Slow light using EIT

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Ben Buchler


Electromagnetically Induced Transparency

A cloud of atomic vapour (in our case rubidium) is normally highly absorptive at wavelengths of light that match an atomic transition. Electromagnetically Induced Transparency (EIT) can occur when two different beams of light interact with a three level atomic system. A strong 'control beam' can cause the atomic vapour to become transparent for a weaker 'probe beam'.


Slow Light

The window of transparency is very narrow. As a result of the Kramers-Kronig relations, a narrow transmission feature gives rise to strong dispersion, which means a rapid change in phase as a function of frequency. This leads to a strongly reduced group velocity for the light that passes through the EIT window. We have measured light up to 30,000 times slower as it passes through our hot atomic vapour. Experiments with cold atoms have measured speeds as low as 17m/s (61km/h), which is 17.6 million times slower than the normal speed of 300 million metres per second.


Stopped Light

There is also the possibility of stopping the light altogether. If the control beam is switched off while the probe is travelling through the atoms, the probe can be brought to a complete halt and stored for surprisingly long periods. The solid state spectroscopy group at the ANU has shown storage of up to 2.3 seconds in cryogenically cooled crystals.


Quantum Memory?

Could this slow light be used as a memory for quantum states? Our experiments aim to answer that question. We carry out experiments that measure the amount of noise added to the light as it passes through the EIT medium to see how well a quantum state might be preserved. In combination with our squeezed light project, we also plan to demonstrate the storage of real quantum states. So far we have demonstrated the preservation of entanglement with EIT mediated slow light.




Characterization of electromagnetically-induced-transparency-based continuous-variable quantum memories.
Phys. Rev. A (2008) vol. 77 (1) 012323
G Hétet, A Peng, M. T Johnsson, J. J Hope, P. K Lam.

Quantum study of information delay in electromagnetically induced transparency
Physical Review Letters, 97(18), 183601, (2006).
M. T. L. Hsu, G. Hétet, O. Glöckl, J. J. Longdell, B. C. Buchler, H.-A. Bachor, and P. K. Lam.

Squeezing and entanglement delay using slow light
Phys. Rev. A 71, 033809 (2005)
A. Peng, M. Johnsson, W. P. Bowen, P. K. Lam, H. -A. Bachor and J. J. Hope







Detail of the EIT experiment