Tunable Amplification and Cooling of a Diamond Resonator with a Microscope

At a Glance

Metadata	Details
Publication Date	2021-07-27
Journal	Physical Review Applied
Authors	Harishankar Jayakumar, Behzad Khanaliloo, David P. Lake, Paul E. Barclay
Institutions	University of Calgary
Citations	4
Analysis	Full AI Review Included

Technical Documentation & Analysis: Tunable Optomechanical Control in Diamond Nanoresonators

Executive Summary

This research demonstrates a novel, cavity-free method for achieving tunable optomechanical damping and amplification in a single-crystal diamond (SCD) nanoresonator, leveraging photothermal back action controlled by a confocal microscope focus. This breakthrough is highly relevant for advancing quantum spin-optomechanics using diamond Nitrogen Vacancy (NV) centers.

Cavity-Free Control: The system achieves tunable optomechanical back action (damping and amplification) without requiring an external optical cavity, etalon, or wavelength-tunable laser, simplifying the experimental setup.
Significant Cooling: Normal mode cooling of the diamond nanobeam was demonstrated from room temperature (300 K) down to an effective temperature (T_eff) of approximately 80 K.
High Q-Factor Performance: The mechanical quality factor (Q_m) increased significantly at cryogenic temperatures, reaching 5.8 x 10⁵ at 5 K, enabling low-power self-oscillation (60 µW).
Quantum Application Potential: The induced dynamic stress fields (~100 MPa) are predicted to enable ultra-high-rate coupling between mechanical motion (phonons) and NV center electronic spins, with coupling rates up to 100 THz.
Material Requirement: The device relies on high-purity, optical-grade SCD material and precise nanoscale fabrication (50 x 0.5 x 0.25 µm³ nanobeam) combined with thin-film Titanium (Ti) metalization to enhance photothermal effects.

Technical Specifications

The following table summarizes the key material and performance parameters extracted from the research paper.

Parameter	Value	Unit	Context
Base Material	Single Crystal Diamond (SCD)	N/A	Optical Grade (Element Six)
Nanobeam Dimensions (L x W x T)	50 x 0.5 x 0.25	µm³	Fabricated via undercut etching
Metalization Layer	Titanium (Ti)	~5 nm	Enhances photothermal effects
Room Temperature Q-Factor (Q_m)	7.5 x 10⁴	N/A	Measured at 300 K, high vacuum
Cryogenic Q-Factor (Q_m)	5.8 x 10⁵	N/A	Measured at 5 K, high vacuum
Cooling Achievement (300K T_s)	~80	K	Effective temperature (T_eff)
Lowest T_eff Achieved (5K T_s)	2.2	K	Limited by photothermal broadening
Self-Oscillation Power (CW Laser)	60	µW	532 nm excitation wavelength
Predicted Dynamic Stress Field	~100	MPa	Near nanobeam clamping points (COMSOL)
Predicted Ground State Spin Coupling (G_g/2π)	~1	MHz	NV Center stress-spin coupling
Predicted Excited State Spin Coupling (G_e/2π)	~100	THz	NV Center stress-spin coupling

Key Methodologies

The experiment relies on precise material preparation, nanoscale fabrication, and sophisticated optical readout techniques:

Material Selection: High-quality, optical-grade Single Crystal Diamond (SCD) plates (3 x 3 mm²) were used as the starting material, essential for minimizing intrinsic mechanical dissipation and hosting NV centers.
Nanobeam Fabrication: Nanobeams (50 x 0.5 x 0.25 µm³) were defined and suspended ~2 µm above the substrate using undercut etching techniques.
Metalization: A thin layer of Titanium (Ti, ~5 nm) was deposited onto the top surface using electron beam evaporation to increase optical absorption and enhance photothermal back action.
Optomechanical Actuation: A 532 nm green laser, focused through a microscope objective mounted on a piezo stage, was used to induce photothermal forces. Translation of the focal position (z_f) controlled the sign and strength of the optomechanical damping (cooling or amplification).
Readout System: Nanobeam motion dynamics were monitored using an evanescently coupled optical fiber taper waveguide (diameter ~1 µm) transmitting a 1570 nm source, providing high sensitivity (f_m/&sqrt;Hz).
Cryogenic Operation: The sample and fiber taper were mounted in a closed-cycle cryostat, allowing measurements in high vacuum over a temperature range of 5 K to 300 K.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-specification MPCVD diamond materials and custom processing required to replicate and advance this quantum optomechanics research.

