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What if ice could conduct electricity, atoms could share one quantum state, and matter could repeat a pattern in time? Explore ten unusual states of matter scientists have created or studied, from superfluid helium and superionic ice to time crystals, liquid glass, and quark-gluon plasma.
This science explainer unpacks the physics behind Bose-Einstein and fermionic condensates, supersolids, Rydberg matter, and supercritical fluids. Discover how extreme temperatures, pressure, and quantum behavior transform familiar substances—and what these strange phases reveal about the early universe, distant planets, and the nature of matter.
This science explainer unpacks the physics behind Bose-Einstein and fermionic condensates, supersolids, Rydberg matter, and supercritical fluids. Discover how extreme temperatures, pressure, and quantum behavior transform familiar substances—and what these strange phases reveal about the early universe, distant planets, and the nature of matter.
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00:00So, let's start!
00:01Number 10, Rydberg matter, the unusual condensed state made from highly excited atoms.
00:08Most atoms are found in their lowest energy states, with their electrons occupying relatively
00:13stable arrangements.
00:14But scientists can supply atoms with energy to push their electrons into much higher energy
00:19levels.
00:20These are known as Rydberg atoms, and their properties can become dramatically different
00:25from those of ordinary atoms.
00:26Under certain conditions, highly excited atoms can form unusual extended structures that
00:32researchers study as Rydberg matter.
00:34When an electron is excited into a high energy level, its orbital can become enormously larger
00:40than it would be in the atom's ground state.
00:42This makes the atom unusually sensitive to nearby atoms and electric fields.
00:46Interactions between highly excited atoms can become strong even when the atoms are separated
00:51by distances much greater than those typical of ordinary atomic interactions.
00:56The term Rydberg matter has been used for proposed and experimentally studied arrangements of
01:01highly excited atoms that form loosely bound extended structures.
01:05However, it is important to distinguish these specialized systems from the better established
01:10Rydberg gases routinely produced in laboratories.
01:13Not every collection of excited atoms forms a stable condensed phase, and claims about long-lived
01:19Rydberg matter depend on the particular experimental conditions.
01:22Researchers are interested in these systems because their enormous atomic dimensions and unusual
01:27interactions make them useful for exploring how matter behaves under extreme quantum conditions.
01:33Rydberg atoms are already important in quantum physics research, including experiments involving
01:38controlled interactions between atoms and the development of quantum technologies.
01:43The surprising part is how much an atom's behavior can change when one of its electrons receives enough energy.
01:48The nucleus remains the same, and the atom has not turned into a different element, yet its size,
01:54interactions, and response to its surroundings can be transformed.
01:58In this corner of physics, even an ordinary atom can become an extraordinary experimental object.
02:03Number 9. The superfluid that flows without ordinary viscosity.
02:08Pour honey onto a plate, and it creeps slowly across the surface.
02:12Pour water, and it spreads much more easily.
02:14Now, imagine a liquid that can flow without ordinary viscosity.
02:19The resistance that makes familiar fluids lose energy as they move.
02:23Under the right conditions, certain quantum liquids can do precisely that.
02:27They are known as superfluids, and their behavior is among the strangest phenomena observed in physics.
02:33One famous example is helium-4 cooled to temperatures just above absolute zero.
02:38At ordinary temperatures, helium behaves like a conventional liquid,
02:42but when it reaches approximately 2.17 Kelvin, it undergoes a transition into a superfluid phase.
02:49Its behavior changes dramatically, allowing it to flow through extremely narrow channels with almost no viscosity.
02:56Superfluid helium can also display effects that look astonishing in a laboratory.
03:00It can creep along the walls of a container in a thin film, circulate in persistent currents,
03:06and pass through tiny openings that would strongly restrict an ordinary liquid.
03:10These effects arise from quantum mechanics becoming important on a collective scale,
03:14rather than from individual atoms behaving independently.
03:17At sufficiently low temperatures, a large fraction of the helium atoms occupy a shared quantum state.
