Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Q73: Novel Devices and Methods for Error MitigationFocus
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Sponsoring Units: DQI Chair: Petar Jurcevic, IBM Quantum Room: Room 405 |
Wednesday, March 8, 2023 3:00PM - 3:12PM Author not Attending |
Q73.00001: Generalized randomized compiling for non-Clifford gates Hammam A Qassim Randomized compiling is a circuit compilation technique with noise-tailoring and suppression effects. The standard implementation of this technique requires all two-qubit gates in the circuit to be Clifford gates. In this paper we extend randomized compiling to circuits containing non-Clifford two-qubit gates, two-qutrit gates , as well as certain k-qubit gates for k > 2. This is achieved by twirling using random gates from suitable subgroups of the unitary group, generalizing the Pauli-twirling method in standard randomized compiling. We give a theoretical characterization of the noise-tailoring effect of twirling using these groups, and provide numerical and experimental evidence of the noise reduction effect due to this technique in various example circuits. |
Wednesday, March 8, 2023 3:12PM - 3:24PM |
Q73.00002: Calibration-free quantum error mitigation with classical shadows Andrew Zhao, Akimasa Miyake Estimating expectation values is a key routine for near-term quantum simulation algorithms. However, the accumulation of noise in current devices severely affects the potential of such algorithms. The method of classical shadows, a randomized protocol for efficiently estimating a large collection of observables, was recently shown to possess inherent noise robustness. This robustness is achieved by performing a series of calibrating experiments, before executing the desired computational algorithm. This calibration step adds overhead to the overall runtime, and its correctness relies on simplifying assumptions about the device noise. In our work, we show that one may bypass these calibrating experiments if the desired (noiseless) quantum state obeys certain symmetries. This technique is enabled whenever the symmetries coincide with the irreducible representations of the classical shadows protocol. Our approach therefore allows for the mitigation of more realistic errors, without requiring a separate calibration step. A prime candidate for this technique is the simulation of electronic systems, wherein the particle-number symmetry can be exploited when performing classical shadows with fermionic measurements. We demonstrate the effectiveness of this idea with numerical simulations of noisy quantum circuits. |
Wednesday, March 8, 2023 3:24PM - 3:36PM |
Q73.00003: Predicting dynamics and measuring crosstalk with simultaneous Rabi experiments Adam Winick, Jan Balewski, Gang Huang, Yilun Xu Crosstalk is a substantial obstacle impeding the realization of practical many-qubit quantum computers. A noteworthy instance of crosstalk affecting superconducting qubits is drive crosstalk, where microwave drive fields intended for one subsystem also interact with other subsystems, inducing correlated local errors. During this talk, we introduce a novel simultaneous Rabi experiment for characterizing drive crosstalk that is robust to SPAM errors. We fit the parameters for a Hamiltonian describing a two-transmon system with crosstalk and find excellent agreement between theory and experiment. By repeating the characterization protocol for all pairs of qubits in a system, we construct a model for the entire chip and accurately predict crosstalk dynamics for more than two concurrently driven qubits. These results show that drive crosstalk is a correctable problem for NISQ devices. Combining this approach with prior theoretical work that we published paves the way to mitigate the effects of crosstalk via digital circuit precompilation. |
Wednesday, March 8, 2023 3:36PM - 3:48PM |
Q73.00004: Quantum error mitigation for GKP qubits Alessandro Ciani In recent years, a plethora of quantum error mitigation techniques have been proposed to undo errors in currently available quantum devices. |
Wednesday, March 8, 2023 3:48PM - 4:00PM |
