Plan:

Introduction

• 1 Properties of Rydberg atoms
  • 1.1 Dipole blockade of Rydberg atoms
• 2 Directions of research and possible applications
Notes

Introduction

Rydberg atoms(named after J. R. Rydberg) - atoms alkali metals, in which the outer electron is in a highly excited state (up to levels n ~ 100). To transfer an atom from its ground state to an excited state, it is irradiated with resonant laser light or an RF discharge is initiated. The size of the Rydberg atom is much larger than the size of the same atom in the ground state by almost 10,000 times for n=100 (see table below).

1. Properties of Rydberg atoms

An electron revolving in an orbit of radius r around the nucleus, according to Newton's second law, it experiences a force:

where k= 1/(4πε 0), e is the charge of an electron.

Orbital moment in units ħ equals:

From these two equations, we obtain an expression for the orbital radius of an electron in the state "n"

Scheme of laser excitation of a rubidium atom into the Rydberg state

The binding energy of such a hydrogen-like atom is

where Ry = 13.6 eV is the Rydberg constant, and δ nuclear charge defect, which at large n insignificant. Energy difference between n-m and n+1-th energy levels is approximately equal to

Characteristic size of an atom rn and typical semiclassical period of electron revolution are equal to

where a B = 0.5×10 −10 m is the Bohr radius, and T 1 ~ 10 −16 s.

Let us compare some numbers of the ground and Rydberg states of the hydrogen atom.

1.1. Dipole blockade of Rydberg atoms

When atoms are excited from the ground state to the Rydberg state, an interesting phenomenon occurs, called dipole blockade. In a discharged atomic vapor, the distance between atoms in the ground state is large and there is practically no interaction between atoms. However, when atoms are excited to the Rydberg state, their orbital radius increases by n 2 up to ~1 µm. As a result, the atoms "approach", the interaction between them increases significantly, which causes a shift in the energy of the states of the atoms. What does this lead to? Let us assume that only one atom can be excited from the ground state to the Rieberg state by a weak light pulse. An attempt to populate the same level with another atom becomes obviously impossible due to the "dipole blockade".

2. Directions of research and possible applications

Studies related to the Rydberg states of atoms can be conditionally divided into two groups: the study of the atoms themselves and the use of their properties for other purposes.

Fundamental areas of research:

• Of several states with large n it is possible to compose a wave packet, which will be more or less localized in space. If, in addition, the orbital quantum number, then we get an almost classical picture: a localized electron cloud rotates around the nucleus for long distance From him.
• If the orbital momentum is small, then the motion of such a wave packet will be quasi-one-dimensional: The electron cloud will move away from the nucleus and approach it again. This is an analogue of a highly elongated elliptical orbit in classical mechanics when moving around the Sun.
• Behavior of the Rydberg electron in external electric and magnetic fields. Ordinary electrons close to the nucleus mostly feel the strong electrostatic field of the nucleus (on the order of 10 9 V/cm), and the external fields for them play the role of only small additions. The Rydberg electron feels a strongly weakened field of the nucleus ( E~E0/n4), and therefore external fields can radically distort the motion of an electron.
• Atoms with two Rydberg electrons have interesting properties, with one electron "spinning" around the nucleus at a greater distance than the other. Such atoms are called planetary.
• According to one of the hypotheses, ball lightning consists of the Rydberg substance.

The unusual properties of Rydberg atoms are already finding applications

• Quantum detectors of radio emission: Rydberg atoms can register even a single photon in the radio range, which is far beyond the capabilities of conventional antennas.
• The stepped energy spectrum of a Rydberg electron serves as an "energy balance" that can be used for accurate energy measurements.
• Rydberg atoms are also observed in the interstellar medium. They are very sensitive pressure sensors, created for us by nature itself.

In 2009, researchers from the University of Stuttgart succeeded in obtaining the Rydberg molecule.

