Quantum info and its indestructability

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Discussion Overview

The discussion revolves around the nature of information, specifically quantum information, and its potential indestructibility. Participants explore the definitions of quantum states and unitarity, as well as the implications of these concepts on the destruction of information in quantum mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question the definition of information and its relationship to bits, specifically in the context of quantum information.
  • There are requests for references that support the claim that information cannot be destroyed.
  • One participant mentions the quantum no-hiding theorem and its experimental confirmation, suggesting it relates to the discussion on information preservation.
  • Concerns are raised about the implications of the quantum eraser experiment on the idea of indestructible information, with some arguing that if information were indestructible, the experiment would not be feasible.
  • Unitarity is presented as a property of quantum theory that supposedly guarantees the indestructibility of quantum information, with claims that unitary operations are reversible and do not create or destroy information.
  • Questions are posed about the meanings of "quantum states" and "unitarity," indicating a need for clarification on these fundamental concepts.
  • Participants share their backgrounds in quantum mechanics, with some expressing limited exposure to the terms discussed, leading to further inquiries about their educational experiences.

Areas of Agreement / Disagreement

Participants express differing views on the implications of quantum mechanics for information destruction, particularly regarding the quantum eraser experiment. There is no consensus on the definitions or interpretations of quantum states and unitarity, nor on the existence of definitive references regarding the indestructibility of information.

Contextual Notes

Some participants express uncertainty about their understanding of key terms and concepts, indicating a potential gap in foundational knowledge that may affect the discussion. The references requested by participants remain unprovided, leaving some claims unsubstantiated.

sayetsu
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TL;DR
Why can't information (or just quantum info?) be destroyed, and what is it?
What is information? IIRC it has something to do with bits. What is quantum information? Can either be destroyed? Why (not)?
 
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Please provide a proper reference which states that information cannot be destroyed.
 
Something's amiss. If this were true, the quantum eraser experiment wouldn't be possible.
 
  • Skeptical
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EPR said:
Please provide a proper reference which states that information cannot be destroyed.

Unitarity is the general property of any quantum theory which guarantees that quantum information cannot be destroyed.

EPR said:
If this were true, the quantum eraser experiment wouldn't be possible.

"Quantum eraser" is a very unfortunate misnomer for this experiment, since it involves unitary operations that do not create or destroy any information.
 
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sayetsu said:
What is quantum information?

The quantum state. It can't be destroyed because the evolution of the quantum state is unitary, and unitary operations cannot create or destroy information, since they are reversible.
 
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But what are quantum states and unitarity? What do these words mean?
 
sayetsu said:
what are quantum states and unitarity? What do these words mean?

First, a note: I have changed the level of this thread to "B" based on the questions quoted just above.

Second, have you ever studied any quantum mechanics?
 
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Some, yes. More than the average bear.
 
  • #10
sayetsu said:
Some, yes. More than the average bear.

And you have never encountered the terms "quantum state" or "unitarity" in your studies? That seems very unlikely if you have studied "more than the average bear", since those terms are basic QM terms that anyone who has studied any QM at all should have encountered.

Can you give some specific textbooks or other references that you have studied?
 
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  • #11
I've only encountered it academically in my college chem class. I don't know a lot, but the average bear couldn't tell you what a quark is, for example. That's what I meant.
 
  • #12
sayetsu said:
I've only encountered it academically in my college chem class.

Even there I would have expected at least some mention of the term "quantum state" (or "wave function"--perhaps you've seen that, it means the same thing). It's just the mathematical object that is used in QM to describe a system.

"Unitarity", for purposes of your question, is simply the fact that the time evolution of the quantum state/wave function is reversible. That means you can always recover any past state from the current state. Any reversible time evolution like this cannot create or destroy information.
 
  • #13
Thanks! :)
 

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