Recently, nonadiabatic geometric quantum computation has been received great attentions, due to its fast operation and intrinsic error resilience. However, compared with the corresponding dynamical gates, the robustness of implemented nonadiabatic geometric gates based on the conventional single-loop geometric scheme still has the same order of magnitude due to the requirement of strict multi-segment geometric controls, and the inherent geometric fault-tolerance characteristic is not fully explored. Here, we present an effective geometric scheme combined with a general dynamical-corrected technique, with which the super-robust nonadiabatic geometric quantum gates can be constructed over the conventional single-loop geometric and two-loop composite-pulse geometric strategies, in terms of resisting the systematic error, i.e., σ x error. In addition, combined with the decoherence-free subspace (DFS) coding, the resulting geometric gates can also effectively suppress the σ z error caused by the collective dephasing. Notably, our protocol is a general one with simple experimental setups, which can be potentially implemented in different quantum systems, such as Rydberg atoms, trapped ions and superconducting qubits. These results indicate that our scheme represents a promising way to explore large-scale fault-tolerant quantum computation.

A series of CaSc2O4:Er3+,Nd3+ nanocrystals were synthesized by the hydrothermal method. The lumines-cence properties of the CaSc2O4:Er3+,Nd3+ oxide crystals in the visible-light and near infrared (NIR) regions were in-vestigated in detail as the Nd3+ concentrations and excited wavelengths vary. Under 808 nm excitation, the lumines-cence intensity of Er3+ ions appears to be enhanced as the concentration of Nd3+ ions increase. The relative red intensi-ty also has the slight enhancement. Under 980 nm excitation, Nd3+ ions hardly absorb 980 nm photons, only the ab-sorption and emission of Er3+ ions are found. The relative red intensity has no change. Furthermore, only the emis-sion of Er3+ ion was observed in NIR spectrum, which is consist as the visible spectrum. The detailed study reveals the possible upconversion luminescence (UCL) mechanism involved in a novel CaSc2O4:Er3+,Nd3+ nanocrystals un-der 808 nm and 980 nm NIR excitation.

Based on the dipole blockade effect and with the aid of the superatom (SA) model, we propose a scheme to investigate the correlated evolution of two Rydberg sub-superatoms (SSAs), formed by two spatially separated atomic Rydberg sub-ensembles but in the same blockade region. Starting from the pure separable states, we investigate the in-phase or anti-phase correlated dynamics and explore how two Rydberg SSAs entangle with each other mediated by a single Rydberg excitation. Starting from the entangled states, we discuss the robustness of the system against decoherence induced by the dephasing rate. Our results show that both the correlated evolution of two Rydberg SSAs and their collective-state entanglement are usually sensitive to the number of each Rydberg SSA. This allows us to coherently manipulate the Rydberg ensemble over long distances from the single-quantum level to the mesoscopic level by changing the number of atoms. Furthermore, the method for dividing an SA into two SSAs and obtaining their spin operators without any approximation can be readily generalized to the case of many SSAs. It may have potential promising applications in quantum information processing and provide an attractive platform to study the quantum-classical correspondence, many-body physics and so on.

We investigate the single-photon scattering and bound states in a finite coupled resonator waveguide with a defect. We find that there is always a bound state when the number of the resonators are even. However, for an odd number of resonators, whether there exist bound states depends on the size, the inter-resonator coupling strength as well as the detunning of the defect from the other identical resonators.

Schemes for converting photonic polarized-entangled Knill-Laflamme-Milburn (KLM) states to Greenberger-Horne-Zeilinger (GHZ) states are proposed using weak cross-Kerr nonlinearity and X-quadrature homodyne measurement. Analyses show that the two-qubit (Bell state) and three-qubit conversion cases have very high fidelities and close-to-unity probabilities. The conversion processes are robust against photon loss. The schemes linking these two entangled states may be helpful to the study of quantum information processing based on them.

We investigate the quantum Fisher information (QFI) dynamics of a dissipative two-level system in homodyne-mediated quantum feedback control. The analytical results demonstrate that the maximum values and stable values of the QFI can be greatly enhanced via feedback control. The quantum feedback plays a more evident role in the improvement of classical Fisher information. The classical part can reach a high stable value, while the quantum part eventually decays to zero whatever the feedback parameter is.

