Cooling of mesoscopic mechanical resonators represents a primary concern in cavity optomechanics. In this Letter, in the strong optomechanical coupling regime, we propose to dynamically control the cavity dissipation, which is able to significantly accelerate the cooling process while strongly suppressing the heating noise. Furthermore, the dynamic control is capable of overcoming quantum backaction and reducing the cooling limit by several orders of magnitude. The dynamic dissipation control provides new insights for tailoring the optomechanical interaction and offers the prospect of exploring mesoscopic quantum physics.

We propose a hybrid photonic-plasmonic resonant structure which consists of a metal nanoparticle (MNP) and a whispering gallery mode (WGM) microcavity. It is found that the hybrid mode enables a strong interaction between the light and matter, and the single-atom cooperativity is enhanced by more than two orders of magnitude compared to that in a bare WGM microcavity. This remarkable improvement originates from two aspects: (1) the MNP offers a highly enhanced local field in the vicinity of an emitter, and (2), surprisingly, the high-Q property of WGMs can be maintained in the presence of the MNP. Thus the present system has great advantages over a single microcavity or a single MNP, and holds great potential in quantum optics, nonlinear optics and highly sensitive biosening.PACS numbers: 42.50. Pq, 42.50.Ct, 42.50.Dv, Owing to the size mismatch between light and single emitters such as single atoms, the interaction between them is very weak, so that it is of importance to create a light-matter interface enabling strong interactions. One way to bridge this mismatch is to employ the strong interaction within cavity quantum electrodynamics (QED) [1,2]. Cavity QED offers an almost ideal platform for the study of physics at the interface of classical and quantum mechanics, and provides a technology for various devices in the field of quantum information [3][4][5]. Experiments on strong coupling regime in cavity QED have made great advances over the past two decades [6]. Among them, whispering gallery mode (WGM) microcavities [7] are promising because they possess ultrahigh quality (Q) factor and allow for mass production on a chip. However, the relatively large cavity mode volume makes it difficult to realize strong coupling. On the other hand, due to the localized surface plasmon resonance (LSPR) [8], metal nanoparticles (MNPs) [9] enable subwavelength confinement of the optical field [10][11][12][13][14]. Unfortunately, MNPs suffer from serious absorption and scattering losses.Against this backdrop, in this Letter, taking advantages from both ultralow-loss WGMs and highly localized plasmon, we propose a WGM microcavity-MNP resonant system. In this composite system, the high-Q WGM microcavity serves as a low-loss storage of the optical field, while the MNP plays the role of an optical antenna which creates a hot spot and magnifies the local optical field. Remarkably, the high-Q property of WGMs can be maintained in the presence of the MNP. As a result, the cooperativity parameter (defined as C = 2G 2 /κγ s [15], with G being the single photon coupling strength, γ s the spontaneous decay of the emitter and κ the decay of the cavity field) achieves a more than 100-fold increase compared with that of the WGM cavity alone. It should be pointed out that, this composite cavity QED structure is significantly different from previous designs where a silica disk or toroid was completely covered with a metal layer, which led to strong degrading of the Q-factor [16,17]. Figure 1 illustrates a schematic of the system. A MNP is ...

