Diamonds levitating in a Paul trap under vacuum - Measurements of laser-induced heating via NV center thermometry

At a Glance

Metadata	Details
Publication Date	2017-07-03
Journal	Applied Physics Letters
Authors	Tom Delord, L. Nicolas, M. Bodini, G. Hétet
Institutions	Université Paris Sciences et Lettres, Sorbonne Université
Citations	53
Analysis	Full AI Review Included

Technical Analysis & Product Solutions: MPCVD Diamond for Levitation Quantum Platforms

Executive Summary

This research demonstrates the viability of utilizing Nitrogen Vacancy (NV) centers embedded in levitating micron-sized diamonds within a Paul trap under vacuum, a critical platform for hybrid-opto-mechanical quantum experiments. The study’s findings directly underscore the need for high-purity, MPCVD-grown diamond to advance the field:

Platform Viability: Electronic Spin Resonance (ESR) of NV centers was successfully observed in levitating diamonds, confirming the potential for coupling quantum spin states with the center-of-mass motion of massive oscillators.
Thermal Barrier Identified: The core limitation observed was significant laser-induced heating, where the diamond temperature rose monotonically up to 470 K at 700 µW green laser power in a 1 mbar vacuum environment.
Root Cause: Heating is explicitly attributed to light absorption by residual nitrogen impurities inherent in the commercial HPHT diamond powder used.
Resolution Requirement: The authors conclude that overcoming this heating requires employing purer diamonds made from Chemical Vapour Deposition (CVD), or using alternative trapping wavelengths.
6CCVD Advantage: 6CCVD’s Optical Grade Single Crystal Diamond (SCD), characterized by ultra-low nitrogen content (< 1 ppb), directly addresses the need for high-purity material, enabling stable operation required for achieving the motional ground state.

Technical Specifications

The following critical parameters highlight the experimental conditions and performance metrics achieved, providing benchmarks for material requirements:

Parameter	Value	Unit	Context
Operating Pressure (PL Detection)	1.0 x 10^-2	mbar	Minimum pressure where photoluminescence was sustained
Operating Pressure (ESR Detection)	2.0 x 10^-1	mbar	Minimum pressure for reliable spin readout
Green Laser Wavelength	532	nm	Excitation and spin readout source
Maximum Diamond Temperature Observed	470	K	Achieved at 700 µW laser power, 1 mbar pressure
Temperature Deduction Method	Zero-Field Splitting (ZFS) Shift	N/A	D(T) shift of up to 12 MHz was measured from the 2.87 GHz baseline (298 K)
Diamond Particle Diameter	~10	µm	Typical size of trapped particles
ESR Contrast Reduction	3.5% down to 1.0%	%	Reduction correlated with increasing temperature at low pressure
Microwave Excitation Power	0.5	W	Used to excite NV center electronic spins
Trap Configuration	Paul-Straubel Ring Trap	N/A	300 µm thick Copper wire; 700 µm inner radius

Key Methodologies

The experiment successfully combined high-vacuum ion trapping techniques with NV center quantum control methods:

Trap Configuration: A ring-geometry Paul-Straubel ion trap was constructed using 300 µm thick copper wire, enclosed within a vacuum chamber mounted on a 3-axis translation stage.
Particle Loading & Preselection: Micron-sized diamonds (approx. 10 µm diameter) were injected. To ensure stable operation at low voltage (600 V) required for vacuum pumping, particles with a high charge-to-mass ratio were preselected by measuring the onset of instability at 4000 V.
Vacuum Cycling Protocol:
- Trap initialized in air at 4000 V.
- Voltage lowered to 600 V at ~500 mbar to prevent plasma arching near the critical 10 mbar range.
- Turbomolecular pump engaged to reach low-pressure regimes (down to 10^-2 mbar).
- Voltage increased back up to 4000 V at pressures < 10^-2 mbar for higher confinement.
NV Spin Manipulation: The copper ring trap itself acted as the antenna for microwave excitation (0.5 W), mixed via a Bias Tee with the high-voltage trapping signal.
Optical Readout & Thermometry:
- A 532 nm green laser was focused onto the levitating diamond.
- Photoluminescence (PL) from the NV centers was collected confocally, filtered via a Notch filter, and measured by an APD.
- Temperature was deduced by monitoring the shift of the Zero-Field Splitting (ZFS), D(T), which is highly dependent on lattice expansion due to temperature.

6CCVD Solutions & Capabilities

The successful replication and extension of this research to achieve ground-state cooling in opto-mechanical hybrid schemes fundamentally relies on sourcing diamond material with significantly higher purity than used in the published work.

6CCVD, as an expert in MPCVD diamond engineering, offers materials and customization services specifically designed to meet the extreme demands of levitation quantum physics.

Applicable Materials

The immediate need identified by the authors is to replace nitrogen-rich commercial HPHT diamond with ultra-pure CVD material to eliminate laser heating.

Material Requirement	6CCVD Solution	Technical Advantage
High Purity (Required)	Optical Grade SCD (Single Crystal Diamond)	Nitrogen impurity concentration < 1 ppb (parts per billion). Eliminates the primary cause of 532 nm light absorption and subsequent thermal runaway, enabling stable, ultra-low-vacuum operation.
Alternate Spin Platform	Polycrystalline Diamond (PCD) / BDD	For high-density NV ensembles or applications requiring integrated sensor layers. 6CCVD provides PCD up to 125 mm diameter.

Customization Potential

Replicating this work requires precise fabrication of micro-objects from high-quality bulk material, which 6CCVD provides as an internal service.

Precision Fabrication: The experiment uses ~10 µm diameter diamonds. 6CCVD offers high-precision laser cutting, dicing, and cleaving services to produce micron-sized diamond particles (plates or custom shapes) from high-purity SCD wafers.
Custom Thickness: 6CCVD can control SCD thickness from 0.1 µm to 500 µm, allowing engineers to optimize the particle mass and NV concentration depth for specific trap frequencies and cooling requirements.
Integrated Spin Control: While this paper used the trap ring for MW delivery, future, more complex schemes often require integrated antennae. 6CCVD offers in-house custom metalization (Ti/Pt/Au, W, Cu, Pd), critical for fabricating robust microwave coplanar waveguides or electrodes directly onto the SCD surface.
Superior Surface Quality: For efficient optical coupling and minimal scattering loss, 6CCVD guarantees atomic-scale polishing (Ra < 1 nm) on Single Crystal Diamond surfaces.

Engineering Support

6CCVD’s in-house team of PhD material scientists and technical engineers specializes in NV center applications and thermal management in quantum platforms.

We provide expert consultation on selecting the optimal diamond purity (e.g., comparing High Purity SCD vs. Electronic Grade) and required dimensions to meet specific secular frequency targets in levitation quantum electrodynamics projects.
Our team assists in designing custom CVD growth recipes tailored to control residual strain and optimize the coherence time (T₂) of NV centers, surpassing limitations found in commercial HPHT powders.

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

View Original Abstract

We present measurements of the electronic spin resonance (ESR) of nitrogen vacancy (NV) centers in diamonds that are levitating in a ring Paul trap under vacuum. We observe ESR spectra of NV centers embedded in micron-sized diamonds at vacuum pressures of 2 × 10−1 mbar and the NV photoluminescence down to 10−2 mbar. Further, we use the ESR to measure the temperature of the levitating diamonds and show that the green laser induces heating of the diamond at these pressures. We finally discuss the steps required to control the NV spin under ultra-high vacuum.

Tech Support

Original Source

DOI: https://doi.org/10.1063/1.4991670