Composite STIRAP

Having suggested that the STIRAP process can be thought of as a special case of an assisted adiabatic process, we now examine another special case of an assisted adiabatic process, namely the composite STIRAP protocol proposed by Torosov and Vitanov [77]. This protocol uses a sequence of an odd number of pairs of delayed pulses (Figure 3.24) with carefully selected phases (listed in Table 3.4) to cancel by destructive interference the nonadiabatic transitions that reduce the efficiency of STIRAP-generated population transfer. We note that this protocol resembles the pulsed incoherent interference control protocol proposed by Shapiro et al. [78]. Torosov and Vitanov show that, for the triad of states illustrated in Figure 3.24, the efficiency of population transfer can be driven arbitrarily close to unity, for example, a deviation from unity of order 10 for the case of resonant excitation with three pairs of pulses. 

We now ask if the composite STIRAP protocol remains efficient in the presence of background states. To answer this question, we consider two examples population transfer between states of the thiophosgene molecule and between states of the HCN molecule. In the thiophosgene example, we consider transfer of population from state 1) to state 6) via state 5 ) embedded in a dense manifold... 

Figure 3.24 Schematic diagram of the pulse sequence in the composite STIRAP protocol. Note the Stokes and pump pulses are reversed between successive pulse pairs when the Stokes and pump pulses are resonant with the level spacing, whereas they are not reversed between successive pulse pairs when the Stokes and pump pulses are off resonance with the level spacing. (From Ref. 77).

Figure 3.25 Composite STIRAP-generated population of state 6) with (a,b) M = 3 pulse pairs, (c,d) M = 5 pulse pairs, and the associated pulse pairs.

Figure 3.26 Comparison of the efficiencies of population transfer generated by conventional STI-RAP (M = 1) and composite STIRAP (M = 3 and M = 5) with the same pulse area.

Figure 3.28 Population transfers generated by M = 3 composite STIRAP processes with the fields shown in Figure 3.25. (a) FWHM = 212.5 ps and (b) FWFIM = 212.5/3 ps.

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