Superfluidity

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Helium II will "creep" along surfaces in order to find its own level--after a short while, the levels in the two containers will equalize. The Rollin film also covers the interior of the larger container; if it were not sealed, the helium II would creep out and escape. Helium-II-creep.svg
Helium II will "creep" along surfaces in order to find its own level—after a short while, the levels in the two containers will equalize. The Rollin film also covers the interior of the larger container; if it were not sealed, the helium II would creep out and escape.
The liquid helium is in the superfluid phase. A thin invisible film creeps up the inside wall of the bowl and down on the outside. A drop forms. It will fall off into the liquid helium below. This will repeat until the cup is empty--provided the liquid remains superfluid. Liquid helium Rollin film.jpg
The liquid helium is in the superfluid phase. A thin invisible film creeps up the inside wall of the bowl and down on the outside. A drop forms. It will fall off into the liquid helium below. This will repeat until the cup is empty—provided the liquid remains superfluid.

Superfluidity is the characteristic property of a fluid with zero viscosity which therefore flows without any loss of kinetic energy. When stirred, a superfluid forms vortices that continue to rotate indefinitely. Superfluidity occurs in two isotopes of helium (helium-3 and helium-4) when they are liquefied by cooling to cryogenic temperatures. It is also a property of various other exotic states of matter theorized to exist in astrophysics, high-energy physics, and theories of quantum gravity. [1] The theory of superfluidity was developed by Soviet theoretical physicists Lev Landau and Isaak Khalatnikov.

Contents

Superfluidity often co-occurs with Bose–Einstein condensation, but neither phenomenon is directly related to the other; not all Bose–Einstein condensates can be regarded as superfluids, and not all superfluids are Bose–Einstein condensates. [2] Superfluids have some potential practical uses, such as dissolving substances in a quantum solvent.

Superfluidity of liquid helium

Superfluidity was discovered in helium-4 by Pyotr Kapitsa [3] and independently by John F. Allen and Don Misener [4] in 1937. Onnes possibly observed the superfluid phase transition on August 2 1911, the same day that he observed superconductivity in mercury. [5] It has since been described through phenomenology and microscopic theories.

In liquid helium-4, the superfluidity occurs at far higher temperatures than it does in helium-3. Each atom of helium-4 is a boson particle, by virtue of its integer spin. A helium-3 atom is a fermion particle; it can form bosons only by pairing with another particle like itself, which occurs at much lower temperatures. The discovery of superfluidity in helium-3 was the basis for the award of the 1996 Nobel Prize in Physics. [1] This process is similar to the electron pairing in superconductivity.

Cold atomic gases

Superfluidity in an ultracold fermionic gas was experimentally proven by Wolfgang Ketterle and his team who observed quantum vortices in lithium-6 at a temperature of 50 nK at MIT in April 2005. [6] [7] Such vortices had previously been observed in an ultracold bosonic gas using rubidium-87 in 2000, [8] and more recently in two-dimensional gases. [9] As early as 1999, Lene Hau created such a condensate using sodium atoms [10] for the purpose of slowing light, and later stopping it completely. [11] Her team subsequently used this system of compressed light [12] to generate the superfluid analogue of shock waves and tornadoes: [13]

These dramatic excitations result in the formation of solitons that in turn decay into quantized vortices—created far out of equilibrium, in pairs of opposite circulation—revealing directly the process of superfluid breakdown in Bose–Einstein condensates. With a double light-roadblock setup, we can generate controlled collisions between shock waves resulting in completely unexpected, nonlinear excitations. We have observed hybrid structures consisting of vortex rings embedded in dark solitonic shells. The vortex rings act as 'phantom propellers' leading to very rich excitation dynamics.