Q73.00005: Beyond spectator qubits: Noise mitigation with continuous measurements, photonic modes, and Heisenberg-limited performance Andrew Lingenfelter, Aashish A Clerk There has recently been significant theoretical (see e.g., [1-3]) and experimental (see e.g., [4]) interest in the use of spectator qubits to detect spatially correlated noise fluctuations and use the acquired information to protect a distinct set of "data" qubits. Here we generalize the concept to that of a "spectator mode": a photonic mode which continuously measures the spatially correlated noise fluctuations and applies a continuous correction drive to a frequency-tunable data qubit. We show that the spectator mode approach has a key advantage over spectator qubits: measurements can be made using many photons, allowing a parametric suppression of measurement imprecision and dramatically enhanced performance. We find that long-time qubit dephasing can in principle be arbitrarily suppressed, even for Markovian dephasing noise. Furthermore, realistic spectator mode architectures can exhibit Heisenberg-limited performance in the number of photons used in the measurement. We also discuss similar performance of analogous spectator mode strategies when applied to mechanical force sensors. |
Wednesday, March 8, 2023 4:00PM - 4:36PM |
Q73.00006: Improving the performance of noisy quantum computers supporting qubit and qutrit operations Invited Speaker: Samuele Ferracin As fault-tolerance is not expected to become available in the immediate future, designing alternative methods to suppress noise in today's quantum computers is of timely importance. In this talk, we describe Noiseless Output Extrapolation (NOX), a recently developed error mitigation protocol that can significantly enhance the performance of noisy, intermediate-scale quantum devices. By leveraging efficient protocols for noise characterization, NOX can mitigate a wide range of noise processes that afflict the existing devices, such as crosstalk and gate-dependent noise. We demonstrate the effectiveness of NOX by testing it on various platforms of different sizes, the largest of which contains sixteen qubits. We also test NOX on a superconducting processor that supports operations on qutrits, performing one of the first error-mitigation experiments on three-level quantum systems. Our tests reveal the significant benefits of performing error mitigation on the available quantum computers, as well the challenges in performing it. |
Wednesday, March 8, 2023 4:36PM - 4:48PM |
Q73.00007: Dynamical Decoupling of Crosstalk on Superconducting Qubit Devices James P Sud, Shon Grabbe, Bram Evert, Matthew Reagor, Hong-Ye Hu, Zoe Gonzalez Izquierdo, Eleanor G Rieffel, Zhihui Wang Current NISQ devices are prone to errors. In order to be used for practical applications or achieve fault-tolerant thresholds, strategies to suppress error rates will be needed to maximize the potential of noisy devices. Dynamical decoupling (DD) is one such strategy for suppressing — or at least alleviating — the effects of decoherence, in which sequences of pulses are applied to qubits to decouple their interaction with the environment. Through experimental runs performed on several Rigetti quantum computing units (QPUs), we first demonstrate that DD is capable of improving coherence times for isolated qubits, as well as suppressing errors caused by the ZZ coupling between pairs of qubits. Extending this framework to cycles containing 2-qubit gates, we show that DD can be inserted to decouple qubits from crosstalk occurring during neighboring 2-qubit gates, and demonstrate the efficacy of this procedure on quantum approximate optimization algorithm (QAOA) circuits. We also explore the usage of tailored DD sequences for the suppression of characterized error channels. We are grateful for support from the NASA Ames Research Center and from the DARPA ONISQ program under interagency agreement IAA 8839, Annex 114. HYH is supported by the USRA Feynman Quantum Academy funded by the NAMS R&D Student Program and a UC Hellman Fellowship. JS, ZGI and ZW are supported by USRA NASA Academic Mission Service (NNA16BD14C). |
Wednesday, March 8, 2023 4:48PM - 5:00PM |
Q73.00008: Crosstalk characterization in high-coherence multi-qudit systems Xinyuan You, Doga M Kurkcuoglu, Taeyoon Kim, Shaojiang Zhu, Tanay Roy, David Zanten, Silvia Zorzetti Recent advancements in building very high-Q superconducting cavities make them excellent choices for encoding quantum information in qudits due to their long lifetimes and the access to large Hilbert spaces. Typically, a nonlinear element like a transmon is used to manipulate the state of the harmonic oscillator, which in turn inherits a small nonlinearity. When scaling up to a multi-qudit system with multiple cavity modes, this nonlinearity results in spurious inter-mode coupling which lowers the gate fidelity. In this presentation, we characterize the effects of such crosstalk by analyzing several popular control protocols. With realistic experimental parameters, we perform numerical estimation of the infidelities, which can provide insight for the development of multi-mode quantum processors. |
Wednesday, March 8, 2023 5:00PM - 5:12PM |
