Quantum non-demolition measurement of microwave photons using engineered quadratic interactions

TL;DR

This paper introduces a quantum electrical circuit with engineered quadratic interactions enabling quantum non-demolition measurement of microwave photons, achieving high fidelity detection of up to 10 photons over microsecond timescales.

Contribution

It presents a novel circuit design with quadratic coupling for non-demolition photon measurement, balancing coupling strength and photon storage capacity.

Findings

High fidelity detection of up to 10 photons

Measurement timescale of microseconds

Potential observation of quantum jumps

Abstract

We present a quantum electrical circuit with Josephson junctions formed of two anharmonic oscillators coupled with an interaction $g\gamma_{1}^{2}\gamma_{2}^{2}$ where $\gamma_{1}$ and $\gamma_{2}$ are position-like coordinates. This type of coupling allows the quantum non-demolition measurement of the energy of one oscillator by monitoring the frequency of the second oscillator. Despite the fundamental tradeoff between the coupling strength $g$ and maximum photon storage capacity of the oscillators, it is possible to achieve high fidelity detection of up to 10 photons over time scale of the order of microseconds. We discuss the possibility of observing quantum jumps in the number of photons and related applications.