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 N75: Novel Superconducting qubit designs and couplingsFocus
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Sponsoring Units: DQI Chair: Daniel Weiss, Yale University Room: Room 401/402 |
Wednesday, March 8, 2023 11:30AM - 12:06PM |
N75.00001: Gradiometric quarton for nonlinear coupling of superconducting qubits and resonators Invited Speaker: Kevin P O'Brien Nonlinear couplings between superconducting qubits and resonators such as the cross-Kerr interaction are used for important operations including qubit readout and gates. Most nonlinear coupling schemes including the long-established dispersive shift have limited cross-Kerr strength and non-ideal interactions such as residual self-Kerr. We previously proposed quarton couplers as promising nonlinear couplers between qubits and resonators that can facilitate cross-Kerr magnitudes of the order of gigahertz. Here, we present a device containing two transmon qubits coupled by a gradiometric quarton coupler. Through flux tuning the gradiometric quarton and transmon SQUID, we explore the potential of purely nonlinear coupling between the qubits and cancellation of qubit self-Kerr to linearize it into a resonator. We present experimental results on a device designed to operate in a parameter space that has large cross-Kerr couplings and large detuning to suppress other unwanted interactions. Large cross-Kerr between qubit and resonator is expected to enable applications including faster high fidelity qubit readout and gates. |
Wednesday, March 8, 2023 12:06PM - 12:18PM |
N75.00002: Properties of superconducting circuits based on Josephson junction arrays beyond the single-mode approximation Ian Mondragon-Shem, Aditya Gandotra, Andrew A Houck, Jens Koch An accurate description of SNAIL and fluxonium devices is fundamental for their use in scalable quantum processors. Both devices belong to a class of circuits consisting of an array of identical junctions forming a loop with an additional junction different from the rest. Frequently, these circuits are described by an approximate one-mode model which disregards internal array modes. As a result, the physics of array modes has remained largely unexplored, both from the perspective of fundamental understanding and potential applications. We discuss the range of validity and eventual breakdown of the one-mode model as the number of junctions and their parameters are varied. We specifically examine the case in which the odd junction has the larger Josephson energy, a scenario not captured by the one-mode model, and discuss spectral properties and potential applications of this circuit. |
Wednesday, March 8, 2023 12:18PM - 12:30PM |
N75.00003: Suspended Superinductors for Novel Qubits Christian Juenger, Trevor Chistolini, Long B Nguyen, Larry Chen, Hyunseong Kim, David I Santiago, Irfan Siddiqi Superinductors based on Josephson junction arrays are a key circuit element for novel superconducting qubits, such as fluxonium, 0-pi, and blochnium qubits. However, dissipation in superinductors due to intrinsic noise sources, such as dielectric loss or parasitic capacitance from the substrate, limits the performance of these elements. In this talk, we present state-of-the-art design and fabrication techniques to realize superinducting circuit elements based on suspended Josephson junction arrays and analyze their performance. Furthermore, we utilize this technique to create a novel suspended fluxonium type of qubit and investigate its characteristics. |
Wednesday, March 8, 2023 12:30PM - 12:42PM |
N75.00004: Noise characterization of suspended Josephson junction arrays Trevor Chistolini, Christian Juenger, Long B Nguyen, Larry Chen, Hyunseong Kim, David I Santiago, Irfan Siddiqi Superinductors are an essential component of many superconducting qubit designs, including fluxonium or the 0-π qubit. One of the most popular methods to realize such superinductors is an array of Josephson junctions, where their quality will impact the qubit's coherence. In this work, we investigate noise and instabilities affecting these arrays, such as arising from phase slips or nonequilibrium quasiparticles, where the arrays are either situated on a silicon substrate or suspended in vacuum above the substrate. Arrays of different junction number and geometry are explored to elucidate the noise processes in Josephson junction arrays, informing us how to best design these components to implement in qubit architectures. |
Wednesday, March 8, 2023 12:42PM - 12:54PM |
