Embedded parametric amplification with intrinsic isolation for time-multiplexed qubit readout

Scalable high-fidelity readout of superconducting qubits remains challenging, in part because of the limitations of parametric amplifiers. State-of-the-art superconducting parametric amplifiers can near-noiselessly amplify signals with GHz bandwidth and sufficient saturation power for frequency-multiplexed qubit readout, but they require additional hardware to protect the coherence of the qubits from pump tones, reflections, and amplified noise. To address these challenges, we report on a directional amplifier that achieves non-reciprocity through a sequence of sequential parametric conversion and squeezing pulses. The device implements SWAP interactions of gaussian states among three electromagnetic modes: the readout resonator, the amplifier mode, and the output mode. While in the amplifier mode, the energy can be greatly amplified under isolation, enabling embedded directional parametric amplification with no circulators. The single output mode radiates all amplified information on-demand, regardless of the number of readout resonators. We will discuss the present performance of the amplifier, showing gain of 18 dB with output-to-input isolation of about 20 dB, and show the role of Kerr nonlinearity in degrading the amplification process. We also demonstrate how this can be immediately applied to time-multiplexed qubit readout.