Extending Coherence in Superconducting Qubits: From microseconds to milliseconds

Michel Devoret, Luigi Frunzio, S. M. Girvin +2 more

Abstract : This is the final report for the IARPA CSQ project at Yale University, on the coherence limits of superconducting charge qubits. During this project, we performed the proposed work investigating the various sources of decoherence and their origins in different materials, using the participation ratio paradigm that we developed and disseminated in the community. The original project goal was to increase by an order of magnitude the coherence time of the state-of-the-art qubits (transmons and fluxonium designs) from a few microseconds to greater than 20 microseconds. By project end, we realized qubit and cavity devices with times in excess of a millisecond, or an improvement by almost three orders of magnitude. These results, especially improved 3D designs, have been widely adopted and successfully reproduced by many groups across the superconducting qubit community. At program end, we have an existence proof that qubits satisfying the quantum error correction threshold are possible with existing materials and fabrication techniques, leading to a growing belief that large-scale quantum computation with solid-state devices will eventually be realized.

Antonio D. Corcoles, Jerry M. Chow, Jay Gambetta +7 more

Matthias Steffen, Antonio D. Corcoles, Jerry M. Chow +8 more

S. M. Girvin

1. Millisecond coherence in a superconducting qubit Authors: Aaron Somoroff, Quentin Ficheux, Raymond A. Mencia, Haonan Xiong, Roman V. Kuzmin, and Vladimir E. Manucharyan arXiv:2103.08578 2. New material platform for superconducting transmon qubits with coherence times exceeding 0.3 milliseconds Authors: Alexander P. M. Place, Lila V. H. Rodgers, Pranav Mundada, Basil M. Smitham, Mattias Fitzpatrick, […]

Diego Ristè, Cornelis Christiaan Bultink, M. J. Tiggelman +3 more

The tunnelling of quasiparticles across Josephson junctions in superconducting quantum circuits is an intrinsic decoherence mechanism for qubit degrees of freedom. Understanding the limits imposed by quasiparticle tunnelling on qubit relaxation and dephasing is of theoretical and experimental interest, particularly as improved understanding of extrinsic mechanisms has allowed crossing the 100 microsecond mark in transmon-type charge qubits. Here, by integrating recent developments in high-fidelity qubit readout and feedback control in circuit quantum electrodynamics, we transform a state-of-the-art transmon into its own real-time charge-parity detector. We directly measure the tunnelling of quasiparticles across the single junction and isolate the contribution of this tunnelling to qubit relaxation and dephasing, without reliance on theory. The millisecond timescales measured demonstrate that quasiparticle tunnelling does not presently bottleneck transmon qubit coherence, leaving room for yet another order of magnitude increase. Superconducting circuits are promising for quantum computing, but quasiparticle tunnelling across Josephson junctions introduces qubit decoherence. Ristè et al. convert a transmon qubit into its own real-time quasiparticle tunnelling detector and accurately measure induced decoherence in the millisecond range.

Irfan A. Siddiqi