We realize a spin-1 Dicke model using magnetic sub-levels of the lowest F = 1 hyperfine level of 87 Rb atoms confined to a high finesse cavity. We study this system under conditions of imbalanced driving, which is predicted to have a rich phase diagram of nonequilibrium phases and phase transitions. We observe both super-radiant and oscillatory phases from the cavity output spectra as predicted by theory. Exploring the system over a wide range of parameters, we obtain the boundaries between the normal, super-radiant and the oscillatory phases, and compare with a theoretical model.

The Dicke model is of fundamental importance in quantum mechanics for understanding the collective behaviour of atoms coupled to a single electromagnetic mode. In this paper, we demonstrate a Dicke-model simulation using cavity-assisted Raman transitions in a configuration using counterpropagating laser beams. The observations indicate that motional effects should be included to fully account for the results and these results are contrasted with the experiments using single-beam and co-propagating configurations. A theoretical description is given that accounts for the beam geometries used in the experiments and indicates the potential role of motional effects. In particular a model is given that highlights the influence of Doppler broadening on the observed thresholds. arXiv:1801.07888v1 [quant-ph]

We investigate the feasibility of precision frequency metrology with large ion crystals. For clock candidates with a negative differential static polarisability, we show that micromotion effects should not impede the performance of the clock. Using Lu + as a specific example, we show that quadrupole shifts due to the electric fields from neighbouring ions do not significantly affect clock performance. We also show that effects from the tensor polarisability can be effectively managed with a compensation laser at least for a small number of ions ( 10 3 ). These results provide new possibilities for ion-based atomic clocks, allowing them to achieve stability levels comparable to neutral atoms in optical lattices and a viable path to greater levels of accuracy.

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