B Quantum info and its indestructability

[sayetsu]

TL;DR Summary

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)?

 

[EPR]

Please provide a proper reference which states that information cannot be destroyed.

 

[sayetsu]

Quantum no-hiding theorem experimentally confirmed for first time (phys.org)

 

[EPR]

Something's amiss. If this were true, the quantum eraser experiment wouldn't be possible.

 

[PeterDonis]

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.

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.

 

[PeterDonis]

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.

 

[sayetsu]

But what are quantum states and unitarity? What do these words mean?

 

[PeterDonis]

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?

 

[sayetsu]

Some, yes. More than the average bear.

 

[PeterDonis]

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?

 

[sayetsu]

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.

 

[PeterDonis]

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.

 

[sayetsu]

Thanks! :)