Atomic spin squeezing in an optical cavity

We consider squeezing of one component of the collective spin vector of an atomic ensemble inside an optical cavity. The atoms interact with a cavity mode, and the squeezing is obtained by probing the state of the light field that is transmitted through the cavity. Starting from the stochastic master equation, we derive the time evolution of the state of the atoms and the cavity field, and we compute expectation values and variances of the atomic spin components and the quadratures of the cavity mode. The performance of the setup is compared to spin squeezing of atoms by probing of a light field transmitted only once through the sample.Comment: 8 pages, 2 figure

Model wavefunctions for interfaces between lattice Laughlin states

We study the interfaces between lattice Laughlin states at different fillings. We propose a class of model wavefunctions for such systems constructed using conformal field theory. We find a nontrivial form of charge conservation at the interface, similar to the one encountered in the field theory works from the literature. Using Monte Carlo methods, we evaluate the correlation function and entanglement entropy at the border. Furthermore, we construct the wavefunction for quasihole excitations and evaluate their mutual statistics with respect to quasiholes originating at the same or the other side of the interface. We show that some of these excitations lose their anyonic statistics when crossing the interface, which can be interpreted as impermeability of the interface to these anyons. Contrary to most of the previous works on interfaces between topological orders, our approach is microscopic, allowing for a direct simulation of e.g. an anyon crossing the interface. Even though we determine the properties of the wavefunction numerically, the closed-form expressions allow us to study systems too large to be simulated by exact diagonalization.Comment: A number of changes were made in response to referees' comments: large parts of the text were rewritten, new results were added, some of the old results were reinterpreted, the discussion of connection to earlier works was expande