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I am going to tell and show you something today about the concept of geometric phases.
It is a very abstract concept.
Let me go back a bit: I had a great opportunity, back when I was a young
assistant of Professor Rauch, the pioneer of applied quantum physics
in Austria, who discovered the technique known as neutron interferometry,
which made it possible for the first time, in a still largely unrivalled process,
to separate microscopic objects, such as the building blocks of an atom nucleus.
This had previously been thought to be completely impossible, that a particle
could appear in two places at the same time, one and the same particle.
It was thought impossible this could be achieved experimentally.
One of the first such experiments, that at the time was very spectacular
and until then had been regarded as impossible to achieve,
we achieved in 1975, together, Anton Zeilinger was there too,
he had worked with Mr Rauch for a couple more years,
with the Group we did an experiment in Grenoble,
at the largest research reactor in the world ever made - where we were actually able,
to use an interferometer to show
that neutrons have the following properties: If you turn it around once,
its wave function would have, as physicians would say, a phase factor of -1.
In a figurative sense, this would basically mean that
if my heart was on the left, and I'm not making some kind of political statement here,
it's just where it is located, on the left hand side of the body,
and I were to turn around once,
then my heart would be on the right,
after one full turn!
So I would have to turn around twice for it to be back in its original position.
That is of course something that
is contradicted by any outlook, any common sense thinking,
however, in quantum physics, with the particles that everything is made of,
neutrons, protons, electrons, that's how it works.
Of course I can't demonstrate this here. For one thing [laughs] the building blocks of an atom nucleus are much too small.
A neutron is something like 10 to the power of -15 meters in size,
but I will show you using this necktie,
that this concept is also present in daily life.
This necktie. It's a nice TU necktie, here it has the "TU Wien" emblem
on the front,
and now I do a half twist of the necktie,
and once again, so that I have done a full twist, and "this" side is at the front again,
facing the camera, but we keep on twisting:
one and a half turns,
two full turns, you can see that this necktie is nicely twisted
and I will show you that it is possible to reverse the process without any twisting,
with only parallel movements!
I feed it towards my body.
This part is still facing the camera,
I haven't twisted it, if you like I can do it slowly. "This" side is always
facing the same direction
and you can see that "the twist" is no longer there.
If, however, we only twist the necktie once,
so half turn, full turn
and we do exactly the same as before,
then we can see that "this" part is still twisted.
So we made the twist disappear
by twisting it further in the same direction.
Now you might say: Very well,
but that is no different from the famous Möbius strip. That is true,
and my idea is actually just showing the same thing but with a necktie.
I had a really interesting experience with this.
It was 1996 and I had been invited to give a lecture in Osaka at Kansai airport
to around 1500 people.
At the end of my lecture, it was the last lecture before the buffet,
I demonstrated "that".
And what happened?
In Japan, almost all men wear neckties, they all then
started twisting their ties with great enthusiasm,
but it then didn't work, because of course, if you don't...
if you don't practice a bit, it won't work.
And that was of course a fantastic experience, they were so excited that they forgot about the buffet.
You might say: OK that's great, but it's useless.
But it isn't!
The geometric phases that are behind this,
(that could also be seen recently with neutrons, by the group
with Helmut Rauch and colleagues) these geometric phases
are a lot less susceptible to disruption, a lot less sensitive
than the commonly-used, time-dependent phases
used in information transfer, known as dynamic phases.
Now, from this it can be justifiably assumed
that in the future (quantum computer being the key word here)
this concept will play an important role and will be used.
Of course, there won't be any neckties built into these computers, but I mean the idea behind it.