Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session B16: Fluxonium and Novel Superconducting Qubits I |
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Sponsoring Units: DQI Chair: Neereja Sundaresan, IBM TJ Watson Research Center Room: 201 |
Monday, March 2, 2020 11:15AM - 11:27AM |
B16.00001: Readout of fluxonium qubits in circuit QED Konstantin Nesterov, Long Nguyen, Aaron Somoroff, Quentin Ficheux, Ivan Pechenezhskiy, Jeremy Stevens, Nathanael Pierre Cottet, Benjamin Huard, Vladimir Manucharyan, Maxim G Vavilov In the idealized dispersive model of circuit QED, a single-shot heterodyne qubit measurement can be made as accurate as desired by increasing the power of the microwave drive. However, in realistic systems, populating the microwave cavity with photons can have many detrimental effects: in addition to nonlinear effects in the cavity itself, its photons can increase qubit relaxation and excitation rates, including excitations to noncomputational states. In addition, a high drive power can induce resonance transitions between qubit states. In this talk, we present the results of the simulation of the readout process in the fluxonium circuit and discuss how the qubit states and integrated readout signal are affected by the cavity occupation. |
Monday, March 2, 2020 11:27AM - 11:39AM |
B16.00002: Microwave-activated entangling gates for fluxonium qubits Yinqi Chen, Konstantin Nesterov, Long Nguyen, Aaron Somoroff, Quentin Ficheux, Ivan Pechenezhskiy, Vladimir Manucharyan, Maxim G Vavilov The main qubit transition of the superconducting fluxonium circuit in its flux sweet spot is characterized by a low frequency and very long coherence time, which reaches 500 μs [1]. At the same time, the transition between the first and second excited states of the fluxonium is comparable to those in transmons: it has an order of magnitude higher frequency and stronger coupling to a microwave field, but shorter lifetime. In this talk, we analyze and compare two-qubit gates between such qubits activated by driving different transitions in the two-qubit spectrum. In one scheme [2], the microwave drive is applied in resonance with a higher-frequency transition leading outside of the computational subspace. In the second scheme, which is similar to the cross-resonance gate with transmons [3], the microwave drive is applied at a low frequency to keep the system in the computational subspace. We calculate fidelity metrics for both gates with decoherence effects accounted for. |
Monday, March 2, 2020 11:39AM - 11:51AM |
B16.00003: Single-shot dynamics of fluxonium in the strong dispersive coupling regime Haonan Xiong, Yen-Hsiang Lin, Long Nguyen, Quentin Ficheux, Aaron Somoroff, Vladimir Manucharyan We report single-shot measurement of a fluxonium qubit in the strong dispersive regime with maximum coherence time T2>200usec. Our results set the stage for a variety of quantum optics experiments where a combination of very strong anharmonicity and long coherence is desirable. In particular, we investigate temporal dynamics involving multiple transitions of fluxonium in order to reveal new information about solid state decoherence mechanisms. |
Monday, March 2, 2020 11:51AM - 12:03PM |
B16.00004: Fluxonium two-qubit gate with simultaneous Raman transitions Jacob Bryon, Andrei Vrajitoarea, Yidan Wang, Przemyslaw Bienias, Rex Lundgren, Ron Belyansky, Alexey V Gorshkov, Alicia Kollar, Andrew Houck Quantum computing applications rely on high-coherence qubits with two-qubit gates to control them. The Fluxonium circuit is a superconducting qubit with favorable coherence properties, but unlike the transmon qubit, there has been no experimental demonstration of a two-qubit gate. We propose a new scheme using a cavity to couple two fluxonium qubits and drive a two-qubit swap gate. We report experimental progress towards driving simultaneous Raman transitions in the two qubits, utilizing the coupling cavity and the lambda energy level structure of fluxonium. This work expands the available coherent controls for the fluxonium circuit and increases its viability for quantum computing as well for interesting quantum simulation applications. |
Monday, March 2, 2020 12:03PM - 12:39PM |
B16.00005: High Coherence Fluxonium Qubits Invited Speaker: Vladimir Manucharyan Vlad Manucharyan has led the push to ever longer fluxonium coherence. |
