Quantum teleportation is a technique for transferring quantum information from a sender at one location to a receiver some distance away. While teleportation is commonly portrayed in science fiction as a means to transfer physical objects from one location to the next, quantum teleportation only transfers [1] quantum information. The sender does not have to know the particular quantum state being transferred. Moreover, the location of the recipient can be unknown, but classical information needs to be sent from sender to receiver to complete the teleportation. Because classical information needs to be sent, teleportation cannot occur faster than the speed of light.

Quantum teleportation was first theoretically proposed in a 1993 paper Teleporting an unknown quantum state via dual classical and Einstein-Podolsky-Rosen channels by Charles Bennett, Gilles Brassard, Claude Crépeau, Richard Jozsa, Asher Peres, and William Wootters. It contained an ingenious idea that “an unknown quantum state can be disassembled into, then later reconstructed from, purely classical information and purely nonclassical Einstein-Podolsky-Rosen (EPR) correlations.

In the process of quantum teleportation, there is no physical spatial movement of matter or particles. Instead, it is the quantum state itself that gets destroyed on one quantum object and recreated elsewhere on another already existing quantum object. A qualification is in order here – it is not the quantum object itself that gets destroyed, but the information about its arbitrary quantum state. This “destruction happens via the processes of measurement, forcing the quantum object (or a qubit in the quantum computing sense) to assume one of the orthogonal states. This is also precisely the reason why the process of teleportation doesn not violate the no-cloning theorem – at no point does the same quantum state exist in two places [2], as original and a copy. In other words, as Eleanor Rieffel and Wolfgang Polak put it in their Quantum Computing: A gentle introduction – “at any given time, only one of Alice or Bob can reconstruct the original quantum state.” Additionally, as we shall see figure1 shows below, the teleportation protocol requires a classical communication channel between the two actors to be available too.

Figure1: Quantum Teleportation

Teleportation works

The initial quantum teleportation paper was theoretical, using the mathematical rules of quantum mechanics to predict the teleportation phenomenon. That prediction has since been followed by many experiments [3] demonstrating the effect. Furthermore, it turns out that quantum teleportation isn't just a fun stunt. It underlies many other phenomena in quantum computing and, more broadly, in quantum information science.

It's a fundamental tool in the toolkit of quantum computing, well-nigh as useful as a chef's knife in a kitchen. So let's get on with understanding it.

Teleportation portocal

The solution – the quantum teleportation protocol – is sufficiently simple that I'm just going to lay out the steps for you. After I've laid out the steps, it'll be pretty easy for us to verify that it works, and to discuss some implications. Note that you shouldn't expect to immediately see why the protocol works, or why we're using these steps in particular. Indeed, it would be shocking if you could! Rather, the point right now is to begin getting familiar with the basic mechanics of teleportation – the gates and measurements involved. Only later in the essay will we verify that these work, and gradually understand in more depth how to think about the protocol.

References:

1. en.wikipedia.org/wiki/Quantum_teleportation
2. https://www.strathweb.com/2020/09/introduction-to-quantum-computing-with-q-part-7-quantum-state-teleportation/#:~:text=%20Introduction%20to%20quantum%20computing%20with%20Q%23%20%E2%80%93,%E2%80%9CQuantum%20Entanglement%20as%20a%20Resource%20for...%20More%20
3. https://quantum.country/teleportation

Cite this article:

S. Nandhinidwaraka (2021) The Technology of Quantum Teleportation, AnaTechmaz, pp.12