Acoustic diamond resonators with ultrasmall mode volumes

Abstract

Quantum acoustodynamics (QAD) is a rapidly developing field of research, offering possibilities to realize and study macroscopic quantum-mechanical systems in a new range of frequencies and implement transducers and new types of memories for hybrid quantum devices. Here we propose a novel design for a versatile diamond QAD cavity operating at gigahertz (GHz) frequencies, exhibiting effective mode volumes of about 10 −4 λ 3. Our phononic crystal waveguide cavity implements a nonresonant analog of the optical lightning-rod effect to localize the energy of an acoustic mode into a deeply subwavelength volume. We demonstrate that this confinement can readily enhance the orbit-strain interaction with embedded nitrogen-vacancy (NV) centers towards the highcooperativity regime and enable efficient resonant cooling of the acoustic vibrations towards the ground state using a single NV. This architecture can be readily translated towards setup with multiple cavities in one-or two-dimensional phononic crystals and the underlying nonresonant localization mechanism will pave the way to further enhance optoacoustic coupling in phoxonic crystal cavities.

A spin-optomechanical quantum interface enabled by an ultrasmall mechanical and optical mode volume cavity

“…1. Diamond 1D nanobeam OMC with embedded concentrator, drawing from previous examples in silicon [5,7] and diamond [19,22,23] as well as ultrasmall mode volume photonic and phononic crystals [21,24] Additionally, the parametric coupling between the mechanical and optical resonators takes the form Ĥom = g om â † â b † + b , i.e., an optical resonance shift dependent on the position of the mechanical resonator. To linearize this interaction, we drive the optical cavity with a pump ω p = ω a + ∆.…”

“…Another interpretation of the increase in g sm with decreasing b is that of mechanical mode volume [21]: as b decreases, the strain energy density of the mechanical mode becomes more highly concentrated in the taper, thereby decreasing the mechanical mode volume V mech dramatically. We estimate through FEM that V mech /Λ 3 p and V mech /Λ 3 s drop from ∼ 10 −4 and ∼ 10 −3 , respectively, to ∼ 10 −6 and ∼ 10 −5 , respectively, as b decreases from 100 nm to 20 nm (Fig.…”

“…3d). Here, Λ p and Λ s are the longitudinal and shear wave velocities in bulk diamond [21]. As V mech decreases, g sm increases, which also increases the "mechanical Purcell enhancement."…”

“…Here, we propose an ultra-small mode volume spinoptomechanical interface in diamond for strong coupling between the mechanical mode of an optomechanical res- * These two authors contributed equally onator and an embedded group IV defect-vacancy complex. Our device introduces an optical resonance to previous ultra-small mechanical cavities for spin interfacing [21], while also improving previous mechanical mode volumes. We show that this device can be used to interact with a vacancy without optically exciting the spin at its native wavelength, operating at the cavity wavelength instead through a optomechanically mediated interaction.…”

“…FIG.1. Diamond 1D nanobeam OMC with embedded concentrator, drawing from previous examples in silicon[5,7] and diamond[19,22,23] as well as ultrasmall mode volume photonic and phononic crystals[21,24]. (a) Diagram of the nanobeam photonic crystal.…”