Magnetic field sensors that exploit quantum effects have shown that they can outperform classical sensors in terms of sensitivity enabling a range of novel applications in future, such as a brain machine interface. Negatively charged nitrogen-vacancy (NV) centers in diamond have emerged as a promising high sensitivity platform for measuring magnetic fields at room temperature. Transferring this technology from laboratory setups into products and applications, the total size of the sensor, the overall power consumption, and the costs need to be reduced and optimized. Here, a fiber-based NV magnetometer featuring a complete integration of all functional components is demonstrated without using any bulky laboratory equipment. This integrated prototype allows portable measurement of magnetic fields with a sensitivity of 344 pT Hz −1/2 .

We report on the measurement of Stark shifted energy levels of 87 Rb Rydberg atoms in static electric fields by means of electromagnetically induced transparency (EIT). Electric field strengths of up to 500 V/cm, ranging beyond the classical ionisation threshold, were applied using electrodes inside a glass cell with rubidium vapour. Stark maps for principal quantum numbers n = 35 and n = 70 have been obtained with high signal-to-noise ratio for comparison with results from ab initio calculations following the method described in [M. L. Zimmerman et al., Phys. Rev. A 20, 2251(1979], which was originally only verified for states around n = 15. We also calculate the dipole matrix elements between low-lying states and Stark shifted Rydberg states to give a theoretical estimate of the relative strength of the EIT signal. The present work significantly extends the experimental verification of this numerical method in the range of both high principal quantum numbers and high electric fields with an accuracy of up to 2 MHz.

We have developed an all-optical method for measuring the lifetimes of nS and nD Rydberg states and demonstrate its capabilities with measurements on a dilute cloud of ultracold 87 Rb atoms in a cryogenic environment. The method is based on the time-resolved observation of resonant light absorption by ground state atoms and selective transfer of Rydberg atoms into the ground state at varying delay times in order to reconstruct Rydberg decay curves. Our measurements of the 87 Rb 30S 1/2 state indicate an increase of the lifetime at lowered environment temperatures, as expected due to decreased black body radiation. For the 38D 5/2 state with an attractive dipoledipole interaction, ionization and lifetime reduction due to collisional effects are observed. For individual Rydberg atoms at an environment temperature T = 0 the lifetime of an excited state is given by the inverse sum over all spontaneous decay rates into lower lying states [8]. Due to the highest energy difference, the lowest lying states contribute most to the decay. This is a limiting factor for calculations because the potentials for low-lying states can not be described as accurately as those of higher states, which become more and more hydrogen-like with increasing n and l quantum numbers. In a finite temperature environment, blackbody radiation (BBR) induced transitions occur. The strongest transitions are those to nearby dipole-allowed Rydberg states both above and below in energy. For a perfect Planck photon distribution and well-known temperature the corresponding rates can be calculated with high accuracy [4,5]. The experimental verification of BBR induced transition rates is possible not only through Rydberg lifetime measurements [9] but also indirectly by e.g. measurements of Stark maps [10], which depend on the same dipole matrix elements. Any incoherent repopulation of the originally excited Rydberg state by multiple BBR transitions can be easily included into theoretical models, but is usually negligible in magnitude. * markus.mack@uni-tuebingen.de † fortagh@uni-tuebingen.de Also, blackbody-induced ionization by transitions to continuum states can be taken into account [11].Direct lifetime measurements at lowered environment temperatures, as well as measurements of temperaturedependent BBR transfer rates, have been conducted for Na atoms [9,12]. The most accurate values for Rb Rydberg lifetimes to date have been measured in a room temperature environment, relying on the knowledge of BBR transition rates in order to extract zero-temperature natural lifetimes. Measurements of nS and nD states in the range of n = 27 to 44 were conducted by exciting Rydberg atoms from a cloud of ultracold atoms prepared in a magneto-optical trap (MOT), waiting some varying delay time, and then applying an electric field pulse while monitoring the time-dependent ionization signals (selective field ionization, SFI) [13,14]. Due to the difficulty of accurately distinguishing between close lying Rydberg states which are populated because of BBR (see discussion ...

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We present an all-optical protocol for detecting population in a selected Rydberg state of alkali atoms. The detection scheme is based on the interaction of an ensemble of ultracold atoms with two laser pulses: one weak probe pulse which is resonant with the transition between the ground state and the first excited state, and a pulse with high intensity which couples the first excited state to the selected Rydberg state. We show that by monitoring the absorption signal of the probe laser over time, one can deduce the initial population of the Rydberg state. Furthermore, it is shown that - for suitable experimental conditions - the dynamical absorption curve contains information on the initial coherence between the ground state and the selected Rydberg state. We present the results of a proof-of-principle measurement performed on a cold gas of $^{87}$Rb atoms. The method is expected to find application in quantum computing protocols based on Rydberg atoms