Interacting collective modes in an optical cavity

E. L. Graca, B. Baseia

Jonathan Kohler

The quantum nature of light makes it a basic component for models of quantum measurement and information exchange between disparate quantum modes, pioneered in the field of cavity quantum electrodynamics. The interaction of atomic ensembles with the mode of an optical cavity provides a flexible platform for exploring the coherent interaction of light with diverse macroscopic dynamics, such as collective motion and spin. This dissertation presents experimental results and theoretical models for continuous measurement and control of the center of mass motion and collective spin precession of an atomic ensemble, mediated by coupling to a high-finesse optical cavity. First, the theory of dispersive coupling between the cavity mode and the collective motion and spin of an atomic ensemble is derived, and then a general time-domain formalism is developed for theoretical analysis of multi-mode optodynamical systems. Single-mode optodynamical effects are introduced through experimental demonstrations of measurement and control of the collective atomic spin, providing a close analogy to cavity optomechanics.Next, multiple collective atomic modes are considered within a single cavity, in order to assemble optically mediated interactions within multi-mode optodynamical systems. A demonstration of optodynamical interactions between the center of mass motion of two atomic ensembles is presented, coupled through an optical spring mediated by the cavity mode. Then simultaneous coupling of the center of mass motion and total spin precession of a single ensemble of atoms is described, yielding an experimental realization of a negative-mass instability, facilitated by the novel resource of the spin ensembles inverted state. A theoretical analysis of the negative-mass instability is presented, which indicates the possibility of generating two-mode squeezed states in the absence of excess incoherent noise. Finally, linear state retrodiction from the optodynamical signals is discussed, providing background and supplemental material for a forthcoming manuscript.

Sara Bergkvist, Emil Lundh, Patrik Henelius +1 more

Ph. W. Courteille, Yajaira Dalila Rivero Jerez, Gustavo Henrique de França +5 more

The strong collective interaction of atoms with an optical cavity causes normal mode splitting of the cavity's resonances, whose width is given by the collective coupling strength. At low optical density of the atomic cloud, the intensity distribution of light in the cavity is ruled by the cavity's mode function, which is determined solely by its geometry. In this regime the dynamics of the coupled atom-cavity system is conveniently described by the open Dicke model, which we apply to calculating normal mode splitting generated by periodically ordered clouds in linear and ring cavities. We also show how to use normal mode splitting as a witness for Wannier-Bloch oscillations in the tight-binding limit. At high optical density the atomic distribution contributes to shaping the mode function. This regime escapes the open Dicke model, but can be treated by a transfer matrix model provided the saturation parameter is low. Applying this latter model to an atomic cloud periodically ordered into a one-dimensional lattice, we observe the formation of photonic bands gaps competing with the normal mode splitting. We discuss the limitations of both models and point out possible pathways to generalized theories.

Dan Stamper-Kurn

F. T. Arecchi