Quantum superposition demonstrated higher-order topological bound states in the continuum

Higher-order topological insulators,as newly found non-trivial materials and structures,possess topological phases beyond the conventional bulk-boundary correspondence.In previous studies,in-gap boundary states such as the corner states were regarded as conclusive evidence for the emergence of higher-order topological insulators.Here,we present an experimental observation of a photonic higher-order topological insulator with corner states embedded into the bulk spectrum,denoted as the higher-order topological bound states in the continuum.Especially,we propose and experimentally demonstrate a new way to identify topological corner states by exciting them separately from the bulk states with photonic quantum superposition states.Our results extend the topological bound states in the continuum into higher-order cases,providing an unprecedented mechanism to achieve robust and localized states in a bulk spectrum.More importantly,our experiments exhibit the advantage of using the time evolution of quantum superposition states to identify topological corner modes,which may shed light on future exploration between quantum dynamics and higher-order topological photonics.

Erratum to‘Topologically protected polarization quantum entanglement on a photonic chip’[Chip 1,100003(2022)]

Given his role as Executive Editor of this journal,Xian-Min Jin had no involvement in the peer-review of the article titled‘Topologically pro-tected polarization quantum entanglement on a photonic chip’(Chip 1,100003),and had no access to information regarding its peer-review.Full responsibility for the editorial process for this article was delegated to Xibo Feng(fred.feng@chipress.org)at Chip Editorial Office.

Topologically protecting squeezed light on a photonic chip

Squeezed light is a critical resource in quantum sensing and information processing. Due to the inherently weak optical nonlinearity and limited interaction volume, considerable pump power is typically needed to obtain efficient interactions to generate squeezed light in bulk crystals. Integrated photonics offers an elegant way to increase the nonlinearity by confining light strictly inside the waveguide. For the construction of large-scale quantum systems performing many-photon operations, it is essential to integrate various functional modules on a chip. However, fabrication imperfections and transmission cross talk may add unwanted diffraction and coupling to other photonic elements, reducing the quality of squeezing. Here, by introducing the topological phase, we experimentally demonstrate the topologically protected nonlinear process of four-wave mixing, enabling the generation of squeezed light on a silica chip. We measure the cross-correlations at different evolution distances for various topological sites and verify the nonclassical features with high fidelity. The squeezing parameters are measured to certify the protection of cavity-free, strongly squeezed states. The demonstration of topological protection for squeezed light on a chip brings new opportunities for quantum integrated photonics,opening novel approaches for the design of advanced multi-photon circuits.

Experimental quantum simulation of dynamic localization on curved photonic lattices

Dynamic localization,which originates from the phenomena of particle evolution suppression under an externally applied AC electric field,has been simulated by suppressed light evolution in periodically curved photonic arrays.However,experimental studies on their quantitative dynamic transport properties and application for quantum information processing are rare.Here we fabricate one-dimensional and hexagonal two-dimensional arrays both with sinusoidal curvatures.We successfully observe the suppressed single-photon evolution patterns,and for the first time,to the best of our knowledge,measure the variances to study their transport properties.For onedimensional arrays,the measured variances match both the analytical electric-field calculation and the quantum walk Hamiltonian engineering approach.For hexagonal arrays as anisotropic effective couplings in four directions are mutually dependent,the analytical approach suffers,whereas quantum walk conveniently incorporates all anisotropic coupling coefficients in the Hamiltonian and solves its exponential as a whole,yielding consistent variances with our experimental results.Furthermore,we implement a nearly complete localization to show that it can preserve both the initial injection and the wave packet after some evolution,acting as a memory of a flexible time scale in integrated photonics.We demonstrate a useful quantum simulation of dynamic localization for studying their anisotropic transport properties and a promising application of dynamic localization as a building block for quantum information processing in integrated photonics.

Topologically Protected Polarization Quantum Entanglement on a Photonic Chip

Quantum entanglement,as the strictly non-classical phenomenon,is the kernel of quantum computing and quantum simulation,and has been widely applied ranging from fundamental tests of quantum physics to quantum information processing.Meanwhile,the topolog-ical phase is found inherently capable of protecting physical fields from unavoidable fabrication-induced disorder,which inspires the po-tential application of topological protection to quantum states.Here,we present the experimental demonstration of topologically protected quantum entangled states on a photonic chip.The process tomogra-phy shows that quantum entanglement can be well preserved by the topological states even when the chip material introduces disorder and relative polarization rotation in phase space.Our work links the fields of materials,topological science and quantum physics,opening the door to wide applications of topological enhancement in quantum regime.