In this article, we present and discuss a board game called QTris that uses a concise set of rules to describe the quantum mechanics of nine qubits through the conceptual framework of preparation, operations, and measurement. Indeed, there is no quantum experiment on nine qubits that is not a game of QTris. Similarly, every game of QTris describes a quantum mechanical experiment. We show how, through its gameplay mechanics and strategies, QTris clearly emphasises the differences between statistical mixtures and coherent superpositions. As a result, the game mechanics of QTris provide an interpretation of quantum mechanics in the form of game strategies. This interpretation is clear-cut and free of metaphors.
We report on the organization and realization of the Joint International Physics Summer School - Optics" devoted to High-School students. The idea of the School is to teach Physics through high-level experimental activities, suitably supported by introductory lectures and complemented by data analysis. The School is also open to the participation of a number of teachers, as an opportunity of refreshing their knowledge and increasing their experimental skills. Students and teachers are directly involved in the experimental activities. The aim of the activity is to stimulate students curiosity and interest and help them decide whether a future job career in Science could be suited for them. The School is organized in two weeks: the first in June-July in Como (Italy) at the Department of Science and High Technology and the second at the end of August in Olomouc (Czech Republic) at the Joint Laboratory of Optics. Two editions of the Summer School took place in 2013 and 2014 (overall 40 students and 3 teachers from Italy, 9 students from Czech Republic) and the third one will be in 2015. The first week of the School is devoted to introductory lectures (theoretical and experimental) to consolidate students' and teachers' knowledge of basic optics. The second week is devoted to several advanced experiments in linear, nonlinear, classical and quantum optics, performed in research laboratories. During the last day of the School, students are required to give a presentation of the results obtained during the experimental sessions.
We present the experimental investigation of the coherence properties of the light produced by parametric down conversion in the macroscopic regime, also including pump depletion. In particular, we compare the results obtained in very similar geometric conditions by using two nonlinear crystals having different lengths. We observe that the number of generated photons, the size of spatio-spectral coherence areas, and the number of modes in the photon number statistics exhibit a similar behavior in the two crystals as a function of pump mean power, even if we notice that the absolute values are different. The available theory of parametric down conversion cannot account for these differences.
The Kennedy-like receiver is a quasi-optimal discrimination scheme employed in binary phase-shift-keyed communication schemes with coherent states. In its standard configuration, it is based on the interference of the two signals encoding the message with a reference local oscillator and on the measurement by means of ON/OFF detectors. Here we demonstrate that, without interrupting the communication, it is possible to monitor the relative phase between the signals and the local oscillator by applying a Bayesian processing to the very data sample used to discriminate the signals at any shot. We show, both numerically and experimentally, that the minimum uncertainty in phase estimation can be achieved both with ON/OFF and photon-number resolving detectors. The performances of our phase-estimation method in the presence of either uniform phase noise or phase diffusion are also investigated and discussed.
We observed the spectral coherence structure of twin beam states generated by spontaneous parametric down-conversion by using a simple fiber spectrometer synchronized with a pulsed laser source. The recorded single-shot spectra exhibit a well-defined peak structure, where the peak wavelengths change values from shot to shot. We studied the number and the width of the peaks as a function of the different parameters in the experimental setup (pump power, iris size, iris distance from the BBO crystal). Moreover, we evaluated the number of modes in the intensity distribution of the light in different portions of the spectrum. The experimental results indicate that the number of modes from statistics and the number and width of the peaks evolve differently with the parameters.
It is well known that optical twin-beam states (TWB) generated by spontaneous parametric down-conversion (PDC) exhibit spatial and spectral correlations, which can appear in single-shot images obtained by using an imaging spectrometer to resolve emission angles and wavelengths simultaneously. By analyzing series of single-shot images recorded by an EMCCD camera at different powers of the pump beam, we studied the evolution of several quantities characterizing the generated TWB. In particular, we demonstrated that correlation widths in spectrum and space increase monotonically at low pump powers and then start decreasing at higher powers due to the onset of pump depletion. In a complementary way, the Fedorov ratio decreases and then increases again. At the same time, the number of modes evaluated from photon statistics follows a complementary behavior to correlation widths that can be interpreted in terms of the evolution of the number of Schmidt modes in the field.
KEYWORDS: Luminescence, Picosecond phenomena, Fluorescence resonance energy transfer, Annealing, Data modeling, Molecules, Solids, Signal detection, Time resolved spectroscopy, Biomedical optics
Site-specific fluorescence-resonance-energy-transfer donor-acceptor dual-labelled oligonucleotide probes are widely used in state-of-art biotechnological applications. Such applications include their usage as primers in polymerase chain reaction. However, the steady-state fluorescence intensity signal emitted by these molecular tools strongly depends from the specificities of the probe conformation. For this reason, the information which can be reliably inferred by steady-state fluorimetry performed on such samples is forcedly confined to a semi-qualitative level. Namely, fluorescent emission is frequently used as ON/OFF indicator of the probe hybridization state, i.e. detection of fluorescence signals indicates either hybridization to or detachment from the template DNA of the probe. Nonetheless, a fully quantitative analysis of their fluorescence emission properties would disclose other exciting applications of dual-labelled probes in biosensing. Here we show how time-correlated single-photon counting can be applied to get rid of the technical limitations and interpretational ambiguities plaguing the intensity analysis, and to derive information on the template DNA reaching single-base.