N75.00005: The inductively shunted transmon: A simple building block for multi-species qubit lattices Simone D Fasciati, Boris Shteynas, Giulio Campanaro, Mustafa S Bakr, James F Wills, Shuxiang Cao, Vivek Chidambaram, Peter J Leek The transmon has become the most widely used superconducting qubit owing to its simplicity, while its limitations have spurred the recent development of other more complex qubit designs, such as the fluxonium and zero-pi qubit. The inductively shunted transmon (IST) has also been proposed [1] as a simple alternative to complement the conventional transmon and enable statically coupled qubit pairs free of unwanted ZZ interaction. Here, we realize an IST in our 3D-integrated coaxial circuit architecture [2]. This qubit is simple to fabricate, has a stable single-well plasmonic spectrum and shows good coherence at the half flux bias point. By coupling it directly to a transmon, we show built-in ZZ suppression thanks to the positive sign of the IST anharmonicity. Numerical simulations indicate that this effect is realizable for a wide variety of circuit parameters. We investigate blue and red sideband transitions, allowed by the asymmetry of the IST potential when biased away from the flux symmetry points, which can be used to implement entangling gates. This work paves the way towards simple multi-species superconducting qubit lattices with direct static coupling and low crosstalk, without the need for tunable coupling elements or multi-path couplers. |
Wednesday, March 8, 2023 12:54PM - 1:06PM |
N75.00006: Fluxonium qubit limited by a collection of two-level systems Martin Spiecker, Patrick Paluch, Niv Drucker, Shlomi Matityahu, Daria Gusenkova, Francesco Valenti, Patrick Winkel, Dennis Rieger, Nicolas Gosling, Simon Günzler, Ivan Takmakov, Richard Gebauer, Oliver Sander, Gianluigi Catelani, Alexander Shnirman, Alexey V Ustinov, Wolfgang Wernsdorfer, Yonatan Cohen, Ioan M Pop By running a quantum Szilard engine we actively heat or cool a two-level-system (TLS) environment [1]. The egnine consists of a granular aluminum fluxonium qubit [2] coupled on one side to the TLS environment and on the other side to a real-time measurement and control apparatus. We show that the TLSs and the qubit are each other's dominant loss mechanism, therefore their understanding and mitigation is not only crucial to improve qubit lifetimes but also to avoid non-Markovian qubit dynamics. We also show that a single pi-pulse on the qubit gives rise to measureable heating in the TLS environment, which complicates the task of superconducting qubit benchmarking. |
Wednesday, March 8, 2023 1:06PM - 1:18PM |
N75.00007: Spectroscopy of a hidden two-level system environment using a fluxonium qubit with fast-flux tunability Patrick Paluch, Martin Spiecker, Nicolas Gosling, Dennis Rieger, Simon Günzler, Wolfgang Wernsdorfer, Ioan M Pop Recent experiments on a granular aluminum (grAl) fluxonium qubit [1] have shown non-exponential relaxation dynamics spanning over tens of milliseconds, |
Wednesday, March 8, 2023 1:18PM - 1:30PM |
N75.00008: Tunable coupler for mediating interactions between a two-level system and a waveguide from a decoupled state to the ultra-strong coupling regime: part I Noah Janzen, Xi Dai, Shaun Ren, Jiahao Shi, Adrian Lupascu Coupling between a two-level system (TLS) and a waveguide is a fundamental paradigm of light-matter interactions. We introduce and experimentally demonstrate a tunable coupler between a TLS, implemented using a flux qubit, and the electromagnetic fields in a superconducting waveguide. The device uses on-chip flux biasing to tune the coupling strength from a decoupled state, to near the ultrastrong-coupling (USC) regime of light-matter interaction where the interaction rate approaches the gap frequency of the TLS. The normalized coupling strength, α, is measured to range from 6.2 × 10-5 to 2.19 × 10-2 and is predicted to have an even broader range by the fitted circuit model, creating an effective switch for the coupling. This wide range of coupling strengths presents a significant advantage over previous TLS-waveguide coupler designs for a range of applications. This work opens new research avenues in several areas including the development of photon sources, the investigation of the spin-boson model at strong coupling, and the experimental realization of entanglement harvesting. In part I, we introduce the tunable coupler design and discuss the characterization of the device including the coupling strength α. |
Wednesday, March 8, 2023 1:30PM - 1:42PM |
N75.00009: Tunable coupler for mediating interactions between a two-level system and a waveguide from a decoupled state to the ultra-strong coupling regime: part II Xi Dai, Noah Janzen, Shaun Ren, Jiahao Shi, Adrian Lupascu Coupling between a two-level system (TLS) and a waveguide is a fundamental paradigm of light-matter interactions. We introduce and experimentally demonstrate a tunable coupler between a TLS, implemented using a flux qubit, and the electromagnetic fields in a superconducting waveguide. The device uses on-chip flux biasing to tune the coupling strength from a decoupled state, to near the ultrastrong-coupling (USC) regime of light-matter interaction where the interaction rate approaches the gap frequency of the TLS. The normalized coupling strength, α, is measured to range from 6.2 × 10-5 to 2.19 × 10-2 and is predicted to have an even broader range by the fitted circuit model, creating an effective switch for the coupling. This wide range of coupling strengths presents a significant advantage over previous TLS-waveguide coupler designs for a range of applications. This work opens new research avenues in several areas including the development of photon sources, the investigation of the spin-boson model at strong coupling, and the experimental realization of entanglement harvesting. In part II, we discuss the theoretical modeling of the coupler and the decoherence sources affecting the qubit. |
