Atom laser

Atom laser

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An atom laser is a coherent state
Coherent state
In quantum mechanics a coherent state is a specific kind of quantum state of the quantum harmonic oscillator whose dynamics most closely resembles the oscillating behaviour of a classical harmonic oscillator...

 of propagating atoms. They are created out of a Bose–Einstein condensate
Bose–Einstein condensate
A Bose–Einstein condensate is a state of matter of a dilute gas of weakly interacting bosons confined in an external potential and cooled to temperatures very near absolute zero . Under such conditions, a large fraction of the bosons occupy the lowest quantum state of the external potential, at...

 of atoms that are output coupled using various techniques. Much like an optical laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

, an atom laser is a coherent
Coherence (physics)
In physics, coherence is a property of waves that enables stationary interference. More generally, coherence describes all properties of the correlation between physical quantities of a wave....

 beam that behaves like a wave. There has been some argument that the term "atom laser" is misleading. Indeed, "laser" stands for "Light Amplification by Stimulated Emission of Radiation" which is not particularly related to the physical object called an atom laser, and if at all describes more accurately the Bose–Einstein condensate (BEC).
The terminology most widely used in the community today is to distinguish between the BEC, typically obtained by evaporation in a conservative trap, from the atom laser itself, which is a propagating atomic wave obtained by extraction from a previously realized BEC. Some ongoing experimental research tries to obtain directly an atom laser from a "hot" beam of atoms without making a trapped BEC first.

Introduction


The first pulsed atom laser was demonstrated at MIT by Professor Wolfgang Ketterle
Wolfgang Ketterle
Wolfgang Ketterle is a German physicist and professor of physics at the Massachusetts Institute of Technology . His research has focused on experiments that trap and cool atoms to temperatures close to absolute zero, and he led one of the first groups to realize Bose-Einstein condensation in these...

 et al. in November 1996. Ketterle used an isotope of sodium and used an oscillating magnetic field as their output coupling technique, letting gravity pull off partial pieces looking much like a dripping tap (See movie in External Links).

From the creation of the first atom laser there has been a surge in the recreation of atom lasers along with different techniques for output coupling and in general research. The current developmental stage of the atom laser is analogous to that of the optical laser during its discovery in the 1960s. To that effect the equipment and techniques are in their earliest developmental phases and still strictly in the domain of research laboratories.

Physics


The physics of an atom laser is similar to that of an optical laser. The main differences between an optical and an atom laser are that atoms interact with themselves, cannot be created as photons can, and possess mass whereas photons do not (they therefore propagate at a speed below that of light). The van der Waals
Van der Waals force
In physical chemistry, the van der Waals force , named after Dutch scientist Johannes Diderik van der Waals, is the sum of the attractive or repulsive forces between molecules other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral...

 interaction of atoms with surfaces makes it difficult to make the atomic mirror
Atomic mirror (physics)
In physics, an atomic mirror is a device which reflects neutral atoms in the similar way as the conventional mirror reflects visible light. Atomic mirrors can be made of electric fields or magnetic fields, electromagnetic waves or just silicon wafer; in the last case, atoms are reflected by the...

s, typical for conventional lasers.

A continuously operating atom laser was demonstrated for the first time by researchers at the Max Planck Institute for Quantum Optics in Munich. Its predecessor produced pulses of atoms, rather than continuous beams. In addition, the atoms emitted from the pulsed atom laser quickly spread out in a moon-like crescent, instead of forming a more desirable narrow beam.

Applications


Atom lasers are critical for atom holography. Similar to conventional holography
Holography
Holography is a technique that allows the light scattered from an object to be recorded and later reconstructed so that when an imaging system is placed in the reconstructed beam, an image of the object will be seen even when the object is no longer present...

 atom holography uses the diffraction of atoms. The De Broglie wavelength of the atoms is much smaller than the wavelength of light, so atom laser can create much higher resolution holographic images. Atom holography might be used to project complex integrated-circuit patterns, just a few nanometres in scale, onto semiconductors.
Another application, which might also benefit from atom lasers, is atom interferometry. In an atom interferometer an atomic wave packet is coherently split into two wave packets that follow different paths before recombining. Atom interferometers, which can be more sensitive than optical interferometers, could be used to test quantum theory, and have such high precision that they may even be able to detect changes in space-time. This is because the de Broglie wavelength of the atoms is much smaller than the wavelength of light, the atoms have mass, and because the internal structure of the atom can also be exploited.

External links