Photon Antibunching in the Photoluminescence Spectra of a Single Carbon Nanotube

We report the first observation of photon antibunching in the photoluminescence from single carbon nanotubes. The emergence of a fast luminescence decay component under strong optical excitation indicates that Auger processes are partially responsible for inhibiting two-photon generation. Additionally, the presence of exciton localization at low temperatures ensures that nanotubes emit photons predominantly one by one. The fact that multiphoton emission probability can be smaller than 5% suggests that carbon nanotubes could be used as a source of single photons for applications in quantum cryptography.Comment: content as publishe

Enhancement of electron spin coherence by optical preparation of nuclear spins

We study a large ensemble of nuclear spins interacting with a single electron spin in a quantum dot under optical excitation and photon detection. When a pair of applied laser fields satisfy two-photon resonance between the two ground electronic spin states, detection of light scattering from the intermediate exciton state acts as a weak quantum measurement of the effective magnetic (Overhauser) field due to the nuclear spins. If the spin were driven into a coherent population trapping state where no light scattering takes place, then the nuclear state would be projected into an eigenstate of the Overhauser field operator and electron decoherence due to nuclear spins would be suppressed: we show that this limit can be approached by adapting the laser frequencies when a photon is detected. We use a Lindblad equation to describe the time evolution of the driven system under photon emission and detection. Numerically, we find an increase of the electron coherence time from 5 ns to 500 ns after a preparation time of 10 microseconds.Comment: 5 pages, 4 figure

A High-resolution Scintillating Fiber Tracker With Silicon Photomultiplier Array Readout

We present prototype modules for a tracking detector consisting of multiple layers of 0.25 mm diameter scintillating fibers that are read out by linear arrays of silicon photomultipliers. The module production process is described and measurements of the key properties for both the fibers and the readout devices are shown. Five modules have been subjected to a 12 GeV/c proton/pion testbeam at CERN. A spatial resolution of 0.05 mm and light yields exceeding 20 detected photons per minimum ionizing particle have been achieved, at a tracking efficiency of more than 98.5%. Possible techniques for further improvement of the spatial resolution are discussed.Comment: 31 pages, 27 figures, pre-print version of an article published in Nuclear Instruments and Methods in Physics Research Section A, Vol. 62

Angular distribution of photons from the delay of the GDR in hot and rotating light Yb nuclei from exclusive experiments

Abstract Angular distributions of photons associated with the damping of excited-state giant dipole resonances (GDR) in hot and rotating 161,162 Yb nuclei have been measured in exclusive experiments using the HECTOR array. In reactions with heavy ions ( 48 T) angular distributions are determined as a function of the angular momentum of the compound nuclei. In reactions with lighter ions ( 17,18 O) a difference method is applied to isolate GDR decays originating from specific excitation regions. The systematics of the measured angular distributions as a function of excitation energy and angular momentum are compared to theories taking into account fluctuations of the shape and orientation of the excited nuclei

GDR in Superdeformed Nuclei

A search for the gamma decay of the Giant Dipole Resonance built on superdeformed nuclear configurations was made. The superdeformed states of the Eu-143 nucleus were populated using the reaction Pd-110(Cl-37, 4n)Eu-143 at a beam energy of 165 MeV. High energy gamma-rays were detected in 8 large BaF2 scintillators in coincidence with discrete transitions measured with part of the NORDBALL array (17 HPGe detectors and a 2 pi multiplicity filter). Spectra of high-energy gamma-rays gated by low-energy transitions from states fed by the superdeformed bands show an excess yield in the 7-10 MeV region with respect to those gated by transitions from states not populated by the superdeformed bands. Because the dipole oscillation along the superdeformed axis of the nucleus is expected to have a frequency corresponding to approximate to 8 MeV (low energy component of the GDR strength function), the present result gives the first experimental indication of gamma-ray emission of the GDR built on a superdeformed states