Optical laser fields have been widely used to achieve quantum control over the motional and internal degrees of freedom of atoms and ions, molecules and atomic gases. A route to controlling the quantum states of macroscopic mechanical oscillators in a similar fashion is to exploit the parametric coupling between optical and mechanical degrees of freedom through radiation pressure in suitably engineered optical cavities. If the optomechanical coupling is 'quantum coherent'--that is, if the coherent coupling rate exceeds both the optical and the mechanical decoherence rate--quantum states are transferred from the optical field to the mechanical oscillator and vice versa. This transfer allows control of the mechanical oscillator state using the wide range of available quantum optical techniques. So far, however, quantum-coherent coupling of micromechanical oscillators has only been achieved using microwave fields at millikelvin temperatures. Optical experiments have not attained this regime owing to the large mechanical decoherence rates and the difficulty of overcoming optical dissipation. Here we achieve quantum-coherent coupling between optical photons and a micromechanical oscillator. Simultaneously, coupling to the cold photon bath cools the mechanical oscillator to an average occupancy of 1.7 ± 0.1 motional quanta. Excitation with weak classical light pulses reveals the exchange of energy between the optical light field and the micromechanical oscillator in the time domain at the level of less than one quantum on average. This optomechanical system establishes an efficient quantum interface between mechanical oscillators and optical photons, which can provide decoherence-free transport of quantum states through optical fibres. Our results offer a route towards the use of mechanical oscillators as quantum transducers or in microwave-to-optical quantum links.

Abstract:We report on the design, fabrication, and measurement of ultrathin film a-Si:H solar cells with nanostructured plasmonic back contacts, which demonstrate enhanced short circuit current densities compared to cells having flat or randomly textured back contacts. The primary photocurrent enhancement occurs in the spectral range from 550 nm to 800 nm. We use angle-resolved photocurrent spectroscopy to confirm that the enhanced absorption is due to coupling to guided modes supported by the cell. Full-field electromagnetic simulation of the absorption in the active a-Si:H layer agrees well with the experimental results. Furthermore, the nanopatterns were fabricated via an inexpensive, scalable, and precise nanopatterning method. These results should guide design of optimized, non-random nanostructured back reflectors for thin film solar cells.

We present experimental observations of strong electric and magnetic interactions between split ring resonators (SRRs) in metamaterials. We fabricated near-infrared (1.4 µm) planar metamaterials with different inter-SRR spacings along different directions. Our transmission measurements show blueshifts and redshifts of the magnetic resonance, depending on SRR orientation relative to the lattice. The shifts agree well with a simple model with simultaneous magnetic and electric near-field dipole coupling. We also find large broadening of the resonance, accompanied by a decrease in effective cross section per SRR with increasing density. These effects result from superradiant scattering. Our data shed new light on Lorentz-Lorenz approaches to metamaterials. 78.20.Ci Since the seminal work of Veselago and Pendry [1], many experimentalists have started to pursue optical materials with negative permittivity ǫ and permeability µ [2]. The key motivation is the prospect of 'transformation optics', which allows arbitrary bending of electromagnetic fields, provided one has full control over ǫ and µ. Particularly exciting examples are perfect lenses, that allow perfect sub-diffraction focusing [1], and 'cloaks' in which light passes an object without scattering [3]. Full control over ǫ and µ requires 'metamaterials' of artificial nano-scatterers with electric and magnetic response, arranged in sub-wavelength arrays. The archetypical building block is the split ring resonator (SRR) consisting of a single cut metal loop with an inductive response. In recent years the field of metamaterials has made tremendous progress in shifting the resonant response from microwave to optical frequencies [4,5,6,7,8]. An important conceptual question is whether the effective response captured by ǫ and µ is influenced by coupling between constituents. Coupling between SRRs in vertical 1D stacks [9,10] has attracted great attention lately outside the scope of metamaterials, e.g., for magnetic waveguides [9,11,12,13] In this Letter we present the first measurements of strong constituent coupling in planar SRR metamaterial arrays. We fabricated and characterized SRR lattices with a magnetic response at λ = 1.4 µm [5,6] in which we vary the spacing between SRRs along different lattice directions independently. We observe large redshifts and blueshifts in the transmission resonances depending on SRR orientation relative to the lattices. We establish that in-plane electric-electric dipole coupling and out-of-plane magnetic-magnetic dipole coupling are strong competing interactions. We explain the shifts by a quasistatic electric and magnetic dipole coupling model [10], that enables us to determine the magnetic and electric polarizability of SRRs. Finally, we discuss the role of dynamic effects on the metamaterial resonance, which are evident in density- We have fabricated Au SRRs on glass substrates by electron beam lithography and lift-off using PMMA resist [13], without any adhesive layers. We took great care to produce SRRs of identical dimens...

Nonreciprocal components, such as isolators and circulators, provide highly desirable functionalities for optical circuitry. This motivates the active investigation of mechanisms that break reciprocity, and pose alternatives to magneto-optic effects in on-chip systems. In this work, we use optomechanical interactions to strongly break reciprocity in a compact system. We derive minimal requirements to create nonreciprocity in a wide class of systems that couple two optical modes to a mechanical mode, highlighting the importance of optically biasing the modes at a controlled phase difference. We realize these principles in a silica microtoroid optomechanical resonator and use quantitative heterodyne spectroscopy to demonstrate up to 10 dB optical isolation at telecom wavelengths. We show that nonreciprocal transmission is preserved for nondegenerate modes, and demonstrate nonreciprocal parametric amplification. These results open a route to exploiting various nonreciprocal effects in optomechanical systems in different electromagnetic and mechanical frequency regimes, including optomechanical metamaterials with topologically non-trivial properties.

