Fast quantum non-demolition readout from longitudinal qubit-oscillator interaction

TL;DR

This paper introduces a high-fidelity quantum non-demolition qubit readout method using longitudinal qubit-oscillator interaction modulated at the cavity frequency, enhancing measurement accuracy through squeezing and circuit QED implementation.

Contribution

It proposes a novel longitudinal coupling modulation technique for QND qubit readout, differing from traditional dispersive methods, with potential for multi-qubit architectures.

Findings

Exponential increase in signal-to-noise ratio via single-mode squeezing.

Implementation feasibility demonstrated in circuit quantum electrodynamics.

Potential for scalable multi-qubit readout architectures.

Abstract

We show how to realize high-fidelity quantum non-demolition qubit readout using longitudinal qubit-oscillator interaction. This is realized by modulating the longitudinal coupling at the cavity frequency. The qubit-oscillator interaction then acts as a qubit-state dependent drive on the cavity, a situation that is fundamentally different from the standard dispersive case. Single-mode squeezing can be exploited to exponentially increase the signal-to-noise ratio of this readout protocol. We present an implementation of this idea in circuit quantum electrodynamics and a possible multi-qubit architecture.