Spin Raman process

At higher temperatures, the two-phonon (Raman) processes may be predominant. In such a process, a phonon with energy hcOq is annihilated and a phonon with energy HcOr is created. The energy difference TicOq — ha>r is taken up in a transition of the electronic spin. In the Debye approximation for the phonon spectrum, this gives rise to a relaxation rate given by... 

I2H2O as a function of the reciprocal temperature. The points are data obtained from fits of the Mdssbauer spectra (Fig. 6.6). The broken curve is a fit to the Einstein model for a Raman process. The dotted curve corresponds to a contribution from a direct process due to interactions between the electronic spins and low-energy phonons associated with critical fluctuations near the phase transition temperature. (Reprinted with permission from [32] copyright 1979 by the Institute of Physics)... 

The temperature dependence of the MRD profile for the protein-water systems where the protein is magnetically a solid, is remarkably weak. The relaxation rate is proportional to IjT, which is consistent with Eq. (4) that was derived on the assumption that the relaxation process is a direct spin-phonon coupling rather than an indirect or Raman process. If it were a Raman process, there would be no magnetic field dependence of the relaxation rate therefore, the temperature dependence provides good evidence in support of the theoretical foundations of Eq. (6). 

The Raman laser temperature-jump technique has been used in studies of a variety of spin-equilibrium processes. It was used in the first experiment to measure the relaxation time of an octahedral spin-equilibrium complex in solution (14). Its applications include investigations of cobalt(II), iron(II), iron(III), and nickel(II) equilibria. 

Fig. 3.3. Lattice and spin transitions are coupled by (A) direct processes, (B) Raman processes, (C) Orbach processes. The proximity of the excited electronic state favors both Orbach and Raman processes. The electronic states are labeled with n, the lattice vibrational states are labeled with V. A and 8 indicate energy separations with excited states coupled to the ground state by spin-orbit coupling.

Fig.l. Stripe models for 1/3 doping.18 Arrows indicate correlated Ni magnetic moments circles indicate oxygen sites filled circles indicate locations of doped holes on oxygen sites. Bold dashed lines indicate positions of domain walls, while bold solid lines outline a magnetic unit cell. The two-magnon Raman process is shown also bold arrows demonstrate spins on adjacent sites and curved lines indicate broken magnetic bonds. 

Raman process the spin center transfer to another energy level via a virtual state involving two phonons and this is called non-resonance scattering process. 

At low temperature, the processes of spin-lattice relaxation between the triplet substates are slow. With temperature increase, the sir rates increase strongly. For Pt(2-thpy)2, three different processes govern the sir. At a temperature below T = 3 K, the sir rate is exclusively determined by the direct process. Above T = 3 K, the Orbach process and above T = 6 K, the Raman process, become additionally important. For Pd(2-thpy)2, the processes that govern the sir have not been determined yet, but it is suggested that the Raman process is of main importance, since no real electronic state lies in the energy vicinity of the Tj state. (Figs. 19, 21, and Refs. [24,60,62,64,65].)... 

We now turn to a quantitative examination of the feasibility of conditional Fock state generation using our preparation and retrieval technique. For applications in long-distance quantum communication, the quality of the atomic state preparation is the most important quantity. Assuming perfect atom-photon correlations in the write Raman processes, we can find the density matrix p for the number of atomic spin-wave excitations conditioned on the detection of ns Stokes photons. Here we consider only the spin-wave modes correlated with our detection mode. For example, in the absence of losses and background, the conditional atomic density matrix is simply p(ns) = ns)(ns. Loss on the Stokes channel (characterized by transmission coefficient a.s) leads to a statistical mixture of spin-wave excitations,... 

To determine the unconditional probability distribution for the spin-wave excitations Psw(n), we must find the effective number of transverse modes which contribute to the Raman processes. We identify two extreme regimes which permit analytic treatment a single mode regime where the number of excitations in the 87Rb cell follows Bose-Einstein (thermal) statistics and a multimode regime where it follows Poisson statistics. We find in both cases that the quantities F and Q depend on two experimental parameters 0 ( number of lost Stokes photons) and v ( noise to signal ratio), which are defined in Tab. 1. 

Conradi and Norberg (1981) assume that the rate t is that for a quadru-polar nucleus relaxing via two-phonon Raman processes. This assumption affects primarily the low temperature behavior of Tf, but not the value of T, at the minimum or its frequency dependences at low and high temperatures, which are determined by the ratio (Wh/ o) and the Tq dependence of Eq. (12) for coqT c 1 and coqT 1, respectively. The term provides a rate below which the relaxation is no longer dominated by rapid spin diffusion to the molecular hydrogen sites. The fits of Conradi and Norberg (1981) to the data of Carlos and Taylor (1980) are shown in Fig. 12 for (Oq/Itc — 42.3 and... 

Ti times between 693 [ts (5.5 K) and 0.55 [ts (11.0 K). The temperature dependence of Tx could be fitted equally well to the equations describing Orbach or Raman processes. The unrealistic obtained exponent value in case of the Raman process led the authors to prefer the Orbach process. The Orbach energy gap was derived to be 57 cm. This energy gap corresponds to the energy of the first excited spin state, which allowed choosing between two sets of exchange coupling parameters that fitted the susceptibility curve equally well. 

Resonance Raman and antisymmetric scattering are involved in a novel technique involving spin-flip Raman transitions in paramagnetic molecules that can function as Raman electron paramagnetic resonance. Figure 3.2a shows a conventional vibrational Stokes resonance Raman process, while 3.2b and 3.2c show the polarization characteristics of the two distinct spin-flip Raman processes for scattering at 90°... 

Various schemes for hybrid quantum processors based on molecular ensembles as quantum memories and optical interfaces have been proposed. In Ref. [17], a hybrid quantum circuit using ensembles of cold polar molecules with solid-state quantum processors is discussed. As described above, the quantum memory is realized by collective spin states (ensemble qubit), which are coupled to a high-Q stripline cavity via microwave Raman processes. This proposal combines both molecular ensemble and stripline resonator ideas. A variant of this scheme using collective excitations of rotational and spin states of an ensemble of polar molecules prepared in a dipolar... 

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