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Welcome, I'm Takis Kontos.
I work here at the physics department of the École normale supérieure.
Hi there !
We are going to talk about quantum mechanics.
Things can be a bit counterintuitive into that world.
In principle, quantum mechanics
only apply to the microscopic world.
And what we are trying to do with the research we are doing here
is to bring this microscopic world into the macroscopic world.
In order to do so, what we are doing is to build a device
which is called a Cooper pair splitter
which hopefully will exploit some of the basic laws of quantum mechanics.
Come in, I'm gonna show you!
I forgot...
QUANTUM FULL SPLIT
We're working with a single electron spin.
Spin is like charge for the electron,
but it's another quantum degree of freedom
that we can't find in the classical world
and that's very interesting for doing all sort of quantum experiments.
If you go on a hiking trip
you can look at your compass
and this compass has got an arrow telling you where the north is.
In the same way we would like to draw our spin as an arrow
except this arrow is pointing in a 3D space.
and it's not telling us about north or south, it's telling us about some information carried by the spin.
If you manage to have more than one spin
you can make them talk to each other and they can work in parallel
and you can take advantage of this shared superposition between many spins.
and work in parallel for example for quantum computing.
We are using a carbon nanotube to trap our electron
It's like a very small piece of cristal.
It is so small that is possible to trap one electron.
and then we apply these magnetic fields
that would allow us to control the spin in a 3D space and then mesure it.
We are in the clean room
that's where we fabricate the artificial nanocircuit to manipulate our spins.
This machine is a scanning electron microscope
With that you can both image very thin structures
and you can also fabricate them.
Even if you use computers,
at some point there must be a contact.
Because we are macroscopic,
we need a transition until the microscopic world.
From the rack of electronical devices in the lab,
you have cables going down in the cryostat, coming on the chip
and then it follows the electrical path of the electrode
approach closer and closer.
Now, they arrive on the nanotube
and they define two portions of tube which are like boxes for electrons.
We want that they split
on electron goes in one box and the other in the other box.
And these two thinner electrodes are used to manipulate the device.
They are like buttons to make the electrons move
from one box to another and to control the system.
That's where our spins are going to dance...
You can see here the superconducting contact
which is a natural source for Cooper pairs
which are pairs of two electrons
with two spins which point in opposite directions.
And our purpose is to inject these Cooper pairs inside the carbon nanotube
by splitting them and sending the two electrons on both sides of the superconducting contact
to push these two electrons very far away one from each other.
We can imagine that these two electrons are two gyroscopes
one in Paris and one in Los Angeles
And these two gyroscopes are in the spin entangled state
It means that if
in Paris, I measure one spin direction for my gyroscope
in Los Angeles, people know immediately the result of the measurement I did.
Because if I measure the DOWN spin state in Paris,
the state of my gyroscope will be instantaniously projected into the UP spin state in Los Angeles.
and vice versa.
If we can produce and manipulate
that kind of very basic two-particle state
we can imagine to do many more complex things.
So doing that is of fundamental interest
because this tell us how we go
from the microscopic world to the macroscopic world.
But application wise
it could provide a very interesting plateform
in order to build more complex machines
which would exploit quantum mechanics.
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