Notes

1. W. Demtroder Laser Spectroscopy: Basic Concepts & Instrumentation. - Springer, 2009. - 924 p. - ISBN 354057171X
2. R. Heidemann et al. (2007). "Evidence for Coherent Collective Rydberg Excitation in the Strong Blockade Regime - link.aps.org/abstract/PRL/v99/e163601". Physical Review Letters 99 (16): 163601. DOI:10.1103/PhysRevLett.99.163601 - dx.doi.org/10.1103/PhysRevLett.99.163601. arΧiv:quant-ph/0701120 - arxiv.org/abs/quant-ph/0701120.
3. Cohesion in ball lightning - scitation.aip.org/journals/doc/APPLAB-ft/vol_83/iss_11/2283_1.html
4. membrana.ru "For the first time in the world, the Rydberg molecule has been obtained" - www.membrana.ru/lenta/?9250

Most people will easily name the three classical states of matter: liquid, solid, and gaseous. Those who know a little science will add plasma to these three. But over time, scientists have expanded the list of possible states of matter beyond these four.

amorphous and solid

Amorphous solids are a rather interesting subset of the well-known solid state. In a typical solid object, the molecules are well organized and don't have much room to move. This gives the solid a high viscosity, which is a measure of flow resistance. Liquids, on the other hand, have a disorganized molecular structure that allows them to flow, spread, change shape, and take on the shape of the container they are in. Amorphous solids are somewhere between these two states. In the process of vitrification, liquids cool down and their viscosity increases to the point where the substance no longer flows like a liquid, but its molecules remain disordered and do not take on a crystalline structure, like ordinary solids.

The most common example of an amorphous solid is glass. For thousands of years people have been making glass from silicon dioxide. When glassmakers cool silica from liquid state, it doesn't actually solidify when it goes below its melting point. As the temperature drops, the viscosity rises and the substance appears to be harder. However, its molecules still remain disordered. And then the glass becomes amorphous and solid at the same time. This transitional process allowed artisans to create beautiful and surreal glass structures.

What is the functional difference between amorphous solids and ordinary solid state? AT Everyday life it's not very noticeable. Glass appears to be perfectly solid until you examine it at the molecular level. And the myth that glass flows over time is not worth a penny. Most often, this myth is reinforced by the arguments that the old glass in churches seems thicker in the lower part, but this is due to the imperfection of the glass blowing process at the time of creation of these glasses. However, studying amorphous solids like glass is interesting from a scientific point of view for research. phase transitions and molecular structure.

Supercritical fluids (fluids)

Most phase transitions occur at a certain temperature and pressure. It is common knowledge that an increase in temperature eventually turns a liquid into a gas. However, when pressure increases with temperature, the fluid makes a leap into the realm of supercritical fluids, which have the properties of both a gas and a liquid. For example, supercritical fluids can pass through solids as a gas, but can also act as a solvent as a liquid. Interestingly, a supercritical fluid can be made more like a gas or a liquid, depending on the combination of pressure and temperature. This has allowed scientists to find many uses for supercritical fluids.

Although supercritical fluids are not as common as amorphous solids, you probably interact with them just as often as you would with glass. Supercritical carbon dioxide is loved by brewing companies for its ability to act as a solvent when interacting with hops, and coffee companies use it to produce better decaffeinated coffee. Supercritical fluids have also been used for more efficient hydrolysis and to keep power plants running at more high temperatures. In general, you probably use supercritical fluid by-products every day.

degenerate gas

Although amorphous solids are at least found on planet Earth, degenerate matter is found only in certain types of stars. A degenerate gas exists when the external pressure of a substance is determined not by temperature, as on Earth, but by complex quantum principles, in particular the Pauli principle. Because of this, the external pressure of the degenerate matter will be maintained even if the temperature of the matter drops to absolute zero. Two main types of degenerate matter are known: electron-degenerate and neutron-degenerate matter.

