Beating the channel capacity limit for superdense coding with entangled ququarts.

Area of Science:

• Quantum Information Science
• Quantum Communication

Background:

• Quantum superdense coding utilizes shared quantum entanglement to enhance communication channel capacity.
• The theoretical channel capacity limit using entangled qubits is 2.
• High-dimensional entanglement offers potential to surpass this qubit-based limit.

Purpose of the Study:

• To experimentally demonstrate superdense coding with high-dimensional entanglement (ququarts).
• To exceed the channel capacity limit achievable with entangled qubits.
• To showcase the practical application of high-dimensional entanglement in quantum information transfer.

Main Methods:

• Utilized high-quality entangled ququarts with fidelities up to 0.98.
• Implemented a quantum superdense coding protocol with these ququarts.
• Measured the resulting channel capacity and image transmission fidelity.

Main Results:

• Achieved a channel capacity of 2.09 ± 0.01, surpassing the qubit limit.
• Demonstrated a channel capacity higher than single-ququart transmission.
• Successfully transmitted a five-color image with a fidelity of 0.952.

Conclusions:

• High-dimensional entanglement significantly enhances quantum communication capacity.
• The experiment validates the advantage of using ququarts over qubits for superdense coding.
• This work stimulates further research into high-dimensional quantum information processing.