Certifying the presence of a photonic qubit by splitting it in two

TL;DR

This paper demonstrates a method for detecting the presence of a photonic qubit by splitting it into two parts, enabling loss-sensitive quantum cryptography and nonlocality tests without destroying the qubit state.

Contribution

It introduces a photonic qubit precertification technique that heralds photon presence while preserving quantum information, enhancing quantum communication robustness.

Findings

Achieved up to 92.3% fidelity in qubit preservation

Enabled photon heralding without destroying quantum information

Potential for immediate application in quantum cryptography

Abstract

We present an implementation of photonic qubit precertification that performs the delicate task of detecting the presence of a flying photon without destroying its qubit state, allowing loss-sensitive quantum cryptography and tests of nonlocality even over long distance. By splitting an incoming single photon in two via parametric down-conversion, we herald the photon's arrival from an independent photon source while preserving its quantum information with up to $92.3\pm0.6$ % fidelity. With reduced detector dark counts, precertification will be immediately useful in quantum communication.