GT scientists create a ring-shaped atom laser
Atlanta (October, 25, 2006) — In 1924 Louis de Broglie proposed that matter, usually regarded as composed of minute particles, i.e. atoms, could also be thought of as waves. Therefore, optical phenomena can, under the right conditions, also be observed using matter waves. Gaseous Bose-Einstein condensate (BEC) produced in the laboratory are among the coldest objects in the universe – temperatures are routinely measured in the nanoKelvin range – and they are the matter wave analog of an optical laser. BECs exhibit quantum mechanical (wave) behavior on a macroscopic scale and the atoms have similar coherence properties to a laser. Unlike laser light, the matter wavelength of an individual atom is not a fixed quantity, but rather, can be varied by the experimenter. One can exploit this property for extremely high resolution lithography and sensitive interferometry not possible with ordinary optical radiation. However, unlike photonic optics, propagation of matter waves is profoundly affected by the interactions between atoms. For example, in an expanding Bose-Einstein condensate, these interactions lead to a broad velocity spread that is undesirable for many atom-optical applications. Therefore, it is of great interest to discover methods of controlling and suppressing interaction effects during propagation of a matter wave field and within atom interferometers. Researchers at the Georgia Institute of Technology in the groups of Chandra Raman and Brian Kennedy have realized a technique to circumvent the velocity broadening using a conical matter wave lens. The repulsive force exerted by a focused laser beam was used to launch a Bose-Einstein condensate into a radially expanding wavepacket with a perfect ring shape. In spite of significant interactions between atoms, the spatial and velocity widths of the ring along its radial dimension remained extremely narrow, an effect which was confirmed by numerical simulations. These results open the possibility for cylindrical atom optics without the perturbing effect of interactions, which could be important in future applications in lithography or atom interferometry. The original work is described in a recent paper in t he online journal Optics Express [ S. R. Muniz, S. D. Jenkins, T. A. B. Kennedy, D. S. Naik, and C. Raman, "Axicon lens for coherent matter waves", Opt. Express 14, 8947-8957 (2006) ].
How it works:
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Artistic rendition of the operation of the atomic axicon. A condensate (wavefunction shown in black and white) is initially localized near the origin. The external potential is shown in false color. (a) At time t=0, the linear potential is turned off, and the optical force is turned on. (b) For times t>0 the atoms rapidly "roll down'' the potential hill, forming a ring-shaped density distribution that expands radially outwards in the x-y plane. |
What happens:
(a) |
(b) |
Far field pattern of the expanded atomic cloud after 20 ms time-of-flight (TOF). Click on the pictures to see the movies of the atomic evolution: (a) the ring-shaped expansion and (b) ordinary BEC expansion. The field of view of each frame is 2.6 mm x 2.6 mm. |
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Seeing it from the side:
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Side view of expanding atomic distributions shown at 10 ms (top: a,b) and 15 ms (below: c,d) for both ring shaped expansions (left: a,c) as well as ordinary BEC expansion (right: b,d). Each image is 0.8 mm x 2.2 mm. |
At the moment the group is working towards developing methods to control the divergence of the atom laser. For example, they hope to collimate and reshape the spatial distribution of the matter waves in order to optimize its coupling into various types of optical potentials. They envision that a very interesting possibility would be to use the technique to transfer a condensate into a toroidal potential.
For more
information:
Reference:Optics Express paper
Technical Contacts:
Related Links
http://www.physics.gatech.edu/
Chandra Raman's Lab (Bose-Einstein Condensation Laboratory)
http://www.physics.gatech.edu/chandra
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