Effect of laser phase noise on the steady-state field-mirror entanglement and ground-state cooling in a Laguerre-Gaussian optorotational system.

Cavity optomechanical systems are considered as one of the best platforms for studying macroscopic quantum phenomena. In this paper, we studied the effect of laser phase noise on the steady-state entanglement between a cavity mode and a rotating mirror in a Laguerre-Gaussian (L-G) optorotational system. We found that the effect of laser phase noise was non-negligible on the field-mirror entanglement especially at a larger input power and a larger angular momentum. We also investigated the influence of laser phase noise on the ground-state cooling of the rotating mirror. In the presence of laser phase noise, the ground-state cooling of the rotating mirror can still be realized within a range of input powers.

Magnon-photon cross-correlations via optical nonlinearity in cavity magnonical system.

We propose an alternative scheme to achieve the cross-correlations between magnon and photon in a hybrid nonlinear system including two microwave cavities and one yttrium iron garnet (YIG) sphere, where two cavities nonlinearly interact and meanwhile one of cavities couples to magnon representing the collective excitation in YIG sphere via magnetic dipole interaction. Based on dispersive couplings between two cavities and between one cavity and magnon with the larger detunings, the nonlinear interaction occurs between the other cavity and magnon, which plays a crucial role in generating quantum correlations. By analyzing the second-order correlation functions via numerical simulations and analytical calculations, the remarkable nonclassical correlations are existent in such a system, where the magnon blockade and photon antibunching could be obtainable on demand. The scheme we present is focused on the magnon-photon cross-correlations in the weak coupling regime and relaxes the requirements of experimental conditions, which may have potential applications in quantum information processing in the hybrid system.

Growth of Mesoscale Ordered Two-Dimensional Hydrogen-Bond Organic Framework with the Observation of Flat Band.

Flat bands (FBs), presenting a strongly interacting quantum system, have drawn increasing interest recently. However, experimental growth and synthesis of FB materials have been challenging and have remained elusive for the ideal form of monolayer materials where the FB arises from destructive quantum interference as predicted in 2D lattice models. Here, we report surface growth of a self-assembled monolayer of 2D hydrogen-bond (H-bond) organic frameworks (HOFs) of 1,3,5-tris(4-hydroxyphenyl)benzene (THPB) on Au(111) substrate and the observation of FB. High-resolution scanning tunneling microscopy or spectroscopy shows mesoscale, highly ordered, and uniform THPB HOF domains, while angle-resolved photoemission spectroscopy highlights a FB over the whole Brillouin zone. Density-functional-theory calculations and analyses reveal that the observed topological FB arises from a hidden electronic breathing-kagome lattice without atomically breathing bonds. Our findings demonstrate that self-assembly of HOFs provides a viable approach for synthesis of 2D organic topological materials, paving the way to explore many-body quantum states of topological FBs.

Quantum Battery Based on Hybrid Field Charging.

A quantum battery consisting of an ensemble two-level atom is investigated. The battery is charged simultaneously by a harmonic field and an electrostatic field. The results show that the hybrid charging is superior to the previous case of only harmonic field charging in terms of battery capacity and charging power, regardless of whether the interaction between atoms is considered or not. In addition, the repulsive interaction between atoms will increase the battery capacity and charging power, while the attractive interaction between atoms will reduce the battery capacity and discharge power.

Augmented reality display system using modulated moiré imaging technique.

To enhance the depth rendering ability of augmented reality (AR) display systems, a modulated moiré imaging technique is used to render the true three-dimensional (3D) images for AR display systems. 3D images with continuous depth information and large depth of field are rendered and superimposed on the real scene. The proposed AR system consists of a modulated moiré imaging subsystem and an optical combiner. The modulated moiré imaging subsystem employs modulated point light sources, a display device, and a microlens array to generate 3D images. A defocussing equal period moiré imaging structure is used, which gives a chance for the point light sources to modulate the depth position of 3D images continuously. The principles of the imaging system are deduced analytically. A custom-designed transparent off-axis spherical reflective lens is used as an optical combiner to project the 3D images into the real world. An experimental AR system that provides continuous 3D images with depth information ranging from 0.5 to 2.5 m is made to verify the feasibility of the proposed technique.

Large mechanical squeezing beyond 3dB of hybrid atom-optomechanical systems in a highly unresolved sideband regime.

