Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session M41: Noise and Decoherence in Superconducting QubitsFocus Recordings Available
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Sponsoring Units: DQI DCMP Chair: Martin Gustafsson, Raytheon BBN Technologies Room: McCormick Place W-196C |
Wednesday, March 16, 2022 8:00AM - 8:12AM |
M41.00001: Experimental characterization of correlated qubit decays in IBM Quantum processors attributable to cosmic rays and background gamma radiation Ted Thorbeck, Andrew Eddins, Isaac Lauer, Douglas T McClure Recent reports in the literature have demonstrated that high-energy cosmic ray muons and background gamma radiation can severely impact the performance of superconducting quantum processors. Quasiparticles generated by these events can degrade not only single-qubit coherence times, but can also introduce errors that are strongly correlated across many qubits, or within a single qubit over time. Such correlated errors are a serious challenge for quantum error correction algorithms, making understanding and characterization of these processes imperative. In this talk we use our multiqubit IBM Quantum systems as detectors of incident radiation by monitoring the qubits for correlated decays as well as charge offset jumps. We characterize the rates at which these events occur and their effect on the coherence of these devices. |
Wednesday, March 16, 2022 8:12AM - 8:24AM |
M41.00002: Continuous Real-Time Detection of Quasiparticle Trapping Part I: Detection and Analysis James Farmer, Azarin Zarassi, Darian M Hartsell, Evangelos Vlachos, Haimeng Zhang, Eli Levenson-Falk Non-equilibrium quasiparticles are ubiquitous in superconducting circuits and are known to be a source of error for qubits. This two-part talk focuses on the use of sub-gap Andreev levels to investigate how non-equilibrium quasiparticles interact and trap in qubit-like circuits. We briefly introduce the Andreev picture of the Josephson effect and describe how Andreev levels may be used as quasiparticle traps. We discuss measurement techniques using Aluminum nanobridge SQUID resonators [Farmer et al. APL 2021] to detect non-equilibrium quasiparticle trapping in Andreev levels. An algorithm for assigning trap occupation from noisy I-Q data is presented and we discuss methods for distinguishing multiple trapping events from excitation of a single Andreev state. We conclude with methods for extracting relevant information from the trap occupation time series data. In part 2, we present measurement results and discuss implications. |
Wednesday, March 16, 2022 8:24AM - 8:36AM |
M41.00003: Continuous Real-Time Detection of Quasiparticle Trapping Part II: Quasiparticles Behavior Azarin Zarassi, James T Farmer, Darian M Hartsell, Evangelos Vlachos, Haimeng Zhang, Eli Levenson-Falk Non-equilibrium quasiparticles are ubiquitous in superconducting circuits and are known to be a source of error for qubits. This two-part talk focuses on the use of sub-gap Andreev levels to investigate how non-equilibrium quasiparticles interact and trap in qubit-like circuits. Quasiparticle behavior depends on many environment variables including temperature, radiation levels, gap quality, and signal line filtering. Part 1 introduced quasiparticle trapping in Aluminum nanobridges [Farmer et al. APL 2021] and the measurement techniques we use. We discuss the effect of readout power on mean trap occupation and transition rates, highlighting how this power scaling can help us understand the interaction of Andreev levels with each other and with localized sub-gap states, such as those induced by magnetic contaminants. We present the temperature dependence of trap occupation and extrapolate to determine our non-equilibrium quasiparticle density. We discuss the effects of introducing eccosorb filters in our apparatus and conclude by discussing spectroscopic measurements of occupied Andreev trap energies. |
Wednesday, March 16, 2022 8:36AM - 9:12AM |
M41.00004: Probing hundreds of individual quantum defects in polycrystalline and amorphous alumina Invited Speaker: Chih-Chiao Hung Two-level systems (TLSs) are present in the materials of qubits and when they exchange energy with the qubit they also limit their coherence. TLSs are described by two energy terms, tunneling and asymmetry energy, and an electrical dipole moment which couples to the ac-mode of quantum systems. There are several strategies to reduce TLS density: material optimization, surface treatments, etc. However, TLSs are not generally understood microscopically -- either structurally or in atomic composition. |
Wednesday, March 16, 2022 9:12AM - 9:24AM |
M41.00005: Investigation of Superconducting Qubit Errors from Ionizing Radiation Patrick M Harrington, Amir H Karamlou, Wouter Van De Pontseele, Daniel Mayer, Mingyu Li, Kyle Serniak, David K Kim, Bethany M Niedzielski, Alexander Melville, Jonilyn L Yoder, Mollie E Schwartz, Simon Gustavsson, Joseph A Formaggio, William D Oliver Ionizing radiation presents a source of errors for superconducting qubits. Recent studies have modeled the various causes of radiation-induced error bursts. We present measurements to detect and quantify sources of high energy impacts in superconducting qubit quantum processors. These measurements clarify the contributing effects of gamma radiation and comic ray muons to spatiotemporally correlated error bursts that challenge quantum error correction schemes. We discuss strategies to reduce the rate of these error events and promote methods to minimize the impact of these errors on superconducting qubit processors. |
