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 G75: Protecting superconducting qubits from noiseFocus
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Sponsoring Units: DQI Chair: Neereja Sundaresan, IBM TJ Watson Research Center Room: Room 401/402 |
Tuesday, March 7, 2023 11:30AM - 12:06PM |
G75.00001: Dynamics of Transmon Ionization Invited Speaker: Alexandru Petrescu Superconducting circuit quantum electrodynamics (circuit QED) is one of the most promising platforms for quantum information processing. In typical circuit QED experiments, the quantum state of the qubit is measured by monitoring a readout resonator weakly and off-resonantly coupled to the qubit. As drive power is increased to achieve a higher-fidelity and faster measurement, unwanted transitions occur, which, for example, decrease the qubit’s energy relaxation time T1. In this talk, focusing on the ubiquitously used transmon qubits, we address the phenomenon of escape into unconfined states [1,2], and unveil a mechanism for rate enhancement during measurement: by interactions between the low-lying states defining the qubit subspace and high-energy chaotic states [3]. This analysis provides important guidelines in the design of current experiments. |
Tuesday, March 7, 2023 12:06PM - 12:18PM |
G75.00002: Interplay of local and induced decoherence in circuit-QED: Theory Archana Kamal, Zhihao Xiao, Ted Thorbeck, Juzar Thingna, Andrew Keefe, Luke Govia Standard quantum open system descriptions are being revisited with the advent of quantum reservoir engineering that aims to control quantum dynamics via strong dissipation. Despite its tremendous success, a full understanding of the interplay between intrinsic system and engineered dissipation channels is lacking. In this work, we present our theoretical framework for constructing quantum master equations that self-consistently incorporate all dissipation channels. Our method allows us to analytically obtain the induced rates on a system influenced by an engineered reservoir, all the way from the deep dispersive to the resonant regimes. Notably, this broad parameter regime is inaccessible within standard approaches based on Lindblad or Hamiltonian perturbation theory. Surprisingly, we find significant modifications to the rates at the leading order in system-reservoir coupling within the Born-Markov regime. We also discuss how our approach can be extended to structured reservoirs with strong quantum correlations and, as a direct experimental signature, quantify dispersive readout induced reduction or enhancement in qubit lifetimes. |
Tuesday, March 7, 2023 12:18PM - 12:30PM |
G75.00003: Interplay of local and induced decoherence in circuit-QED: Experiment Ted Thorbeck, Zhihao Xiao, Juzar Thingna, Archana Kamal, Luke C. G. Govia It has long been known in the field that the lifetime of a superconducting qubit (T1) can change dramatically during dispersive measurement and that it typically changes for the worse. A T1 event during readout results in a nonQND readout error, reducing readout fidelity. Increasingly quantum algorithms require conditional (or mid-circuit) measurements, in which an operation is performed on the qubit based on the measurement result. A T1 event during a mid-circuit measurement can result in the wrong feedback being given to the qubit. While several theories have been put forward to explain the change in T1 during measurement, there has been a lack of experimental evidence for or against these theories. In this talk we put forward a new explanation for T1 reduction during dispersive readout. The modification of the qubit T1 can be described within a self-consistent theoretical framework for calculating engineered dissipation on the qubit post-adiabatic elimination of the readout resonator. We support this new theory with experimental evidence on an IBM Quantum processor. |
Tuesday, March 7, 2023 12:30PM - 12:42PM |
G75.00004: Optimizing Signal to Noise Ratio for Superconducting Qubit Readout with a Purcell Filter Ross Shillito, François Swiadek, Sebastian Krinner, Andreas Wallraff, Alexandre Blais Superconducting qubit readout remains one of the most important aspects to improve in circuit quantum electrodynamics, with the fidelity and length of the operation typically lagging in comparison to state-of-the-art single and two qubit gates. Purcell filters have been a significant advancement in this field, demonstrating to be vital in suppressing the resonator-induced qubit decay rate, known as the Purcell decay rate. However, the introduction of an additional mode increases the complexity of readout, with many parameters requiring simultaneous optimization. In this work, we explore calibration of the parameter space for the combined readout resonator-Purcell filter system to maximize the Signal-to-Noise ratio for readout given a finite readout time. |
Tuesday, March 7, 2023 12:42PM - 12:54PM |
