Quantum search of many vertices on the joined complete graph

The quantum search on the graph is a very important topic.In this work,we develop a theoretic method on searching of single vertex on the graph[Phys.Rev.Lett.114110503(2015)],and systematically study the search of many vertices on one low-connectivity graph,the joined complete graph.Our results reveal that,with the optimal jumping rate obtained from the theoretical method,we can find such target vertices at the time O(√N),where N is the number of total vertices.Therefore,the search of many vertices on the joined complete graph possessing quantum advantage has been achieved.

Optimization of Light Field for Generation of Vortex Knot

The theory of knots and links focuses on the embedding mode of one or several closed curves in three-dimensional Euclidean space.In an electromagnetic field system,all-optical knots or links composed of phase or polarization singularities have been verified theoretically and experimentally.Recent studies have shown that robust topological all-optical coding can be achieved by using optical knots and links.However,in the current design of optical knots and links based on phase or polarization singularities,the amplitude of light between adjacent singularities is relatively weak.This brings great pressure to detection of optical knots and links and limits their applications.Here,we propose a new optimization method in theory.Compared with the existing design methods,our design method improves the relative intensity distribution of light between adjacent singularities.We verify the feasibility of our design results in experiments.Our study reduces the detection difficulty of optical knots and links,and has a positive significance for promotion of applications of optical knots and links.

Observation of topological rainbow in non-Hermitian systems

Topological photonic states have promising applications in slow light,photon sorting,and optical buffering.However,realizing such states in non-Hermitian systems has been challenging due to their complexity and elusive properties.In this work,we have experimentally realized a topological rainbow in non-Hermitian photonic crystals by controlling loss in the microwave frequency range for what we believe is the first time.We reveal that the lossy photonic crystal provides a reliable platform for the study of non-Hermitian photonics,and loss is also taken as a degree of freedom to modulate topological states,both theoretically and experimentally.This work opens a way for the construction of a nonHermitian photonic crystal platform,will greatly promote the development of topological photonic devices,and will lay a foundation for the real-world applications.

Electric-Circuit Realization of Fast Quantum Search

Quantum search algorithm,which can search an unsorted database quadratically faster than any known classical algorithms,has become one of the most impressive showcases of quantum computation.It has been implemented using various quantum schemes.Here,we demonstrate both theoretically and experimentally that such a fast search algorithm can also be realized using classical electric circuits.The classical circuit networks to perform such a fast search have been designed.It has been shown that the evolution of electric signals in the circuit networks is analogies of quantum particles randomly walking on graphs described by quantum theory.The searching efficiencies in our designed classical circuits are the same to the quantum schemes.Because classical circuit networks possess good scalability and stability,the present scheme is expected to avoid some problems faced by the quantum schemes.Thus,our findings are advantageous for information processing in the era of big data.

Superchiral fields generated by nanostructures and their applications for chiral sensing

Chirality is ubiquitous in natural world.Although with similar physical and chemical properties,chiral enantiomers could play different roles in biochemical processes.Discrimination of chiral enantiomers is extremely important in biochemical,analytical chemistry,and pharmaceutical industries.Conventional chiroptical spectroscopic methods are disadvantageous at a limited detection sensitivity because of the weak signals of natural chiral molecules.Recently,superchiral fields were proposed to effectively enhance the interaction between light and molecules,allowing for ultrasensitive chiral detection.Intensive theoretical and experimental works have been devoted to generation of superchiral fields based on artificial nanostructures and their application in ultrasensitive chiral sensing.In this review,we present a survey on these works.We begin with the introduction of chiral properties of electromagnetic fields.Then,the optical chirality enhancement and ultrasensitive chiral detection based on chiral and achiral nanostructures are discussed respectively.Finally,we give a short summary and a perspective for the future ultrasensitive chiral sensing.

Photonic-plasmonic hybrid microcavities: Physics and applications

Photonic-plasmonic hybrid microcavities,which possess a higher figure of merit Q/V(the ratio of quality factor to mode volume)than that of pure photonic microcavities or pure plasmonic nano-antennas,play key roles in enhancing light–matter interaction.In this review,we summarize the typical photonic-plasmonic hybrid microcavities,such as photonic crystal microcavities combined with plasmonic nano-antenna,whispering gallery mode microcavities combined with plasmonic nano-antenna,and Fabry–Perot microcavities with plasmonic nano-antenna.The physics and applications of each hybrid photonic-plasmonic system are illustrated.The recent developments of topological photonic crystal microcavities and topological hybrid nano-cavities are also introduced,which demonstrates that topological microcavities can provide a robust platform for the realization of nanophotonic devices.This review can bring comprehensive physical insights of the hybrid system,and reveal that the hybrid system is a good platform for realizing strong light–matter interaction.

Correlated optical convolutional neural network with“quantum speedup”

Compared with electrical neural networks,optical neural networks(ONNs)have the potentials to break the limit of the bandwidth and reduce the consumption of energy,and therefore draw much attention in recent years.By far,several types of ONNs have been implemented.However,the current ONNs cannot realize the acceleration as powerful as that indicated by the models like quantum neural networks.How to construct and realize an ONN with the quantum speedup is a huge challenge.Here,we propose theoretically and demonstrate experimentally a new type of optical convolutional neural network by introducing the optical correlation.It is called the correlated optical convolutional neural network(COCNN).We show that the COCNN can exhibit“quantum speedup”in the training process.The character is verified from the two aspects.One is the direct illustration of the faster convergence by comparing the loss function curves of the COCNN with that of the traditional convolutional neural network(CNN).Such a result is compatible with the training performance of the recently proposed quantum convolutional neural network(QCNN).The other is the demonstration of the COCNN’s capability to perform the QCNN phase recognition circuit,validating the connection between the COCNN and the QCNN.Furthermore,we take the COCNN analog to the 3-qubit QCNN phase recognition circuit as an example and perform an experiment to show the soundness and the feasibility of it.The results perfectly match the theoretical calculations.Our proposal opens up a new avenue for realizing the ONNs with the quantum speedup,which will benefit the information processing in the era of big data.

