Quantum digital spiral imaging

We demonstrate that the combination of digital spiral imaging with high-dimensional orbital angular momentum (OAM) entanglement can be used for efficiently probing and identifying pure phase objects, where the probing light does not necessarily touch the object, via the experimental, non-local decomposition of non-integer pure phase vortices in OAM-entangled photon pairs. The entangled photons are generated by parametric downconversion and then measured with spatial light modulators and single-mode fibers. The fractional phase vortices are defined in the idler photons, while their corresponding spiral spectra are obtained non-locally by scanning the measured OAM states in the signal photons. We conceptually illustrate our results with the biphoton Klyshko picture and the effective dimensionality to demonstrate the high-dimensional nature of the associated quantum OAM channels. Our result is a proof of concept that quantum imaging techniques exploiting high-dimensional entanglement can potentially be used for remote sensing

Making and identifying optical superposition of very high orbital angular momenta

We report the experimental preparation of optical superpositions of high orbital angular momenta(OAM). Our method is based on the use of spatial light modulator to modify the standard Laguerre-Gaussian beams to bear excessive phase helices. We demonstrate the surprising performance of a traditional Mach-Zehnder interferometer with one inserted Dove prism to identify these superposed twisted lights, where the high OAM numbers as well as their possible superpositions can be inferred directly from the interfered bright multiring lattices. The possibility of present scheme working at photon-count level is also shown using an electron multiplier CCD camera. Our results hold promise in high-dimensional quantum information applications when high quanta are beneficial.Comment: Submitted for publication consideration (4 figures

Violation of a Bell inequality in two-dimensional spin-orbit hypoentangled subspaces

Based on spin-orbit coupling induced by q-plates, we present a feasible experimental proposal for preparing two-dimensional spatially inhomogeneous polarizations of light. We further investigate the quantum correlations between these inhomogeneous polarizations of photon pairs generated by spontaneous parametric down-conversion, which in essence describe the so-called hypoentanglement that is established between composite spin-orbit variables of photons. The violation of the Clauser-Horne-Shimony-Holt-Bell inequality is predicted with S=2\sqrt2 to illustrate the entangled nature of the cylindrical symmetry of spatially inhomogeneous polarizations.Comment: 14pages,3 figures, submitte

How our brains utilize real-world structures to create coherent visual experiences

We live in a structured world, where objects rarely exist in isolation but are often surrounded by similar environments. When objects consistently co-occur with certain objects and scene contexts, our neural systems can implicitly extract and learn such regularities in real-world environments. Predictive processing theories propose that our brains can use learned statistical regularities to predict the structure of incoming sensory input across space and time during visual processing. The predictions may allow us to efficiently recognize objects and understand scenes, thus forming coherent visual experiences in natural vision. In this dissertation, we conducted three studies to explore how our brains use real-world structures to create coherent visual experiences using neuroimaging techniques (EEG & fMRI) and multivariate pattern analyses (MVPA). Study 1 investigated how scene context affects object processing across time by recording EEG signals while participants viewed semantically consistent or inconsistent objects within scenes. The results reveal that semantically consistent scenes facilitate object representations, but this facilitation is task-dependent rather than automatic. In Study 2, we investigated how cortical feedback mediates the integration of visual information across space by manipulating the spatiotemporal coherence of naturalistic video stimuli shown in both visual hemifields. By analytically combining EEG and fMRI data, we demonstrated that spatial integration of naturalistic visual inputs is mediated by cortical feedback in alpha dynamics that fully traverse the visual hierarchy. In Study 3, we further investigated what level of spatiotemporal coherence is needed to trigger such integration-related alpha dynamics. The findings suggest that integration-related alpha dynamics have some flexibility so that they can accommodate information from videos belonging to the same basic-level category. Together, the dissertation provides multimodal evidence demonstrating that contextual information facilitates object perception and scene integration, highlighting the critical role of predictions related to real-world regularities in constructing coherent visual experiences

The algebraic multiplicity of the spectral radius of a hypertree

It is well-known that the spectral radius of a connected uniform hypergraph is an eigenvalue of the hypergraph. However, its algebraic multiplicity remains unknown. In this paper, we use the Poisson Formula and matching polynomials to determine the algebraic multiplicity of the spectral radius of a uniform hypertree

Polarization Entanglement from Parametric Down-Conversion with a LED Pump

Spontaneous parametric down-conversion (SPDC) is a reliable platform for entanglement generation. Routinely, a coherent laser beam is an essential prerequisite for pumping the nonlinear crystal. Here we break this barrier to generate polarization entangled photon pairs by using a commercial light-emitting diode (LED) source to serve as the pump beam. This effect is counterintuitive, as the LED source is of extremely low spatial coherence, which is transferred during the down-conversion process to the biphoton wavefunction. However, the type-II phase-matching condition naturally filters the specific frequency and wavelength of LED light exclusively to participate in SPDC such that localized polarization Bell states can be generated, regardless of the global incoherence over the full transverse plane. In our experiment, we characterize the degree of LED light-induced polarization entanglement in the standard framework of the violation of Bell inequality. We have achieved the Bell value $S=2.33\pm 0.097$, obviously surpassing the classical bound $S=2$ and thus witnessing the quantum entanglement. Our work can be extended to prepare polarization entanglement by using other natural light sources, such as sunlight and bio-light, which holds promise for electricity-free quantum communications in outer space