Monday, March 2, 2020 12:39PM - 12:51PM |
B16.00006: Fast flux qubit gates on a heavy fluxonium Helin Zhang, Srivatsan Chakram, Nathan D Earnest, Yao Lu, Ziwen Huang, Daniel Weiss, Jens Koch, David I Schuster A capacitively shunted fluxonium qubit has both long life time and coherence time at the half-flux sweet spot. However, the suppressed matrix elements and low transition frequency make it challenging to perform fast fluxon gates via charge coupling. Here, we present schemes for state initialization, fast single-qubit flux gates, and plasmon assisted readout for a fluxonium qubit, demonstrating the feasibility of controlling a superconducting qubit at background temperatures much higher than the operating frequency. This scheme improves the quantum control of fluxonium qubits, making it a strong candidate for quantum information processing. We additionally present schemes for fluxonium two-qubit gates without using lossier higher levels. |
Monday, March 2, 2020 12:51PM - 1:03PM |
B16.00007: Spectroscopy and logic gates in a strongly coupled two-fluxonium device Ebru Dogan, Dario Rosenstock, Long Nguyen, Aaron Somoroff, Vladimir Manucharyan, Chen Wang The fluxonium is one of the leading candidates as an upgrade to the mainstream transmon qubits in large-scale superconducting quantum processors: With stronger anharmonicity, longer coherence times and the ability to engineer selection rules, it has the qualities to in principle deliver better logic gate fidelity than transmons. Towards validating fluxonium as a viable qubit for scaling up, it is essential to go from one fluxonium to two or more; yet two coupled fluxoniums in various coupling regimes still remain to be better explored. Our experimental study focuses on two fluxonium qubits under strong capacitive coupling and we analyze the hybridization of computational states and higher excited states as a function of external flux bias. We also show that the ZZ coupling between two fluxonium qubits makes it straightforward to realize single and two qubit operations and report our progress on benchmarking single and two qubit gates. |
Monday, March 2, 2020 1:03PM - 1:15PM |
B16.00008: Fluxonium-like qubit design for improved coherence Pranav Mundada, Andrew Houck, Andras Gyenis, Ziwen Huang, Jens Koch Fluxonium qubits provide high anharmonicity and can offer states with disjoint support and large relaxation time. There has been significant progress in exploring different parameter regimes of the fluxonium for optimizing coherence times. However, in traditional fluxonium qubits, the external flux sweet spot is only present when external magnetic flux threading through the superconducting loop is either 0 or 0.5 flux quantum. Additional sweet spots can be achieved via the careful engineering of the Hamiltonian. We present experimental data on the implementation of such a fluxonium-like qubit architecture with extra sweet spots. |
Monday, March 2, 2020 1:15PM - 1:27PM |
B16.00009: The Most Coherent Superconducting Qubit? Aaron Somoroff, Long Nguyen, Yen-Hsiang Lin, Ray Mencia, Nicholas Grabon, Quentin Ficheux, Konstantin Nesterov, Maxim G Vavilov, Vladimir Manucharyan We report superconducting fluxonium qubits with coherence times limited by energy relaxation and reproducibly satisfying T2 > 100 μs (T2 > 400 μs in one device). Moreover, given the state-of-the-art values of the surface loss tangent and 1/f flux noise amplitude, coherence times can be further improved beyond 1 ms. Our results violate a common viewpoint that the number of Josephson junctions in a superconducting circuit - over 102 here - must be minimized for the best qubit coherence. We outline how the combination of long coherence times and large anharmonicity unque to fluxonium can benefit both gate-based and adiabtic quantum computing. |
Monday, March 2, 2020 1:27PM - 1:39PM |
