Coherent control experiments resonances

The value of coherent control experiments lies not only in their ability to alter the outcome of a reaction but also in the fundamental information that they provide about molecular properties. In the example of phase-sensitive control, the channel phase reveals information about couplings between continuum states that is not readily obtained by other methods. Examination of Eq. (15) reveals two possible sources of the channel phase—namely, the phase of the three-photon dipole operator and that of the continuum function, ESk). The former is complex if there exists a metastable state at an energy of (D or 2 >i, which contributes a phase to only one of the paths, as illustrated in Fig. 3b. In this case the channel phase equals the Breit-Wigner phase of the intermediate resonance (modulo n),... 

A beautiful experiment demonstrating coherent control in the sense of the Tannor-Kosloff-Rice scheme was carried out by Baumert et al. [17] using resonant three-photon ionization and fragmentation of Na2. 

The ability to create and observe coherent dynamics in heterostructures offers the intriguing possibility to control the dynamics of the charge carriers. Recent experiments have shown that control in such systems is indeed possible. For example, phase-locked laser pulses can be used to coherently amplify or suppress THz radiation in a coupled quantum well [5]. The direction of a photocurrent can be controlled by exciting a structure with a laser field and its second harmonic, and then varying the phase difference between the two fields [8,9]. Phase-locked pulses tuned to excitonic resonances allow population control and coherent destruction of heavy hole wave packets [10]. Complex filters can be designed to enhance specific characteristics of the THz emission [11,12]. These experiments are impressive demonstrations of the ability to control the microscopic and macroscopic dynamics of solid-state systems. 

MQ coherence (REDOR-fj-MQ/MAS NMR, F. 24, left) or single-quantum coherence (REDOR-f2-MQ/MAS NMR, Fig. 24, ri t), the signals of structural units dipolarly interacting with protons are suppressed, leaving only the resonances of H-isolated species in the spectrum (Fig. 23, red (gray in the print version) line). These REDOR-f , -MQ/MAS NMR experiments [85,92,93], in which the FI REDOR n pulses are synchronized with the rotation period, cause controlled attenuation of the Al coherences. Following this attenuation, as a function of rotor count (N) provides a direct measurement of the Al dipolar coupling constant... 

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. 

---