Quantum Teleportation: Send a Qubit Without Sending a Qubit

Quantum teleportation is the most famous trick in the field and the most misunderstood. Nothing travels faster than light, and no matter is beamed anywhere. What moves is information: the complete quantum state of one qubit is reconstructed on another, using shared entanglement and two classical bits. In this walkthrough we teleport a qubit live and watch its state arrive intact. It is a one-click template in the ZKSF console.

What teleportation really transfers

You cannot read a qubit's state without destroying it, and you cannot copy it: the no-cloning theorem forbids a quantum photocopier. So how do you move an unknown state from one qubit to another? Teleportation answers this. Alice has a qubit in some unknown state she wants to give Bob. They share an entangled pair beforehand. Alice makes a joint measurement on her qubit and her half of the pair, which yields two ordinary classical bits, and sends those bits to Bob. Bob applies one of four simple corrections, and his qubit is now in Alice's original state. Alice's copy is gone, as it must be, and the state has moved without any qubit crossing the gap.

The circuit

Our template lays this out on three qubits. Qubit 0 is Alice's message, prepared here to be about 75 percent likely to read 1. Qubits 1 and 2 are the shared entangled pair, one held by Alice and one by Bob. Alice entangles her message with her half of the pair and applies a Hadamard, the equivalent of her joint measurement. The two corrections Bob would apply, conditioned on Alice's results, are written here as a CNOT and a controlled-Z, so the whole protocol runs as one circuit. We then measure only Bob's qubit.

OPENQASM 2.0;
include "qelib1.inc";
qreg q[3];
creg c[1];
ry(2.0944) q[0];        // Alice's state, ~75% |1>
h q[1];
cx q[1],q[2];           // the shared Bell pair
cx q[0],q[1];
h q[0];                 // Alice's Bell measurement
cx q[1],q[2];           // Bob's X correction
cz q[0],q[2];           // Bob's Z correction
measure q[2] -> c[0];

In the diagram, the blue Ry on q0 prepares Alice's state. The Hadamard and CNOT on q1 and q2 build the entangled pair. The middle block is Alice's side of the protocol; the CNOT and controlled-Z reaching down to q2 are Bob's corrections. Only Bob's qubit is measured at the end, because Bob's qubit is where Alice's state should now live.

Running it live: the state arrives

Alice's qubit was prepared to read 1 with probability 0.75 and 0 with probability 0.25. If teleportation works, Bob's qubit, which never touched Alice's directly, should show the same split. We ran the circuit on ZKSF at 1,000 shots on the exact statevector engine:

counts:     {"1": 741, "0": 259}
error_info: {"method": "exact statevector",
             "truncation_error": 0.0,
             "shot_noise_only": true, "shots": 1000}

Bob measured 1 in 741 shots and 0 in 259, a 74 to 26 split. That is Alice's original 75/25 state, reproduced on a qubit at the other end of the circuit, within shot noise. The state made the trip. The run carries a public ZCC-v0.1 certificate.

Why it matters, and the simplest quantum program

Teleportation is not a party trick. It is the transport layer of a future quantum internet, the way distant quantum processors will exchange states, and it is the mechanism behind gate teleportation, a building block of fault-tolerant quantum computing. Its ingredient list, a shared Bell pair plus two classical bits, is the standard unit of quantum communication.

If teleportation is the flashiest short circuit, the simplest is its opposite number: a single Hadamard followed by a measurement is a true random number generator, a coin flip whose outcome is fundamentally unpredictable rather than merely hard to guess. Between those two, one line and eight lines, sits most of what makes quantum computing feel different.

Try it yourself

Choose Quantum teleportation in the console and run it. Change the Ry angle on Alice's qubit to teleport a different state and watch Bob's distribution follow. The entanglement it relies on is built in the GHZ walkthrough, and the six templates together are the fastest way to go from curious to running real quantum circuits.