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.
Highlights
Quantum superconducting circuits based on Josephson tunnel junctions have become a leading platform in the pursuit of quantum computing [1]
We present a specific design of fluxonium qubits which repeatedly yield high-coherence times T2 at the half-integer flux bias, with the best device satisfying T2 > 400 μs
This is the longest coherence time found in a superconducting qubit today
Summary
Quantum superconducting circuits based on Josephson tunnel junctions have become a leading platform in the pursuit of quantum computing [1]. These artificial “atoms” can be printed on a chip in large numbers, wired together for strong interactions, and precisely manipulated and read out by radio-frequency electronics [2]. The Josephson tunnel junction provides the necessary nondissipative nonlinearity required to turn linear electrical circuits into quantum bits (qubits) and strong circuitcircuit coupling into fast logical operations. Decoherence introduces errors during gate operations [3] and constrains the number of qubits that can coherently tunnel in a quantum annealer [4]. With the growing interest in complex quantum processors [5,6,7,8,9], improving intrinsic coherence of superconducting qubits without sacrificing their controllability remains a central problem
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