8,030 research outputs found
Non-exponential spontaneous emission dynamics for emitters in a time-dependent optical cavity
We have theoretically studied the effect of deterministic temporal control of
spontaneous emission in a dynamic optical microcavity. We propose a new
paradigm in light emission: we envision an ensemble of two-level emitters in an
environment where the local density of optical states is modified on a time
scale shorter than the decay time. A rate equation model is developed for the
excited state population of two-level emitters in a time-dependent environment
in the weak coupling regime in quantum electrodynamics. As a realistic
experimental system, we consider emitters in a semiconductor microcavity that
is switched by free-carrier excitation. We demonstrate that a short temporal
increase of the radiative decay rate depletes the excited state and drastically
increases the emission intensity during the switch time. The resulting
time-dependent spontaneous emission shows a distribution of photon arrival
times that strongly deviates from the usual exponential decay: A deterministic
burst of photons is spontaneously emitted during the switch event.Comment: 12 pages, 4 figure
Single File Diffusion of particles with long ranged interactions: damping and finite size effects
We study the Single File Diffusion (SFD) of a cyclic chain of particles that
cannot cross each other, in a thermal bath, with long ranged interactions, and
arbitrary damping. We present simulations that exhibit new behaviors
specifically associated to systems of small number of particles and to small
damping. In order to understand those results, we present an original analysis
based on the decomposition of the particles motion in the normal modes of the
chain. Our model explains all dynamic regimes observed in our simulations, and
provides convincing estimates of the crossover times between those regimes.Comment: 30 pages, 9 figure
Optimal all-optical switching of a microcavity resonance in the telecom range using the electronic Kerr effect
We have switched GaAs/AlAs and AlGaAs/AlAs planar microcavities that operate
in the "Original" (O) telecom band by exploiting the instantaneous electronic
Kerr effect. We observe that the resonance frequency reversibly shifts within
one picosecond. We investigate experimentally and theoretically the role of
several main parameters: the material backbone and its electronic bandgap, the
pump power, the quality factor, and the duration of the switch pulse. The
magnitude of the shift is reduced when the backbone of the central
layer has a greater electronic bandgap; pumping with photon energies
near the bandgap resonantly enhances the switched magnitude. Our model shows
that the magnitude of the resonance frequency shift depends on the pump pulse
duration and is maximized when the duration matches the cavity storage time
that is set by the quality factor. We provide the settings for the essential
parameters so that the frequency shift of the cavity resonance can be increased
to one linewidth
Differential ultrafast all-optical switching of the resonances of a micropillar cavity
We perform frequency- and time-resolved all-optical switching of a GaAs-AlAs
micropillar cavity using an ultrafast pump-probe setup. The switching is
achieved by two-photon excitation of free carriers. We track the cavity
resonances in time with a high frequency resolution. The pillar modes exhibit
simultaneous frequency shifts, albeit with markedly different maximum switching
amplitudes and relaxation dynamics. These differences stem from the
non-uniformity of the free carrier density in the micropillar, and are well
understood by taking into account the spatial distribution of injected free
carriers, their spatial diffusion and surface recombination at micropillar
sidewalls.Comment: 4 pages, 3 figure
Single Crystal Sapphire at milli-Kelvin Temperatures: Observation of Electromagnetically Induced Thermal Bistability in High Q-factor Whispering Gallery Modes
Resonance modes in single crystal sapphire (-AlO) exhibit
extremely high electrical and mechanical Q-factors ( at 4K),
which are important characteristics for electromechanical experiments at the
quantum limit. We report the first cooldown of a bulk sapphire sample below
superfluid liquid helium temperature (1.6K) to as low as 25mK. The
electromagnetic properties were characterised at microwave frequencies, and we
report the first observation of electromagnetically induced thermal bistability
in whispering gallery modes due to the material dependence on thermal
conductivity and the ultra-low dielectric loss tangent. We identify "magic
temperatures" between 80 to 2100 mK, the lowest ever measured, at which the
onset of bistability is suppressed and the frequency-temperature dependence is
annulled. These phenomena at low temperatures make sapphire suitable for
quantum metrology and ultra-stable clock applications, including the possible
realization of the first quantum limited sapphire clock.Comment: 5 pages, 4 figure
A New Embedded Measurement Structure for eDRAM Capacitor
Submitted on behalf of EDAA (http://www.edaa.com/)International audienceThe embedded DRAM (eDRAM) is more and more used in System On Chip (SOC). The integration of the DRAM capacitor process into a logic process is challenging to get satisfactory yields. The specific process of DRAM capacitor and the low capacitance value (~30F) of this device induce problems of process monitoring and failure analysis. We propose a new test structure to measure the capacitance value of each DRAM cell capacitor in a DRAM array. This concept has been validated by simulation on a 0.18µm eDRAM technology
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