— Lene Hau, SIAM Conference on Nonlinear Waves and Coherent Structures

Superfluids in astrophysics

The idea that superfluidity exists inside neutron stars was first proposed by Arkady Migdal. [14] [15] By analogy with electrons inside superconductors forming Cooper pairs because of electron–lattice interaction, it is expected that nucleons in a neutron star at sufficiently high density and low temperature can also form Cooper pairs because of the long-range attractive nuclear force and lead to superfluidity and superconductivity. [16]

In high-energy physics and quantum gravity

Superfluid vacuum theory (SVT) is an approach in theoretical physics and quantum mechanics where the physical vacuum is viewed as superfluid.[ citation needed ]

The ultimate goal of the approach is to develop scientific models that unify quantum mechanics (describing three of the four known fundamental interactions) with gravity. This makes SVT a candidate for the theory of quantum gravity and an extension of the Standard Model.[ citation needed ]

It is hoped that development of such a theory would unify into a single consistent model of all fundamental interactions, and to describe all known interactions and elementary particles as different manifestations of the same entity, superfluid vacuum.[ citation needed ]

On the macro-scale a larger similar phenomenon has been suggested as happening in the murmurations of starlings. The rapidity of change in flight patterns mimics the phase change leading to superfluidity in some liquid states. [17]

Light behaves like a superfluid in various applications such as Poisson's Spot. As the liquid helium shown above, light will travel along the surface of an obstacle before continuing along its trajectory. Since light is not affected by local gravity its "level" becomes its own trajectory and velocity. Another example is how a beam of light travels through the hole of an aperture and along its backside before diffraction.[ citation needed ]

See also

Related Research Articles

<span class="mw-page-title-main">Bose–Einstein condensate</span> State of matter

In condensed matter physics, a Bose–Einstein condensate (BEC) is a state of matter that is typically formed when a gas of bosons at very low densities is cooled to temperatures very close to absolute zero, i.e., 0 K. Under such conditions, a large fraction of bosons occupy the lowest quantum state, at which microscopic quantum-mechanical phenomena, particularly wavefunction interference, become apparent macroscopically. More generally, condensation refers to the appearance of macroscopic occupation of one or several states: for example, in BCS theory, a superconductor is a condensate of Cooper pairs. As such, condensation can be associated with phase transition, and the macroscopic occupation of the state is the order parameter.

Superfluid helium-4 is the superfluid form of helium-4, an isotope of the element helium. A superfluid is a state of matter in which matter behaves like a fluid with zero viscosity. The substance, which resembles other liquids such as helium I, flows without friction past any surface, which allows it to continue to circulate over obstructions and through pores in containers which hold it, subject only to its own inertia.

<span class="mw-page-title-main">State of matter</span> Forms, such as solid, liquid and gas, which matter can take

In physics, a state of matter is one of the distinct forms in which matter can exist. Four states of matter are observable in everyday life: solid, liquid, gas, and plasma. Many intermediate states are known to exist, such as liquid crystal, and some states only exist under extreme conditions, such as Bose–Einstein condensates and Fermionic condensates, neutron-degenerate matter, and quark–gluon plasma.

This is a timeline of states of matter and phase transitions, specifically discoveries related to either of these topics.

Quantum turbulence is the name given to the turbulent flow – the chaotic motion of a fluid at high flow rates – of quantum fluids, such as superfluids. The idea that a form of turbulence might be possible in a superfluid via the quantized vortex lines was first suggested by Richard Feynman. The dynamics of quantum fluids are governed by quantum mechanics, rather than classical physics which govern classical (ordinary) fluids. Some examples of quantum fluids include superfluid helium, Bose–Einstein condensates (BECs), polariton condensates, and nuclear pasta theorized to exist inside neutron stars. Quantum fluids exist at temperatures below the critical temperature at which Bose-Einstein condensation takes place.

<span class="mw-page-title-main">Roton</span> Collective excitation in superfluid helium-4 (a quasiparticle)

In theoretical physics, a roton is an elementary excitation, or quasiparticle, seen in superfluid helium-4 and Bose–Einstein condensates with long-range dipolar interactions or spin-orbit coupling. The dispersion relation of elementary excitations in this superfluid shows a linear increase from the origin, but exhibits first a maximum and then a minimum in energy as the momentum increases. Excitations with momenta in the linear region are called phonons; those with momenta close to the minimum are called rotons. Excitations with momenta near the maximum are called maxons.

<span class="mw-page-title-main">Supersolid</span> State of matter

In condensed matter physics, a supersolid is a spatially ordered material with superfluid properties. In the case of helium-4, it has been conjectured since the 1960s that it might be possible to create a supersolid. Starting from 2017, a definitive proof for the existence of this state was provided by several experiments using atomic Bose–Einstein condensates. The general conditions required for supersolidity to emerge in a certain substance are a topic of ongoing research.

