Improving Continuous-Variable Quantum Key Distribution with Shannon-Kotel'nikov Maps

We propose a continuous-variable quantum key distribution (CVQKD) protocol that uses a Shannon- Kotel'nikov expansion map for preparing coherent states. This kind of mapping acts like an analog error correcting code that improves the fidelity between the source signal and the reconstructed one at the receiver. It is well known that a limitation for extending CVQKD to larger distances is the reconciliation efficiency. Such lack of efficiency in reconciliation is mainly due to the difficulty of finding good error correcting codes for low signal-to-noise ratios. Having this limitation in mind, our protocol allows increasing the signal-to-noise ratio between Alice and Bob, thus making reconciliation easier.