Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session E52: Semiconductor Qubits: Quantum Dot Readout and SensingFocus
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Sponsoring Units: GQI Chair: Ferdinand Kuemmeth, University of Copenhagen Room: 399 |
Tuesday, March 14, 2017 8:00AM - 8:36AM |
E52.00001: Threshold Dynamics of a Semiconductor Single Atom Maser Invited Speaker: Yinyu Liu Photon emission from single emitters provides fundamental insight into the detailed interaction between light and matter. Here we demonstrate a semiconductor single atom maser (SeSAM) that consists of a single InAs double quantum dot (DQD) that is coupled to a high quality factor microwave cavity. A finite bias results in population inversion in the DQD, enabling sizable cavity gain and stimulated emission. We develop a pulsed-gate approach that allows the SeSAM to be tuned across the masing threshold. The cavity output power as a function of DQD current is in good agreement with single atom maser theory once a small correction for lead emission is included. Photon statistics measurements show that the second-order correlation function of intra-cavity photon number, $n_{\mathrm{c}}$, crosses over from $\langle n_{\mathrm{c}}^{\mathrm{2}}\rangle $/$\langle n_{\mathrm{c}}\rangle^{\mathrm{2}}=$ 2.1 below threshold to $\langle n_{\mathrm{c}}^{\mathrm{2}}\rangle $/$\langle n_{\mathrm{c}}\rangle^{\mathrm{2}}=$ 1.2 above threshold. Large fluctuations are observed at threshold. [Preview Abstract] |
Tuesday, March 14, 2017 8:36AM - 8:48AM |
E52.00002: Mixing-Chamber Preamplifier for Spin Qubit Readout Matthew Curry, Andrew Mounce, Troy England, Ronald Manginell, Joel Wendt, Tammy Pluym, Stephen Carr, Malcolm Carroll Spin qubit states are often read out with a nearby charge sensor. To improve signal-to-noise ratio (SNR) and bandwidth, we amplify a charge sensor with a low-current-bias, silicon-germanium heterojunction-bipolar-transistor (HBT) [Curry et al., APL 106, 203505 (2015)]. The HBT is located at the mixing chamber of a dilution refrigerator, which minimizes parasitic capacitance and amplifies signal before fridge noise is introduced. Using the HBT-charge-sensor circuit, we tune a few-electron quantum dot (QD) into resonance with a donor-like object and observe singlet-triplet (ST) behavior. ST separation in this MOS donor-implanted-QD molecular system is measured using magnetospectroscopy to be approximately 100 $\mu$eV. The low current bias of the HBT minimizes both heating of the charge-sensed QD as well as maintains an overall low power at the mixing chamber. HBT bias impact on QD electron temperature is examined and we find that the HBT preamplifier can operate at around 100 nW with a current gain of around 500 without influencing the electron temperature, which is around 150 mK. We will also examine single-shot readout of a charge state using the HBT preamplifier. [Preview Abstract] |
Tuesday, March 14, 2017 8:48AM - 9:00AM |
E52.00003: Comparing SiGe HBT Amplifier Circuits for Fast Single-shot Spin Readout Troy England, Matthew Curry, Stephen Carr, Andrew Mounce, Ryan Jock, Peter Sharma, Chloe Bureau-Oxton, Martin Rudolph, Terry Hardin, 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. 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 compare two amplifiers based on single-transistor circuits implemented with silicon germanium heterojunction bipolar transistors. Both amplifiers provide gain at low power levels, but the dynamics of each circuit vary significantly. We will explore the gain mechanisms, linearity, and noise of each circuit and explain the situations in which each amplifier is best used. 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] |
Tuesday, March 14, 2017 9:00AM - 9:12AM |
E52.00004: High-Sensitivity Charge Detection with a Single-Lead Quantum Dot for Scalable Quantum Computation Matthew House, Ian Bartlett, Prasanna Pakkiam, Matthias Koch, Eldad Peretz, Joost van der Heijden, Takashi Kobayashi, Sven Rogge, Michelle Simmons We report the development of a high sensitivity semiconductor charge sensor based on a quantum dot coupled to a single lead, designed to minimize the geometric requirements of a charge sensor for scalable quantum computing architectures. The quantum dot is fabricated in Si:P using atomic precision lithography and its charge transitions are measured with rf reflectometry. A second quantum dot with two leads placed 42\,nm away serves as both a charge for the sensor to measure and as a conventional rf single electron transistor (rf-SET) with which to make a comparison of the charge detection sensitivity. We demonstrate sensitivity equivalent to an integration time of 550\,ns to detect a single charge with a signal-to-noise ratio of 1, compared with an integration time of 55\,ns for the rf-SET. This level of sensitivity is suitable for fast ($<15\,\mu$s) single-spin readout in quantum information applications, with a significantly reduced geometric footprint compared to the rf-SET. [Phys. Rev. Applied 6, 044016 (2016)] [Preview Abstract] |
Tuesday, March 14, 2017 9:12AM - 9:24AM |
