Designing optimal linear detectors -- a bottom-up approach

TL;DR

This paper presents a systematic method for designing optimal linear detectors with enhanced sensitivity, utilizing quantum network synthesis and exploring minimal and non-minimal realizations to achieve superior detection capabilities.

Contribution

It introduces a bottom-up approach for realizing linear detectors with optimized sensitivity, including the derivation of constraints and physical realization techniques.

Findings

Optimal detectors are identified as internal squeezing schemes.

Quantum non-demolition measurement is systematically recovered.

Minimal realization reduces internal modes for enhanced performance.

Abstract

This paper develops a systematic approach to realising linear detectors with an optimised sensitivity, allowing for the detection of extremely weak signals. First, general constraints are derived on a specific class of input-output transfer functions of a linear detector. Then a physical realization of transfer functions in that class is found using the quantum network synthesis technique, which allows for the inference of the physical setup directly from the input-output transfer function. By exploring a minimal realization which has the minimum number of internal modes, it is shown that the optimal such detectors are internal squeezing schemes. Then, investigating non-minimal realizations, which is motivated by the parity-time symmetric systems, a quantum non-demolition measurement is systematically recovered.