Superdense Coding

Superdense coding sends two classical bits by transmitting a single qubit — the mirror image of teleportation, powered by shared entanglement.

Ratio

2 classical bits per 1 qubit sent

Resource

1 pre-shared Bell pair

Dual of

teleportation

What it does

Alice and Bob pre-share a Bell pair. Alice encodes two bits by applying one of {I, X, Z, XZ} to her qubit, then sends it to Bob, who undoes the entanglement and reads both bits.

Where it's used

A conceptual cornerstone of quantum communication and a demonstration that entanglement is a usable resource.

In code (Qiskit)

# Alice: apply I/X/Z/XZ to encode 00/01/10/11
# Bob: CX, H, measure both