Spin‑controlled topological phase transition in non‑Euclidean space

Modulation of topological phase transition has been pursued by researchers in both condensed matter and optics research fields,and has been realized in Euclidean systems,such as topological photonic crystals,topological metamaterials,and coupled resonator arrays.However,the spin-controlled topological phase transition in non-Euclidean space has not yet been explored.Here,we propose a non-Euclidean configuration based on Mobius rings,and we demonstrate the spin-controlled transition between the topological edge state and the bulk state.The Mobius ring,which is designed to have an 8πperiod,has a square cross section at the twist beginning and the length/width evolves adiabatically along the loop,accompanied by conversion from transverse electric to transverse magnetic modes resulting from the spin-locked effect.The 8πperiod Mobius rings are used to construct Su–Schrieffer–Heeger configuration,and the configuration can support the topological edge states excited by circularly polarized light,and meanwhile a transition from the topological edge state to the bulk state can be realized by controlling circular polarization.In addition,the spin-controlled topological phase transition in non-Euclidean space is feasible for both Hermitian and non-Hermitian cases in 2D systems.This work provides a new degree of polarization to control topological photonic states based on the spin of Mobius rings and opens a way to tune the topological phase in non-Euclidean space.

Low-threshold topological nanolasers based on the second-order corner state

Topological lasers are immune to imperfections and disorder.They have been recently demonstrated based on many kinds of robust edge states,which are mostly at the microscale.The realization of 2D on-chip topological nanolasers with a small footprint,a low threshold and high energy efficiency has yet to be explored.Here,we report the first experimental demonstration of a topological nanolaser with high performance in a 2D photonic crystal slab.A topological nanocavity is formed utilizing the Wannier-type 0D corner state.Lasing behaviour with a low threshold of approximately 1μW and a high spontaneous emission coupling factor of 0.25 is observed with quantum dots as the active material.Such performance is much better than that of topological edge lasers and comparable to that of conventional photonic crystal nanolasers.Our experimental demonstration of a low-threshold topological nanolaser will be of great significance to the development of topological nanophotonic circuitry for the manipulation of photons in classical and quantum regimes.

Intelligent algorithms: new avenues for designing nanophotonic devices [Invited]

The research on nanophotonic devices has made great progress during the past decades. It is the unremitting pursuit of researchers that realize various device functions to meet practical applications. However, most of the traditional methods rely on human experience and physical inspiration for structural design and parameter optimization, which usually require a lot of resources, and the performance of the designed device is limited. Intelligent algorithms, which are composed of rich optimized algorithms, show a vigorous development trend in the field of nanophotonic devices in recent years. The design of nanophotonic devices by intelligent algorithms can break the restrictions of traditional methods and predict novel configurations, which is universal and efficient for different materials, different structures, different modes, different wavelengths, etc. In this review, intelligent algorithms for designing nanophotonic devices are introduced from their concepts to their applications, including deep learning methods, the gradient-based inverse design method, swarm intelligence algorithms, individual inspired algorithms, and some other algorithms. The design principle based on intelligent algorithms and the design of typical new nanophotonic devices are reviewed. Intelligent algorithms can play an important role in designing complex functions and improving the performances of nanophotonic devices, which provide new avenues for the realization of photonic chips.

Loss-induced nonreciprocity

Nonreciprocity is important in both optical information processing and topological photonics studies.Conventional principles for realizing non reciprocity rely on magnetic fields,spatiotemporal modulation,or nonlinearity.Here we propose a generic principle for generating nonreciprocity by taking advantage of energy loss,which is usually regarded as harmful.The loss in a resonance mode induces a phase lag,which is independent of the energy transmission direction.When multichannel lossy resonance modes are combined,the resulting interference gives rise to nonreciprocity,with different coupling strengths for the forward and backward directions,and unidirectional energy transmission.This study opens a new avenue for the design of nonreciprocal devices without stringent requirements.

Topologically protected long-range coherent energy transfer

The realization of robust coherent energy transfer with a long range from a donor to an acceptor has many important applications in the field of quantum optics.However,it is hard to be realized using conventional schemes.Here,we demonstrate theoretically that robust energy transfer can be achieved using a photonic crystal platform,which includes the topologically protected edge state and zero-dimensional topological corner cavities.When the donor and the acceptor are put into a pair of separated topological cavities,the energy transfer between them can be fulfilled with the assistance of the topologically protected interface state.Such an energy transfer is robust against various kinds of defects,and can also occur over very long distances,which is very beneficial for biological detections,sensors,quantum information science,and so on.

Topological rainbow trapping based on non-Hermitian twisted piecing photonic crystals

Topological rainbow trapping,which can separate and trap different frequencies of topological states into different positions,plays a key role in topological photonic devices.However,few schemes have been proposed to realize topological rainbow trapping effects in lossy photonic crystal systems,which has restricted their practical applications,since loss is ubiquitous in nanophotonic devices.Here,we propose a method to realize a topological rainbow based on non-Hermitian twisted piecing photonic crystals.Different frequencies of topological photonic states are separated and trapped in different positions without overlap in the lossy photonic crystals.Moreover,the frequencies of interface states can be modulated by loss,and a topological rainbow can also be achieved in both TE and TM modes.This work brings an effective method to realize robust nanophotonic multiwavelength devices in non-Hermitian systems.