All-optical 3D Quantum Sensor for Magnetic Fields

Within the scope of the research project, an attempt is made to realize a magnetic field measuring instrument which puts atoms into a quantum mechanical superposition state. This state is composed simultaneously of two energy states, which atoms can usually assume. "Non-classical energy states" are a phenomenon of the quantum nature of matter, which do not occur in this form in everyday life. These special states allow the energy levels of specially prepared atoms to be measured with a resolution 1,000,000 times greater than that of conventional methods. In the present case, for example, magnetic fields 100,000 times smaller than the Earth`s magnetic field are sufficient! The experimental setup works as a highly sensitive magnetometer, which allows to measure magnetic fields with highest absolute accuracy. Another special feature of this research project is that besides the mere value of the magnetic field strength also its direction is extracted from the observed signals of the quantum mechanical superposition state. Furthermore, it is investigated whether this method can be applied for the detection of land mines, the measurement of the earth`s magnetic field or the detection of mineral resources.

Laser light, which spectrally consists of several suitable frequency components, can excite atoms (in this case rubidium) energetically in such a way that the "outermost" electron in the rubidium atom, which is the weakest in terms of energy, assumes a so-called quantum mechanical superposition state. This superposition state is simultaneously composed of two energy states of the atom (in this case rubidium). This so-called non-classical state reacts extremely sensitively to the parameters of the exciting laser light and the energetic position of the energy states of the atom itself. The slightest disturbance causes this state (also known as dark resonance) to disappear. In the case investigated here, such "disturbances" are external magnetic fields, which can be detected very sensitively and precisely in this way. Previously, this type of optical magnetic field measurement using these dark resonances only succeeded in detecting the strength of the magnetic field. This project investigated how a quantum interference magnetometer (known as a coupled dark state magnetometer) can be extended so that the strength and direction of the magnetic field can be detected and precisely measured. As part of the project, it turned out that four such laser beams, each with several frequency components, are required to accomplish this measurement task. One of the surprises was that the desired angular accuracy of the vector CDSM magnetometer was 100 times better than originally assumed! This opens up future possibilities for using this new type of magnetometer in compact devices with excellent accuracy and stability properties.