03:23This collective behavior allows the liquid to support flow without the ordinary energy losses associated with viscosity.
03:30The details are more complicated than simply saying every atom moves in perfect synchrony,
03:35but quantum coherence is central to understanding the phenomenon.
03:39Superfluidity is not limited to liquid helium.
03:42Certain ultra-cold atomic gases can also become superfluid, allowing scientists to study the effect in highly controlled experiments.
03:49Researchers can manipulate the atoms and observe how superfluid flow responds to obstacles, rotation, and changes in temperature.
03:57The practical applications are more specialized than the dramatic demonstrations might suggest,
04:02but superfluidity is valuable in low temperature physics and sensitive measurement systems.
04:06It also helps scientists investigate the relationship between quantum mechanics and large collections of particles.
04:12A liquid with virtually no ordinary viscosity sounds like something designed for a science fiction laboratory.
04:18Yet superfluidity has been studied for decades,
04:21and it reveals that matter can behave collectively in ways that ordinary fluids never could.
04:26Number 8. Superionic ice.
04:29Where oxygen forms a solid structure while hydrogen ions move through it.
04:33Ice is usually associated with frozen water molecules locked into a rigid structure.
04:39Break a piece apart, and you get smaller pieces of ice.
04:41Warm it enough, and it melts.
04:43But under the enormous pressures and temperatures found deep inside certain planets,
04:48water can enter a state that combines properties we normally associate with solids and liquids.
04:53This state is called superionic ice.
04:56In superionic ice, oxygen atoms form a relatively stable crystalline framework,
05:02while hydrogen ions can move through that structure.
05:05The oxygen arrangement remains solid-like, but the hydrogen behaves much more freely than it does in ordinary ice.
05:11The result is a material with a combination of properties that sounds contradictory
05:16until you consider how differently its two components behave.
05:20Scientists predicted this unusual phase decades before they obtained strong experimental evidence for it.
05:25In 2018, researchers reported evidence of superionic water ice using powerful shock compression experiments.
05:33They subjected water ice to extreme conditions and measured its response,
05:37finding evidence consistent with the predicted superionic state.
05:40Later research has further investigated the conditions under which it forms.
05:44The pressures and temperatures involved are far beyond anything encountered in everyday environments.
05:50They are relevant, however, to the deep interiors of icy giant planets such as Uranus and Neptune.
05:56Scientists suspect that superionic water may occur in substantial regions within these worlds,
06:01although the exact internal structures of the planets remain under investigation.
06:05One particularly interesting property of superionic ice is its electrical conductivity.
06:10Because hydrogen ions can move through the oxygen framework,
06:14the material can conduct electricity much more effectively than ordinary ice.
06:18This could have consequences for understanding the magnetic fields of giant planets,
06:22which are thought to be generated by electrically conducting material moving inside them.
06:27Superionic ice is not simply ordinary ice heated until it becomes a little softer.
06:31It is a distinct phase that appears under extreme conditions,
06:35with its components behaving in fundamentally different ways.
06:39The oxygen structure remains organized while the hydrogen ions become mobile.
06:43Somewhere deep inside a distant planet, water may therefore exist in a form
06:48that resembles neither the ice cubes in a freezer nor the liquid in an ocean.
06:52It is a reminder that familiar substances can adopt extraordinary structures
06:57when nature pushes them far beyond ordinary conditions.
07:00Number seven, the super solid that combines a crystal structure with superfluid properties.
07:06Solids and liquids seem to have opposite characteristics.
07:10A solid maintains an organized structure and resists flowing, while a liquid can move and change shape.
07:16A super solid challenges that simple division by combining crystalline order
07:20with certain superfluid-like properties in the same physical system.
07:24The idea of a super solid was proposed theoretically in the 20th century,
07:29but producing and identifying one experimentally proved difficult.
07:33Scientists needed to find a system that maintained a solid-like pattern
07:37while also displaying the distinctive quantum behavior associated with superfluidity.
07:42Ordinary crystals do not automatically become super solids,
07:45and simply cooling a material is not enough.
