The high-coherence fluxonium qubit

TL;DR

This paper demonstrates superconducting fluxonium qubits with coherence times exceeding 100 microseconds, challenging the belief that fewer Josephson junctions lead to better coherence, and highlights their potential for quantum computing.

Contribution

It presents fluxonium qubits with long coherence times despite having over 100 Josephson junctions, showing advantages for quantum computing applications.

Findings

Coherence times > 100 microseconds, up to 300 microseconds.

Coherence can be improved beyond 1 millisecond with current surface and flux noise levels.

Long coherence and large anharmonicity benefit quantum computing.

Abstract

We report superconducting fluxonium qubits with coherence times largely limited by energy relaxation and reproducibly satisfying T2 > 100 microseconds (T2 > 300 microseconds in one device). Moreover, given the state of the art values of the surface loss tangent and the 1/f flux noise amplitude, coherence can be further improved beyond 1 millisecond. Our results violate a common viewpoint that the number of Josephson junctions in a superconducting circuit -- over 100 here -- must be minimized for best qubit coherence. We outline how the unique to fluxonium combination of long coherence time and large anharmonicity can benefit both gate-based and adiabatic quantum computing.