Search for neutrino oscillations

A search for ν_μ→ν_e and oscillations has been conducted with the AGS wide-band neutrino beam at the Brookhaven National Laboratory. We find more ν_e ( _e) interactions than were expected on the basis of the number of incident ν_e ( _e) calculated as part of the neutrino beam. The excess is about a factor two over the expectation, the statistical significance being about two and a half standard deviations for ν_e and weaker for _e.     

Search for free neutron-antineutron oscillations

A search for free neutron-antineutron oscillations has been carried out at the Pavia Triga Mark II research reactor. A thin carbon target is crossed by a beam of thermal neutrons propagating in a 18.5 m long channel where the earth magnetic field is attenuated by a factor of 50. The total neutron current through the target is 3.2×10¹⁰ n/s. Possible antineutron annihilations are identified by a large track detector surrounding the target. A lower limit on the oscillation time of 4.7×10⁵ s (90% C.L.) has been reached.     

Characterizations at high temperatures of long-period gratings written in germanium-free air-silica microstructure fiber

We report what is to our knowledge the first characterization at high temperatures of long-period fiber gratings written in Ge-free air-silica microstructure fiber. The gratings written with the electric-arc technique suffer a low shift of the resonance wavelengths when the temperature is increased from 20 degrees C to 1200 degrees C. This shift is studied and compared with that of a long-period fiber grating written in a standard single-mode fiber by the same technique. Good thermal stability of the grating and of the fiber after annealing at 1200 degrees C for 1 h is demonstrated.     

Search for neutrino oscillations today and tomorrow

Current and future experiments searching for neutrino oscillations are reviewed.     

Search for muon to electron neutrino oscillations

A search for _e and oscillations has been carried out with the CHARM II detector exposed to the CERN wide band neutrino beam. The data were collected over five years, alternating beams mainly composed of muon-neutrinos and muon-antineutrinos. The number of interactions of _e and observed is comparable with the number of events expected from flux calculations. For large squared mass differences the upper limits obtained on the mixing angle aresin ²2 < 9.4=" ·=">^–3 for oscillating to _e andsin ²2 < 4.8=" ·=">^–3 for to , at the 90% confidence level. Combining neutrino and antineutrino data the upper limit is 5.6 · 10^–3.On leave of absence from ITEP (Moscow)     

Finite-size effect on magnetic ordering temperatures in long-period antiferromagnets: holmium thin films

The thickness dependence of the helical antiferromagnetic ordering temperature T(N) was studied for thin Ho metal films by resonant magnetic soft x-ray and neutron diffraction. In contrast with the Curie temperature of ferromagnets, T(N) was found to decrease with film thickness d according to [T(N)(infinity)-T(N)(d)]/T(N)(d) proportional variant (d-d(0))(-lambda(')), where lambda(') is a phenomenological exponent and d(0) is of the order of the bulk magnetic period L(b). These observations are reproduced by mean-field calculations that suggest a linear relationship between d(0) and L(b) in long-period antiferromagnets.     

Search for neutrino oscillations at the palo verde nuclear reactors

We report on the initial results from a measurement of the antineutrino flux and spectrum at a distance of about 800 m from the three reactors of the Palo Verde Nuclear Generating Station using a segmented gadolinium-loaded scintillation detector. We find that the antineutrino flux agrees with that predicted in the absence of oscillations excluding at 90% C.L. nu;(e)-nu;(x) oscillations with Deltam(2)>1.12x10(-3) eV(2) for maximal mixing and sin (2)2straight theta>0.21 for large Deltam(2). Our results support the conclusion that the atmospheric neutrino oscillations observed by Super-Kamiokande do not involve nu(e).     

Search for exotic contributions to atmospheric neutrino oscillations

The energy spectrum of neutrino-induced upward-going muons in MACRO has been analyzed in terms of effects of violating relativity principles, keeping standard mass-induced atmospheric neutrino oscillations as the dominant source of ν _μ → ν _τ transitions. The data disfavor these exotic possibilities even at a subdominant level, and stringent 90% C.L. limits are placed on the Lorentz invariance violation parameter |Δυ| < 6 × 10⁻²⁴ at sin(2ϑ_υ) = 0 and |Δυ| < (2.5–5) × 10⁻²⁶ at sin(2ϑ_υ) = ±1. These limits can also be reinterpreted as upper bounds on the parameters describing violation of the equivalence principle. The text was submitted by the author in English.     

