Squeezed Light

Light is composed of individual photons. When light is detected there is therefore an amount of noise due to the random photon arrival times. This is the reason for the "quantum noise limit" which sets the ultimate sensitivity bound for optical measurement. Squeezed states of light have specially prepared quantum noise properties. An amplitude squeezed state has less noise in the amplitude of the light, so the intensity of the laser is more stable. As a consequence, the phase noise of an amplitude squeezed laser is greater, since there is an uncertainty relation between the amplitude and phase quadratures of light.



Squeezed light can be used for improved optical measurement. More recently, it has become the key resource for continuous variable quantum information science. Squeezed states are central to experiments that show continuous variable quantum entanglement and quantum teleportation. An exciting new direction in quantum atom optics is the transfer of quantum states of light, like entangled states and squeezed states, between atoms and photons.


Squeezed Light at 795nm

795nm is the wavelength that corresponds to the D1 line of Rubidium 87. This is the same transition used in our EIT experiments. Our aim is to combine our source of squeezed light with atomic phenomena such as such as EIT, coherent spin states of cold atoms and atom lasers. So far we have about 5dB of squeezing at 795nm, a record for this wavelength. We use an optical parametric oscillator generate our squeezed states of light.


Delay of Squeezed Light and Entanglement

Our most recent experiment combines squeezed light and EIT. Our measurements showed that 2dB of squeezing was transmitted through our EIT gas cell. In a further experiment, the squeezing was split in 2 parts, with one part delayed using EIT before detection and the other part detected directly. This measurement demonstrated preservation of entanglement with a 2.2Ás delay in EIT. Read the paper here.


Past Projects

Polarisation self rotation

This experiment investigated squeezing generation via self rotation in a hot atomic vapour. Our experiment showed that there are sources of noise that make this kind of squeezing tricky. We (and collaborators in Paris) observed no squeezing, but the story is not quite over. Others have seen it and we would like to find out why!

Publication: Physical Review A 73, 023806 (2006).


Squeezed light for bandwidth-limited atom optics experiments at the rubidium D1 line.
Journal of Physics B, 40(1), 221, (2007).
G. HÚtet, O. Gl÷ckl, K. A. Pilypas, C. C. Harb, B. C. Buchler, H.-A. Bachor and P. K. Lam


Delay of squeezing and entanglement using electromagnetically induced transparency in a vapour cell.
Opt Express (2008) vol. 16 (10) pp. 7369-7381
G HÚtet, B. C Buchler, O Gl÷ckl, M. T. L Hsu, A. M Akulshin, H. A Bachor, P. K Lam.

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Measurements of entanglement transmission through EIT. Details here.


Squeezing for atoms

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Ben Buchler