Electronically degenerate matter exists mainly in white dwarfs. It is formed in the core of a star when the mass of matter around the core tries to compress the core's electrons to a lower energy state. However, according to the Pauli principle, two identical particles cannot be in the same energy state. Thus, the particles "repel" matter around the nucleus, creating pressure. This is possible only if the mass of the star is less than 1.44 solar masses. When a star exceeds this limit (known as the Chandrasekhar limit), it simply collapses into a neutron star or black hole.

When a star collapses and becomes neutron star, it no longer has electron-degenerate matter, it consists of neutron-degenerate matter. Because a neutron star is heavy, electrons fuse with protons in its core to form neutrons. Free neutrons (neutrons are not bound in atomic nucleus) have a half-life of 10.3 minutes. But in the core of a neutron star, the mass of the star allows neutrons to exist outside the cores, forming neutron-degenerate matter.

Other exotic forms of degenerate matter may also exist, including strange matter, which may exist in a rare form of stars - quark stars. Quark stars are the stage between the neutron star and the black hole, where the quarks in the core are unbound and form a soup of free quarks. We have not yet observed this type of star, but physicists admit their existence.

Superfluidity

Let's go back to Earth to discuss superfluids. Superfluidity is a state of matter that exists in certain isotopes of helium, rubidium, and lithium, cooled to near absolute zero. This state is similar to a Bose-Einstein condensate (Bose-Einstein condensate, BEC), with a few differences. Some BECs are superfluid and some superfluids are BECs, but not all are identical.

Liquid helium is known for its superfluidity. When helium is cooled to the "lambda point" of -270 degrees Celsius, some of the liquid becomes superfluid. If most substances are cooled to a certain point, the attraction between the atoms overcomes the thermal vibrations in the substance, allowing them to form a solid structure. But helium atoms interact with each other so weakly that they can remain liquid at a temperature of almost absolute zero. It turns out that at this temperature, the characteristics of individual atoms overlap, giving rise to strange properties of superfluidity.

Superfluids do not have intrinsic viscosity. Superfluid substances placed in a test tube begin to crawl up the sides of the test tube, seemingly violating the laws of gravity and surface tension. Liquid helium leaks easily, as it can slip through even microscopic holes. Superfluidity also has strange thermodynamic properties. In this state, substances have zero thermodynamic entropy and infinite thermal conductivity. This means that two superfluid substances cannot be thermally distinct. If heat is added to a superfluid substance, it will conduct it so quickly that thermal waves are formed that are not characteristic of ordinary liquids.

Bose-Einstein condensate

The Bose-Einstein condensate is probably one of the most famous obscure forms of matter. First, we need to understand what bosons and fermions are. A fermion is a particle with a half-integer spin (like an electron) or a composite particle (like a proton). These particles obey the Pauli principle, which allows the existence of electron-degenerate matter. The boson, however, has a full integer spin, and one quantum state can occupy several bosons. Bosons include any force-carrying particles (such as photons), as well as some atoms, including helium-4 and other gases. Elements in this category are known as bosonic atoms.

In the 1920s, Albert Einstein took the work of Indian physicist Satyendra Nath Bose to propose new form matter. Einstein's original theory was that if you cool certain elemental gases to a fraction of a degree above absolute zero, their wave functions will merge, creating one "superatom". Such a substance will exhibit quantum effects at the macroscopic level. But it wasn't until the 1990s that the technology needed to cool elements to these temperatures emerged. In 1995, scientists Eric Cornell and Carl Wiemann were able to fuse 2,000 atoms into a Bose-Einstein condensate that was large enough to be seen under a microscope.

Bose-Einstein condensates are closely related to superfluids, but also have their own set of unique properties. It's also funny that the BEC can slow down the normal speed of light. In 1998, Harvard scientist Lene Howe was able to slow light down to 60 kilometers per hour by passing a laser through a cigar-shaped BEC sample. In later experiments, Howe's group succeeded in completely stopping the light in the BEC by turning off the laser as the light passed through the sample. These experiments opened up a new field of communication based on light and quantum computing.

