Bosonic Quantum Communication across Arbitrarily High Loss Channels

Area of Science:

• Quantum Information Theory
• Quantum Optics
• Quantum Communication

Background:

• General attenuators are bosonic quantum channels modeled as beam splitters combining input with an environment state.
• Thermal attenuators, a specific case, have vanishing quantum capacity for transmissivity λ≤1/2.

Purpose of the Study:

• To investigate the quantum capacity of general attenuators for arbitrary environment states σ.
• To determine if constant-rate quantum communication is achievable under specific conditions.

Main Methods:

• Analysis of quantum channels Φ_{λ,σ} using beam splitter models.
• Mathematical derivation of quantum capacity for generic environment states σ.
• Exploration of energy-constrained scenarios.

Main Results:

• Demonstrated that for any λ>0, a specific environment state σ(λ) exists, yielding a quantum capacity greater than a universal constant c>0.
• Showed that constant-rate quantum communication is possible even with arbitrarily low transmissivity if the environment state is controlled.
• Identified environment states σ for which quantum capacity is not monotonic with λ.

Conclusions:

• Quantum capacity is not limited by low transmissivity in general attenuators when the environment state is optimized.
• Findings suggest potential for robust quantum communication in integrated optical circuits.
• The control of environment states is crucial for maintaining quantum communication rates.