Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session T36: Spin Qubit Measurement IIFocus Recordings Available
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Sponsoring Units: DQI Chair: Patrick Harvey-Collard, IBM Zurich Room: McCormick Place W-194A |
Thursday, March 17, 2022 11:30AM - 11:42AM |
T36.00001: Optimizing Charge Sensing Bias Conditions in the Presence of Noise Yanxue Hong, Joshua Pomeroy A heuristic, capacitance model including temperature and noise is used to evaluate quantum dot charge transitions detected by single-electron transistor (SET) charge sensing, finding that the optimal sensing condition occurs at surprisingly large charge sensor bias. We model the device with a capacitance solver, calculate the charge stability diagram, incorporate broadening due to temperature and noise, and evaluate the signal-to-noise ratio (SNR) for spin qubit measurements at different SET sensor bias conditions. The predicted sensor performance can be used to feedback on the design parameters and adjust coupling capacitance, dot size, etc. The optimal conditions are found at surprisingly large sensor bias, rather than the smallest bias that gives rise to the narrowest noise broadening. In general, this analytical method can be used to optimize the device design and to guide the device measurements. |
Thursday, March 17, 2022 11:42AM - 11:54AM |
T36.00002: Improved spin readout fidelity in the presence of noise Michael D Stewart, Michael J Gullans, Thomas McJunkin, Tommy O Boykin II, Kyungjean Min High-fidelity spin readout in semiconducting qubits is most commonly performed using the technique pioneered by Elzerman \emph{et. al} (2004). The higher energy spin state is identified during a readout pulse by the change in current of a nearby charge sensor caused by tunneling off and back onto the dot. However, the technique requires high signal-to-noise and low device drift to maintain acceptable fidelity. Here, we present an alternative analysis technique for the same readout scheme, which is simple to implement and which lessens the demands on obtaining a high signal-to-noise ratio. Rather than setting a threshold in the maximum of the readout trace for state identification, our simulations treat the charge sensor current like noise and effectively differentiate between f-2 noise (excited spin state) and f-1 or f0 noise (ground spin states). This is done by utilizing the B1 bias function [1] developed for noise identification in time and frequency standards. Initial simulations suggest that this readout method increases the amount of tolerable f-1 noise where the fidelity is above 50% by a factor of 2 in amplitude (4 in power) and the amount of tolerable f0 noise by at least a factor of 2 in amplitude. We also benchmark our results against the optimal readout fidelity obtained from Bayesian inference methods. |
Thursday, March 17, 2022 11:54AM - 12:06PM |
T36.00003: Dependence of an exchange gate on valley orbit couplings in silicon quantum dots Bilal Tariq, Xuedong Hu The mixing of conduction band valleys plays a critical role in determining electronic spectrum and dynamics in a silicon nanostructure. In this work we use Schrieffer-Wolf transformation to show that the exchange energy depends on the interdot valley phase difference as cos2(φ/2) in a symmetric two-electron silicon double quantum dot. We show that the necessary condition for exchange gate protocol to be valid in a Si double quantum dots is that the valley splitting in each of the dots is much larger than the thermal broadening of the reservoir used for initialization. The contributions of the higher orbital states also play a vital role in determining the value of the exchange energy in general. |
Thursday, March 17, 2022 12:06PM - 12:42PM |
T36.00004: Hole spin qubits in silicon fin field-effect transistors Invited Speaker: Andreas V Kuhlmann Quantum computing's greatest challenge is scaling up. Several decades ago, classical computers faced the same problem and a single solution emerged: very-large-scale integration using silicon. Today's silicon chips consist of billions of field-effect transistors (FinFETs) in which current flow along the fin-shaped channel is controlled by wrap-around gates. The semiconductor industry currently employs fins of sub-10 nm width, small enough for quantum applications: at low temperature, an electron or hole can be trapped under the gate and serve as a spin qubit. An attractive benefit of silicon's advantageous scaling properties is that quantum hardware and its classical control circuitry can be integrated in the same package. This, however, requires qubit operation at temperatures greater than 1 K where the cooling is sufficient to overcome the heat dissipation [Petit et al., Nature 580, 355 (2020); Yang et al., Nature 580, 350 (2020)]. |