Jan-Teller Metals

Jahn-Teller metals are the newest baby in the world of states of matter, as scientists were only able to successfully create them for the first time in 2015. If the experiments are confirmed by other laboratories, these metals could change the world, as they have the properties of both an insulator and a superconductor.

Scientists led by chemist Cosmas Prassides experimented by introducing rubidium into the structure of carbon-60 molecules (commonly known as fullerenes), which led to the fullerenes taking on a new form. This metal is named after the Jahn-Teller effect, which describes how pressure can change the geometric shape of molecules in new electronic configurations. In chemistry, pressure is achieved not only by squeezing something, but also by adding new atoms or molecules to a pre-existing structure, changing its basic properties.

When Prassides' research group began adding rubidium to carbon-60 molecules, the carbon molecules changed from insulators to semiconductors. However, due to the Jahn-Teller effect, the molecules tried to stay in the old configuration, which created a substance that tried to be an insulator, but had electrical properties superconductor. The transition between an insulator and a superconductor was never considered until these experiments began.

The interesting thing about Jahn-Teller metals is that they become superconductors at high temperatures (-135 degrees Celsius, not at 243.2 degrees as usual). This brings them closer to acceptable levels for mass production and experimentation. If all is confirmed, perhaps we will be one step closer to creating superconductors that work at room temperature, which, in turn, will revolutionize many areas of our lives.

Photonic matter

For many decades it was believed that photons are massless particles that do not interact with each other. Yet over the past few years, scientists at MIT and Harvard have discovered new ways to "endow" light with mass - and even create "light molecules" that bounce off each other and bind together. Some felt that this was the first step towards the creation of a lightsaber.

The science of photonic matter is a little more complicated, but it is quite possible to comprehend it. Scientists began to create photonic matter by experimenting with supercooled rubidium gas. When a photon shoots through the gas, it is reflected and interacts with rubidium molecules, losing energy and slowing down. After all, the photon exits the cloud very slowly.

Strange things start to happen when you send two photons through a gas, which creates a phenomenon known as Rydberg blockade. When an atom is excited by a photon, nearby atoms cannot be excited to the same extent. The excited atom is in the path of the photon. In order for an atom nearby to be excited by a second photon, the first photon must pass through the gas. Photons do not normally interact with each other, but when they encounter a Rydberg blockade, they push each other through the gas, exchanging energy and interacting with each other. From the outside, photons appear to have mass and act as a single molecule, although they remain in fact massless. When photons come out of the gas, they appear to coalesce, like a molecule of light.

The practical application of photonic matter is still in question, but it will certainly be found. Maybe even lightsabers.

Disordered hyperhomogeneity

When trying to determine whether a substance is in a new state, scientists look at the structure of the substance as well as its properties. In 2003, Salvatore Torquato and Frank Stillinger of Princeton University proposed a new state of matter known as disordered hyperhomogeneity. Although this phrase seems to be an oxymoron, at its core it suggests a new type of matter that seems disordered up close, but super-homogeneous and structured from afar. Such a substance must have the properties of a crystal and a liquid. At first glance, this already exists in plasmas and liquid hydrogen, but recently scientists have discovered natural example where no one expected: in the chicken eye.

Chickens have five cones in their retinas. Four detect color and one is responsible for light levels. However, unlike the human eye or the hexagonal eyes of insects, these cones are scattered randomly, with no real order. This is because the cones in the eye of a chicken have alienation zones around them, which do not allow two cones of the same type to be side by side. Due to the exclusion zone and the shape of the cones, they cannot form ordered crystal structures(as in solids), but when all the cones are considered as one, they appear to have a highly ordered pattern, as seen in the Princeton images below. Thus, we can describe these cones in the retina of a chicken eye as liquid on closer inspection and as solid when viewed from afar. This is different from the amorphous solids we talked about above, because this ultra-homogeneous material will act as a liquid, and the amorphous solid- No.

Scientists are still investigating this new state of matter because it may also be more common than originally thought. Now scientists at Princeton University are trying to adapt such ultra-homogeneous materials to create self-organizing structures and light detectors that respond to light with a certain wavelength.

