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Stopped Light
| Chien Liu, Zachary Dutton, Cyrus H. Behroozi, Lene Vestergaard Hau. Observation of coherent optical information storage in an atomic medium using halted light pulses. Nature 409, 490-493 (25 January 2001) |
| Electromagnetically induced transparency is a quantum interference effect that permits the propagation of light through an otherwise opaque atomic medium; a 'coupling' laser is used to create the interference necessary to allow the transmission of resonant pulses from a 'probe' laser. This technique has been used to slow and spatially compress light pulses by seven orders of magnitude, resulting in their complete localization and containment within an atomic cloud. Here we use electromagnetically induced transparency to bring laser pulses to a complete stop in a magnetically trapped, cold cloud of sodium atoms. Within the spatially localized pulse region, the atoms are in a superposition state determined by the amplitudes and phases of the coupling and probe laser fields. Upon sudden turn-off of the coupling laser, the compressed probe pulse is effectively stopped; coherent information initially contained in the laser fields is 'frozen' in the atomic medium for up to 1 ms. The coupling laser is turned back on at a later time and the probe pulse is regenerated: the stored coherence is read out and transferred back into the radiation field. We present a theoretical model that reveals that the system is self-adjusting to minimize dissipative loss during the 'read' and 'write' operations. We anticipate applications of this phenomenon for quantum information processing |
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Reprinted by permission from Nature, 409, 490-493, copyright (2001) Macmillan Magazines Ltd.
| B. D. Busch, Chien Liu, Z. Dutton, C. H. Behroozi, L. Vestergaard Hau. Observation of interaction dynamics in finite-temperature Bose condensed atom clouds. Europhys. Lett., 51 (5), pp. 485-491 (2000) |
We present measurements of finite-temperature atom clouds cooled below the transition temperature for Bose-Einstein condensation. We study the dynamics of the interface region between the Bose condensed and noncondensed components of the atom clouds, where the time-dependent density profile is highly sensitive to interactions between the two components. We observe directly the effects of repulsion from the condensate on the dynamics of noncondensed atoms. The measurements are compared to calculations based on Hartree-Fock-Bogoliubov mean-field theory. We infer a value for the spatial second-order correlation function for noncondensed atoms of  . |
Slowing Light to 17 m/s
| Lene Vestergaard Hau; SE Harris; Zachary Dutton; Cyrus H. Behroozi. Light speed reduction to 17 metres per second in an ultracold atomic gas. Nature 397, 594-598 (18 February 1999) |
| Techniques that use quantum interference effects are being actively investigated to manipulate the optical properties of quantum systems1. One such example is electromagnetically induced transparency, a quantum effect that permits the propagation of light pulses through an otherwise opaque medium2-5. Here we report an experimental demonstration of electromagnetically induced transparency in an ultracold gas of sodium atoms, in which the optical pulses propagate at twenty million times slower than the speed of light in a vacuum. The gas is cooled to nanokelvin temperatures by laser and evaporative cooling6-10. The quantum interference controlling the optical properties of the medium is set up by a 'coupling' laser beam propagating at a right angle to the pulsed 'probe' beam. At nanokelvin temperatures, the variation of refractive index with probe frequency can be made very steep. In conjunction with the high atomic density, this results in the exceptionally low light speeds observed. By cooling the cloud below the transition temperature for Bose-Einstein condensation11-13 (causing a macroscopic population of alkali atoms in the quantum ground state of the confining potential), we observe even lower pulse propagation velocities (17 m s-1) owing to the increased atom density. We report an inferred nonlinear refractive index of 0.18 cm2 W-1 and find that the system shows exceptionally large optical nonlinearities, which are of potential fundamental and technological interest for quantum optics. |
The article in .pdf
Reprinted by permission from Nature, 397, 594-598, copyright (1999) Macmillan Magazines Ltd.
| Lene Vestergaard Hau; BD Busch; Chien Liu; Zachary Dutton; Michael M. Burns; JA Golovchenko. "Near Resonant Spatial Images of Confined Bose-Einstein Condensates in the 4-Dee Magnetic Bottle" Phys. Rev. A 58, R54-R57 (1998). |
| We present quantitative measurements of the spatial density profile of Bose-Einstein condensates of sodium atoms confined in a new '4D' magnetic bottle. The condensates are imaged in transmission with near resonant laser light. We demonstrate that the Thomas-Fermi surface of a condensate can be determined to better than 1%. More generally, we obtain excellent agreement with mean-field theory. We conclude that precision measurements of atomic scattering lengths and interactions between phase separated cold atoms in a harmonic trap can be measured with high precision using this method. |
The article in .pdf
| Lene Vestergaard Hau; BD Busch; Chien Liu; Michael M. Burns; JA Golovchenko. "Cold Atoms and Creation of New States of Matter: Bose-Einstein Condensates, Kapitza States, and '2D Magnetic Hydrogen Atoms" Photonic, Electronic and Atomic Collisions (Invited papers of the 20th International Conference of Electronic and Atomic Collisions (ICEAC) Vienna, Austria, July 23-29, 1997) F. Aumayr and H.P. Winter, editors (World Scientific, Singapore 1998), pp. 41-50. |
| We have succeeded in creating Bose-Einstein condensates with 2 million sodium atoms in a '4D' magnetic trap. We show the dynamic formation of a condensate as evaporative cooling proceeds. We also present a series of trap-release pictures clearly showing the distinctly different modes of expansion of condensate and thermal cloud. We further give two examples of wave guides for atomic de Broglie matter waves. One structure, the Kapitza wave guide, uses the interaction between an electrically polarizable atom and a charged wire. For stably bound orbits, a dynamical stabilization with time dependent potentials is necessary. This system, which can be tuned freely between classical and quantum regimes, shows chaotic behavior in the classical limit. The static counterpart of this wave guide leads to the introduction of the 'angular momentum quantum ladder'. The second wave guide structure is based upon the interaction between a current carrying wire and the magnetic dipole moment of an atom. A hydrogenic spectrum of bound states is derived through the concept of supersymmetry. |
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