Macroscopic Coherence for a Trapped Electron

We investigate the possibility of generating quantum macroscopic coherence phenomena by means of relativistic effects on a trapped electron.Comment: 6 pages, RevTex, accepted by Phys. Rev.

Measuring the Cyclotron State of a Trapped Electron

We propose the cyclotron state retrieval of an electron trapped in a Penning trap by using different measurement schemes based on suitable modifications of the applied electromagnetic fields and exploiting the axial degree of freedom as a probe. A test for matter-antimatter symmetry of the quantum state is proposed.Comment: 8 pages, RevTex, 2 figures available from the authors, accepted by Phys. Rev.

Optomechanical detection of weak forces

Optomechanical systems are often used for the measurement of weak forces. Feedback loops can be used in these systems for achieving noise reduction. Here we show that even though feedback is not able to improve the signal to noise ratio of the device in stationary conditions, it is possible to design a nonstationary strategy able to improve the sensitivity.Comment: 12 pages, 6 figures, contribution to the proceedings of the SPIE Conference on Fluctuations and Nois

Quantum state protection using all-optical feedback

An all-optical feedback scheme in which the output of a cavity mode is used to influence the dynamics of another cavity mode is considered. We show that under ideal conditions, perfect preservation against decoherence of a generic quantum state of the source mode can be achieved.Comment: 10 pages, 4 figures, to appear in the Dan Walls Memorial Volume, edited by H. Carmichael, R. Glauber, and M. Scully, to be published by Springe

Feedback Control of Two-mode Output Entanglement and Steering in Cavity Optomechanics

We show that the closed-loop control obtained by feeding back the derivative of the signal from the homodyne measurement of one mode of the light exiting a two-mode optical cavity interacting with a mechanical resonator permits to control and increase optical output entanglement. In particular, the proposed feedback-enhanced setup allows to achieve a fidelity of coherent state teleportation greater than the threshold value of 2/3 for secure teleportation, and two-way steering between the two cavity's output modes down the line in presence of loss, which otherwise would not be possible without feedbackComment: 10 page

Endoscopic Tomography and Quantum-Non-Demolition

We propose to measure the quantum state of a single mode of the radiation field in a cavity---the signal field---by coupling it via a quantum-non-demolition Hamiltonian to a meter field in a highly squeezed state. We show that quantum state tomography on the meter field using balanced homodyne detection provides full information about the signal state. We discuss the influence of measurement of the meter on the signal field.Comment: RevTeX, 10 pages, 1 eps figure with psfig. To appear In Physical Review A 59 (January 1999

Stationary entanglement between macroscopic mechanical oscillators

We show that the optomechanical coupling between an optical cavity mode and the two movable cavity end mirrors is able to entangle two different macroscopic oscillation modes of the mirrors. This continuous variable entanglement is maintained by the light bouncing between the mirrors and is robust against thermal noise. In fact, it could be experimentally demonstrated using present technology.Comment: 9 pages, 4 figures. To be published on the Special Issue of EPJD "Quantum fluctuations and coherence in optical and atomic structures", edited by J. Eschner, A. Gatti, A. Maitre and G. Morigi v3: an error in a parameter definition correcte