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De Broglie - Bohm (dBB) theory is a deterministic theory, built for reproducing almost all Quantum Mechanics (QM) predictions, where position plays the role of a hidden variable. It was recently shown that different coincidence patterns are predicted by QM and dBB when a double slit experiment is realised under specific conditions and, therefore, an experiment can test the two theories. In this letter we present the first realisation of such a double slit experiment by using correlated photons produced in type I Parametric Down Conversion. Our results confirm QM contradicting dBB predictions.

Many beautiful experiments have been addressed to test standard quantum mechanics against local realistic models. Even if a strong evidence favouring standard quantum mechanics is emerged, a conclusive experiment is still lacking, because of low detection efficiencies. Recently, experiments based on pseudoscalar mesons have been proposed as a way for obtaining a conclusive experiment. In this paper, we investigate if this result can effectively be obtained. Our conclusions, based on a careful analysis of the proposed set ups, are that this will not be possible due to intrinsic limitations of these kind of experiments.

An experimental set-up based on correlated photons has been developed at the Istituto Elettrotecnico Nazionale G. Ferraris (IEN) for the absolute measurement of the quantum efficiency and dead time of single-photon counting photodiodes. The overall accuracy is improved with respect to previously reported results, by using a thin and highly transmitting non-linear crystal. For comparison, a conventional set-up has been developed at 632.8 nm with a He-Ne laser, a trap detector and calibrated neutral-density filters. Measurements at different count levels have been performed with both techniques and results are compared for the quantum efficiency in the limit of zero count, η0, and for the dead-time measurement, tD. Contributions to the final uncertainty are analysed for both techniques. The results obtained are η0 = 0.3372 (standard uncertainty u(η0) = 0.0016) and tD = 33.8 ns (u(tD) = 2.0 ns) in the case of the two-photon technique and η'0 = 0.3376 (u(η'0) = 0.0036) and t'D = 31.7 ns (u(t'D) = 5.4 ns) in the case of the conventional technique.

Besides many interesting application to the study of foundations of quantum mechanics, entangled state are now assuming a large relevance for some practical application. In particular, we discuss most recent results obtained in our laboratory on the use of two photons entangled states produced in parametric down conversion for absolute quantum efficiency calibration of photodetectors, in photon counting regime., to be published in Journ. of Mod. Opt. As proceeding of "Entanglement and Decoherence", Gargnano, September 1999

The aim of this paper is a critical investigation of some correction factors in the quantum-efficiency calibration of photodetectors, in the photon-counting regime, by means of correlated photons generated through a parametric down-conversion process inside a non-linear crystal. An analysis is given of the main correction factors found in a real experimental situation, with different techniques for performing coincidence counts.

We discuss the possibility of generating and detecting, by a tomographic reconstruction of the Wigner function, a macroscopic superposition of two coherent states. The superposition state is created using a conditioned measurement on the polarisation of a probe photon entangled to a coherent state. The entanglement is obtained using a Kerr cell inserted in a Mach-Zender interferometer. Some hint about generation of GHZ states is given as well., Comment: accepted for publication

We report on the first realisation of a test of Bell inequalities using non-maximally entangled states. It is based on the superposition of type I parametric down conversion produced in two different non-linear crystals pumped by the same laser, but with different polarisations. We discuss the advantages and the possible developments of this configuration., accepted for publication

An experimental setup has been developed at the Istituto Elettrotecnico Nazionale G. Ferraris (IEN) for the absolute calibration of photodetectors in the photon-counting regime by means of correlated photons in parametric fluorescence. A nonlinear crystal of lithium iodate is pumped by an argon-ion laser at 351.2 nm, generating a broadband source of correlated photons from the incoming wavelength to the far-infrared. Photomultipliers and solid-state, single-photon detectors are employed, operating in the photon-counting regime with very low dark counts. Quantum efficiency is measured at 633 nm. The results show the correlated photons to be a promising technique for radiometry. The advantages of this as opposed to a conventional method at low power levels are shown.

This paper presents the first results of parametric amplification obtained at the Istituto Elettrotecnico Nazionale G. Ferraris (IEN) at a wavelength of 633.5 nm in a crystal of lithium iodate, pumped by an argon laser at a wavelength of 351 nm and injected by a diode laser at 788.2 nm in the noncollinear phase-matching case. Amplified and spontaneous parametric signals around 633 nm were measured in a photon-counting setup, at different powers of both the argon and the diode laser. This experiment is preliminary to the absolute radiance measurement of a thermal source.

