Graphene plasmons provide a suitable alternative to noble-metal plasmons because they exhibit much larger confinement and relatively long propagation distances, with the advantage of being highly tunable via electrostatic gating. We report strong lightmatter interaction assisted by graphene plasmons, and in particular, we predict unprecedented high decay rates of quantum emitters in the proximity of a carbon sheet, large vacuum Rabi splitting and Purcell factors, and extinction cross sections exceeding the geometrical area in graphene ribbons and nanometer-sized disks. Our results provide the basis for the emerging and potentially far-reaching field of graphene plasmonics, offering an ideal platform for cavity quantum electrodynamics and supporting the possibility of single-molecule, single-plasmon devices. * To whom correspondence should be addressed Surfaces plasmons (SPs), the electromagnetic waves coupled to charge excitations at the surface of a metal, are the pillar stones of applications as varied as ultrasensitive optical biosensing, 1-3 photonic metamaterials, 4 light harvesting, 5,6 optical nano-antennas, 7 and quantum information processing. [8][9][10][11] However, even noble metals, which are widely regarded as the best available plasmonic materials, 12 are hardly tunable and exhibit large ohmic losses that limit their applicability to optical processing devices.In this context, doped graphene emerges as an alternative, unique two-dimensional plasmonic material that displays a wide range of extraordinary properties. 13 This atomically thick sheet of carbon is generating tremendous interest due to its superior electronic and mechanical properties, 14-20 which originate in part from its charge carriers of zero effective mass (the so-called Dirac fermions 18 ) that can travel for micrometers without scattering, even at room temperature. 21 Furthermore, rapid progress in growth and transfer techniques have sparked expectations for large-scale production of graphene-based devices and a wide range of potential applications such as high-frequency nanoelectronics, nanomechanics, transparent electrodes, and composite materials. 17 Recently, graphene has also been recognized as a versatile optical material for novel photonic 22 and optoelectronic applications, 23 such as solar cells, photodetectors, 24 light emitting devices, ultrafast lasers, optical sensing, 25 and metamaterials. 26 The outstanding potential of this atomic monolayer is emphasized by its remarkably high absorption 27,28 ≈ πα ≈ 2.3%, where α = e 2 /hc ≈ 1/137 is the fine-structure constant. Moreover, the linear dispersion of the Dirac fermions enables broadband applications, in which electric gating can be used to induce dramatic changes in the optical properties. 29All of these photonic and optoelectronic applications rely on the interaction of propagating far-field photons with graphene. Additionally, SPs bound to the surface of doped graphene exhibit a number of favorable properties that make graphene an attractive alternative to tr...

Control over the interaction between single photons and individual optical emitters is an outstanding problem in quantum science and engineering. It is of interest for ultimate control over light quanta, as well as for potential applications such as efficient photon collection, single-photon switching and transistors, and long-range optical coupling of quantum bits. Recently, substantial advances have been made towards these goals, based on modifying photon fields around an emitter using high-finesse optical cavities. Here we demonstrate a cavity-free, broadband approach for engineering photon-emitter interactions via subwavelength confinement of optical fields near metallic nanostructures. When a single CdSe quantum dot is optically excited in close proximity to a silver nanowire, emission from the quantum dot couples directly to guided surface plasmons in the nanowire, causing the wire's ends to light up. Non-classical photon correlations between the emission from the quantum dot and the ends of the nanowire demonstrate that the latter stems from the generation of single, quantized plasmons. Results from a large number of devices show that efficient coupling is accompanied by more than 2.5-fold enhancement of the quantum dot spontaneous emission, in good agreement with theoretical predictions.

It is well known that light quanta (photons) can interact with each other in nonlinear media, much like massive particles do, but in practice these interactions are usually very weak. Here we describe a novel approach to realize strong nonlinear interactions at the single-photon level. Our method makes use of recently demonstrated efficient coupling between individual optical emitters and tightly confined, propagating surface plasmon excitations on conducting nanowires. We show that this system can act as a nonlinear two-photon switch for incident photons propagating along the nanowire, which can be coherently controlled using quantum optical techniques. As a novel application, we discuss how the interaction can be tailored to create a single-photon transistor,where the presence or absence of a single incident photon in a "gate" field is sufficient to completely control the propagation of subsequent "signal" photons.

THEORY OF OPTOMECHANICAL EIT, EIA AND PARAMETRIC AMPLIFICATIONHere we provide a theoretical treatment of some of the main aspects of EIT [1][2][3][4], EIA [5] and parametric amplification [6][7][8] in optomechanical systems. Modeling the optomechanical system with the Hamiltonianit is possible to linearize the operation of the system, under the influence of a control laser at ω c , about a particular steady-state given by intracavity photon amplitude α 0 and a static phonon shift β 0 . The interaction of the mechanics and pump photons at ω c with secondary "probe" photons at ω s = ω c ± ∆ with two-photon detuning ∆ can then be modeled by making the substitutionŝAssuming that the pump is much larger than the probe, |α 0 | |α ± |, the pump amplitude is left unaffected and the equations for each sideband amplitude α ± are found to beWe have defined ∆ OC = ω o − ω c as the pump detuning from the optical cavity (including the static optomechanical shift, ω o ), and β + = β * − . In these situations it is typical to define G = gα 0 , as the effective optomechanical coupling rate between a sideband and the mechanical subsystem, mediated by the pump. Red-detuned pump: Electromagnetically Induced TransparencyWith the pump detuned from the cavity by a two-photon detuning ∆, the spectral selectivity of the optical cavity causes the sideband populations to be skewed in a drastic fashion. It is then an acceptable approximation to neglect one of these sidebands, depending on whether the pump is on the red or blue side of the cavity. When the pump resides on the red side (∆ OC > 0), the α + is reduced and can be neglected. This is the rotating wave approximation (RWA) and is valid so long as ∆ κ. Then Eqs. (S3-S4) may be solved for the reflection and transmission coefficients r(ω s ) and t(ω s ) of the side-coupled cavity system. We find that These equations are plotted in Figs. S1 and S2.