Coherent driving

Control of the type discussed above, in which quantum interference effects are used to constructively or destructively alter product properties, is called coherent control (CC). Photodissociation of a superposition state, the scenario described above, will be seen to be just one particular implementation of a general principle of coherent control Coherently driving a state with phase coherence through multiple, coherent,... 

From the master equation (103), we find equations of motion for the populations of the collective atomic states, which in the absence of the coherent driving field (Hi =02 = 0) can be written as... 

There are several unresolved issues in the problem of coherent vibrational pumping by shock fronts. These include (1) to what degree can a shock front be viewed as a coherent phonon source (2) can a shock front coherently drive vibrational excitations, and (3) could shock front coherent pumping cause selective bond breaking, especially bonds other than those broken by ordinary thermochemical reactions One way to look at the first issue is to look at the shock front as a superposition of phonons. Since phonons form a complete set... 

Giordmaine J A and Kaiser W 1966 Light scattering by coherently drive lattice vibrations Phys. Rev. 144 676-88... 

The probe pulses are applied within the intermissions of the coherent driving, not during the driving pulses. Thus, nonlinear interaction of the ion with simultaneously present drive and probe fields is avoided. 

A quantum-beat laser can be initialized by using lasing without population inversion. The mechanism for lasing without inversion essentially is CPT/EIT absorption is reduced while stimulated emission remains unaffected [50-56]. At the same time, the coherence leads to noise squeezing [57-61]. The fluctuations of the laser intensity are suppressed up to or more than 50% below the shot noise. We also note that noise squeezing is possible even when neither initial coherence nor external coherent driving is used. This is caused by dynamic noise reduction... 

A quantum-beat laser with external coherent driving [67,78]. Shown in Fig. 13 is a pumping and coupling scheme. The atoms are pumped from the ground state 10 ) to the excited states (/=1,2) to provide necessary population for the laser gain. An external coherent field of circular frequency coq is applied to the 2 )- 3 ) transitions to create atomic coherence, by which the system can operate without population inversion. Atoms emit photons into the laser modes o of circular frequencies a 12. In the dynamics, the atoms recycle throngh the snccessive channels... 

Figure 13 A quantum-beat laser scheme with coherent drive. Qnantnm-beat is created by using a microwave field to couple the two closely spaced states 11) and 2). Atoms are pnmped incoherently from the ground state 0) to the excited states 1, 2) with rate A. Atomic coherence is created by coupling an external field to the 2)- 3> with half Rabi frequency Q. Atoms emit photons into two lasing modes (ai,2) on the 1,2)- 3> transitions.

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