QUROPE Quantum Information Processing and Communication in Europe

T. Lunghi, J. Kaniewski, F. Bussières, R. Houlmann, M. Tomamichel, A. Kent, N. Gisin, S. Wehner and H. Zbinden
Physical Review Letters 111, 180504 (2013)

Bit commitment is a fundamental cryptographic primitive in which Bob wishes to commit a secret bit to
Alice. Perfectly secure bit commitment between two mistrustful parties until recently was thought to be
impossible even when the parties exchange quantum messages.

However, Kent recently showed that perfect security is indeed theoretically possible, if Alice and Bob split
into several agents exchanging classical and quantum messages at times and locations suitably chosen to
satisfy specific relativistic constraints.

In their work Lunghi and colleagues report on the first implementation of a bit commitment protocol using
quantum communication based on the theoretical proposal of Kent but extended to be practical by including
experimental imperfections in the analysis. Their experiment demonstrates the possibility of implementing
commitments in real time, important as it shows their scheme is practical for situations where high speed
short term commitments are required. The work then combines quantum physics and special relativity to
perform a bit commitment protocol between Geneva and Singapore.