September 2016

Abstracts of the QSIT Lunch Seminar, Thursday, September 1, 2016

Rydberg-atom macrodimers and aggregates

Heiner Saßmannshausen - Molecular Physics and Spectroscopy, ETH Zurich

Atoms in Rydberg states of high principal quantum number n exhibit unusual physical properties such as a large size, long lifetimes, and strong interatomic interactions. Using ultracold atomic samples and narrow-bandwidth lasers it is possible to generate experimental conditions where these exaggerated properties can be studied at high precision. My talk will focus in particular on the formation of extremely weakly bound molecules and of Rydberg-atom aggregates.

Diatomic molecules in which both atoms are excited to high Rydberg states, so-called macrodimers,  exhibit bond lengths of more than 1 mm and have binding energies corresponding to only a few hundred MHz. They are observed in our experiments following Rydberg excitation of an ultracold dense sample of Cs atoms with two successive laser pulses of different colour [1]. In such experiments, we also observe the formation of larger Rydberg-atom aggregates [2], for which non-Poissonian counting distributions are characteristic.

The interactions between the Rydberg atoms giving rise to the formation of macrodimers and aggregates are modeled using a long-range multipole expansion, with relevant contributions from the dipole-dipole, dipole-quadrupole, and higher-order contributions [3].

[1]  H. Saßmannshausen  and J. Deiglmayr, Phys. Rev. Lett. 117, 083401 (2016).
[2] H. Saßmannshausen , J. Deiglmayr, and F. Merkt, arXiv:1607.04060 (2016).
[3]  J. Deiglmayr, H. Saßmannshausen, P. Pillet, and F. Merkt, Phys. Rev. Lett. 113, 193001 (2014).

A two-qubit quantum heat engine assited by a quantum Maxwell demon

Andrey Lebedev - Quantum Condensed and Coherent Systems, ETH Zurich

We describe a quantum partial swap process where during an unitary evolution a qubit exchanges its entropy with an environment without energy exchange. This entropy-decreasing  process is naturally expressed through the action of a quantum Maxwell demon and we propose a quantum-thermodynamic engine with two qubits that extracts work from a single heat reservoir when provided with a reservoir of pure qubits. The special feature of this engine, which derives from the energy-conservation in the non-unital quantum channel, is its
separation into two cycles, a working cycle and an entropy cycle, allowing to run this engine with no local waste heat.