Wednesday, March 16, 2022 9:24AM - 9:36AM |
M41.00006: Investigation into Low Frequency Charge Noise Mechanisms in a Tantalum Transmon Daniel M Tennant, Luis A Martinez, Kristen M Beck, Sean R O'Kelley, Christopher D Wilen, Robert McDermott, Jonathan L DuBois, Yaniv J Rosen Recent measurements of the low frequency charge noise environment of a tantalum transmon [1] revealed two unexpected results: a noise power spectral density approximately two orders of magnitude less than that found on comparable aluminum and niobium devices and the presence of preferred charge offsets. In this work, we present our investigation into the material origins of the tantalum’s novel charge noise environment. By repeating our measurements over a range of cryogenic temperatures, it is possible to discern two categorical sources of noise. One type of charge noise event is temperature dependent and causes predominantly nearest-neighbor charge offset transitions. The other is temperature independent and causes large charge offsets. The temperature independent noise compares favorably to ionizing radiation events while temperature dependent noise is likely on-chip charge fluctuations which may be a function of tantalum’s uniquely uniform surface chemistry. |
Wednesday, March 16, 2022 9:36AM - 9:48AM |
M41.00007: Quasiparticle Poisoning Mediated by Spurious Antenna Modes of the Transmon Qubit Chuanhong Liu, David C Harrison, Shravan Patel, Chris D Wilen, Owen Rafferty, Spencer Weeden, Gabriel Spahn, Matthew Snyder, Francisco Schlenker, Andrew L Ballard, Vito M Iaia, Jaseung Ku, Britton L Plourde, Robert McDermott Superconducting qubits are a leading candidate for realization of a fault-tolerant quantum computer. However, nonequilibrium quasiparticles can seriously degrade device fidelity. We find that the dominant mechanism for quasiparticle poisoning is direct absorption of pair-breaking photons at the qubit junction. The island of the qubit acts as a resonant antenna for millimeter-wave blackbody radiation, providing an efficient impedance match from the qubit tunnel junction to the impedance of free space. We describe a series of experiments involving different qubit geometries corresponding to fundamental antenna resonances spanning a broad range from 100 GHz to 500 GHz. We use broadband blackbody radiators and coherent Josephson mm-wave sources to characterize the resonant absorption of pair-breaking photons by the qubit. Photon absorption events induce a change in the quasiparticle parity of the qubit island, which we detect using a parity-sensitive Ramsey gate sequence. In addition, we characterize spurious upward and downward qubit transitions induced by photon-assisted quasiparticle poisoning. A deep understanding of this physics will pave the way to realization of a new class of quantum sensors for dark matter detection and to next-generation superconducting qubits that are robust against quasiparticle poisoning. |
Wednesday, March 16, 2022 9:48AM - 10:00AM |
M41.00008: Spatiotemporally-correlated quasiparticle-induced transitions in arrays of transmon qubits Kyle Serniak, Greg Calusine, Patrick M Harrington, Max Hays, Thomas M Hazard, David K Kim, Alexander Melville, Bethany M Niedzielski, Jonilyn L Yoder, Mollie E Schwartz, William D Oliver Spatiotemporally-correlated errors present a significant challenge for quantum error-correction schemes. Recent work has identified burst events, attributed to energy deposited in the device by muons and radioactive decay products from the environment, that result in correlated errors effecting millimeter-scale regions of a superconducting processor with millisecond-scale duration. Here we probe these events using an array of offset-charge-sensitive transmons. Observation of a spatiotemporally-correlated increase of quasiparticle-induced charge-parity transitions that accompany the offset-charge signatures of the aforementioned burst events would provide a direct link between these errors and a nonequilibrium quasiparticle population. These devices also serve as a testbed for strategies to mitigate high-energy bursts of quasiparticle-induced decoherence in superconducting qubits. |
Wednesday, March 16, 2022 10:00AM - 10:12AM |
