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Photon-photon polaritons in microresonators. Credit: University of Bath

Researchers exploring the interactions between light particles, photons, and matter find that optical microresonators host quasiparticles made by two photons.

Scientists at the University of Bath have found a way to bind together two photons of different colors, paving the way for important advancements in quantum-electrodynamics the field of science that describes how light and matter interact. In time, the teams findings are likely to impact developments in optical and quantum communication, and precision measurements of frequency, time, and distances.

An apple falling from a tree has velocity and mass, which together give it momentum. Apple energy derived from motion depends on the fruits momentum and mass.

Most people find the concept of momentum and energy (and therefore mass) an easy one to grasp when its associated with solid objects. But the idea that non-material objects, such as light waves (everything from sunlight to laser radiation), also have a mass is surprising to many. Among physicists, however, its a well-known fact. This apparently paradoxical idea that waves have a mass marks the place where quantum physics and the physical world come together.

The wave-particle duality, proposed by French physicist Louis de Broglie in 1924, is a powerful concept that describes how every particle or quantum entity can be described as either a particle or a wave. Many so-called quasiparticles have been discovered that combine either two different types of matter particles, or light waves bound to a particle of matter. A list of exotic quasiparticles includes phonons, plasmons, magnons, and polaritons.

The team of physicists at Bath has now reported a way to create quasiparticles that bind together two differently colored particles of light. They have named these formations photon-photon polaritons.

The opportunity to discover, and manipulate, photon-photons is possible thanks to the relatively new development of high-quality microresonators. For light, microresonators act as miniature racetracks, with photons zipping around the internal structure in loops. The signature left by photon-photons in the light exiting the microresonator can be linked to the AutlerTownes effect, a peculiar phenomenon in quantum theory that describes strong photon-atom interactions. To achieve this effect in microresonators, a laser is tuned to the specific resonance frequency where a photon is expected to be absorbed, yet no resonance absorption happens. Instead, the photon-photon interaction makes up two new resonance frequencies away from the old one.

A significant feature that has emerged from the Bath research is that the microresonator provided a whole set of split resonances, where each photon-photon pair displayed its own momentum and energy, allowing the researchers to apply the quasiparticle concept and calculate mass. According to the researchers predictions, photon-photons are 1,000+ times lighter than electrons.

Professor Dmitry Skryabin, the physicist who led the research, said: We now have a situation where microresonators which are millimeter-scale objects behave like giant atoms. The artificial atoms concept is rapidly gaining ground in the quantum-electrodynamics of microwaves in superconducting circuits, while here we are looking at the similar opportunity in the optical range of frequencies.

The small mass of photon-photons could lead to further developments of many important analogies between light and fluids, where other families of quasiparticles have already being used.

PhD student Vlad Pankratov, who participated in the project, said: After a year of running models and collecting data, these are incredibly exciting findings for us. The potential applications of our results are in the terabit and quantum optical communication schemes, and in the area of precision measurements.

Reference: Photon-photon polaritons in (2) microresonators by D. V. Skryabin, V. V. Pankratov, A. Villois and D. N. Puzyrev, 17 February 2021, Physical Review Research.DOI: 10.1103/PhysRevResearch.3.L012017

This work was supported by the European Union Marie Skodowska-Curie Actions (812818, MICROCOMB).

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Physicists Create Quasiparticles That Bind Together Two Differently Colored Particles of Light - SciTechDaily

This month is a time to celebrate. CERN has just announced the discovery of four brand new particles at the Large Hadron Collider (LHC) in Geneva.

This means that the LHC has now found a total of 59 new particles, in addition to the Nobel prize-winning Higgs boson, since it started colliding protons particles that make up the atomic nucleus along with neutrons in 2009.

Excitingly, while some of these new particles were expected based on our established theories, some were altogether more surprising.

The LHC's goal is to explore the structure of matter at the shortest distances and highest energies ever probed in the lab testing our current best theory of nature: the Standard Model of Particle Physics. And the LHC has delivered the goods it enabled scientists to discover the Higgs boson, the last missing piece of the model. That said, the theory is still far from being fully understood.

