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Oxford quantum computer recreates Aharonov–Bohm effect
The AB effect is very interesting as it shows how something changes because of the geometry not because of a force of some kind. Apparently, this result means more things in physics can be tested.
What is most interesting about the effect (not necessarily the quantum computing) is that two paths can have a different phase rotation even though classically the phase shifts should identical. The AB effect uses a test solenoid, and one path is around it one way and the other path is around it another way, and classically both paths should produce the same classical phase shift if any. Surprisingly, when there is flux through the solenoid the two paths, although the same, produce two different phase shifts and so a phase difference is measured. There is no classical explanation for this difference, but one thing interesting is that a single phase has no phase reference, it's only when the two phases are compared that it makes any sense. The conclusion must be that something caused the two phases to be different, and it is usually attributed to the potential. The potential acts almost like a rate of change of phase, and even that seems like it should be the same and I think it is, yet there is still a difference in phase. This is also sometimes referred to as the holonomy.
As an electronics example, imagine we have two filters A and B, and as compared to a reference one shifts the phase by 30 degrees and the other by 10 degrees. When we measure the phase difference between the two outputs, we should measure 20 degrees, but we measure something different like maybe 5 degrees, 37.3 degrees, etc. That's what happens with the AB effect. Although this would not really happen with the two electronic filters, imagine the surprise if we did see that kind of measurement. Because we usually think in classical terms, i am sure we would all immediately assume something was wrong with one of the filters and proceed to find out what is not working. With the AB effect though, everything has been tried when it comes to finding something 'wrong' with the experiments, and nothing ever turned up, yet the two phases are different. The only explanation seems to be that the gauge field has some unusual properties that causes this effect, yet I don't think anybody knows exactly why that field can cause this.
An interesting (but not an explanation) of how geometry can change things is an airplane flying north from the equator along some longitudinal line. When it gets to the north pole, it makes a right turn (a right turn would now point it to the right from out viewpoint of course). Now it follows another longitudinal line and when it reaches the equator it is now pointed down. So a right turn at the north pole (90 degrees) led to a change in angle of 180 degrees, just because of the way it moved, but it always moved along straight lines intrinsically.
A simple example might be it flies through the north pole, never turning, and down the back side to the equator. Now it is again pointing down. Here we never rotated it intrinsically but it rotated by 180 degrees globally.
To visualize this you have to imagine looking at a globe of the earth from one angle like right in front of the globe. Up is north, down is south, right is the right side of the globe, left is the left side.
When the plane moves it is assumed that it flies in the normal way which is mostly parallel to the tangent plane of the earth (globe) it flies over and heading in the given directions.
One of the ideas in the AB effect is that none of this takes any energy. Nothing comes up out of the flux to influence the two paths. If there was anything though (none ever measured though even at tiny tiny energy levels hard to imagine possible) it would be something that may be responsible for the gauge field, which could be magnetic monopoles. That has not been proven however, and as I am sure you know, magnetic monopoles have not been proved to exist either, yet.
Oxford quantum computer recreates Aharonov–Bohm effect
The AB effect is very interesting as it shows how something changes because of the geometry not because of a force of some kind. Apparently, this result means more things in physics can be tested.
What is most interesting about the effect (not necessarily the quantum computing) is that two paths can have a different phase rotation even though classically the phase shifts should identical. The AB effect uses a test solenoid, and one path is around it one way and the other path is around it another way, and classically both paths should produce the same classical phase shift if any. Surprisingly, when there is flux through the solenoid the two paths, although the same, produce two different phase shifts and so a phase difference is measured. There is no classical explanation for this difference, but one thing interesting is that a single phase has no phase reference, it's only when the two phases are compared that it makes any sense. The conclusion must be that something caused the two phases to be different, and it is usually attributed to the potential. The potential acts almost like a rate of change of phase, and even that seems like it should be the same and I think it is, yet there is still a difference in phase. This is also sometimes referred to as the holonomy.
As an electronics example, imagine we have two filters A and B, and as compared to a reference one shifts the phase by 30 degrees and the other by 10 degrees. When we measure the phase difference between the two outputs, we should measure 20 degrees, but we measure something different like maybe 5 degrees, 37.3 degrees, etc. That's what happens with the AB effect. Although this would not really happen with the two electronic filters, imagine the surprise if we did see that kind of measurement. Because we usually think in classical terms, i am sure we would all immediately assume something was wrong with one of the filters and proceed to find out what is not working. With the AB effect though, everything has been tried when it comes to finding something 'wrong' with the experiments, and nothing ever turned up, yet the two phases are different. The only explanation seems to be that the gauge field has some unusual properties that causes this effect, yet I don't think anybody knows exactly why that field can cause this.
An interesting (but not an explanation) of how geometry can change things is an airplane flying north from the equator along some longitudinal line. When it gets to the north pole, it makes a right turn (a right turn would now point it to the right from out viewpoint of course). Now it follows another longitudinal line and when it reaches the equator it is now pointed down. So a right turn at the north pole (90 degrees) led to a change in angle of 180 degrees, just because of the way it moved, but it always moved along straight lines intrinsically.
A simple example might be it flies through the north pole, never turning, and down the back side to the equator. Now it is again pointing down. Here we never rotated it intrinsically but it rotated by 180 degrees globally.
To visualize this you have to imagine looking at a globe of the earth from one angle like right in front of the globe. Up is north, down is south, right is the right side of the globe, left is the left side.
When the plane moves it is assumed that it flies in the normal way which is mostly parallel to the tangent plane of the earth (globe) it flies over and heading in the given directions.
One of the ideas in the AB effect is that none of this takes any energy. Nothing comes up out of the flux to influence the two paths. If there was anything though (none ever measured though even at tiny tiny energy levels hard to imagine possible) it would be something that may be responsible for the gauge field, which could be magnetic monopoles. That has not been proven however, and as I am sure you know, magnetic monopoles have not been proved to exist either, yet.
