The latest issue of *Science News * describes a quantum refrigerator using entangled qubits. There are three qubits involved. I’m not sure if all three are entangled or just two, but that doesn’t matter for my question.
Basically the idea is: There are two entangled qubits. One of these is warmed. That induces its entangled partner to siphon energy from the third qubit so that it warms up as well cooling the third qubit. They describe this as a refrigeration system, but my question is about information transfer.
I thought it was not possible to send information using quantum entanglement. All discussions I’ve seen indicate that entanglement somehow communicates the measured state “instantly” or faster than light speed, but that you can’t control which measured state will occur so no information can be sent and relativity is preserved. But here it seems they were actually warming one of the qubits, so it would seem you can communicate some information by choosing to do so or not or by how fast you warm it.
So it would seem that either I could potentially transmit information faster than c, or that entanglement in this system transfer the warming information slower than c. But then wouldn’t this imply a completely different channel of entanglement “communication”?
I am not a physicist or quantum mechanic by any stretch of the imagination, but to my layman’s knowledge, the third particle is as much an observer of the entangled pair as anything else. As soon as they become “adjacent” or in some way transmit information from one to the other, the waveform between the entangled pair collapses… or something. I think.
Thanks for the answer, but that’s not my question. Quantum entanglement is also called quantum non-local connectedness. See e.g.
Non-local means, as I understand it, that the entangled items can “communicate” to each other faster than the speed of light. Suppose you have two entangled electrons one of which is spin up and the other spin down. If you measure the spin of one, the other one “immediately” has the opposite spin when measured even if you measure this when they are physically separated and measure before a signal at the speed of light to “tell” the other electron the first was measured and how." Furthermore the EPR paradox and experiment
shows this cannot be because there is a hidden variable that set the spins ahead of time.
This does not directly violate relativity because there is no way to set the spin of one of the electrons so only random “information” is sent and random information isn’t really information at all.
But this experiment seems to indicate that you can warm one of the qubits or not warm it and that this information is transmitted by the entanglement. If this is correct, then information (whether you decided to warm or not) is being transmitted. If it’s transmitted by the same mechanism, it’s apparently being transmitted faster than c.
In the meantime, note that the resolution of these situations is always that the pop-sci article was misleadingly written and that, in fact, the tenets of quantum mechanics and relativity are still as you know them. (When this isn’t the case, you’ll know.)
I’m an avid SN reader and I saw that article but honestly, it didn’t make any sense to me. I figured I had to be missing something but since I didn’t even really get the point of the article, I just wrote it off.
I wanted to put that out there so you at least know others also had trouble with that particular article.
This isn’t an entanglement-driven system. The “quantum connection” mentioned in the SN article is just some arbitrary, relativity-respecting interaction. In the original journal article [Phys. Rev. Lett. 105, 130401 (2010)], the authors do not specify a particular interaction. An example, though, might be a weak spin-spin coupling amongst the individual qubits.
In short: one picks the energy levels of the three qubits such that a de-excitation of #3 releases the same amount of energy as a de-excitation of #1 plus an excitation of #2. If, due to a heat bath, #3 is rather likely to be in an excited state, then you’ll often find yourself in the scenario where the underlying interaction can swap the states around (#3 down, #1 down, #2 up) without requiring any work. Consequently, the probability that state #1 would be found in its ground state is higher than it would otherwise be, so one says it is “cooler”.
If useful: this scheme is akin to optical pumping.
Better: “If the analogy is useful, note that this scheme is akin to optical pumping” (…in case anyone misreads this as denying that the scheme is akin to optical pumping if it is not useful.)