Applicable Materials

To achieve the high Q-factors and low dissipation necessary for quantum applications, the following 6CCVD materials are recommended:

6CCVD Material	Specification	Relevance to Research
Optical Grade SCD	High purity, low strain, low nitrogen content (< 1 ppb).	Essential for maximizing Q_m and minimizing optical absorption losses. Required for creating high-coherence NV centers.
SCD Thin Films	Thickness range: 0.1 µm to 500 µm.	Directly supports the required 0.25 µm thickness for the nanobeam structure, ensuring precise control over mechanical resonance frequency.
Nitrogen-Doped SCD	Controlled doping (e.g., 1 ppm N) available.	For researchers specifically targeting high-density NV center creation via post-growth irradiation or in-situ doping.

Customization Potential

The success of this experiment hinges on precise geometry and specialized surface modification. 6CCVD offers comprehensive customization services to meet these demands:

Custom Dimensions and Thickness: While the paper used a 3 x 3 mm² sample, 6CCVD supplies SCD plates up to 10 mm x 10 mm and PCD wafers up to 125 mm, allowing for scaling and array fabrication.
Precision Thinning and Polishing: The high Q-factor performance is dependent on surface quality. 6CCVD guarantees Ra < 1 nm polishing for SCD, crucial for minimizing surface scattering and mechanical dissipation losses in thin nanobeams.
Integrated Metalization Services: The experiment required a 5 nm Titanium (Ti) layer. 6CCVD offers in-house deposition of critical metals including Ti, Au, Pt, Pd, W, and Cu, enabling researchers to optimize photothermal coupling or integrate electrical contacts directly.
Substrate Engineering: 6CCVD can provide custom substrates (up to 10 mm thick) necessary for complex undercut etching processes used to suspend the nanobeam 2 µm above the diamond surface.

Engineering Support

6CCVD’s in-house team of PhD material scientists specializes in the intersection of MPCVD diamond growth and quantum device engineering.

Material Selection for Quantum Applications: Our experts can assist researchers in selecting the optimal SCD grade (e.g., low-strain vs. controlled nitrogen doping) to maximize NV center coherence times while maintaining the necessary mechanical properties for Quantum Spin-Optomechanics projects.
Process Optimization: We provide consultation on how material parameters (e.g., crystal orientation, surface termination) influence the thermal conductivity and stress fields, which are critical factors in photothermal cooling efficiency and spin-phonon coupling rates (G_g/2π and G_e/2π).
Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) of sensitive, high-value diamond materials, supporting international research collaborations.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Controlling the dynamics of mechanical resonators is central to many quantum\nscience and metrology applications. Optomechanical control of diamond\nresonators is attractive owing to diamond’s excellent physical properties and\nits ability to host electronic spins that can be coherently coupled to\nmechanical motion. Using a confocal microscope, we demonstrate tunable\namplification and damping of a diamond nanomechanical resonator’s motion.\nObservation of both normal mode cooling from room temperature to 80K, and\namplification into self—oscillations with $60\,\mu\text{W}$ of optical power\nis observed via waveguide optomechanical readout. This system is promising for\nquantum spin-optomechanics, as it is predicted to enable optical control of\nstress-spin coupling with rates of $\sim$ 1 MHz (100 THz) to ground (excited)\nstates of diamond nitrogen vacancy centers.\n

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevapplied.16.014063