  We present a scheme to encode M extra classical bits to a dense-coded pair of
photons. By tuning the delay of an entangled pair of photons to one of 2^M
time-bins and then applying one of the quantum dense coding protocols, a
receiver equipped with a synchronized clock of reference is able to decode M
bits (via classical time-bin encoding) + 2 bits (via quantum dense coding).
This protocol, yet simple, does not dispense several special features of the
used programmable delay apparatus to maintain the coherence of the two-photon
state. While this type of time-domain encoding may be thought to be ideally of
boundless photonic capacity (by increasing the number of available time-bins),
errors due to the environmental noise and the imperfect devices and channel
evolve with the number of time-bins.

Quantum Physics;Optics