07:48A major breakthrough came through experiments with ultra-cold atomic gases.
07:52Researchers used carefully controlled lasers and interactions between atoms
07:57to create quantum systems in which the density developed a repeating pattern
08:01while the system retained quantum coherence.
08:04These experiments provided evidence of super solid behavior in specially engineered systems.
08:09The crystal-like structure is important,
08:11because the atoms are not distributed uniformly throughout space.
08:15Instead, their density forms an organized pattern,
08:18somewhat like the repeating arrangement of atoms in a conventional crystal.
08:21At the same time, the system can exhibit superfluid characteristics associated with collective quantum motion.
08:28There is a subtle distinction here.
08:30A super solid is not simply a normal solid with a few liquid pockets trapped inside it.
08:35The remarkable feature is the coexistence of crystalline order
08:38and superfluid properties within the same quantum system.
08:42The precise microscopic details depend on the experimental platform,
08:46and researchers continue to investigate how these phases form and behave.
08:50Super solids are difficult to create because the conditions must be carefully controlled.
08:55Many demonstrations require ultra-cold temperatures and specialized equipment
08:59that allows scientists to manipulate atomic interactions.
09:02These are not materials that can be produced by freezing water in a household freezer.
09:07Studying super solids helps researchers explore how competing forms of order can coexist in quantum matter.
09:13It also offers a way to investigate collective behavior that cannot be understood by looking at each atom separately.
09:20The strange part is that the categories we use for everyday materials are not always mutually exclusive at the quantum
09:27scale.
09:27Under carefully engineered conditions, matter can maintain a crystal-like structure
09:32while displaying behavior associated with a fluid that flows without ordinary viscosity.
09:38The quark-gluon plasma that recreates conditions found in the early universe.
09:44Everyday matter is built from atoms, and the nuclei of those atoms contain protons and neutrons.
09:50Those particles, in turn, contain even smaller constituents called quarks, held together by particles known as gluons.
09:57Under normal conditions, quarks and gluons remain confined inside composite particles.
10:02But, if matter is heated and compressed to extraordinary extremes, that familiar arrangement can break down.
10:09The resulting state is called quark-gluon plasma.
10:12In this state, quarks and gluons are no longer confined inside individual protons and neutrons in the usual way.
10:19Instead, they form an extremely hot, dense medium in which these fundamental constituents can move within the plasma.
10:26The conditions are so extreme that ordinary atomic structures cannot survive.
10:32Scientists have recreated this state in particle accelerators by smashing heavy atomic nuclei together at enormous energies.
10:39Facilities such as the Large Hadron Collider at CERN collide lead nuclei to generate tiny fireballs that briefly reach temperatures
10:47trillions of degrees.
10:48The resulting plasma exists for an incredibly short time before expanding and cooling, allowing quarks and gluons to combine again
10:56into ordinary particles.
10:58What makes the result particularly remarkable is that the plasma does not behave like a simple, thin gas of freely
11:04moving particles.
11:05Experiments show that it behaves more like a fluid with exceptionally low viscosity.
11:10Researchers study how particles produced in the collision travel through the plasma and lose energy, using these measurements to understand
11:17its properties.
11:18This state of matter is especially important to cosmology because scientists believe the universe passed through a quark-gluon plasma
11:25phase during its earliest moments,
11:27before cooling enough for protons and neutrons to form.
11:30By producing the plasma in the laboratory, physicists can investigate conditions that existed shortly after the Big Bang.
11:37There is a catch. These experiments do not recreate the entire early universe.
11:42They produce microscopic quantities of the plasma for extraordinarily brief periods.
11:46The challenge is to extract useful information from the particles that emerge after the fireball disappears.
11:53Quark-gluon plasma reveals what happens when matter is pushed beyond the conditions that allow familiar particles to remain intact.
12:00By briefly dismantling the building blocks of atomic nuclei, scientists can study a state that has not naturally existed on
12:07Earth under ordinary conditions since the universe was extremely young.
