Cambridge University Press eBooks

Protocols with continuous variables

Gilles Van Assche

Published Jun 29, 2006• 0 citations

Abstract

The discrete modulation of quantum states as in BB84 stems fairly naturally from the need to produce zeroes and ones for the final secret key. But since secret-key distillation can also process continuous key elements, there is no reason not to investigate the continuous modulation of quantum states. In fact, continuous-variable protocols are fairly elegant alternatives to their discrete counterparts and allow for high secret key rates. In this chapter, I describe two important QKD protocols involving continuous variables: first a protocol involving the Gaussian modulation of squeezed states and then a protocol with coherent states. These QKD protocols must be seen as a source of Gaussian key elements, from which we can extract a secret key. Finally, I detail the implementation of the protocol with coherent states. From discrete to continuous variables In the scope of continuous-variable QKD, we focus on quantum states that are represented in a continuous Hilbert space, of which their most notable examples are the coherent and squeezed states. The BB84 protocol was designed with single photon states in mind. The coherent states, much easier to produce, are used only as an approximation of single photon states.

DOI: 10.1017/cbo9780511617744.013

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