Tradeoff between Leakage and Dephasing Errors in the Fluxonium Qubit

TL;DR

This paper explores how increasing circuit impedance in fluxonium qubits reduces dephasing errors exponentially while maintaining anharmonicity for fast gates, balancing leakage and dephasing errors.

Contribution

It demonstrates the tradeoff between leakage and dephasing errors in fluxonium qubits, highlighting how impedance tuning can optimize qubit performance.

Findings

Dephasing rate decreases exponentially with impedance increase.

Qubit remains anharmonic enough for short gate times.

Significant reduction in computational error rates achieved.

Abstract

We present a tradeoff between leakage and pure dephasing errors for the fluxonium circuit. We show that in the insulating regime, i.e., when the persistent current flowing across the circuit is suppressed, the pure dephasing rate decreases exponentially as the impedance of the circuit is increased. In contrast to this exponential decrease, the qubit remains sufficiently anharmonic so that gates times can still be short, allowing for significant reduction in the computational error rates.