12:12Number five, the fermionic condensate, where pairs of atoms form a collective quantum state.
12:18Most particles in nature belong to one of two broad categories, bosons and fermions.
12:23The distinction matters because the two types follow different quantum rules.
12:28Bosons can occupy the same quantum state in large numbers, while identical fermions cannot all occupy an identical state.
12:35This restriction is known as the Pauli exclusion principle, and it helps explain why ordinary matter has the structure it
12:41does.
12:42Under extremely cold conditions, however, fermionic atoms can form pairs that behave collectively in a way that allows a new
12:49quantum state to emerge.
12:51These paired atoms can act like composite bosons, allowing many pairs to participate in a shared macroscopic quantum state.
12:58The resulting system is called a fermionic condensate.
13:02Scientists created fermionic condensates in ultra-cold atomic gases by cooling fermionic atoms to temperatures close to absolute zero and
13:10carefully controlling how the atoms interact.
13:13Under suitable conditions, pairs form and develop collective quantum behavior.
13:18The process is related to the physics of superconductivity, where electrons form pairs that enable electrical current to flow without
13:25ordinary electrical resistance.
13:27One of the fascinating features of these systems is that researchers can adjust the strength of the interaction between atoms.
13:34Depending on the conditions, the atoms may form tightly bound pairs or loosely bound pairs that resemble those found in
13:40conventional superconductors.
13:42This lets scientists investigate how different forms of pairing connect to one another.
13:46A fermionic condensate is different from a Bose-Einstein condensate, even though both involve collective quantum behavior.
13:53In a typical Bose-Einstein condensate, the particles themselves are bosons, or atoms that behave as bosons.
14:00In a fermionic condensate, the original particles are fermions, and the collective state arises through the formation of pairs.
14:07These experiments are useful because they give researchers a controllable way to investigate questions that are difficult to answer inside
14:14ordinary materials.
14:16The same underlying physics that produces paired states in ultra-cold gases is relevant to superconductors and other complex quantum
14:24systems.
14:25The surprising part is that particles forbidden from sharing one identical quantum state can still form pairs that collectively behave
14:33in a coordinated way.
14:34The rules governing individual particles remain in place, but the pairs create a new route to collective behavior.
14:40Number 4. The time crystal that repeats its pattern in time.
14:45Crystals are known for their repeating structures.
14:48In a conventional crystal, atoms arrange themselves in a pattern that repeats across space.
14:53Salt, diamonds, and many metals contain this kind of spatial order.
14:57But physicists have investigated a different possibility.
15:00A system whose behavior repeats in time rather than only in space.
15:05This is the basic idea behind a time crystal.
15:08The concept was proposed by physicist Frank Wilczek in 2012.
15:12His original idea involved a system that would spontaneously repeat its motion in its lowest energy state,
15:18somewhat like a spatial crystal repeating its structure.
15:21However, later theoretical work showed that the simplest version of this idea cannot occur in equilibrium under ordinary conditions.
15:28Researchers therefore explored more specialized forms of time crystals.
15:32One important example is the discrete time crystal.
15:35These systems are driven by an external sequence of pulses, but their response repeats at a longer period than the
15:42driving cycle.
15:43For example, a system might be stimulated at regular intervals, but respond in a pattern that repeats only after every
15:49two pulses.
15:51This repeating behavior can persist despite certain disturbances, provided the system remains within the conditions required for the time crystalline
15:58phase.
15:59Scientists have observed time crystalline behavior in several carefully engineered systems, including interacting spin systems and quantum processors.
16:08In these experiments, researchers measure how the system changes over time and look for a stable pattern that distinguishes it
16:14from ordinary periodic motion.
16:16The results show that time crystalline order can emerge in specific non-equilibrium quantum systems.
16:22Time crystals do not provide perpetual motion machines, and they do not generate unlimited energy.
16:28The driven versions receive energy from an external source, while the unusual feature lies in the pattern of their response.
