Showing papers by "Jay E. Sharping published in 2020"

Casimir spring and dilution in macroscopic cavity optomechanics

Abstract: The Casimir force was predicted in 1948 as a force arising between macroscopic bodies from the zero-point energy. At finite temperatures, it has been shown that a thermal Casimir force exists due to thermal rather than zero-point energy and there are a growing number of experiments that characterize the effect at a range of temperatures and distances. In addition, in the rapidly evolving field of cavity optomechanics, there is an endeavour to manipulate phonons and enhance coherence. We demonstrate a way to realize a Casimir spring and engineer dilution in macroscopic optomechanics, by coupling a metallic SiN membrane to a photonic re-entrant cavity. The attraction of the spatially localized Casimir spring mimics a non-contacting boundary condition, giving rise to increased strain and acoustic coherence through dissipation dilution. This provides a way to manipulate phonons via thermal photons leading to ‘in situ’ reconfigurable mechanical states, to reduce loss mechanisms and to create additional types of acoustic nonlinearity—all at room temperature. An optomechanical cavity comprising a re-entrant cavity and membrane resonators can be tuned in and out of the Casimir regime. At the transition between the two regimes, the mechanical resonators exhibit a change in stiffness—the Casimir spring.

Joints and shape imperfections in high-Q 3D SRF cavities for RF optomechanics

Abstract: In this paper, we report on simulations of two types of high-Q 3-dimensional cavities: cylindrical TE011 and coaxial quarter-wave stub. We investigate the dependence of Q on the practical implementation tolerances of gaps between components, shape imperfections, and frequency tuning strategies. We find that cylindrical cavities can maintain high Q for designs that include frequency tuning and mechanical elements, provided extraordinary care is taken with shape and gap tolerance during construction and assembly. Coaxial stub cavities can be made with variable frequency while maintaining high Q, but they require more creativity to include a mechanical element. Finally, we report on a coaxial stub cavity, incorporating a conically shaped stub that confines the electric field near the stub’s tip, thus enhancing field–matter interactions near the tip.

Meissner levitation of a millimeter size neodymium magnet within a superconducting radio frequency cavity

Abstract: We report on the magnetic levitation of a millimeter sized neodymium permanent magnet within the interior of a superconducting radio frequency (SRF) cavity. To the best of our knowledge, this is the first experimental work on levitating a magnet within an SRF cavity. The cavity is a coaxial quarter wave microwave resonator made from 6061 aluminum, having a resonance frequency of 10GHz and a loaded Q of 1400. The cylindrical magnet (N50) has a height of 1 mm, a diameter of 0.75 mm, a mass of 4 mg, and a remanence of 1.44 T. This produces a peak magnetic field 140 times greater than the critical field of aluminum. Our measurements are consistent over several heating and cooling cycles. Our work provides a path towards a novel optomechanical system.

Casimir spring and dilution in macroscopic cavity optomechanics

Abstract: The Casimir force was predicted in 1948 as a force arising between macroscopic bodies from the zero-point energy. At finite temperatures it has been shown that a thermal Casimir force exists due to thermal rather than zero-point energy and there are a growing number of experiments that characterise the effect at a range of temperatures and distances. Additionally, in the rapidly evolving field of cavity optomechanics there is an endeavor to manipulate phonons and enhance coherence. We demonstrate a new way to achieve this through the first observation of Casimir spring and dilution in macroscopic optomechanics, by coupling a metallic SiN membrane to a photonic re-entrant cavity. The attraction of the spatially-localised Casimir spring mimics a non-contacting boundary condition giving rise to increased strain and acoustic coherence through dissipation dilution. This work invents a new way to manipulate phonons via thermal photons leading to ``in situ'' reconfigurable mechanical states, to reduce loss mechanisms and to create new types of acoustic non-linearity -- all at room temperature.