Beating the channel capacity limit for superdense coding with entangled ququarts

TL;DR

This paper demonstrates that using high-dimensional entangled ququarts in superdense coding surpasses the traditional channel capacity limit of 2, achieving a capacity of approximately 2.09 and enabling high-fidelity transmission of complex information.

Contribution

The experiment shows that high-dimensional entanglement with ququarts can exceed the known channel capacity limit for superdense coding, advancing quantum communication capabilities.

Findings

Channel capacity exceeded 2, reaching 2.09

Fidelities of entangled ququarts up to 0.98

Successful transmission of a five-color image with 0.952 fidelity

Abstract

Quantum superdense coding protocols enhance channel capacity by using shared quantum entanglement between two users. The channel capacity can be as high as 2 when one uses entangled qubits. However, this limit can be surpassed by using high-dimensional entanglement. We report an experiment that exceeds the limit using high-quality entangled ququarts with fidelities up to 0.98, demonstrating a channel capacity of $2.09\pm0.01$. The measured channel capacity is also higher than that obtained when transmitting only one ququart. We use the setup to transmit a five-color image with a fidelity of 0.952. Our experiment shows the great advantage of high-dimensional entanglement and will stimulate research on high-dimensional quantum information processes.