Eelectromagnetically Induced Transparency and

Four Wave Mixing in Coherently Coupled A System

Min Kyeong Kim, Lim Lee, Xumei Su*, J. B. Kim

Department ofPhysics Education, Korea National University ofEducation, Chung-buk 363-791, S. Korea

* College ofPhysics, Jilin University, Changchun 130023, P R. China

Abstract: We have measured electromagnetically induced transparency (EIT) and four wave mixing

(FWM) signals in a three level . atomic system to enhance nonlinearity for a weak field due to quantum

coherence with standing fields. We were able to observe quite different EIT signals according to a

traveling or standing coupling field. 1) We obtained EIT and FWM signals depending on detunings,

polarization,2) and power of the coupling field. Our results will be analyzed theoretically in viewpoint of

a photonic band gap model.

Introduction

We have observed an EIT and a FWM signals in a Cs atomic vapor cell. A transmitted and a reflected lights of a

weak probe field cop were measured where Cs atomic vapors in a room temperature are coherently coupled by a

standing or traveling field cwc, which is strong, to make a typical scheme. Fig.1 shows a energy level

diagram(a) and experimental setup(b).

~Probe field

Cs Cell

Eg / Q/ Ep 12>

1> Coupling field

Fig.1 (a) A scheme of energy level diagram (b) experimental setup

Fig.2 shows typical spectra obtained by scanning the frequency of the weak probe field of 0.4 mW in the room

temperature. The frequency of the strong coupling field of 18mW was stabilized to the atomic transition line by

using error signals obtained by a saturated absorption spectroscopy. Fig.2(b) and Fig3(d) are saturated absorption

spectrum of the probe field, which are used for monitoring the probe frequency detuning. Fig.2(d) and Fig3(b)

are the reflected signals, and Fig.2(c) and Fig3(a) are the transmitted signals in the case of the traveling and the

standing coupling, respectively. We are able to see convert from EIT with traveling coupling field to reflection

with standing coupling field. We can point out that a standing coupling field induces spatially periodical grating

not to transmit but to reflect the probe field. This reflection can be analyzed by a photonic band gap theory.

Fig.3 shows the case of off-resonant coupling field. We can see again a dispersion like spectrum where two

photon resonant condition is satisfied in the case of traveling coupling field as shown in Fig.3(c), however, this

signal is converted into the just dip, which means reflection.

SASI

........................~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~i......... BASSL

Xnd~injwe{ _

D 1/ a'D 200 1 400 S.O.0

Frequency Frequency

Fig. 2 On resonant coupling field Fig.3 Off resonant coupling field

References

[1] X. M. Su and B. S. Ham "Dynamic control of the photonic band pap using quantum coherence", Phys. Rev A 71, 013821 (2005).

[2]A.Lezama,G. C. Cardoso,and J. W. R. Tabosa"Polarization dependence of four-wave mixing in a degenerate two-level

system",Phys.Rev A 63,013805 (2000)

[3]A.Andre and M. D. Lukin, Phys. Rev. Lett. 89, 143602