Superdense Coding

Category: fundamentals  |  Difficulty: beginner  |  Qubits: 2  |  Gates: 6  |  Depth: 6

Superdense coding is the 'dual' of teleportation: it uses a shared entangled pair and a single qubit transmission to communicate 2 classical bits. Alice applies local Pauli operations to encode her 2-bit message, then sends her qubit to Bob. Bob performs a Bell measurement to decode the message. This circuit encodes '11'.

Expected Output

c[0]=1, c[1]=1 (message '11' decoded)

Circuit

The OpenQASM 2.0 circuit is in circuit.qasm.

OPENQASM 2.0;
include "qelib1.inc";
// Superdense coding — encodes classical message "11"
qreg q[2];
creg c[2];
// Preparation: create Bell pair
h q[0];
cx q[0],q[1];
// Alice encodes "11": apply X then Z to her qubit q[0]
x q[0];
z q[0];
// Bob decodes: reverse Bell circuit
cx q[0],q[1];
h q[0];
measure q[0] -> c[0];
measure q[1] -> c[1];

Tags

superdense-coding fundamentals entanglement communication

References

• Bennett & Wiesner (1992). Communication via One- and Two-Particle Operators. PRL 69, 2881

License

MIT — part of the OpenQC Algorithm Catalog.