16:34Their behavior is governed by the system's interactions and the way it is driven.
16:39Researchers are interested in time crystals because they offer a way to study new kinds of order in quantum systems.
16:44They may also help scientists understand how complex quantum states remain stable in the presence of disturbances.
16:51The name sounds as if someone has frozen time into a repeating loop, but that is not what happens.
16:57A time crystal is a physical system with a distinctive temporal pattern.
17:01Its importance lies in showing that the ways matter can organize themselves are not limited to repeating arrangements in space.
17:09Number three, liquid glass, where particles become trapped in competing arrangements.
17:14Glass is familiar in windows, bottles, and screens, but its physical structure is unusual.
17:20Unlike a conventional crystal, whose particles form a repeating pattern,
17:24glass has a disordered arrangement more similar to a liquid structure.
17:28Yet, glass behaves mechanically like a solid on everyday timescales.
17:33This combination makes glass an important example of matter that does not fit neatly into the usual categories.
17:39Liquid glass refers to a different, more specialized phenomenon
17:43studied in certain systems of particles.
17:45Researchers have investigated materials in which particles form local structures
17:50that can move and rearrange in some ways while remaining trapped or constrained in others.
17:55Rather than settling into a simple crystal or becoming a freely flowing liquid,
18:00the system develops a complicated form of arrested motion.
18:03In a 2021 study, scientists used colloidal particles, which are tiny particles suspended in a fluid,
18:09to investigate this behavior.
18:11The particles had shapes and interactions that allowed them to develop two competing kinds of orientational order.
18:17Instead of forming one uniform arrangement, different groups of particles became constrained
18:22by the surrounding structure while retaining limited freedom to move.
18:26The result was called liquid glass because it combined features associated with a liquid and a glassy material.
18:32Its particles did not settle into a conventional crystalline structure, but their movement became
18:38restricted in a way that prevented the system from behaving like an ordinary liquid.
18:42The phenomenon illustrates how complex collective behavior can emerge when particles compete
18:47between different possible arrangements.
18:50It is important not to confuse liquid glass with the glass used in windows,
18:54or with the common liquid glass coatings sold for surfaces.
18:57The scientific term refers to a specific kind of particle dynamics and structural arrest
19:02investigated under controlled experimental conditions.
19:06It is not a universal new state that every glass material passes through.
19:10Researchers study such systems to understand why some materials stop flowing
19:15even though their particles remain disordered.
19:17This question is relevant to glasses, dense suspensions, and other complex materials,
19:22where motion slows dramatically without the orderly structure of a crystal.
19:26Liquid glass is unusual because its particles become constrained
19:30without organizing themselves into a simple repeating pattern.
19:34The system occupies a complicated middle ground between ordinary fluid motion
19:38and the rigidity associated with glassy behavior.
19:41Number 2.
19:43The supercritical fluid that behaves differently from both ordinary liquids and gases.
19:48Heat water enough at normal atmospheric pressure, and it boils into steam.
19:52Increase the pressure, however, and the transition between liquid and gas
19:56changes.
19:57Beyond a particular temperature and pressure, the distinction between these two phases disappears.
20:02The substance enters a state called a supercritical fluid,
20:05which combines properties that we normally associate with both liquids and gases.
20:10For water, the critical point occurs at approximately 374 degrees Celsius
20:15and 22.1 megapascals of pressure.
20:18Above both values, there is no sharp boundary separating liquid water from water vapor.
20:23Instead, the material becomes a single supercritical phase, whose density and other properties
20:29can vary continuously as the temperature and pressure change.
20:32A supercritical fluid can spread through spaces like a gas while retaining a density more typical
20:37of a liquid.
20:38Its ability to dissolve substances depends on its conditions, making it useful for chemical processes.
20:44By adjusting pressure and temperature, engineers can change the fluid's properties without crossing a
20:49conventional liquid-to-gas phase boundary.
20:52Carbon dioxide is another widely used supercritical fluid.
20:55When placed above its critical temperature and pressure, supercritical carbon dioxide can extract
21:00certain compounds from materials.
