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...