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SPINSQAV Résumé de rapport

Project ID: 4652
Financé au titre de: FP6-MOBILITY
Pays: Greece

Final Activity Report Summary - SPINSQAV (Spin Squeezing in Thermal Alkali Vapors)

Atomic vapours with spin degrees of freedom which we can manipulate are very interesting systems, both in terms of precision measurements of fundamental physical quantities as well as in terms of applications such as medical imaging. In particular, optical pumping atomic magnetometers have recently become extremely sensitive, offering the possibility to non-invasively image the magnetic activity of the human brain. The sensitivity of these magnetometers is limited, among other things, by the spin fluctuations (spin-projection noise) of the alkali vapour used to measure the magnetic field. Our goal in this project was to investigate the factors coming into the determination of the magnetic sensitivity of these magnetometers and investigate ways to reduce the noise sources limiting the sensitivity. One of the noise sources severely limiting the magnetometer's sensitivity is thermal magnetic noise originating from the conductive material used to shield the sensor from the ambient magnetic fields. However, this particular noise, termed Johnson noise, has the property that, if dominant, allows the operation of the magnetometer at high frequencies, quite higher than the fundamental bandwidth of the device.

Being able to detect high frequency magnetic fields with high sensitivity can open up a vast range of new applications. In this project we have found a way, to amplify the magnetometer's response to magnetic fields, and at the same time amplify the existing thermal magnetic noise. This counterintuitive approach does not improve on the magnetometer's sensitivity, but it does expand the range of frequencies at which the magnetometer can respond with a signal of adequate quality (signal-to-noise). Before going into studying ways of reducing the fundamental spin fluctuations, we have been and currently still are investigating these fluctuations, since they can provide information on the spin relaxation properties of the alkali vapour. This is quite intriguing, since by essentially detecting noise, we can infer physical properties of the system under study.

Furthermore, we have extended these studies into laser-cooled and trapped atomic vapours, which represent a very productive synergy with the afore-mentioned studies with thermal vapours. In conclusion, with the support of the Marie-Curie Reintegration grant, we have managed to develop the first experimental quantum optics laboratory in Greece, and to complete the setup of two experiments with a common research direction.


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