We demonstrate a non-equilibrium phase transition in a dilute thermal atomic gas. The phase transition, between states of low and high Rydberg occupancy, is induced by resonant dipole-dipole interactions between Rydberg atoms. The gas can be consider
ed as dilute as the atoms are separated by distances much greater than the wavelength of the optical transitions used to excite them. In the frequency domain we observe a mean-field shift of the Rydberg state which results in intrinsic optical bistability above a critical Rydberg number density. In the time domain we observe critical slowing down where the recovery time to system perturbations diverges with critical exponent $tau=0.53 pm 0.10$. The atomic emission spectrum of the phase with high Rydberg occupancy provides evidence for a superradiant cascade.
We present a fast and Quasideterministic protocol for the production of single ions and electrons from a cloud of laser cooled atoms. The approach is based on a two-step process where first a single Rydberg atom is photo-excited from a dipole-blockad
e configuration and subsequently ionized by an electric field pulse. We theoretically describe these excitation-ionization cycles via dynamical quantum maps and observe a rich behavior of the ionization dynamics as a function of laser Rabi frequency, pulse duration and particle number. Our results show that a fast sequential heralded production of single charged particles is achievable even from an unstructured and fluctuating atomic ensemble.
We present a design for a switchable nanomagnetic atom mirror formed by an array of 180{deg} domain walls confined within Ni80Fe20 planar nanowires. A simple analytical model is developed which allows the magnetic field produced by the domain wall ar
ray to be calculated. This model is then used to optimize the geometry of the nanowires so as to maximize the reflectivity of the atom mirror. We then describe the fabrication of a nanowire array and characterize its magnetic behavior using magneto-optic Kerr effect magnetometry, scanning Hall probe microscopy and micromagnetic simulations, demonstrating how the mobility of the domain walls allow the atom mirror to be switched on and off in a manner which would be impossible for conventional designs. Finally, we model the reflection of 87Rb atoms from the atom mirrors surface, showing that our design is well suited for investigating interactions between domain walls and cold atoms.
