Dark resonances

T. Halfmann, K. Bergmann, Coherent population transfer and dark resonances in SO2,... 

When the frequency of one laser is kept constant and the frequency of the other laser is tuned over the resonance, a very narrow dip in the fluorescence intensity is observed for coi — 022 = ( 1 - 2)/ . This dark resonance is extremely narrow, because the lifetimes of the ground state levels 11) and 2) are nearly infinitely long. The resonance width is therefore only determined by collision processes and by the diffusion of the atoms out of the laser beams. 

There are a couple of interesting applications where these narrow dark resonances are used for precision spectroscopy. One example is the realization of a very sensitive magnetometer [918]. When cesium atoms are brought into an external magnetic field the detection of dark resonances on transitions between selected Zee-man components can be measured with very high precision. This allows for example... 

Up to now the hyperfine transition in the ground state of the Cs-atom at 9.192 GHz represents the accepted frequency standard. An alternative to the cesium atomic fountain is the dark resonance of Cs atoms in a cell when a coherent dark state of the hyperfine levels is realized where the optical transition is excited by a frequency modulated laser with a modulation frequency which matches the hyperfine splitting in the Cs ground state. This modulation frequency can be used for the stabilization of the microwave which modulates the laser output. Since the dark resonance is very narrow, the uncertainty of the stable frequency is small. 

C. Cohen-Tannoudji, Dark resonances from optical pumping to cold atoms and molecules. http //www.phys.ens.fr/ cct/articles/Kosmos/Kosmos.pdf... 

Proof-of-principle experiments have been performed on homonuclear Rb2 molecules [89] and heteronuclear " K Rb molecules [90], demonstrating the transfer by one or a few vibrational quanta. The STIRAP transfer of Rb2 started with trapped Feshbach molecules. In order to characterize and optimize the experimental parameters, the study of a dark resonance was an essential step (Figure 9.18). STIRAP could then be efficiently implemented to transfer the molecules from the last bound vibrational level (fib = x 24 MHz) to the second-to-last state (/i x 637 MHz) with an efficiency close to 90%. In the experiment with the heteronuclear K Rb molecules, STIRAP was demonstrated with final molecular binding energies of up to h X 10 GHz. 

In this present article, we will give a brief review of some of our recent research work related to atomic localization via the effects of atomic coherence and quantiun interferences atom localization based on double-dark resonance effects [23,24], sub-half-wavelength local ization via two standing-wave fields [27], as well as its application in atom nano-lithograph[28]. Then we will introduce some of our recent related work in quantum well systems[62,63]. 

Atom localization based on double-dark resonance effects... 

Double-dark resonances have been demonstrated in a variety of four-level systems [39-50], where the probe absorption spectrum is characterized by two HIT windows, separated by a sharp absorption peak [51]. The appearance of the central narrow structure is due to the coherent interaction between the two dark states [39], which greatly enhances the Kerr nonlinear susceptibility [55]. In this section, we present our atom localization schemes based on double-dark resonance effects in two different four-level atomic systems. 

Figurel Four-state atomic system displaying donble dark resonances, and y represents...

From Eqs. (3)-(5), it is easy to see that the behavior of atom localization can be manipulated by parameters of the additional control field. This feature reflects the idea that applying an additional field to disturb the original dark state may produce double-dark resonances, and that the interaction between the double-dark states can be engineered by the parameters of the additional control field. 

In this article we reviewed some of oiu recent research work related to atomic localization via the effects of atomic coherence and quantum interferences. It was found that the localization property was significantly improved due to the interaction of double-dark resonances. The probability of finding the atom at a particular position could be doubled, as well as the loealization preeision could be dramatically enhanced. A scheme of sub-half-wavelength localization was proposed via two standing-wave fields in a ladder-type system. We also presented an application of atom localization in 2D atom nano-lithograph, through two cavities orthogonal to each other. The feasibility of control the atom localization behaviors by the external optical fields is shown. Those work may be helpful in the experimental research of atom localization. 

D. C. Cheng, Y. P. Niu, and S. Q. Gong. Controllable atom localization via double-dark resonances in a tripod system. Journal of Physics B Atomic Molecular and Optical Physics 2006 Oct 10 23(10) 2180-2184. 

M. D. Lukin, S. F. Yelin, M. Fleischhauer, and M. O. Scully. Quantum interference effects induced by interacting dark resonances. Physical Revew A1999 Jan 15 60(4) 3225-3228. 

Y. F. Li, J. F. Sun, X. Y. Zhang, and Y. C. Wang. Laser-induced double-dark resonances and double-transparencies in a four-level system. Optics Communications 2002 Feb l 202(l-3) 97-102. 

C. Goren, A. D. Wilson-Gordon, M. Rosenbluh, and H. Friedmann. Sub-Doppler and subnatural narrowing of an absorption line induced by interacting dark resonances in a tripod system. Physical Revew A 2004 Jun 2 69(6) 063802(5). 

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