Quantum dense coding

In quantum mechanics quantum dense coding refers to a method of "transmitting" two bits of data using a single particle from an EPR pair. There exists a set of states accessible from an initial EPR state using one-particle operations that allows two bits to be reliably encoded in one spin-1/2 particle. Alice prepares an EPR pair and sends one of the particles to Bob, who applies one of four unitary operators to the particle, and then returns it to Alice. By measuring the two particles jointly, Alice can reliably learn which of the four operators Bob used.

References

• C. Bennett and S.J. Wiesner. Communication via one- and two-particle operators on Einstein-Podolsky-Rosen states. Phys. Rev. Lett., 69:2881, 1992[1]