B16.00010: Towards Bell-state stabilization using the Very Small Logical Qubit (VSLQ) device: Part I Yao Lu, Tanay Roy, Eliot Kapit, David I Schuster Preparing and stabilizing entangled states is critical to many quantum information tasks, including autonomous quantum error correction. Inspired by previous dissipation-engineering schemes[1,2], we propose an autonomous protocol that prepares and stabilizes an arbitrary Bell state between a pair of superconducting qubits. This is achieved by parametrically coupling the superconducting qubits to each other, and to two dissipative baths that are made of low-Q resonators. The parametric couplings are engineered through the dynamical modulation of the qubit-qubit and the qubit-cavity interaction strengths at three different frequencies with appropriate phases. Numerical simulation shows that high fidelities of >95% are reached for all the Bell states, under realistic circuit parameters well-achievable by current circuit-QED technology. We further demonstrate how this scheme is fully compatible and can be experimentally realized on the VSLQ circuit[1]. |
Monday, March 2, 2020 1:39PM - 1:51PM |
B16.00011: Towards Bell-state stabilization using the Very Small Logical Qubit (VSLQ) device: Part II Tanay Roy, Yao Lu, Eliot Kapit, David I Schuster We report our experimental progress towards the stabilization of an arbitrary Bell-state. We first describe our circuit implementation of the Very Small Logical Qubit [1] that substantially reduces operational complexity by reducing the number of RF drive lines and is fully compatible with the stabilization scheme. The circuit is composed of two superconducting qubits coupled through a small Josephson junction with a time-dependent flux bias and two low-Q resonators each coupled to the qubits. The experiment requires calibration of the static circuit parameters under DC flux biasing and mitigation of the flux cross-talks. Next, we demonstrate the generation of various sideband interactions required for the stabilization scheme by modulating the coupler using RF drives with appropriate frequencies, amplitudes, and phases. Finally, we compare our experimental results with the simulation and discuss the scope for further improvements. Our results pave the way towards the realization of the passively protected arbitrary logical qubit states from single-qubit error channels [1]. |
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B16.00012: Towards high-fidelity quantum operations with fluxonium qubits: Part II-experimental progress Hsiang-Sheng Ku, Gengyan Zhang, Tenghui Wang, Wenlong Yu, Hao Deng, Jingwei Zhou, Yingshan Zhang, Hantao Sun, Zhijun Song, Xiaohang Zhang, Chengchun Tang, Ran Gao, Hua Xu, Zhisheng Li, Jin Qin, Xun Jiang, Xing Zhu, Huihai Zhao, Feng Wu, Dawei Ding, Chunqing Deng Superconducting quantum circuits, controlled and readout by using RF electronics, have demonstrated the potential to outperform classical computers. The state-of-art multi-qubit superconducting circuits are capable of performing two-qubit gates with infidelity less than 1%. To further improve the precision of superconducting quantum processors, qubits with longer coherence times and larger anharmonicities are desirable. Fluxonium, created by introducing a large linear inductance, is a promising candidate for the next generation quantum processors. In this talk, we present the experimental progresses on developing fluxonium quantum processors. The fabrication process and measurement results on qubit operations and readout are discussed. |
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B16.00013: Towards high-fidelity quantum operations with fluxonium qubits: Part I-design and simulation Hsiang-Sheng Ku, Gengyan Zhang, Tenghui Wang, Wenlong Yu, Hao Deng, Jingwei Zhou, Yingshan Zhang, Hantao Sun, Zhijun Song, Xiaohang Zhang, Chengchun Tang, Ran Gao, Hua Xu, Zhisheng Li, Jin Qin, Xun Jiang, Xing Zhu, Hui-Hai Zhao, Feng Wu, Dawei Ding, Chunqing Deng Superconducting quantum circuits, controlled and readout by using RF electronics, have demonstrated the potential to outperform classical computers. The state-of-art multi-qubit superconducting circuits are capable of performing two-qubit gates with infidelity less than 1%. To further improve the precision of superconducting quantum processors, qubits with longer coherence times and larger anharmonicities are desirable. Fluxonium, created by introducing a large linear inductance, is a promising candidate for the next generation quantum processors. In the talk, we present the design of fluxonium quantum processors. The simulation and optimization of the superconducting circuits and gates are discussed. |
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