The link doesn’t make it explicit, but a reversible machine intelligence which can actually reverse a measurement is a quantum computer. In this context, a measurement occurs when the AI purposefully entangles its computing elements with the electron. The AI can now choose whether to let the information it gains leak out of it or not. Provided it does not allow the entanglement between the electron and the outside world to increase, it can choose to unentangle its state from that of the electron. In the simplest case, where it does not allow the rest of its mind to become entangled with the part of itself that it is using as a measurement apparatus, all it need do is run the inverse of the unitary transform that it used to entangle the apparatus with the electron. However, it can theoretically do quite a bit more. It can use the information in other computations, and then carefully carry out an operation that restores the original state of the electron and turns the results it obtains into superpositions.
Humans don’t have such fine-grained control over where they shuffle quantum information, nor can they keep themselves from becoming entangled with their environment. Using macroscopic devices to register phosphorescence is right out.
It seems to me that this makes assumptions about entanglement and disentanglement which I find suspect (but I am not an expert on entanglement, so they may hold). It doesn’t appear to be “choosing” to unentangle its state from the electron- we’re assuming that the information it generates through entanglement is not leaked to the outside world, and that the information can be thrown away and the system returned to where it was before. If it’s making a choice, it seems that that choice would cause information leak.
If those assumptions hold, I don’t see why they hold for just MWI. That is, I believe it may be possible to get to a final situation where you have your initial configuration despite the fact that your apparatus poked the system- but I don’t think that gives you any meaningful information differentiating the flavors of QM.
Quantum Information cannot be thrown away. Nor can it be copied. Information is conserved. *Apart, perhaps, from Copenhagen collapse). Information can be made difficult to retrieve by e.g. entanglement with the environment, specifically propagating modes that take it beyond your control, but it’s still “in principle” there.
Is there a meaningful difference between “propagating modes that take it beyond your control” and “throwing it away”? In my mind, the first is a much longer restatement of the second, but I apologize that it was unclear. (Here, you’re throwing it back into the electron, not the outside world, but the idea is the same from the computer’s point of view.)
Yes, they have very different effects. Throwing it into the electron allows recoherence in principal. Throwing it into the environment makes that impossible.
The link doesn’t make it explicit, but a reversible machine intelligence which can actually reverse a measurement is a quantum computer. In this context, a measurement occurs when the AI purposefully entangles its computing elements with the electron. The AI can now choose whether to let the information it gains leak out of it or not. Provided it does not allow the entanglement between the electron and the outside world to increase, it can choose to unentangle its state from that of the electron. In the simplest case, where it does not allow the rest of its mind to become entangled with the part of itself that it is using as a measurement apparatus, all it need do is run the inverse of the unitary transform that it used to entangle the apparatus with the electron. However, it can theoretically do quite a bit more. It can use the information in other computations, and then carefully carry out an operation that restores the original state of the electron and turns the results it obtains into superpositions.
Humans don’t have such fine-grained control over where they shuffle quantum information, nor can they keep themselves from becoming entangled with their environment. Using macroscopic devices to register phosphorescence is right out.
It seems to me that this makes assumptions about entanglement and disentanglement which I find suspect (but I am not an expert on entanglement, so they may hold). It doesn’t appear to be “choosing” to unentangle its state from the electron- we’re assuming that the information it generates through entanglement is not leaked to the outside world, and that the information can be thrown away and the system returned to where it was before. If it’s making a choice, it seems that that choice would cause information leak.
If those assumptions hold, I don’t see why they hold for just MWI. That is, I believe it may be possible to get to a final situation where you have your initial configuration despite the fact that your apparatus poked the system- but I don’t think that gives you any meaningful information differentiating the flavors of QM.
Quantum Information cannot be thrown away. Nor can it be copied. Information is conserved. *Apart, perhaps, from Copenhagen collapse). Information can be made difficult to retrieve by e.g. entanglement with the environment, specifically propagating modes that take it beyond your control, but it’s still “in principle” there.
Is there a meaningful difference between “propagating modes that take it beyond your control” and “throwing it away”? In my mind, the first is a much longer restatement of the second, but I apologize that it was unclear. (Here, you’re throwing it back into the electron, not the outside world, but the idea is the same from the computer’s point of view.)
Yes, they have very different effects. Throwing it into the electron allows recoherence in principal. Throwing it into the environment makes that impossible.