  In this letter we show that communication when restricted to a single
information carrier (i.e. single particle) and finite speed of propagation is
fundamentally limited for classical systems. On the other hand, quantum systems
can surpass this limitation. We show that communication bounded to the exchange
of a single quantum particle (in superposition of different spatial locations)
can result in "two-way signaling" which is impossible in classical physics. We
quantify the discrepancy between classical and quantum scenarios by the
probability of winning a game played by distant players. We generalize our
result to an arbitrary number of parties and we show that the probability of
success is asymptotically decreasing to zero as the number of parties grows,
for all classical strategies. In contrast, quantum strategy allows players to
win the game with certainty.

Quantum Physics