We propose a mechanism to actively tune optical bistable/tristable behavior with the external magnetic field in nonlinear coated nanospheres. We show that such nanostructures can exhibit typical bistable/tristable phenomena near surface plasmon resonant wavelengths, which can be modified through the magnitude of external magnetic field B. In addition, because of the different refractive indices of the gyrotropic material for LCP and RCP waves, the corresponding results show an opposite trend with the augmentation of the magneto-optical (MO) effect. For the system consists of a MO shell and nonlinear metallic core. We demonstrate numerically that the optical bistability exists only when the volume fraction of the metallic core is larger than a critical one. The application of an external magnetic field does not only increase (or decrease) the upper/lower threshold fields but also changes the critical volume fractions. If nonlinear metallic material appears in the shell, a tunable Fano resonance which is regulated by both the incident electric field E₀ and the external magnetic field B can be generated in this system with properly designed geometric parameters, and it may lead to the emergence of optical tristability. In the strong nonlinear case, the self-consistent mean-field approximation is established to study the optical bistable behavior. Our studies are naturally reduced to the quasistatic results when the particle sizes are much smaller than the incident wavelengths. Such nanostructures with magneto-controllable optical bistability/tristability may be designed for us as nonlinear nanodevices, such as optical nanoswitches, optical isolators and so on.

We demonstrate in this paper the tunable electromagnetically induced transparency (EIT) made from superconducting (SC) niobium nitride (NbN) induced by intense terahertz (THz) field. The experimental results and simulation show that bright resonator is altered greatly due to strong and direct coupling to incident intense THz field, while the dark resonator has little coupling with incident THz field via a weak near-filed coupling to the bright-mode resonator. This implies that we can partially control the selective mode or part of metamaterial by introducing the incident intense THz field, which offer an effective manner to design and selectively control the metamaterial, and thus may bring tunable EIT-like metamaterial into novel applications.

Traditional objective lenses based on refraction of light are quite critical in modern microscopy but the focusing and imaging resolutions are diffraction-limited to be half a wavelength. Recently, through manipulating diffraction of light with binary masks or gradient metasurfaces, many miniaturized and planar lenses have been reported with intriguing functionalities such as ultra-high numerical aperture (NA), long focal length, large depth of focus and a diffraction-limit-broken spot for far-field, non-invasive, label-free and super-resolution imaging.  Here I introduce the recent advances in planar diffractive lenses (PDLs) from the viewpoint of a united theory “diffraction-based focusing optics”, reveal the underlying physics in their fighting against the diffraction limit via constructive or destructive interference, and redefine the new diffraction limit of PDLs to be 0.38λ/NA (λ is the wavelength). Various approaches of realizing PDLs are introduced in terms of their unique performances and rechecked by using optical aberration theory. A detailed tutorial about applying PDLs in nano-imaging and nano-fabrication will be provided.  

Engineering local angular momentum in structured light fields enables unprecedented development in many fields, such as photonic quantum-information processing [1] and selective excitation of valleys in photonic crystals [2,3]. As a kind of structured light fields, pseudo-spin source is an indispensable issue for unidirectional transport in topological photonic crystals; however, it is difficult to construct, especially in optical frequency. Here, we show angular momentum of pseudo-spins in a silicon topological photonic crystal. Due to the fact that optical circularly polarized source is naturally in terms of electric fields, we restrict on transverse electric polarization in such two-dimensional photonic crystal with nontrivial topology. In this way, the pseudo-spin source is related to transverse spin and orbital angular momentum, a true spin that can be possible to achieve by either quantum dot or customized-fiber nanotip, which is totally different from those in previous literatures [4-6]. It is interesting to observe circularly polarized (CP) points at certain positions in the map of ellipticity angle between Ex and Ey components, near the interface of topologically nontrivial silicon photonic crystal; while the handedness of circular-polarization is locked to the direction of pseudo-spins. Meanwhile, we also find similar phase vortices with its handedness locking to the pseudo-spin direction for orbital angular momentum. The above findings enable to realize unidirectional robust transport of pseudo-spin edge states. For example, a right-handed circularly-polarized (RCP) source at the correct position will lead to the light flow leftward, while a left-handed circularly-polarized (LCP) source will excite the light flow towards the opposite direction. The simulation results are illustrated in Figure 1 below. Our work paves the way for observing unidirectional transport of light in optical regime and may lead to potential applications in integrated photonic circuits such as robust delay line.

