High efficiency measurement of a superconducting qubit using a directional, phase-sensitive, parametric amplifier

The measurement of a superconducting quantum bit is often performed by encoding its state in a single quadrature of a microwave field. Ideal measurement efficiency of this observable could in principle be achieved by noiselessly amplifying the information-carrying quadrature, but in practice is limited by technical losses due to circulators, cables and connectors used in state-of-the-art amplification chains.
In this talk we will discuss how one can approach ideal measurement efficiency by directly connecting a 3D transmon to a non-reciprocal phase-sensitive amplifier [1]. After describing the setup and tuning of the amplifier, we will extract the measurement efficiency by comparing the qubit dephasing rate to the measurement rate.
[1] F. Lecocq. et al, ‘Microwave measurement beyond the quantum limit with a nonreciprocal amplifier’, ArXiv 1909.12964 (2019)