65 research outputs found
Non-ergodic Intensity Correlation Functions for Blinking Nano Crystals
We investigate the non-ergodic properties of blinking nano-crystals using a
stochastic approach. We calculate the distribution functions of the time
averaged intensity correlation function and show that these distributions are
not delta peaked on the ensemble average correlation function values; instead
they are W or U shaped. Beyond blinking nano-crystals our results describe
non-ergodicity in systems stochastically modeled using the Levy walk framework
for anomalous diffusion, for example certain types of chaotic dynamics,
currents in ion-channel, and single spin dynamics to name a few.Comment: 5 pages, 3 figure
Evidence for a diffusion-controlled mechanism for fluorescence blinking of colloidal quantum dots
Fluorescence blinking in nanocrystal quantum dots is known to exhibit power-law dynamics, and several different mechanisms have been proposed to explain this behavior. We have extended the measurement of quantum-dot blinking by characterizing fluctuations in the fluorescence of single dots over time scales from microseconds to seconds. The power spectral density of these fluctuations indicates a change in the power-law statistics that occurs at a time scale of several milliseconds, providing an important constraint on possible mechanisms for the blinking. In particular, the observations are consistent with the predictions of models wherein blinking is controlled by diffusion of the energies of electron or hole trap states
Diffraction limited optics for single atom manipulation
We present an optical system designed to capture and observe a single neutral
atom in an optical dipole trap, created by focussing a laser beam using a large
numerical aperture N.A.=0.5 aspheric lens. We experimentally evaluate the
performance of the optical system and show that it is diffraction limited over
a broad spectral range (~ 200 nm) with a large transverse field (+/- 25
microns). The optical tweezer created at the focal point of the lens is able to
trap single atoms of 87Rb and to detect them individually with a large
collection efficiency. We measure the oscillation frequency of the atom in the
dipole trap, and use this value as an independent determination of the waist of
the optical tweezer. Finally, we produce with the same lens two dipole traps
separated by 2.2 microns and show that the imaging system can resolve the two
atoms.Comment: 8 pages, 9 figures; typos corrected and references adde
Recent progress on the manipulation of single atoms in optical tweezers for quantum computing
This paper summarizes our recent progress towards using single rubidium atoms
trapped in an optical tweezer to encode quantum information. We demonstrate
single qubit rotations on this system and measure the coherence of the qubit.
We move the quantum bit over distances of tens of microns and show that the
coherence is reserved. We also transfer a qubit atom between two tweezers and
show no loss of coherence. Finally, we describe our progress towards
conditional entanglement of two atoms by photon emission and two-photon
interferences.Comment: Proceedings of the ICOLS07 conferenc
Experimental open air quantum key distribution with a single photon source
We present a full implementation of a quantum key distribution (QKD) system
with a single photon source, operating at night in open air. The single photon
source at the heart of the functional and reliable setup relies on the pulsed
excitation of a single nitrogen-vacancy color center in diamond nanocrystal. We
tested the effect of attenuation on the polarized encoded photons for inferring
longer distance performance of our system. For strong attenuation, the use of
pure single photon states gives measurable advantage over systems relying on
weak attenuated laser pulses. The results are in good agreement with
theoretical models developed to assess QKD security
Statistical Aging and Non Ergodicity in the Fluorescence of Single Nanocrystals
The relation between single particle and ensemble measurements is adressed
for semiconductor CdSe nanocrystals. We record their fluorescence at the single
molecule level and analyse their emission intermittency, which is governed by
unusual random processes known as Levy statistics. We report the observation of
statistical aging and ergodicity breaking, both related to the occurrence of
Levy statistics. Our results show that the behaviour of ensemble quantities,
such as the total fluorescence of an ensemble of nanocrystals, can differ from
the time averaged individual quantities, and must be interpreted with care.Comment: 4 pages, 3 figure
Resonant nonstationary amplification of polychromatic laser pulses and conical emission in an optically dense ensemble of neon metastable atoms
Experimental and numerical investigation of single-beam and pump-probe
interaction with a resonantly absorbing dense extended medium under strong and
weak field-matter coupling is presented. Significant probe beam amplification
and conical emission were observed. Under relatively weak pumping and high
medium density, when the condition of strong coupling between field and
resonant matter is fulfilled, the probe amplification spectrum has a form of
spectral doublet. Stronger pumping leads to the appearance of a single peak of
the probe beam amplification at the transition frequency. The greater probe
intensity results in an asymmetrical transmission spectrum with amplification
at the blue wing of the absorption line and attenuation at the red one. Under
high medium density, a broad band of amplification appears. Theoretical model
is based on the solution of the Maxwell-Bloch equations for a two-level system.
Different types of probe transmission spectra obtained are attributed to
complex dynamics of a coherent medium response to broadband polychromatic
radiation of a multimode dye laser.Comment: 9 pages, 13 figures, corrected, Fig.8 was changed, to be published in
Phys. Rev.
Vortices in polariton OPO superfluids
This chapter reviews the occurrence of quantised vortices in polariton
fluids, primarily when polaritons are driven in the optical parametric
oscillator (OPO) regime. We first review the OPO physics, together with both
its analytical and numerical modelling, the latter being necessary for the
description of finite size systems. Pattern formation is typical in systems
driven away from equilibrium. Similarly, we find that uniform OPO solutions can
be unstable to the spontaneous formation of quantised vortices. However,
metastable vortices can only be injected externally into an otherwise stable
symmetric state, and their persistence is due to the OPO superfluid properties.
We discuss how the currents charactering an OPO play a crucial role in the
occurrence and dynamics of both metastable and spontaneous vortices.Comment: 40 pages, 16 figure
Probing and controlling fluorescence blinking of single semiconductor nanoparticles
In this review we present an overview of the experimental and theoretical development on fluorescence intermittency (blinking) and the roles of electron transfer in semiconductor crystalline nanoparticles. Blinking is a very interesting phenomenon commonly observed in single molecule/particle experiments. Under continuous laser illumination, the fluorescence time trace of these single nanoparticles exhibit random light and dark periods. Since its first observation in the mid-1990s, this intriguing phenomenon has attracted wide attention among researchers from many disciplines. We will first present the historical background of the discovery and the observation of unusual inverse power-law dependence for the waiting time distributions of light and dark periods. Then, we will describe our theoretical modeling efforts to elucidate the causes for the power-law behavior, to probe the roles of electron transfer in blinking, and eventually to control blinking and to achieve complete suppression of the blinking, which is an annoying feature in many applications of quantum dots as light sources and fluorescence labels for biomedical imaging
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