When you think about the temperatures associated with “cold,” you probably imagine a cold winter day, or a block of ice (32 °F, 0 °C, or 273.15 K). This is downright balmy compared to the nanokelvin (10-9 K) temperatures physicists can regularly achieve in the lab. Now, things are about to get even chillier with a new technique that can reduce the entropy—and therefore temperature—of a cold gas to near-absolute zero by finely controlling the number and energy level of atoms.
At near-absolute-zero temperatures, atoms can be held in an optical lattice—formed by standing light waves, where the atoms sit in the troughs of the waves at low potential energy. At these temperatures, they lose most of their thermal fluctuations and begin to act like an ideal quantum system. Atoms held in an optical lattice can be used to simulate electrons trapped in a crystalline solid, so this quantum system can be helpful in studying important phenomena like quantum magnetism and high-temperature superconductivity. The atoms could also be used for quantum logic gates and registers (the working memory of quantum computers).
Unfortunately, to truly create an ideal quantum system, physicists have to reach temperatures extremely close to absolute zero, in the picokelvin (pK, 10-12 K) range. The current record for low temperature is 100 pK, but this wasn’t a gas held in an optical lattice.