Quantum

Quantum Telatar formula: fading quantum capacity of Haar-random multimode attenuators

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Based on a feed excerpt; full article content has not been acquired. Source evidence retrieved 13/11/2026, 07:43:25 UTC.

Briefings

A 2026 study by Telatar demonstrates that classical and quantum communication capacity in multimode fading channels scales linearly with the number of modes, even when the sender lacks precise channel knowledge. The research applies this to a Haar-random passive bosonic network at zero and nonzero temperatures, showing that quantum capacity grows linearly with modes at fixed photon numbers, mirroring classical antenna scaling. Numerical simulations confirm positive achievable rates for cryogenic microwave networks and room-temperature multimode fibers.

Key points

• Classical and quantum capacity of multimode fading channels scales linearly with the number of modes at fixed signal-to-noise ratio.
• Quantum capacity at zero temperature grows linearly with modes at fixed photon number per mode, matching classical antenna scaling.

Context

Cellular communication faces imperfectly predictable multimode environments where sender knowledge is limited to signal distribution. Telatar's proof shows this uncertainty does not hinder efficiency, with capacity growing linearly in modes. This applies to quantum information transmission in a Haar-random passive bosonic network.

Limitations

Quantum capacity at nonzero temperature is bounded below by Haar-averaged coherent information per mode, which converges to an integral against Wachter's law. Numerical results identify positive rates only for specific cryogenic and room-temperature fiber models.

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