Electron spin control of optically levitated nanodiamonds in vacuum

At a Glance

Metadata	Details
Publication Date	2016-07-19
Journal	Nature Communications
Authors	Thai M. Hoang, Jonghoon Ahn, Jaehoon Bang, Tongcang Li
Institutions	Purdue University West Lafayette
Citations	114
Analysis	Full AI Review Included

Technical Analysis and Documentation: MPCVD Diamond for Quantum Optomechanics

Executive Summary

This paper successfully demonstrates the electron spin control of Nitrogen-Vacancy (NV) centers within optically levitated nanodiamonds in a low-vacuum environment, a critical step toward creating hybrid spin-optomechanical quantum systems.

Core Achievement: Electron Spin Resonance (ESR) control of NV centers in 100 nm nanodiamonds levitated by a 1550 nm laser in vacuum (down to 31 Torr).
Key Finding (Vacuum Effect): The ESR contrast was surprisingly enhanced by a factor of >2 in low vacuum compared to atmospheric pressure, attributed to the quenching of low-quality surface NV- centers due to moderate heating.
Sensing Potential: The differential response of NV centers to oxygen (O₂) versus helium (He) confirms potential applications for reversible, unheated, miniature oxygen gas sensors.
Thermal Dynamics: Internal temperature of the nanodiamonds reached up to 450 K in low vacuum due to heating from the trapping laser, successfully measured via NV center spectroscopy (D(T)).
Material Limitation: The researchers noted that the commercial nanodiamonds used exhibited high optical absorption, limiting the capability to trap particles in high vacuum.
6CCVD Solution: Replication and extension of this research requires high-purity Single Crystal Diamond (SCD) with negligible absorption at 1550 nm and 532 nm, a core offering of 6CCVD.

Technical Specifications

The following hard data points were extracted from the experimental results presented in the paper.

Parameter	Value	Unit	Context
Nanodiamond Hydrodynamic Diameter	94 ± 7	nm	Consistent with manufacturer’s 100 nm specification
Estimated NV Centers	~500	Centers	Per nanodiamond
Trapping Laser Wavelength	1550	nm	Used for optical levitation
Excitation Laser Wavelength	532	nm	Used for NV center excitation
Trapping Laser Power (Max)	500	mW	Max power used in initial experiments
Zero Phonon Line (ZPL)	640	nm	Observed NV- fluorescence peak
Operational Pressure Range	759 to 31	Torr	ESR control demonstrated across this range
Critical Particle Loss Pressure	~9	Torr	Below this threshold, nanodiamonds are lost
Internal Temperature Rise (Atm-to-Vacuum)	300 K to 450+ K	K	Measured via thermal shift of D(T)
ESR Contrast Increase	>2	Factor	Observed improvement from 759 Torr to 31 Torr
Gas Sensing Sensitivity (Estimated)	100	photon Torr^-1 s^-1	Current unoptimized imaging setup sensitivity

Key Methodologies

The experiment utilized a combination of optical levitation, microwave spin control (ODMR), and high-resolution spectroscopic detection within a controlled vacuum environment.

Nanodiamond Launch: Commercial nanodiamonds (Adamas ND-NV-100nm-COOH) mixed with water (30 µg/ml density) were introduced into the vacuum chamber using an ultrasonic nebulizer.
Optical Trapping: A 1550 nm laser beam was focused by a Numerical Aperture (NA)=0.85 infrared objective lens to capture and levitate the nanodiamonds in a single-beam trap.
Vacuum Control: A turbomolecular pump was used to evacuate the chamber. Pressure was monitored by an absolute piezo sensor (>10 Torr) and a micropirani sensor (<10 Torr).
NV Excitation and Detection: NV centers were excited using a 532 nm (green) laser. The visible fluorescence signal (600 nm to 800 nm) was collected and analyzed using an Andor spectrometer and a Newton EMCCD camera.
Electron Spin Resonance (ESR) Control: Microwave radiation was delivered via a coplanar waveguide antenna (0.5 mm distance) using an optically detected magnetic resonance (ODMR) technique to induce |m_s = 0> ↔ |m_s = ±1> transitions.
Internal Temperature Measurement: The internal temperature (T) was calculated by fitting the zero-field splitting parameter D(T) obtained from the double Gaussian fit of the ESR spectra, which required careful calibration of internal strain (A_strain).
Gas Exchange: Surrounding gases (O₂ and He, >99% purity) were repeatedly evacuated and filled to investigate effects on photoluminescence and ESR contrast.

6CCVD Solutions & Capabilities

This research highlights the potential of NV-center diamond systems for quantum optomechanics and robust gas sensing. The primary limitation identified—high optical absorption and impurity of commercial nanodiamonds leading to significant laser heating—is directly mitigated by 6CCVD’s advanced Material Science capabilities.

Applicable Materials for Replication and Extension

To achieve stable optical levitation in high vacuum, the next generation of experiments requires ultra-low absorption diamond materials.

Application Requirement	6CCVD Recommended Material	Material Justification & Benefit
High Vacuum Levitation	Optical Grade SCD Plates (0.1µm - 500µm)	SCD offers the highest purity and lowest optical absorption, minimizing the 1550 nm laser heating that limits high-vacuum trapping (Purity <1 ppb N).
Integrated Sensing Arrays	High Quality PCD Wafers (up to 125mm)	For scaling up oxygen sensor applications (as proposed in the paper), large, inch-size PCD provides a stable substrate with low Ra < 5nm polishing, suitable for integrating thousands of nanodiamonds.
Optimized NV Density	Custom Doped SCD/PCD	6CCVD offers precise control over nitrogen concentration during growth to tailor the density of NV centers, optimizing the signal-to-noise ratio for ESR contrast measurements.

Customization Potential for Optomechanical Systems

The complexity of hybrid spin-optomechanical systems necessitates bespoke material engineering, a specialty of 6CCVD.

Substrate Integration: While the paper levitated nanodiamonds, future sensor architectures place nanodiamonds on stable substrates. 6CCVD supplies robust diamond substrates up to 10mm thick, perfectly polished (Ra < 1nm for SCD) for demanding optical setups.
Microwave Integration: The experiment relied on an external antenna and coplanar waveguide (CPW) for microwave delivery. 6CCVD offers internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu) allowing researchers to design and integrate on-chip CPW antennas directly onto the diamond substrate surface, enhancing coupling efficiency and minimizing microwave losses for improved ESR control.
Custom Dimensions: For replication or large-scale array development (e.g., placing nanodiamonds in a 5 µm x 5 µm area for high-density sensing), 6CCVD provides custom laser cutting and shaping services for both SCD and PCD plates up to 125mm.

Engineering Support

The challenges encountered in this research—specifically internal temperature measurement via strain calibration and mitigating surface effects (O₂ termination)—fall squarely within 6CCVD’s domain expertise.

6CCVD’s in-house PhD material science team offers dedicated consultation services to assist engineers and researchers in selecting the optimal SCD or PCD grade for low-absorption quantum experiments.
We provide expert guidance on thermal management solutions and material selection necessary to achieve the ultra-stable, high-vacuum environments required for ambitious quantum proposals (e.g., testing macroscopic quantum mechanics or quantum gravity).

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

Tech Support

Original Source

DOI: https://doi.org/10.1038/ncomms12250