21:02This property is used in industrial processes, including the decaffeination of coffee and the
21:07extraction of useful substances from plants.
21:10After extraction, the pressure can be reduced so the carbon dioxide separates from the extracted material.
21:16Supercritical fluids also occur in research on energy, chemistry, and environmental systems.
21:21Scientists investigate their ability to transport materials, accelerate certain reactions,
21:26and interact with substances that are difficult to dissolve in ordinary liquids.
21:31Supercritical water, for example, has distinctive chemical properties that
21:35can be useful in specialized waste treatment and industrial processes.
21:39Despite the name, a supercritical fluid is not a mixture of liquid and gas.
21:44It is a single phase beyond the critical point, where the familiar distinction between those
21:49two states no longer applies.
21:51Its behavior depends on pressure, temperature, and the substance itself.
21:55This state of matter is less exotic than a super solid or a time crystal,
22:00but it has a major practical advantage.
22:02Scientists can use it in real industrial processes.
22:05By crossing a critical point, a familiar substance can acquire a combination of properties
22:10that makes it useful for jobs that ordinary liquids and gases cannot perform as effectively.
22:16Number 1. The Bose-Einstein condensate, where many atoms occupy a shared quantum state.
22:22At everyday temperatures, the atoms in a gas move around with a wide range of energies and directions.
22:28Even if the gas is contained in a small chamber, its atoms behave largely as individual particles,
22:34colliding and moving independently.
22:36But when certain atoms are cooled to temperatures extraordinarily close to absolute zero,
22:42a remarkable transformation can occur.
22:44Many of them begin occupying the same lowest energy quantum state.
22:49This is known as a Bose-Einstein condensate.
22:51The possibility was predicted in the 1920s through work by Satyendra Nath Bose and Albert Einstein.
22:57At sufficiently low temperatures, bosonic particles can no longer be treated as completely independent
23:03classical objects.
23:05Their quantum wave functions overlap, and a large fraction of the particles can occupy a shared
23:10quantum state.
23:11The result is a system in which quantum behavior becomes visible on a scale large enough for
23:16scientists to measure directly.
23:18Creating a Bose-Einstein condensate is extremely challenging.
23:22Researchers typically use laser cooling to slow atoms,
23:25then employ magnetic or optical traps to hold them in place while further cooling them through
23:30techniques such as evaporative cooling.
23:32In 1995, researchers at the University of Colorado Boulder and the Massachusetts Institute of Technology
23:38independently reported the creation of Bose-Einstein condensates in dilute atomic gases,
23:44opening a new field of experimental research.
23:47A condensate is not simply a solid frozen to an extraordinarily low temperature.
23:52The atoms remain in a dilute gas, but their collective quantum state becomes important.
23:57The system can display wave-like behavior on a macroscopic scale, allowing scientists to study
24:03interference, collective excitations, and other quantum effects using carefully controlled experiments.
24:09Bose-Einstein condensates have become valuable tools for exploring fundamental physics.
24:14Researchers use them to investigate superfluidity, simulate complex quantum systems, and develop
24:19extremely sensitive measurement techniques.
24:22They can also be used to create more specialized states, including some super-solid systems,
24:27when additional interactions and carefully designed conditions produce the required structure.
24:32There is an important distinction between a Bose-Einstein condensate and a fermionic condensate.
24:37Bosons can share the same quantum state directly, while fermions cannot all occupy an identical state.
24:44Fermionic systems can nevertheless form collective condensates through pairing, which is why both
24:49kinds of condensation appear in research on unusual quantum matter.
24:54The striking thing about a Bose-Einstein condensate is that the boundary between individual particles
24:59and collective behavior becomes less intuitive.
25:02Instead of acting like a crowd of completely independent atoms, the system can behave in ways
25:07described by a shared quantum state.
25:10Scientists have effectively made quantum behavior visible across a collection of atoms,
25:15providing a powerful way to investigate some of the deepest rules governing matter.
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