Verifiable homodyne measurement for detecting non-local properies of light

TL;DR

This paper introduces a verifiable homodyne detection scheme that reliably detects non-local properties of light without assuming ideal local oscillator pulses, closing potential loopholes in quantum optical measurements.

Contribution

The authors propose a new homodyne detection method that does not rely on ideal local oscillator assumptions, enhancing the reliability of quantum state measurements.

Findings

Verifiable detection scheme works without presuming ideal LO pulses

Closes loopholes caused by noise or malicious interference

Maintains effectiveness similar to conventional homodyne detection

Abstract

The homodyne detection is one of the most basic tools for identifying the quantum state of light. It has been used to detect useful non-local properties, such as entanglement for the quantum teleportation and distillability of a secret key in quantum key distribution. In so doing, the detection scheme employs a bright optical pulse, called the local oscillator (LO) pulse, and the LO pulse is usually transmitted along with the signal pulses. The LO pulse is presumed to be a coherent state with an infinite intensity. However, it is difficult in practice to hold this presumption owing to noise in the optical transmission channels or an intervention by a malicious third party. As a result, the implementation may no longer be the homodyne detection, and those outcomes may merely disguise successful detection of entanglement or a secret key. Here, we present an alternative scheme that works as the homodyne detection to detect the non-local properties of light in a verifiable manner, without any presumption for the LO pulses. This scheme is essentially based on the same setup as the conventional implementation for the homodyne detection. This result contributes to close any possible loophole in the homodyne detection caused by the deviation from the ideal LO pulses.