[en] We reply to Akhavan and Golshani's comment on our double-slit experiment addressed to test standard quantum mechanics versus de Broglie-Bohm theory. We show that their results, albeit representing a relevant contribution to the discussion on the realizability of a test of de Broglie-Bohm theory, do not allow us to draw any conclusion about our experiment since their wavefunction does not describe well the photon states produced by our set-up. On the other hand, we give arguments of why our experiment can be considered a good realization of the theoretical proposal of Ghose (1999 Foundations of Quantum Theory and Quantum Optics ed S M Roy), Ghose et al (2001 Phys. Lett. A 290 205) and Golshani and Akhavan (2001 J. Phys. A: Math. Gen. 34 5259). (reply)

[en] Quantum mechanics is a pillar of modern physics, confirmed by a huge number of experiments. Nevertheless, it presents many unintuitive properties, strongly differing from classical mechanics due to its intrinsic non-epistemic probabilistic nature. Many attempts have been devoted to building a deterministic theory reproducing all the results of standard quantum mechanics (SQM). One of the most successful attempts, in this sense, is de Broglie-Bohm (dBB) theory. This theory is built in order to reproduce almost all SQM predictions. However, it has recently been suggested that different coincidence patterns are predicted by SQM and dBB when a double-slit experiment is realized under specific conditions. In this paper we present the first realization of such a double-slit experiment with correlated photons produced in type I parametric down-conversion. We observe a perfect agreement with SQM prediction, whilst our result is almost eight standard deviations from the dBB prediction

[en] A conditional unitary transformation (90 deg. polarization rotation) is performed at single-photon level. The transformation is realized by rotating polarization for one of the photons of a polarization-entangled biphoton state (signal photon) by means of a Pockel cell triggered by the detection of the other (idler) photon after polarization selection. As a result, the state of the signal photon is losslessly changed from being completely unpolarized to being partially polarized, so that the final polarization degree is given by the idler detector quantum efficiency. This experiment can be used for developing a different method of absolute quantum efficiency calibration

[en] Two-photon entangled quantum states are a fundamental tool for quantum information and quantum cryptography. A complete description of a generic quantum state is provided by its density matrix: the technique allowing experimental reconstruction of the density matrix is called quantum state tomography. Entangled states density matrix reconstruction requires a large number of measurements on many identical copies of the quantum state. An alternative way of certifying the amount of entanglement in two-photon states is represented by the estimation of specific parameters, e.g., negativity and concurrence. If we have a priori partial knowledge of our state, it’s possible to develop several estimators for these parameters that require lower amount of measurements with respect to full density matrix reconstruction. The aim of this work is to introduce and test different estimators for negativity and concurrence for a specific class of two-photon states. (paper)

[en] The ability to access high dimensionality in Hilbert spaces represents a demanding key-stone for state-of-the-art quantum information. The manipulation of entangled states in continuous variables, wavevector as well frequency, represents a powerful resource in this sense. The number of dimensions of the Hilbert space that can be used in practical information protocols can be determined by the number of Schmidt modes that it is possible to address one by one. In the case of wavevector variables, the Schmidt modes can be losslessly selected using single-mode fibre and a spatial light modulator, but no similar procedure exists for the frequency space. The aim of this work is to present a technique to engineer the spectral properties of biphoton light, emitted via ultrafast spontaneous parametric down conversion, in such a way that the two-photon spectral amplitude (TPSA) contains several non-overlapping Schmidt modes, each of which can be filtered losslessly in frequency variables. Such TPSA manipulation is operated by a fine balancing of parameters like the pump frequency, the shaping of pump pulse spectrum, the dispersion dependence of spontaneous parametric down-conversion crystals as well as their length. Measurements have been performed exploiting the group velocity dispersion induced by the passage of optical fields through dispersive media, operating a frequency-to-time two-dimensional Fourier transform of the TPSA. Exploiting this kind of measurement we experimentally demonstrate the ability to control the Schmidt modes structure in TPSA through the pump spectrum manipulation. (paper)

[en] In this paper we present a double-slit experiment where two indistinguishable photons produced by type-I parametric down-conversion are each sent to a well-defined slit. Data about the diffraction and interference patterns for coincidences are presented and discussed. An analysis of these data allows a test of standard quantum mechanics against the de Broglie-Bohm theory

[en] The ’’problem of time” in present physics substantially consists in the fact that a straightforward quantization of the general relativistic evolution equation and constraints generates for the Universe wave function the Wheeler-De Witt equation, which describes a static Universe. Page and Wootters considered the fact that there exist states of a system composed by entangled subsystems that are stationary, but one can interpret the component subsystems as evolving: this leads them to suppose that the global state of the universe can be envisaged as one of this static entangled state, whereas the state of the subsystems can evolve. Here we synthetically present an experiment, based on PDC polarization entangled photons, that shows a practical example where this idea works, i.e. a subsystem of an entangled state works as a ’clock” of another subsystem. (paper)

[en] We describe a new realization of Ghose, Home, Agarwal experiment on wave particle duality of light where some limitations of the former experiment, realized by Mizobuchi and Ohtake, are overcome. Our results clearly indicate that wave-particle complementarity must be understood between interference and 'whelcher weg' knowledge and not in a more general sense