1,720,964 research outputs found
Spatio–temporal entanglement of twin photons: An intuitive picture
No full textWe draw an intuitive picture of the spatio–temporal properties of the entangled state of twin
photons, where they are described as classical wave-packets. This picture predicts a precise
relation between their temporal and transverse spatial separations at the crystal output. The
space-time coupling described by classical arguments turns out to determine in a precise way the
spatio–temporal structure of the quantum entanglement, analyzed by means of the biphotonic
correlation and of the Schmidt dimensionality of the entanglement
Entangled imaging in the large photon number regime
No full textWe formulate a theory for entangled imaging that includes the case of a large number of photons in
the two entangled beams. We show that the results for imaging and the wave–particle duality features, which
have been demonstrated in the microscopic case, persist in the macroscopic domain. Although the visibility of
the information retrieved via correlation measurements in the regime of a high number of photons is lower than
in the coincidence counting regime, we show that efficient reconstruction of both the image and the diffraction
pattern of an object is possibl
Optical pattern formation
No full textThis chapter focuses on the concept of optical pattern formation. The field of optical pattern formation (OPF) studies the spatial and spatiotemporal phenomena that arise in the structure of electromagnetic field in the planes orthogonal with respect to the direction of propagation. Most theoretical treatments of the interaction between matter and radiation introduce the plane wave approximation—that is, they assume that the electric field is uniform in each transverse plane. However, the field of OPF studies mainly the interaction with nonlinear media, where the phenomena emerge spontaneously as a consequence of an instability; another name that is commonly used to designate OPF is “transverse nonlinear optics.” Historically, the broad interest in OPF emerged as a natural evolution of the previous development of the field of optical instabilities and chaos, when the main attention shifted gradually from purely temporal effects to spatio-temporal phenomena. For both the fields of optical instabilities and OPF, continuous inspiration arose from the formulation of general disciplines as Haken's synergetics or Prigogine's theory of dissipative structures
Tailoring the spatiotemporal structure of biphoton entanglement in type-I parametric down-conversion
No full textWe investigate the spatiotemporal structure of the biphoton entangled state produced by parametric down-conversion (PDC) at the output face of the nonlinear crystal. We analyze the geometry of biphoton correlation for different gain regimes (from ultralow to high), different crystal lengths, and different tuning angles of the crystal. While for collinear or quasicollinear phase matching a X-shaped geometry, nonfactorizable in space and time, dominates, in the highly noncollinear conditions we observe a remarkable transition to a factorizable geometry. We show that the geometry of spatiotemporal correlation is a consequence of the angle-frequency relationship imposed by phase matching and that the fully spatiotemporal analysis provides a key to control the spatiotemporal properties of the PDC entangled state and in particular to access a biphoton localization in time and space in the femtosecond and micrometer range, respectively
Squeezing and Einstein-Podolsky-Rosen correlation in the mirrorless optical parametric oscillator
No full textThis work analyses the quantum properties of counterpropagating twin beams generated by a mirrorless optical parametric oscillator in the continuous-variable regime. Despite the lack of the filtering effect of a cavity, we show that in the vicinity of its threshold it may generate high levels of narrowband squeezing and Einstein-Podolsky-Rosen correlation, completely comparable to what can be obtained in standard optical parametric oscillators
Improving the observation of spatial quantum correlation of twin beams by means of a sub-pixel symmetry centre retrieval algorithm
No full textWe propose a method to improve the observation of spatial quantum correlation of twin beams produced by parametric down-conversion in a non-linear crystal. By applying our post-acquisition algorithm to experimental data we are able to reduce the uncertainty in the determination of the symmetry centre of the signal-idler pattern in the far-field plane, by searching it with sub-pixel accuracy. Reducing the uncertainty leads to an improvement of the observation of spatial quantum correlation of the twin beams. We perform theoretical and numerical investigation in order to test potentialities and limits of our algorithm, and we identify a proper experimental configuration that minimises the problem of symmetry centre uncertainty
Temporal coherence and correlation of counterpropagating twin photons
No full textThis work analyzes the temporal coherence and correlation of counterpropagating twin photons generated in a
quasiphase matched nonlinear crystal by spontaneous parametric down-conversion.We find out different pictures
depending on the pump pulse duration relative to two characteristic temporal scales, determined, respectively, by
the temporal separation between the counterpropagating and the co-propagating wave packets. When the pump
duration is intermediate between the two scales, we show a transition from a highly entangled state to an almost
separable state, with strongly asymmetric spectral properties of the photons
High-sensitivity imaging with multi-mode twin beams
No full textTwin entangled beams produced by single-pass parametric down-conversion (PDC) offer the opportunity to detect weak amount of absorption with an improved sensitivity with respect to standard techniques which make use of classical light sources. We propose a differential measurement scheme which exploits the spatial quantum correlation of type-II PDC to image a weak amplitude object with a sensitivity beyond the standard quantum limit imposed by shot noise. By applying a quantitative numerical model to a specific PDC system (a type-II beta-barium borate crystal), we are able to identify conditions in parameter space suitable for a substantial enhancement of the imaging sensitivity, and we investigate the robustness of this enhancement against experimental imperfections
Experimental investigation of the X-shaped spatio-temporal correlation of twin photons via sum frequency generation
No full textIn this paper we report about the experimental investigation of the non factorable spatio-temporal correlation of twin beams generated in parametric down conversion (PDC) at the crystal output. We present the correlation features to be reconstructed by means of the inverse process of PDC, that is sum frequency generation, in a scheme based on achromatic imaging. In particular we show the ultra-narrow temporal localization (6fs) observed thanks to the huge spectral bandwidth detected in the near field of the crystal. We illustrate the deteriorating effects of imperfect imaging conditions or spatial modes selection on the temporal correlation, giving evidence of the interdependence of spatial and temporal degrees of freedom in PDC as claimed by the theory. Throughout the paper we shall discuss about the characteristics of the experimental set-up being used for the investigation of the twin beam correlation in both the temporal and spatial domain, highlighting the important features for the success of the experiment and the demonstration of the X-shaped structure of the space-time correlation, already emerging from preliminary results
Superresonant parametric generation in nonlinear photonic crystals
No full textTrough experiments performed in hexagonally poled lithium tantalate
we unveil a novel superresonant regime for parametric generation,
coherently locking and enhancing the gain of signal and idler outputs
around 800 and 1550 nm
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