This work presents a new technique for the measurement of second-order optical nonlinear coefficients from the absolute radiant power of the parametric fluorescence emission. It is based on calibrated detectors regarded as secondary radiometric standards. This technique makes it possible to skip a number of problems usually encountered with standard techniques based on calibrated neutral density filters and reference sources of light at much higher power levels. We infer a value for the d31 nonlinear coefficient of LiIO3 from spectral measurements of the fluorescence power integrated over all solid angles, by denning the wavelength bandwidths with interference filters. Moreover, by performing the measurements on the ultraviolet and visible emission lines of an argon ion laser in the range from 351 to 488 nm, the wavelength dependence of d31 is compared with the expected one obtained by Miller’s dispersion law.

The /sup 87/Rb cell frequency standard, optically pumped by a laser diode, is of great interest in the development of high short-term stability oscillators. We report experiments performed on a rubidium cell prototype aiming at evaluate the transfer of the laser noise to the hyperfine clock transition via the light shift effect, which appears to be the main contribution to the observed short term frequency stability in this kind of standard. Pulsed optical pumping will also be examined in order to strongly reduce the light shift effect and to achieve the theoretical limit never approached up to now despite the strong detected microwave signals.

The frequency comparisons between Cs and Mg atomic standards performed during a period of 420 days are reported with an analysis of the effect of the temperature on the stability and the repeatability of the Mg output frequency. The Mg prototype shows a short-term stability /spl sigma//sub y/=1.2/spl middot/10/sup -11/ /spl tau//sup -1/2/ and a repeatability of 3/spl middot/10/sup -13/; its accuracy has been evaluated to be at the level of 1/spl middot/10/sup -12/. The results reported here for the frequency comparisons may well be interpreted from the point of view of the time stability of the quantity g/sub I/m/sub e//m/sub p/, with g/sub I/ the gyromagnetic ratio of Cs, obtaining the limit 2.6/spl middot//sup -13/ yr./sup -1/ for the relative rate of change. From this value one can deduce a limit for the relative rate of change of g/sub p/m/sub e//m/sub p/ and of /spl alpha/ too, The results here reported may also be interpreted as a "null" gravitational red-shift experiment allowing a new test of the Einstein equivalence principle.

We report on a double slit experiment where indistinguishable correlated photons generated through spontaneous parametric down-conversion, are each sent to a well-defined slit. An analysis of the results allows a test of de Broglie-Bohm mechanics against standard quantum mechanics.

This paper reports on an experiment performed at the Istituto Elettrotecnico Nazionale G. Ferraris (IEN), aiming at the production of biphoton fields by parametric scattering of light in a nonlinear crystal of lithium iodate. The blue line at 457,9 nm from an argon laser is used as pumping radiation, thereby resulting in a fluorescence in the visible region with degenerate pairs of photons at about 916 nm. These biphoton fields are well suited to the measurement of the quantum efficiency of photodetectors in the photon-counting regime and to the realization of an absolute source of radiation.

We report in this paper the first evaluation of the second-order Doppler shift in the Mg frequency standard. Three methods are considered: direct theoretical computation, Fourier analysis of the experimental Ramsey curve, and Fourier analysis of the discrimination curve. The results obtained are compared in a practical experimental case and turn out in satisfactory agreement, allowing a good confidence on the determination of the shift at the accuracy level of /spl plusmn/3/spl times/10/sup -13/. The considerations reported in this paper may be of general interest for frequency standards based on atomic or molecular beams with transverse dimensions much larger than the transition wavelength. >

Energy separations between fine-structure levels of the metastable 3s3p3P term of neutral magnesium have been calculated making use of asymptotic value of quantum defect for the 3snp orbits. Lande interval anomalies expressed as ratioLa=3(3P0-3P1)/3P0-3P2) obtained from the available experimental data along the isoelectronic sequence have been fitted to be well represented by a series in ascending powers of the atomic number Z of the species concerned. The results so obtained are compared with the high-resolution measurements: they agree at the level of 200 MHz which lies well inside the estimated uncertainty bar of ±1.1 GHz of our calculations.

We report a complete description of a frequency standard based on the 3P1-3P0 24Mg transition at 601 GHz; in particular the metastable atomic source, the Ramsey-type interaction region, the submillimetric frequency synthesizer and the frequency-control loop are described both theoretically and experimentally. The main experimental results concerning the operation of the atomic beam, the Ramsey signal intensity and width versus some important parameters and the signal-to-noise ratio, with and without optical pumping, are reported and compared with theoretical predictions. The clock transition frequency has been measured with respect to UTC (IEN) with an uncertainty of ± 1 × 10-12; at present the frequency instability reaches the value of 2 × 10-13 for counting times of 3 000 s and the repeatability the level of 3 × 10-13. The accuracy budget is also reported and discussed as are possible improvements of the present prototype.

We report the measurements of the3D(3s4d)-3P(3s3p)3D(3s5d)-3P(3s3p), and3P(3p2)-3P(3s3p) transition frequency of MgI, the fine-structure separation and isotope shift between24Mg and26Mg. The measurements have been performed in a metastable atomic beam; a good agreement is found for data already existing in the literature. The accuracy of the measurements reported in this paper is mainly limited by the Doppler broadening of theI2 transitions used as a reference and by the precision in the knowledge of the related wavelengths.

