We show how stationary entanglement between an optical cavity field mode and a macroscopic vibrating mirror can be generated by means of radiation pressure. We also show how the generated optomechanical entanglement can be quantified, and we suggest an experimental readout scheme to fully characterize the entangled state. Surprisingly, such optomechanical entanglement is shown to persist for environment temperatures above 20 K using state-of-the-art experimental parameters.

We show how stationary entanglement between an optical cavity field mode and a macroscopic vibrating mirror can be generated by means of radiation pressure. We also show how the generated optomechanical entanglement can be quantified and we suggest an experimental readout-scheme to fully characterize the entangled state. Surprisingly, such optomechanical entanglement is shown to persist for environment temperatures above 20K using state-of-the-art experimental parameters.PACS numbers: 03.67. Mn, 42.50.Lc, 05.40.Jc Entanglement, "the characteristic trait of quantum mechanics" [1], has raised widespread interest in different branches of physics. It provides insight into the fundamental structure of physical reality [2] and it has become a basic resource for many quantum information processing schemes [3]. So far entanglement has been experimentally prepared and manipulated using microscopic quantum systems such as photons, atoms and ions [3, 4]. Nothing in the principles of quantum mechanics prevents macroscopic systems to attain entanglement. However, the answer to the question as to what extent entanglement should hold when going towards "classical" systems is yet unknown [5]. Therefore it is of crucial importance to investigate the possibilities to obtain entangled states of macroscopic systems [6] and to study the robustness of entanglement against temperature [7]. Experiments in this direction include single-particle interference of macro-molecules [8], the demonstration of entanglement between collective spins of atomic ensembles [9], and of entanglement in Josephson-junction qubits [10]. Mechanical oscillators are of particular interest since they resemble a prototype of "classical" systems. Thanks to the fast-developing field of microfabrication, micro-or nano-mechanical oscillators can now be prepared and controlled to a very high precision [11]. In addition, several theoretical proposals exist that suggest how to reach the quantum regime for such systems [12]. Experimentally, quantum limited measurements have been developed that could allow ground state detection [13]. However, quantum effects in mechanical oscillators have not been demonstrated to date.Optomechanical coupling via radiation pressure [14] is a promising approach to prepare and manipulate quantum states of mechanical oscillators. Proposals range from the quantum state transfer from light to a mechanical oscillator to entangling two such oscillators [15,16,17,18]. In this paper we propose an experimen-tal scheme to create and probe optomechanical entanglement between a light field and a mechanical oscillator. This is achieved using a bright laser field that resonates inside a cavity and couples to the position and momentum of a moving (micro)mirror. The proposal is based on feasible experimental parameters in accordance with current state of the art optics and microfabrication. In contrast to other proposals [15,18] it neither requires non-classical states of light nor temperatures close to the oscillator's ground state. Entanglement is s...

Can entanglement and the quantum behavior in physical systems survive at arbitrary high temperatures? In this Letter we show that this is the case for a electromagnetic field mode in an optical cavity with a movable mirror in a thermal state. We also identify two different dynamical regimes of generation of entanglement separated by a critical coupling strength.

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It is shown here that a straightforward procedure can be used to quantize the linearized equations for an electromagnetic field in a plasma. This leads to a definition of an effective mass for the transverse photons, and a different one for the longitudinal photons, or plasmons. Both masses are simply proportional to the electron plasma density. A nonlinear perturbative analysis can also be used to extend the quantization procedure, in order to include the ponderomotive force effects. This leads to the definition of a photon charge operator. The mean value of this operator, for a quantum state with a photon occupation number equal to 1, is the equivalent charge of the photon in a plasma.