Quantum secure direct communication of digital and analog signals using continuum coherent states

In this work, we present optical schemes for secure direct quantum communication of digital and analog signals using continuum coherent states and frequency-dependent phase modulation. The main advantages of the proposed schemes are that they do not use entangled states and they can be implemented with today technology. The theory of quantum interference of continuum coherent state is described, and the optical setups for secure direct communication are presented and their securities are discussed.