Stimulated Raman Pumping STIRAP

Fig. 13. Schematic view of the irradiated STIRAP process (Stimulated Raman pumping) (a) The chirped pump pulse excites the system the electronic ground state (b) the system is stimulated back down to the electronic ground state, but a Stokes-shifted higher vibrational level, (c) The resulting wave packet is probed by the delayed probe pulse, which ionizes the particle from the oscillating ground state.

Coherent excitation of quantum systems by external fields is a versatile and powerful tool for application in quantum control. In particular, adiabatic evolution has been widely used to produce population transfer between discrete quantum states. Eor two states the control is by means of a varying detuning (a chirp), while for three states the change is induced, for example, by a pair of pulses, offset in time, that implement stimulated Raman adiabatic passage (STIRAP) [1-3]. STIRAP produces complete population transfer between the two end states 11) and 3) of a chain linked by two fields. In the adiabatic limit, the process places no temporary population in the middle state 2), even though the two driving fields - pump and Stokes-may be on exact resonance with their respective transitions, 1) 2)and... 

STIRAP Transfer of population by means of Stimulated Raman Adiabatic Passage, using a pump and Stokes laser. Population in a three-level system is completely transferred without populating the intermediate state if the Stokes laser precedes the pump laser in a counterintuitive order. 

Population transfer in a three-level system can be achieved by using one laser (known as the pump laser, which may be either continuous wave or pulsed) to connect the ground and intermediate levels, and a second laser (the Stokes laser ) to connect the intermediate and final levels. This method, known as stimulated Raman adiabatic passage or STIRAP, is illustrated in Fig. 22. In this example, the three levels have a A-type configuration, where... 

Complete population transfer in AP was shown theoretically [20] and independently implemented experimentally a few years later in a method called STIRAP [21, 187]. In this method, which is a variant of the stimulated Raman process, the two ("pump" and "Stokes") pulses are employed in the reverse ("counter-intuitive") order to that of the usual stimulated Raman process, namely in STIRAP the Stokes pulse precedes the pump pulse. This method designed to work with discrete states clearly complements CC by being able to transfer populations completely but at the same time not being phase sensitive, in contrast to the CC that is typically used in continua of states in weak-field but phase-sensitive regimes. We later explore the advantages resulting from the combination of both approaches. 

Starting with very weakly bound molecules produced by MA, coherent transfer to more deeply bound levels has been achieved in both Rb2 [134] and KRb [135]. The stimulated Raman adiabatic passage (STIRAP) process, incorporating pump and dump pulses in the counterintuitive order (see Figure 5.29), enabled high transfer efficiency. Pulses of cw laser light were used in order for the process to be phase coherent. In this initial work, the final states were not very deeply bound, 600 MHz for Rb2 and 10 GHz for KRb. In more recent work, very deeply bound states have been reached. In Cs2, levels bound by >1000cm have been populated... 

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