Quantum dense coding without entanglement

TL;DR

This paper introduces a quantum cryptography protocol utilizing high-dimensional states that is experimentally feasible, error-tolerant, and offers higher efficiency than traditional BB84 protocols by leveraging time, polarization, and phase encoding.

Contribution

It presents a novel high-dimensional quantum cryptography protocol that operates without entanglement and achieves improved efficiency using existing technology.

Findings

Quantum protocol uses 24-dimensional states with polarization, phase, and time encoding.

Achieves a quantum bit-rate of 2 bits per transmission/detection.

Offers up to double the efficiency of BB84-like protocols.

Abstract

We describe a quantum cryptography protocol with up to twenty four-dimensional ($\mathcal{D} =4$) states generated by a polarization-, phase- and time-encoding transmitter. This protocol can be experimentally realized with existing technology, drawing from time-encoded and polarization-encoded systems. The protocol is error tolerant and has a quantum bit-rate of 2 per transmission/detection, which when combined with state detection efficiency yields a qubit efficiency of up to 1 or double that of BB84-{\it like} protocols.