1,785 research outputs found
A highly efficient single photon-single quantum dot interface
Semiconductor quantum dots are a promising system to build a solid state
quantum network. A critical step in this area is to build an efficient
interface between a stationary quantum bit and a flying one. In this chapter,
we show how cavity quantum electrodynamics allows us to efficiently interface a
single quantum dot with a propagating electromagnetic field. Beyond the well
known Purcell factor, we discuss the various parameters that need to be
optimized to build such an interface. We then review our recent progresses in
terms of fabrication of bright sources of indistinguishable single photons,
where a record brightness of 79% is obtained as well as a high degree of
indistinguishability of the emitted photons. Symmetrically, optical
nonlinearities at the very few photon level are demonstrated, by sending few
photon pulses at a quantum dot-cavity device operating in the strong coupling
regime. Perspectives and future challenges are briefly discussed.Comment: to appear as a book chapter in a compilation "Engineering the
Atom-Photon Interaction" published by Springer in 2015, edited by A.
Predojevic and M. W. Mitchel
Dynamic percolation theory for particle diffusion in a polymer network
Tracer-diffusion of small molecules through dense systems of chain polymers
is studied within an athermal lattice model, where hard core interactions are
taken into account by means of the site exclusion principle. An approximate
mapping of this problem onto dynamic percolation theory is proposed. This
method is shown to yield quantitative results for the tracer correlation factor
of the molecules as a function of density and chain length provided the
non-Poisson character of temporal renewals in the disorder configurations is
properly taken into account
Collisional decay of 87Rb Feshbach molecules at 1005.8 G
We present measurements of the loss-rate coefficients K_am and K_mm caused by
inelastic atom-molecule and molecule-molecule collisions. A thermal cloud of
atomic 87Rb is prepared in an optical dipole trap. A magnetic field is ramped
across the Feshbach resonance at 1007.4 G. This associates atom pairs to
molecules. A measurement of the molecule loss at 1005.8 G yields K_am=2 10^-10
cm^3/s. Additionally, the atoms can be removed with blast light. In this case,
the measured molecule loss yields K_mm=3 10^-10 cm^3/s
Dynamic Variation in Sexual Contact Rates in a Cohort of HIV-Negative Gay Men
Human immunodeficiency virus (HIV) transmission models that include variability in sexual behavior over time have shown increased incidence, prevalence, and acute-state transmission rates for a given population risk profile. This raises the question of whether dynamic variation in individual sexual behavior is a real phenomenon that can be observed and measured. To study this dynamic variation, we developed a model incorporating heterogeneity in both between-person and within-person sexual contact patterns. Using novel methodology that we call iterated filtering for longitudinal data, we fitted this model by maximum likelihood to longitudinal survey data from the Centers for Disease Control and Prevention's Collaborative HIV Seroincidence Study (1992–1995). We found evidence for individual heterogeneity in sexual behavior over time. We simulated an epidemic process and found that inclusion of empirically measured levels of dynamic variation in individual-level sexual behavior brought the theoretical predictions of HIV incidence into closer alignment with reality given the measured per-act probabilities of transmission. The methods developed here provide a framework for quantifying variation in sexual behaviors that helps in understanding the HIV epidemic among gay men
A Mott-like State of Molecules
We prepare a quantum state where each site of an optical lattice is occupied
by exactly one molecule. This is the same quantum state as in a Mott insulator
of molecules in the limit of negligible tunneling. Unlike previous Mott
insulators, our system consists of molecules which can collide inelastically.
In the absence of the optical lattice these collisions would lead to fast loss
of the molecules from the sample. To prepare the state, we start from a Mott
insulator of atomic 87Rb with a central region, where each lattice site is
occupied by exactly two atoms. We then associate molecules using a Feshbach
resonance. Remaining atoms can be removed using blast light. Our method does
not rely on the molecule-molecule interaction properties and is therefore
applicable to many systems.Comment: Proceedings of the 20th International Conference on Atomic Physics
(ICAP 2006), edited by C. Roos, H. Haffner, and R. Blatt, AIP Conference
Proceedings, Melville, 2006, Vol. 869, pp. 278-28
Feshbach blockade: single-photon nonlinear optics using resonantly enhanced cavity-polariton scattering from biexciton states
We theoretically demonstrate how the resonant coupling between a pair of
cavity-polaritons and a biexciton state can lead to a large single-photon Kerr
nonlinearity in a semiconductor solid-state system. A fully analytical model of
the scattering process between a pair of cavity-polaritons is developed, which
explicitly includes the biexcitonic intermediate state. A dramatic enhancement
of the polariton-polariton interactions is predicted in the vicinity of the
biexciton Feshbach resonance. Application to the generation of non-classical
light from polariton dots is discussed
Atom-molecule Rabi oscillations in a Mott insulator
We observe large-amplitude Rabi oscillations between an atomic and a
molecular state near a Feshbach resonance. The experiment uses 87Rb in an
optical lattice and a Feshbach resonance near 414 G. The frequency and
amplitude of the oscillations depend on magnetic field in a way that is well
described by a two-level model. The observed density dependence of the
oscillation frequency agrees with the theoretical expectation. We confirmed
that the state produced after a half-cycle contains exactly one molecule at
each lattice site. In addition, we show that for energies in a gap of the
lattice band structure, the molecules cannot dissociate
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