Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session F41: Superconducting Qubit Readout and SensingFocus Recordings Available
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Sponsoring Units: DQI DCMP Chair: Florent Lecocq, National Institute of Standards and Technology, Boulder Room: McCormick Place W-196C |
Tuesday, March 15, 2022 8:00AM - 8:12AM |
F41.00001: Quantum sensors based on resonant transduction of pair-breaking photons to quasiparticles David C Harrison, Chuan-Hong Liu, Shravan Patel, Owen Rafferty, Francisco Schlenker, Robert McDermott Superconducting qubits are resonant absorbers of pair-breaking radiation, as the qubit structure is the aperture dual of a wire loop antenna. Typical Josephson junction parameters result in a junction impedance that is reasonably well matched to the fundamental antenna mode. Here we exploit this physics to realize a new class of quantum sensors for mm-wave radiation based on the resonant transduction of pair-breaking photons to quasiparticles. We use broadband thermal radiation and coherent mm-wave radiation derived from a Josephson photon source to characterize these detectors over the band from 100 GHz to 1 THz. We present experimental measurements of upward and downward transition rates and charge-parity rates as a function of radiator temperature or coherent drive frequency. This scheme could form the basis for next-generation detectors of dark-matter axions. |
Tuesday, March 15, 2022 8:12AM - 8:24AM |
F41.00002: Reinforcement Learning assisted Pulse Shaping for Superconducting Qubit Readout Benjamin Lienhard, Antti Vepsalainen, Cole Hoffer, Luke C Govia, Vilhelm L Andersen Woltz, David K Kim, Alexander Melville, Bethany Huffman, Jonilyn L Yoder, Mollie E Schwartz, Terry P Orlando, William D Oliver The readout performance of resource-efficient quantum processors comprising multiple superconducting qubits is often not on par with that of qubit-gate operations. Nonidealities such as crosstalk limit the readout performance. Some of these nonidealities can be mitigated or compensated by qubit-state discrimination or qubit-readout pulse shaping. Quantum error correction protocols depend on fast and efficient readout. Quick resonator ring-up and ring-down in a dispersive readout scheme ensure fast measurements and limited qubit dephasing in future operations. This talk focuses on readout pulse shaping for multiple superconducting qubits using deep reinforcement learning. Relative to conventional readout methods, our results reveal that deep reinforcement learning can significantly reduce measurement times. |
Tuesday, March 15, 2022 8:24AM - 8:36AM |
F41.00003: Tomography of a continuously monitored qubit Tathagata Karmakar, John Steinmetz, Shengshi Pang, Andrew N Jordan Time continuous measurements have proven themselves to be useful in real-time tracking and feedback control of quantum systems. In our work, we theoretically investigate the state tomography of a superconducting qubit coupled to a resonator in the strong dispersive regime. When the qubit is continuously monitored, the evolution of the qubit-resonator system is characterized by a stochastic master equation. Our numerical exploration suggests the requirement of an additional spectroscopy drive for a successful tomography of the full qubit state. Finally, complemented by the Bayesian mean estimation procedure, we reconstruct the state of the qubit conditioned on the measurement outcomes. Our analysis provides insights into the state estimation of a continuously monitored system and bears direct relevance for circuit QED experiments. |
Tuesday, March 15, 2022 8:36AM - 9:12AM |
F41.00004: Ultrafast superconducting qubit readout and gates with a quarton coupler Invited Speaker: Yufeng Ye Faster entangling operations in the form of readout and two-qubit gates for superconducting qubits are essential for achieving the next milestones such as scalable quantum error correction. Entangling gate speed is directly proportional to the interaction energy, thus for CZ gates and operations involving photons including readout and bosonic code control, gate times are limited by the typically perturbatively weak nonlinear cross-Kerr or ZZ coupling energy. Here, we propose and present experimental progress towards ultrafast (order 1 nanosecond) entangling gates by using a new tunable quarton coupler capable of ultrastrong (order 1 GHz) cross-Kerr coupling. The quarton coupler is compatible with existing transmon architectures and can facilitate resonator-resonator, resonator-qubit, or qubit-qubit cross-Kerr coupling for a wide range of applications including ultrafast transmon qubit readout, CZ gates, bosonic code control, and single microwave photon detection. |