Rabi oscillations of excitons in single quantum dots

Transient nonlinear optical spectroscopy, performed on excitons confined to single GaAs quantum dots, shows oscillations that are analogous to Rabi oscillations in two-level atomic systems. This demonstration corresponds to a one-qubit rotation in a single quantum dot which is important for proposals using quantum dot excitons for quantum computing. The dipole moment inferred from the data is consistent with that directly obtained from linear absorption studies. The measurement extends the artificial atom model of quantum dot excitonic transitions into the strong-field limit, and makes possible full coherent optical control of the quantum state of single excitons using optical pi pulses.     

Search for neutrino oscillations in “Gargamelle” at SPS

The ν events collected in “Gargamelle” exposed at the CERN SPS wide band beam are reanalyzed to search for possible ν_μ → ν_e oscillations. No effect is found and an upper limit of 1.2 eV at 68% c.l. is determined for the mass parameters $\text{Δm = (m}{}_1{}^2\text{? m}{}_2{}^2\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ in the case of maximum neutrino mixing. A limit on the ν_μ → ν_τ transition probability is also quoted, but the sensitivity is smaller.     

Observation of coherent oscillations in a single electron spin

Rabi nutations and Hahn echo modulation of a single electron spin in a single defect center have been observed. The coherent evolution of the spin quantum state is followed via optical detection of the spin state. Coherence times up to several microseconds at room temperature have been measured. Optical excitation of the spin states leads to decoherence. Quantum beats between electron spin transitions in a single spin Hahn echo experiment are observed. A closer analysis reveals that beats also result from the hyperfine coupling of the electron spin to a single 14N nuclear spin. The results are analyzed in terms of a density matrix approach of an electron spin interacting with two oscillating fields.     

Decoherence of rabi oscillations in a single quantum dot

We develop a realistic model of Rabi oscillations in a quantum-dot photodiode. Based in a multiexciton density matrix formulation we show that for short pulses the two-level model fails and higher levels should be taken into account. This affects some of the experimental conclusions, such as the inferred efficiency of the state rotation (population inversion) and the deduced value of the dipole interaction. We also show that the damping observed cannot be explained using constant rates with fixed pulse duration. We demonstrate that the damping observed is in fact induced by an off-resonant excitation to or from the continuum of wetting layer states. Our model describes the nonlinear decoherence behavior observed in recent experiments.     

Evidence of an anthropogenic climatic change in the daily temperatures of Modena, Italy

Summary The daily minimum, mean and maximum temperatures, measured in Modena, Italy, in the years 1869–1976 have been analysed in order to detect possible long-term trends. An increasing trend appears to be present both in the minimum and in the mean temperature with a reasonable confidence level. The presence of a trend in the maximum temperatures instead is questionable. The trends have been estimated by means of a procedure which provides also the statistical uncertainty of the parameter representing the trend. The uncertainty due to the errors of the measuring instruments has been also evaluated. The trends do not show any clear seasonal pattern. The overall behaviour of the trends (for the three daily temperatures) and the lack of a seasonal pattern can be explained by a ?greenhouse? effect due to the increasing town. The experimental results and the explanation suggested are quite consistent with similar results and conclusions found elsewhere.

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Riassunto Sono state analizzate le temperature giornaliere minime, medie e massime misurate nella città di Modena nel periodo 1869–1976, at fine di mettere in evidenza eventuali tendenze a lungo termine. Nelle temperature giornaliere minime e medie esiste una tendenza all'aumento con un ragionevole livello di affldabilità. Viceversa è più dubbia la presenza di una tendenza nelle temperature giornaliere massime. Il parametro che rappresenta la tendenza a lungo termine è stato stimato mediante una procedura che permette di ottenere la sua varianza. Oltre alla parte statistica è stata stimata anche l'incertezza causata dagli errori strumentali. Le tendenze a lungo termine stimate non risentono di effetti stagionali. Il comportamento delle tendenze a lungo termine (caratterizzate dall'aumento in due sole temperature giornaliere) e la mancanza di effetti stagrionali può essere spiegata da un effetto ?serra? causato dall'accrescimento della città. I risultati sperimentali e la spiegazione che è proposta sono compatibili con analoghi risultati e conclusioni già trovati altrove.

