1,721,039 research outputs found
Direct detection of super-thermal photon-number statistics in second-harmonic generation
No full textChanges in the statistical properties of light undergoing second-harmonic generation are investigated in the photon- number-resolving domain. We theoretically demonstrate that when a portion of multimode thermal light produced by parametric down-conversion is up-converted, both the second-harmonics and the residual beam at the fundamental wavelength are endowed with super-thermal photon-number distributions. The experimental results, which were obtained by exploiting the photo-numberresolving capability of hybrid photodetectors, are in excellent agreement with the theoretical expectations
Towards underwater quantum communication in the mesoscopic intensity regime
Full text linkThe problem of secure underwater communication can take advantage of the exploitation of quantum resources and novel quantum technologies. At variance with the current experiments performed at the single photon level, here we propose a different scenario involving mesoscopic twin-beam states of light and two classes of commercial photon-number-resolving detectors. We prove that twin-beam states remain nonclassical even if the signal propagates in tubes filled with water, while the idler is transmitted in free space. We also demonstrate that from the study of the nonclassicality information about the loss and noise sources affecting the transmission channels can be successfully extracted
Multi-mode twin-beam states in the mesoscopic intensity domain
No full textParametric down conversion is a quantum nonlinear process of paramount importance in the Quantum Optics context since it produces entangled states of light. Such states, usually called twin-beam (TWB) states, exhibit perfect correlations in many degrees of freedom, among which the number of photons. In this review paper, we focus on their generation and characterization in the rather unusual mesoscopic intensity regime. The use of photon-number-resolving detectors allows the experimental reconstruction of the statistical properties of TWB states and the demonstration of their nonclassical nature. This characterization is preliminary and necessary in view of the application of TWB states to the development of Quantum Technologies. In this work we focus on the robustness of mesoscopic TWB states against losses and noise sources for their exploitation in the field of Quantum Communication
Statistics of twin-beam states by photon-number resolving detectors up to pump depletion
No full textWe use hybrid photodetectors endowed with partial photon-number resolution to characterize the photon-number distribution of twin-beam states produced at different intensity regimes up to pump depletion. To match the detectors’ dynamics, the light of signal and idler is strongly attenuated by neutral-density filters. Since the filters do not modify the nature of any classical-light statistics, we find that signal and idler are described by a multimode thermal distribution at any pump power. The number of modes decreases at increasing pump power until pump depletion, when the number starts increasing again. The effect is qualitatively interpreted as a selective mode amplification induced by the high-gain parametric process
Novel scheme for secure data transmission based on mesoscopic twin beams and photon-number-resolving detectors
Full text linkQuantum resources can improve the quality and security of data transmission. A novel communication protocol based on the use of mesoscopic twin-beam (TWB) states of light is proposed and discussed. The message sent by Alice to Bob is encoded in binary single-mode thermal states having two possible mean values, both smaller than the mean value of the TWB. Such thermal states are alternately superimposed to the portion of TWB sent to Bob. We demonstrate that in the presence of an eavesdropping attack that intercepts and substitutes part of the signal with a thermal noise, Bob can still successfully decrypt the message by evaluating the noise reduction factor for detected photons. The protocol opens new perspectives in the exploitation of quantum states of light for applications to Quantum Communication
Autocorrelation functions: a useful tool for both state and detector characterisation
Full text linkThe calculation of autocorrelation functions represents a routinely used tool to characterise quantum states of light. In this paper, we evaluate the g(2) function for detected photons in the case of mesoscopic multi-mode twin-beam states in order to fully investigate their statistical properties starting from measurable quantities. Moreover, we show that the second-order autocorrelation function is also useful to estimate the spurious effects affecting the employed Silicon-photomultiplier detectors
Underwater Transmission of Mesoscopic Twin-Beam States for Applications in Quantum Communication
No full textCan nonclassical correlations survive in the presence of asymmetric lossy channels?
No full textNonclassical correlations are a fundamental resource for applications involving multipartite systems. To assess nonclassicality, several different criteria can be applied to measured data. Here we compare three inequalities by applying them to a multi-mode twin-beam state, in which one of the two parties is transmitted through a varying lossy channel. We demonstrate, both theoretically and experimentally, that the asymmetry introduced by losses affects the three criteria in different ways, thus offering a tool for quantum optics applications
Antibunching-like behavior of mesoscopic light
Full text linkWe present the implementation of a compact setup for the generation of sub-Poissonian states of light exhibiting the analogous of antibunching behavior in the so-called mesoscopic intensity domain. In the scheme, the idler arm of a pulsed multi-mode twin-beam state is directly measured by a photon-number-resolving detector, whereas the signal arm is divided at a balanced beam splitter, at whose outputs other two photon-number-resolving detectors measure the number of photons. The three detectors measure synchronous with each laser pulse. Due to the nonclassical correlations in the twin beam, when a given value of photons is measured in the idler arm, the conditional states obtained in post processing at the two beam-splitter outputs are nonclassical, showing lower-than-one values of the Fano factor and of the photon autocorrelation coefficient. The possibility to engineer sub-Poissonian states nearly approaching the Fock state with one photon is also addressed
Preserving Nonclassicality in Noisy Communication Channels
Full text linkNowadays, the transmission of quantum information, especially for the distribution of cryptographic keys, is required on a global scale. The main obstacle to overcome in free-space communication is the presence of turbulence, which causes both spatial and temporal deformations of the light signals that code information. Here we investigate the extent at which the transmission of mesoscopic twin-beam states through asymmetric noisy channels degrades the nonclassical nature of the photon-number correlations between signal and idler. We consider three nonclassicality criteria, all written in terms of measurable quantities, and demonstrate, both theoretically and experimentally, that the asymmetry introduced by losses affects the three criteria in different ways
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