Quantum gas free fall experiment creates coldest temperature ever recorded
Physicists in Germany have produced the coldest temperature ever recorded – a chilly 38 trillionths of a degree above absolute zero. The strange experiment involved dropping a quantum gas, and switching a magnetic field on and off to bring its atoms to an almost complete standstill.
Measured as -273.15 °C (-459.67 °F), absolute zero is the coldest temperature possible on the thermodynamic scale, representing the point where there’s no atomic motion or heat at all. However, it’s impossible for scientists to ever reach that mark, since we can’t ever remove all the kinetic energy from the atoms in a system.
But scientists consistently come pretty close – a few years ago, a Harvard team studied the coldest-ever chemical reaction at 500 nanoKelvin, or 500 millionths of a degree above absolute zero. And the Cold Atom Lab onboard the International Space Station has conducted experiments at just 100 nanoKelvin.
But those temperatures are balmy compared to those achieved in the new study. A German team has now recorded an effective temperature of just 38 picoKelvin, or 38 trillionths of a degree above absolute zero.
To do so, the researchers started with a cloud of 100,000 rubidium atoms trapped in a magnetic field in a vacuum chamber. They then cooled this down to form a quantum gas called a Bose-Einstein Condensate (BEC), where the atoms begin acting essentially like one big atom, allowing strange quantum effects to become visible on the macro scale.
At two billionths of a degree above absolute zero, however, this wasn’t quite cold enough. So the team ran an experiment at the Bremen Drop Tower research facility, dropping the BEC trap 120 m (393.7 ft). During the free fall, the team switched the magnetic field containing the gas off and on repeatedly.
When the magnetic field is off, the gas begins to expand, and when it’s turned back on the gas is forced to contract again. This switching slows the expansion of the gas almost to a complete stop, and reducing this molecular speed effectively reduces the temperature.
While the experiment only managed to achieve this record-breaking temperature for up to two seconds, simulations showed that it should be possible to maintain it for up to 17 seconds in a weightless environment, such as onboard a satellite.
The research was published in the journal Physical Review Letters.