When you enter the field of quantum communications, you run at some point into the concept of superdense coding.

Basically it is a way to encode classical bits on the qubits of a quantum channel, which sounds interesting in the first place to increase classical throughput by benefitting of the exponential growth of the Hilbert space with multiple qubits.

Yet when you look at the protocol in more detail, you understand that even though it seems that you have encoded 2 classical bits in 1 qubit, you actually need a second, entangled, qubit to retrieve the information from the 1st qubit.

So there is no real benefit - if you need to send two photons, you can encode two bits classically.

So apart from a textbook example, where is the practical interest? Are there more subtle points I am missing? Are there more intricatre protocols to avoid that?

Cross-posted on qc.SE

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    $\begingroup$ You might want to consider posting on the Quantum Computing Stack Exchange instead, as they may be more engaged with the latest on this topic. I hope this helps. $\endgroup$ – ad2004 Jan 1 at 21:56
  • $\begingroup$ Thanks for the advice! Done! $\endgroup$ – Mathias Jan 4 at 8:25

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