A recent collaboration of researchers has shown that it is possible, in principle, to measure temperatures below a billionth of a kelvin without significantly disturbing the Bose-Einstein condensate used in the study. Such research could potentially revolutionize low-temperature physics and uncover cold atomic gas applications within emerging quantum technologies.

The research involved both the UK’s University of Nottingham and the Institute of Photonic Sciences from Barcelona, Spain. In the study, researchers modeled a Bose-Einstein condensate—a unique state of matter achieved by cooling an atomic gas down to extremely low temperatures—using realistic experimental parameters.

According to the team, an expanded thermometric technique would work by embedding an impurity atom into the atomic condensate so that it acquires information about the temperature of the sample through interaction. In particular, position and velocity would become temperature dependent so that, by monitoring them, the temperature could be inferred with high accuracy without disturbing the condensate.

Cooling atomic gases
Ultra-cold atomic gases are a very versatile experimental platform for a number of applications. According to the team, this includes simulation of strongly correlated systems, quantum information processing or the production of high-quality (cold) electron beams for electron microscopy or electron diffraction. For most of these applications it is essential to cool down the atomic gas to the lowest temperatures possible, while determining the temperature of these systems precisely is also critical for applications.

“The most common  thermometric techniques currently available  for cold atoms are  destructive; that is, the  sample is destroyed as a result of the measurement,” says Mohammad Mehboudi, lead author of group research published in Physical Review Letters. “On the other hand, non-destructive techniques usually lack the necessary accuracy at very low temperature. Our research provides a solution that overcomes both of these problems”.

Outstanding experimental achievements allow high precision thermometry at very low temperatures. However, depending on the specific experimental platform, the underlying physical  mechanism, accuracy and effective temperature range of different thermometric schemes varies appreciably.

“The newly-developed  theoretical framework of quantum thermometry seeks to determine the fundamental limits on the precision of temperature measurements close to absolute zero; and it applies universally to any system,” says Dr. Luis Correa. “Importantly, this can provide clues as to how to improve current low-temperature thermometric standards.”