Energy-efficient quantum non-demolition measurement with a spin-photon interface

TL;DR

This paper proposes a quantum non-demolition measurement scheme using a spin-photon interface that leverages quantum superpositions of photon states for improved distinguishability and energy efficiency in quantum measurements.

Contribution

It introduces a Hamiltonian-based analysis showing quantum superpositions outperform coherent states in QND measurements, with robustness against device imperfections.

Findings

Quantum superpositions provide better distinguishability than coherent states.

Quantum pulses are more energy-efficient for QND measurements.

The scheme is robust against current device imperfections.

Abstract

Spin-photon interfaces (SPIs) are key devices of quantum technologies, aimed at coherently transferring quantum information between spin qubits and propagating pulses of polarized light. We study the potential of a SPI for quantum non demolition (QND) measurements of a spin state. After being initialized and scattered by the SPI, the state of a light pulse depends on the spin state. It thus plays the role of a pointer state, information being encoded in the light's temporal and polarization degrees of freedom. Building on the fully Hamiltonian resolution of the spin-light dynamics, we show that quantum superpositions of zero and single photon states outperform coherent pulses of light, producing pointer states which are more distinguishable with the same photon budget. The energetic advantage provided by quantum pulses over coherent ones is maintained when information on the spin state is extracted at the classical level by performing projective measurements on the light pulses. The proposed schemes are robust against imperfections in state of the art semi-conducting devices.