Experimental demonstration of tripartite entanglement and controlled dense coding for continuous variables.

Area of Science:

• Quantum optics
• Quantum information science
• Experimental physics

Background:

• Quantum entanglement enables advanced communication protocols.
• Einstein-Podolsky-Rosen (EPR) entangled states are crucial for continuous-variable quantum information.
• Controlled dense coding requires multipartite entanglement for enhanced capabilities.

Purpose of the Study:

• To experimentally generate a tripartite entangled state of bright optical fields.
• To demonstrate controlled dense coding among three parties (sender, receiver, controller).
• To analyze the performance improvements in signal-to-noise ratios and channel capacity.

Main Methods:

• Generation of tripartite entanglement using an EPR entangled state and linear optics.
• Implementation of controlled dense coding protocol.
• Measurement of "position" and "momentum" correlations.
• Calculation of signal-to-noise ratio improvements and channel capacity.

Main Results:

• Successful experimental production of a tripartite entangled state.
• Demonstration of controlled dense coding with significant improvements in signal-to-noise ratios (3.28 dB for amplitude, 3.18 dB for phase) beyond the shot noise limit.
• Controllable inversion of channel capacity between 2.91 and 3.14 at a mean photon number of 11.
• Prediction of exceeding ideal single-channel capacity for coherent and squeezed states under specific conditions.

Conclusions:

• Tripartite entanglement is a viable resource for advanced quantum communication protocols like controlled dense coding.
• The demonstrated protocol offers substantial improvements in signal detection and information transmission efficiency.
• Controlled dense coding with tripartite entanglement shows potential for surpassing classical and single-channel quantum communication limits.