Subnanosecond spectral diffusion of a single quantum dot in a nanowire

We have studied spectral diffusion of the photoluminescence of a single CdSe quantum dot inserted in a ZnSe nanowire. We have measured the characteristic diffusion time as a function of pumping power and temperature using a recently developed technique [G. Sallen et al, Nature Photon. \textbf{4}, 696 (2010)] that offers subnanosecond resolution. These data are consistent with a model where only a \emph{single} carrier wanders around in traps located in the vicinity of the quantum dot

Single-photon excitation of a coherent state: catching the elementary step of stimulated light emission

When a single quantum of electromagnetic field excitation is added to the same spatio-temporal mode of a coherent state, a new field state is generated that exhibits intermediate properties between those of the two parents. Such a single-photon-added coherent state is obtained by the action of the photon creation operator on a coherent state and can thus be regarded as the result of the most elementary excitation process of a classical light field. Here we present and describe in depth the experimental realization of such states and their complete analysis by means of a novel ultrafast, time-domain, quantum homodyne tomography technique clearly revealing their non-classical character.Comment: 9 pages, 9 figures. Accepted for publication in Phys. Rev.

Mode-coupling theory for structural and conformational dynamics of polymer melts

A mode-coupling theory for dense polymeric systems is developed which unifyingly incorporates the segmental cage effect relevant for structural slowing down and polymer chain conformational degrees of freedom. An ideal glass transition of polymer melts is predicted which becomes molecular-weight independent for large molecules. The theory provides a microscopic justification for the use of the Rouse theory in polymer melts, and the results for Rouse-mode correlators and mean-squared displacements are in good agreement with computer simulation results.Comment: 4 pages, 3 figures, Phys. Rev. Lett. in pres

Efficient single-photon emission from electrically driven InP quantum dots epitaxially grown on Si(001)

The heteroepitaxy of III-V semiconductors on silicon is a promising approach for making silicon a photonic platform for on-chip optical interconnects and quantum optical applications. Monolithic integration of both material systems is a long-time challenge, since different material properties lead to high defect densities in the epitaxial layers. In recent years, nanostructures however have shown to be suitable for successfully realising light emitters on silicon, taking advantage of their geometry. Facet edges and sidewalls can minimise or eliminate the formation of dislocations, and due to the reduced contact area, nanostructures are little affected by dislocation networks. Here we demonstrate the potential of indium phosphide quantum dots as efficient light emitters on CMOS-compatible silicon substrates, with luminescence characteristics comparable to mature devices realised on III-V substrates. For the first time, electrically driven single-photon emission on silicon is presented, meeting the wavelength range of silicon avalanche photo diodes' highest detection efficiency

Subnanosecond spectral diffusion measurement using photon correlation

Spectral diffusion is a result of random spectral jumps of a narrow line as a result of a fluctuating environment. It is an important issue in spectroscopy, because the observed spectral broadening prevents access to the intrinsic line properties. However, its characteristic parameters provide local information on the environment of a light emitter embedded in a solid matrix, or moving within a fluid, leading to numerous applications in physics and biology. We present a new experimental technique for measuring spectral diffusion based on photon correlations within a spectral line. Autocorrelation on half of the line and cross-correlation between the two halves give a quantitative value of the spectral diffusion time, with a resolution only limited by the correlation set-up. We have measured spectral diffusion of the photoluminescence of a single light emitter with a time resolution of 90 ps, exceeding by four orders of magnitude the best resolution reported to date

Spectroscopy by frequency entangled photon pairs

Quantum spectroscopy was performed using the frequency-entangled broadband photon pairs generated by spontaneous parametric down-conversion. An absorptive sample was placed in front of the idler photon detector, and the frequency of signal photons was resolved by a diffraction grating. The absorption spectrum of the sample was measured by counting the coincidences, and the result is in agreement with the one measured by a conventional spectrophotometer with a classical light source.Comment: 11 pages, 5 figures, to be published in Phys. Lett.

Tumor stroma-derived TGF-beta limits Myc-driven lymphomagenesis via Suv39h1-dependent senescence

Activated RAS/BRAF oncogenes induce cellular senescence as a tumor-suppressive barrier in early cancer development, at least in part, via an oncogene-evoked DNA damage response (DDR). In contrast, Myc activation-although producing a DDR as well-is known to primarily elicit an apoptotic countermeasure. Using the Emu-myc transgenic mouse lymphoma model, we show here in vivo that apoptotic lymphoma cells activate macrophages to secrete transforming growth factor beta (TGF-beta) as a critical non-cell-autonomous inducer of cellular senescence. Accordingly, neutralization of TGF-beta action, like genetic inactivation of the senescence-related histone methyltransferase Suv39h1, significantly accelerates Myc-driven tumor development via cancellation of cellular senescence. These findings, recapitulated in human aggressive B cell lymphomas, demonstrate that tumor-prompted stroma-derived signals may limit tumorigenesis by feedback senescence induction

Quantum state reconstruction of the single-photon Fock state

We have reconstructed the quantum state of optical pulses containing single photons using the method of phase-randomized pulsed optical homodyne tomography. The single-photon Fock state |1> was prepared using conditional measurements on photon pairs born in the process of parametric down-conversion. A probability distribution of the phase-averaged electric field amplitudes with a strongly non-Gaussian shape is obtained with the total detection efficiency of (55+-1)%. The angle-averaged Wigner function reconstructed from this distribution shows a strong dip reaching classically impossible negative values around the origin of the phase space.Comment: 4 pages, 4 figures, to appear in Physical Review Letters. Avoid downloading PDF due to extremely poor figure resolution. Use Postscrip

Simulation study of Non-ergodicity Transitions: Gelation in Colloidal Systems with Short Range Attractions

Computer simulations were used to study the gel transition occurring in colloidal systems with short range attractions. A colloid-polymer mixture was modelled and the results were compared with mode coupling theory expectations and with the results for other systems (hard spheres and Lennard Jones). The self-intermediate scattering function and the mean squared displacement were used as the main dynamical quantities. Two different colloid packing fractions have been studied. For the lower packing fraction, $\alpha$-scaling holds and the wave-vector analysis of the correlation function shows that gelation is a regular non-ergodicity transition within MCT. The leading mechanism for this novel non-ergodicity transition is identified as bond formation caused by the short range attraction. The time scale and diffusion coefficient also show qualitatively the expected behaviour, although different exponents are found for the power-law divergences of these two quantities. The non-Gaussian parameter was also studied and very large correction to Gaussian behaviour found. The system with higher colloid packing fraction shows indications of a nearby high-order singularity, causing $\alpha$-scaling to fail, but the general expectations for non-ergodicity transitions still hold.Comment: 13 pages, 15 figure