Minimizing the discrimination time for quantum states of an artificial atom

Understand

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.