Superdense Coding
Steps
Circuit
Initial State
Both qubits start in |0⟩.
What's happening?
Alice and Bob each have one qubit. They will share entanglement before Alice sends her message.
Key Insight
The entanglement must be established beforehand.
Bloch Spheres
Note: Individual Bloch spheres cannot fully represent entangled states.
Probabilities
Statevector |ψ⟩
| State | Amplitude | |ψ| | Phase | Prob |
|---|---|---|---|---|
| |00⟩ | 1 | 1.000 | 0 | 100% |
| |01⟩ | 0 | 0.000 | — | 0% |
| |10⟩ | 0 | 0.000 | — | 0% |
| |11⟩ | 0 | 0.000 | — | 0% |
Algorithm Overview
Send 2 classical bits of information using only 1 qubit transmission.
Classical Approach
Classically, 1 bit can carry at most 1 bit of information. Superdense coding beats this limit by using pre-shared entanglement as a resource.
Quantum Advantage
Doubles the classical capacity of a quantum channel. While entanglement distribution has a cost, in scenarios where entanglement can be pre-distributed, this provides a genuine advantage.
Complexity
Circuit depth: 6, Gate count: 6 (4 single-qubit, 2 two-qubit)
Applications
- •Quantum communication
- •Quantum networks
- •Entanglement-assisted communication
- •Quantum channel capacity
Try it yourself
Want to experiment with this circuit? Open it in the Playground to modify and explore.
Open in PlaygroundExercises and quizzes coming soon!