Q73.00009: Direct observation and manipulation of non-equilibrium quasiparticle tunneling: Part 1/2 Heekun Nho, Pavel Kurilovich, Thomas Connolly, Spencer Diamond, Valla Fatemi, Michel H Devoret Tunneling of excess non-equilibrium quasiparticles is a source of decoherence in superconducting qubits. In transmons, identifying quasiparticle tunneling events is difficult since their experimental signature -- charge-parity switching -- can be mimicked by high-energy photons that break Cooper pairs. Here, we strongly suppress photon-induced pair breaking with radiation filtering and shielding, which allows us to directly probe the tunneling of the remaining excess quasiparticles. By measuring the temperature dependence of the quasiparticle tunneling rates in the ground and excited states of the transmon, we find evidence for the effective thermalization of the quasiparticles. A resulting asymmetry between the quasiparticle tunneling rates in the two qubit states allows us to transfer quasiparticles on-demand, thus actively manipulating the charge-parity of the transmon. |
Wednesday, March 8, 2023 5:12PM - 5:24PM |
Q73.00010: Direct observation and manipulation of non-equilibrium quasiparticle tunneling: Part 2/2 Thomas Connolly, Pavel Kurilovich, Heekun Nho, Spencer Diamond, Valla Fatemi, Michel H Devoret Tunneling of excess non-equilibrium quasiparticles is a source of decoherence in superconducting qubits. In transmons, identifying quasiparticle tunneling events is difficult since their experimental signature -- charge-parity switching -- can be mimicked by high-energy photons that break Cooper pairs. Here, we strongly suppress photon-induced pair breaking with radiation filtering and shielding, which allows us to directly probe the tunneling of the remaining excess quasiparticles. By measuring the temperature dependence of the quasiparticle tunneling rates in the ground and excited states of the transmon, we find evidence for the effective thermalization of the quasiparticles. A resulting asymmetry between the quasiparticle tunneling rates in the two qubit states allows us to transfer quasiparticles on-demand, thus actively manipulating the charge-parity of the transmon. |
Wednesday, March 8, 2023 5:24PM - 5:36PM |
Q73.00011: Reduction of correlated errors in superconducting qubits using normal metal back-side metallization Vito M Iaia, Jaseung Ku, Andrew L Ballard, Clayton Larson, Eric Yelton, Chuan-Hong Liu, Shravan Patel, Robert McDermott, B.L.T. Plourde The impact of high-energy particles, such as gamma rays and cosmic ray muons, in superconducting qubit chips generates pair-breaking phonons that can travel long distances generating excitations above the superconducting ground state, known as quasiparticles, leading to correlated errors across many qubits. These correlated errors between distant qubits are fatal to error-correction schemes, such as the surface code. Therefore, it is critical to develop strategies for mitigating quasiparticle poisoning to protect large qubit systems from such errors. We have fabricated devices with normal metal reservoirs for phonon downconversion on the opposite face of the chip from an array of charge-sensitive transmon qubits. We present measurements of devices with and without this back-side metallization. We utilize a pump-probe injection technique of pair-breaking phonons in the device to examine the influence of back-side metallization compared to the control device. We demonstrate the effectiveness of the phonon downconversion by measuring a factor of 20 decrease in the flux of injected pair-breaking phonons. In addition, we observe a two-order of magnitude reduction in correlated poisoning due to background radiation. |
Wednesday, March 8, 2023 5:36PM - 5:48PM |
Q73.00012: Numerical Modeling of Phonon-Mediated Quasiparticle Generation in Superconducting Qubits Eric Yelton, Clayton Larson, Natalie Isenberg, Gabriel Spahn, Spencer Weeden, Robert McDermott, B.L.T. Plourde Correlated errors in qubit arrays are detrimental to quantum error correction schemes. Recent studies have shown that on-chip impacts of gamma-rays and muons can cause correlated errors in superconducting qubit arrays due to phonon-mediated quasiparticle (QP) poisoning. Understanding the dynamics of phonons in these devices is paramount to developing and improving existing mitigation strategies. In this talk, we present a numerical model of acoustic phonon transport in a Si-crystal using Geant4 for Condensed Matter Physics (G4CMP), a low-temperature Monte-Carlo simulation package. We include both normal metal and superconducting film boundaries, in order to model recent experiments demonstrating a QP poisoning mitigation strategy based on back-side normal metal reservoirs. With this model, we make quantitative predictions of the efficiency of phonon downconversion for different device configurations. |
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