Tuesday, March 15, 2022 9:12AM - 9:24AM |
F41.00005: Two-Port Cryogenic Calibration for Microwave Measurements John Pitten, Suren Singh, Haozhi Wang, SHENG-XIANG LIN, David Pappas, Corey Rae H McRae Accurate superconducting resonator measurements and materials loss characterization are vitally important for the improvement of single-qubit performance and the development of quantum processors for superconducting quantum computing. Obtaining an accurate calibration is a challenge that prevents accurate and repeatable characterization of these superconducting microwave devices at cryogenic temperatures. A multiline through-reflect-line (TRL) calibration implemented on a commercial Vector Network Analyzer (VNA) can provide a solution to this problem, and is an avenue for further improvements in cryogenic microwave measurements. By accounting for impedance mismatches along the measurement chain before the calibration plane, we can measure those of the various connections at the device level --- including at the sample box, SMA connectors, and wirebonds. Furthermore, achieving a reliable impedance-correction based calibration is an important first step to implementing a source power calibration, which will allow an accurate determination of the power delivered to the device itself. |
Tuesday, March 15, 2022 9:24AM - 9:36AM |
F41.00006: Characterization of a qubit–amplifier artificial molecule in 3D circuit QED architecture Zhixin Wang, Wei Dai, Jayameenakshi Venkatraman, Xu Xiao, Luigi Frunzio, Michel H Devoret In circuit quantum electrodynamics (cQED) systems, high-efficiency qubit readout has been realized by employing microwave quantum-limited parametric amplifiers, which are able to suppress the total added noise of the measurement circuit close to the level of vacuum fluctuations. To further improve measurement efficiency, one is obliged to alleviate the impact of parasitic dissipation between the readout resonator and the external parametric amplifier. To this effect, we introduce a superconducting artificial molecule that integrates a transmon qubit and a Josephson amplifier on the same chip, the whole being enclosed into a 3D superconducting readout cavity. In this artificial molecule, the electric dipoles of the qubit and the on-chip amplifier are perpendicular to each other such that the former is linearly decoupled from the electromagnetic field in the readout cavity. The combination of a "dark" qubit, a flux-loop-free layout, and a two-stage readout scheme is intended to simultaneously achieve long qubit coherence times, high readout efficiency, and low measurement back-action. We will present the experimental characterization of this artificial molecule, demonstrate the qubit readout mechanism, and discuss further improvements. |
Tuesday, March 15, 2022 9:36AM - 9:48AM |
F41.00007: Implementation of a Broadband Superconducting Qubit-Compatible Microwave Isolator Mahdi Naghiloo, Kaidong Peng, Yufeng Ye, Jennifer Wang, Gregory D Cunningham, Kevin P O'Brien We present a practical design of a proposed scheme for broadband microwave isolation that uses adiabatic parametric mode conversion in a pair of coupled nonlinear transmission lines [1]. This design utilizes a flip-chip configuration in the standard aluminum fabrication process allowing for negligible insertion loss and direct integration with the superconducting quantum circuits. Combining linear and nonlinear adiabatic mode conversion in the design, we expect to get more than 3 GHz bandwidth of isolation centered at 6 GHz. We discuss various aspects of the design such as implementing the spatial phase-mismatch and nonlinear coupling variations and mitigating the unwanted couplings. We also present preliminary experimental results. |
Tuesday, March 15, 2022 9:48AM - 10:00AM |
F41.00008: Floquet theory for dispersive readout in circuit QED Alexandru Petrescu, Joachim Cohen, Ross Shillito, Alexandre Blais In circuit QED, qubit relaxation rates can depend on the strength of the measurement tone, which hinders efforts to make readout fast and high-fidelity enough for large-scale quantum error correction. Within a Floquet theory, we study the typical circuit QED setup consisting of a superconducting qubit (transmon or fluxonium) coupled to a readout resonator. We find that qubit relaxation is determined by the interplay of drive-dressed spectra and transition rates. For a number of realistic environmental couplings, we compute drive-strength-dependent qubit relaxation rates that illustrate how resonant multi-photon processes alter the quantum non-demolition character of the measurement. |
