Recent content by Talisman

Here is Artur Ekert, a major figure in QIS, giving the single-qubit + environment example a year ago: The textbook version is here https://qubit.guide/12.2-decoherence-and-interference.html For better or worse, this usage does indeed seem to well-established in this particular field.

Sure, that's fair. This is physicsforums, after all, and not computerscienceforums. CS people (like Aaronson) tend to look for the simplest example that captures the interesting mathematical details, even if it loses important physical details, and that can indeed be problematic. I don't know...

Start with a pure state (the system + detector in Zurek's example, or the single qubit in mine). Maximally entangle it (with E in Zurek's case, or a second qubit in mine). If you now ignore / discard the second system, the first must be modeled as a mixed state. The off-diagonal terms...

Ah. The equations are identical to his 1991 paper, but I did not realize he had (and cannot find) earlier ones. Equation 13, p.10.

For whatever it's worth, I went and revisited Zurek's original paper (or at least, one of the originals) here: https://arxiv.org/abs/quant-ph/0306072 His example is to start with a system-detector state: $$|\uparrow\rangle|d_{\uparrow}\rangle + |\downarrow\rangle|d_{\downarrow}\rangle$$ And...

Perhaps I should be more clear here. I agree that nobody in their right mind actually prepares an entangled state, only to "lose" one of the partners, so as to make the other look incoherent, and then cries "decoherence." But using a well-defined state (like the one given here) exemplifies the...

Well, there are sub-communities within QC, based on specific implementation. Of course NMR-based labs will understand it to be T1 and T2 relaxation. Now that I've read up on those (both in N&C and Wikipedia), I see why they (T2 in particular) are described as loss of polarization information. At...

Anyway, all's well that ends well. They have a complete section on phase and amplitude damping, and those will probably help me understand those effects from the QC perspective, which is the one I understand best. Thanks again, and sorry for the confusion!

I honestly don't know how you took all this from the N&C quote. They simply say that there exists unfortunate confusion, which they even seem to be trying to correct by avoiding the term where possible. I would describe this as "seeming to occur to them": But I am happy to agree to disagree...

And on that note, here is what Nielsen & Chuang (the bible of QC -- at least when I was in school) have to say about the confusion:

I am prepared to accept that "decoherence" is more commonly used in the literature for uncontrolled entanglement because (1) the environment state is generally unknown and (2) what's the point of preparing a known entangled state if you're just going to ignore one of the partners? At the same...

Or, as Demystifier says here: https://www.physicsforums.com/threads/irreversibility-vs-reversibility.909761/ When it becomes "irreversible in practice" depends on the technology available to you.

I'm afraid we keep talking past each other, and I don't know how to resolve it. I will try one more time, but I am afraid I have reached the limit of my ability to communicate here. Yes, I agree that you can't know the state of a random photon passing through your lab. And yet it is also the...

Please see the example again. He writes down the state explicitly: ##\frac{|00\rangle + |11\rangle}{2}##. But it doesn't matter, because you can take the partial trace yourself and see that it results in the maximally mixed state that he (and others) equate with decoherence -- provided that you...

Yes, here he's giving an example of decoherence using two entangled qubits. https://www.scottaaronson.com/democritus/lec9.html He goes on to give exactly the same example of single-qubit interference that I do. I'm afraid it's very common in quantum computing, and you're going to have to...