Photothermal convection has been a major obstacle for stable particle trapping in plasmonic optical

tweezer at high optical power. Here, we demonstrate a strategy to suppress the plasmonic

photothermal convection by using vanishingly small thermal expansion coefficient of water at low

temperature. A simple square nanoplasmonic array is illuminated with a loosely Gaussian beam to

produce a two dimensional optical lattice for trapping of micro particles. We observe stable

particle trapping due to near-field optical gradient forces at elevated optical power at low temperature.

In contrast, for the same optical power at room temperature, the particles are convected away

from the center of the optical lattice without their accumulation. This technique will greatly

increase usable optical power and enhance the trapping capability of plasmonic optical tweezer.

In this paper, we investigate the characteristics of optical chirality in multi-particles systems. In assembled multi-particles systems, optical chirality is present due to the different arrangements of the particles. The different arrangements results in the change of charge polarization in the nanostructures at left and right circular polarization. Polarization modes in the nanostructures are excited via different incident sources. The polarization modes interact between the nanostructures and results in different charge distributions, which change the circular dichroism (CD) properties of the whole systems. In this paper, we demonstrate the phenomenon through two case studies; One, changing the orientation of the incident light source, and two, changing the positions of the nanostructures. In the first case, the light source is incident onto a spiral chain of nanoparticles. Through different incident angles, we observed different absorption characteristics of the nanoparticle chain and this resulted in different CD properties at incident angle of 30 and 60 degree. This observation could be a huge advantage to obtain two CDs with single design. In the second case, we consider a dimer system. We have one nanoparticle moving in different positions and we observed that the CD of the dimer system has different characteristic compared to the normal system. Both case studies show us that the CD of the systems can be manipulates via external components. We also learn that via the changes at the external components, we can obtain two CD plots with single design. This further reduces the need to fabricate two chiral nanostructures to detect molecules with different secondary structures.

 

 

We develop single-photon sources that simultaneously combines high purity, efficiency, and indistinguishability. We demonstrate entanglement among ten single photons. We construct high-performance multi-photon boson sampling machines to race against classical computers to reach the goal of quantum computational supremacy.

Quantum acoustics is an emerging field focusing on interactions between acoustic waves and artificial atoms that can be exploited in quantum science.  Acoustic waves propagate at a speed that is five orders of magnitude slower than the speed of light and couple to artificial atoms through mechanical processes, thereby enabling a new paradigm for on-chip quantum operation and communication.  The extensive technologies developed for micro-electro-mechanical systems (MEMS) can also be adapted for quantum acoustics. 

Among the various artificial atoms or qubits that have been explored, nitrogen vacancy (NV) color centers in diamond are of special interest because of their robust spin coherence and the ease with which these qubits can be measured and controlled.  In this talk, I will discuss our recent experimental advance in coupling NV centers to surface acoustic waves (SAWs).  By exploiting strain coupling to orbital degrees of freedom, we are able to induce strong and coherent spin-mechanical interactions with SAW amplitudes at only a fraction of a picometer.  This platform opens a new avenue for experimental exploration of spin-based quantum acoustics.

 

The ability to prepare, optically read out and coherently control single quantum states is a key requirement for quantum information processing. Optically active solid-state emitters have emerged as promising candidates with their prospects for on-chip integration as quantum nodes and sources of coherent photons connecting these nodes. Under a strongly driving resonant laser field, such quantum emitters can exhibit quantum behaviour such as Autler–Townes splitting and the Mollow triplet spectrum. Here we demonstrate coherent control of a strongly driven optical transition in silicon vacancy centre in diamond. Rapid optical detection of photons enabled the observation of time-resolved coherent Rabi oscillations and the Mollow triplet spectrum. Detection with a probing transition further confirmed Autler–Townes splitting generated by a strong laser field. The coherence time of the emitted photons is comparable to its lifetime and robust under a very strong driving field, which is promising for the generation of indistinguishable photons.

 

Electron spins of diamond nitrogen-vacancy (NV) centers are important quantum resources for nanoscale sensing and quantum information. Combining such NV spin systems with levitated optomechanical resonators will provide a hybrid quantum system for many novel applications. Here we optically levitate a nanodiamond and demonstrate electron spin control of its built-in NV centers in vacuum. We observe that the strength of electron spin resonance (ESR) is enhanced when the air pressure is reduced. We also observe that oxygen and helium gases have different effects on both the photoluminescence and the ESR contrast of nanodiamond NV centers, indicating potential applications of NV centers in oxygen gas sensing. For spin-optomechanics, it is important to control the orientation of the nanodiamond and NV centers in a magnetic field. Recently, we have observed the angular trapping and torsional vibration of a levitated nanodiamond, which paves the way towards levitated torsional optomechanics in the quantum regime. We also propose a scheme to achieve torsional ground state cooling, and utilize the electron spin-torsional coupling to do quantum many-body simulation.