Controlling the polarization rotation of an optical field via asymmetry in electromagnetically
induced transparency
Bo Wang,
1
Shujing Li,
1
Jie Ma,
1
Hai Wang,
1,
*
K. C. Peng,
1
and Min Xiao
1,2
1
The State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University,
Taiyuan 030006, People’s Republic of China
2
Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
Received 11 November 2005; revised manuscript received 10 March 2006; published 3 May 2006
We propose and experimentally demonstrate a mechanism to achieve coherent control of the polarization
rotation of an optical field in a multilevel electromagnetically induced transparency EIT system in rubidium
atoms. By choosing a properly polarized coupling field and transition energy levels, the symmetry of the
atomic medium to the propagation of two orthogonal polarization components of a weak linearly polarized
probe field can be broken, which leads to a coherently controlled rotation of the probe field polarization. This
mechanism of coherently controlled optical polarization rotation makes use of asymmetry in EIT subsystems
for the two circular polarization components of the probe beam with a contribution from different transition
strengths due to different Clebsh-Gordan coefficients in this multilevel atomic system.
DOI: 10.1103/PhysRevA.73.051801 PACS numbers: 42.50.Gy, 33.55.Ad, 42.25.Ja
A linearly polarized light beam will experience a polar-
ization rotation when passing through a chiral medium. The
chirality of the medium can be caused by either the intrinsic
helicity of the molecules in the medium called optical activ-
ity or induced by external electrical or magnetic fields. For
example, when a magnetic field is applied along the direction
of the light beam propagation in an atomic medium, the
asymmetry in Zeeman level splittings of the atoms will pro-
duce a polarization rotation for the linearly polarized light
beam, which is the well-known Faraday effect. Optical fields
can also induce chirality in an atomic medium through opti-
cal pumping 1, resonant two-photon dispersion 2,
magneto-optical effects 3,4, self-induced birefringence 5,
etc. In the past few years, several groups had experimentally
demonstrated optical birefringence by using a circularly po-
larized laser beam to change the polarization rotation of a
weak linearly polarized probe beam in multilevel ladder-type
atomic systems 6–8. In these experiments, the asymmetry
for the two circularly polarized components
+
and
-
of
the probe beam, therefore the optical birefringence, is gener-
ated by the circularly polarized coupling laser beam in the
ladder configuration connecting to only one of the two probe
circular polarization components. In this situation, strong cir-
cular dichroism always exists, which is the major limitation
of such experimental systems. Also, control and enhance-
ment of magneto-optical polarization rotation of a laser beam
by another coupling laser beam 9 and electromagnetically
induced magnetochiral anisotropy in a resonant medium 10
have been proposed, and the latter effect was experimentally
demonstrated recently 11.
In this paper, we propose and experimentally demonstrate
a system to achieve large optical polarization rotation up to
45° of a linearly polarized probe beam controlled by a cou-
pling laser beam under the condition of electromagnetically
induced transparency EIT in a -type configuration
12,13. The relevant atomic levels of
87
Rb atoms are shown
in Fig. 1. We denote Zeeman sublevels of 5S
1/2
, F =1 as |a
i
i =1,2,3 for m =-1,0,+1, of 5S
1/2
, F =2 as |b
j
j =1–5
for m =-2,-1,0,+1,+2, and of 5P
1/2
, F' =2 as |c
k
k =1–5 for m =-2,-1,0,+1,+2, respectively. When both
the probe and coupling laser beams are linearly polarized,
this system is completely symmetric to the two circular po-
larization components of the probe beam for realizing EIT as
demonstrated in Ref. 13. We choose the coupling beam
with frequency
c
to be a left-circularly polarized
-
beam driving the |b
j+1
to |c
j
transitions. The probe beam
with frequency
p
is a linearly polarized laser beam con-
sisting of two circularly polarized components
-
and
+
,
which are near resonant with transitions between levels |a
i
and |c
k
. We can clearly see that the left-circularly polarized
coupling beam E
c
-
and the left-circularly polarized probe
beam E
p
-
form three simple -type EIT systems, while E
c
-
and the right-circularly polarized probe beam E
p
+
form only
two simple -type EIT systems. This asymmetry in the EIT
subsystems for the two circular probe beam components is
the key for causing the chirality in this special atomic sys-
tem. The major advantages of this scheme, compared to the
previously demonstrated schemes 6–8, include relative low
*Corresponding author; e-mail address: wanghai@sxu.edu.cn
FIG. 1. Color online Relevant energy diagram of the D1 line in
a
87
Rb atom. Solid lines: transitions for the left-circularly polarized
coupling beam; dotted lines: transitions for the left-circularly polar-
ized probe beam; dashed lines: transitions for the right-circularly
polarized probe beam
PHYSICAL REVIEW A 73, 051801R2006
RAPID COMMUNICATIONS
1050-2947/2006/735/0518014 ©2006 The American Physical Society 051801-1