Wednesday, March 8, 2023 1:42PM - 1:54PM |
N75.00010: Nanowire-based RF-SQUID quantum memory device Sarah Jones, Trevyn Larson, Heli Vora, Varun Verma, Katarina Cicak, Jose Aumentado, Sae Woo Nam, Jens Koch, Raymond W Simmonds, András Gyenis Superconducting qubits are a promising avenue for quantum computing devices due to their high fidelity operation and scalability. Most superconducting qubit designs use Al-AlOx-Al based Josephson junctions as nonlinear inductors, but this solution has disparities given that the junction area and thickness are not consistent enough to reproduce precise qubit frequencies. Additionally, aluminum-oxide based junctions limit the types of qubits that can be fabricated. Here, we use a high-kinetic inductance material that has shown excellent performance in single-photon detectors to construct a nonlinear constriction or weak-link type element in a 3D RF-SQUID resonator. We demonstrate the strong non-sinusoidal behavior of the nanowire and the existence of non-hysteretic behavior and switching between meta-stable flux states. |
Wednesday, March 8, 2023 1:54PM - 2:06PM |
N75.00011: High coherence 2D Kerr-cat qubit: Experimental realization and technical challenges AHMED HAJR, Gerwin Koolstra, Bingcheng Qing, Long B Nguyen, Christian Jünger, Larry Chen, Zahra Pedramrazi, Shruti Puri, Justin G Dressel, Andrew N Jordan, David I Santiago, Irfan Siddiqi, Nicholas E Frattini The Kerr-cat qubit is a bosonic qubit with promising potential to implement quantum error correction codes tailored for noise-biased qubits. Its intrinsic nonlinearities enable fast logic gates and QND measurements. However, since it is a strongly driven matter qubit it comes with many technical challenges when scaling to multi-qubit chips. In this talk, we present our experimental progress toward realizing large cat states with high coherence in 2D architectures paving the way for scalable multi-qubit operations. |
Wednesday, March 8, 2023 2:06PM - 2:18PM |
N75.00012: Two-mode qubit design inspired by the GKP Hamiltonian Catherine Leroux, Ross Shillito, Charles Marcus, Morten Kjaergaard, András Gyenis, Alexandre Blais Protected qubits are promising candidates for quantum computation, for example with the fluxonium qubit showing greatly improved coherence times relative to the transmon [1]. It was also proposed that a two-mode qubit, the $0-pi$ qubit, could offer optimal protection against both charge and flux noise [2,3]. This qubit was experimentally realized, albeit in a regime where the protection is not complete [4]. Additionally, there has been a recent proposal to implement a GKP qubit with the help of a gyrator and two fluxonium circuits [5]. The logical subspace of a GKP qubit would be equally strongly decoupled from its environment. In this talk, we derive an effective two-mode circuit that shares a similar eigenspectrum at low energies and is based on a recently proposed charge-phase interaction [6]. We provide analytical expressions for the low-energy spectrum, eigenstates and qubit operators which show strong agreement with numerical diagonalisation. We analyze the robustness of this qubit to both noise and disorder, and compare this qubit with both the GKP qubit and the $0-pi$ qubit. We also present a longitudinal readout scheme and single-qubit gates protocols. |
Wednesday, March 8, 2023 2:18PM - 2:30PM |
N75.00013: Correlated parametric oscillations of capacitively-coupled Josephson parametric oscillators Tomohiro Yamaji, Shumpei Masuda, Aiko Yamaguchi, Tetsuro Satoh, Ayuka Morioka, Yuichi Igarashi, Masayuki Shirane, Tsuyoshi Yamamoto A Kerr Parametric Oscillator (KPO) has been recently proposed as a new candidate for a building block of a quantum annealer [1]. Although the KPOs have been experimentally realized by using trapped ions and Josephson parametric oscillators (JPOs) [2], realization of the KPO network remains elusive. We study simultaneous parametric oscillations in a system composed of two distributed-element-circuit Josephson parametric oscillators in the single-photon Kerr regime coupled via a static capacitance. The phases of oscillations states are correlated with each other due to the coupling in the condition that the JPOs are modulated at the same pump frequency. The energy of the system is described by a two-bit Ising Hamiltonian with variable local fields and coupling, where the effective coupling can be controlled by adjusting the relative phase between parametric pumps. The present result paves the way for the realization of a quantum annealer consisting of a network of Kerr parametric oscillators. |
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