We propose a scheme for the generation of strong mechanical squeezing beyond 3dB in hybrid atom-optomechanical systems in the highly unresolved sideband (HURSB) regime where the decay rate of cavity is much larger than the frequency of the mechanical oscillator. The system is formed by two two-level atomic ensembles and an optomechanical system with cavity driven by two lasers with different amplitudes. In the HURSB regime, the squeezing of the movable mirror can not be larger than 3dB if no atomic ensemble or only one atomic ensemble is put into the optomechanical system. However, if two atomic ensembles are put into the optomechanical system, the strong mechanical squeezing beyond 3dB is achieved even in the HURSB regime. Our scheme paves the way toward the implementation of strong mechanical squeezing beyond 3dB in hybrid atom-optomechanical systems in experiments.

Large and robust mechanical squeezing of optomechanical systems in a highly unresolved sideband regime via Duffing nonlinearity and intracavity squeezed light.

We propose a scheme to generate strong and robust mechanical squeezing in an optomechanical system in the highly unresolved sideband (HURSB) regime with the help of the Duffing nonlinearity and intracavity squeezed light. The system is formed by a standard optomechanical system with the Duffing nonlinearity (mechanical nonlinearity) and a second-order nonlinear medium (optical nonlinearity). In the resolved sideband regime, the second-order nonlinear medium may play a destructive role in the generation of mechanical squeezing. However, it can significantly increase the mechanical squeezing (larger than 3dB) in the HURSB regime when the parameters are chosen appropriately. Finally, we show the mechanical squeezing is robust against the thermal fluctuations of the mechanical resonator. The generation of large and robust mechanical squeezing in the HURSB regime is a combined effect of the mechanical and optical nonlinearities.

Tunneling-induced phase grating in quantum dot molecules.

We present an alternative scheme for the preparation of the phase grating in quantum-dot molecules, where the tunnel coupling occurs between two quantum dots. In the presence of interdot tunneling, the nonlinear dispersion can be significantly enhanced with nearly vanishing linear and nonlinear absorption due to the tunneling-induced quantum coherence. With the help of a standing-wave control field, the weak probe light could be diffracted into high-order direction. It is shown that parameters such as the weak-driving intensity, driving detuning, tunneling strength, and interaction length could be used to adjust the diffraction intensity effectively. Our scheme is focused on the weak standing-wave driving and weak tunneling strength, which may provide an easy and actual way to obtain the phase grating and may have potential applications in quantum-optics and quantum-information-processing devices in the solid-state system.

Bandwidth-enhanced depth priority integral imaging using a band-limited diffusing illumination technique.

The display bandwidth and display mechanism determine the performance of the three-dimensional (3D) display system. In this paper, a bandwidth-enhanced depth priority integral imaging (DPII) technique is proposed. Information transmission efficiency (ITE) defined as the output display bandwidth divided by the input display bandwidth is used to assess the II system. By analyzing the ITE, we find that only a part of the input display bandwidth is used efficiently to present the 3D image in the traditional DPII system. The DPII system sacrifices the ITE for depth enhancement. The low ITE that fundamentally limits the 3D performance of the DPII system is ascribed to the diffusing illumination mechanism of the display system. To enhance the 3D performance, a collimated illumination DPII system as a special case of band-limited diffusing illumination technique has been proposed and demonstrated first. The bandwidth and ITE of such a DPII system are increased. The depth of field (DOF) of the system is doubled. The resolution of the 3D image is increased to the level of the resolution priority II system without sacrificing the viewing angle. A more general case, band-limited illumination DPII system is also demonstrated. By modulating the divergence angle of the illumination system, the 3D image's resolution and DOF can be controlled. The bandwidth and ITE of the DPII system using band-limited illumination are also higher than that of the traditional DPII system. Experiments are presented to prove the bandwidth-enhanced mechanism of the DPII system.

Surface-Assisted Alkane Polymerization: Investigation on Structure-Reactivity Relationship.

Surface-assisted polymerization of alkanes is a remarkable reaction for which the surface reconstruction of Au(110) is crucial. The surface of (1×2)-Au(110) precovered with molecules can be completely transformed into (1×3)-Au(110) by introducing branched methylidene groups on both sides of the aliphatic chain (18, 19-dimethylidenehexatriacontane) or locally shifted into (1×3)-Au(110) under exposure to low-energy electrons (beam energy from 3.5 to 33.6 eV, for alkane dotriacontane). Scanning tunneling microscopy investigations demonstrate that alkane chains adsorbed on (1×3)-Au(110) are more reactive than on (1×2)-Au(110), presenting a solid experimental proof for structure-reactivity relationships. This difference can be ascribed to the existence of an extra row of gold atoms in the groove of (1×3)-Au(110), providing active sites of Au atoms with lower coordination number. The experimental results are further confirmed by density functional theory simulations.

