Scientists at the US Department of Energy’s National SLAC Accelerator Laboratory cooled liquid helium to -456° F (-271° C) or 2 Kelvin using a free-electron X-ray laser as part of the LCLS II project. This temperature is only 2 Kelvin higher than the absolute zero, the lowest possible temperature at which the motion of particles stops.
Such a low temperature is very important for technology because it causes superconductivity, a phenomenon in which the loss of energy transfer is almost zero. Even the “vacuum” areas of space are not as cold, as they are still filled with cosmic microwave background radiation left from the Big Bang and have a uniform temperature of -454° F (-271° C) or 3 Kelvin.
The LCLS-II laser can accelerate electrons at a rate of 1 million pulses per second, which is a world record. Such a spec will allow scientists to study complex materials with unprecedented detail. High-intensity high-frequency laser pulses allow us to see how electrons and atoms interact in materials, how natural and artificial molecular systems convert sunlight into fuel, and how to control these processes. It will also help to understand the fundamental properties of materials that will enable quantum computing.
By the way, at a temperature of 2 Kelvin helium becomes superfluid, and is called helium II, which has unusual properties – it conducts heat hundreds of times more efficiently than copper, and has such a low viscosity that it is simply impossible to measure.