Quantum key distribution using vacuum-one-photon qubits: maximum number of transferable bits per particle

TL;DR

This paper analyzes quantum key distribution using vacuum-one-photon qubits, showing it can transfer more bits per particle than traditional methods, especially with optimized measurements, reaching up to two bits per particle securely.

Contribution

It calculates the maximum secure bits per particle for BB84 and B92 protocols with vacuum-one-photon qubits, highlighting the advantage of generalized measurements.

Findings

Maximum of two bits per particle can be securely transferred with generalized B92.

Optimized unambiguous discrimination measurements significantly expand the parameter range for high transfer.

Vacuum-one-photon qubits outperform polarization or phase coding in bits transferred per particle.

Abstract

Quantum key distribution schemes which employ encoding on vacuum-one-photon qubits are capable of transferring more information bits per particle than the standard schemes employing polarization or phase coding. We calculate the maximum number of classical bits per particle that can be securely transferred when the key distribution is performed with the BB84 and B92 protocols, respectively, using the vacuum-one-photon qubits. In particular, we show that for a generalized B92 protocol with the vacuum-one-photon qubits, a maximum of two bits per particle can be securely transferred. We also demonstrate the advantage brought about by performing a generalized measurement that is optimized for unambiguous discrimination of the encoded states: the parameter range where the transfer of two bits per particle can be achieved is dramatically enhanced as compared to the corresponding parameter range of projective measurements.