<span class="mw-page-title-main">Fermionic condensate</span> State of matter

A fermionic condensate is a superfluid phase formed by fermionic particles at low temperatures. It is closely related to the Bose–Einstein condensate, a superfluid phase formed by bosonic atoms under similar conditions. The earliest recognized fermionic condensate described the state of electrons in a superconductor; the physics of other examples including recent work with fermionic atoms is analogous. The first atomic fermionic condensate was created by a team led by Deborah S. Jin using potassium-40 atoms at the University of Colorado Boulder in 2003.

<span class="mw-page-title-main">Lene Hau</span> Danish physicist and educator (born 1959)

Lene Vestergaard Hau is a Danish physicist and educator. She is the Mallinckrodt Professor of Physics and of Applied Physics at Harvard University.

A quantum fluid refers to any system that exhibits quantum mechanical effects at the macroscopic level such as superfluids, superconductors, ultracold atoms, etc. Typically, quantum fluids arise in situations where both quantum mechanical effects and quantum statistical effects are significant.

In condensed matter physics, an ultracold atom is an atom with a temperature near absolute zero. At such temperatures, an atom's quantum-mechanical properties become important.

<span class="mw-page-title-main">Quantum vortex</span> Quantized flux circulation of some physical quantity

In physics, a quantum vortex represents a quantized flux circulation of some physical quantity. In most cases, quantum vortices are a type of topological defect exhibited in superfluids and superconductors. The existence of quantum vortices was first predicted by Lars Onsager in 1949 in connection with superfluid helium. Onsager reasoned that quantisation of vorticity is a direct consequence of the existence of a superfluid order parameter as a spatially continuous wavefunction. Onsager also pointed out that quantum vortices describe the circulation of superfluid and conjectured that their excitations are responsible for superfluid phase transitions. These ideas of Onsager were further developed by Richard Feynman in 1955 and in 1957 were applied to describe the magnetic phase diagram of type-II superconductors by Alexei Alexeyevich Abrikosov. In 1935 Fritz London published a very closely related work on magnetic flux quantization in superconductors. London's fluxoid can also be viewed as a quantum vortex.

Macroscopic quantum phenomena are processes showing quantum behavior at the macroscopic scale, rather than at the atomic scale where quantum effects are prevalent. The best-known examples of macroscopic quantum phenomena are superfluidity and superconductivity; other examples include the quantum Hall effect, Josephson effect and topological order. Since 2000 there has been extensive experimental work on quantum gases, particularly Bose–Einstein condensates.

Lev Petrovich Pitaevskii was a Russian theoretical physicist, who made contributions to the theory of quantum mechanics, electrodynamics, low-temperature physics, plasma physics, and condensed matter physics. Together with his PhD supervisor Evgeny Lifshitz and with Vladimir Berestetskii, he was also the co-author of a few volumes of the influential Landau–Lifschitz Course of Theoretical Physics series. His academic status was professor.

Bose–Einstein condensation can occur in quasiparticles, particles that are effective descriptions of collective excitations in materials. Some have integer spins and can be expected to obey Bose–Einstein statistics like traditional particles. Conditions for condensation of various quasiparticles have been predicted and observed. The topic continues to be an active field of study.

Sandro Stringari is an Italian theoretical physicist, who has contributed to the theory of quantum many-body physics, including atomic nuclei, quantum liquids and ultra-cold atomic Bose and Fermi gases. He has developed in a systematic way the sum rule approach to the collective behavior of interacting systems.

Tin-Lun "Jason" Ho is a Chinese-American theoretical physicist, specializing in condensed matter theory, quantum gases, and Bose-Einstein condensates. He is known for the Mermin-Ho relation.

YuryMikhailovich Bunkov is a Russian experimental physicist, specializing in condensed matter physics. He is known as one of the co-discoverers of the quantum spin liquid state.

Turbulent phenomena are observed universally in energetic fluid dynamics, associated with highly chaotic fluid motion, and typically involving excitations spreading over a wide range of length scales. The particular features of turbulence are dependent on the fluid and geometry, and specifics of forcing and dissipation.

