Turning on the atom laser

The first practical atom laser is a step closer today thanks to Australian researchers.

The researchers have shown how to refuel the laser with ‘quantum foam’ allowing continuous operation. The results, reported today in Nature Physics, hold great promise for precision measurement in navigation, industry and mining and for fundamental tests of quantum mechanics.

Ten years ago the first atom laser brought its US inventers a Nobel prize. They discovered how to persuade ‘quantum foam’ (more properly known as Bose-Einstein condensate) to produce a beam of matter waves just as lasers produce an intense light beam.

Scientists 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: the atom laser quickly drained the source material, and the device switched off. Such short-term operation is fine for fundamental research, but for applications it’s a dead end.
“We discovered how to refuel the material, potentially allowing continuous operation of the atom laser,” says lead author, Nick Robins from the Australian National University.
“We had to overcome a series of theoretical and technical hurdles, mainly related to the delicate nature of the Bose-Einstein condensate. It only exists at near absolute zero and is hard to maintain.”
“Our work paves the way for a potentially unlimited source of ultra-high brightness atoms. It’s like going from a trickle of atoms leaking from a thimble to turning on an atom tap,” says Nick.
The atom laser offers 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 medical research, mineral exploration, and navigation both on earth and in space.
“We all march to the beat of precision measurement. Modern atomic clocks, for example, lose or gain about one second in one hundred-million years and are at the heart of GPS navigation,” says Nick.
“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.”
John Close, an ANU co-author on the paper says “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 that industry and government are waiting for.”
An ‘atom laser’ is essentially an ultra-bright beam of atoms.  Normally atoms behave like microscopic billiard balls, bouncing around, independently of one another.  However, in an atom laser they are made to behave like waves, flowing and moving together in a highly organised, or coherent, way.  The difference between an atom laser and normal atoms is analogous to the difference between an optical laser and a light bulb. 
Nick Robins is one of 16 early-career scientists chosen for Fresh Science 2008, a national program sponsored by the Federal and Victorian governments.



A Next-Generation Source of Ultra-Cold Atoms: Turning on the Atomic Tap

In 1995, a new state of matter, known as a Bose-Einstein condensate (BEC), that only exists at temperatures below one-millionth of a degree above absolute zero, was created in three leading US labs. In 2001, the ANU atom optics group led by Dr John Close and Dr Nick Robins, produced the first BEC in Australia. Since that time, the ANU group has used this exotic state of matter to develop the atom laser, a laser that produces matter waves that can be exploited in a host of high technology applications.

BEC occurs when atoms undergo a phase transition. A common phase transition occurs when water freezes into ice at 0 Celsius. In the case of BEC, the transition occurs in a gas at a temperature ten orders of magnitude lower, at 100 billionths of a degree above absolute zero.

What makes this phase transition special is that it causes the atoms to loose their individuality. A sample that was originally composed of millions of separate atoms suddenly becomes a giant ‘super atom’ (Figure 1).

Although this super atom could be visible to the naked eye, it is a purely quantum mechanical object. BEC brings the strange microscopic world of quantum mechanics (a world where, for example, being in at least two places at the same time is considered normal) up to the human scale. We can even hold the atoms in a simple magnetic bowl, in a similar way to holding water in a tiny thimble.

A spectacular consequence of BEC is that this thimble full of ultra-cold atoms can be poured out without disturbing their delicate quantum state. As the atoms fall away, they form a stream of atoms, an atom laser (Figure 2).

In this type of laser, a matter wave is equivalent to the light wave produced by an optical laser. The development of the atom laser is at the centre of a fascinating and rapidly moving new field: Quantum Atom Optics. The atom laser will be a key tool and a driving component of future quantum technologies such as coherent atomic circuits. Future industrial devices based on the atom laser are ultra precise atomic holography and atomic interferometers for mineral exploration.

At present only small samples of quantum fluids can be made. In a recent experiment performed at the Australian National University, the Atom Optics Group invented and studied the first method to continuously load the BEC, or atom laser source, with cold atoms. When combined with a “conveyor belt for atoms”, also under development at ANU, this will allow the atom laser beam to run continuously. The thimble that holds the BEC and that is the source for the atom laser, becomes a bottomless bucket

Current Bose-Einstein condensation experiments are equivalent to having a thimble sized tank filled with fluid. Puncturing the thimble allows the fluid to flow, forming a stream that falls under gravity. The tank is quickly emptied, and the flow turns off (Figure 2). Now imagine that a tap is installed that allows fluid to be directed into the top of the tank to replenish the fluid. The amount of fluid entering the tank equals the amount leaving and the stream flows forever.

The ANU group has invented a technique, “a tap”, operating at a temperature 100 billionths of a degree above absolute zero that refills the magnetic trap holding the BEC. Atoms are then trickled out of the BEC to produce the atom laser beam. It is the tap to replenish the atoms that was missing from every atom laser experiment in the world. The ANU group has overcome a major hurdle in turning the atom tap on. The work will be published in Nature Physics this month. 


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