Experimental orthogonalization of highly overlapping quantum states with single photons

TL;DR

This paper demonstrates a linear optical quantum protocol that induces effective nonlinearity through measurement, enabling the orthogonalization of highly overlapping quantum states and advancing quantum information processing capabilities.

Contribution

It introduces an experimental method to realize quantum nonlinearity using linear optics and measurement, facilitating quantum state discrimination.

Findings

Successful implementation of nonlinear quantum protocol with single photons

Rapid convergence of similar states to orthogonal states through iteration

Potential for enhanced quantum information processing applications

Abstract

We experimentally realize a nonlinear quantum protocol on single-photon qubits with linear optical elements and appropriate measurements. The quantum nonlinearity is induced by post-selecting the polarization qubit based on a measurement result obtained on the spatial degree of freedom of the single photon which plays the role of a second qubit. Initially, both qubits are prepared in the same quantum state and an appropriate two-qubit unitary transformation entangles them before the measurement on the spatial part. We analyze the result by quantum state tomography on the polarization degree of freedom. We then demonstrate the usefulness of the protocol for quantum state discrimination by iteratively applying it on either one of two slightly different quantum states which rapidly converge to different orthogonal states by the iterative dynamics. Our work opens the door to employ effective quantum nonlinear evolution for quantum information processing.