We report the measurement of the photons flux produced in parametric down-conversion, performed in photon counting regime with actively quenched silicon avalanche photodiodes as single photon detectors. Measurements are done with the detector in a well defined geometrical and spectral situation. By comparison of the experimental data with the theory, a value for the second order susceptibilities of the non linear crystal can be inferred., 6 pages, HTML file from word97

We have measured the isotopic shifts of the (3)S(3s6s)-(3)P(3s3p) and (3)S(3s7s)-(3)P(3s3p) transitions of Mg I and the values of the hyperfine-structure constant A((3)S(1)) for the 3s6s and 3s7s terms of (25)Mg. The absolute wavelengths have been measured at an accuracy level of +/-3 x 10(-7), mainly limited by the Doppler broadening of the I(2) transitions used as a reference and by the precision of the knowledge of the related wavelengths. The measurements have been performed in an atomic beam rich in metastable atoms by scanning a ring dye laser and observing simultaneously the fluorescence of the beam.

In this proceeding we describe various proposals of application of an high coefficient Kerr cell to quantum states manipulation, ranging from fast modulation of quantum interference, GHZ states generation, Schroedinger cats creation, translucent eavesdropping, etc.

In this paper we describe a test of Bell inequalities using a non- maximally entangled state, which represents an important step in the direction of eliminating the detection loophole. The experiment is based on the creation of a polarisation entangled state via the superposition, by use of an appropriate optics, of the spontaneous fluorescence emitted by two non-linear crystals driven by the same pumping laser.

We present a first experimental test of the existence of Spontaneus Parametric Up Conversion, predicted by a specific local realistic model based on Wigner function formalism. The measurement has been made using a ccd camera on the emission of a LiIO3 crystal pumped by a 351 nm and/or a 789 (1064) nm lasers. We obtain an upper limit of 160 times on the ratio between intensity of Spontaneus Parametric Up Conversion and Spontaneous Parametric Down conversion.

In a recent paper P. Ghose [1] has proposed an experiment addressed to compare de Broglie -Bohm theory and standard quantum mechanics, based on different predictions for coincidence counts in a double slit experiment.

We report in this paper the frequency comparisons between UTC (IEN) and the Mg standard prototype performed during a period of 420 days. We shall also discuss the implications of our results on testing the time stability of an important product of fundamental constants (g/sub p/m/sub e//m/sub p/) as well as the local position invariance principle. >

The first results of optical pumping of the /sup 3/P/sub 1/ level in the excited metastable triplet of Mg are reported. A nearly total depletion of the above level has been achieved in a metastable atomic beam through resonant interaction with the /sup 3/S/sub 1/ (3s4s) level. For this purpose, a cavity-stabilized coumarin 6 ring dye laser has been used. The outlook for an optically pumped Mg frequency standard is also discussed on the basis of the results reported. >

We perform a first experimental test of a local realistic model, recently proposed, based on the Wigner function as probability distribution for the hidden variable. Our results disfavour the model and confirm standard quantum mechanics predictions.

A new experimental limit to the possible time variation of the proton gyromagnetic ratio times the electron-to-proton mass ratio has been obtained from the frequency comparison data between Cs and Mg atomic beam standards. The measurements, made over a period of one year, lead to an upper limit for the rate of change of [ital g][sub [ital p]]([ital m][sub [ital e]]/[ital m][sub [ital p]]) of 5.4[times]10[sup [minus]3]/yr. This result, based only on the validity of the quantum mechanical theory of the atomic spectra, together with astrophysical data regarding analogous products of atomic fundamental constants, leads also to a new limit for the time stability of the fine structure constant [alpha] (2.7[times]10[sup [minus]13]/yr).

We discuss if experimental tests of Bell inequalities performed with pseudoscalar mesons (K or B) can be definitive. Our conclusion is that this is not the case, for the efficiency loophole cannot be eliminated., submitted for publication

We describe a Bell state source based on two type I PDC crystals, which will be used for experiments on quantum communication and in particular in connection with a quantum phase gate based on Bose Einstein condensate.

We propose a quantum transmission based on bi-photons which are doubly-entangled both in polarisation and phase. This scheme finds a natural application in quantum cryptography, where we show that an eventual eavesdropper is bound to introduce a larger error on the quantum communication than for a single entangled bi-photon communication, when steeling the same information.

We report on the realisation of a new test of Bell inequalities using the superposition of type I parametric down conversion produced in two different non-linear crystals pumped by the same laser, but with different polarisation. The produced state is non-maximally entangled. We discuss the advantages and the possible developments of this configuration.

