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Martin Bauer @martinmbauer.bsky.social · 2h

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

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Martin Bauer @martinmbauer.bsky.social · 2h

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

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Martin Bauer @martinmbauer.bsky.social · 2h

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

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Martin Bauer @martinmbauer.bsky.social · 2h

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

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Martin Bauer @martinmbauer.bsky.social · 2h

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

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Martin Bauer @martinmbauer.bsky.social · 2h

..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

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Martin Bauer @martinmbauer.bsky.social · 2h

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..

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Martin Bauer @martinmbauer.bsky.social · 3d

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!

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Martin Bauer @martinmbauer.bsky.social · 29d

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

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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...

indico.cern.ch

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Martin Bauer @martinmbauer.bsky.social · 29d

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

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Martin Bauer @martinmbauer.bsky.social · 29d

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

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Martin Bauer @martinmbauer.bsky.social · 29d

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

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Martin Bauer @martinmbauer.bsky.social · 29d

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

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Martin Bauer @martinmbauer.bsky.social · 29d

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

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Martin Bauer @martinmbauer.bsky.social · 29d

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!

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Martin Bauer @martinmbauer.bsky.social · Aug 1

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

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Martin Bauer @martinmbauer.bsky.social · Aug 1

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)

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Martin Bauer @martinmbauer.bsky.social · Aug 1

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

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Martin Bauer @martinmbauer.bsky.social · Aug 1

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

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Martin Bauer @martinmbauer.bsky.social · Aug 1

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

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Martin Bauer @martinmbauer.bsky.social · Aug 1

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

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Martin Bauer @martinmbauer.bsky.social · Aug 1

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

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Martin Bauer @martinmbauer.bsky.social · Aug 1

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

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Martin Bauer @martinmbauer.bsky.social · Aug 1

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)

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Martin Bauer @martinmbauer.bsky.social · Aug 1

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

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