Stopped Light With Storage Times Greater than 1 second using Electromagnetically Induced
Transparency in a Solid
J.J Londell, E. Fravel, M.J. Sellars and N.B. Manson, Phys. Rev. Lett. 95 063601 (2005)
Motivation
Experiment
• Advances in quantum computers means there is a need for devices
which can act as quantum memories.
• Slowing down and stopping light pulses in a medium provides a way of
mapping all the information from the pulse into the medium in the form of
a spin wave.
Below: experimental setup used for light storage experiments
Results
Below: Gray line indicates the transmission in Pr+SiO5 when the
coupling beam is off. Dark line is with coupling beam on
Transmission Through Pr+SiO5
• transmission peak is exhibited
at the resonance frequency (EIT
was demonstrated)
Dynamic EIT
EIT (electromagnetically induced transmission
makes use of the Dark State of a system. In this
state, the simultaneous presence of the control and
signal beam couple with the system atomic states to
forbid some excitations (thus absorptions of
photons) of the atomic states. The beams are then
transmitted. As a toy model, it is helpful to think of:
x^2 - x^4
+ x^6
| g1 | g2   | g2 | g1   | e | e   | e | e  0
The rapid change of refractive index within the
transparency window (∆ω) slows down the beams as:
1
1
1
d  dk 
1  dn( ) 
 d kvacuumn( ) 
[dn(ω)/dω]-1


dk
 d 


∆ω and
are proportional to the
control beam intensity. When the control beam
is switched off, ∆ω and vg go to 0 and there is no
photon transmitted. However, the Dark State
(excitations of Polaritons) is maintained and the
signal beam information is mapped to the spin
coherence of system atomic states. When the
control beam is switched on again, the process
reverses and the signal beam is retrieved.
d
• light stored in Pr+ SiO5 crystal - material chosen because 5/2 spin of Pr+ nuclei
provide ground states for EIT via Zeeman splitting in a B field
Storage Time
• counterpropogating beams for distinguishing probe and coupling beams easily
absorption
vg 
•Narrow transparency window



kvacuum  d 
Left: energy levels of Pr+SiO5 in B field
• fine splitting due to B field
•repump pulses prepare the
correct conditions for EIT
• probe beam and coupling
beam form transparent state
• coupling beam turned off after probe applied
• RF pulses applied with two techniques: 1. with 2
pulses (top) 2. with many pulses (bottom)
Below: sequence of laser pulses
applied towith Pr+SiO5
• efficiency decreases
exponentially as the storage time
increases
• due to decoherence of spin
wave from scattering process
Above: (a) 2 rephasing pulses used (b) many rephasing pulses used
Future work
• Decoherence due to the environment
•Optimization of photon storage
• Generalization to photonic crystal
•Application to quantum memory