ultracold

Ultracold refers to a regime of matter in which temperatures are so low that quantum mechanical effects dominate the behavior of the system. In atomic and molecular physics, ultracold gases are typically cooled to the microkelvin to nanokelvin range, with Bose-Einstein condensates and degenerate Fermi gases realized at tens to hundreds of nanokelvin. At these temperatures the thermal de Broglie wavelength becomes comparable to interparticle spacing, enabling coherent quantum states and the influence of quantum statistics on macroscopic properties.

Techniques to reach ultracold temperatures begin with laser cooling, often in a magneto-optical trap that precools atoms to microkelvin temperatures. Subsequent evaporative cooling in magnetic or optical dipole traps reduces the temperature further to nanokelvin scales. Sympathetic cooling extends ultracold techniques to mixtures. Interactions are commonly tuned with Feshbach resonances, and atoms can be loaded into optical lattices to simulate crystal lattices. For ultracold molecules, methods include assembling molecules from ultracold atoms or direct cooling, though full control remains more challenging due to complex internal structure.

Quantum degenerate gases exhibit phenomena such as Bose-Einstein condensation, superfluidity, and quantum vortices in bosonic systems, and degenerate Fermi motion and pairing in fermionic systems. These systems provide platforms for quantum simulation of many-body physics, precision metrology, and fundamental studies of quantum statistics. Applications include advances in atomic clocks, quantum sensors, interferometry, and exploratory work in quantum information processing.