Laser cooling of cavitating bubbles for quantum technology applications

Abstract

Since its invention almost 50 years ago, laser cooling has become a very powerful technique for cooling single atomic particles to very low temperatures. Laser cooling has been an essential tool in many fun- damental tests of quantum physics but also enabled a wide range of quantum technologies. Unfortunately, laser cooling does not work for macroscopic systems, since these have a continuum of phonon modes and cooling all of them simultaneously becomes impossible without also inducing heating processes. Some tricks have been found to trans- fer atomic gases to very low temperatures, as needed for example for the preparation of Bose-Einstein condensates. But these techniques, like evaporative cooling have many disadvantages, and require for ex- ample the removal of atoms from the trap. Here we have a closer look at alternative techniques for cooling atomic gases to very low temperatures. We propose to cool only a single collective mode of the gas but then use energy transfer pro- cesses due to thermalisation to lower the temperature of the remain- ing modes. As we shall see below,these thermalisation processes occur naturally in cavitating bubbles. Moreover, bubble collapse phases can be used to establish a collective phonon mode, which can be cooled very eciently. In summary, this thesis discusses the collective laser cooling of an atomic gas in cavitating bubbles. Moreover, we show that these might have applications as quantum heat exchangers, which cool a surrounding liquid for micro and nano technology applications. We hope that our work helps to initiate novel quantum optics experiments with cavitating bubbles.