May 2016

Exciton induced directed motion of unconstrained atoms in an ultracold gas

We demonstrate, that through localized Rydberg excitation in a three-dimensional cold atom cloud, atomic motion can be rendered directed and nearly confined to a plane without spatial constraints for the motion of individual atoms. This enables creation and observation of non-adiabatic electronic Rydberg dynamics in atoms accelerated by dipole-dipole interactions under natural conditions. Using the full l=0,1 m=-1,0,1 angular momentum state space, our simulations show that conical intersection crossings are clearly evident, both in atomic mean position information and excited state spectra of the Rydberg system. This suggests Rydberg aggregates as a test-bench for quantum chemical effects in experiments on much inflated length scales as compared to the standard molecular situation. [URL]


February 2016

Coupling of a nanomechanical oscillator and an atomic three-level medium

We now venture into opto-mechanics: We theoretically investigate the coupling of an ultracold three-level atomic gas and a nanomechanical mirror via classical electromagnetic radiation. The radiation pressure on the mirror is modulated by absorption of a probe light field, caused by the atoms which are electromagnetically rendered nearly transparent, allowing the gas to affect the mirror. In turn, the mirror can affect the gas as its vibrations generate optomechanical sidebands in the control field. We show that the sidebands cause modulations of the probe intensity at the mirror frequency, which can be enhanced near atomic resonances. Through the radiation pressure from the probe beam onto the mirror, this results in resonant driving of the mirror. Controllable by the two-photon detuning, the phase relation of the driving to the mirror motion decides upon amplification or damping of mirror vibrations. This permits direct phase locking of laser amplitude modulations to the motion of a nanomechanical element opening a perspective for cavity-free cooling through coupling to an atomic gas. [URL]


January 2016

We have relocated to Bilkent University, from the MPIPKS in Dresden, Germany.

March 2015

Quantum Simulation of Energy Transport with Embedded Rydberg Aggregates

We show that an array of ultracold Rydberg atoms embedded in a laser driven background gas can serve as an aggregate for simulating exciton dynamics and energy transport with a controlled environment. Energetic disorder and decoherence introduced by the interaction with the background gas atoms can be controlled by the laser parameters. This allows for an almost ideal realization of a Haken-Reineker-Strobl-type model for energy transport. The transport can be monitored using the same mechanism that provides control over the environment. The degree of decoherence is traced back to information gained on the excitation location through the monitoring, turning the setup into an experimentally accessible model system for studying the effects of quantum measurements on the dynamics of a many-body quantum system. [URL]

February 2015

Phase-Imprinting of Bose-Einstein Condensates with Rydberg Impurities

We show how the phase profile of Bose-Einstein condensates can be engineered through its interaction with localized Rydberg excitations. The interaction is made controllable and long-range by off-resonantly coupling the condensate to another Rydberg state. Our technique allows the mapping of entanglement generated in systems of few strongly interacting Rydberg atoms onto much larger atom clouds in hybrid setups. As an example we discuss the creation of a spatial mesoscopic super- position state from a bright soliton. Additionally, the phase imprinted onto the condensate using the Rydberg excitations is a diagnostic tool for the latter. For example a condensate time-of-flight image would allow the reconstruction of an embedded Rydberg crystal pattern. [URL]

November 2014

Switching exciton pulses through conical intersections

Exciton pulses transport excitation and entanglement adiabatically through Rydberg aggregates, assemblies of highly excited light atoms, which are set into directed motion by resonant dipole-dipole interaction. Here, we demonstrate the coherent splitting of such pulses as well as the spatial segregation of electronic excitation and atomic motion. Both mechanisms exploit local non-adiabatic effects at a conical intersection, turning them from a decoherence source into an asset. The intersection provides a sensitive knob controlling the propagation direction and coherence properties of exciton pulses. [URL]

May 2013

Entangling distant atom clouds through Rydberg dressing

In Rydberg dressed ultracold gases, ground-state atoms inherit properties of a weakly admixed Rydberg state, such as sensitivity to long-range interactions. We show that through hyperfine-state-dependent interactions, a pair of atom clouds can evolve into a spin and subsequently into a spatial mesoscopic superposition state: The pair is in a coherent superposition of two configurations, with cloud locations separated by micrometers. The mesoscopic nature of the state can be proven with absorption imaging, while the coherence can be revealed though recombination and interference of the split wave packets. [URL]

April 2011

Conical intersections in an ultracold gas

We find that energy surfaces of more than two atoms or molecules interacting via dipole-dipole potentials generically possess conical intersections (CIs). Typically only few atoms participate strongly in such an intersection. For the fundamental case, a circular trimer, we show how the CI affects adiabatic excitation transport via electronic decoherence or geometric phase interference. These phe- nomena may be experimentally accessible if the trimer is realized by light alkali atoms in a ring trap, whose dipole-dipole interactions are induced by off-resonant dressing with Rydberg states. Such a setup promises a direct probe of the full many-body density dynamics near a conical intersection. [URL]

July 2010

Communicating quantum properties through Newton's cradle

The metal balls that swing against one another in a classical cradle only exchange energy and momentum. We proposed a microscopic version of Newton's cradle made of highly excited Rydberg atoms. We find that these atoms additionally transport delicate quantum properties such as coherence and entanglement. Entanglement is a crucial ingredient of quantum computing and may even be involved in of the most important processes of life: photosynthesis. Thus, systems to control or study its migration may be of great relevance. [URL]