Symmetry breaking phase transitions occurring in the early Universe are expected to leave behind long-lived topologically stable structures such as monopoles, strings or domain walls1–6. Here I discuss the analogy between cosmological strings and vortex lines in the superfluid, and suggest a cryogenic experiment which tests key elements of the cosmological scenario for string formation. In a superfluid obtained through a rapid pressure quench, the phase of the Bose condensate wavefunction—the 4He analogue of the broken symmetry of the field-theoretic vacuum—will be chosen randomly in domains of some characteristic size d. When the quench is performed in an annulus of circumference C the typical value of the phase mismatch around the loop will be ∼(C/d)1/2. The resulting phase gradient can foe sufficiently large to cause the superfluid to flow with a measurable (mm s−1), randomly directed velocity.

The Physics of Liquid and Solid Helium

Cosmological Experiments in Superfluid Helium

background or methods

Cosmological experiments in condensed matter systems

We report the attainment of simultaneous quantum degeneracy in a mixed gas of bosons (lithium-7) and fermions (lithium-6). The Fermi gas has been cooled to a temperature of 0.25 times the Fermi temperature by thermal collisions with the evaporatively cooled bosons. At this temperature, the spatial size of the gas is strongly affected by the Fermi pressure resulting from the Pauli exclusion principle and gives clear experimental evidence for quantum degeneracy.

https://science.sciencemag.org/content/sci/291/5513/2570.full.pdf

Observation of Fermi pressure in a gas of trapped atoms.

Reaction dynamics with exotic nuclei

▪ Abstract Laser ablation of in situ metals has recently made it possible to immerse a large number of different metal atoms and ions and small clusters of metal atoms in liquid helium (He) and thus study their absorption and emission spectra in the visible region. Atoms and molecules are readily picked up by large ( ≥ 103 atoms) He droplets, and their spectra are sensitively detected through the use of either beam depletion following absorption or laser-induced fluorescence. Within the past three years, a wide variety of molecules, ranging from OCS to large organic molecules such as amino acids and a number of van der Waals complexes and even large metal clusters, have been embedded in He droplets and studied either in infrared or in the visible region. These results are discussed here in detail, and the evidence for the effect of superfluidity on the spectral features is reviewed.

The Physics of Liquid and Solid Helium

Citations

Cosmological Experiments in Superfluid Helium

Cosmological experiments in condensed matter systems

Observation of Fermi pressure in a gas of trapped atoms.

Reaction dynamics with exotic nuclei

Spectroscopy of atoms and molecules in liquid helium

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