No-cloning and stimulated emission

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Discussion Overview

The discussion centers on the relationship between stimulated emission and the no-cloning theorem in quantum mechanics. Participants explore whether stimulated emission can be considered a form of cloning and its implications for superluminal communication, addressing various aspects such as polarization, spontaneous emission, and the nature of quantum states.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants suggest that stimulated emission does not violate the no-cloning theorem because it does not clone an arbitrary and unknown state, as it only works for specific frequencies.
  • Others argue that the polarization of photons can encode arbitrary two-dimensional states, raising questions about the implications for cloning and communication.
  • A participant proposes that the entangled nature of the photons produced in stimulated emission complicates the notion of cloning.
  • Concerns are raised about spontaneous emission introducing noise, which may prevent the creation of perfect clones and thus hinder superluminal communication.
  • Some participants question the relevance of other properties of photons when discussing their polarization in the context of quantum computing.
  • A later reply challenges the idea that one can deduce the polarization of the original photon from the produced photons due to the influence of spontaneous emission.
  • There is a proposal that if one could clone the polarization of a photon, it could enable superluminal communication, but this is contested by others who cite the constraints of quantum field theory (QFT) and special relativity (SR).

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the implications of stimulated emission and the no-cloning theorem. The discussion remains unresolved, with no consensus on whether stimulated emission can be considered a form of cloning or if it allows for superluminal communication.

Contextual Notes

Participants highlight limitations related to the definitions of cloning, the role of spontaneous emission, and the specific conditions under which stimulated emission occurs. The discussion also touches on the complexities of quantum states and their representation in quantum field theory.

  • #31
greypilgrim said:
So one time out of three stimulated emission produces a V photon from an H photon? Does this mean the textbook treatment of stimulated emission is only true in two out of three times?
Yes, that's probably the simplest way to understand why stimulated emission does not allow perfect cloning. In an attempt of cloning there is always some probability for an error, even if a very small one. But imperfect cloning which tollerates an error is, of course, possible.
 
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  • #32
Do we need QFT to prove this? I guess so, since photons are described by QFT.

Interestingly though, the proof of the general no-cloning theorem only uses Hilbert space properties and doesn't need special relativity.
 
  • #33
greypilgrim said:
Do we need QFT to prove this? I guess so, since photons are described by QFT.

I think its more that in QFT particle numbers are not fixed so its required to explain particle creation.

This is actually a deep requirement of combining relativity and QM. See:
https://www.amazon.com/dp/019969933X/?tag=pfamazon01-20

It has a chapter giving the gory mathematical detail - contour integration and all.

Thanks
Bill
 

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