References

  1. 1 2 "The Nobel Prize in Physics 1996 – Advanced Information". www.nobelprize.org. Retrieved 2017-02-10.
  2. ↑ Liu, Jerry Z. (2021), Superfluids Are Not Fluids (PDF), Stanford University, retrieved 15 November 2024
  3. ↑ Kapitza, P. (1938). "Viscosity of Liquid Helium Below the λ-Point". Nature. 141 (3558): 74. Bibcode:1938Natur.141...74K. doi: 10.1038/141074a0 . S2CID   3997900.
  4. ↑ Allen, J. F.; Misener, A. D. (1938). "Flow of Liquid Helium II". Nature. 142 (3597): 643. Bibcode:1938Natur.142..643A. doi:10.1038/142643a0. S2CID   4135906.
  5. ↑ van Delft, Dirk; Kes, Peter (2010-09-01). "The discovery of superconductivity". Physics Today. 63 (9): 38–43. Bibcode:2010PhT....63i..38V. doi: 10.1063/1.3490499 . ISSN   0031-9228.
  6. ↑ "MIT physicists create new form of matter". mit.edu. 22 June 2005. Retrieved November 22, 2010.
  7. ↑ Grimm, R. (2005). "Low-temperature physics: A quantum revolution". Nature. 435 (7045): 1035–1036. Bibcode:2005Natur.435.1035G. doi: 10.1038/4351035a . PMID   15973388. S2CID   7262637.
  8. ↑ Madison, K.; Chevy, F.; Wohlleben, W.; Dalibard, J. (2000). "Vortex Formation in a Stirred Bose–Einstein Condensate". Physical Review Letters. 84 (5): 806–809. arXiv: cond-mat/9912015 . Bibcode:2000PhRvL..84..806M. doi:10.1103/PhysRevLett.84.806. PMID   11017378. S2CID   9128694.
  9. ↑ Burnett, K. (2007). "Atomic physics: Cold gases venture into Flatland". Nature Physics. 3 (9): 589. Bibcode:2007NatPh...3..589B. doi: 10.1038/nphys704 .
  10. ↑ Hau, L. V.; Harris, S. E.; Dutton, Z.; Behroozi, C. H. (1999). "Light speed reduction to 17 metres per second in an ultracold atomic gas". Nature. 397 (6720): 594–598. Bibcode:1999Natur.397..594V. doi:10.1038/17561. S2CID   4423307.
  11. ↑ "Lene Hau". Physicscentral.com. Retrieved 2013-02-10.
  12. ↑ Hau, Lene Vestergaard (2003). "Frozen Light" (PDF). Scientific American: 44–51.
  13. ↑ Hau, Lene (September 9–12, 2006). "Shocking Bose–Einstein Condensates with Slow Light". SIAM.org. Society for Industrial and Applied Mathematics.
  14. ↑ A. B. Migdal (1959). "Superfluidity and the moments of inertia of nuclei". Nucl. Phys. 13 (5): 655–674. Bibcode:1959NucPh..13..655M. doi:10.1016/0029-5582(59)90264-0.
  15. ↑ A. B. Migdal (1960). "Superfluidity and the Moments of Inertia of Nuclei". Soviet Phys. JETP. 10 (5): 176. Bibcode:1959NucPh..13..655M. doi:10.1016/0029-5582(59)90264-0.
  16. ↑ U. Lombardo & H.-J. Schulze (2001). "Superfluidity in Neutron Star Matter". Physics of Neutron Star Interiors. Lecture Notes in Physics. Vol. 578. pp. 30–53. arXiv: astro-ph/0012209 . doi:10.1007/3-540-44578-1_2. ISBN   978-3-540-42340-9. S2CID   586149.
  17. ↑ Attanasi, A.; Cavagna, A.; Del Castello, L.; Giardina, I.; Grigera, T. S.; Jelić, A.; Melillo, S.; Parisi, L.; Pohl, O.; Shen, E.; Viale, M. (2014). "Information transfer and behavioural inertia in starling flocks". Nature Physics. 10 (9): 615–698. arXiv: 1303.7097 . Bibcode:2014NatPh..10..691A. doi:10.1038/nphys3035. PMC   4173114 . PMID   25264452.

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