Continuous variable quantum cryptography

TL;DR

A quantum key distribution scheme in which small phase and amplitude modulations of cw light beams carry the key information and the presence of EPR-type correlations provides the quantum protection.

Abstract

We propose a quantum cryptographic scheme in which small phase and amplitude modulations of CW light beams carry the key information. The presence of EPR type correlations provides the quantum protection.

Figures (3)

• Figure 1: Schematic of coherent light cryptographic set-up. AM is an amplitude modulator whilst PM is a phase modulator.
• Figure 2: Schematics of three eavesdropper strategies. Only the (a) is available in single quanta schemes.
• Figure 3: Schematic of squeezed light cryptographic set-up. Sqza and sqzb are phase locked squeezed light sources. Rna and Rnb are independent random number sources. Bs and pbs are non-polarizing and polarizing beamsplitters respectively. Half-wave plates to rotate the polarizations are indicated by $\lambda/2$ and optical amplification by $A$. The $\pi/2$ phase shift is also indicated. HD stands for homodyne detection system.