Entangled State Quantum Pulse Position Modulation for Communication Security

We present the Quantum Pulse Position Modulation (QPPM) protocol, which is an entanglement-based communications format approach designed to enhance the security of pulse position modulation (PPM) in optical communications. QPPM interleaves states from two-mode entangled light with thermal noise states resulting in a data transmission method that is stealthy and secure. We have calculated various quantum-information theoretic bounds, namely the Helstrom bound and the quantum Chernoff bound, for correctly decoding the transmitted symbols at the receiver. These bounds were computed numerically using a two-mode squeezed vacuum state to carry data, interleaved with a thermal state. A passive eavesdropper's inability to discriminate one half of a two-mode squeezed vacuum state from a thermal state renders them ineffective at identifying the presence of an active communication channel.