We just submitted the first QUINTO draft of paper to a journal. Let's see what the editors and reviewers think.

The paper is about fractional quantum Hall states in atomic arrays. Here is the popular summary we submitted alongside:

"When atoms are arranged in a regular, dense array, their response to light can change drastically. The photons can bounce between the atoms, getting absorbed and re-emitted again and interfering with themselves. This field of quantum optics with atomic arrays is of active interest. Due to interactions, the limit of many absorbed photons generally remains hard to model, but at the same time may result in new, counterintuitive physical phenomena. In the search for ways to understand such systems, we can look for analogies in condensed matter physics, where the behavior of many interacting particles (electrons in this case) has been studied for decades. Here, we report on finding such an analogy between the behavior of few photons absorbed by an array and peculiar many-electron quantum states known as fractional quantum Hall (FQH) states. FQH states display many counterintuitive properties -- for example the electrons behave like they decomposed into pieces (e.g. "one third of an electron"), even though we know that in reality they are indivisible. Now we know that photons in arrays can behave similarly."

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#physics #science #CondensedMatterPhysics #CondensedMatter #condMat #QuantumOptics #Quantum @physics

We just came back from the "Light-Matter Interactions and Collective Effects" workshop in Paris. We heard some interesting talks on how quantum emitters (not only atoms, but also e.g. molecules and quantum dots) interact with each other and how people try to arrange them into arrays (like, putting chains of molecules inside a carbon nanotube). Darrick (my boss and supervisor of the project) gave a talk on spin liquids, while I presented a poster on fractional quantum Hall states in atom arrays.

#physics #quantum #science #QuantumOptics #CondensedMatter #CondMat

💔 A new law gives the energy needed to fracture stretchable networks

https://phys.org/news/2025-03-law-energy-fracture-stretchable-networks.html

#physics #fracture #condmat #networks

Fractional quantum Hall states in atom arrays

Our second approach to create a topological order in atom arrays is to focus on a different kind of topological order: fractional quantum Hall (FQH) states. These were first discovered in condensed matter. It is possible to confine electrons to move in two-dimensions only (such as in the 2D material graphene or in so-called metal-oxide-semiconductor transistors) and then put them in a strong perpendicular magnetic fields. The electrons then move in circles (so-called “cyclotron motion”), but since they are quantum objects, only some values of radius are allowed. Thus, the energy can only take certain fixed values (we call them “Landau levels”). There are however different possibilities of an electron having the same energy, because the center of the orbit can be located in different places – we say that Landau levels are “degenerate”. And when there is degeneracy, the interaction between electrons becomes very important. Without interactions, there are many possible ways of arranging electrons within a Landau level, all with the same energy. In the presence of interactions, some arrangements become preferred – and it turns out those correspond to topological orders known as the FQH states. Such systems host anyons which look like fractions of an electron – like somehow the electron split into several parts.

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#Physics #science #TopologicalOrder #Quantum #QuantumOptics #CondensedMatter #CondMat #cond_mat #QuantumHall

Spin liquids in Rydberg atom arrays in cavities

What is our proposal for the realization of spin liquid?

We consider an atom array held by optical tweezers and placed in an optical cavity. The cavity consists of two mirrors placed on the opposite sides of the system. The photons which normally would escape the system (at least some of them) will bounce back and forth between the mirrors. In such a configuration, the distance between atoms becomes irrelevant and the probability of an excitation hopping between any two atoms becomes the same.

The second ingredient is that the excited state of the atoms would be a Rydberg state – a very high-energy state where the electron is far away from the nucleus. The atoms in Rydberg states interact strongly by van der Waals forces. In our case it would mean that two excitations will have much higher energy when they are at nearest-neighboring atoms than if they are far away.

This setting seems much different from usual crystals. In the typical material, the electrons are much more likely to hop between nearest-neighboring atoms than far-away ones, while in our case they would be able hop arbitrarily far with the same probability. But it turns out that there is in equivalence between such “infinite-range hopping + Rydberg” model and the Heisenberg model, commonly used to describe magnets, including the frustrated ones.
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#Physics #Quantum #TopologicalOrder #CondMat #CondensedMatter #QuantumOptics #Science

Atom arrays

Scientists have developed ways of trapping atoms and arranging them in space using laser beams (such as “optical tweezers” and “optical lattices”). What can one do using these tools? One possibility is arranging the atoms in a regular array.

Why people find it interesting? It was found that such systems have properties much different than clouds of atoms randomly flying around. The lattice structure changes how the atoms emit and absorb light. This is because light emitted from different atoms can interfere, and a regular structure of array works like a diffraction grating. This happens especially if the distance between atoms is smaller than one wavelength.

For example, a 1D chain of atoms in a certain state emits light only on its ends. And a 2D array can act as a perfect mirror (for certain wavelength), even though it is only one atom thin.

It was theoretically shown that these effects can be used to boost the efficiency of optical quantum devices such as memories and gates, which may be used in the future for a “quantum internet” and quantum computers.

#Physics #Science #Quantum #QuantumOptics #atoms #CondensedMatter #CondMat

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💔 New general law governs fracture energy of networks across materials and length scales

https://techxplore.com/news/2025-01-general-law-fracture-energy-networks.html

#fracture #physics #scaling #condmat #materials

Anyons in spin liquids

To see how anyons can arise in topological orders, one can look again on the simplified picture of the Z2 spin liquid (see the previous post: https://fediscience.org/@quinto/113465683021157305). Anyons can be created on the top of the spin liquid by altering the singlet pattern.

First, we can break one singlet bond into two spins, one up and one down, which can move freely throughout the pattern by rearranging the singlets. The two spins can be thought of as (quasi)particles called spinons.

By the way, spinons can also be created by flipping a spin. In a spin liquid ground state, we have as many up spins as down spins, so all of them can be paired into singlets. But if we flip one of, say, down spins, we have *two* up spins that cannot be paired – two spinons. One flipped spin somehow turns into two quasiparticles. This is known as “fractionalization”.

Secondly, we can do something more complicated. We can draw a line intersecting some bonds. Then, in the sum over all singlet configurations, we put a plus if the line intersect an even number of singlets and minus if this number is odd. The ends of the line are quasiparticles called visons. It does not matter how we draw the line – it only matters where it starts and ends.
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#physics #science #CondensedMatter #CondMat #TopologicalOrder #Anyons

Yesterday Charlie-Ray Mann gave a talk as a part of the "Many-Body Quantum Optics" program at KITP. Charlie is a postdoc working in the same group as me. Part of presented work (2D numerics which is not directly referenced) was done by me within the QUINTO project. You can listen to the recording of the talk here: https://online.kitp.ucsb.edu/online/mbqoptics24/mann/

#CondensedMatter #condMat #Cond_mat #TopologicalOrder #SpinLiquid #QuantumOptics #Optics #Physics #ColdAtoms #Science

We are now in Santa Barbara, California, for a program “Many-body quantum optics” at Kavli Institute for Theoretical Physics. The program is co-organized by the supervisor of QUINTO, prof Darrick Chang, and is aimed at fostering collaborations between the condensed matter and quantum optics researchers. We already had a couple of interesting discussions and are looking forward to more!

#physics #science #CondensedMatter #CondMat #QuantumOptics #quantum