The radio waves have been cooled to close to their quantum ground state, a process that suppresses noise from radio detection, allowing even the weakest signals to stand out. This achievement could advance many areas of research where small fluctuations in temperature hamper progress, including the detection of dark matter, a step necessary to explain the composition of 85% of the mass of the universe.
Radio stations may aspire to be cool, but for most people the idea that the radio waves themselves have a temperature sounds like a category mistake. However, the antenna with which we detect radio waves is made up of atoms which, like everything else in the universe, move around in a random fashion, introducing noise into the system. Because movements reflect the temperature of the antenna, physicists qualify the affected radio signals as hot.
A strong radio signal nearby can overwhelm any heat in the system, allowing us to listen to our favorite music with clarity. However, when we are trying to harness radio waves to the limit of our ability to hear, it is essential to cool the antenna, and therefore the waves themselves, to avoid being overwhelmed by static electricity. A team from Delft University of Technology announced in Science Advances that it has brought radio waves to temperatures close to the coolest possible temperatures.
For ordinary cooling purposes, an object can be bathed in a very cold medium, such as liquid nitrogen, which dissipates heat. When even cooler temperatures are needed, for example to remove heat that could overpower signals from an MRI machine, liquid helium is used instead, bringing temperatures down to just 2.2 degrees at- above absolute zero.
Even that is way too hot for research purposes, however. Optical, infrared, and gigahertz telescopes have used quantum techniques to cool electromagnetic radiation, but these have failed at frequencies of several hundred megahertz, coincidentally those used by FM radio stations.
It is this part of the spectrum that Professor Gary Steele and his co-authors seek to calm down. They used an adaptation of laser cooling techniques that recently set a world record of 38 picoKelvins (38 trillion degrees above absolute zero). The adapted process is known as photon pressure coupling and uses the radiation pressure of photons at a frequency to extract heat from those located elsewhere on the electromagnetic spectrum. Steele and his co-authors coupled two superconducting circuits and transferred heat between them to obtain their superb cold radio waves.
“The dominant noise that remains in the circuit is only due to quantum fluctuations, the noise that comes from the weird quantum jumps predicted by quantum mechanics,” Steele said in a statement.
The general idea of photo-pressure coupling has been around for several years, but the article claims that the authors achieved about 10 times the coupling strength of anything previously reported. This caused the radio signals to record low temperatures, but the team describes ways in which they expect to descend even lower, taking actual temperatures “well below the physical temperature of any bath. “. These could allow much more sensitive radio detection than anything that has been achieved so far, which could prove invaluable for dark matter detection or some quantum computing operations.
