No abstract

The control of one light field by another, ultimately at the single photon level 1-6 , is a challenging task which has numerous interesting applications within nonlinear optics 4,5 and quantum information science 6,7 . Due to the extremely weak direct interactions between optical photons in vacuum, this type of control can in practice only be achieved through highly nonlinear interactions within a medium 1-9 . Electromagnetic induced transparency (EIT) 1,5 constitutes one such meansto obtain the extremely strong nonlinear coupling needed to facilitate interactions between two faint light fields 2-6,8-11 . Here, we demonstrate for the first time EIT as well as all-optical EIT-based light switching using ion Coulomb crystals situated in an optical cavity. Unprecedented narrow cavity EIT feature widths down to a few kHz and a change from essentially full transmission to full absorption of the probe field within a window of only ~100 kHz are achieved. By applying a weak switching field, we furthermore demonstrate nearly perfect switching of the transmission of the probe field. These results represent important milestones for future realizations of quantum information processing devices, such as high-efficiency quantum memories 12,13 , single-photon transistors 14,15 and single-photon gates 4,6,8 .Electromagnetically induced transparency is a quantum interference phenomenon appearing when two electromagnetic fields excite resonantly two different transitions

We study experimentally and theoretically structural defects which are formed during the transition from a laser cooled cloud to a Coulomb crystal, consisting of tens of ions in a linear radio frequency trap. We demonstrate the creation of predicted topological defects ("kinks") in purely two-dimensional crystals and also find kinks which show novel dynamical features in a regime of parameters not considered before. The kinks are always observed at the center of the trap, showing a large nonlinear localized excitation, and the probability of their occurrence saturates at ∼0.5. Simulations reveal a strong anharmonicity of the kink's internal mode of vibration, due to the kink's extension into three dimensions. As a consequence, the periodic Peierls-Nabarro potential experienced by a discrete kink becomes a globally confining potential, capable of trapping one cooled defect at the center of the crystal.