Practical amplification for a single photon qudit encoded in three degrees of freedom

Abstract

A single-photon qudit encoded in more than one degree of freedom (DOF) can effectively enlarge a single photon’s capacity and has great potential for applications in future high-capacity quantum communication fields. During the photon transmission in practical noisy channels, photon qudits may suffer from photon transmission loss, which largely limits their application. In this paper, we propose a practical noiseless linear amplification (NLA) protocol for protecting the single-photon qudit encoded in polarization and double-longitudinal momentum DOFs. This NLA adopts the imperfect entangled state generated from a practical spontaneous parametric down-conversion (SPDC) source as the auxiliary state and can be realized under current experimental conditions. After performing the NLA protocol, the fidelity of the target single-photon qudit can be increased and the encoded information in all DOFs can be well preserved. We show the adoption of the imperfect entangled state generated from SPDC source is superior to that of the imperfect single-photon state from a practical heralded single-photon source. Our NLA protocol has application potential in current and future quantum communications.