Nonlinear magneto-optics in alkali vapors at room temperature

Introduction

Nonlinear magneto-optical rotation (NMOR) is a light-intensity dependent rotation of a polarization plane of linearly polarized light during its propagation through a medium placed in an external magnetic field. In NMOR the polarization rotation strongly depends on the magnetic field which enables measurements of weak magnetic fields with extremely high sensitivity (up to 10-15 T/√Hz). This powerful magnetometric technique, however, has the significant drawback which is its narrow dynamic range; the higher the sensitivity of the field measurements, the narrower is its dynamic range. Due to this fact, the method can be applied for measurements of very weak fields only which implies a necessity of shielding external magnetic fields. This requirement is a stringent limit of the method's applicability.

Nonlinear magneto-optical rotation with amplitude modulated light

The stringent limit on a dynamic range of the traditional NMOR magnetometry can be successfully overcame by application of a modulated light. Application of amplitude-modulated light (AM) for NMOR measurements was suggested and first realized in our Center. In the amplitude-modulated nonlinear magneto-optical rotation (AMOR), in addition to the zero-field signals observed in traditional NMOR around B=0, extra resonances appear at nonzero magnetic fields. The field at which these signals are recorded is precisely determined by the light-modulation frequency. Since, the amplitudes and widths of these high-field resonances are similar to the amplitude and width of the traditional NMOR signal, it enables measurements of much stronger magnetic fields, for example, fields comparable with the Earth magnetic field, with the sensitivity achievable previously only for measurements of very weak fields.

Magnetometry based on AMOR

One result of the research realized in CMOR was demonstration of the magnetometric method based on AMOR. The method enables obtaining very high sensitivity of 4×10-13 T/√Hz within a broad dynamic range of about 10 μT. The current works are concentrated on an increase of the sensitivity and extension of the dynamic range of the AMOR based magnetometric method. Simultaneously, an independent project towards increasing the AMOR magnetometer bandwidth above 1 kHz is realized in the Center. Such a high bandwidth in addition to the device's very high sensitivity would enable application of the magnetometer in many areas, in particular for measurements of biofields.

Precise measurements of magnetic fields using NMOR with modulated light found already a number of interesting applications, for instance, in nuclear magnetic resonance and magnetic resonance imaging. Other applications are currently being developed in CMOR.

Quantum-state engineering

The nonlinear rotation of a polarization plane is associated with existence of quantum superpositions between atomic Zeeman states. In fact, the same superpositions are also fundamental for storage of quantum information and quantum-state engineering (atoms may be employed as qubits). The techniques of slowing down coherence relaxation, broadly employed in AMOR, allows the qubit's lifetime to be extended to hundreds of ms which is extremely difficult with other quantum information techniques. One of the results obtained in the Center was demonstration of controllable generation and modification of atomic quantum states. Moreover, it was shown that in more complex systems, i.e., in the systems with more than 2 magnetic sublevels in the atomic ground state, selective creation and detection of the coherences between given magnetic sublevels is possible. The ability of generation and modification of specific quantum superpositions (quantum-state engineering) is crucial for creation of n-dimensional quantum nits of information.

Cooperation

Some of the works discussed herein are realized in close collaboration with the prof. D. Budker's group from the University of California at Berkeley within the Joint Krakow-Berkeley Atomic Physics and Photonics Laboratory. The group also cooperates with the prof. M. Auzinsh's group from the University of Latvia.

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Last updated: 05.04.2011