We report a photon shot-noise-limited (SNL) optical magnetometer based on amplitude modulated optical rotation using a room-temperature (85)Rb vapor in a cell with anti-relaxation coating. The instrument achieves a room-temperature sensitivity of 70 fT / √Hz at 7.6 μT. Experimental scaling of noise with optical power, in agreement with theoretical predictions, confirms the SNL behaviour from 5 μT to 75 μT. The combination of best-in-class sensitivity and SNL operation makes the system a promising candidate for application of squeezed light to a state-of-the-art atomic sensor.
We study the possibility of creating quantum superposition states in alkali atoms. Our methodology is based on the phenomenon of nonlinear magneto-optical rotation (NMOR) [1]. The effect of magneto-optical rotation occurs whenever the resonant light propagates through the medium immersed in a longitudinal magnetic field and manifests itself as a rotation of the polarization plane of light. The effect is strongly enhanced by the nonlinearity of light-atom interaction and allows state-of-the art atomic magnetometry [2].On the other hand, the nonlinear magneto-rotation provides means to controllably affect and detect atom's quantum state [3,4]. We present the work on this topic and report on some characteristics of superposition quantum states such as lifetimes or efficiency of it's creation in various conditions.The experiments are performed in warm 85 Rb vapour placed in homogeneous magnetic field (Fig. 1a). Two laser beams are used to interact with the medium. The stronger pump beam forces the medium to occupy the coherent quantum state. The weak probe beam is used to probe the medium optical properties and to give feedback on its quantum state. The quantum states that we manipulate are the Zeeman sublevels of the atomic ground state. These are associated with atomic magnetic momentum distribution and, as such, they are affected by the magnetic field that reinforces Larmor precession. This dynamics must be taken into account if one wants to interact with the atom's quantum states. We do so by employing the amplitude modulated light synchronized to the Larmor frequency. Fulfilling this conditions enables efficient creation of desired quantum states.Several cases are achievable, namely the creation of superpositions between Zeeman sublevels of Δm = 2, 4 or 6. Each case manifests itself as a resonant occurrence of medium's anisotropy and affects directly the rotation of light polarization (Fig. 1b). Basing on these resonances widths the superposition lifetimes as long as ~1s are measured. The amplitudes of resonances reveals on the other hand the characteristic nonlinear dependence on the light intensity.We are planning to extend the method to enable quantum state manipulation with specific pulse sequences and/or with the use of light of revolving plane of polarization. It is predicted, that this will enable us to perform EIT-like and STIRAP-like experimens with Zeeman sublevels. Fig. 1 (a) Experimental setup. (b) Basic measurement revealing three distinctive resonances associated with specific quantum states of superposition created between Zeemans sublevels of Δm = 2, 4 or 6 respectively.
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