Tuesday, March 15, 2022 10:00AM - 10:12AM |
F41.00009: Improvement strategies for multiplexed readout of superconducting qubits with fidelity beyond 99% Liangyu Chen, Hangxi Li, Yong Lu, Shahnawaz Ahmed, Janka Biznarova, Anton Frisk Kockum, Christian Krizan, Sandoko Kosen, Amr Osman, Anita Fadavi Roudsari, Marcus Rommel, Christopher Warren, Per Delsing, Jonas Bylander, Giovanna Tancredi We present our recent results on improving single-shot readout fidelity of superconducting qubits utilizing various techniques. We take advantage of higher energy levels of the qubits to circumvent the coherence limit, apply additional readout tones to extract more information and employ machine learning algorithms to improve classification success probabilities. With these mitigation strategies, we boost our readout fidelity for a multi-qubit system beyond 99%. |
Tuesday, March 15, 2022 10:12AM - 10:24AM |
F41.00010: Saturable Purcell filter for circuit QED Ivan Iakoupov, Kazuki Koshino We consider a way to decrease the number of the transmission lines in the superconducting quantum computers by combining the separate lines used for control and measurement into one. While a combined control and measurement line can be used in the setup where an artificial atom is dispersively coupled to a resonator that in turn is attached to the line, this usually limits the coherence of the artificial atom due to the Purcell decay originating from a small effective coupling of the artificial atom to the line. Adding an unsaturable Purcell filter that suppresses frequencies close to the artificial atom transition and thereby the Purcell decay, makes the control of the artificial atom through the same line impossible, necessitating another line for control. We propose a saturable Purcell filter that consists of an artificial atom attached to the transmission line at a particular position. Such a Purcell filter is saturated and hence effectively turned off by the strong control pulses, and therefore a separate control transmission line is not needed. Our approach could be used together with the frequency multiplexing to further decrease the number of the required lines. |
Tuesday, March 15, 2022 10:24AM - 10:36AM |
F41.00011: Capacitive Coupling of Coherent Quantum Phase Slip Qubits to a Resonator Teresa Hoenigl-Decrinis A Coherent quantum phase slip (CQPS) is the tunneling of quantised fluxes across a nanowire in a superconducting loop (accompanied by a phase jump 2π) as a result of the quantum fluctuation of the order parameter. These quantum phase slips [1] are dual to Cooper-pair tunnelling in Josephson junctions (JJ), and were thus proposed as the non-linear element, dual to the JJ, which allows to design a current standard. |
Tuesday, March 15, 2022 10:36AM - 10:48AM |
F41.00012: Optimizing multi-qubit readout for mid-circuit measurements and low latency feedback based applications Yonatan Cohen, Niv Drucker, Nir Halay, Uri Abend Multi-qubit readout fidelity is extremely important both for NISQ era quantum machines as well as towards developing fault tolerant error corrected quantum computers. Optimizing multi-qubit readout fidelity in quantum processors based on superconducting qubits is a challenging task as typically many readout resonators must be probed simultaneously via frequency multiplexing and the crosstalk effects should be considered. Moreover, in some applications, it is desirable to apply low latency feedback-based operations on qubits, which depend on the results of mid-circuit, multi-qubit readout, e.g. in quantum error correction. In such applications, reducing the readout duration and the state estimation classical processing are critical. Here we propose a novel approach for multi-qubit readout where a multi-tone signal is processed in real-time to achieve low latency multi-qubit readout, while optimizing for cross talk considerations. Moreover, we demonstrate how QM's flexible control platform, the Quantum Orchestration Platform, allows to explore such multi-tone signal processing from easy-to-use SW interface. |
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