Thursday, March 17, 2022 12:42PM - 12:54PM |
T36.00005: Coherent singlet-triplet dynamics in CMOS Sofia M Patomäki, David J Ibberson, Maud Vinet, Louis Hutin, Fernando Gonzalez-Zalba, John Morton Electric dipole spin resonance (EDSR) may be preferable over electron spin resonance, which requires large-footprint on-chip microwave lines carrying large currents that can cause heating. Then, the spin-driving electric fields can be generated locally with gate voltages, where industry-standard complementary metal-oxide-semiconductor (CMOS) processes can be applied to manufacture dense gate structures [1]. In silicon, intrinsic spin-orbit coupling (SOI) based EDSR has been demonstrated for hole spins [2,3]. For electron spin EDSR, SOI is typically introduced artificially with micromagnets [4], or by utilizing the valley-orbit interaction instead [5]. Here, we study magnetic field and power dependence of inter-dot charge transitions in a $n$-doped CMOS nanowire few-quantum-dot device with gate-based radiofrequency (RF) reflectometry. We observe coherent double-passage Landau-Zener-Stuckelberg oscillations in a $S$-$T^{-}$ system, when driven at RF powers above the linear response regime. We vary the Stuckelberg phase with external magnetic field and detuning. Based on RF drive frequency of approximately $610$ MHZ, we estimate $T_{2}^{*} > 1.7 $ns. We numerically evaluate the parametric capacitance [6], to model the effective state space, and to estimate the relevant energy parameters, such as the SOI strength. |
Thursday, March 17, 2022 12:54PM - 1:06PM |
T36.00006: Coupling a Ge/Si nanowire quantum dot to a high-impedance resonator Pierre Chevalier Kwon, Jann H Ungerer, Taras Patlatiuk, Joost Ridderbos, Deepankar Sarmah, Floris Braakman, Leon Camenzind, Artem Kononov, Erik P. A. M. Bakkers, Christian Schonenberger, Dominik M Zumbuhl Hole spins in Ge/Si core/shell nanowires show a strong and electrically tunable spin-orbit (SO) interaction, allowing strong coupling between spins and photons, e.g. of a superconducting resonator. In addition, the hyperfine interaction is expected to be weak, reducing hyperfine decoherence. Recently, a highly tunable hole spin qubit with SO switch was demonstrated [1]. However, the readout so far has relied on transport through the nanowire, so the qubit was not operated in the few-hole regime. |
Thursday, March 17, 2022 1:06PM - 1:18PM |
T36.00007: Spin triplet-singlet relaxation in silicon quantum dots sensed via high-fidelity dispersive charge sensing Giovanni A Oakes, Louis Hutin, David J Ibberson, Benoit Bertrand, Nadia Stelmashenko, Jason Robinson, Lisa Ibberson, Maud Vinet, Alpha A Lee, Frederico Martins, Charles G Smith, Fernando Gonzalez-Zalba Silicon quantum dot devices can be industrially fabricated, allowing to scale-up spin-based quantum computers using large-scale integration processes. To assess the viability of this approach, benchmarking the spin dynamic figures of merit becomes of primary importance. Here, we present a parametric characterisation of the spin triplet-singlet relaxation time in a linear array of three industry-fabricated silicon quantum dots contained in a fully-depleted silicon nanowire multi-gate transistor. We use one of the dots as a radio-frequency single-electron box (SEB) for single-shot readout of the spin state of a double quantum dot via Pauli-spin blockade. We probe the SEB dispersively via a high-impedance LC resonator to enhance sensitivity which allows us to achieve average readout fidelities above 99% in less than 1 ms. We study the magnetic field and temperature on the triplet-singlet relaxation time along the (3,1)-(4,0) transition and find a dependence compatible with relaxation mediated by a combination of direct phonon plus Raman relaxation. Finally, we find relaxation times up to 250 ms, on par with state-of-the-art results in academic devices. |
Thursday, March 17, 2022 1:18PM - 1:30PM |
