Martin Bauer

The Nobel laureates were the first to show this effect for systems containing billions of Cooper pairs. 'Macroscopic' objects described by a collective wavefucntion. Their work laid the foundations for superconducting qubits

They also showed other properties like energy quantisation

7/7

In superconductors you can build have states where many, many Cooper pairs (pairs of electrons) are described by the same wavefunction, which allows them collectively to tunnel through thin insulator barriers called Josephson junctions

6/7

But in quantum mechanics one wavefunction doesn't mean one particle. Many particles can be described by the same wavefunction. Entanglement is an example in which multiple particles are described by one wavefunction

5/7

It is also responsible for field electron emission, used in electron microscopes and tunnel diodes, nuclear fusion in stars, etc

4/7

This effect isn't uncommon in nature

It explains radioactive alpha-decay where a whole Helium nucleus is emitted from a heavy decaying element even if the binding forces wouldn't allow this process classically

3/7

..is on the other side of the barrier (unless its an infinitely strong force field)

If you measure the position of the particle there is a finite probability it's outside the trap even if it never had enough kinetic energy to overcome the barrier. It 'tunnels' through the barrier

2/7

Short explanation of the physics Nobel Prize 2025

In classical mechanics you can know where a particle is and its momentum at the same time. In Quantum mechanics you can't. All information is in the wavefunction. Even if a particle is trapped, part of the wavefunction..

🧵1/7

This night 102 years ago, Hubble discovered that there're stars outside our galaxy by observing a Cepheid variable star 1 million light years away

Until barely a century ago, no human ever knew whether there was more than one galaxy in the Universe. Think about that!

Searching for new physics at LHCb with the flavour changing neutral current decay $B^{0}\to K^{\ast 0}\mu^{+}\mu^{-}$ Flavour changing neutral currents are suppressed in the Standard Model, making them a prime avenue to search for new physics. Over the past decade a consistent set of discrepancies between experimenta...

Full presentation:
indico.cern.ch/event/1584446/

7/6

These results use Run 2 data. By the end of Run 4, the much larger dataset would push the significance beyond discovery thresholds, if the central value holds

In the plot below we were at the blue, we are now at the red and could be as sensitive as the green markers

6/6

This type of new physics would have the properties of a new vector boson (like the Z boson) or a leptoquark, a completely new state that connects color-charged quarks with color-neutral muons

5/6

If it is indeed physics beyond the standard model, the data points toward the same types of interactions that have already been shown to consistently explain several other anomalies in B-meson decays

4/6

It's an open question whether there is a systematic effect here that shows up in both experiments in the same way, or a theoretical uncertainty that has been underestimated or whether this is a genuine signal that the Standard Model cannot account for

3/6

The statistical significance is 4.1 standard deviations.

Intriguingly, CMS, another experiment at the Large Hadron Collider, has also measured this process and sees the same anomaly, too

2/6

Today LHCb presented a new measurement of the decay of a B meson into a K* and a μ+ μ- pair

Previous results disagreed with the Standard Model prediction for the branching fraction and angular distribution

The new measurement has almost twice as much data and still disagrees!

🧵1/6

And if you consider the limit of x_1 -> x_2 you can see how the Pauli principle follows for fermions

14/14

The number of different ways to exchange particles and ending up in exactly the same configuration corresponds to different ways a WF transforms under particle exchange. There are only two classes in 3D, so only fermions and bosons. In 2D instead there're anyons (that can have any phase)

13/

In 2D this can be any complex number with a different phase factor for each winding number. In 3D+ it can be only +1 or -1

12/

In Quantum mechanics the question is how does the wavefunction describing two identical particles transform under this exchange. This corresponds to an operator O(\lambda) with is a 1-dimensional unitary representation of the fundamental group acting on the WF

11/

So the fundamental group of the configuration space in 3D+ is the group with exactly 2 elements

10/

Here is a representation of a non-contractible loop that can't be continuously transformed into a point

9/

Here is a representation of how the contractible loop can be continuously transformed into a point (=no exchange of the two particles)

Again, the bar on the right part is the line connecting the two particles

8/14

And closing the q2 loop twice is equivalent to a contractible loop

7/14

Here, there're only 2 different classes of loops that can't be transformed into each other. Contractible loops (q1) and non-contractible loops (q2)

6/14

Now in 3D (or higher) the situation is different. Here, the configuration space is a half sphere, or a disk with opposite points identified

5/14

The different classes of such loops that can't be transformed into each other by stretching and moving them around the cone (w/o a tip) form the first fundamental group of the configuration space

While R^2 is simply connected (every loop can be contracted to a dot), this space is not

4/14

Any exchange of these two particles corresponds to a loop on this cone

Two loops that can be continually transformed into each other are equivalent. But because the tip of the cone is missing, any number of rotations around the cone can't be transformed into one with fewer or more windings

3/14

For 2 indistinguishable particles, the configuration in which particle 1 is at r and particle 2 is at -r is equivalent to the configuration where they swap positions

So in 2D, the configuration space is R^2 with opposite points identified (excluding the origin)

This space is a cone w/o a tip

2/14

In 3 (or more) dimensions, all fundamental particles are either fermions and bosons. But why?

This is a direct consequence of the properties of the configuration space for identical particles

🧵 1/14

Here is it: The worlds best measurement of the anomalous magnetic moment of the muon

In great agreement with previous experimental results and in agreement with the Standard Model prediction using the LO HVP contribution from lattice input