We propose an experiment where quantum interference between two different paths is modulated by means of a QND measurement on one or both the arm of the interferometer. The QND measurement is achieved in a Kerr cell. We illustrate a scheme for the realisation of this experiment and some further developments., accepted for publication

The wavelengths of the3S(3s 4s) −3P(3s 3p) MgI transitions have been measured for the24Mg isotope with a precision of ±2 × 10−7; moreover the isotope shifts of the above transitions have been measured for the three natural Mg isotopes as well as the hyperfine constants of the3S(3s 4s) level of25Mg. The measurements have been performed in a metastable atomic beam.

We report the first results obtained at the Istituto Elettrotecnico Nazionale Galileo Ferraris of quantum-efficiency measurements of actively quenched avalanche photodiodes in the photon-counting regime. The measurements were performed with the technique of correlated photons generated by a parametric downconversion process in a nonlinear crystal of lithium iodate, an absolute technique that does not require any standard. We pay special attention to the problem of alignment of the optical bench and to the implementation of a parametric amplifier scheme with a diode-laser source. The technique is described, and results of quantum-efficiency measurements of two photodiodes are presented.

In a particular case, we show how to determine exactly hadronic production cross-sections σn(s) satisfying general phenomenological constraints such as the asymptotic proportionality of and σin and the empirical rule obeyed by the dispersion. KNO scaling is automatically a property of σn. Whereas the predictions for higher moments do not compare unfavourably with the data, they suggest that the method can be improved.

The phase lock of backward-wave-oscillators operating in the submillimeter range requires the reconsideration of some theoretical aspects in order to take into account the high operation frequency and the high flicker noise level of these sources. Experimental data referring to the frequency noise spectrum of a 600-GHz carcinotron are reported together with some guidelines for properly designing the control phase-locked loop. The results achieved in a practical realization are presented and compared to the theoretical considerations developed. The experimental results demonstrate the possibility of achieving a satisfactory signal-to-noise ratio and narrow linewidth in the phase stabilization of a 600-GHz carcinotron. >

In high resolution atomic or molecular beam spectroscopy, where the Ramsey interrogation method is used, one of uncertainty sources in determining the resonance frequency accurately is the phase-shift of the electromagnetic radiation in the cavity. This phenomenon, which depends on losses and asymmetries, is analyzed in a general way for a transverse atomic beam dimension much larger than the transition wavelength, a case which occurs in Mg or Ca beam frequency standards and the effects of different misalignments in collimated or divergent beams are examined. Numerical evaluations have been performed in the special case of an experimental Mg beam frequency standard. Divergence plays an important role in determining the cavity phase shift frequency error which is reduced about 100 times with respect to the case of a collimated beam.

We describe the realization of a source of Mg atoms in the metastable triplet 3s3p3P and we report a theoretical model describing the dynamic process of production of metastable atoms via electron impact excitation. Experimental results concerning atomic flux and velocity distribution are reported and compared with the theoretical model; the efficiency of production of metastable atoms was 40%, in good agreement with the computed value, and the velocity distribution showed a dependence from the discharge current close to the theoretical prediction.

Advances towards the realization of an absolute frequency standard in the submillimetre region are reported. The 3P1 ↔ 3P0, Δmj = 0 fine-structure transition in the metastable triplet of 24Mg has been observed in an atomic beam with a Ramsey-type interrogation technique. Its frequency, measured with an accuracy of ± 3 × 10-11 with respect to a Cs standard, turned out to be ν0 = (601 277 157 860 ± 20) Hz.

The expressions for the corrections to the frequency of the3P2−3P1 and3P1−3P0 π-transitions of Mg and Ca are derived, taking into account the anomalous magnetic moment of the electron as well as the diamagnetic term of the Hamiltonian. Numerical results for24Mg are given.

The fine structure transition 3 P 1 - 3 P 0 at λ=498 μm in the metastable triplet of 24 Mg has been excited in a spatially-modulated atomic beam via a two zones interaction technique of the Ramsey type. A full width at half maximum (fwhm) of 1.1. kHz ( Q ≈5×10 8 ) has been obtained with a folded open resonator; the distance between the two zones of interaction is 30 cm. Experimental results and a previous theoretical analysis are compared showing a satisfactory agreement.

Recent advances towards the realization of an absolute frequency standard in the submillimeter region are reported. The3p 1 -3 P_{0} \Delta m_{j} = 0 fine structure transition in the metastable triplet of24Mg has been observed in an atomic beam with both Rabi and Ramsey interrogation techniques. Experimental results and theoretical predictions are compared and discussed in view of an Mg frequency standard.

The description of the technical realization of a Mg beam frequency standard and the experimental results are here reported. Moreover the main sources of uncertainty are examined in order to provide the evaluation of the accuracy achievable with such a standard.