We show with both experiment and calculation that highly confined surface plasmon polaritons can be efficiently excited on metallic nanowires through the process of mode transformation. One specific mode in a metallic waveguide is identified that adiabatically transforms to the confined nanowire mode as the waveguide width is reduced. Phase- and polarization-sensitive near-field investigation reveals the characteristic antisymmetric polarization nature of the mode and explains the coupling mechanism.

† These authors contributed equally to this work.Quantum control of engineered mechanical oscillators can be achieved by coupling the oscillator to an auxiliary degree of freedom, provided that the coherent rate of energy exchange exceeds the decoherence rate of each of the two sub-systems. We achieve such quantumcoherent coupling between the mechanical and optical modes of a micro-optomechanical system. Simultaneously, the mechanical oscillator is cooled to an average occupancy of n=1.7±0.1 motional quanta. Pulsed optical excitation reveals the exchange of energy between the optical light field and the micromechanical oscillator in the time domain at the level of less than one quantum on average. These results provide a route towards the realization of efficient quantum interfaces between mechanical oscillators and optical fields.Mechanical oscillators are at the heart of many precision experiments, such as single spin detection [1] or atomic force microscopy and can exhibit exceptionally low dissipation. The possibility to control the quantum states of such engineered micro-or nanomechanical oscillators, similar to the control achieved over the motion of trapped ions [2], has been a subject of longstanding interest [3, 4], with prospects of quantum state transfer [5][6][7][8], entanglement of mechanical oscillators [9] and testing of quantum theory in macroscopic systems [10, 11]. However, such experiments require coupling the mechanical oscillator to an auxiliary system-whose quantum state can be controlled and measured-with a coherent coupling rate that exceeds the decoherence rate of each of the subsystems. Equivalent control of atoms has been achieved in the context of cavity Quantum Electrodynamics (cQED [12]) and has over the past decades been extended to various other systems such as superconducting circuits [13], solid state emitters [14] or the light field itself [15].Recently, elementary quantum control at the single-phonon level has been demonstrated for the first time, by coupling a piezo-electrical dilatation oscillator to a superconducting qubit [16]. An alternative and highly versatile route is to use the radiation-pressure-induced coupling of optical and mechanical degrees of freedom, inherent to opti- * Electronic address: tobias.kippenberg@epfl.ch cal microresonators [17], which can be engineered in numerous forms at the micro-or nanoscale [18][19][20]. This coupling can be described by the interaction Hamiltonian H = g 0â †â (b † +b), whereâ (b) is the photon (phonon) annihilation operator, is the reduced Planck constant and g 0 is the vacuum optomechanical coupling rate. In the resolved sideband regime (where the mechanical resonance frequency Ω m exceeds the cavity energy decay rate κ), with an intense laser tuned close to the lower optomechanical sideband, one obtains in the rotating wave approximation the effective Hamiltonianfor the operatorsâ andb now displaced by their steady state values. We have introduced here the field-enhanced coupling rate [21, 22] g = √n c g 0 , wheren c de...

We investigate the focusing of surface plasmon polaritons (SPPs) excited with 1.5 microm light in a tapered Au waveguide on a planar dielectric substrate by experiments and simulations. We find that nanofocusing can be obtained when the asymmetric bound mode at the substrate side of the metal film is excited. The propagation and concentration of this mode to the tip is demonstrated. No sign of a cutoff waveguide width is observed as the SPPs propagate along the tapered waveguide. Simulations show that such concentrating behavior is not possible for excitation of the mode at the low-index side of the film. The mode that enables the focusing exhibits a strong resemblance to the asymmetric mode responsible for focusing in conical waveguides. This work demonstrates a practical implementation of plasmonic nanofocusing on a planar substrate.

Strong interaction between light and a single quantum emitter is essential to a great number of applications, including single photon sources. Microcavities and plasmonic antennas have been used frequently to enhance these interactions through the Purcell effect. Both can provide large emission enhancements: the cavity typically through long photon lifetimes (high Q), and the antenna mostly through strong field enhancement (low mode volume V ). In this work, we demonstrate that a hybrid system, which combines a cavity and a dipolar antenna, can achieve stronger emission enhancements than the cavity or antenna alone. We show that such systems can be used as a versatile platform to tune the bandwidth of enhancement to any desired value, while simultaneously boosting emission enhancement. Our fully consistent analytical model allows to identify the underlying mechanisms of boosted emission enhancement in hybrid systems, which include radiation damping and constructive interference between multiple-scattering paths. Additionally, we find excellent agreement between strongly boosted enhancement spectra from our analytical model and from finite-element simulations on a realistic cavity-antenna system. Finally, we demonstrate that hybrid systems can simultaneously boost emission enhancement and maintain a near-unity outcoupling efficiency into a single cavity decay channel, such as a waveguide.