In-cavity parametric amplification for qubit readout in 3D circuit QED architecture

High-efficiency qubit readout is essential for implementing quantum feedback and remote entanglement schemes as well as studying the basic physics related to quantum measurement processes. In circuit quantum electrodynamics (QED) systems, one typically reads out superconducting qubits by monitoring the qubit-state-dependent phase shift of a microwave tone, which is first amplified by a quantum-limited parametric amplifier before being processed by classical electronics. In this configuration, readout efficiency is mainly limited by the loss between the readout microwave resonator and the parametric amplifier. The optimized arrangement is therefore to place the latter inside the former. Here we introduce a design that uses two coupled transmon artificial atoms housed in a 3D readout cavity/waveguide to perform quantum-limited amplification within the circuit QED module. Compatible with 3D cold cavity attenuators, this layout minimizes the qubit dephasing induced by residual thermal photons and can potentially achieve the single-shot readout for qubits with long coherence times. Preliminary results will be presented.