The light diffused by an illuminated object contains information about it but, as it propagates, the information changes its appearance and sometimes seems even lost. The more conventional way to retrieve this information is to make an image of the object by means of some optical device, like a lens or a mirror. Nevertheless this is not the only way to proceed: pin-hole photography, for instance, recovers some part of the information by simply selecting a single light ray from each point of the object, on the other hand, holography recovers the largest part of information about the object by registering an interference pattern. Moreover, propagating light can be manipulated in such a way that the final recovered information results dramatically different from the original one. The only way not to get confused in the description of all these phenomena in the didactic practice with High-School students is to follow the path of light asking how the information is present during the propagation of the light. We tested this approach experimentally by realizing 2D images with pin-hole cameras and photo-cameras and 3D images with a holographic setup and implementing spatial filtering in the focal plane of a lens: the result was a deeper understanding by students.
The “LuNa” (La natura della Luce nella luce della Natura - The nature of Light in the light of Nature) Project is devoted to the experimental teaching of optics in the different school grades. The basic idea of the Project is that the history of optics and the debate about the nature of light are a meaningful example of how science proceeds in the development of a physical model. Moreover optical phenomena can be presented at different levels of complexity in order to be accessible to students of different age. At the core of the Project are several portable setups that support experimental and partially interactive lectures covering all the aspects of optical phenomena, from geometrical optics to single-photon interference passing through atmospheric optics, spectroscopy, holography and theory of perception. When possible, the setups are realized with simple and easy to find materials so as to be reproducible by teachers and students. Of course, for the most complicated setups (interferometers and holography) research materials are used. Each module is calibrated to fit teachers’ requirements either to be included in the curricula of their classes or to be used as an expansion of the optics program.
We follow the reductio ad absurdum reasoning described in the book “Sneaking a Look at God’s Cards” by Giancarlo Ghirardi to demonstrate the wave-particle duality of light in a Mach-Zehnder interferometric setup analog to the conventional Young double-slit experiment. We aim at showing the double nature of light by measuring the existence of interference fringes down to the single-photon level. The setup includes a strongly attenuated laser, polarizing beam splitters, half-waveplates, polarizers and single-photon detectors.
During our activities of physics dissemination with High School students especially concerning optics, we are used to distribute a questionnaire about colors and image formation by mirrors and lenses. The answers to some questions clearly show misconceptions and naïve ideas about colors, ray tracing, image formation in reflection and refraction. These misconceptions are widespread and do not depend on the gender, the level, and the age of the students: they seem to depend on some wrong ideas and explanatory models that are not changed by the curricular studies at school. In fact, the same errors are present in groups of students before and after taking optics courses at High School. On the other hand we have also found some misleading explanations of the phenomena both in textbooks and websites. Most of the time, errors occur in the explanatory drawings accompanying the text, which are based on some hybrid description of the optical processes: sometimes the description of the path of the ray light is confused with the image reconstruction by the lenses. We think that to partially avoid some errors it is important to use a teaching path centered on the actual path of the rays and not on what eyes see (the vision). Here we present the results of data collected from more than 200 students and some considerations about figures and explanations found in textbooks.
By tens-of-picosecond resolved fluorescence detection we study Förster resonance energy transfer between a donor
and a black-hole-quencher bound at the 5'- and 3'-positions of an oligonucleotide probe matching the highly
polymorphic region between codons 51 and 58 of the human leukocyte antigen DQB1 0201 allele, conferring
susceptibility to type-1 diabetes. The probe is annealed with non-amplified genomic DNAs carrying either the
0201 sequence or other DQB1 allelic variants. We detect the longest-lived donor fluorescence in the case of
hybridization with the 0201 allele and definitely faster and distinct decays for the other allelic variants, some of
which are single-nucleotide polymorphic.
We present the characterization of a multi-pixel detector (SiPM, Hamamatsu) in the presence of dark-count
and cross-talk effects. Our description yields a self-consistent calibration of the device, based on the light
under investigation, which is used to evaluate shot-by-shot detected-photon numbers including dark-counts and
cross-talk. The analysis allows us to reliably reconstruct the detected-photons statistics of different light states
by taking into account the modifications introduced by detector features. Finally we quantify photon-number
correlations in bipartite states and use the data to produce conditional states: only if dark-count and cross-talk
effects can be neglected, the experimental results match theory.
By using hybrid photodetectors we exploited the photon-number correlations existing in bipartite optical states
to demonstrate the effect of multiple-photon subtraction on the generation of conditional states in the pulsed
regime. We operated on both classical and quantum Gaussian bipartite states in the mesoscopic regime without
background subtraction and corrections. The obtained conditional states are non-Gaussian in nature, thus particularly
useful for applications to Quantum Information. All the experimental results are in excellent agreement
with theoretical models.
