Nondegenerate Noise-Resilient Superconducting Qubit
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dd96-gcb6.pdf
Description
Published version
Size
2.24 MB
Format
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Checksum (MD5)
99923582b62a1f3969e77ca7f02611e5
Author(s)
Hays, Max
Kim, Junghyun
Oliver, William D
Date Issued
October 30, 2025
Journal
PRX Quantum
Publisher
American Physical Society (APS)
Version
Final published version
Abstract
We propose a superconducting qubit based on engineering the first and second harmonics of the Josephson energy and phase relation 𝐸𝐽1cos𝜑 and 𝐸𝐽2cos2𝜑. By constructing a circuit such that 𝐸𝐽2 is negative and |𝐸𝐽1| ≪|𝐸𝐽2|, we create a periodic potential with two nondegenerate minima. The qubit, which we dub “harmonium,” is formed from the lowest-energy states of each minimum. Bit-flip protection of the qubit arises due to the localization of each qubit state to their respective minima, while phase-flip protection can be understood by considering the circuit within the Born-Oppenheimer approximation. We demonstrate with time-domain simulations that single- and two-qubit gates can be performed in approximately 100 ns. Finally, we compute the qubit coherence times using numerical diagonalization of the complete circuit in conjunction with state-of-the-art noise models. We estimate out-of-manifold heating times on the order of milliseconds, which can be treated as erasure errors using conventional dispersive readout. We estimate pure-dephasing times on the order of many tens of milliseconds, and bit-flip times on the order of seconds.
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DOI of Published Version
https://doi.org/10.1103/dd96-gcb6
