[HN Gopher] A Thermometer for Measuring Quantumness
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A Thermometer for Measuring Quantumness
Author : rbanffy
Score : 43 points
Date : 2025-10-03 12:24 UTC (10 hours ago)
(HTM) web link (www.quantamagazine.org)
(TXT) w3m dump (www.quantamagazine.org)
| Mr_Eri_Atlov wrote:
| Needs to be called a Steins Gate
| tsimionescu wrote:
| I'd be curious if someone who understands exactly what and how
| they are proposing this measurement works could speak on whether
| it would contradict the no-signalling theorem (and so, the effect
| can't be real).
|
| That is, given that destroying the correlation between two
| entangled particles can't be used to send information between the
| particles' locations, how could a measurement of whether a system
| contains entangled particles work? Does it just require all
| entangled particles to be present for the extra heat transfer to
| work?
| supernetworks wrote:
| "given that destroying the correlation between two entangled
| particles" i think this is the assumption that is easy to make
| without digging deeper into entanglement.
|
| i am still in the process of reading this article
| (https://arxiv.org/pdf/2408.06418) however entanglement
| witnesses can be realized in several ways and are one of the
| underlying aspects of how quantum networking can be made
| reliable.
|
| under the category of heralded entanglement, one realization
| uses photons striking photo detectors after they meet in a
| beamsplitter under the hong-ou-mandel effect scenario. for type
| 1 entanglement with HOM: if the photons at the two input modes
| are identical, they always bunch due to quantum interference,
| and if the photons resulted from emissions in the respective
| quantum nodes those nodes are now entangled, and the detection
| is the classical signal that the entangled link was created.
| the nodes can now transmit information unidirectionally into
| the entangled qubits. for type 2 entanglement with HOM it's a
| little bit more complicated although the underlying concept of
| indistinguishability is what results in the entanglement just
| the same.
|
| heres one experiment from oxford,
| https://www.nature.com/articles/s41586-024-08404-x, where they
| achieved this with high fidelity although the particular
| details of the beam splitter experiment are not as well
| detailed.
| dawnofdusk wrote:
| Although I am not an expert in quantum information, I think the
| problem you pose is resolved by the fact that the no-signalling
| theorem is about measurements of a quantum state, which is a
| microscopic state, and heat transfer is a measurement of a
| thermodynamic quantity, which is macroscopic. In much the same
| way that measuring the temperature of a classical gas doesn't
| give information on the location or momenta of the constituent
| particles, a thermodynamic probe of entanglement doesn't
| necessarily furnish precise information on how a state is
| entangled (e.g., Eq. 2 in https://arxiv.org/pdf/quant-
| ph/0406040).
| eigenket wrote:
| Yeah the whole entangled system is present and interacting with
| the "thermal ancilla" in their setup.
| ourmandave wrote:
| I have Absolute Zero interest in this.
| IncRnd wrote:
| Are you sure?
| czbond wrote:
| They're referencing the temperature Absolute Zero as a ...
| pun
| chermi wrote:
| Intro bugs me. Second law is "violated" all the time at small
| enough scales. Aka, fluctuation theorems. Of course the violation
| just means you're not really in the thermodynamic regime.
| Thermodynamics is kind of circularly defined, and that's fine.
| Thermodynamics is valid when it works. Temperature is emergent,
| it's only well defined, quantum or classically, for sufficient
| large system or sufficient strong coupling to bath. Rest of the
| articles seems fine, but I just hate these kind of set ups trying
| to make things more mysterious than they are.
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