Quantum Nondemolition Dispersive Readout of a Superconducting Artificial Atom Using Large Photon Numbers
Résumé
Reading out the state of superconducting artificial atoms typically relies on dispersive coupling to a readout resonator. For a given system noise temperature, increasing the circulating photon number n ¯ in the resonator enables a shorter measurement time and is therefore expected to reduce readout errors caused by spontaneous atom transitions. However, increasing n ¯ is generally observed to also monotonously increase these transition rates. Here we present a fluxonium artificial atom in which, despite the fact that the measured transition rates show nonmonotonous fluctuations within a factor of 6, for photon numbers up to n ¯ ≈200 , the signal-to-noise ratio continuously improves with increasing n ¯ . Even without the use of a parametric amplifier, at n ¯ =74 , we achieve fidelities of 99% and 93% for feedback-assisted ground and excited state preparations, respectively. At higher n ¯ , leakage outside the qubit computational space can no longer be neglected and it limits the fidelity of quantum state preparation.
Domaines
Planète et Univers [physics]
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