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Synchronous Observation of Bell Nonlocality and State-Dependent Contextuality
- raattgift 4y agoPreprint at <https://arxiv.org/abs/2204.05385 https://arxiv.org/abs/2204.05385>
- p1esk 4y ago[flagged]
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- habibur 4y agoWhat's the implication? A faster than light message transmission possibility?
- hackandthink 4y agoThis won't happen and the paper does not speculate in any way about it. But they are vague about the implications and I'm generally unsure about the practical relevance of quantum protocols like superdense coding ...
- eigenket 4y agoSuperdense coding specifically is unlikely to ever be practically relevant. Even for people quite optimistic about the future of quantum computing it is hard to imagine a scenario where a single qubit will be cheaper than two classical bits. Other quantum protocols are much more likely to be useful, perhaps particularly for cryptography.
- amluto 4y agoI sometimes consider a qubit to be worth two classical bits in a very heuristic sense. One can superdense-code two bits into a qubit. Similarly, one can send two classical bits to teleport one qubit. Both of these require spending entanglement, so it’s not a very useful heuristic.
- hackandthink 4y ago"one can send two classical bits to teleport one qubit" How do you do this? (it goes against my intuition of a qubit as state in a hilbert space)
- hackandthink 4y ago"However, by taking advantage of two classical bits and an entangled qubit pair" Yes one needs entanglement. https://qiskit.org/textbook/ch-algorithms/teleportation.html https://qiskit.org/textbook/ch-algorithms/teleportation.html
- eigenket 4y agoThe cost is two classical bits and one entangled Bell pair to teleport a qubit. You make the Bell pair, send one half of it to Alice (who wants to transmit the qubit) and one half to Bob (who wants to receive it). Alice then does a Bell basis measurement on the qubit she wants to transmit and the half of Bell pair she owns. The Bell basis measurement has four outcomes. For convenience you can label them 00 01 10 11 Alice tells Bob the measurement outcome she got (this is the part that requires two bits of classical communication), and depending on which outcome she got Bob has to apply either no correction or a Pauli X, Y or Z gate. This is known as quantum teleportation https://en.wikipedia.org/wiki/Quantum_teleportation https://en.wikipedia.org/wiki/Quantum_teleportation and has quite a long history at this point (proposed in the early '90s and first performed in the late '90s).
- hackandthink 4y agoThanks, nice explanation.
- eigenket 4y agoThe no-communication theorem [1] fairly comprehensively rules out any attempt to send messages faster than light using quantum theory. It essentially says that in order to send any message using quantum mechanics you also have either physically move your system from place to place, or send some classical information (which can be smaller than your quantum message but have non-zero size). This means that in order to use quantum theory to send a message faster than light you either have to already have a way to move you quantum system faster than light, or a way to send classical messages faster than light. The summary is that you can only send messages ftl using quantum theory if you already know a way to send messages ftl without using quantum theory. [1] https://en.wikipedia.org/wiki/No-communication_theorem https://en.wikipedia.org/wiki/No-communication_theorem
- guerrilla 4y ago> contrary to the previous results, allows for joint violation of them. What does this mean? Wouldn't this be expected? Why wouldn't previous results have demonstrated this?
- eigenket 4y agoDetecting Bell-nonlocality requires two parties doing measurements on separated systems. Contextuality (in the formulation used here) is detected by measuring two out of a possible five measurements on a single particle. Quantum mechanics says you can't measure arbitrary observables simultaneously, so you can only choose two out of five rather than the whole set of five. A previous work combined the nonlocality and contextuality setup and showed that you couldn't detect the contextuality on one particle and the nonlocality between the two particles simultaneously. However the previous work assumed you only use the results of one of the two contextuality measurements you do as part of your nonlocality detection. I.e. the previous work had both measurements on particle A being used to detect contextuality, and used the results of one of those combined with the results of a measurement on particle B to detect nonlocality. In this work they show that if you lift this assumption, so the nonlocality is now being detected by both measurements on A as well as the measurement on B, you can detect the nonlocality and contextuality simultaneously.
- naasking 4y ago> In this work they show that if you lift this assumption, so the nonlocality is now being detected by both measurements on A as well as the measurement on B, you can detect the nonlocality and contextuality simultaneously Which makes me think that Bell was right that Bohmian mechanics places the real problem with QM, non-locality, front and centre where it can't be ignored.
- eigenket 4y agoWhile I disagree (quite strongly) with the claim that non-locality is a problem with QM (on the contrary it seems like an extremely interesting and useful property), I would like to know why you think this paper has anything specifically interesting for Bohemian mechanics rather than any other interpretation.
- qwerty456127 4y agoUnfortunately, Sci-Hub doesn't have the requested document
- eigenket 4y agoEssentially every paper in quantum info and foundations is posted on arxiv first before being submitted to a journal for publication https://arxiv.org/abs/2204.05385 https://arxiv.org/abs/2204.05385 just search for the paper name with the word arxiv after it on your favourite search engine and you'll find it 99% of the time. Usually when they get published in a real journal the arxiv version is updated to match the published version as well.
- 6gvONxR4sf7o 4y agoDoes this distinguish between any QM interpretations that we previously couldn’t rule out?
- eigenket 4y agonope