Coherent manipulation of Andreev states in superconducting atomic contacts

TL;DR

This paper demonstrates the coherent control and readout of Andreev bound states in superconducting weak links, establishing a new type of qubit with microsecond coherence times for quantum information and fundamental physics studies.

Contribution

It introduces the first coherent manipulation and single-shot readout of Andreev bound states, a microscopic quasiparticle system in superconductors, as a new qubit platform.

Findings

Excited state lifetime and coherence time are in the microsecond range.

Quantum jumps and parity switchings are observed during continuous measurements.

Andreev qubits serve as a testbed for studying elementary excitations in superconductors.

Abstract

Coherent control of quantum states has been demonstrated in a variety of superconducting devices. In all these devices, the variables that are manipulated are collective electromagnetic degrees of freedom: charge, superconducting phase, or flux. Here, we demonstrate the coherent manipulation of a quantum system based on Andreev bound states, which are microscopic quasiparticle states inherent to superconducting weak links. Using a circuit quantum electrodynamics setup we perform single-shot readout of this "Andreev qubit". We determine its excited state lifetime and coherence time to be in the microsecond range. Quantum jumps and parity switchings are observed in continuous measurements. In addition to possible quantum information applications, such Andreev qubits are a testbed for the physics of single elementary excitations in superconductors.