Experimental generation and characterization of partially spatially coherent qubits

TL;DR

This paper demonstrates the experimental generation of partially spatially coherent qubits via SPDC using a GSM pump beam, transferring classical coherence features to quantum biphotons, advancing free-space quantum communication.

Contribution

It is the first to experimentally show the transfer of spatial coherence from classical pump beams to quantum biphotons in SPDC, enabling tunable partially coherent qubits.

Findings

Successfully generated partially coherent qubits in SPDC.

Observed spatial profiles of partially coherent biphotons.

Confirmed multi-mode nature of the generated qubits.

Abstract

Partially spatially coherent qubits are more immune to turbulent atmospheric conditions than coherent qubits, which makes them excellent candidates for free-space quantum communication. In this article, we report the generation of partially spatially coherent qubits in a spontaneous parametric down-conversion (SPDC) process using a Gaussian Schell model (GSM) pump beam. For this non-linear process, we demonstrate experimentally for the first time, the transfer of spatial coherence features of the pump (classical) to the biphotons (quantum) field. Also, the spatial profiles of partially coherent qubits generated in type-I and type-II non-collinear SPDC process are experimentally observed and multi-mode nature of partially coherent photons (qubit) is ascertained. These investigations pave the way toward the efficient generation of partially spatially coherent qubits with a tunable degree of spatial coherence, which lead to wide range of applications in frontier areas such as quantum cryptography, teleportation, imaging, and lithography.