submicrokelvin

Submicrokelvin refers to temperatures below one microkelvin (10^-6 kelvin). This extreme low-temperature regime is most prominently explored in ultracold atomic physics, where quantum effects become dominant, and in certain solid-state systems prepared with nuclear demagnetization techniques. The term emphasizes temperatures well into the quantum degenerate domain, often in the nanokelvin range for atomic gases.

In atomic systems, submicrokelvin temperatures are typically reached by a sequence of cooling stages. Laser cooling and sub-Doppler techniques first bring atoms to the microkelvin or tens of microkelvin range. Evaporative cooling in magnetic or optical traps then reduces the temperature further, producing Bose-Einstein condensates or degenerate Fermi gases at tens to hundreds of nanokelvin. In such gases, phenomena like quantum degeneracy, superfluidity, and quantum phase transitions can be studied with exquisite control over interactions and geometry.

In solid-state and spin systems, submicrokelvin temperatures are often achieved using nuclear demagnetization refrigeration or adiabatic demagnetization. These methods can bring specific spin systems and devices, including some superconducting and magnetic materials, into the nanokelvin to microkelvin range, enabling investigations of quantum magnetism, coherence properties, and decoherence mechanisms in solid-state platforms.

Measuring temperature at submicrokelvin scales relies on techniques such as time-of-flight expansion and momentum-space thermometry for atomic gases, and specialized thermometers calibrated to ultra-low temperatures for solid-state samples. The field faces challenges from residual heating and precise thermometry, but the submicrokelvin regime continues to enable exploration of fundamental quantum behavior and highly controllable quantum systems.