Optical qudit-type entanglement creation at long distances by means of small cross-Kerr nonlinearities

TL;DR

This paper proposes a method to generate entangled optical qudit states over long distances using weak cross-Kerr nonlinearities, leveraging a probe field and measurement-based enhancement despite practical noise and inefficiencies.

Contribution

It introduces a novel protocol for creating entangled qudit states with weak nonlinearities and noisy conditions, expanding feasible quantum communication methods.

Findings

Protocol works with limited nonlinearities and noise.

Entanglement can be probabilistically enhanced via measurement.

Applicable despite detector inefficiencies and dark counts.

Abstract

Entanglement represents an important resource for quantum information processing, but its generation itself requires physical resources that are limited. We propose a scheme for generating a wide class of entangled qudit-type states of optical field modes at sites separated by noisy medium when only weak optical nonlinearities are available at both sites. The protocol is also based on exploiting a weak probe field, transmitted between the sites and used for generation of quantum correlations between two spatially separated field modes. The idea of probabilistic entanglement enhancement by measurement is discussed, and corresponding scheme for measuring the probe field state with linear optics and photodetectors not resolving photon numbers is proposed. It is shown that the protocol is applicable in the case when decoherence, limited efficiency and dark counts of photodetectors, and uncertainty of nonlinear coupling constants are present.