Josephson parametric phase-locked oscillator and its application to dispersive readout of superconducting qubits

TL;DR

This paper demonstrates a Josephson parametric phase-locked oscillator (PPLO) for microwave signal demodulation and applies it to achieve high-fidelity, non-destructive readout of superconducting qubits with minimal photon usage.

Contribution

It introduces a Josephson-junction based PPLO for microwave demodulation and applies it to superconducting qubit readout, achieving high speed and fidelity with low photon numbers.

Findings

Successful demodulation of binary phase-shift keyed signals.

High-fidelity, single-shot qubit readout with over 90% Rabi contrast.

Low photon number requirement for effective qubit measurement.

Abstract

The parametric phase-locked oscillator (PPLO), also known as a parametron, is a resonant circuit in which one of the reactances is periodically modulated. It can detect, amplify, and store binary digital signals in the form of two distinct phases of self-oscillation. Indeed, digital computers using PPLOs based on a magnetic ferrite ring or a varactor diode as its fundamental logic element were successfully operated in 1950s and 1960s. More recently, basic bit operations have been demonstrated in an electromechanical resonator, and an Ising machine based on optical PPLOs has been proposed. Here, using a PPLO realized with Josephson-junction circuitry, we demonstrate the demodulation of a microwave signal digitally modulated by binary phase-shift keying. Moreover, we apply this demodulation capability to the dispersive readout of a superconducting qubit. This readout scheme enables a fast and latching-type readout, yet requires only a small number of readout photons in the resonator to which the qubit is coupled, thus featuring the combined advantages of several disparate schemes. We have achieved high-fidelity, single-shot, and non-destructive qubit readout with Rabi-oscillation contrast exceeding 90%, limited primarily by the qubit's energy relaxation.