Controlling the dynamics of an open many-body quantum system with localized dissipation

We experimentally investigate the action of a localized dissipative potential on a macroscopic matter wave, which we implement by shining an electron beam on an atomic Bose-Einstein condensate (BEC). We measure the losses induced by the dissipative potential as a function of the dissipation strength observing a paradoxical behavior when the strength of the dissipation exceeds a critical limit: for an increase of the dissipation rate the number of atoms lost from the BEC becomes lower. We repeat the experiment for different parameters of the electron beam and we compare our results with a simple theoretical model, finding excellent agreement. By monitoring the dynamics induced by the dissipative defect we identify the mechanisms which are responsible for the observed paradoxical behavior. We finally demonstrate the link between our dissipative dynamics and the measurement of the density distribution of the BEC allowing for a generalized definition of the Zeno effect. Due to the high degree of control on every parameter, our system is a promising candidate for the engineering of fully governable open quantum systems

Universal behavior of spin-mediated energy transport in S=1/2 chain cuprates: BaCu2Si2O7 as an example

The thermal conductivity of the spin-1/2 chain cuprate BaCu2Si2O7 was measured along different crystallographic directions in the temperature region between 0.5 and 300 K. The thermal conductivity along the chain direction considerably exceeds that along perpendicular directions. Near the antiferromagnetic transition at T_N = 9.2 K the data indicates enhanced scattering of phonons by critical fluctuations in the spin system. A comparison of the data above T_N with available results on similar materials reveals similarities in the main features of the temperature dependence of the mean free path of itinerant spin excitations. This universal behavior is most likely caused by the spin-lattice interaction.Comment: 7 pages, 3 figure