String networks

What state of matter is space vacuum? Most people don't think about it, but in the past ten years Xiao Gang-Wen of the Massachusetts Institute of Technology and Michael Levin of Harvard have proposed a new state of matter that could lead us to the discovery of fundamental particles beyond the electron.

The path to developing a string-net fluid model began in the mid-90s, when a group of scientists proposed the so-called quasi-particles, which seemed to have appeared in an experiment when electrons passed between two semiconductors. There was a stir as the quasi-particles acted as if they had a fractional charge, which seemed impossible for the physics of the time. Scientists analyzed the data and suggested that the electron is not a fundamental particle of the universe and that there are fundamental particles that we have not yet discovered. This work brought them Nobel Prize, but later it turned out that an error in the experiment crept into the results of their work. About quasiparticles safely forgotten.

But not all. Wen and Levin took the idea of ​​quasiparticles as a basis and proposed a new state of matter, the string-network state. The main property of such a state is quantum entanglement. As in the case of disordered hyperhomogeneity, if you close range look at the string-network substance, it will look like a disordered collection of electrons. But if you look at it as a whole structure, you will see a high order due to the quantum entangled properties of the electrons. Wen and Levin then expanded their work to cover other particles and properties of entanglement.

After running computer models for the new state of matter, Wen and Levin found that the ends of string networks can produce a variety of subatomic particles, including the legendary "quasiparticles." An even bigger surprise was that when the string-net substance vibrates, it does this in accordance with the Maxwell equations responsible for light. Wen and Levin proposed that the cosmos is filled with string networks of entangled subatomic particles, and that the ends of these string networks represent the subatomic particles that we observe. They also suggested that the string-network liquid can provide the existence of light. If the vacuum of space is filled with a string-net fluid, this could allow us to combine light and matter.

All this may seem very far-fetched, but in 1972 (decades before the string-net proposals), geologists discovered a strange material in Chile - herbertsmithite. In this mineral, the electrons form triangular structures that seem to contradict everything we know about how electrons interact with each other. In addition, this triangular structure was predicted by the string-network model, and the scientists worked with artificial herbertsmithite to accurately confirm the model.

Quark-gluon plasma

Speaking of the last state of matter on this list, consider the state that started it all: quark-gluon plasma. In the early Universe, the state of matter differed significantly from the classical one. To start, a little background.

Quarks are elementary particles, which we find inside hadrons (for example, protons and neutrons). Hadrons are made up of either three quarks or one quark and one antiquark. Quarks have fractional charges and are held together by gluons, which are the exchange particles of the strong nuclear force.

We don't see free quarks in nature, but right after the Big Bang, free quarks and gluons existed for a millisecond. During this time, the temperature of the universe was so high that quarks and gluons moved almost at the speed of light. During this period, the universe consisted entirely of this hot quark-gluon plasma. After another fraction of a second, the universe has cooled down enough to form heavy particles like hadrons, and quarks begin to interact with each other and gluons. From that moment, the formation of the Universe known to us began, and hadrons began to bind with electrons, creating primitive atoms.

Already in the modern universe, scientists have tried to recreate the quark-gluon plasma in large particle accelerators. During these experiments, heavy particles like hadrons collided with each other, creating a temperature at which quarks separated for a short time. In the course of these experiments, we learned a lot about the properties of the quark-gluon plasma, in which there was absolutely no friction and which was more like a liquid than an ordinary plasma. Experiments with an exotic state of matter allow us to learn a lot about how and why our universe formed as we know it.

Nov 15, 2017 Gennady

Looking at the world in a new light: Scientists have created an unprecedented form of matter. (translation of the article)

• tutorial

Scientists at Harvard and the Massachusetts Institute of Technology (MIT - MIT) are changing the generally accepted point of view about light and for this they did not have to fly to another galaxy far, far away.
Working with colleagues at the Harvard-Massachusetts Center for Ultracold Atoms, a group of Harvard physics professor Mikhail Lukin and MIT physics professor Vladan Vuletich were able to speak photons to bind together to form a molecule, a state of matter previously only in pure theory. The work is described in a September 25 Nature article.

