Experimental Detection of Quantum Channel Capacities.

Area of Science:

• Quantum Information Science
• Quantum Communication
• Experimental Quantum Physics

Background:

• Quantum channels are essential for quantum communication but are susceptible to noise.
• Characterizing the capacity of noisy quantum channels is crucial for reliable quantum information transfer.
• Existing methods like quantum process tomography can be experimentally demanding.

Purpose of the Study:

• To present an efficient experimental procedure for certifying non-vanishing quantum capacities of qubit noisy channels.
• To establish a method that bypasses the need for quantum process tomography.
• To provide lower bounds for quantum capacities of unknown channels.

Main Methods:

• Utilizing a fixed bipartite entangled state with one qubit sent to the channel input.
• Performing local measurements on the channel output and ancilla qubit.
• Encoding entangled qubits in photon polarization and using a Bell state configuration.
• Estimating Shannon and von Neumann entropies using an optimized basis by measuring specific observables (σₓ⊗σₓ, σ<0xE1><0xB5><0xA7>⊗σ<0xE1><0xB5><0xA7>, σ<0xE2><0x82><0x9B>⊗σ<0xE2><0x82><0x9B>).

Main Results:

• Successfully certified non-vanishing quantum capacities for qubit noisy channels.
• Obtained lower bounds for quantum capacities without requiring quantum process tomography.
• Demonstrated the effectiveness of the proposed measurement strategy using optimized bases.

Conclusions:

• The presented experimental procedure offers an efficient way to certify quantum capacities of noisy qubit channels.
• The method provides a practical alternative to quantum process tomography for channel characterization.
• This work contributes to the understanding and reliable implementation of quantum communication protocols.