E52.00005: Single-shot readout of accumulation mode Si/SiGe spin qubits using RF reflectometry Christian Volk, Frederico Martins, Filip Malinowski, Charles M. Marcus, Ferdinand Kuemmeth Spin qubits based on gate-defined quantum dots are promising systems for realizing quantum computation. Due to their low concentration of nuclear-spin-carrying isotopes, Si/SiGe heterostructures are of particular interest. While high fidelities have been reported for single-qubit and two-qubit gate operations, qubit initialization and measurement times are relatively slow. In order to develop fast read-out techniques compatible with the operation of spin qubits, we characterize double and triple quantum dots confined in undoped Si/Si$_{0.7}$Ge$_{0.3}$ heterostructures using accumulation and depletion gates and a nearby RF charge sensor dot. We implement a RF reflectometry technique that allows single-shot charge read-out at integration times on the order of a few $\mu$s. We show our recent advancement towards implementing spin qubits in these structures, including spin-selective single-shot read-out. [Preview Abstract] |
Tuesday, March 14, 2017 9:24AM - 9:36AM |
E52.00006: Response of a SET to large rf interference signals Rupert Lewis, C. Thomas Harris, Eric Shaner Single electron transistors (SETs) fabricated from aluminum thin films and Al/AlOx Josephson tunnel junctions can be added to other structures as charge sensors with large intrinsic bandwidth---for example, the charge sensing corral of an electrons on helium quantum chip. We characterized a SET at temperature T$=$40 mk for its ability to tolerate extraneous radio frequency (rf) interference in such applications at frequencies from 10 kHz to 50 MHz. Our SET, with charging energy, Ec $\approx $1 K, normal resistance R$_{n} \quad \approx $ 600 k$\Omega $, and peak measured charge sensitivity of S$_{p} \quad =$ 5 $\times$ 10$^{-5\, }$electrons/$\surd $Hz maintained usable sensitivity (S \textless 1 $\times$ 10$^{-3\, }$electrons/$\surd $Hz) when subjected to rf signals of strength greater than $+$/- 9 electrons. This suggests for frequencies well below f$_{c}$ $\approx $ 1/2$\pi $R$_{n}$C$_{j}$ where C$_{j}$ is the junction capacitance, that SETs respond nearly instantaneously even to large rf signals. Exploiting this knowledge, we were able to cancel a known rf signal at 1 MHz nearly recovering the charge sensitivity in the absence of rf signals---a result we expect will hold to higher frequencies. Work 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 by Los Alamos National Laboratory (Contract DE-AC52-06NA25396) and Sandia National Laboratories (Contract DE-AC04-94AL85000). Sandia National Laboratories is a multi-mission 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 14, 2017 9:36AM - 9:48AM |
E52.00007: Towards ultra-high single-shot readout fidelity of an electron spin qubit through an enhanced latching mechanism Patrick Harvey-Collard, Benjamin D’Anjou, Jason Dominguez, Gregory A. Ten Eyck, Joel R. Wendt, Tammy Pluym, Michael P. Lilly, William A. Coish, Michel Pioro-Ladrière, Malcolm S. Carroll The readout of semiconductor spin qubits relies on a spin-to-charge conversion that maps spin states to a transient charge state detected by a charge sensor. Readout fidelities currently lag behind qubit control fidelities and have become a significant bottleneck. In this work, we study an enhanced latching readout and directly compare the mechanisms and benefits with the conventional spin blockade readout. Using a silicon quantum dot coupled to a single donor atom, we demonstrate that the single shot signal lifetime and amplitude can be enhanced by at least factors of 10 and 5 respectively, potentially leading to $> 99.9\, \%$ fidelity. Finally, the enhanced latching readout functions with double quantum dot singlet-triplet qubits and also works when the charge sensor position is such that the conventional (2,0)-(1,1) charge signal would vanish. 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 wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DOE under contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, March 14, 2017 9:48AM - 10:00AM |
E52.00008: Role of metastable charge states in a quantum-dot spin-qubit readout Jeffrey Mason, Sergei Studenikin, Alicia Kam, Zbig Wasilewski, Andrew Sachrajda, Jan Kycia Readout of a singlet-triplet qubit requires a spin-to-charge conversion mechanism, typically employing the spin blockade phenomenon, by which each spin state is mapped to a unique charge state followed by a charge state measurement using an electric field sensor such as a quantum point contact.\footnote{Petta et al., Science 327, 669 (2010).} We investigate alternative mechanisms for spin-to-charge conversion involving metastable excited charge states made possible by an asymmetry in the tunneling rates to the leads.\footnote{Studenikin et al., Appl. Phys. Lett. 101, 233101 (2012).} This technique is used to observe Landau-Zener-St\"uckelberg oscillations of the S-T$_{+}$ qubit within the (1,0) region of the charge stability diagram.\footnote{Mason et al., Phys. Rev. B 92, 125434 (2015).} The oscillations are $\pi$ phase shifted relative to those detected using the standard technique and display a non-sinusoidal waveform due to the increased relaxation time from the metastable state.\footnote{Granger et al., Phys. Rev. B 91, 115309 (2015).} [Preview Abstract] |
