Go further · Chapter 5 · 5a · Real-world case
What is quantum teleportation?
The short answer (tap to open)
Quantum teleportation moves the state of one particle onto another, far away, without sending the particle. It uses a shared entangled pair plus an ordinary message of two bits. The process destroys the original state, so nothing gets copied, and the message limits it to light speed or slower. It moves information, not matter.
What problem does it solve?
You can't simply measure a qubit and phone through the result: measuring changes the state (chapter 2) and reveals only one answer. And quantum rules forbid making a perfect copy of an unknown state, a result physicists call the no-cloning theorem (1982). So how do you move a qubit's exact state from London to Paris?
How does it work?
Alice and Bob each hold one photon of an entangled pair. Alice also has the qubit she wants to send.
- Alice measures her qubit and her half of the pair together, in a special joint measurement. She gets one of four results, two bits of information.
- That measurement destroys her qubit's state. At the same moment, Bob's photon ends up in one of four versions of that state, each a known twist away from the original.
- Alice sends Bob her two bits by any ordinary means: a phone call, a fibre, a radio.
- Bob applies the matching correction. His photon now carries exactly the state Alice's qubit had.
The four steps, in words
- Alice measures her qubit and her half of the pair together, in a special joint measurement. She gets one of four results, two bits of information.
- That measurement destroys her qubit's state. At the same moment, Bob's photon ends up in one of four versions of that state, each a known twist away from the original.
- Alice sends Bob her two bits by any ordinary means: a phone call, a fibre, a radio.
- Bob applies the matching correction. His photon now carries exactly the state Alice's qubit had.
Without the two bits, Bob's photon is pure randomness.
What isn't it?
It isn't Star Trek. No matter moves, only a state. It isn't faster than light: without Alice's two bits, Bob's photon is pure randomness. And it isn't copying: the process destroys Alice's original, so only one copy ever exists.
Has it been done?
Charles Bennett and five colleagues proposed it in 1993. Teams in Innsbruck and Rome did it with photons in 1997. In 2017 China's Micius satellite teleported states from the ground to orbit, up to 1,400 kilometres away. In 2025 a team at Oxford used teleportation to link two small quantum computers in separate boxes, a step towards quantum networks (chapter 13).
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Teleportation moves a state, not a thing.
Entanglement plus two ordinary bits, the original destroyed, and never faster than light.