#condmat

Paul HouleUP8
2026-01-01
Paul HouleUP8
2025-12-12

◍ Diverse particles form identical geometric patterns when confined, model reveals

phys.org/news/2025-11-diverse-

Paul HouleUP8
2025-10-08

⚡ Pioneering recipe for conductive plastics paves way for human bodies to go online

techxplore.com/news/2025-09-re

Paul HouleUP8
2025-09-30
Paul HouleUP8
2025-09-14
Paul HouleUP8
2025-09-08

💎 Scientists design superdiamonds with theoretically predicted hexagonal crystal structure

phys.org/news/2025-08-scientis

Paul HouleUP8
2025-08-23
Paul HouleUP8
2025-08-11

🧊 Boil, freeze, bubble, crack, repeat! Scientists simulate the solar system's 'ice volcanoes' in the lab

phys.org/news/2025-07-scientis

2025-05-13

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

The abstract of the paper with "PREPRINT" written with big letters on top of it.
2025-04-30

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

Entrance to Ecole Normale Superieure Paris-Saclay - the site of the conference
Paul HouleUP8
2025-04-03

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

phys.org/news/2025-03-law-ener

2025-03-31

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

On the left: a hexagonal array of atoms (red balls with small arrows arranged in the xy plane) in a magnetic field (big arrow in the z direction). On the right: the energy levels of each atom: black bar on the bottom denoting the ground state, dashed black line denoting the frequency of atomic transition, and two bars denoting excited states: red bar below the dashed line and blue bar above the dashed line. The distance between the dashed line and each of the bar is mu*B. Each of the excited states is connected with the ground state with double-sided arrow in respective colour, denoting the fact that it can absorb and emit circularly polarized light (red and blue correspond to opposite circular polarizations).The figure comes from the following paper: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.023603
2025-03-10

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

A tweezer array in a cavity. The cavity is the two mirrors on left and right trapping a yellow beam of light between them. Inside the cavity, there are several atoms arranged in a “star of David” pattern (a small instance of the frustrated kagome lattice). The atoms are held by optical tweezers (vertical red beams of light)
2025-02-12

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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Paul HouleUP8
2025-02-07

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

techxplore.com/news/2025-01-ge

2025-01-13

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: fediscience.org/@quinto/113465). 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

Three pictures of a triangular lattice covered by singlet bonds (blue lines). In the first picture (“spinons”), two lattice sites are not connected by any singlet bonds, instead, free spins (blue arrows) are placed there. Two such configurations are shown and a plus sign is placed between them, and a “+…” on the right side, indicating that one should add up all such configurations.

In the second picture (“visons”), also two configurations are shown. Now, each site is connected to some singlet bond. A red line is drawn through the middles of some triangles. In the first configuration, the line does not cross any singlet bond. In the second configuration, it crosses one singlet bond, marked in red. There is a red minus sign in front of the second configuration and a “+…” on its right side, indicating that one should sum all configurations, but the ones where the line crosses an odd number of singlet bonds enter the sum with a minus sign.

The third picture (“braiding”) also consists of two parts. The first part shows a configuration with two visons (a red line through the middles of triangles) and two spinons located near each other (just created by destroying one singlet bond). One of the spinons will move on a path encircling one of the visons, shown in green. The second part shows the same configuration after the spinon moved along the path. The singlet bonds within the paths are rearranged, and one more singlet bond is crossing the red line.
2024-12-11

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: online.kitp.ucsb.edu/online/mb

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

First slide of the talk. Title: "Emergence of Quantum Spin Liquids from Atom-Cavity Interactions", author: Charlie-Ray Mann. Below a schematic picture of an array of atoms held by optical tweezers (vertical laser beams) in an optical cavity (two mirrors on the left and right, and the light confined by the two mirrors). There are circles around two neighboring atoms, signifying the Rydberg blockade interaction. The slide contains also the logo of ICFO (the institute in Barcelona where our group works, as well as the logo of Marie Skłodowska-Curie Action, from which the research was financed).
2024-12-04

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

Door with inscription above: "Kohn Hall, Kavli Institute for Theoretical Physics"Some scribbles on the blackboard (including drawings of hexagonal lattice, Haldane Chern insulator model and Hofstadter model)
2024-11-11

Spin liquid

As an example of how a topological order can look like, one can look at simplified picture of so-called Z2 spin liquid. This type of topological order is postulated to occur in some “frustrated magnets”.
#physics #TopologicalOrder #science #CondensedMatter #CondMat
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The picture has three parts. The first explain frustration. There is a triangle on whose corners there are spins (arrows). The first spin points up, the second points down. The third is replaced by a question mark because it cannot “decide” if it points up or down.

The second part presents the singlet state, which is written as: arrow up, arrow down minus arrow down, arrow up. 

The third part presents the spin liquid. It shows a triangular lattice. On some of its “bonds” there is a blue line, which represents a singlet state. Then, next to it, there is another instance of triangular lattice with different arrangement of blue lines. There is a plus sign between them and three dots on the right, signifying that many such arrangements are possible and that the spin liquid consists of a sum of all of them.
2024-09-27

Interactions and order

Interactions can do many things, but one of the most important effects is causing the system to order. A simple example is a magnet. As I mentioned in the previous post, electrons have a quantum property called “spin”. In a crude, cartoon picture, it means that they can rotate around an axis (say, the “z” axis) clockwise or anticlockwise, which is represented by up and down arrow.
#physics #CondensedMatter #CondMat #science #topology #quantum #QuantumComputing
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Two pictures 

Left – “ferromagnetic” – spins (arrows), all pointing up, on the sites of a square lattice.

Right – “topological” – a cup gradually transforming into a donut (image by Lucas Vieira, public domain via Wikimedia Commons)

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