A design for a “quantum thermometer” that can probe the ultracold temperatures of Bose–Einstein condensates (BECs) without damaging them has been unveiled by physicists in Spain and the UK. The team, led by Mohammad Mehboudi at the Barcelona Institute of Science and Technology, validated their design by doing theoretical calculations but the technique has yet to be tested in the lab. If successful, the thermometer could lead to better quantum simulations.
BECs are atomic gases that have been trapped and chilled to ultracold temperatures so that nearly all the atoms condense into one macroscopic quantum state. BECs have a wide range of applications including simulating quantum states of matter and quantum metrology. These applications require the precise tuning of BEC properties including its temperature.
Today, the most accurate methods for monitoring BEC temperatures involve releasing the atoms from the trap and measuring their speeds. Although this method allows highly precise measurements of temperatures below 1 nK, it destroys the BEC. Less destructive techniques are also available, but these are not very accurate at nanoKelvin and lower temperatures.
Bose polaron model
Mehboudi’s team proposes that BEC temperatures could be measured both accurately and non-destructively by introducing impurity atoms to the atomic gas to act as temperature probes. This is described by the “Bose polaron model”, whereby measurements on an embedded impurity cause minimal disturbance of the BEC.
Using mathematical models of a 1D BEC, the researchers have shown that the BEC temperature could be determined by making repeated measurement of the speed and position of the impurity atoms. Their calculations suggest that this could be done without unduly affecting the BEC
The physicists calculated that for a potassium atom BEC between 200 pK and 2 nK, temperatures could be probed within an error of less than 14%, when using ytterbium atoms as impurities. Such a high level of accuracy would not only make the technique an order of magnitude more effective than existing non-destructive techniques; it could also compete directly with destructive measurements.
Mehboudi and colleagues believe that with further research, their technique could be extended to work with 2D and even 3D BECs in the future. They also stress that their design is within the experimental capabilities of many current physics labs, potentially allowing for BEC-based quantum simulations to become commonplace.
The research is described in Physical Review Letters.