Design of novel catalysts for the reduction of N-2 to ammonia has been urgently pursued because of various issues related to the industrial reduction technology. In this work, we perform first-principles calculations on the basis of the density-functional theory to control the edges of two-dimensional (2D) transition-metal disulfides (TMDs), including MoS2, WS2, VS2, NbS2, TiS2, and TaS2, for the achievement of optimal efficiency in nitrogen-fixation. Our calculations show that nitrogen molecules prefer to stay at the bridge-on sites of the metal edges of TMD nanoribbons because of exothermic reactions. The calculated energy barrier at each step illustrates that VS2 has the lowest potential-determining step of 0.16 eV in the distal pathway, leading to its best catalytic activity in the N-2 reduction reaction (NRR). Additionally, we find that the trend of catalytic activity of 2D TMD nanoribbons is as follows: VS2 > NbS2 > TiS2 > MoS2 > WS2 > TaS2. We show that charge transfer is critical to the reduction reaction. We further demonstrate that the edges of TMDs, especially VS2, show a higher selectivity for NRR over the hydrogen evolution reaction (HER) by investigating the competition between HER and NRR Our findings not only reveal the effect of the edges of TMDs on NRR, but also provide theoretical support to the reported experimental results in the literature. It is expectable that the 2D TMD nanoribbons, especially VS2, may find application for efficient N-2-fixation. At the same time, our work may guide the design of new catalysts for NRR.

The recently synthesized two-dimensional metal bis(dithiolene) complex (MDT), a kind of metal-organic framework with a kagome lattice structure, has been found to be a promising material for electronic devices. Here we report the surface adsorption effects of gas molecules on the electronic properties and transport behaviors of two-dimensional MDT (M = Fe, Co, Ni, Pd, and Pt) films. The first-principles results reveal that the MDT nanosheets are selectively sensitive to different adsorbed molecules, such as CO, NO, and O2 molecules. All the studied gas molecules can be chemically adsorbed on the ferromagnetic FeDT and CoDT nanosheets, whereas the non-magnetic PdDT and PtDT films are only sensitive to NO molecules, showing quite weak interaction with CO and O2. The physisorption of CO on PdDT and PtDT originates from the mismatch of energy levels between the metal dz2 orbitals and the CO σ orbitals. In contrast, the Pd and Pt dxz and dyz orbitals can well align with the NO π* orbitals, causing strong chemisorption. More importantly, the adsorption of NO on PdDT and PtDT not only induces a magnetism of 1.0 μB for the two films but also greatly enhances the conductivity. In the case of PtDT, we observe a transition from the semiconducting to the metallic phase on NO adsorption. This significant change in the electronic structure can be understood from the adsorption-induced interfacial charge transfer and the strong orbital hybridization between the metal d states and the NO π* states. Our results suggest the potential application of the PdDT and PtDT nanosheets in gas sensing and spintronics.

We study the pump-probe response in an optomechanical cavity accommodating an ensemble of two-level atoms interacting with a cavity mode, which is pumped by a strong driving field and probed by a weak signal field. The atomic excitation is examined without taking any approximations and may be in any regimes ranging from the low limit to the high limit for a given collective coupling constant between the atomic ensemble and the cavity mode. This then results in different absorption and dispersion spectra (such as optomechanically induced transparency, Fano-resonance, normal-mode splitting) when the excitation transfer from cavity mode to atomic ensemble is controlled to change from ineffective to effective. This indicates that a hybrid optomechanical response is indeed determined by the excitation of the atomic ensemble embedded in the optomechanical cavity. It is also of interest that the output signal component and the inside atomic polarization show either synchronous or asynchronous behaviors depending on how the atom-field detuning is chosen, i.e. equal to the mechanical resonator frequency or its negative. Such features may open up an effective avenue in coherently manipulating the internal atomic polarization via the external signal field, and vice versa.

Concurrence is an important parameter for quantifying quantum entanglement, but usually the state tomography must be determined before quantification. In this paper we propose a scheme, based on cavity-assisted atom–light interaction, to measure the concurrence of two-atom pure states and the Collins–Gisin state directly, without tomography. The concurrence of atomic states is encoded in the output coherent optical beams after interacting with cavities and the atoms therein, so the results of detection applied to the output coherent optical beams provide the concurrence data of the atomic states. This scheme provides an alternative method for directly measuring atomic entanglement by detecting coherent light, rather than measuring the atomic systems, which thus greatly simplifies the realization complexity of the direct measurement of atomic entanglement. In addition, as the cavity-assisted atom–light interaction used here is robust and scalable in realistic applications, the current scheme may be realized in the near future.

An experiment demonstrating computational ghost imaging with structured illumination and a single-pixel detector has been performed. Our experimental setup utilized a general computer for generating pseudo-random patterns on the liquid crystal display screen to illuminate a partially-transmissive object. With this similar true thermal light source, this object is imaged. The formula of the computational ghost imaging with this light source has been derived. The experimental results agree with the theoretical analysis. The liquid crystal display screen is more applicable for ghost imaging with ordinary incoherent light as the source of illumination.

We demonstrate quantum information can be transferred between two distant participants without any physical particles traveling between them. The key procedure of the counterfactual scheme is to entangle two nonlocal qubits with each other without interaction, so the scheme can also be used to generate nonlocal entanglement counterfactually. We here illustrate the scheme by using flying photon qubits and Rydberg atom qubits assisted by a mesoscopic atomic ensemble. Unlike the typical teleportation, the present scheme can transport an unknown qubit in a nondeterministic manner without prior entanglement sharing or classical communication between the two distant participants.

