Quantum metamaterials: Electromagnetic waves in a Josephson qubit line

We consider the propagation of a classical electromagnetic wave through a transmission line, formed by identical superconducting charge qubits inside a superconducting resonator. Since the qubits can be in a coherent superposition of quantum states, we show that such a system demonstrates interesting new effects, such as a ``breathing'' photonic crystal with an oscillating bandgap, and a ``quantum Archimedean screw'' that transports, at an arbitrary controlled velocity, Josephson plasma waves through the transmission line. The key ingredient of these effects is that the optical properties of the Josephson transmission line are controlled by the quantum coherent state of the qubits.Comment: References adde

Transport of free surface liquid films and drops by external ratchets and self-ratcheting mechanisms

We discuss the usage of ratchet mechanisms to transport a continuous phase in several micro-fluidic settings. In particular, we study the transport of a dielectric liquid in a heterogeneous ratchet capacitor that is periodically switched on and off. The second system consists of drops on a solid substrate that are transported by different types of harmonic substrate vibrations. We argue that the latter can be seen as a self-ratcheting process and discuss analogies between the employed class of thin film equations and Fokker-Planck equations for transport of discrete objects in a 'particle ratchet'.Comment: 10 pages, 13 figure

Discontinuous conductance of bichromatically ac-gated quantum wires

We study the electron transport through a quantum wire under the influence of external time-dependent gate voltages. The wire is modelled by a tight-binding Hamiltonian for which we obtain the current from the corresponding transmission. The numerical evaluation of the dc current reveals that for bichromatic driving, the conductance depends sensitively on the commensurability of the driving frequencies. The current even possesses a discontinuous frequency dependence. Moreover, we find that the conductance as a function of the wire length oscillates with a period that depends on the ratio between the driving frequencies.Comment: 7 pages, 4 figure

Coherent emission from disordered arrays of driven Josephson vortices

We propose a mechanism of coherent emission from driven vortices in stacked intrinsic Josephson junctions. In contrast to super-radiance, which occurs only for highly ordered vortex lattices, we predict resonant radiation emission from weakly correlated vortex arrays. Our analytical results for the THz wave intensity, resonance frequencies, and the dependence of THz emission power on dissipation are in good agreement with the ones obtained by recent simulations.Comment: 2 figure

Generation of tunable Terahertz out-of-plane radiation using Josephson vortices in modulated layered superconductors

We show that a moving Josephson vortex in spatially modulated layered superconductors generates out-of-plane THz radiation. Remarkably, the magnetic and in-plane electric fields radiated are of the same order, which is very unusual for any good-conducting medium. Therefore, the out-of-plane radiation can be emitted to the vacuum without the standard impedance mismatch problem. Thus, the proposed design can be more efficient for tunable THz emitters than previous proposals, for radiation only propagating along the ab-plane.Comment: 7 pages, 1 figure. Phys. Rev. B (2005), in pres

Ring-shaped luminescence patterns in a locally photoexcited electron-hole bilayer

We report the results of molecular dynamics simulation of a spatiotemporal evolution of the locally photoexcited electrons and holes localized in two separate layers. It is shown that the ring-shaped spatial pattern of luminescence forms due to the strong in-layer Coulomb interaction at high photoexcitation power. In addition, the results predict (i) stationary spatial oscillations of the electron density in quasi one-dimensional case and (ii) dynamical phase transition in the expansion of two-dimensional electron cloud when threshold electron concentration is reached. A possible reason of the oscillations and a theoretical interpretation of the transition are suggested.Comment: 6 pages, 5 figures. Final version as published + Erratum has been adde

Temperature-resonant cyclotron spectra in confined geometries

We consider a two-dimensional gas of colliding charged particles confined to finite size containers of various geometries and subjected to a uniform orthogonal magnetic field. The gas spectral densities are characterized by a broad peak at the cyclotron frequency. Unlike for infinitely extended gases, where the amplitude of the cyclotron peak grows linearly with temperature, here confinement causes such a peak to go through a maximum for an optimal temperature. In view of the fluctuation-dissipation theorem, the reported resonance effect has a direct counterpart in the electric susceptibility of the confined magnetized gas

Controlling the motion of interacting particles: Homogeneous systems and binary mixtures

We elaborate on recent results on the transport of interacting particles for both single-species and binary mixtures subject to an external driving on a ratchetlike asymmetric substrate. Moreover, we also briefly review motion control without any spatial asymmetric potential (i.e., no ratchet). Our results are obtained using an analytical approach based on a nonlinear Fokker–Planck equation as well as via numerical simulations. By increasing the particle density, the net dc ratchet current in our alternating (ac)-driven systems can either increase or decrease depending on the temperature, the drive amplitude, and the nature of the inter-particle interactions. This provides an effective control of particle motion by just changing the particle density. At low temperatures, attracting particles can condense at some potential minima, thus breaking the discrete translational symmetry of the substrate. Depending on the drive amplitude, an agglomeration or condensation results either in a drop to zero or in a saturation of the net particle velocity at densities above the condensation density—the latter case producing a very efficient rectification mechanism. For binary mixtures we find three ways of controlling the particle motion of one (passive) BB species by means of another (active) AA species: (i) Dragging the target particles BB by driving the auxiliary particles AA, (ii) rectifying the motion of the BB particles on the asymmetric potential created by the A–BA–B interactions, and (iii) dynamically modifying (pulsating) this potential by controlling the motion of the AA particles. This allows to easily control the magnitude and direction of the velocity of the target particles by changing either the frequency, phase and/or amplitude of the applied ac drive(s).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87889/2/026112_1.pd

Noise enhanced performance of adiabatic quantum computing by lifting degeneracies

We investigate the symmetry breaking role of noise in adiabatic quantum computing using the example of the CNOT gate. In particular, we analyse situations where the choice of initial configuration leads to symmetries in the Hamiltonian and degeneracies in the spectrum. We show that, in these situations, there exists an optimal level of noise that maximises the success probability and the fidelity of the final state. The effects of an artificial noise source with a time-dependent amplitude are also explored and it is found that such a scheme would offer a considerable performance enhancement.Comment: 12 pages and 4 figures in preprint format. References in article corrected and journal reference adde