Asymptotical Locking Tomography of High-Dimensional Entanglement

High-dimensional(HD)entanglement provides a very promising way of transcending the limitations of the twodimensional entanglement between qubits for increasing channel capacity in many quantum protocols.In the pursuit of capitalizing on the HD entangled states,one of the central issues is to unambiguously and comprehensively quantilfy and reconstruct them.The full quantum state tomography is a unique solution,but it is undesirable and even impractical because the measurements increase rapidly in d^4 for a bipartite d-dimensional quantum state.Here we present a very efficient and practical tomography method—asymptotical locking tomography(ALT),which can harvest full information of bipartite d-dimensional entangled states by very few measurements less than 2 d^2 only.To showcase the validity and reasonableness of our ALT,we carry out the test with the two-photon spin-orbital angular momentum hyperentangled states in a four-dimensional subspace.Besides high-efficiency and practicality,our ALT is also universal and can be generalized into multipartite HD entanglement and other quantum systems.

Multi-Path Ghost Imaging by Means of an Additional Time Correlation

Ghost imaging functions achieved by means of the spatial correlations between two photons is a new modality in imaging systems. With a small number of photons, ghost imaging is usually realized based on the position correlation of photon pairs produced from the spontaneous parametric down-conversion process. Here we demonstrate a way to realize multi-path ghost imaging by introducing an additional time correlation. Different delays of paths will induce the shift of the coincidence peak, which carries the information about objects. By choosing the suitable coincidence window, we obtain images of three objects simultaneously, with a visibility of 87.2%.This method provides insights and techniques into multi-parameter ghost imaging. It can be applied to other correlated imaging systems, for example, quantum spiral imaging.

Identifying the Symmetry of an Object Based on Orbital Angular Momentum through a Few-Mode Fiber

In recent years,orbital angular momentum(OAM),as a new usable degree of freedom of photons,has been widely applied in both classical optics and quantum optics.For example,digital spiral imaging uses the OAM spectrum of the output beam from the object to restore the symmetry information of the object.However,the related experiments have been carried out in free space so far.Due to the poor anti-noise performance,limited transmission distance and other reasons,the practicability is seriously restricted.Here,we have carried out a digital spiral imaging experiment through a few-mode fiber,to achieve the identification of the symmetry of object by measuring the OAM spectrum of the output beam.In experiment,we have demonstrated the identification of the symmetry of amplitude-only and phase-only objects with the two-,three-and four-fold rotational symmetries.We also give the understanding of the physics.We believe that our work has greatly improved the practical application of digital spiral imaging in remote sensing.

Double-slit interference of single twisted photons

Optical orbital angular momentum(OAM) is a special property of photons and has evoked research onto the light–matter interaction in both classical and quantum regimes. In classical optics, OAM is related to an optical vortex with a helical phase structure. In quantum optics, photons with a twisted or helical phase structure will carry a quantized OAM. To our knowledge, however, so far, no experiment has demonstrated the fundamental property of the OAM at the single-photon level. In this Letter, we have demonstrated the average photon trajectories of twisted photons in a double-slit interference. We have experimentally captured the double-slit interference process of twisted photons by a time-gated intensified charge-coupled device camera, which is trigged by a heralded detection. Our work provides new perspectives for understanding the micro-behaviors of twisted particles and enables new applications in imaging and sensing.

Stronger Hardy-like proof of quantum contextuality

A Hardy-like proof of quantum contextuality is a compelling way to see the conflict between quantum theory and noncontextual hidden variables(NCHVs),as the latter predict that a particular probability must be zero,while quantum theory predicts a nonzero value.For the existing Hardy-like proofs,the success probability tends to 1/2when the number of measurement settings n goes to infinity.It means the conflict between the existing Hardy-like proof and NCHV theory is weak,which is not conducive to experimental observation.Here we advance the study of a stronger Hardy-like proof of quantum contextuality,whose success probability is always higher than the previous ones generated from a certain n-cycle graph.Furthermore,the success probability tends to 1 when n goes to infinity.We perform the experimental test of the Hardy-like proof in the simplest case of n=7 by using a four-dimensional quantum system encoded in the polarization and orbital angular momentum of single photons.The experimental result agrees with the theoretical prediction within experimental errors.In addition,by starting from our Hardy-like proof,one can establish the stronger noncontextuality inequality,for which the quantumclassical ratio is higher with the same n,which provides a new method to construct some optimal noncontextuality inequalities.Our results offer a way for optimizing and enriching exclusivity graphs,helping to explore more abundant quantum properties.