The Talbot effect, a wave-optical self-imaging phenomenon originally observed in real-space, has developed into a powerful framework for programmable modal transformations across diverse physical platforms. Here, we report the experimental demonstration of nonlocal Talbot transformations within a high-dimensional, orbital angular momentum (OAM) entangled two-photon system. By exploiting the intrinsic nonlocal correlations generated through spontaneous parametric down-conversion, we show that applying an azimuthal Talbot phase on one photon of an entangled pair is sufficient to coherently reshape the OAM modal distribution of its spatially separated partner, without any direct local operation on the latter. As a proof of principle, we further demonstrate the inverse Talbot transformation within the same platform by incorporating the required quadratic phase during the state-preparation stage. These results extend Talbot physics from local mode manipulation to entanglement-assisted nonlocal transformations in a high-dimensional discrete basis. The demonstrated platform opens versatile routes toward conditional remote OAM-mode conversion, structured entangled-state engineering, and high-dimensional quantum information processing.
The Talbot effect, a wave-optical self-imaging phenomenon originally observed in real-space, has developed into a powerful framework for programmable modal transformations across diverse physical platforms. Here, we report the experimental demonstration of nonlocal Talbot transformations within a high-dimensional, orbital angular momentum (OAM) entangled two-photon system. By exploiting the intrinsic nonlocal correlations generated through spontaneous parametric down-conversion, we show that applying an azimuthal Talbot phase on one photon of an entangled pair is sufficient to coherently reshape the OAM modal distribution of its spatially separated partner, without any direct local operation on the latter. As a proof of principle, we further demonstrate the inverse Talbot transformation within the same platform by incorporating the required quadratic phase during the state-preparation stage. These results extend Talbot physics from local mode manipulation to entanglement-assisted nonlocal transformations in a high-dimensional discrete basis. The demonstrated platform opens versatile routes toward conditional remote OAM-mode conversion, structured entangled-state engineering, and high-dimensional quantum information processing.
The self-imaging, or Talbot effect, that occurs with the propagation of periodically structured waves has enabled several unique applications in optical metrology, image processing, data transmission, and matter-wave interferometry. In this paper, we report on a demonstration of a Talbot effect with single photons prepared in a lattice of orbital angular momentum (OAM) states. We observe that upon propagation the wavefronts of the single photons manifest self-imaging whereby the OAM lattice intensity profile is recovered. Furthermore, we show that the intensity at fractional Talbot distances is indicative of a periodic helical phase structure corresponding to a lattice of OAM states. This phenomenon is a powerful addition to the toolbox of orbital angular momentum and spin-orbit techniques that have already enabled many recent developments in quantum optics.
The thesis introduces two single-photon experiments with the lattice of spin-orbit arrays. The basic background knowledge has been introduced in Chapter 1. Chapters 2-4 describe the detailed techniques used in these two experiments. \n \nIn the first work, we implement a remote state preparation protocol on our single-photon orbital angular momentum (OAM) lattice state via hybrid-entanglement. Remote state preparation is a variant of quantum state teleportation where the sender knows the transmitted state. It is known to require fewer classical resources and exhibit a nontrivial trade-off between the entanglement and classical communication compared with quantum teleportation. Here we propose a state preparation scheme between two spatially separated photons sharing a hybrid-entangled polarization-OAM state. By sending one of the polarization-entangled photon pairs through Lattice of Optical Vortex prism pairs, we generate a two-dimensional lattice of spin-orbit coupled single-photons. We show that the measurement taken by an electron-multiplying intensified CCD camera on the transformed photons can be remotely prepared by the polarization projection of the other. Our protocol could have a significant impact on long-distance quantum communication with higher channel capacity and lead to more efficient and compatible quantum information processing techniques. \n \nThe second experiment investigates the single-photon Talbot Effect in spin-orbit arrays. The Talbot Effect is a near-field diffraction effect, that occurs with the propagation of periodically structured waves. It has enabled several unique applications in optical metrology, image processing, data transmission, and matter-wave interferometry. We observe that upon propagation, the wavefronts of the single photons manifest self-imaging whereby the OAM lattice intensity profile is recovered. Furthermore, we show that the intensity distribution at each fractional Talbot distance is indicative of the periodic helical phase structure corresponding to a lattice of OAM states. This phenomenon is a significant addition to the toolbox of orbital angular momentum and spin-orbit techniques that are becoming increasingly important in optical implementations of quantum information.
