Control over group velocity in a three-level closed Λ system via spontaneously generated coherence and dynamically induced coherence

Abstract

The light propagation of a probe field in a three-level Λ system with incoherent pumping has been studied when both dynamically induced coherence (DIC) and spontaneously generated coherence (SGC) play a significant role. We have investigated the group velocity of probe field and hence the group index of a three-level Λ system with incoherent pumping when both DIC and SGC play a significant role. We have shown that by varying the probe field Rabi frequency one can control the interference between these two coherences which leads to different nonlinear response (amplification without inversion, electromagnetically induced transparency and electromagnetically induced absorption) leading to different (positive and negative) dispersion. Hence control over switching of group velocity from subluminal to superluminal and vice versa can be achieved. We have also shown that when the contributions from both the coherences are comparable, the dependence of group velocity of probe field in a three-level Λ system with incoherent pumping on phase difference between probe and coherent fields is different from that obtained under the weak probe field condition. Going beyond the weak probe field approximation we have derived analytical expressions for group velocity and hence the group index in the steady state limit (keeping all orders of system parameters) to generalize the analysis, and these expressions can be used for any set of system parameters without any restriction. The numerical values obtained by solving the density matrix equations agree well with these exact analytical values at a large time limit. We have proposed a scheme for experimental realization of EIT and hence subluminal light propagation in molecules by invoking spontaneously generated coherence.

Study of group velocity in the negative refractive index region in three level closedΛsystem via spontaneously generated coherence

“…To show the importance of the effect of SGC for achieving simultaneous negative real values of r and r , we have calculated Re( r ) and Re( r ) in the absence of SGC. Previously we have proposed a scheme for experimental realization of EIT considering SGC in the LiH molecular system [40] and have shown how the group velocity can be controlled by controlling the incoherent pump rate in the band of positive refraction [41]. Here we will show how the negative refraction in the LiH molecular system can be realized and the group velocity can be controlled from superluminal to subluminal in this band of negative refraction.…”

“…In our previous work [40], we have shown how SGC in molecules can be invoked by an external field. However this scheme can also be effective in atoms.…”

“…This is true when the dipole transition moments on the probe and coherent field transitions are orthogonal. However, the situation is completely different when the dipole transition moments from the upper level to two closely lying lower levels are nonorthogonal [38][39][40][41][42][43]. In this case another coherence, i.e.…”

“…Previously [38] we have shown that when the probe field Rabi frequency is comparable to the coherent field Rabi frequency, one can obtain the electromagnetically induced transparency (EIT) in the three-level à system due to the destructive interference of absorptions induced by spontaneously generated coherence (SGC) and dynamically induced coherence (DIC). In another paper, we showed how the control over the susceptibility and the group velocity in a closed three-level à system can be achieved in the presence of SGC and DIC in the positive refractive index region [40]. Several other groups have studied the group velocity in the presence of SGC in the positive refractive index region [44][45][46].…”

Vacuum-induced coherence in ultracold photoassociative rovibrational excitations

“…It is known that under appropriate conditions, VIC can lead to population trapping in excited states [2,5]. This can be utilized in manipulating environment-induced relaxation processes in a wide variety of systems, such as atoms, ions, molecules, quantum dots [5][6][7][8][9][10][11][12], and it has also been found to be effective against decoherence in quantum information processing [13]. One of the key conditions for VIC to occur is the nonorthogonality of the dipole moments of two spontaneous transitions.…”