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Quantum Teleportation
Computation desk
Quantum teleportation moves an unknown quantum state from one qubit to another. It uses a shared entangled pair and two classical bits. The Computation desk treats it as a small circuit with a clear accounting of what is consumed.
- Unknown state, qubit 1
- Bell measurement, qubits 1 and 2
- Entangled pair, qubits 2 and 3
- Two classical bits
- Pauli correction on qubit 3
The arrangement
Two parties share an entangled pair of qubits. The sender also holds a third qubit in a state she does not know. The receiver holds the other half of the pair. The aim is to leave the receiver's qubit in the sender's unknown state.
The sender entangles her unknown qubit with her half of the pair, then measures both of her qubits. In the language of the quantum circuit model, that is a controlled-NOT, a Hadamard gate and two measurements. The result is two classical bits.
What the classical bits do
The two bits select one of four outcomes. Each outcome leaves the receiver's qubit related to the original state by a known Pauli operation. Before he hears the bits, his qubit looks random to him. It carries no usable information.
Once the bits arrive, he applies the matching correction. The measurement and the conditional gate form a small hybrid execution pattern. A classical result decides which quantum operation runs next. Without that channel the protocol fails, and no signal passes faster than light.
What the desk would check
The protocol is small enough to check exactly in a state-vector simulation. The desk would compare the receiver's final state with the intended one for each of the four measurement branches. We state that as a plan. We have not recorded the outcome here.
Real devices add imperfect entanglement and imperfect gates. They also add readout error. Those effects belong under noise and error, and the way outcomes are gathered belongs under measurement and sampling. Teleportation fidelity depends on both. We do not quote a figure for it.
Finding from this desk
The protocol transfers a state, not matter or energy. It needs one entangled pair and two classical bits, and it destroys the original. The classical bits are why it cannot carry a signal faster than light. This note records no run and no measured result.