Twin imaging phenomenon of integral imaging.

The imaging principles and phenomena of integral imaging technique have been studied in detail using geometrical optics, wave optics, or light filed theory. However, most of the conclusions are only suit for the integral imaging systems using diffused illumination. In this work, a kind of twin imaging phenomenon and mechanism has been observed in a non-diffused illumination reflective integral imaging system. Interactive twin images including a real and a virtual 3D image of one object can be activated in the system. The imaging phenomenon is similar to the conjugate imaging effect of hologram, but it base on the refraction and reflection instead of diffraction. The imaging characteristics and mechanisms different from traditional integral imaging are deduced analytically. Thin film integral imaging systems with 80µm thickness have also been made to verify the imaging phenomenon. Vivid lighting interactive twin 3D images have been realized using a light-emitting diode (LED) light source. When the LED is moving, the twin 3D images are moving synchronously. This interesting phenomenon shows a good application prospect in interactive 3D display, argument reality, and security authentication.

Squeezing induced high-efficiency diffraction grating in two-level system.

We show the effect of squeezed vacuum on laser-induced grating in a weak standing-wave-driving two-level atomic system. Using the optical Bloch equation and the Floquet harmonic expansion, we obtain the linear response of the medium with respect to the probe field, which determines the transmission spectrum and diffraction intensity. At the presence of the squeezing, the grating with large intensity both in the first- and higher-order directions can be obtainable even though the driving is relatively weak. The responsible mechanism is due to squeezing-induced gain accompanied by the large dispersion. Based on the spatial gain and phase modulations, the first- and high-order diffraction intensities simultaneously could have the large values. Such a scheme we present could have potential applications in implementing lensless imaging and developing the photon devices in quantum information processing.

A new on-surface synthetic pathway to 5-armchair graphene nanoribbons on Cu(111) surfaces.

We report a new pathway to fabricate armchair graphene nanoribbons with five carbon atoms in the cross section (5-AGNRs) on Cu(111) surfaces. Instead of using haloaromatics as precursors, the 5-AGNRs are synthesized via a surface assisted decarboxylation reaction of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). The on-surface decarboxylation of PTCDA can produce extended copper-perylene chains on Cu(111) that are able to transform into graphene nanoribbons after annealing at higher temperatures (ca. 630 K). Due to the low yield (ca. 20%) of GNRs upon copper extrusion, various gases are introduced to assist the transformation of the copper-perylene chains into the GNRs. Typical reducing gases (H2 and CO) and oxidizing gas (O2) are evaluated for their performance in breaking aryl-Cu bonds. This method enriches on-surface protocols for the synthesis of AGNRs using non-halogen containing precursors.

Cooling mechanical motion via vacuum effect of an ensemble of quantum emitters.

We design a hybrid optomechanical setup, in which an ensemble of quantum emitters is coupled with a movable mirror through vacuum interaction. The optical cavity is driven along with the quantum emitters and therefore the coupling between the cavity field and the ensemble determines the dynamics of the coupled system. In particular, we investigated the influence of the vacuum coupling strength on the effective frequency and the effective damping rate of the movable mirror, which shows that the vacuum interaction enhances greatly the effective damping rate. Further, the cooling characteristics of the mechanical resonator is analyzed in detail by counting the effective phonon number in the mirror's motion. It is found that the ground-state cooling of the mechanical motion can be approached in the bad cavity limit when the vacuum coupling is included. The dependence of the cooling of the mechanical motion on the parameters of the cavity and the quantum emitter is investigated in detail numerically.

Phonon induced phase grating in quantum dot system.

Electromagnetically induced phase grating is theoretically investigated in the driven two-level quantum dot exciton system at the presence of the exciton-phonon interactions. Due to the phonon-induced coherent population oscillation, the dispersion and absorption spectra are sharply changed and the phase modulation is enhanced via the high refractive index with nearly-vanishing absorption, which could effectively diffract a weak probe light into the first-order direction with the help of a standing-wave control field. Moreover, the diffraction efficiency of the grating can be easily manipulated by controlling the Huang-Rhys factor representing the exciton-phonon coupling, the intensity and detuning of the control field, and the detuning of the probe field. The scheme we present has potential applications in the photon devices for optical-switching and optical-imaging in the micro-nano solid-state system.

Ultrafast optical switching in quantum dot-metallic nanoparticle hybrid systems.

