Nonreciprocal microwave amplifier for efficient qubit measurements

In a typical circuit QED architecture, the dispersive coupling between a superconducting qubit and microwave resonator leads to state-dependent frequency shifts. By probing the cavity with a weak coherent state one can achieve a QND qubit readout, whose fidelity is directly tied to the measurement efficiency of the photons leaving the readout cavity. While developments in quantum-limited parametric amplifiers have enabled rapid single-shot qubit readout, these measurements require circulators to protect the device under test from amplifier backaction and to control signal flow. The losses inherent to the use of these nonreciprocal commercial components are now the primary bottleneck in the overall measurement efficiency.
In this talk I will describe a compact and lossless superconducting circuit that can be programmed in situ by a set of microwave drives to perform nonreciprocal frequency conversion and both phase-insensitive and phase-sensitive amplification [1]. We will discuss demonstrated device performance as well as our progress towards direct integration with superconducting qubits.
[1] F. Lecocq. et al, ‘Nonreciprocal Microwave Signal Processing with a Field-Programmable Josephson Amplifier’, Phys. Rev. Applied 7, 024028 (2017).