Turning on the atom tap

19 August 2003

By Nick Robins, Cristina Figl, Matthew Jeppesen, Graham Dennis and John D. Close 

The atom laser team of the ARC Centre of Excellence for Quantum-Atom Optics (ACQAO) at the Australian National University has recently produced a pumped atom laser. The results have been published in nature physics [Nature Physics 4, 731 - 736 (2008)]. 

Precision measurement is a research field that most of society is blissfully unaware of. We all benefit from precision measurement, and we all march to the beat of its drum. Modern atomic clocks, for example, lose or gain about one second in one hundred-million years and are the basis of the global positioning system that tells us where we are.  Our ability to precisely measure length has allowed us to produce ever smaller and faster electronics that form the basis of our mobile phones, our computers and the internet. Precision measurement is at the heart of our technology driven society.  

There are many reasons to think that coherent ultra-cold atoms will be the basis for a new revolution in measurement science. They offer the possibility of measurement of magnetic fields, electric fields, gravitational fields, rotations and accelerations with a sensitivity undreamt of a few years ago. Applications can be expected in mineral exploration, and navigation both on earth and in space. 

Coherent ultra-cold atoms are known as Bose-Einstein condensates: Macroscopic quantum mechanical materials that can be coerced to produce a coherent beam of matter waves, in analogy to the light beam produced by a conventional optical laser.   We hope to use this ‘atom laser’ as the basis for a swathe of new devices, some offering staggering improvements in measurement sensitivity.    

However, until now there has been a problem. “Ah-ha” I hear you say.  The atom laser quickly drained the source Bose-Einstein condensate, and the device switched off.  Such short-term operation is fine for fundamental research, but for applications it’s a dead end.  New research from our group shows how to refuel the material, potentially allowing continuous operation of the atom laser.  

Schematic diagram of the operation of the pumped atom laser. a–f, Schematic diagram of the experiment (a) and pumping steps (b–f). A radiofrequency field spin-flips the atoms to the |2,0> state (b), and they fall under gravity (c). The light field couples the atoms to the F' =1 excited state from which they are stimulated to emit into the |1,-1> BEC. The atomic momentum is cancelled by the absorption and emission of the photons (d,e). A second radiofrequency field finally output-couples the atoms into the |1,0> atom laser (f). g, Absorption image of the experimental system, showing source, laser mode and output beam.

By overcoming a number of serious, long standing theoretical and technical hurdles, mainly related to the delicate nature of the Bose-Einstein condensate that forms the source of the atom laser, our team has made a real breakthrough in this field. Using the technique of sympathetic cooling (evaporative cooling of one type of atom cools a second species via thermal contact) we produce two independent, spatially separated clouds of ultra-cold atoms in different internal atomic states, thus creating the source and laser modes. The source is coupled to the laser mode via a three-step process: radio-frequency coupling to an appropriate magnetic state; excitation by an optical field that is resonant only with the source atoms; and finally stimulated transitions from an excited atomic state into the laser mode. This technique paves the way for a potentially unlimited source of ultra-high brightness atoms.  

Scientists Graham Dennis, Nick Robins, Cristina Figl, John Close, and Matthew Jeppesen (circled, from left to right) have produced a pumped atom laser.

Our job right now is to compare devices made with an atom laser to the current cutting edge of measurement technology and really answer the question: how much better are these devices.  That’s the next big step, and the one industry and Government are waiting for. 

For more information, please visit our website (http://atomlaser.anu.edu.au) or see our [Nature Physics 4, 731 - 736 (2008)].

Media comments on our work can also be found on our website (http://atomlaser.anu.edu.au/publications/media_coverage.html).