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I just read another sensationally titled article in Quanta magazine, Physicists Use Quantum Mechanics to Pull Energy out of Nothing where they discuss the work of Masahiro Hotta on transferring energy from a distant lab to another by analyzing the quantum fields and vacua. Putting this theory aside, the article claims that two experimental results (Rodriguez-Briones et al (March 2022) and Ikeda (January 2023)) have been simulated using qubits, under what they call quantum energy teleportation. I want to focus the discussion on these demonstrations.

Looking at Ikeda's paper and a follow up paper it seems to me that quantum energy teleportation is just quantum state teleportation, in particular:

  • Alice wants to teleport energy to Bob
  • Alice and Bob start with a quantum system in the ground state
  • Alice performs some operations on her system (this leads either to an excited state or some superposition of ground state and other stuff)
  • Alice and Bob follow the usual quantum state teleportation protocol
  • Bob receives a quantum state that has in average more energy than the ground state

Is this what is happening in quantum energy teleportation (at least in the case where we use qubits instead of quantum fields) or is this an oversimplification?

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    $\begingroup$ I think these might be better described as energy encryption and decryption. There is energy available for use, but it is masked in a way that prevents it from being used for useful work and also there is information (Alice's measurement results) that if you knew you would be able to remove the mask. $\endgroup$ Feb 27, 2023 at 0:20
  • $\begingroup$ related: physics.stackexchange.com/q/754024/58382 $\endgroup$
    – glS
    Mar 7, 2023 at 14:59

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Here I'll answer with respect to the (Rodriguez-Briones 2022) paper - I'm not familiar with the Ikeda papers.

Your characterization doesn't seem quite right, especially the step "Alice and Bob follow the usual quantum state teleportation protocol". You can see in Fig. 2 of (Rodriguez-Briones 2022) that an example of this protocol can be done with just LOCC on an entangled (ground) state. This doesn't really map onto teleportation because Alice didn't really 'transmit' a state to Bob, she just modified her half of an entangled system and after using classical information Bob 'ended up with' a local state that he can extract energy from.

I spoke with a few of the authors of this paper and they sometimes preferred to describe what was happening in Bob's system as 'activation' instead of teleportation - Alice's actions and communication convert Bob's locally passive system (from which energy cannot be extracted via local CPTP maps) to an active system.

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Although Bob's qubit was at the beginning in ground state and finally it is in excited state, I think this is not pumping energy from nowhere.

Not only this is forbidden by Second law of thermodynamics, but you did a measurement on Alice side, then you transmitted information via classical line and Bob manipulated his qubit. All these require to do a work. And this is the reason why Bob's qubit is now on excited state. Moreover, the state is no longer with Alice, so energy was transferred from one qubit to another. Hence, energy is conserved and no perpetuum mobile takes place.

It seems that the authors focused only on one qubit at Bob and omitted other energy flows.

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    $\begingroup$ The articles are more careful than that (except for Quanta's usual titles). They are not claiming to pull energy from nowhere, they pump energy in one system and transfer it to the other using teleportation. $\endgroup$
    – Mauricio
    Feb 27, 2023 at 9:17
  • $\begingroup$ @Mauricio: Yes, however, it seems to me logical that energy is transferred in the teleportation as classical channel is involved. In classical telecommunication energy is also transferred via wire or optical fiber. $\endgroup$ Feb 28, 2023 at 7:36

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