A general mapping of qubit-based quantum communication protocols to coherent-states-based protocols is introduced, which provides a framework for transforming quantum communication protocols into a form that allows implementation with current technology.
We introduce a general mapping for encoding quantum communication protocols involving pure states of multiple qubits, unitary transformations, and projective measurements into another set of protocols that employ coherent states of light in a superposition of optical modes, linear optics transformations and measurements with single-photon threshold detectors. This provides a general framework for transforming a wide class of protocols in quantum communication into a form in which they can be implemented with current technology. In particular, we apply the mapping to quantum communication complexity, providing general conditions under which quantum protocols can be implemented with coherent states and linear optics while retaining exponential separations in communication complexity compared to the classical case. Finally, we make use of our results to construct a protocol for the Hidden Matching problem that retains the known exponential gap between quantum and classical one-way communication complexity.
Most of the quantum voting protocols are impractical due to the currently limited quantum storage capabilities. In this article, based on the interference principle of light, we proposed a new quantum voting protocol without quantum memory. In our protocol, the ballot is a sequence of non-orthogonal coherent states, the voting information is encoded by implying different phase shifts on the coherent states, and the vote counting is carried out by performing USD measurement on the coherent states. Particularly, the design of USD measurement on coherent states eliminates the need for quantum storage. Our protocol satisfies the general security requirements of quantum voting protocols and can resist various attacks. In addition, our protocol can be implemented by only linear optics and thus can be experimentally achieved with current technology.
For several decades, scientists have been aware of significant benefits allowing quantum information processing technologies to surpass their classical counterparts. Recent technological development allows these benefits to be tested experimentally and in some cases also implemented in practical devices. So far the majority of experimental quantum networks was limited to peer-to-peer communications between two parties. Practical implementation of quantum communications networks, however, needs to address the problem of scalability to serve large numbers of users. Similarly to classical computer networks, their quantum counterparts would require routing protocols to direct the signal from its source to destination. Devices implementing these routing protocols are called quantum routers and have recently been subject of an intense research. In this paper, we report on experimental implementation of a linear-optical quantum router. Our device allows single-photon polarization-encoded qubits to be routed coherently into two spatial output modes depending on the state of two identical control qubits. The polarization qubit state of the routed photon is maintained during the routing operation. The success probability of our scheme can be increased up to 25% making it the most efficient linear-optical quantum router developed to this date.