Quantum key distribution using squeezed light

Quantum key distribution, often abbreviated QKD, deals with the problem of transmitting a secure key between two parties, often named Alice and Bob. Classical channels can only be made conditionally secure by various forms of encryption. Conditionally secure means that the channel is secure as long as certain assumptions are made as to the abilities of a possible eavesdropper, Eve. Because of the inherent statistical nature of quantum mechanics it is possible to construct new communications protocols which are unconditionally secure, since the eavesdropper will be limited only by the laws of physics. It turns out that using squeezed light rather than the ordinary coherent laser states drastically improves the performance of these protocols, by at the same time increasing the range and minimizing the amount of data needed to create a secure key. Physically this happens because the correlations between Alice and Bob can be hidden in the squeezed quadrature so Eve will be unable to detect them and obtain useful information about the transmitted key. Depending on the type of attack Eve applies to the channel this attack will a ect the transmission of information. The aim of the QKD project is to investigate how the protocol  disguising of the data can be more or less effective, and the goal of the project is to investigate how the strongest possible behaves when the eavesdropper interferes the channel with a squeezed state of her own. Under certain assumptions this can be shown to be the strongest possible attack, and so it is important to investigate the performance of the protocol for this attack experimentally, to show that it stays secure.