One of its most troublesome features is its description of the strong force which holds the atomic nucleus together. The nucleus is made up of protons and neutrons, which are in turn each composed of three tiny particles called quarks (there are six different kinds of quarks: up, down, charm, strange, top and bottom).

If we switched the strong force off for a second, all matter would immediately disintegrate into a soup of loose quarks a state that existed for a fleeting instant at the beginning of the universe.

Don't get us wrong: the theory of the strong interaction, pretentiously called "quantum chromodynamics", is on very solid footing. It describes how quarks interact through the strong force by exchanging particles called gluons. You can think of gluons as analogues of the more familiar photon, the particle of light and carrier of the electromagnetic force.

However, the way gluons interact with quarks makes the strong force behave very differently from electromagnetism. While the electromagnetic force gets weaker as you pull two charged particles apart, the strong force actually gets stronger as you pull two quarks apart.

As a result, quarks are forever locked up inside particles called hadrons particles made of two or more quarks which includes protons and neutrons. Unless, of course, you smash them open at incredible speeds, as we are doing at Cern.

To complicate matters further, all the particles in the standard model have antiparticles which are nearly identical to themselves but with the opposite charge (or other quantum property). If you pull a quark out of a proton, the force will eventually be strong enough to create a quark-antiquark pair, with the newly created quark going into the proton.

You end up with a proton and a brand new "meson", a particle made of a quark and an antiquark. This may sound weird but according to quantum mechanics, which rules the universe on the smallest of scales, particles can pop out of empty space.

This has been shown repeatedly by experiments we have never seen a lone quark. An unpleasant feature of the theory of the strong force is that calculations of what would be a simple process in electromagnetism can end up being impossibly complicated. We therefore cannot (yet) prove theoretically that quarks can't exist on their own.

Worse still, we can't even calculate which combinations of quarks would be viable in nature and which would not.

Illustration of a tetraquark. (CERN)

When quarks were first discovered, scientists realized that several combinations should be possible in theory. This included pairs of quarks and antiquarks (mesons); three quarks (baryons); three antiquarks (antibaryons); two quarks and two antiquarks (tetraquarks); and four quarks and one antiquark (pentaquarks) as long as the number of quarks minus antiquarks in each combination was a multiple of three.

For a long time, only baryons and mesons were seen in experiments. But in 2003, the Belle experiment in Japan discovered a particle that didn't fit in anywhere. It turned out to be the first of a long series of tetraquarks.

In 2015, the LHCb experiment at the LHC discovered two pentaquarks.

The four new particles we've discovered recently are all tetraquarks with a charm quark pair and two other quarks. All these objects are particles in the same way as the proton and the neutron are particles. But they are not fundamental particles: quarks and electrons are the true building blocks of matter.

Is a pentaquark tightly (above) or weakly bound (see image below)? (CERN)

The LHC has now discovered 59 new hadrons. These include the tetraquarks most recently discovered, but also new mesons and baryons. All these new particles contain heavy quarks such as "charm" and "bottom".

These hadrons are interesting to study. They tell us what nature considers acceptable as a bound combination of quarks, even if only for very short times.

They also tell us what nature does not like. For example, why do all tetra- and pentaquarks contain a charm-quark pair (with just one exception)? And why are there no corresponding particles with strange-quark pairs? There is currently no explanation.

Is a pentaquark a molecule? A meson (left) interacting with a proton (right). (CERN)

Another mystery is how these particles are bound together by the strong force. One school of theorists considers them to be compact objects, like the proton or the neutron.

Others claim they are akin to "molecules" formed by two loosely bound hadrons. Each newly found hadron allows experiments to measure its mass and other properties, which tell us something about how the strong force behaves. This helps bridge the gap between experiment and theory. The more hadrons we can find, the better we can tune the models to the experimental facts.

These models are crucial to achieve the ultimate goal of the LHC: find physics beyond the standard model. Despite its successes, the standard model is certainly not the last word in the understanding of particles. It is for instance inconsistent with cosmological models describing the formation of the universe.

