Coldness can be very low {cryogenics}|. Lasers cool by slowing atoms to 50 microKelvin. Magnetic fields can trap and compress gas. Cooling can be by both lasers and magnetic traps {magneto-optical trap} (MOT).
Evaporation cools to below 50 microKelvin by removing hottest atoms. Time-averaged orbital potential (TOP) magnetic trap allows evaporation at point that moves in circle to build gas ellipsoid. Ioffe trap holds plasmas. Ioffe-Pritchard trap can use parallel magnetic fields or other arrangements to form various gas shapes.
properties
Quantum-mechanical effects can change low-temperature material properties, such as superconductivity.
Metal superconductors have bound-electron pairs, each with same spin, which make metal ions, streamline flow, and make bosons that can condense {Bose-Einstein condensation, cryogenics} (BEC). All bosons in same quantum state can condense from gas to make liquid. Repulsive bosons condense better.
At low temperature, fluids {superfluid}| can have no viscous resistance. Liquid helium is the only known superfluid. Vortexes but no overall rotation can appear in spun superfluids. Space-time can be like fluid, and black-hole event horizon can be like superfluid with quantum-phase transition. General relativity has same equations as sound waves in moving fluid.
Helium 4 can cool and compress to solid {supersolid}, with no viscous resistance.
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Date Modified: 2022.0225