Atomic systems phase control

Collisions in applied electric and magnetic fields are important for several reasons. Most importantly, applied fields provide ways to control ultracold gases, and for atomic systems this control has already led to the observation of a wide range of new phenomena including molecule formation and transitions to superfluid phases [45]. There is little doubt that applied fields will provide the key to controlling the much richer behavior expected for ultracold molecules. 

In addition, we have proposed some other atom loealization schemes in four-level atomic systems. Phase-sensitive atom localization has been realized in a loop A -system[25]. Due to the sensitivity of the loop system to the relative phases between the eoupled fields, the detection probability of atoms within the sub-wavelength domain of the standing wave can be improved by a factor of 2 while appropriate choosing the relative phase. In a four-level alkaline earth atomie system[26], not only the positions bnt also the widths of the localization peaks are investigated systemically. It is shown that the nnmbers and the widths of the localization peaks can be controlled by adjusting the additional control field. 

Physical properties may be insensitive to details of the interatomic potential for a variety of reasons. For example at low temperatures, the atomic system may probe a bounded region of phase space, most often the elastic regime around the equilibrimn state and in this bounded region, the interatomic interactions may be represented well by a suitable model potential. Some classes of physical properties, like critical phenomena, are intrinsically insensitive to many details in the interatomic potentials, as they axe controlled by collective behavior. For other physical phenomena, like melting, effects of fine details in the interatomic potentials tend to average out. 

Phase control of two-channel photo-ionization rates and coherent population trapping induced by four laser fields operating on an atomic system initially in its ground state 1), which proceeds via a pair of intermediate bound states, 2) and 3), to a manifold of structureless continua, has also... 

Here we extend the simple three-level EIT system to mote complicated and versatile configurations in a multi-level atomic system coupled by multiple laser fields. We show that with multiple excitation paths provided by different laser fields, phase-dependent quantum interference is induced either constractive or destractive interfereiKe can be realized by varying the relative phases among the laser fields. Two specific examples are discussed. One is a three-level system coupled by bichromatic coupling and probe fields, in which the phase dependent interference between the resonant two-photon Raman transitions can be initiated and controlled. Another is a four-level system coupled by two coupling fields and two probe fields, in which a double-EIT confignration is created by the phase-dependent interference between three-photon and one-photon excitation processes. We analyze the coherently coupled multi-level atomic system and discuss the control parameters for the onset of constructive or destructive quantum interference. We describe two experiments performed with cold Rb atoms that can be approximately treated as the coherently coupled three-level and four-level atomic systems respectively. The experimental results show the phase-dependent quantum coherence and interference in the multi-level Rb atomic system, and agree with the theoretical calculations based on the coherently coupled three-level or four-level model system. 

Phase-dependent coherence and interference can be induced in a multi-level atomic system coupled by multiple laser fields. Two simple examples are presented here, a three-level A-type system coupled by four laser fields and a four-level double A-type system coupled also by four laser fields. The four laser fields induce the coherent nonlinear optical processes and open multiple transitions channels. The quantum interference among the multiple channels depends on the relative phase difference of the laser fields. Simple experiments show that constructive or destructive interference associated with multiple two-photon Raman channels in the two coherently coupled systems can be controlled by the relative phase of the laser fields. Rich spectral features exhibiting multiple transparency windows and absorption peaks are observed. The multicolor EIT-type system may be useful for a variety of application in coherent nonlinear optics and quantum optics such as manipulation of group velocities of multicolor, multiple light pulses, for optical switching at ultra-low light intensities, for precision spectroscopic measurements, and for phase control of the quantum state manipulation and quantum memory. 

J. H. Wu and J. Y. Gao. Phase and amplitude control of the inversionless gain in a mierowave-driven A-type atomic system. The European Physical Journal D 2003 Mar 4 23(2) 315-319. 

Such a reaction is controlled by the rate of addition of the acid. The two-phase system is stirred throughout the reaction the heavy product layer is separated and washed thoroughly with water and alkaU before distillation (Fig. 3). The alkaU treatment is particularly important and serves not just to remove residual acidity but, more importantiy, to remove chemically any addition compounds that may have formed. The washwater must be maintained alkaline during this procedure. With the introduction of more than one bromine atom, this alkaU wash becomes more critical as there is a greater tendency for addition by-products to form in such reactions. Distillation of material containing residual addition compounds is ha2ardous, because traces of acid become self-catalytic, causing decomposition of the stiU contents and much acid gas evolution. Bromination of alkylthiophenes follows a similar pattern. 

The purpose of this work is to demonstrate that the techniques of quantum control, which were developed originally to study atoms and molecules, can be applied to the solid state. Previous work considered a simple example, the asymmetric double quantum well (ADQW). Results for this system showed that both the wave paeket dynamics and the THz emission can be controlled with simple, experimentally feasible laser pulses. This work extends the previous results to superlattices and chirped superlattices. These systems are considerably more complicated, because their dynamic phase space is much larger. They also have potential applications as solid-state devices, such as ultrafast switches or detectors. 

The previous sections focused on the case of isolated atoms or molecules, where coherence is fully maintained on relevant time scales, corresponding to molecular beam experiments. Here we proceed to extend the discussion to dense environments, where both population decay and pure dephasing [77] arise from interaction of a subsystem with a dissipative environment. Our interest is in the information content of the channel phase. It is relevant to note, however, that whereas the controllability of isolated molecules is both remarkable [24, 25, 27] and well understood [26], much less is known about the controllability of systems where dissipation is significant [78]. Although this question is not the thrust of the present chapter, this section bears implications to the problem of coherent control in the presence of dissipation, inasmuch as the channel phase serves as a sensitive measure of the extent of decoherence. 

Although coherent control is now a mature field, much remains to be accomplished in the study of the channel phase. There is no doubt that coherence plays an important role in large polyatomic molecules as well as in dissipative systems. To date, however, most of the published research on the channel phase has focused on isolated atoms and diatomic molecules, with very few studies addressing the problems of polyatomic and solvated molecules. The work to date on polyatomic molecules has been entirely experimental, whereas the research on solvated molecules has been entirely theoretical. It is important to extend the experimental methods from the gas to the condensed phase and hence explore the theoretical predictions of Section VC. Likewise interesting would be theoretical and numerical investigations of isolated large polyatomics. A challenge to future research would be to make quantitative comparison of experimental and numerical results for the channel phase. This would require that we address a sufficiently simple system, where both the experiment and the numerical calculation could be carried out accurately. 

Gill and Fitzgerald [481] determined picomolar quantities of mercury in seawater using stannous chloride reduction and two-stage amalgamation with gas-phase detection. The gas flow system used two gold-coated bead columns (the collection and the analytical columns) to transfer mercury into the gas cell of an atomic absorption spectrometer. By careful control and estimation of the blank, a detection limit of 0.21 pM was achieved using 21 of seawater. The accuracy and precision of this method were checked by comparison with aqueous laboratory and National Bureau of Standards (NBS) reference materials spiked into acidified natural water samples at picomolar levels. Further studies showed that at least 88% of mercury in open ocean and coastal seawater consisted of labile species which could be reduced by stannous chloride under acidic conditions. 

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