Physicists Beat the Distance Record for Teleporting Light Into Matter

A team of physicists at the University of Geneva (UNIGE) has for the first time demonstrated quantum teleportation over a large distance between particles of light and particles of matter. Spanning 25 kilometers of optical fiber, the researchers successfully transported the quantum state of photon particles to the massive particles of a crystal.

The current distance record for quantum teleportation still stands at 143 kilometers. That was achieved last year in an experimental setup bridging two Canary islands with high-energy beams of light. The crucial distinction is that the Canary Islands experiment and most other such experiments teleport between light particles and other light particles, rather than the light particles into massive particles of the Geneva scheme.

A quick refresher on quantum teleportation. It's possible to take a bunch of particles and mix them together into a unified state where they're all together in a "superposition," which is that mystical-seeming property in which a particle is allowed to exist in many different configurations at once. Rather than having a set configuration, it instead lives as a wavefunction describing all of the probabilities of the particle being in this or that configuration. In a superposition, many particles can share the same set of probabilities.

When you actually measure the particle, peeling all of those probabilities away so that you're left with just the single current observation, the wavefunction is said to "collapse." The neat thing is that it collapses for all of the particles sharing the same wavefunction, even over long distances. That's quantum teleportation, a concept thought to have big implications for the communications and computing future.

This sort of teleportation doesn't actually have much to do with sci-fi teleportation. That is, it's not quite the possibility of super-liminal communication/transportation it's often made out to be (among other things, information about the initial wavefunction still has to be communicated via the normal, sub-light speed way), but it still has a whole lot of potential just as a viable mechanism for transporting information without having to transport something physical. In particular, it allows for the transportation of qubits, the quantum versions of classical bits that carry probabilistic information rather than discrete "1" or "0" information. Qubits are the foundation of quantum computing.

Teleporting between light particles and particles of matter is tricky business. The previous distance record for this sort of transfer is only 6 kilometers, which was achieved in the same University of Geneva lab.

The scheme works by first entangling a pair of photons (light particles), as you would in a conventional teleportation scheme. But, rather than merely moving one of the photons to some distant location, the photon is blasted at a crystal. The crystal then acquires the quantum state of the entangled photon pair, effectively becoming a memory bank. Next, a third photon is blasted at the first photon (the one that didn't meet the crystal), which results in a collapse of its wavefunction in a particular way which encodes information about the third photon, kind of like how a dent in a car encodes information about whatever caused it. This information is then effectively transported into the crystal.

So, a quantum state is then something that transcends the matter and light. This kind of resilience is at the very least another promising sign for the quantum future.

The latest UNIGE experiments are described in the journal Nature Photonics.