Discrete, Tunable Color Entanglement

TL;DR

This paper demonstrates a novel hybrid quantum gate that transfers polarization entanglement onto the color degree of freedom, creating high-quality, discretely color-entangled photon states without filtering or postselection, advancing quantum communication capabilities.

Contribution

The work introduces the first experimental realization of high-quality, discretely color-entangled states transferred from polarization entanglement, with potential for generalization to other photonic degrees of freedom.

Findings

Created high-quality, discretely color-entangled states with up to 8.4 THz energy gap

Verified entanglement with a tangle of 0.611±0.009

Generated a set of maximally entangled states, including mutually unbiased bases

Abstract

Although frequency multiplexing of information has revolutionized the field of classical communications, the color degree of freedom (DOF) has been used relatively little for quantum applications. We experimentally demonstrate a new hybrid quantum gate that transfers polarization entanglement of non-degenerate photons onto the color DOF. We create, for the first time, high quality, discretely color-entangled states (with energy bandgap up to 8.4 THz) without any filtering or postselection, and unambiguously verify and quantify the amount of entanglement (tangle, 0.611$\pm$0.009) by reconstructing a restricted density matrix; we generate a range of maximally entangled states, including a set of mutually unbiased bases for an encoded qubit space. The technique can be generalized to transfer polarization entanglement onto other photonic DOFs, like orbital angular momentum.