The LHC is searching for new fundamental particles that could explain these discrepancies. These particles could be visible at the LHC, but hidden in the background of particle interactions.Or they could show up as small quantum mechanical effects in known processes.

In either case, a better understanding of the strong force is needed to find them. With each new hadron, we improve our knowledge of nature's laws, leading us to a better description of the most fundamental properties of matter.

Patrick Koppenburg, Research Fellow in Particle Physics, Dutch National Institute for Subatomic Physics and Harry Cliff, Particle physicist, University of Cambridge.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Physicists Just Found 4 New Subatomic Particles That May Test The Laws of Nature - ScienceAlert

In the past few innovation-led ease-enabled years, the best-performing Artificial-intelligence systems such as the speech recognizers, automatic translators or most welcomed virtual assistants have resulted from a technique called deep learning, a part of Neural network approach.

Neural nets have occupied a major area of research in both neuroscience and computer science and has seen its zenith in 1970s as well as its nadir in years later.

It is a means of performing machine learning, in which a computer learns to perform some task by analyzing training examples.

When we train our neural networks we run thousands or millions of cycles until the AI is properly trained.

The first Mind-Machine collab:The very first trainable neural network was named the PerceptronIt was demonstrated by the Cornell University psychologist Frank Rosenblatt in 1957.

It exhibited the qualities of executing certain fairly common computations on Perceptrons would be impractically time consuming otherwise.

The latest but surely not the last of such revelation regarding neural networks is a recent enlightening study regarding a possible collusion between our worldly phenomenons and the neural network model.

Vitaly Vanchurin( professor of physics at the University of Minnesota Duluth) published a paper by the name The World as a Neural Network that has recently found hightened resurgence among peers.

The study attempted to describe the scope between quantum and classical physics.

We get hold of quantum physics to understand universal processes at the scale of atoms and subatomic particles including photons and even cells but on large scale, we seek refuge under classical physics.

Undoubted is that general relativity works pretty well on large scales and Quantum on small levels.

For years, physicists have tried unsuccessfully to reconcile quantum mechanics and general relativity. This is known as the problem of quantum gravity.

The study clearly proposes of an entire universe at its most fundamental level to be simulating a neural network.

What has Vanchurin said:We are not just saying that the artificial neural networks can be useful for analyzing physical systems or for discovering physical laws, we are saying that this is how the world around us actually works.

With this respect it could be considered as a proposal for the theory of everything, and as such it should be easy to prove it wrong. All that is needed is to find a physical phenomenon which cannot be described by neural networks.

Unfortunately (or fortunately) it is easier said than done.

The two available explanations for our universe based on distinct interpretations deriving from quantum mechanics. These are:

1. many worlds- there are many worlds existing in parallel at the same space and time as our own. Therefore it becomes possible to remove randomness and action at a distance from quantum theory and thus from all physics.

This implies that all possible outcomes of quantum measurements are physically realized in some world or universe. Stephen Hawking, Everett and Sean Carrolls are its proponents.

2. hidden variables-this approach is championed by Albert Einstein and David Bohm, among others, basically states that the wave function is just a temporary fix and that physicists will eventually replace it.

Vanchurins concept tries to reconcile the two distinct Quantum theories. Though adding nothing new in existing ones, just exhibiting the approximate behaviours of both.

If such a theory found more proponents and leads to more work in this era, it could soon yield the absolute Theory of everything ie. How the World around us actually works.

Since it is widely believed that most of the fundamental ideas of entire universe are governed by the rules of quantum mechanics, even gravity should somehow emerge from it.

This may definitely resolve a few things but triggers a few more questions that will require inherent research:

If the Universe is a neural network, do we act as deep learning nodes connecting inputs and yielding output connections?

If so, whats the networks purpose?

Is it one giant closed network or just a single layer in a grander network?

Are there other universes connected to the same network?

Are we just being trained for some larger-than-universal machines greater purpose?

These questions will rule our minds for some considerable time as this idea is definitely crazy, but is it crazy enough to be true?

That remains to be seen. We may never find it different enough!

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Living in a simulation: Is Universe a Neural Network? - The Indian Wire