We study ultrafast excitonic population inversion resulting from the interaction of a semiconductor quantum dot (SQD) with localized surface plasmons. The plasmonic enhanced fields are generated when a metallic nanoparticle (MNP) is subject to a nonlinear chirped few-cycle pulse train. By numerically solving the time-dependent Bloch equations beyond the rotating-wave approximation, we show that the complete population inversion can be achieved for small interparticle distance and the dynamic in population inversion exhibits a steplike transition between absorption and amplifying. This phenomenon can be exploited as an all-optical ultrafast switching device. Moreover, the final state of population inversion is shown to be modified significantly with the interparticle distances, which is not only robust against the variation of probe pulse parameters but also suggests a straightforward method for measuring the interparticle distances via probing the final populations.

Comparison of actively Q-switched laser performance of disordered Yb:Ca3La2(BO3)4 crystals cut along the crystallographic axes.

In this paper, actively Q-switched laser operation with an acousto-optic switch has been demonstrated by using Yb:Ca3La2(BO3)4 crystals cut along the a, b, and c crystallographic axes. The most efficient Q-switched laser operation was obtained by using b-cut Yb:Ca3La2(BO3)4 crystal with 1 kHz pulse repetition frequency, generating laser pulses of 0.5 mJ, 42.56 KW peak power and 9 ns pulse width, when the output couplings were 3%, 5%, and 5%, respectively. Pulse performances and output laser spectra of the a-, b-, and c-cut Yb:Ca3La2(BO3)4 crystals were compared under similar experimental conditions.

Coherent manipulation of spontaneous emission spectra in coupled semiconductor quantum well structures.

In triple coupled semiconductor quantum well structures (SQWs) interacting with a coherent driving filed, a coherent coupling field and a weak probe field, spontaneous emission spectra are investigated. Our studies show emission spectra can easily be manipulated through changing the intensity of the driving and coupling field, detuning of the driving field. Some interesting physical phenomena such as spectral-line enhancement/suppression, spectral-line narrowing and spontaneous emission quenching may be obtained in our system. The theoretical studies of spontaneous emission spectra in SQWS have potential application in high-precision spectroscopy. Our studies are based on the real physical system [Appl. Phys. Lett.86(20), 201112 (2005)], and this scheme might be realizable with presently available techniques.

Enhanced four-wave mixing efficiency in four-subband semiconductor quantum wells via Fano-type interference.

We propose and analyze an efficient way to enhance four-wave mixing (FWM) signals in a four-subband semiconductor quantum well via Fano-type interference. By using Schrödinger-Maxwell formalism, we derive explicitly analytical expressions for the input probe pulse and the generated FWM field in linear regime under the steady-state condition. With the aid of interference between two excited subbands tunneling to the common continuum, the efficiency to generate FWM field is found to be significantly enhanced, up to 35%. More interestingly, a linear growth rate in the FWM efficiency is demonstrated as the strength of Fano-type interference increases in presence of the continuum states, which can be maintained for a certain propagation distance (i.e., 50µm).

HFIST-Net: High-throughput fast iterative shrinkage thresholding network for accelerating MR image reconstruction.

BACKGROUND AND OBJECTIVES: Compressed sensing (CS) is often used to accelerate magnetic resonance image (MRI) reconstruction from undersampled k-space data. A novelty deeply unfolded networks (DUNs) based method, designed by unfolding a traditional CS-MRI optimization algorithm into deep networks, can provide significantly faster reconstruction speeds than traditional CS-MRI methods while improving image quality. METHODS: In this paper, we propose a High-Throughput Fast Iterative Shrinkage Thresholding Network (HFIST-Net) for reconstructing MR images from sparse measurements by combining traditional model-based CS techniques and data-driven deep learning methods. Specifically, the conventional Fast Iterative Shrinkage Thresholding Algorithm (FISTA) method is expanded as a deep network. To break the bottleneck of information transmission, a multi-channel fusion mechanism is proposed to improve the efficiency of information transmission between adjacent network stages. Moreover, a simple yet efficient channel attention block, called Gaussian context transformer (GCT), is proposed to improve the characterization capabilities of deep Convolutional Neural Network (CNN,) which utilizes Gaussian functions that satisfy preset relationships to achieve context feature excitation. RESULTS: T1 and T2 brain MR images from the FastMRI dataset are used to validate the performance of the proposed HFIST-Net. The qualitative and quantitative results showed that our method is superior to those compared state-of-the-art unfolded deep learning networks. CONCLUSIONS: The proposed HFIST-Net is capable of reconstructing more accurate MR image details from highly undersampled k-space data while maintaining fast computational speed.