Optical storage of orbital angular momentum via
Rydberg electromagnetically induced transparency
Kai Wang (王 锴)
1,2,
*, Wei Zhang (张 伟)
1,2
, Zhiyuan Zhou (周志远)
1,2
,
Mingxing Dong (董明新)
1,2
, Shuai Shi (施 帅)
1,2
, Shilong Liu (刘世隆)
1,2
,
Dongsheng Ding (丁冬生)
1,2,
**, and Baosen Shi (史保森)
1,2
1
Key Laboratory of Quantum Information, CAS, University of Science and Technology of China,
Hefei 230026, China
2
Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and
Technology of China, Hefei 230026, China
*Corresponding author: wkhy@ustc.edu.cn; **corresponding author: dds@ustc.edu.cn
Received December 7, 2016; accepted February 24, 2017; posted online March 16, 2017
In this Letter, we report on the successful optical storage of orbital angular momentum (OAM) using Rydberg
electromagnetically induced transparency (EIT) in cold rubidium atoms. With a storage time of 1.4 μs, the
retrieved structure is highly similar, showing the ability of storing light’s OAM at a principal quantum number
of 20. The results at higher principal quantum numbers (n ¼ 25; 30) are also measured. These results show the
promise of image processing based on a Rydberg atomic system.
OCIS codes: 160.2900, 020.5780.
doi: 10.3788/COL201715.060201.
Photons are robust carriers of information, and memory
for the state of light is a key step in the realization of
long-distance communications. Many optical memories
are based on light –atom interactions, such as electromag-
netically induced transparency (EIT)
[1,2]
, coherent popula-
tion oscillation (CPO)
[3,4]
, gradient echo memories
[5]
,
and the atomic frequency comb
[6]
. The combination of
EIT and Rydberg atoms provides an effective interaction
between photons. Such a process requires coherently map-
ping photonic states into and out of a Rydberg polariton
on demand. Rydberg atoms are ideal for nonlinear inter-
action because of the strong dipole–dipole (DD) interac -
tion between the Rydberg atoms
[7–9]
. The strong DD
interaction leads to Rydberg blockade and can be used
to implement a controlled-NOT gate
[10]
, single-photon
switches
[11]
, transistors
[12]
, and a controlled π phase shift
[13]
.
Structured vortex beams with phase front expðilθÞ
carry an orbital angular momentum (OAM) of lℏ per
photon
[14–16]
, where l is a topological charge and θ repre-
sents an azimuthal angle. Photons with OAM could be
regarded as helices with their left- and right-handedness
twisted to varying degrees. Light encoded in OAM space
could offer high channel capacity and also can provide
capability for spatial manipulating
[17]
. Many groups and
researchers have demonstrated the optical storage of
OAM in atomic gas and solid matter s ystems
[18–22]
.
The Rydberg interaction, which is dependent on the
separation distance between the Rydberg atoms, creates
an obstacle on subsequent excitations of neighboring
ground state atoms. Such spatial dependent interaction
could bring rich spatial dynamics behaviors, showing po-
tential manipulation in image information processing.
Moreover, exciting Rydberg atoms with OAM structure
gives an additional degree of freedom for manipulating
an image. Storing a structured vortex beams as a
structured Rydberg collective excitation is a preliminary
step.
In this Letter, we experimentally investigate the optical
storage of OAM in cold rubidium atoms using the
Rydberg EIT. We use a time-resolution camera to monitor
the spatial structure of the probe beam carrying OAM
before and after storage. The storage time could be
up to 1.4 μs at a principal quantum number of 20. Higher
principal numbers (n ¼ 25; 30) are also given.
The experimental setup is similar to our previous
device
[23]
:
85
Rb atoms are trapped in two-dimensional
magneto-optical traps (MOTs); the atoms are prepared
to the 5S
1∕2
(F ¼ 2) state; the temperature of the atomic
cloud is ∼200 μK; the size is 2 mm × 2 mm × 30 mm; and,
the optical depth of the cold atoms is 20. The experiment
is run periodically with an MOT trapping time of 7.5 ms
and an experiment operation time of 1.5 ms, which con-
tains 300 cycles of Rydberg excitation operations. The
probe laser is an external-cavity diode laser (DL100,
Toptica), operating at a wavelength of 795 nm, which cor-
responds to the transition 5P
1∕2
ðF ¼ 2Þ → 5P
1∕2
ðF ¼ 3Þ.
The coupling laser is a frequency-doubled laser (SHG,
Toptica) with an output power of 680 mW, operating
at around 480 nm, which corresponds to the transition
5P
1∕2
ðF ¼ 3Þ → nD
3∕2
, shown in Fig. 1(a). The probe la-
ser is locked via saturated absorption spectroscopy, the
coupling laser is locked via two-photon dichroic atomic va-
por laser locking (DAVLL). The probe and coupling
beams collinearly counter-propagate through the MOT
with the same horizontal linear polarization and are fo-
cused by a lens with a focal length of 200 mm to increase
the interaction between the atoms and the laser. After the
probe and coupling beams propagate through the cloud of
COL 15(6), 060201(2017) CHINESE OPTICS LETTERS June 10, 2017
1671-7694/2017/060201(4) 060201-1 © 2017 Chinese Optics Letters