Efficient qubit measurements with a nonreciprocal microwave amplifier

In typical circuit quantum electrodynamics and microwave optomechanics system, the measurement of the observable of interest --- the state of a quantum bit or the position of a mechanical oscillator --- hinges on the efficient detection of the phase shift that it imparts on a microwave field. Ideal measurement efficiency can only be achieved with a lossless single quadrature measurement apparatus and has been a longstanding challenge. Nonreciprocal parametric amplifiers could enable such high measurement efficiency as they can be directly integrated with the quantum system, avoiding common technical losses due to circulators, cables and connectors used in state-of-the-art amplification chains.
In this talk we will discuss the measurement of a 3D transmon qubit with a Field-Programmable Josephson Amplifier (FPJA, [1]). The FPJA is programmed in situ by a set of microwave drives to perform reciprocal or nonreciprocal frequency conversion or amplification. For each mode of operation, we will monitor the qubit coherence and lifetime, as well as measurement efficiency and backaction.
[1] F. Lecocq. et al, ‘Nonreciprocal Microwave Signal Processing with a Field-Programmable Josephson Amplifier’, PHYSICAL REVIEW APPLIED 7, 024028 (2017)