According to Lukin, the discovery reveals a decade-long conventional contradiction underlying the nature of light. "Photons have long been thought of as massless particles that don't interact with each other - after all, the glare of two laser beams just passes through each other," he says.
"Photonic molecules", however, do not behave quite like traditional lasers, but more like lightsabers in the pages of science fiction.

“Most of the known properties of light come from the fact that photons have no mass and do not interact with each other. What we have done is create a special type of medium in which photons begin to interact with each other so strongly that they begin to act as if they have mass and bind together into molecules.
This type of photonic coupling state has been theoretically discussed for quite some time, but it has not yet been observed.
You shouldn't draw a direct analogy with lightsabers," adds Lukin. “When these photons interact with each other, they repel and reflect each other. The physics of what happens in these molecules is similar to what we see in the movies.”
But Lukin and his colleagues, including Ofer Fisterberg, Alexei Gorshkov, Thibault Peyronel and Chi-Yu Lian, did not have the opportunity to use the "Force", they had to use a set of extreme conditions.
The researchers started by pumping rubidium atoms in a vacuum chamber, then using lasers to cool the cloud of atoms to a minimum, just above absolute zero, using extremely weak laser pulses, they fired a single photon into the cloud of atoms.
"After a photon leaves the medium, it retains its identity," - Lukin. “It is similar to the refraction of light that we see when light passes through a glass of water. Light penetrates into water and splashes part of its energy in the medium, but inside it it exists as light and matter connected together, and when it comes out, it continues to be light. Here, approximately the same process occurs, only even cooler - the light slows down greatly and releases much more energy than during refraction.

When Lukin and his colleagues fired two photons into the cloud, they were surprised that the photons at the exit combined into one molecule.
What made them form the never-seen-before molecule?

“This effect is called Rydberg blockade,” said Lukin, “which describes the state of atoms when an atom is excited—neighboring atoms cannot be excited to the same degree. In practice, the effect means that as soon as two photons enter an atomic cloud, the first excites the atom, but must be ahead before the second photon can excite neighboring atoms.
As a result, in his words, it turns out that two photons, as it were, pull and push each other through the cloud, while their energy is transferred from one atom to another.
"It's a photon interaction mediated by an atomic interaction," says Lukin. "This makes the photons behave like molecules and when they leave the medium, they are more likely to do so together, rather than as single photons."
Although the effect is unusual, practical applications are possible for it.
“We did it for fun (for entertainment), and because we are pushing the boundaries of science,” says Lukin.
“But it fits into the bigger picture of what we're doing because photons remain the best possible medium for transmitting quantum information. The main disadvantage was that photons do not interact with each other.
To build a quantum computer,” he explains, “researchers need to build a system that can store quantum information and process it using quantum logic operations.
But the problem was that quantum logic requires interaction between individual quanta so that these quantum systems can switch to perform information processing.
What we have demonstrated in this process will allow us to go further,” said Harvard professor Mikhail Lukin.

“Before we get to the practical application of a quantum switch or a photonic logic converter, we have to improve performance, so this is still at the level of a proof of concept, but this is an important step.
The physical principles we have established here are important. The system can also be useful in classical computing, to reduce the power losses currently experienced by chip manufacturers.
Some companies, including IBM, have developed systems based on optical routers that convert light signals into electrical signals, but they have had certain difficulties.
Lukin also suggested that the system could one day even be used to create a complex three-dimensional structure - such as a crystal - entirely from light.
“What it will be useful for we don’t really know yet, but this is a new state of matter, so we are full of hope that applications for it may arise as we continue our research into the properties of these photonic molecules,” he said.

