Organic semiconductors have generated considerable interest for their potential for creating inexpensive and flexible devices easily processed on a large scale [1][2][3][4][5][6][7][8][9][10][11]. However technological applications are currently limited by the low mobility of the charge carriers associated with the disorder in these materials [5][6][7][8]. Much effort over the past decades has therefore been focused on optimizing the organisation of the material or the devices to improve carrier mobility. Here we take a radically different path to solving this problem, namely by injecting carriers into states that are hybridized to the vacuum electromagnetic field. These are coherent states that can extend over as many as 10 5 molecules and should thereby favour conductivity in such materials. To test this idea, organic semiconductors were strongly coupled to the vacuum electromagnetic field on plasmonic structures to form polaritonic states with large Rabi splittings ∼ 0.7 eV. Conductivity experiments show that indeed the current does increase by an order of magnitude at resonance in the coupled state, reflecting mostly a change in field-effect mobility as revealed when the structure is gated in a transistor configuration. A theoretical quantum model is presented that confirms the delocalization of the wave-functions of the hybridized states and the consequences on the conductivity. While this is a proof-of-principle study, in practice conductivity mediated by light-matter hybridized states is easy to implement and we therefore expect that it will be used to improve organic devices. More broadly our findings illustrate the potential of engineering the vacuum electromagnetic environment to modify and to improve properties of materials.Light and matter can enter into the strong coupling regime by exchanging photons faster than any competing dissipation processes. This is normally achieved by placing the material in a confined electromagnetic environment, such as a Fabry-Perot (FP) cavity composed of two parallel mirrors that is resonant with an electronic transition in the material. Alternatively, one can use surface plasmon resonances as in this study. Strong coupling leads to the formation of two hybridized light-matter polaritonic states, P+ and P-, separated by the so-called Rabi splitting, as illustrated in Figure 1a. According to quantum electrodynamics, in the absence of dissipation, the Rabi splitting for a single molecule is given bywhere ω is the cavity resonance or transition energy ( the reduced Planck constant), 0 the vacuum permittivity, v the mode volume, d the transition dipole moment of the material and n ph the number of photons present in the system. The last term implies that, even in the dark, the Rabi splitting has a finite value which is due to the interaction with the vacuum electromagnetic field. This vacuum Rabi splitting can be further increased by coupling a large number N of oscillators to the electromagnetic mode since Ω N R ∝ √ N [12]. In this ensemble coupling, in addition to P+ an...

We provide a general framework to describe cooling of a micromechanical oscillator to its quantum ground state by means of radiation-pressure coupling with a driven optical cavity. We apply it to two experimentally realized schemes, back-action cooling via a detuned cavity and cold-damping quantum-feedback cooling, and we determine the ultimate quantum limits of both schemes for the full parameter range of a stable cavity. While both allow to reach the oscillator's quantum ground state, we find that back-action cooling is more efficient in the good cavity limit, i.e. when the cavity bandwidth is smaller than the mechanical frequency, while cold damping is more suitable for the bad cavity limit. The results of previous treatments are recovered as limiting cases of specific parameter regimes.

Equations ͑22͒-͑28͒, which give the exact expressions for the stationary position and momentum variances of the mechanical oscillator in the detuning-induced back-action cooling case, contain a number of misprints. The correct expression of the two variances instead readsThe parameters s 1 and s 2 are, respectively, given by the stability conditions of Eqs. ͑20a͒ and ͑20b͒. At the ground state both variances are equal to 1 / 2 and therefore realizing ground state cooling means achieving b q , b p , d q , d p → 0. We also take the opportunity to comment on the definition of the feedback force of Eq. ͑39b͒ in terms of the estimated phase quadrature ␦Y est defined in Eq. ͑42͒. Dividing by ͱ in the definition of ␦Y est is customary in quantum feedback theory ͓1͔, and means assuming that the feedback action automatically compensates for the loss of signal due to nonideal detection, independently of the value of the feedback gain g cd . However, this choice may be misleading because the parameter g cd becomes the feedback gain without taking into account this automatic compensation and it is therefore dependent upon . A simpler choice which avoids this problem is to define ␦Y est without dividing by ͱ , i.e.,which is a sort of output phase quadrature integrated over the cavity bandwidth. In this way the parameter g cd coincides with the actual gain of the feedback loop. All the subsequent equations of the paper remain correct provided that one performs the rescaling g͑͒ → ͱ g͑͒, which implies g cd → ͱ g cd and g 2 → ͱ g 2 . This means in particular that the measurement noise term of Eq. ͑44͒ is independent of , while the feedback correction to the mechanical susceptibility in Eq. ͑45͒ becomes proportional to ͱ . In the limit → 0 therefore feedback is no longer able to modify the mechanical response and has the only effect of adding the measurement noise. ͓1͔ H. M. Wiseman and G. J. Milburn, Phys. Rev. Lett. 70, 548 ͑1993͒.PHYSICAL REVIEW A 79, 039903͑E͒ ͑2009͒

We perform an analysis of the optomechanical entanglement between the experimentally detectable output field of an optical cavity and a vibrating cavity end-mirror. We show that by a proper choice of the readout (mainly by a proper choice of detection bandwidth) one can not only detect the already predicted intracavity entanglement but also optimize and increase it. This entanglement is explained as being generated by a scattering process owing to which strong quantum correlations between the mirror and the optical Stokes sideband are created. All-optical entanglement between scattered sidebands is also predicted and it is shown that the mechanical resonator and the two sideband modes form a fully tripartite-entangled system capable of providing practicable and robust solutions for continuous variable quantum communication protocols.