197 research outputs found
Dipole lasing phase transitions in media with singularities in polarizabilities
We show that a divergence in the optical polarizability of a heterogeneous medium with nonlinear amplification and a strong dipole-dipole interaction between particles can lead to a phase transition, for which the dipole momentum of the particles or the dipole radiation rate can be taken as order parameters. The "dipole laser" (Phys. Rev. A 71, 063812 (2005)) can be used both as a simple example of such a second-order phase transition and to provide a recipe for its analysis. We show that similar phase transitions may be possible for a nanoparticle on the surface of an optically active medium and at the "Clausius-Mossotti" catastrophe in a bulk heterogeneous medium
Conditional quantum logic using two atomic qubits
In this paper we propose and analyze a feasible scheme where the detection of
a single scattered photon from two trapped atoms or ions performs a conditional
unitary operation on two qubits. As examples we consider the preparation of all
four Bell states, the reverse operation that is a Bell measurement, and a CNOT
gate. We study the effect of atomic motion and multiple scattering, by
evaluating Bell inequalities violations, and by calculating the CNOT gate
fidelity.Comment: 23 pages, 8 figures in 11 file
Dipole nanolaser
A "dipole" laser is proposed consisting of a nanoparticle and a two-level system with population inversion. If the threshold conditions are fulfilled, the dipole interaction between the two-level system and the nanoparticle leads to coherent oscillations in the polarization of the particles, even in the absence of an external electromagnetic field. The emitted radiation has a dipolar distribution. It does not need an optical cavity, and has a very small volume, 0.1 mu m(3), which can be important for applications in microelectronics. Estimates of the threshold conditions are carried out for a dipole laser composed of a quantum dot and a silver nanoparticle
Zeros of Rydberg-Rydberg Foster Interactions
Rydberg states of atoms are of great current interest for quantum
manipulation of mesoscopic samples of atoms. Long-range Rydberg-Rydberg
interactions can inhibit multiple excitations of atoms under the appropriate
conditions. These interactions are strongest when resonant collisional
processes give rise to long-range C_3/R^3 interactions. We show in this paper
that even under resonant conditions C_3 often vanishes so that care is required
to realize full dipole blockade in micron-sized atom samples.Comment: 10 pages, 4 figures, submitted to J. Phys.
Quantum Noise Limits for Nonlinear, Phase-Invariant Amplifiers
Any quantum device that amplifies coherent states of a field while preserving
their phase generates noise. A nonlinear, phase-invariant amplifier may
generate less noise, over a range of input field strengths, than any linear
amplifier with the same amplification. We present explicit examples of such
nonlinear amplifiers, and derive lower bounds on the noise generated by a
nonlinear, phase-invariant quantum amplifier.Comment: RevTeX, 6 pages + 4 figures (included in file; hard copy sent on
request
Fe/TiO2 composite coatings: electrodeposition and application for photo-catalytic dye degradation
The electrodeposition of iron-titania composite coatings from a methanesulfonate plating bath is studied in this work. The TiO2 content in deposits is shown to increase with increasing titania concentration in suspension electrolyte and decreasing cathode current density. The kinetics of composite Fe/TiO2 electrodeposition obeys the model proposed by Guglielmi. The photo-catalytic activity of synthesized Fe/TiO2 composite electrochemical coatings was estimated in the model reaction of decomposition of Methyl Orange dye in an alkaline solution. The use of the Fe/TiO2 composite electroplated films as a photo-catalyst allows accelerating the decomposition of Methyl Orange dye in aqueous media under the action of UV radiation
Broadening of Plasmonic Resonance Due to Electron Collisions with Nanoparticle Boundary: Đ° Quantum Mechanical Consideration
We present a quantum mechanical approach to calculate broadening of plasmonic
resonances in metallic nanostructures due to collisions of electrons with the
surface of the structure. The approach is applicable if the characteristic size
of the structure is much larger than the de Broglie electron wavelength in the
metal. The approach can be used in studies of plasmonic properties of both
single nanoparticles and arrays of nanoparticles.Comment: 9 page
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