Minimizing the discrimination time for quantum states of an artificial atom

TL;DR

This paper demonstrates that by employing a high-dynamic-range amplifier and Bayesian inference, quantum state discrimination in superconducting artificial atoms can be significantly accelerated, surpassing the resonator response time.

Contribution

The study introduces a method combining a large dynamic range amplifier with Bayesian inference to minimize discrimination time for quantum states in superconducting artificial atoms.

Findings

Quantum jumps detected faster than the resonator response time.

Readout remained quantum-non-demolition up to high photon numbers.

Discrimination speed improved over two orders of magnitude in readout power.

Abstract

Fast discrimination between quantum states of superconducting artificial atoms is an important ingredient for quantum information processing. In circuit quantum electrodynamics, increasing the signal field amplitude in the readout resonator, dispersively coupled to the artificial atom, improves the signal-to-noise ratio and increases the measurement strength. Here we employ this effect over two orders of magnitude in readout power, made possible by the unique combination of a dimer Josephson junction array amplifier with a large dynamic range, and the fact that the readout of our granular aluminum fluxonium artificial atom remained quantum-non-demolition (QND) at relatively large photon numbers in the readout resonator, up to $\overline{n} = 110$. Using Bayesian inference, this allows us to detect quantum jumps faster than the readout resonator response time $2/\kappa$, where $\kappa$ is the bandwidth of the readout resonator.