By tens-of-picosecond resolved fluorescence detection (TCSPC, time-correlated single-photon counting) we study
Förster resonance energy transfer between a donor and a black-hole-quencher acceptor bound at the 5'- and 3'-positions of a synthetic DNA oligonucleotide. This dual labelled oligonucleotide is annealed with either the
complementary sequence or with sequences that mimic single-nucleotide polymorphic gene sequences: they differ
in one nucleotide at positions near either the ends or the center of the oligonucleotide. We find donor fluorescence
decay times whose values are definitely distinct and discuss the feasibility of single nucleotide polymorphism
genotyping by this method.
We present an experimental scheme for the reconstruction of the Wigner function of optical states. The method
is based on direct intensity measurements by non-ideal photodetectors operated in the linear regime. We mix,
at a beam-splitter, the signal state with a set of coherent probes of known complex amplitudes, and measure the
probability distribution of the detected photons for each probe. The Wigner function is given by a suitable sum of
those probability distributions. For comparison, the same data are analyzed to obtain the number distributions
and the Wigner functions for photons.
A snake photon detection based imaging technique developed by our group is explained in details and its performances
compared with those obtained by other experimentalists. The technique is based on simultaneous
application of time and spatial-mode selection. We also show that in these very particular working conditions
commonly used plastic tissue phantoms display non tissue-like scattering properties.
Joint signal-idler photoelectron distributions of twin beams have been measured recently in two distinct regimes:
either the mean number of photon pairs per one pump pulse is lower that the number of independent modes or
vice versa. Exploiting a microscopic quantum theory for joint quasi-distributions in parametric down-conversion
based on the model of superposition of signal and noise we characterize properties of twin beams in terms of quasidistributions
using experimental data. In parallel to the microscopic model, joint signal-idler photon-number
distribution is reconstructed using the method of maximum likelihood. Negative values as well as oscillating
behavior in quantum region are characteristic for the joint signal-idler quasi-distributions of integrated intensities.
The larger the mean number of photon pairs per mode the weaker the quantum features are. However, they
survive even in the mesoscopic regime, i.e. when tens of photon pairs per mode are present on average. Also
the conditional and difference photon-number distributions are shown to be sub-Poissonian and sub-shot-noise,
respectively. Violation of classical inequalities for photon-number distributions is discussed.
We implement a frequency degenerate seeded downconversion process in which the seed field is a spatially
multimode chaotic field. The two output fields are quantum correlated in space and intensity and maintain the
same spatial and temporal structure as the seeding field and thus represent two almost twin multimode fields
that can be used for ghost imaging applications.
We demonstrate, by direct measurement of the number of photons in signal and idler, that the twin-beam of light
produced by ps-pulsed spontaneous parametric downconversion is endowed with sub-shot-noise photon-number
correlations in a mesoscopic intensity regime (more than 1000 detected photons). The noise reduction, calculated
from the variance of the difference in the numbers of detected-photons, resulted to be 3.25 dB below the shot-noise
level. From experimental data we can recover joint photon-number distribution and a negative-valued
joint signal-idler quasi-distributions of integrated intensities, which demonstrates the nonclassical character of
the generated field.
In the interaction among three non-collinear plane-waves under type I phase matching conditions, if one among the fields is non-depleted, the remaining two are holographic replicas of each other. We calculate the holographic wave-front generated by a non-plane object wave-front and a plane reference wave-front and present experimental holographic images, ofpoint-source objects, obtained by choosing object- and reference-field frequencies among o, ''2 and w in any possible combination. With the plane reference at (03, the holographic field generated by downconversion is phase-conjugate with respect to the object field, an effect suitable for all-optical real-time treatments of optical bits. Preliminary applications to optical computing and imaging are presented. The feasibility of frill correction ofphase distortions in powerftil-laser beam profiles is discussed.
3-D holographic images of extended diffusing objects are simultaneously recorded and reconstructed by optical cross- correlation in a second-order non-linear crystal. An interaction geometry in which the phase-matched object and reference fields propagate slightly non-colinearly is particularly convenient to obtain these Second Harmonic Generated (SHG) holograms.
A method of wavefronts' cross-correlation by means of Second Harmonic Generated Hologram (SHG hologram) is considered. According to this method, the interference pattern of an object and reference waves is recorded in a nonlinear light-sensitive material using its second order nonlinearity. The SHG hologram generates a wave that forms the reconstructed image of the object, the frequency of the reconstructed wave being doubled. An expression that describes the electrical field of the reconstructed wave is deduced. It is suggested to use the transforming properties of the SHG hologram for constructing the network of changeable interconnection lines which operates on the principle 'light is controlled by light'. The experiment has confirmed the ability of the SHG hologram of forming high quality images of arbitrary objects. The ways of overcoming the effect of doubling the frequency of the light after each act of a signal transformation are considered. The theory has shown that by using the effect of 'down-conversion' it is possible either to return the frequency of the signal to its initial value or to sustain the value of the frequency at the constant level.
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