Control of Population Flow in Coherently Driven Quantum Ladders

Abstract

A technique for adiabatic control of the population flow through a preselected decaying excited level in a three-level quantum ladder is presented. The population flow through the intermediate or upper level is controlled efficiently and robustly by varying the pulse delay between a pair of partly overlapping coherent laser pulses. The technique is analyzed theoretically and demonstrated in an experiment with Na2 molecules.

Experimental control of excitation flow produced by delayed pulses in a ladder of molecular levels

“…Of course, when there is no overlap or the P-laser field precedes the S field d Ͼ 0, excitation flows almost entirely through the intermediate level e. The population that flows through level f will decay to other levels, including level e. For our level scheme according to previous calculations, 14 a fraction of about r = 0.35 of the molecules which are excited to level f will decay to level e. The population dynamics takes place during the relevant time interval that begins with the arrival of the P pulse and ends within T flow ϳ f , where i =1/⌫ i is the total spontaneous emission rate from level i. 6 Since the lifetime f is much shorter than the pulse duration, after spontaneous transitions from level f to level e the S-laser intensity is still large, while the P-laser intensity is small. Thus, the strong S laser will induce damped Rabi oscillations between levels e and f with a frequency that is much larger than the level decay rates ⌫ i =1/ i .…”

“…6 Now we put them on an absolute scale and add some numerical simulation. Unlike the signal from level f, the normalization of the signal from level e is not possible with the current experimental setup for reasons discussed in Sec.…”

“…However, few methods can accomplish a two-photon transfer with high probability. The technique presented earlier 6 for the preparation of molecules or atoms in highly excited levels has remarkable advantages over existing methods. In particular, it requires smaller intensities.…”

“…We present data that demonstrate the control of the population flow through the degenerate levels e and f by means of the delay between two laser pulses. 6 The coupling scheme is shown in Fig. 1.…”

Gaussian and sinc-shaped few-cycle-pulse-driven ultrafast coherent population transfer inΛ-like atomic systems

“…For robust and efficient controlling of population transfer between quantum states, many novel strategies have been proposed and exploited by several authors. Stimulated Raman adiabatic passage (STI-RAP) [3][4][5][6], adiabatic rapid passage (ARP) [7], Raman chirped adiabatic passage (RCAP) [8][9][10], and temporal coherent control (TCC) [11,12], etc., are some of the well-known methods. Recently, the field of coherent control of atoms and molecules has received a tremendous boost owing to the recent progress in the generation of femtosecond and attosecond laser pulses and its possible future applications [13][14][15][16][17][18].…”