T36.00008: Initialisation and measurement of semiconductor spin qubits in the high-temperature/low magnetic field limit Daniel Keith, Yousun Chung, Ludwik Kranz, Brandur Thorgrimsson, Samuel K Gorman, Michelle Y Simmons State preparation and measurement of single-electron spin qubits typically relies on spin-to-charge conversion where a spin dependent charge transition of the electron is detected by a coupled charge sensor [1, 2]. Typically, this process requires that the qubit energy be much larger than the temperature of the system [3]. Here, we demonstrate an initialisation and measurement technique that is resilient to charge noise and high-temperature qubit operation. Using a new measurement procedure, we show readout fidelities above 90% for qubit energies just 3 times larger than the thermal energy. The initialisation procedure allows for single-electron spin state preparation with a fidelity of 99% within 20ms. Finally, the readout technique opens up a new regime of high-temperature/low magnetic field single-spin physics. |
Thursday, March 17, 2022 1:30PM - 1:42PM |
T36.00009: Efficient and complete spin state readout of two electrons in a double quantum dot Martin Nurizzo, Baptiste Jadot, Pierre-André Mortemousque, Vivien Thiney, Emmanuel Chanrion, Matthieu C Dartiailh, David J Niegemann, Arne Ludwig, Andreas D Wieck, Christopher Bäuerle, Matias Urdampilleta, Tristan Meunier Spin-qubits based on gate defined semiconductor quantum dots are a promising platform for quantum computation and simulation. However the readout fidelity of the spin states is still too low to reach the quantum error correction threshold. The only readout method for spin qubits approaching the threshold consists in a spin to charge conversion using the Pauli spin blockade (PSB) principle. However reaching a high fidelity readout using this technique is a trade-off between the time needed to distinguish the two charge states and the lifetime of those states. We demonstrate the operation of a Singlet-Triplet (S-T) qubit by controlling the inter-dot tunnel coupling from a few Hz to tens of GHz. This level of control allowed us to perform a PSB projection followed by a freeze of the charge configuration preventing any T1 relaxation. Using this new measurement protocol the PSB projection becomes only limited by the charge configuration readout and we reach a fidelity as high as 97.7 % in 500 µs. Moreover the spin measurement becomes repeatable and non-destructive enabling the possibility to perform a complete readout of the state discriminating between S, T0, T+ and T-. Thanks to this complete readout we benchmark diverse operation of the qubit on a complete set of states. |
Thursday, March 17, 2022 1:42PM - 1:54PM |
T36.00010: Readout of singlet-triplet spin qubit in donor-based devices in silicon Edyta N Osika, Samuel K Gorman, Serajum Monir, Yu-ling Hsueh, Marcus Borscz, Helen Geng, Brandur Thorgrimsson, Michelle Y Simmons, Rajib Rahman Singlet-triplet qubits have been investigated in gate-defined quantum dot systems where micromagnets are used to generate large magnetic field gradients for high-fidelity electrically-controlled qubit operations. However, the large magnetic field gradients increase the triplet relaxation making readout difficult. Here, we theoretically examine shelving and latching singlet-triplet readout techniques for donor-based devices in silicon where the large phosphorus hyperfine interaction leads to large effective magnetic field gradients. Using numerical simulations, we analyse how devices can be engineered for maximum readout visibility and show that singlet-triplet qubits based on phosphorus donors are a promising route for future electrically controlled qubits in silicon without the need of micromagnet. |
Thursday, March 17, 2022 1:54PM - 2:06PM |
T36.00011: Dispersive charge sensing in Ge/Si core/shell nanowire quantum dots Taras Patlatiuk, Simon Svab, Miguel J Carballido, Rahel Kaiser, Leon Camenzind, Erik P. A. M. Bakkers, Floris Braakman, Dominik M Zumbuhl Germanium/silicon core/shell nanowires are a powerful platform to study and optimize the properties of the hole spin qubits. The p-type hole wavefunction does not suffer from the contact hyperfine interaction, promising long coherence times. Another advantageous property is the strong and electrically tunable direct Rashia spin-orbit interaction (dr-SOI) [1], which allows switching between ultrafast qubit manipulation with Rabi frequency above 400 MHz [2], and an idling regime with weak SOI and long coherence time. Additionally, strong SOI enables the electrical tunability of the Lande g-factor useful e.g. for the implementation of a phase-gate but also opens a decoherence channel by coupling the spin to the charge noise. |
Thursday, March 17, 2022 2:06PM - 2:18PM |
T36.00012: Coulomb Blockade in a Fully Integrated Commercial CMOS Technology Quantum Dot Array with Charge Readout Panagiotis Giounanlis Coulomb blockade is usually used to demonstrate the quantization of the |
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