Harvard University (2013, September 25). Seeing light in a new light: Scientists create never-before-seen form of matter. ScienceDaily. Retrieved September 25, 2013

Alkali metals, in which the outer electron is in a highly excited state (up to levels n about 1000). To transfer an atom from its ground state to an excited state, it is irradiated with resonant laser light or an RF discharge is initiated. The size of a Rydberg atom can exceed the size of the same atom in the ground state by almost 106 times for n = 1000 (see table below).

Properties of Rydberg atoms

An electron revolving in an orbit of radius r around the nucleus, according to Newton's second law, it experiences a force

where ( - dielectric susceptibility), e is the charge of an electron.

Orbital moment in units ħ equals

From these two equations, we obtain an expression for the orbital radius of an electron in the state n :

Scheme of laser excitation of a rubidium atom into a Rydberg state.

The binding energy of such a hydrogen-like atom is

where Ry= 13.6 eV is the Rydberg constant, and δ - nuclear charge defect, which at large n insignificant. Energy difference between n-th and n+1-th energy levels is approximately equal to

Characteristic size of an atom rn and typical semiclassical period of electron revolution are equal to

where a B= 0.5 10 −10 m is the Bohr radius, and T 1 ~ 10 −16 s.

The wavelength of the emission of a hydrogen atom during the transition from n′ = 91 on the n = 90 equal to 3.4 cm

Dipole blockade of Rydberg atoms

When atoms are excited from the ground state to the Rydberg state, an interesting phenomenon occurs, called "dipole blockade".

In a rarefied atomic vapor, the distance between atoms in the ground state is large, and there is practically no interaction between atoms. However, when atoms are excited to the Rydberg state, their orbital radius increases in and reaches a value of the order of 1 μm. As a result, the atoms "approach", the interaction between them increases significantly, which causes a shift in the energy of the states of the atoms. What does this lead to? Let us assume that only one atom can be excited from the ground state to the Rieberg state by a weak light pulse. An attempt to populate the same level with another atom becomes obviously impossible due to the "dipole blockade".

Directions of research and possible applications

Research related to the Rydberg states of atoms can be conditionally divided into two groups: the study of the atoms themselves and the use of their properties for other purposes.

Fundamental areas of research:

The unusual properties of Rydberg atoms are already finding applications

In 2009, researchers from managed to obtain the Rydberg molecule (English) Russian .

radio astronomy

The first experimental data on Rydberg atoms in radio astronomy were obtained in 1964 by R. S. Sorochenko et al. (FIAN) on a 22-meter mirror radio telescope designed to study the radiation of space objects in the centimeter frequency range. When focusing the telescope on the Omega Nebula, in the spectrum of radio emission coming from this nebula, an emission line was detected at a wavelength of λ ≃ 3.4 cm. This wavelength corresponds to the transition between Rydberg states n′ = 91 and n = 90 in the spectrum of the hydrogen atom.

Notes

Literature

• Neukamner J., Rinenberg H., Vietzke K. et al. Spectroscopy of Rydberg Atoms at n ≅ 500 // Phys. Rev. Lett. 1987 Vol. 59. P. 26.
• Frey M. T. Hill S.B.. Smith K.A.. Dunning F.B., Fabrikant I.I. Studies of Electron-Molecule Scattering at Microelectronvolt Energies Using Very-High-n Rydberg Atoms // Phys. Rev. Lett. 1995 Vol. 75, No. 5. P. 810-813.
• Sorochenko R. L., Salomonovich A. E. Giant atoms in space // Nature. 1987. No. 11. S. 82.
• Dalgarno A. Rydberg atoms in astrophysics // Rydberg states of atoms and molecules: Per. from English. / Ed. R. Stebbins, F. Dunning. M.: Mir. 1985, p. 9.
• Smirnov BM Excited atoms. Moscow: Energoizdat, 1982. Ch. 6.

Links

• Delaunay N. B. Rydberg atoms // Soros Educational Journal, 1998, No. 4, p. 64-70
• "Condensed Rydberg matter", E. A. Manykin, M. I. Ozhovan, P. P. Poluektov, article from the journal "Priroda" N1, 2001.

