Reliable source of conditional non-Gaussian states from single-mode thermal fields

We address both theoretically and experimentally the generation of pulsed non-Gaussian states from classical Gaussian ones by means of conditional measurements. The setup relies on a beam splitter and a pair of linear photodetectors able to resolve up to tens of photons in the two outputs. We show the reliability of the setup and the good agreement with the theory for a single-mode thermal field entering the beam splitter and present a thorough characterization of the photon statistics of the conditional states.Comment: 18 pages, 12 figure

Non canonical polarizations of gravitational waves

We hereby propose an alternative and additional angle on the nature of gravitational waves (GWs), postulating the theoretical and experimental possibility that GWs carry a deformation of the time component of spacetime, other than the spatial one. By explicitly working outside of the transverse-traceless gauge, we propose how events with well-defined time duration, when hit by a GW, would consequently be expected to show a difference in their characteristic time, as measured from the rest frame of an outside observer, whose clock is to remain unaffected by the GW. This constitutes a theoretically viable way in the sense of detecting the passing of the wave itself and may prove relevant as a standalone method for GWs detection other than laser interferometers, or as well be implemented as a complementary but independent system of signal triggering, improving the statistical significance of existing methods. A simple but physically realistic scenario in which the appropriate conditions for the generation and detection of GWs with time dilation are met is presented, along with the conceptual design of an experimental detector

Special issue on basics and applications in quantum optics

Quantum technologies are advancing very rapidly and have the potential to innovate communication and computing far beyond current possibilities. Among the possible plat- forms suitable to run quantum technology protocols, in the last decades quantum optics has received a lot of attention for the handiness and versatility of optical systems. In addition to studying the fundamentals of quantum mechanics, quantum optical states have been exploited for several applications, such as quantum-state engineering, quantum communication and quantum cryptography protocols, enhanced metrology and sensing, quantum optical integrated circuits, quantum imaging, and quantum biological effects. In this Special Issue, we collect some papers and also a review on some recent research activities that show the potential of quantum optics for the advancement of quantum technologies

Conditional measurements on multimode pairwise entangled states from spontaneous parametric downconversion

We address the intrinsic multimode nature of the quantum state of light obtained by pulsed spontaneous parametric downconversion and develop a theoretical model based only on experimentally accessible quantities. We exploit the pairwise entanglement as a resource for conditional multimode measurements and derive closed formulas for the detection probability and the density matrix of the conditional states. We present a set of experiments performed to validate our model in different conditions that are in excellent agreement with experimental data. Finally, we evaluate nonGaussianity of the conditional states obtained from our source with the aim of discussing the effects of the different experimental parameters on the efficacy of this type of conditional state preparation

State reconstruction by on/off measurements

We demonstrate a state reconstruction technique which provides either the Wigner function or the density matrix of a field mode and requires only avalanche photodetectors, without any phase or amplitude discrimination power. It represents an alternative, of simpler implementation, to quantum homodyne tomography.Comment: 6 pages, 4 figures, revised and enlarged versio

Introducing Quantum Technologies at Secondary School Level: Challenges and Potential Impact of an Online Extracurricular Course

Stimulated by the European project “QTEdu CSA”, within the flagship “Quantum Technologies”, a community of researchers active in the fields of quantum technologies and physics education has designed and implemented an extracurricular course on quantum physics concepts and quantum technologies applications for high school. The course, which featured eight interactive lectures, was organized online between March and May 2021 and attended by about 250 students from all over Italy. In this paper, we describe the main tenets and activities of the course. Moreover, we report on the effectiveness of the course on students’ knowledge of the basic concepts of quantum physics and students’ views about epistemic aspects and applications of quantum technologies. Results show that the designed activities were effective in improving students’ knowledge about fundamental aspects of quantum mechanics and familiarizing them with quantum technology applications

Quantum state engineering assisted by entanglement

We suggest a general scheme for quantum state engineering based on conditional measurements carried out on entangled twin-beam of radiation. Realistic detection schemes such as {\sc on/off} photodetection, homodyne detection and joint measurement of two-mode quadratures are analyzed in details. Imperfections of the apparatuses, such as nonunit quantum efficiency and finite resolution, are taken into account. We show that conditional {\sc on/off} photodetection provides a reliable scheme to verify nonclassicality, whereas conditional homodyning represents a tunable and robust source of squeezed light. We also describe optical teleportation as a conditional measurement, and evaluate the degrading effects of finite amount of entanglement, decoherence due to losses, and nonunit quantum efficiency.Comment: Some pics with low resolution. Originals at http://www.qubit.i

Manipulating the non-Gaussianity of phase-randomized coherent states

We experimentally investigate the non-Gaussian features of the phase-randomized coherent states, a class of states exploited in communica- tion channels and in decoy state-based quantum key distribution protocols. In particular, we reconstruct their phase-insensitive Wigner functions and quantify their non-Gaussianity. The measurements are performed in the mesoscopic photon-number domain by means of a direct detection scheme involving linear detectors

On the role of the local oscillator intensity in optical homodyne-like tomography

In a recent research (Olivares et al., 2019 [18]) we have demonstrated that a homodyne-like scheme, exploiting a \u201clow-intensity\u201d local oscillator, can be used to perform optical state tomography of both quantum and classical states of light. The reconstruction method directly uses the homodyne-like probability distribution retrieved from the detector. Here, we further investigate the role played by the local oscillator in this respect. In particular, we study to some extent how its intensity affects the quantum-state reconstruction procedure by focusing on the case of the Fock states |1\u3009 and |2\u3009, whose homodyne-like probability distributions are sensibly affected by the actual value of the LO intensity. The analysis is performed on Monte Carlo simulated experiments taking also into account the quantum detection efficiency