Muhammad Asjad

Reservoir engineering of a mechanical resonator: generating a macroscopic superposition state and monitoring its decoherence

A deterministic scheme for generating a macroscopic superposition state of a nanomechanical resonator is proposed. The nonclassical state is generated through a suitably engineered dissipative dynamics exploiting the optomechanical quadratic interaction with a bichromatically driven optical cavity mode. The resulting driven dissipative dynamics can be employed for monitoring and testing the decoherence processes affecting the nanomechanical resonator under controlled conditions.

Quantum phase gate for optical qubits with cavity quantum optomechanics

We show that a cavity optomechanical system formed by a mechanical resonator simultaneously coupled to two modes of an optical cavity can be used for the implementation of a deterministic quantum phase gate between optical qubits associated with the two intracavity modes. The scheme is realizable for sufficiently strong single-photon optomechanical coupling in the resolved sideband regime, and is robust against cavity losses.

Suppression of Stokes scattering and improved optomechanical cooling with squeezed light

We develop a theory of optomechanical cooling with a squeezed input light field. We show that Stokes heating transitions can be \emph{fully} suppressed when the driving field is squeezed below the vacuum noise level at an appropriately selected squeezing phase and for a finite amount of squeezing. The quantum backaction limit to laser cooling can be therefore moved down to zero and the resulting final temperature is then solely determined by the ratio between the thermal phonon number and the optomechanical cooperativity parameter, independently of the actual values of the cavity linewidth and mechanical frequency. Therefore driving with a squeezed input field allows to prepare nanomechanical resonators, even with low resonance frequency, in their quantum ground state with a fidelity very close to one.

Mechanical Einstein-Podolsky-Rosen entanglement with a finite-bandwidth squeezed reservoir

We describe a scheme for entangling mechanical resonators which is efficient also beyond the resolved sideband regime. It employs the radiation pressure force of the squeezed light produced by a degenerate optical parametric oscillator, which acts as a reservoir of quantum correlations (squeezed reservoir), and it is effective when the spectral bandwidth of the reservoir and the fields frequencies are appropriately selected. It allows for the steady state preparation of mechanical resonatrs in entangled EPR states and can be extended to the preparation of many entangled pairs of resonators which interact with the same light field, in a situation in which the optomechanical system realizes a star-like harmonic network.

Large distance continuous variable communication with concatenated swaps

The radiation–pressure interaction between electromagnetic fields and mechanical resonators can be used to efficiently entangle two light fields coupled to the same mechanical mode. We analyze the performance of this process under realistic conditions, and we determine the effectiveness of the resulting entanglement as a resource for quantum teleportation of continuous-variable light signals over large distances, mediated by concatenated swap operations. We study the sensitiveness of the protocol to the quality factor of the mechanical systems, and its performance in non-ideal situations in which losses and reduced detection efficiencies are taken into account.

Quantum Enhanced optomechanical cooling with squeezed light

We analyze the performance of optomechanical cooling in the presence of a squeezed reservoir. We discuss a dynamics which allows for the full suppression of light-induced heating transitions in an optomechanical system when the driving field is squeezed below the vacuum noise level at an appropriately selected squeezing phase and for a finite amount of squeezing.

Enhancing the Entanglement by Negative Feedback

Using a negative feedback in the cold damping approach it will be shown that it is possible to increase the entanglement between two optical modes exiting from a Fabry-Perot cavity with an oscillating end mirror.