G75.00005: Protecting transmon qubits from Purcell decay and other external sources of decoherence Param J Patel, Mingkang Xia, Chao Zhou, Ryan Kaufman, Israa Yusuf, Michael J Hatridge In quantum information processing, qubit coherence is one of the most important factors limiting the ultimate size of quantum cicuits. A fundamental limitation of superconducting qubit coherence is the Purcell limit of qubit photon decay via coupling to the port of its associated readout cavity. In many quantum circuits, this limitation is removed by using an external Purcell filter to stop photon transmission at the qubit frequency. This limit requires us to separate out and protect against other sources of loss in the qubits too. In this talk, we will present both our efforts to regularly achieve high-coherence transmons in 2D and 3D geometries and our implementation of a technique to incorporate protection from the Purcell effect directly into the sample design and geometry [Sunada, et al. PhysRevApplied (2022)]. By visualizing the transmon fields interacting with a resonator, an optimal and unique port placement can be determined to achieve large cavity bandwidths and longer qubit lifetimes. Placing the strongly coupled resonator port within the null point of the transmon fields innately reduces the photon emissions of the qubit while providing fast readout and is applicable to both 2D and 3D sample geometries. We will show that this built-in Purcell protecton is able to reliably produce qubits with 100 us lifetimes with fast readout in tubes and post cavity geometries while icnreasing the coherence limit due to Purcell decay to at least 1 ms. |
Tuesday, March 7, 2023 12:54PM - 1:06PM |
G75.00006: Modeling Superconducting Microwave Systems with DEC-QED: Performance and Applications Dzung Pham, Richard Li, Wentao Fan, Nicholas T Bronn, Thomas G McConkey, Hakan E Tureci DEC-QED is a gauge-invariant flux-based modeling approach to Josephson-junctions-based elements embedded in three-dimensional electromagnetic environments of arbitrary complexity. The system of Maxwell's equations coupled to nonlinear order parameter equations of the electronic condensate field of a superconductor is solved by defining coarse-grained flux fields living on the discrete edges of the tetrahedral discretization of the domain. This approach naturally captures the nonlinear response of induced supercurrents to applied fields, enabling accurate modeling of the dynamics in superconducting microwave systems. We analyze the performance of DEC-QED as a complete computational toolbox including a mesher on the modeling of currents and cross-talk in a test geometry. We also discuss the implementation of open boundary conditions for accurate computation of radiative contribution to T1 times of weakly anharmonic superconducting qubits. |
Tuesday, March 7, 2023 1:06PM - 1:18PM |
G75.00007: Acoustically shielded TLS exceeding 100us T1 time Mo Chen, Oskar Painter State-of-the-art superconducting (SC) transmon qubits are limited in energy relaxation time by microscopic two-level state (TLS) defects living at the amorphous material interfaces making up the qubits [1]. Although the microscopic origin is yet to be confirmed, TLS defects are believed to be tunneling states between two configurations in disordered materials, and they respond coherently to both electric and acoustic fields. The short relaxation time of TLSs is theoretically attributed to decay into the phonon bath of the bulk material. Based on this model (known as the standard tunneling model (STM) developed for glassy materials [2]), we engineered the phonon bath such that isolated TLS defects at microwave frequencies, resonant with transmon qubits, could become long-lived and a useful quantum resource. |
Tuesday, March 7, 2023 1:18PM - 1:30PM |
G75.00008: Simulating noise on a quantum processor: interactions between a qubit and resonant two-level system bath Yaniv J Rosen, Yujin Cho, Daniel M Tennant, Vincenzo Lordi, Jonathan L DuBois, Dipti Jasrasaria, Keith G Ray Two-level system (TLS) defects are one of the limiting factors affecting qubit coherence. The two primary models for TLS behavior are the standard model, which describes the interactions of distributions of TLSs with continuous wave devices, and single TLS models. However, there is very little work exploring the experimentally observed intermediate range where countable numbers of TLSs interact with quantum devices. Our work closes the gap on this regime. We start with one million TLSs distributed around the surface of a qubit and pick the 200 highest coupled TLSs. We then perform a full Lindbladian simulation to analyze the effects of resonant TLSs defects on qubit energy relaxation times. We find that 150 of the strongest coupled TLSs are enough to accurately describe the qubit energy relaxation time. We show that T1 dropouts can occur due to a strongly coupled TLS as far as a few microns away from the junction. We then draw conclusions about TLS distribution limitations based on experimental observation. |
Tuesday, March 7, 2023 1:30PM - 1:42PM |
G75.00009: Diagnosis and Mitigation of Correlated Errors in Superconducting Qubits from Ionizing Radiation Patrick M Harrington, Mingyu Li, Wouter Van De Pontseele, Daniel Mayer, David K Kim, Bethany M Niedzielski, Alexander Melville, Mollie E Schwartz, Jonilyn L Yoder, Jeffrey A Grover, Kyle Serniak, Joseph A Formaggio, William D Oliver Ionizing radiation causes momentary events of spatially-correlated superconducting qubit errors. We present the detection of multi-qubit correlated relaxation events in coincidence with cosmic ray secondary particles using scintillating detectors. These measurements identify the overall proportion of qubit errors caused by cosmic ray secondary particles versus all other sources of relaxation errors. The in-situ detection of radiation informs the sensitivity of each qubit to cosmic rays that penetrate the device substrate. Our findings reveal qubit device architectures that are less susceptible to the quasiparticles created by radiation absorption. The results of this cosmic ray coincidence measurement informs strategies that reduce the impact of ionizing radiation on quantum error correction schemes. |