Coherent light-matter interaction at the single photon and electronic qubit level promises the remarkable potential for nonclassical information processing. Against the efforts of improving the figure of merit of the cavities, here we demonstrate strong anharmonicity in the polariton dressed states via dark state resonances in a highly dissipative cavity. It is shown that vacuum Rabi oscillation occurs for a single quantum emitter inside a cavity even with bosonic decay-to-interaction rate ratio exceeding 10 2 , when the photon field is coupled to an auxiliary high-Q cavity. Moreover, photon blockade is observable in such a highly-dissipative cavity quantum electrodynamics system. This study provides a promising platform for overcoming decoherence and advancing the coherent manipulation of polariton qubits. PACS numbers: 42.50.Pq, 42.50.Ct Cavity quantum electrodynamics (QED) (for a review, see [1]) provides a critical resource for quantum information processing [2][3][4][5][6][7][8][9][10][11][12] . For coherent manipulation, a key prerequisite is to reach the strong coupling regime, where the emitter-field coupling strength exceeds the decay rates of the emitter and the cavity field. In the past two decades great efforts have been made to improve the quality (Q) factor and reduce the mode volume (V ) of the resonators for stronger interactions, using Fabry-Pérot cavities [13,14], Bragg cavities [15-17], whispering-gallery mode cavities [18-23] , photonic crystal cavities [24-30], hybrid plasmonic-photonic cavities [31] and transmission-line microwave cavities [32], along with theoretical studies of coupled-cavity QED through a waveguide [33][34][35][36]. However, it remains difficult to achieve high Q and small V simultaneously for the sametype resonator. Fundamentally, this is related to the diffraction limit. A smaller V corresponds to a larger radiative decay rate and more significant roughness scattering, leading to a lower Q. Different-type resonators possess their own unique properties, but the trade-off between high Q and small V still exists. For example, whispering-gallery mode cavities possess ultrahigh Q factors, while the mode volumes are relatively large; for photonic crystal cavities, sub-wavelength light confinement can be realized whereas the Q factors are relatively low.Unlike the efforts to improve the Q/ √ V figure of merit of the cavities, here we propose to reach the strong coupling regime via dark state resonances, which removes the requirement for high Q and small V for the same cavity. By coupling the originally weak-coupled cavity QED system with high cavity dissipation to an auxiliary cavity mode with high-Q but large V , a strong dark state interaction takes place. We demonstrate that vacuum Rabi oscillations and anharmonicity in the polariton dressed states occur even when the cavity decay rate is FIG. 1. (color online) (a) Schematic of the cavity QED system coupled to an auxiliary cavity. (b) Energy level diagram of the coupled system. The lowest four energy levels are plotted, i...

Motional ground-state cooling and quantum-coherent manipulation of mesoscopic mechanical systems are crucial goals in both fundamental physics and applied science. We demonstrate that the motional ground state can be achieved in the highly unresolved sideband regime, through coherent auxiliary cavity interferences. We further illustrate coherent strong Rabi coupling between indirectly coupled and individually optimized mechanical resonators and optical cavities through effective dark-mode interaction. The proposed approach provides a platform for quantum manipulation of mesoscopic mechanical devices beyond the resolved sideband limit.

Anti-Stokes one-photon luminescence from a single gold nanorod is experimentally investigated. The anti-Stokes emission of gold nanorods is enhanced and strongly modulated by localized surface plasmon resonance (LSPR). It is found that the polarization dependence of the anti-Stokes emission is in strong correlation with that of the Stokes emission. Further experiments provide evidence that LSPR significantly enhanced both excitation and emission processes. Moreover, the line shape of the anti-Stokes emission is dependent on the surface temperature, which is related to the distribution of free electrons near the Fermi level. This discovery provides an effective method in principle to probe localized temperature at nanoscale dimension. Here, the reported results about the anti-Stokes emission provide more understanding for the photoemission process from the plasmonic nanostructures.

Quantum manipulation of macroscopic mechanical systems is of great interest in both fundamental physics and applications ranging from high-precision metrology to quantum information processing.A crucial goal is to cool the mechanical system to its quantum ground state. In this review, we focus on the cavity optomechanical cooling, which exploits the cavity enhanced interaction between optical field and mechanical motion to reduce the thermal noise. Recent remarkable theoretical and experimental efforts in this field have taken a major step forward in preparing the motional quantum ground state of mesoscopic mechanical systems. This review first describes the quantum theory of cavity optomechanical cooling, including quantum noise approach and covariance approach; then the up-to-date experimental progresses are introduced. Finally, new cooling approaches are discussed along the directions of cooling in the strong coupling regime and cooling beyond the resolved sideband limit.

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We demonstrate that the nonlinear optomechanical interaction leads to parametric down-conversion, capable of generating polariton pairs formed by photons and phonons. The nonlinearity is resonantly enhanced through frequency matching, and such parametric down-conversion does not require the stringent condition that the single-photon optomechanical coupling strength g be on the order of the mechanical resonance frequency ω(m). We provide analytical results for the frequency matching condition and derive the nonlinear coefficient. Numerical simulations on polariton pair generation are presented, showing that photonlike polaritons, phononlike polaritons, and mixed photon-phonon polaritons can be selectively generated. Such nonlinear interaction offers a promising way for harnessing the optomechanical nonlinearity to manipulate photons and phonons.