Tuesday, March 14, 2017 10:00AM - 10:12AM |
E52.00009: Keldysh meets Lindblad: Correlated Gain and Loss in Higher Order Perturbation Theory Tom Stace, Clemens Mueller Motivated by correlated decay processes driving gain, loss and lasing in driven artificial quantum systems, we develop a theoretical technique using Keldysh diagrammatic perturbation theory to derive a Lindblad master equation that goes beyond the usual second order perturbation theory. We demonstrate the method on the driven dissipative Rabi model, including terms up to fourth order in the interaction between the qubit and both the resonator and environment. This results in a large class of Lindblad dissipators and associated rates which go beyond the terms that have previously been proposed to describe similar systems. All of the additional terms contribute to the system behaviour at the same order of perturbation theory. We then apply these results to analyse the phonon-assisted steady-state gain of a microwave field driving a double quantum-dot in a resonator. We show that resonator gain and loss are substantially affected by dephasing- assisted dissipative processes in the quantum-dot system. These additional processes, which go beyond recently proposed polaronic theories, are in good quantitative agreement with experimental observations. [Preview Abstract] |
Tuesday, March 14, 2017 10:12AM - 10:24AM |
E52.00010: Gate-Sensing the Potential Landscape of a GaAs Two-Dimensional Electron Gas Xanthe Croot, Alice Mahoney, Sebastian Pauka, James Colless, David Reilly, John Watson, Saeed Fallahi, Geoff Gardner, Michael Manfra, Hong Lu, Arthur Gossard In situ dispersive gate sensors hold potential as a means of enabling the scalable readout of quantum dot arrays. Sensitive to quantum capacitance, dispersive sensors have been used to detect inter- and intra-dot transitions in GaAs double quantum dots [1], and can distinguish the spin states of singlet triplet qubits [2]. In addition, the gate-sensing technique is likely of value in probing the physics of Majorana zero modes in nanowire devices [3]. Beyond the readout signatures associated with charge and spin configurations of qubits, gate-sensing is sensitive to trapped charge in the potential landscape. Here, we report gate-sensing signals arising from tunnelling of electrons between puddles of trapped charge in a GaAs 2DEG. We examine these signals in a family of different devices with varying mobilities, and as a function of temperature and bias. Implications for qubit readout using the gate-sensing technique are discussed. [1] Colless, J. et al. PRL 110, 046805 (2013), [2] House, M.G. et al, Nat. Comms. 6, 8848 (2015), [3] Karzig, T. et al, arXiv:1610.05289v2 (2016) [Preview Abstract] |
Tuesday, March 14, 2017 10:24AM - 10:36AM |
E52.00011: Quantum memristor based on coupled quantum dots Gregory W. Holloway, Ying Li, Simon C. Benjamin, G. Andrew D. Briggs, Jonathan Baugh, Jan A. Mol The memristor is a proposed fourth fundamental circuit element whose electrical resistance is determined by the current that has previously passed through it. Realization of devices that exhibit these characteristics could allow for the implementation of low power non-volatile memory and neuromorphic computing. Here, we propose and demonstrate a novel memristive system using two capacitively coupled Si metal-oxide-semiconductor quantum dots in a parallel configuration. The current flowing through one dot is controlled by the charge state of the other dot via the capacitive coupling. By connecting the applied bias to both dots (making this a two-terminal device), the charge state of the control dot depends on the bias. This allows a hysteretic evolution to take place with an applied AC bias, under certain conditions. The properties of the current hysteresis are modulated through the application of DC voltages to the electrostatic gates that define the dots, providing a means to tune the behavior in-situ. Unlike classical memristive systems, this quantum memristive system shows stochastic behavior due to quantum jumps of the charge state of the control dot. [Preview Abstract] |
Tuesday, March 14, 2017 10:36AM - 10:48AM |
E52.00012: Time Division Multiplexing of Semiconductor Qubits Marie Claire Jarratt, John Hornibrook, Xanthe Croot, John Watson, Geoff Gardner, Saeed Fallahi, Michael Manfra, David Reilly Readout chains, comprising resonators, amplifiers, and demodulators, are likely to be precious resources in quantum computing architectures. The potential to share readout resources is contingent on realising efficient means of time-division multiplexing (TDM) schemes that are compatible with quantum computing. Here, we demonstrate TDM using a GaAs quantum dot device with multiple charge sensors. Our device incorporates chip-level switches that do not load the impedance matching network. When used in conjunction with frequency multiplexing, each frequency tone addresses multiple time-multiplexed qubits, vastly increasing the capacity of a single readout line. [Preview Abstract] |
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