20 years of Bose–Einstein condensates: current trends and applications of ultracold quantum gases

The year 2015 marked the twentieth anniversary of the achievement of Bose–Einstein condensation in dilute alkali gases. The two decades following these landmark experiments have demonstrated an impact extending far beyond their initial setting. This Special Issue of Journal of Modern Optics showcases a few of the directions that research and scientific developments, indebted to the BEC machinery, have taken. These include systems where the internal quantum states come into play [1, 2] as well as the study of ultracold fermions [3] and particles with dipolar interactions [4]. Such diverse and rich systems have become of more than academic interest due to an ever-increasing technical ability to harness and manipulate multiple atomic species, simultaneously [5]. In this context, mastering of optical potentials to confine ultracold atoms has played a crucial role. This may take the form of optical lattices [6, 7] of various symmetries or trapping in quasi 1-D and 2-D geometries [8]. The remarkable level of control over ultracold atoms encountered in today’s experiments can be used to implement paradigmatic quantum mechanical models from condensed matter theory and other areas. Indeed, the development of experimental platforms for manipulating well-defined ultracold bosonic and fermionic systems has paved the way for performing quantum simulations [9]. Along with prospects of quantum metrology and quantum information processing, this fuels device-oriented efforts such as atom chips [10] – an indicator that the field has come to a considerable maturity. For several of modern day directions, the Bose–Einstein condensate (BEC) could be considered an enabling resource, in the same sense as the magneto-optical trap enabled BEC production and frequency tunable lasers enabled magneto-optical trapping. Nevertheless, BECs continue to fascinate in their own right and still interesting questions are explored within the framework of the original pioneering experiments [11].

The 1995 experiments triggered a true avalanche of experimental and theoretical efforts, opening up the field of ultracold and quantum degenerate matter. The amount of ground that was covered in the years immediately following the BEC discovery was quite remarkable, if not awe-inspiring. Some slowing down could have been anticipated, but what is really remarkable is that progress has remained at a very high pace and that, 20 years later, we are witnessing a field that is not only alive and well, but is still able to spur research in new and surprising directions. The current Special Issue serves as a small testimony to this and we would like to say ‘Happy Birthday, BEC and many happy returns’!

Gabriele De Chiara
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Niels Kjærgaard
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Ludwig Mathey
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Patrick Windpassinger
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