Year: 2013
Type: other
Abstract: This thesis focuses on cavity optomechanics with an optically levitated dielectric object.We develop the underlying theory and propose and analyze various protocols to prepare these macroscopic systems in superposition states.Optical levitation circumvents the direct thermal coupling of the mechanical oscillator to its environment and holds the promise to enable ground-state cooling even at room temperature.This thesis approaches this novel optomechanical system from two different angles reflected in the division into the main parts of Theory and Protocols.In the first part of the thesis, we derive a theoretical description of the system from first principles.A master equation describing the interaction of light with dielectric objects of arbitrary sizes and shapes is developed.It does not rely on the point-particle approximation by taking into account scattering processes to all orders in perturbation theory and treats both the motion of the object and the light quantum-mechanically.This formalism extends the standard master-equation approach to the case where interactions among different modes of the environment are considered.We apply this general method to the specific setup of levitating dielectrics in optical cavities.Apart from photon scattering, we also take into account various other dissipation processes, e.g., blackbody radiation, scattering of gas molecules, or coupling to internal vibrational modes, and compare them to the coherent coupling rates of the system.To analyze the feasibility of ground-state cooling, we derive the steady-state phonon numbers without relying on resolved-sideband or bad-cavity approximations.Within this theoretical framework, the optomechanical performance for realistic experimental parameters is analyzed.We show that cavity cooling of the center-of-mass (cm) mode to the motional ground state is possible for spheres with radius R 260nm.The focus of the second part of the thesis is to provide protocols for the preparation of the mechanical oscillator in nonclassical states.The realization of superposition states is essential to most of the proposed applications of nano-mechanical oscillators, i.e., for sensing or to find an answer to foundational questions.We confront this problem from three different angles.First, we propose several state-preparation protocols relying on the efficient coupling to single photons, thus projecting their nonclassical ii Abstract state to the mechanical oscillator.These protocols require different cavity finesses and coupling strengths and thus are suitable for implementation in various regimes.Second, preparation of the nonclassical state by coupling to a qubit, e.g., a two-level atom, via the cavity mode is proposed.We show that it is possible to use such a coupling for the dissipative preparation of nonclassical states with high fidelity.This setup can be extended to a nonlinear many-partite system via stroboscopic driving of the oscillators and we illustrate the effectiveness of the state-preparation protocols even in this case.Results from both the single-photon and the dissipative-qubit protocol are not restricted to levitating spheres and may be applied to other optomechanical systems.Third, the last protocol exploits the levitation of the mechanical oscillator and is thus in particular suitable for the setup described above.We propose an optomechanical version of a double-slit experiment achieving spatial superpositions of the order on the size of the dielectric.This method provides unprecedented bounds for objective collapse models of the wave function by merging techniques and insights from cavity quantum optomechanics and matter-wave interferometry.In summary, this thesis aims at advancing the field of optomechanics with levitating dielectrics by providing a theoretical description for this system and various protocols for the preparation of nonclassical states.
Source: Max Planck Digital Library
Author: Anika C. Pflanzer
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W1523016157