Tuesday, March 7, 2023 1:42PM - 1:54PM |
G75.00010: Directional readout resonator with interference Purcell filter for scalable and modular qubit readout Alec Yen, Yufeng Ye, Kaidong Peng, Gregory D Cunningham, Jennifer Wang, Kevin P O'Brien In transmission-based readout of superconducting qubits, a weakly-coupled port is often used at the input of the readout bus to provide directionality close to unity for the readout microwave signal. However, this weakly-coupled port often requires the addition of large and high-magnetic field circulators and isolators for impedance matching, posing a significant challenge to quantum error correction, for which the number of qubits is expected to scale to thousands to millions. Moreover, the weakly-coupled port creates spatial dependence of the couplings to the readout resonators and limits the modularity of typical qubit readout design. In this work, we present a design for "directional readout", which avoids using a weakly-coupled port while preserving near-unity directionality. We also include in our design an "interference Purcell filter," a new form of bandstop Purcell suppression compatible with directional readout. We present progress towards an experimental implementation of directional readout designed to have near-unity directionality and high-fidelity readout of a transmon qubit. This design is expected to facilitate more scalable and modular qubit readout and design. |
Tuesday, March 7, 2023 1:54PM - 2:06PM |
G75.00011: Development of Ring Resonators for Non-Reciprocal Devices Zhiyin Tu, Alicia Kollar Circulators and isolators are vital for protecting quantum devices from undesired signals, but currently these devices are based on ferrite materials and the Faraday effect. The large magnetic fields required to achieve significant rotation necessitate a bulky independent housing and significant shielding. The bulky form factor and unavoidable insertion losses associated with the packaging limit the ultimate performance of ferrite isolators, as well as the quantity that can be housed in a dilution refrigerator. We propose another regime of potentially low insertion-loss, high directional-contrast nonmagnetic microwave isolator based on ring resonators and the use of temporal modulation to break the chiral symmetry of wave propagation. This technique was previously used to produce high-performance narrow-band optical isolators [1]. Here we present first steps toward a cryogenic microwave implementation, including the development of a compatible low-backscattering microwave ring resonator. This work will help take a crucial step towards developing practical low insertion loss, high directionality isolators possessing on-chip integrability with superconducting circuits for parametric amplifiers and other potential applications. |
Tuesday, March 7, 2023 2:06PM - 2:18PM |
G75.00012: Impact of charge dispersion on lifetime of transmon with different electrode gaps Kungang Li, Sudeep Dutta, Zachary Steffen, Benjamin S Palmer, Christopher J Lobb, Frederick C Wellstood Non-equilibrium quasiparticles tunneling across the Al/AlOx/Al Josephson junction is a source of energy relaxation for transmon qubits. To suppress the quasiparticle tunneling, the superconducting gaps across the junction should be different. We fabricated a 3D transmon qubit where the bottom oxygen doped Al base electrode has the largest superconducting gap, a less doped counter-electrode with a smaller gap, and finally a third pure Al capping electrode. At a base temperature of 20 mK, the T1 for the qubit transition temporally varied from 80 to 150 μs. The charge dispersion of g-f transition from the spectrum is around 1MHz. By adding a time delay to this standard spectroscopy sequence, we measured the lifetime of |f> state as a function of g-f transition frequency as well as the life time of |e> state from the subsequent |e> to |g> decay. |
Tuesday, March 7, 2023 2:18PM - 2:30PM |
G75.00013: Trapping quasiparticles on superconducting qubits through double gap engineering. Ugur Alyanak, Ziwen Huang, Wei-Ting Lin, Xinyuan You, Alexander Romanenko, Anna Grassellino, Shaojiang Zhu Non-equilibrium quasiparticles have been identified as a major decoherence source in superconducting qubits. Strategies to mitigate the quasiparticle loss are highly demanded. Based on the diffusion theory1, we propose a double gap engineering model to analytically and numerically simulate the quasiparticle diffusion in the superconducting transmon qubit under realistic assumptions, and we quantitatively calculate the improvement of trapping efficiency with this technique. Based on this model, we explore new qubit architectures and demonstrate the improvement of qubit relaxation and dephasing times experimentally, compared to those for single gap engineered and regular transmon qubits. |
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