We design proposals to generate a remote Greenberger-Horne-Zeilinger（GHZ） state and a W state of nitrogenvacancy（NV） centers coupled to microtoroidal resonators（MTRs） through noisy channels by utilizing time-bin encoding processes and fast-optical-switch-based polarization rotation operations.The polarization and phase noise induced by noisy channels generally affect the time of state generation but not its success probability and fidelity.Besides,the above proposals can be generalized to n-qubit between two or among n remote nodes with success probability unity under ideal conditions.Furthennore,the proposals are robust for regular noise-changeable channels for the n-node case.This method is also useful in other remote quantum information processing tasks through noisy channels.

We report the novel synthesis of luminescent carbon nanoparticles (CNPs) and their applications as yellow emission conversion phosphors. CNPs were obtained in a hydrothermal process using hexamethylenetetramine (HMT)/glucose mixed solution as precursor. The mixed glucose is found to facilitate the decomposition of HMT, which leads to rapid and low-temperature growth of CNPs. CNPs (quantum yield exceeding 58%) solutions exhibit strong blue-green emission with ultraviolet light illumination and possess typical excitation-dependent photoluminescence (PL) behavior. CNPs were also coated onto ultraviolet and blue LEDs. Broad yellow emission was both achieved with ultraviolet or blue light excitation, indicating such CNPs phosphors can be used in fluorescent lamps or white LEDs. The nontoxic nature and broad yellow emission indicates potential applications of CNPs for phosphor-based white light-emitting devices.

We propose a scheme for realizing a quantum controlled phase flip (CPF) gate between two distant nitrogen-vacancy-center spin ensembles (NVEs). The two NVEs couple magnetically with two inductively coupled superconducting flux qubits (FQs). By using an additional energy level of the nitrogen-vacancy (NV) center, the CPF gate can be implemented within the null- and single-excitation subspaces and the external classical driven field is needless in our scheme. Because of the adoption of NVE instead of single NV center, the CPF operation can be greatly speeded up. Besides, we show that this gate provides us a source of cluster states generation on NVEs. Analyses on the influences of dissipation show that this gate is robust.

we propose a scheme for physical implementation for the optimal asymmetric (symmetric) 1→2 universal quantum cloning, the optimal symmetric economical 1→3 phase-covariant cloning and the optimal asymmetric (symmetric) real state cloning based on an iSWAP gate between separated nitrogen-vacancy (NV) centers embedded inphotonic crystal cavities. This two-qubit iSWAP gate is produced by the long-range interaction between two distributed NV centers mediated by the vacuum fields of the cavities. The analysis results show that our scheme is efficient and may be useful for scalable quantum information processing.

A robust and scalable scheme to generate a steady three-dimensional entangled state for a V-type atom and a Λ-type atom trapped in a strongly dissipative bimodal cavity is proposed by direct feedback control based on quantum-jump detection. The robustness of this scheme reflects in the insensitivity to detection inefficiencies and the strong ability against the parameter fluctuations in the feedback, driving, and coupling strengths. The influence of atomic spontaneous emission can be suppressed by using the local feedback control. The scalability is ensured that N-dimensional entangled states of two atoms can be deterministically generated.

The existing distributed quantum gates required physical particles to be transmitted between two distant nodes in the quantum network. We here demonstrate the possibility to implement distributed quantum computation without transmitting any particles. We propose a scheme for a distributed controlled-phase gate between two distant quantum-dot electron-spin qubits in optical microcavities. The two quantum-dot-microcavity systems are linked by a nested Michelson-type interferometer. A single photon acting as ancillary resource is sent in the interferometer to complete the distributed controlled-phase gate, but it never enters the transmission channel between the two nodes. Moreover, we numerically analyze the effect of experimental imperfections and show that the present scheme can be implemented with high fidelity in the ideal asymptotic limit. The scheme provides further evidence of quantum counterfactuality and opens promising possibilities for distributed quantum computation.

We demonstrate quantum information can be transferred between two distant participants without any physical particles travelling between them. The key procedure of the counterfactual scheme is to entangle two nonlocal qubits with each other without interaction, so the scheme can also be used to generate nonlocal entanglement counterfactually. We here illustrate the scheme by using flying photon qubits and stationary electron-spin qubits assisted by quantum dots inside double-sided optical microcavities. Unlike the typical teleportation, the present scheme does not require prior entanglement sharing or classical communication between the two distant participants.

To date, all schemes for entanglement distribution needed to send entangled particles or a separable mediating particle among distant participants. Here, we propose a counterfactual protocol for entanglement distribution against the traditional forms, that is, two distant particles can be entangled with no physical particles travel between the two remote participants. We also present an alternative scheme for realizing the counterfactual photonic entangled state distribution using Michelson-type interferometer and self-assembled GaAs/InAs quantum dot embedded in a optical microcavity. The numerical analysis about the effect of experimental imperfections on the performance of the scheme shows that the entanglement distribution may be implementable with high fidelity.