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Резюме Чтобы определить возможные долгосрочные тенденции, анализируются ежедневные минимальные, средние и максимальные температуры, измеренные в Модене (Италия) в период 1869–1976 г.г. Обнаружена тенденция увеличения минимальных и средних температур. Однако наличие тенденции для максимальной температуры является сомнительным. Указанные тенденции установлены с помощью процедуры, которая дает также статистическую неопределенность параметра, характеризующего тенденцию. Также оценивалась неопределенность, обусловловленная ошибками аппаратуры измерений. Тенденции не обнаруживают каких-либо ясных сезонных характеристик. Общее поведение тенднций (для трех ежедневных температур) и отсутствие сезонных особенностей может быть объяснено с помощью эффекта, обусловленного растущими городами. Полученные экспериментальные результаты и предложенное объяснение сотласуются с аналотичными результатами и выводами, полученными ранее.

     

Quantum oscillations of thermopower of gallium single crystals

We present experimental results of the transverse thermopower of high- purity gallium single crystals in magnetic fields up to 41.8kG. Giant quantum oscillations in the magnetothermopower appear for a magnetic field parallel to the c-axis and a temperature gradient ▽T along the b-axis. The results are compared with the existing data of the transverse magneto- resistivity, the de Haas-van Alphen effect as well as with the Fermi surface model of gallium due to Reed's calculation.     

Photon statistics in single molecule fluorescence with Rabi oscillations

An expression for the distribution function of photons detected in non-resonant single molecule fluorescence excited by CW-laser light is derived. Numerical calculations of the photon distribution for fluorescence whose autocorrelation function exhibits Rabi oscillations are carried out. It is found that phase memory does not influence noticeably on the photon distribution function in non-resonant fluorescence.     

Effect of ultrasonic oscillations on the fluidity of heavy oil products at low temperatures

We develop a laboratory setup to estimate the force of rotation of a metal branch pipe in a viscoelastic medium. We show that 2-min action of shearing ultrasonic oscillations (frequency, 32.5 kHz; specific power, no more than 0.008 W/cm²) reduces by 17% the static limit of fluidity brought to an initial temperature of ì-100 fuel oil cooled to −15°C in the wall layer of a rotating branch pipe. We obtain a linear regression dependence between the ratio of the threshold force of the onset of branch pipe motion to the consumption current of the ultrasonic transducer and the fuel temperature.     

Commensurability oscillations in NdBa2Cu3Oy single crystals

Commensurability between inter-vortex distance and crystal lattice constant is investigated by angular dependent magnetization in very pure twinned and twin-free NdBa₂ Cu₃ O_y single crystals. With increasing temperature the incommensurate states split up and become finally commensurate with half the vortex distance. These new commensurate states are related to a substructure of the intrinsic pinning potential within the unit cell and discussed with respect to temperature, field, anisotropy, and twin structure.     

Rabi type oscillations in damped two-dimensional single electron quantum dots

We present a quantized model of a harmonically confined dot atom with inherent damping in the presence of a transverse magnetic field. The model leads to a non-Hermitian Hamiltonian in coordinate space. We have analytically studied the effects of damping on Rabi type oscillations of the system. The model explains the decoherence of Rabi oscillations in a Josephson Junction.     

Landau oscillations in single quantum wells observed by microwave detection

Magneto-oscillations of Shubnikov-de Haas type originating in a single quantum well of 150 Å In_0.53Ga_0.47As surrounded by modulation-doped InP are measured without contacts using a conventional EPR spectrometer. The two-dimensional properties of the signals are verified, the effective mass, m* = 0.044m₀, is deduced from the temperature dependence of the amplitude of the oscillations and the carrier concentration in the quantum well is calculated from the period of the oscillations.