M41.00009: Long-time-scale energy relaxation dynamics of tunable transmon qubits as a tool for loss metrology SHENG-XIANG LIN, Tongyu Zhao, Nicholas Materise, John Pitten, David Pappas, Corey Rae H McRae Superconducting qubits are one of the promising platforms demonstrating quantum speedupin terms of quantum computation. However, there are numerous loss factors acting on supercon-ducting qubits, and they pose a limitation on qubit coherence [1]. Fluctuations in qubit energyrelaxation time (T1) over time and frequency can be used to discriminate between coherent two-level-system (TLS) defects and other loss mechanisms [2]. In this talk, I will illustrate the implementation of this method to improve cryogenic microwave metrology toward optimization of qubit performance. Here, I will focus on our implementation of a frequency-tunable transmon qubit as both a detector for TLS and a method to distinguish between loss mechanisms, and demonstrateits excellence on doing inter-laboratory comparisons, for example the SQMS Round Robin experiment. In addition, I will discuss calibration and measurement details, and include comparisons ofTLS dynamics and populations between subsequent cooldowns in my discussion. |
Wednesday, March 16, 2022 10:12AM - 10:24AM |
M41.00010: Mitigation of quasiparticle poisoning in superconducting qubits using normal metal backside metallization Vito M Iaia, Jaseung Ku, Andrew L Ballard, Chuan-Hong Liu, Robert McDermott, B.L.T. Plourde The absorption of high-energy particles, such as gammas and cosmic ray muons, in superconducting qubit chips generates pair-breaking phonons that can travel long distances and generate quasiparticles over significant areas of a device. The quasiparticle poisoning from such events can lead to correlated errors between distant qubits, resulting in the breakdown of error-correction schemes, such as the surface code. Therefore, it is critical to develop strategies for mitigating such quasiparticle poisoning to protect large qubit systems from such errors. We have fabricated devices with normal metal phonon absorbers on the opposite face of the chip from an array of charge-sensitive transmon qubits. We present measurements of devices with and without this backside metallization. We demonstrate the effectiveness of the phonon absorbers on the mitigation of quasiparticle poisoning by measuring the qubit behavior in the presence of direct quasiparticle injection by biasing on-chip Josephson tunnel junctions in both pulsed and continuous modes. |
Wednesday, March 16, 2022 10:24AM - 10:36AM |
M41.00011: Geometric Superinductance Qubits: Controlling Phase Delocalization across a Single Josephson Junction Andrea Trioni, Matilda Peruzzo, Farid Hassani Bijarbooneh, Grisha Szep, Elena Redchenko, Martin Zemlicka, Johannes M Fink We present the characterization of a large variety of loop-based qubits [1] made by the parallel connection of a single Josephson junction with a geometric superinductor [2], an uninterrupted coiled aluminum wire. They are all stemming from the same rf-SQUID circuit but with drastically different characteristic energy scales. Just changing the coil's number of turns it is possible to delocalize the phase variable from the flux-qubit and fluxonium regimes up to the recently introduced quasicharge regime with strongly enhanced zero-point phase fluctuations and a heavily suppressed flux dispersion. The use of geometric superinductors allows a direct implementation of the rf-SQUID Hamiltonian without approximations, and a precise control of the inductive and capacitive energy as guaranteed by top-down lithography - a key ingredient for intrinsically protected superconducting qubits. |
Wednesday, March 16, 2022 10:36AM - 10:48AM |
M41.00012: Geometric and thermal effect on non-equilibrium quasiparticles in superconducting qubit Xianchuang Pan, Yuxuan Zhou, Jian Li, Zhihao Jiang, Gianluigi Catelani, Ling Hu, Fei Yan, Song Liu Non-equilibrium quasiparticles are a source of decoherence and instability for superconducting qubits, a potential threat to fault-tolerant quantum computing. In this work, we investigate how they are affected by circuit geometry and temperature with revisited charge qubits. We observe state-of-the-art quasiparticle tunneling rate (less than 1Hz) which is associated with radiation loss from the qubit antenna mode. We also found that thermally activated quasiparticles can be explained by difference in thin film thickness. |
Wednesday, March 16, 2022 10:48AM - 11:00AM |
M41.00013: Characterizing the reliability and coherence-time impact of laser annealing on transmon-qubit Josephson junctions. Sean van der Meer, Nandini Muthusubramanian, Matvey Finkel, Christos Zachariadis, Alessandro Bruno, Leonardo DiCarlo Laser annealing is a demonstrated technique for tuning the normal-state resistance of Josephson junctions and thereby the operating frequency of superconducting qubits. However, before entrusting laser annealing as a viable post-fabrication trimming process for multi-qubit quantum processors, it is paramount to characterize its reliability and impact on qubit coherence times. We demonstrate a simple, fully automated, closed-loop, laser annealing implementation that iteratively and selectively increases junction resistances towards an arbitrary target up to 15% above the starting value. Our setup minimizes complexity, showcasing the simplicity with which reliable frequency targeting can be achieved. We investigate the reliability and coherence impact of laser annealing performed on 17-transmon quantum processors. |
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