It was shown [New J. Phys. 17, 103037 (2015)] that large and robust entanglement between two different mechanical resonators could be achieved, either dynamically or in the steady state, in an optomechanical system in which the two mechanical resonators are coupled to a single cavity mode driven by a suitably chosen two-tone field. An important limitation of the scheme is that the cavity decay rate must be much smaller than the two mechanical frequencies and their difference. Here we show that the entanglement can be remarkably enhanced, and the validity of the scheme can be largely extended, by adding a coherent feedback loop that effectively reduces the cavity decay rate

An evanescent optical mode existing in various nanophotonic structures always acts as a cavity mode rather than an electromagnetic vacuum in the study of cavity quantum electrodynamics (CQED). Here we show that taking the evanescent mode as an electromagnetic vacuum in which the nanocavity is located is possible through the optical mode design. The proposed evanescent vacuum enables us to enhance both the reversible photon-exciton interaction and fluorescence collection. By embedding the custom-designed plasmon nanocavity into the evanescent vacuum provided by a metallic or dielectric nanowire, the photon-exciton coupling coefficient can achieve 4.2 times that in vacuum due to the exponential decay of the evanescent wave, and spontaneously emitted photons with Rabi splitting can be guided by an evanescent wave with a collection efficiency of 47% at most. Electromagnetic vacuum engineering at subwavelength scale holds promise for controlling the light-matter interaction in quantum optics, CQED, and on-chip quantum information.

The mechanism of using the anisotropic Purcell factor to control the spontaneous emission linewidths in a four-level atom is theoretically demonstrated; if the polarization angle bisector of the two dipole moments lies along the axis of large/small Purcell factor, destructive/constructive interference narrows/widens the fluorescence center spectral lines. Large anisotropy of the Purcell factor, confined in the subwavelength optical mode volume, leads to rapid spectral line narrowing of atom approaching a metallic nanowire, nanoscale line width pulsing following periodically varying decay rates near a periodic metallic nanostructure, and dramatic modification on the spontaneous emission spectrum near a custom-designed resonant plasmon nanostructure. The combined system opens a good perspective for applications in ultracompact active quantum devices. KEYWORDS: Surface plasmon, spontaneous emission, Purcell factor, quantum emitter, quantum interference R ecent developments in nanotechnology and information technologies have made nanoscale light-matter interaction a tremendous research focus. 1 Small optical mode area in nanofiber-based photonic structures plays a significant role allowing low-light level quantum optical phenomena, such as electromagnetically induced transparency in the nanowatt regime, 2,3 four wave mixing with great gain, 4 and two-photon absorption with sharp peaks in the Rubidium vapor. 5 Ultrasmall optical mode volume in plasmon nanostructures 6 leads to strong coupling between surface plasmons and quantum emitters, which enables the vacuum Rabi splitting, 7,8 the Fano lineshapes in the absorption spectrum, 9−12 and its obvious influence on the two-photon statistics. 13 Superior to many available photonic nanostructures, associated with ultrasmall optical mode volume, 6 plasmonic structures present the key advantage of a large subwavelengthconfined anisotropic vacuum, that is, large anisotropic Purcell factor, 14,15 which originates from an anisotropic electric mode density of collective oscillations of free electrons in metals. 16−19 Another advantage is strong evanescent field of metallic nanostructures, which has promoted many applications, for example, SERS, 20 nanometer biosensors and waveguides, 21 nonlinear optical frequency mixing, 22−24 solar cell, 25,26 and so forth. Through modifying the population of excited states and decay rate of quantum emitters near plasmon structure, the fluorescence enhancement and quenching of fluorescent molecules and semiconductor quantum dots can be controlled well. 27−32 By confining the light into nanoscale volumes, plasmonic elements allow for a nanoscale realization of Mollow triplet of emission spectra and antibunching of emission photons of single molecules that traditional technique can not be accessible. 1,33,34 Through the nanoscale coupling between the surface plasmon modes and single quantum emitter, the directional and efficiency generation of single photons 17−19 and entanglement of two qubits 35 were proposed. These advantages, t...

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Hierarchical superstructures assembled by binary mixed homopolymer-grafted nanoparticles are investigated by using a self-consistent field theory (SCFT). Our results demonstrate that grafting mixed homopolymer brushes provides an effective way to program the spatial lattice arrangement of the nanoparticles. For the polymer-grafted nanoparticles with specific interaction parameter and total grafting density, the unusual non-close-packed simple cubic (SC) crystal lattice is obtained at small spherical core/polymer size ratios (R/( N b) < 1). As the size ratio increases to R N b /() > 1, the nanoparticle arrangement transforms into a body-centered cubic (BCC) crystal lattice. Meanwhile, some unconventional microphases are formed in the polymer matrix, such as the tetragonal cylinder and simple cubic sphere phases. Furthermore, the two-dimensional (2D) model calculations reveal that the binary hairy nanoparticles prefer to arrange into the lattice in a way they can maintain the free energy-minimizing morphology as an isolated particle. Our findings suggest a possible strategy to design hierarchical nanomaterials composed of unique inorganic/organic hybrid superstructures.