An Optical Implementation of Quantum Bit Commitment Using Infinite-Dimensional Systems

Unconditionally secure quantum bit commitment (QBC) was widely believed to be impossible for more than two decades, but recently, based on an anomalous behavior found in quantum steering, we proposed a QBC protocol which can be unconditionally secure in principle. The protocol requires the use of infinite-dimensional systems, so it may seem less feasible in practice. Here, we propose a quantum optical method based on the Mach–Zehnder interferometer, which gives a very good approximation to such infinite-dimensional systems. Thus, it enables a proof-of-principle experimental implementation of our protocol, which can also serve as a practically secure QBC scheme. Other multi-party cryptographic protocols such as quantum coin tossing can be built upon it too. Our approach also reveals a relationship between infinity and non-locality, which may have an impact on the research of fundamental theories.