Timothy C. Ralph

In conventional laser communications, classical information is transmitted by modulating the laser beam's amplitude and is measured via direct detection. Our research introduces a layer of quantum security to this standard process, specifically designed for free-space channels. We explore a hybrid communication method that simultaneously handles classical information in the traditional manner and quantum information through fluctuations in a sub-Poissonian noise-floor. Our approach utilizes a continuous-variable quantum key distribution (CV QKD) protocol, employing a Gaussian ensemble of squeezed states combined with direct detection. This allows for the generation of secure keys while maintaining classical communication, under passive attacks. This quantum-enhanced method offers simplicity, robustness, and efficiency without compromising classical data transfer rates. We have conducted detailed simulations to evaluate the protocol's performance in a free-space atmospheric channel and assessed the security of the CV QKD protocol in the composable finite-size scenario. This added quantum layer provides a practical, secure enhancement to standard laser communication systems.

We demonstrate continuous variable Gaussian entanglement distillation using a measurement-based noiseless linear amplifier. Our scheme relies on a heterodyne detection scheme, followed by a classical non-deterministic post selection of the measurements. We demonstrate that we are able to extract a subset of data presenting a stronger entanglement than the original resource, and that we can recover entanglement after transmission loss.