Wikimedia Foundation. 2010 .

A team of physicists from the Center for Ultracold Atoms at Harvard University and the Massachusetts Institute of Technology (Harvard-MIT Center for Ultracold Atoms), led by our compatriot Mikhail Lukin, has obtained a previously unseen type of matter.

This substance, according to the authors of the study, contradicts the ideas of scientists about the nature of light. Photons are considered to be massless particles unable to interact with each other. For example, if you direct two laser beams at each other, they will simply pass through without interacting with each other.

But this time, Lukin and his team managed to experimentally refute this belief. They forced light particles to form a strong bond with each other and even assemble into molecules. Previously, such molecules were only in theory.
"Photonic molecules don't behave like ordinary laser beams, but rather like something close to science fiction - Jedi lightsabers, for example," says Lukin.
“Most of the described properties of light come from the belief that photons have no mass. That is why they do not interact with each other in any way. All we did was create a special environment in which light particles interact with each other so strongly that they begin to behave , as if they have mass, and form into molecules," explains the physicist.
Lukin and his colleagues could not count on the Force in creating photonic molecules, or rather, the medium suitable for their formation. They had to conduct a complex experiment with precise calculations, but absolutely amazing results.
To begin, the researchers placed rubidium atoms in a vacuum chamber and used lasers to cool the atomic cloud to just a few degrees above absolute zero. Then, creating very weak laser pulses, the scientists sent one photon into the rubidium cloud.
"When photons enter a cloud of cold atoms, their energy causes the atoms to go into an excited state. As a result, light particles slow down. Photons move through the cloud, and energy is transferred from atom to atom until it leaves the medium along with the photon itself. When In this case, the state of the environment remains the same as it was before the “visit” of the photon,” says Lukin.

The authors of the study compare this process to the refraction of light in a glass of water. When the beam penetrates the medium, it gives it a part of its energy and inside the glass it is a "link" between light and matter. But when it comes out of the glass, it is still light. Practically the same process takes place in Lukin's experiment. The only physical difference is that light slows down a lot and gives off more energy than normal refraction in a glass of water.
At the next stage of the experiment, the scientists sent two photons into the rubidium cloud. Imagine their surprise when they caught two photons bound into a molecule at the exit. It can be called a unit of a previously unseen substance. But what is the reason for this connection?
The effect was described earlier theoretically and is called the Rydberg blockade. According to this model, when one atom is excited, other neighboring atoms cannot go into the same excited state. In practice, this means that when two photons enter a cloud of atoms, the first photon will excite the atom and move forward before the second photon excites neighboring atoms.
The result is that the two photons will push and pull each other as they pass through the cloud as their energy is transferred from one atom to the next.
"This is a photon interaction, which is mediated by atomic interaction. Thanks to this, two photons will behave like one molecule, rather than like two separate particles, when they leave the medium," explains Lukin.
The authors of the study admit that they conducted this experiment more for fun, to test the strength of the fundamental boundaries of science. However, such an amazing discovery can have a lot of practical applications.

For example, photons are the optimal carrier of quantum information, the only problem was the fact that light particles do not interact with each other. To build a quantum computer, it is necessary to create a system that will store units of quantum information and process it using quantum logic operations.
The problem is that such logic requires interaction between individual quanta in such a way that systems switch and perform information processing.
"Our experiment proves that this is possible. But before we can create a quantum switch or a photonic logic gate, we need to improve the performance of photonic molecules," says Lukin. Thus, the current result is only a proof of the concept in practice.
The discovery of physicists will also be useful in the production of classical computers and calculating machines. It will help solve a number of power loss problems faced by computer chip manufacturers.
In the distant future, one day Lukin's followers will probably be able to create a three-dimensional structure, like a crystal, consisting entirely of light.
A description of the experiment and the conclusions of scientists can be found in the article by Lukin and his colleagues, published in the journal Nature.