are realised within the coherent evolution resulting in the disappearance of the interference pattern. Our results demonstrate a way to increase the readout signal of coherent quantum systems and replicate single-electron analogues of optical interferometry within a CMOS transistor. |
Wednesday, March 7, 2018 4:42PM - 4:54PM |
P28.00010: Sub 10 μeHz-1/2 Gate-based Sensing Imtiaz Ahmed, James Haigh, Sylvain Barraud, Jason Robinson, M. Fernando Gonzalez-Zalba Semiconductor-based quantum computing architectures require sensitive electrometers to readout the state of the qubits. This requires high-precision external electrometers. A compact alternative, in-situ gate based dispersive readout has been proposed to facilitate scalability. However, single-shot dispersive readout of an electron spin state, which is a crucial requirement for error correction protocols, has not been performed yet. In order to facilitate time-resolved gate-based reflectometry, improvements in the sensitivity of this technique need to be achieved. Large coupling of the quantum system to a high-Q resonator is hence desired. Here, we present results on gate-based sensing of a silicon corner state quantum dot with a large gate-coupling α = 0.89. The quantum device is connected via the gate to a lumped-element resonator with a high loaded Q factor ~ 400. We find a charge sensitivity of 7.7 μeHz-1/2, an improvement by a factor of ~ 5 with respect to the best value reported for this technique. Additionally, we perform a circuit analysis to determine the optimal resonator design. Overall, our results place the sensitivity of gate-based sensing at par with the best semiconductor-based radio frequency single-electron transistors. |
Wednesday, March 7, 2018 4:54PM - 5:06PM |
P28.00011: High Bandwidth Electron Spin Readout with the Radio Frequency Single Electron Transistor in the Strong Response Regime Daniel Keith, Matthew House, Thomas Watson, Bent Weber, Michelle Simmons, Matthew Donnelly Surface code architectures capable of fault tolerant error correction need high fidelity, and high bandwidth qubit state readout to minimise errors. High bandwidth readout enables faster qubit gate operations, greater statistics for experiments involving electron spin readout, and the measurement of faster electron transitions. Collectively these result in lower errors on both measured and idling qubits during readout operations. Previously, electron spin readout fidelities above 99% were achieved with a d.c. single electron transistor (SET) by limiting the bandwidth to 100 kHz. Here we present results of charge and spin readout using a radio frequency SET (rf-SET) which can achieve the strong response regime, in which the SET conductance contrast is large compared to its average conductance. At the rf circuit’s full bandwidth (9.5 MHz) and B=1.5 T, we demonstrate single-shot electron spin readout with a signal-to-noise ratio (SNR) of 7.2. For detection of the electron charge states the SET input power was increased to achieve an SNR of 12.7. Optimised single-shot electron spin readout with readout fidelities above 98% for 50 kHz tunnel rates was found to be limited by the base electron temperature (200 mK) and local heating of the SET by dissipation of the rf power. |
Wednesday, March 7, 2018 5:06PM - 5:18PM |
P28.00012: Noninvasive Quantum Measurement of Arbitrary Operator Order in a Mesoscopic Double-Dot Detector Setup Johannes Bülte, Adam Bednorz, Christoph Bruder, Wolfgang Belzig The development of solid-state quantum technologies requires the understanding of quantum measurements in interacting, non-isolated systems. Historically the interpretation of quantum measurement uses the projection postulate implying an instantaneous collapse of the wave function. In many real systems the interaction is much weaker and a collapse is avoided which is crucial to observe non-commuting observables simultaneously. |
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