The efficient transport and engineering of photonic orbital angular momentum (OAM) lie at the heart of various related classical and quantum applications. Here, by leveraging the spatial-mode-engineered frequency conversion, we realize the remote transport of high-dimensional orbital angular momentum (OAM) states between two distant parties without direct transmission of information carriers. We exploit perfect vortices for preparing high-dimensional yet maximal O AM entanglement. Based on nonlinear sum-frequency generation working with a strong coherent wave packet and a single photon, we conduct the Bell-like state measurements for high-dimensional perfect vortices. We experimentally achieve an average transport fidelity 0.879 ± 0.048 and 0.796 ± 0.066 for a complete set of 3-dimensional and 5-dimensional OAM mutually unbiased bases, respectively. Furthermore, by exploring the full transverse entanglement, we construct another strategy of quantum imaging with interaction-free light. It is expected that, with the future advances in nonlinear frequency conversion, our scheme will pave the way for realizing truly secure high-dimensional quantum teleportation in the upcoming quantum network.
High-dimensional quantum entanglement is an important resource for fundamental research and quantum technological application. Recently, the orbital angular momentum (OAM) of light has received much attention to realize high-dimensional quantum systems, and generating and manipulating the OAM entanglement has become an important topic. Here, we propose an inverse design technique to manipulate the OAM entanglement of the photon pair generated through spontaneous parametric down-conversion. The proposed technique directly tailors the OAM states of entangled photon pairs by shaping the incident pump beam. In particular, we construct a physics-informed model by leveraging the backpropagation algorithm and adhering to the overlap integral relation. Our model automatically optimizes diffractive masks, allowing the structured pump to quantitatively modulate the OAM distribution. The generation of maximally entangled states in different dimensions is demonstrated numerically and experimentally.
Orbital angular momentum (OAM) is one of the most recently discovered properties of light, and it is only in the past decade its quantum properties have been the subject of experimental investigations and have found applications. Unlike polarization, which is only bidimensional, orbital angular momentum provides, with relative ease, unprecedented access to a theoretically unbounded discrete state space. The process of spontaneous parametric down-conversion has long been used as a source of two-photon states that can be entangled in several degrees of freedom, including OAM. In this thesis, the properties of the natural OAM spectrum associated with the entangled states produced by parametric down-conversion were investigated. Chapters 2 and 3 describe the production and detection of tunable high-dimensional OAM entanglement in a down-conversion system. By tuning the phase-matching conditions and improving the detection stage, a substantial increase in the half-width of the OAM correlation spectrum was observed. The conjugate variable of OAM, angular position, was also considered when examining high-dimensional states entangled in OAM. In order to efficiently determine their dimension, high-dimensional entangled states were probed by implementing a technique based on phase masks composed of multiple angular sectors, as opposed to narrow single-sector analysers. Presented in chapter 4, this technique allows the measurements of tight angular correlations while maintaining high optical throughput. The states so produced were then used for a number of applications centred around the concept of mutually unbiased bases. One can define sets of mutually unbiased bases for arbitrary subspaces of the OAM state space. Two bases are mutually unbiased if the measurement of a state in one basis provides no information about the state as described in the other basis. Complete measurements in mutually unbiased bases of high-dimensional OAM spaces are presented in chapter 5. Measurements in sets of mutually unbiased bases are integral to quantum science and can be used in a variety of protocols that fully exploit the large size of the OAM state space; we describe their use in efficient quantum state tomography, quantum key distribution and entanglement detection. Caution is however necessary when dealing with state spaces embedded in higher-dimensional spaces, such as that provided by OAM. Experimental tests of Bell-type inequalities allow us to rule out local hidden variable theories in the description of quantum correlations. Correlations inconsistent with the states observed, or even with quantum mechanics, known as super-quantum correlations, have however been recorded previously in experiments that fail to comply with the fair-sampling conditions. Chapter 6 describes an experiment that uses a particular choice of transverse spatial modes for which super-quantum correlations persist even if the detection is made perfectly efficient. The sets of modes carrying OAM allow a complete description of the transverse field. The ability to control and combine additional degrees of freedom provides the possibility for richer varieties of entanglement and can make quantum protocols more powerful and versatile. One such property of light, associated with transverse modes possessing radial nodes in the field distribution, can be accessed within the same type of experimental apparatus used for OAM. In chapter 7, the radial degree of freedom is explored, together with OAM, in the context of Hong-Ou-Mandel interference.
The experimental realization of multidimensional quantum states may lead to unexplored and interesting physics, as well as advanced quantum communication protocols. The orbital angular momentum of photons is a well suitable discrete degree of freedom for implementing high-dimensional quantum systems. The standard method to generate and manipulate such photon modes is to use bulk and fixed optics. Here the authors demonstrate the utilization of a spatial light modulator to manipulate the orbital angular momentum of entangled photons generated in spontaneous parametric downconversion. They show that their setup allows them to realize photonic entanglement of up to 21 dimensions, which in principle can be extended to even larger dimensions.