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. TheRollin 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.
Superfluidity often co-occurs withBose–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] Even when superfluidity and condensation co-occur, their magnitudes are not linked: at low temperature, liquid helium has a large superfluid fraction but a low condensate fraction; while a weakly interacting BEC, with almost unity condensate fraction, can display a vanishing superfluid fraction.[3]
Superfluids have some potential practical uses, such as dissolving substances in aquantum solvent.
In liquid helium-4, the superfluidity occurs at far higher temperatures than it does inhelium-3. Each atom of helium-4 is aboson particle, by virtue of itsinteger spin. A helium-3 atom is afermion 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 1996Nobel Prize in Physics.[1] This process is similar to theelectron pairing insuperconductivity.
Superfluidity in anultracoldfermionic gas was experimentally proven byWolfgang Ketterle and his team who observedquantum vortices inlithium-6 at a temperature of 50 nK atMIT in April 2005.[7][8] Such vortices had previously been observed in an ultracoldbosonic gas usingrubidium-87 in 2000,[9] and more recently intwo-dimensional gases.[10] As early as 1999,Lene Hau created such a condensate usingsodium atoms[11] for the purpose of slowing light, and later stopping it completely.[12] Her team subsequently used this system of compressed light[13] to generate the superfluid analogue of shock waves and tornadoes:[14]
These dramatic excitations result in the formation ofsolitons that in turn decay intoquantized 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
The idea that superfluidity exists insideneutron stars was first proposed byArkady Migdal.[15][16] By analogy with electrons insidesuperconductors formingCooper pairs because of electron–lattice interaction, it is expected thatnucleons 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.[17]
In the theory of superfluid dark matter, dark matter can exist in a superfluid state at certain scales that then mediates aMOND like force through phonons in the superfluid, this theory intends to replicate the partial successes of dark matter and modified gravity - at smaller scales the theory produces MOND like dynamics and then allows for a replication of the successes of MOND for example in predicting galaxy rotation curves and a tight Tully-Fisher relation, and avoids problems caused by ordinary cold dark matter theory where dense dark matter halos produce too much dynamical friction.[18][19][20] At larger scales the theory produces behavior similar to warm or hot dark matter which allows for additional mass at the galaxy cluster scale, where MOND under-predicts the strength of gravity, and allows for replication of phenomena that can be well described by dark matter such as the cosmic microwave background.
The ultimate goal of the approach is to develop scientific models that unify quantum mechanics (describing three of the four known fundamental interactions) withgravity. This makes SVT a candidate for the theory ofquantum gravity and an extension of theStandard 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 themurmurations ofstarlings. The rapidity of change in flight patterns mimics the phase change leading to superfluidity in some liquid states.[23]
^Khoury, Justin. 2016. “Another Path for the Emergence of Modified Galactic Dynamics from Dark Matter Superfluidity.” Physical Review D 93 (10): 103533.https://doi.org/10.1103/PhysRevD.93.103533.
