Creation of coherence

N. V. Vitanov, K.-A. Suominen, and B. W. Shore. Creation of coherent atomic superpositions by fractional stimulated Raman adiabatic passage. J. Phys. B, 32(18) 4535 546 (1999). 

Impulsive stimulated Raman scattering (ISRS) Impulsive stimulated Raman scattering (ISRS) is the creation of coherent ground-state nuclear motion through an impulsive force caused by the interaction of a Raman-active medium with an ultrashort light pulse. 

D. Resonant Processes—Creation of Coherent Superposition of States—Half-Scrap... 

Since the development of ultrashort lasers, nudear wavepacket dynamics of various matters have attracted continuing attention [1,2]. The research targets extend from gas phase molecules [3, 4] to molecules in solution [5, 6], and solids [7]. In general, an excitation of matter by an ultrashort pulse with sufficient bandwidth leads to the creation of coherence between vibrational (or vibronic) eigenstates [1]. The induced nuclear wavepacket then starts to evolve on a certain potential energy surface and the dynamics is probed by a suitable pump-probe spectroscopy. The direct time-domain observation of the nudear motion provides us with valuable information on photochemical reaction dynamics, vibrational excitation/relaxation mechanisms, electron-vibration (phonon) coupling, and so on. 

The interpretation is now straightforward the n pulse leads to the inversion of the populations of the m = 1/2 states, with no creation of coherence. Therefore, after such pulse the magnetization is simply inverted, pointing now in the -z-direction, with no transverse magnetization appearing as consequence of the pulse. 

Linde, C. (1993). Life stories The creation of coherence. Oxford Oxford University Press. 

Suppose the first pulse resulted in the creation of a phase coherence across the Ai transition between the aa and a/3 states (Fig. 1.44). It is possible to transfer this phase information from the a)3 state to the )3/3 state by applying a selective it pulse across the Xi transition. The two successive pulses would therefore transfer the phase of the aa state to the )8)3 state, with the two states now becoming phase coherent with one another. 

The objective of this NoE is to strengthen research in catalysis by the creation of a coherent framework of research, know-how and training between the various disciplinary catalysis communities (heterogeneous, homogeneous, and biocatalysis) with the objective of achieving a lasting integration between the main European Institutions in this area. IDECAT will create the virtual European Research Institute on Catalysis (ERIC) that is intended to be the main reference point for catalysis in Europe. 

The preparation period consists of the creation of a non-equilibrium state and, possibly, of the frequency labeling in 2D experiments. Usually, the preparation period should be designed in such a way that in the created non-equilibrium state, the population differences or coherences under consideration deviate as much as possible from the equilibrium values. During the relaxation period, the coherences or populations evolve towards an equilibrium (or a steady-state) condition. The behavior of the spin system during this period can be manipulated in order to isolate one specific type of process. The detection period can contain also the mixing period of the 2D experiments. The purpose of the detection period is to create a signal which truthfully reflects the state of the spin system at the end of the relaxation period. As always in NMR, sensitivity is a matter of prime concern. 

Figure 6.1 shows simulation of the population dynamics of the two vibronic manifolds. The populations pbv>b and pcw>cw(T) after excitation are calculated for (a) the weak coupling case and (b) the strong coupling case. Figure 6.1 clearly shows the population transfer between the two electronic states due to the creation of the vibronic coherence. 

The interaction between light and matter can be viewed as the creation of a coherent quantum superposition of initial and final electron states that has an associated polarization [3], as shown in Figure 1. The coherence between states with different wave vector requires an intermediate virtual state and the presence of a coherent phonon. A transition between the initial and final states may occur when the coherence of the system is broken either due to the finite width of an optical wave packet or by scattering from the environment. The transition results in the absorption of a photon and the creation of a hot electron-hole pair. Otherwise, the photon is re-radiated with a different phase and, perhaps, polarisation. 

The results in this chapter make clear that a chiral outcome, the enhancement off j particular enantiomer, can arise by coherently encoding quantum interference infqjS mation in the laser excitation of a racemic mixture. The fact that the initial stall displays a broken symmetry and that the excited state has states that are eith jj symmetric or antisymmetric with respect to ah allows for the creation of a si position state that does not have these symmetry properties. Radiatively couplingfhf states in the superposition then allows for the transition probabilities from L and fi t differ, allowing for depletion of the desired enantiomer. 

Figure 2.9. Detail of the 0-0, b-polarized reflectivity at 5 K (cf. Fig. 2.8). The arrow indicates the threshold of creation of 46-cm phonons. Part A is due to reflection from the front face alone, part B to the total reflectivity of incoherent contributions from front and back faces, and part C to the reflectivity resulting from coherent superposition of front and back faces (oscillations).

For the HCCH and HCC segments, which are of particular interest to polyaromatic compounds, high relative sensitivity (0.5 and 0.25) was also predicted for the DEPT2-INADEQUATE pulse sequence (Figure 8 C). The main reason why this pulse sequence performs so well is that it incorporates refocusing of AP proton-carbon coherences prior to the creation of DQ carbon coherences. Its performance is also boosted by a smaller number of pulses (6 H and 7 C vs. 11 H and 10 C) and delays compared to those of the COS-INADEQUATE pulse sequence. 

---