Embedded Amplifier for Efficient Superconducting Qubit Readout, Part 1: Theory

High fidelity qubit readout is a cornerstone of quantum computing. In superconducting architecture, this is typically achieved by routing signals from a readout cavity to a parametric amplifier via microwave circulators. The use of these off-chip components enables the independent design and optimization of the readout cavity and parametric amplifier. However, the intrinsic losses and large magnetic fields of these circulators reduces measurement efficiency and inhibits scalability. Our strategy to circumvent this is to perform the amplification and signal routing directly on-chip, by coupling a transmon qubit to a nonreciprocal multimode parametric system. As a consequence of this, the qubit and amplifier become a single open quantum system with a large Hilbert space. In this talk, we will discuss the theoretical challenges in understanding the quantum dynamics, focusing on extracting qubit measurement and dephasing rates.