Scientists at Kyoto University and Hiroshima University have achieved a breakthrough in quantum physics by successfully identifying the elusive W state of quantum entanglement, solving a 25-year-old challenge in the field[^1].
The team developed a method to measure entangled W states using photonic quantum circuits, demonstrating it successfully with three photons. This achievement is significant because W states, along with GHZ states, are fundamental building blocks for quantum networks[^1][^3].
"More than 25 years after the initial proposal concerning the entangled measurement for GHZ states, we have finally obtained the entangled measurement for the W state as well," said Shigeki Takeuchi, the study's corresponding author[^1].
The breakthrough enables single-shot identification of quantum states, eliminating the need for numerous measurements that grow exponentially with added photons. This advancement opens paths for:
- Quantum teleportation of information between distant locations
- New quantum communication protocols
- More efficient quantum computing methods
- Transfer of multi-photon quantum entangled states[^1][^8]
The research team used highly stable optical quantum circuits that could operate for extended periods without active control. They validated their method by successfully distinguishing different types of three-photon W states[^8].
[^1]: ScienceDaily - New quantum breakthrough could transform teleportation and computing
[^3]: RSInc - New Quantum breakthrough could transform Teleportation and Computing
[^8]: SciTechDaily - Scientists Capture W State, Unlocking Quantum Teleportation
wait wait wait, you're telling me they just claimed to invent the core technology for an ansible? FTL communications?
But this still requires the emissions of entangled photos from a single source right? and keeping the entangled photons entangled requires preventing them from being absorbed/split by interacting with molecules?
Hmm... maybe this means potential elimination of long-fiberoptic data lag (which is tiny)? Or can they actually capture entangled photos in separate systems for meaningfully long times to transport?
Woah, holy crappie, we are already a lot further along on this than I thought.
"Northwestern University engineers are the first to successfully demonstrate quantum teleportation over a fiberoptic cable already carrying Internet traffic."
Unfortunately not. Quantum teleportation is an awful name: it's called that way because it implies "destroying" a quantum state somewhere, and "recreating" it identically somewhere else, effectively transmitting information. However, the process also requires a classical information transfer at some point, and is absolutely not instantaneous . It's only useful for cryptography because it's mathematically impossible to listen in on this information being transferred without disturbing it.
It's one of the most unfavorable coolness-of-name vs. coolness-of-actual-thing ratio in physics.
The reason you are able to transfer an infinite-complex quantum state over a finite-complex classical communication channel is because the "quantum state" doesn't even exist, at least not in a single experiment. You can only ever measure it over an ensemble of systems, i.e. infinitely many systems prepared in the same way, as it is a statistical stat only. Your classical measurement results from the qubits to be "teleported" are also random, and you send that classical information over, and then that is used to construct another qubit in a particular state.
Over an ensemble of systems (repeating the experiment an infinite number of times), it's guaranteed the statistics on the qubit to be "teleported" will be transferred to now be the same as the statistics of the qubit it was "teleported" onto. Hence, you end up transferring the quantum state from one qubit to another using a classical channel. Quantum teleportation is trivial to reproduce in a classical model and it's not even inherently a "quantum" phenomena, see the Spekkens toy model for example.
It's not really that horrible of a name, because what the people who coined the term had in mind was something akin to Star Trek teleportation where you are not actually causing the object to disappear and reappear elsewhere nonlocally, but instead you are doing something "destructive" to the original object, transmitting information over a traditional communication channel, and then using that information to reassemble it with different material on the other end. Quantum teleportation is "destructive" to the original qubit in the sense that it places the qubit into a state that no longer matches what you are trying to transmit, but you gain enough information from doing this to transmit it to the other party who can use that information to (statistically) reconstruct the quantum state using their own qubits on their own end.
There are definitely more potential usages than cryptography (not really even sure I'd classify quantum direct communication as a kind of "cryptography" but that's nitpicking; it doesn't encrypt anything, it just lets you detect if someone physically disturbed the message in transit), precisely because it does it over a classical channel, that means the transfer would be much more robust to noise (and thus robust to decoherence). You need to establish an entangled Bell pair first before you can perform quantum teleportation which requires a quantum channel, but you can use quantum distillation to transfer many, many Bell pairs over a noisy network and then "distill" out a low-noise Bell pair, and then once you have achieved that you can then use quantum teleportation to transfer over a qubit via a classical communication channel.
I could also see it potentially being useful to transfer quantum information from one medium to another. Let's say you have qubits encoded in light and qubits encoded in electron spin and you want to transfer a qubit encoded on one onto the other. For example, in this paper they use quantum teleportation to transfer the information from one medium to the next.