Description du projet :
Although known since the 1950s, atomic magnetometry based on paramagnetic atoms polarized by resonant light has received a new boost in the past decade due to the implementation of low-cost solid state diode lasers. Atomic magnetometers, and their close relative the atomic clock, are quantum sensors whose production in terms of sensitive, small, portable, and scalable quantum devices will become a key industrial development for the near future. Besides research laboratory applications in fundamental science, such devices will have a large range of practical uses, ranging from geology, archaeology to medicine, and even to airborne and satellite applications. Benefiting from recent technological developments in microelectronics, fibre optics, and diode laser technology, atomic magnetometers can be deployed in systems, in which many (lightweight, small volume) sensor heads can be placed at a large distance (10 m and more) from the driving/readout optics and electronics. This opens the way to measure, e.g., very weak biomagnetic signals (heart and brain fields) from humans and animals in a non-invasive way, and to record spatial maps thereof.Until recently the magnetometers with highest sensitivity (about 1 fT Hz^(-1/2)) were SQUIDs (superconducting quantum interference device). Unfortunately, SQUID systems are expensive to build and only operate where cryogenic cooling to liquid helium temperatures is available. Today, the sensitivity range for atomic magnetometers becomes competitive with (or even surpasses) SQUID sensors. The promise of optical atomic sensors is in their potential to be miniaturized (the smallest sensor so far realized has a dimension of 12 mm^3). In principle, atomic magnetometers can be adapted to the requirements of many different applications, and thus extended into daily life where such technology is currently rare.In the above context, this proposal aims at investigating a newly discovered branch of atomic magnetometry which has been only poorly explored to date. The proposed atomic magnetometers measure the magnetic field by a phase-sensitive comparison of the atomic Larmor precession frequency (itself proportional to the field strength) with the frequency of specific external electromagnetic radiation interacting with the atoms. For precise and sensitive applications, the external frequency should be referenced to a frequency standard such as an atomic clock. The proposed technique will exploit the (hitherto unexplored) fact that vapour cell atomic clocks and vapour cell atomic magnetometers are based on similar interactions of atoms and electromagnetic (light, microwave/radio-frequency) radiation. Herein we will attack the (obvious) question of whether it is possible to develop a device consisting of a sensitive atomic magnetometer containing its own intrinsic time-reference in terms of an atomic clock. The goal of the project is to answer this question.The work will be based on a recent proposal originating from the Happer group at Princeton University exploiting the so-called push-pull pumping, a variant of coherent population trapping (CPT) spectroscopy. Since its discovery in 1976 the CPT effect was studied in various dilute atomic samples (vapors, beams, condensates) and was applied in a number of fundamental experiments. The CPT effect has found applications in atom cooling to reach sub-Doppler and sub-photon recoil temperatures. The anomalously steep dispersion of CPT resonances exhibit have allowed the preparation of ultra-slow light, used for probing Bose-Einstein condensates, and provide potential applications in quantum communication and optical data storage. Here we focus on the fact that the push-pull variant of CPT spectroscopy can access both magnetic field sensitive and magnetic field insensitive resonances. The enhancement of the resonance contrast in the case of push-pull excitation of hyperfine coherences (clock application) has already been proven, but its use in magnetometry has not yet been explored. Here we want to use a doubly modulated laser source to generate simultaneously both magnetically sensitive (magnetometer) and magnetically insensitive (clock) resonances in an atomic cesium vapour sample. In three phases we plan to build the necessary apparatus, to fully investigate the features of this novel light-atom interaction and finally to realize and characterize a self-referenced magnetometer. The (mainly) experimental work will be backed by theoretical model calculations for which suitable algebraic and numerical tools for quantifying the atom-light interaction will be developed.
Forschungsteam innerhalb von HES-SO:
Durée du projet:
01.01.2011 - 28.07.2014
Montant global du projet: 484'746 CHF