Cooling of mechanical motion with a two level system: the high temperature regime

We analyze cooling of a nano-mechanical resonator coupled to a dissipative solid state two level system focusing on the regime of high initial temperatures. We derive an effective Fokker-Planck equation for the mechanical mode which accounts for saturation and other non-linear effects and allows us to study the cooling dynamics of the resonator mode for arbitrary occupation numbers. We find a degrading of the cooling rates and eventually a breakdown of cooling at very high initial temperatures and discuss the dependence of these effects on various system parameters. Our results apply to most solid state systems which have been proposed for cooling a mechanical resonator including quantum dots, superconducting qubits and electronic spin qubits

Quantum limited velocity readout and quantum feedback cooling of a trapped ion via electromagnetically induced transparency

We discuss continuous observation of the momentum of a single atom by employing the high velocity sensitivity of the index of refraction in a driven $\Lambda$-system based on electromagnetically induced transparency (EIT). In the ideal limit of unit collection efficiency this provides a quantum limited measurement with minimal backaction on the atomic motion. A feedback loop, which drives the atom with a force proportional to measured signal, provides a cooling mechanism for the atomic motion. We derive the master equation which describes the feedback cooling and show that in the Lamb-Dicke limit the steady state energies are close to the ground state, limited only by the photon collection efficiency. Outside of the Lamb-Dicke regime the predicted temperatures are well below the Doppler limit.Comment: 13 pages, 6 figure

Cavity quantum electrodynamics in the non-perturbative regime

We study a generic cavity-QED system where a set of (artificial) two-level dipoles is coupled to the electric field of a single-mode LC resonator. This setup is used to derive a minimal quantum mechanical model for cavity QED, which accounts for both dipole-field and direct dipole-dipole interactions. The model is applicable for arbitrary coupling strengths and allows us to extend the usual Dicke model into the non-perturbative regime of QED, where the dipole-field interaction can be associated with an effective finestructure constant of order unity. In this regime, we identify three distinct classes of normal, superradiant and subradiant vacuum states and discuss their characteristic properties and the transitions between them. Our findings reconcile many of the previous, often contradictory predictions in this field and establish a common theoretical framework to describe ultrastrong coupling phenomena in a diverse range of cavity-QED platforms

Superconducting Circuits for Quantum Simulation of Dynamical Gauge Fields

We describe a superconducting-circuit lattice design for the implementation and simulation of dynamical lattice gauge theories. We illustrate our proposal by analyzing a one-dimensional U(1) quantum-link model, where superconducting qubits play the role of matter fields on the lattice sites and the gauge fields are represented by two coupled microwave resonators on each link between neighboring sites. A detailed analysis of a minimal experimental protocol for probing the physics related to string breaking effects shows that despite the presence of decoherence in these systems, distinctive phenomena from condensed-matter and high-energy physics can be visualized with state-of-the-art technology in small superconducting-circuit arrays

Parametricismus v Čechách

S rozvojem nových digitálních technologií, softwaru a výrobních nástrojů se objevily zcela nové názory na tvorbu a navrhování architektury. Tento různorodý proud nových způsobů uvažování byl poprvé souhrnně pojmenovány Patrikem Schumachrem jako nový styl – Parametricismus

Analysis of air pollution mortality in terms of life expectancy changes : relation between time series, intervention, and cohort studies.

Disponible sur internet : http://www.ehjournal.net/content/5/1/

Theory of cavity-assisted microwave cooling of polar molecules

We analyze cavity-assisted cooling schemes for polar molecules in the microwave domain, where molecules are excited on a rotational transition and energy is dissipated via strong interactions with a lossy stripline cavity, as recently proposed by A. Andre et al., Nature Physics 2, 636 (2006). We identify the dominant cooling and heating mechanisms in this setup and study cooling rates and final temperatures in various parameter regimes. In particular we analyze the effects of a finite environment temperature on the cooling efficiency, and find minimal temperature and optimized cooling rate in the strong drive regime. Further we discuss the trade-off between efficiency of cavity cooling and robustness with respect to ubiquitous imperfections in a realistic experimental setup, such as anharmonicity of the trapping potential

Hybrid quantum device with nitrogen-vacancy centers in diamond coupled to carbon nanotubes

We show that nitrogen-vacancy (NV) centers in diamond interfaced with a suspended carbon nanotube carrying a dc current can facilitate a spin-nanomechanical hybrid device. We demonstrate that strong magnetomechanical interactions between a single NV spin and the vibrational mode of the suspended nanotube can be engineered and dynamically tuned by external control over the system parameters. This spin-nanomechanical setup with strong, \emph{intrinsic} and \emph{tunable} magnetomechanical couplings allows for the construction of hybrid quantum devices with NV centers and carbon-based nanostructures, as well as phonon-mediated quantum information processing with spin qubits.Comment: Selected by PRL as "Editors' Suggestion

The Vacua of Dipolar Cavity Quantum Electrodynamics

The structure of solids and their phases is mainly determined by static Coulomb forces while the coupling of charges to the dynamical, i.e., quantized degrees of freedom of the electromagnetic field plays only a secondary role. Recently, it has been speculated that this general rule can be overcome in the context of cavity quantum electrodynamics (QED), where the coupling of dipoles to a single field mode can be dramatically enhanced. Here we present a first exact analysis of the ground states of a dipolar cavity QED system in the non-perturbative coupling regime, where electrostatic and dynamical interactions play an equally important role. Specifically, we show how strong and long-range vacuum fluctuations modify the states of dipolar matter and induce novel phases with unusual properties. Beyond a purely fundamental interest, these general mechanisms can be important for potential applications, ranging from cavity-assisted chemistry to quantum technologies based on ultrastrongly coupled circuit QED systems.Comment: Submission to SciPost, 23 pages, 5 figures (+ 5 in Appendix