Coherent control of a single nitrogen-vacancy center spin in optically levitated nanodiamond

At a Glance

Metadata	Details
Publication Date	2017-05-11
Journal	Journal of the Optical Society of America B
Authors	Robert M. Pettit, Levi P. Neukirch, Yi Zhang, A. Nick Vamivakas
Institutions	University of Rochester, Los Alamos National Laboratory
Citations	38
Analysis	Full AI Review Included

Technical Documentation and Analysis: Coherent Quantum Control in Nanodiamond

This documentation analyzes the key technical advancements and material requirements presented in LA-UR-17-20272 concerning the coherent control of Nitrogen-Vacancy (NV) center spins in levitated nanodiamonds. The findings directly support the demand for high-purity, low-strain Single Crystal Diamond (SCD) materials essential for advancing quantum computing and nanoscale sensing applications.

Executive Summary

This paper presents a critical advancement in quantum sensing and optomechanics by achieving coherent control of a single NV- center spin within an optically levitated nanodiamond.

Quantum Qubit Validation: Achieved the first demonstration of coherent control (spin manipulation) of a single NV- center electron spin in an optically trapped nanodiamond.
Environmental Robustness: Successful spin manipulation was achieved under both atmospheric pressure (101 kPa) and low vacuum (2.5 kPa).
Coherence Time Established: The measured transverse coherence time (T₂) was 101.4 ns (mean value), demonstrating robustness across a wide range of optical trapping powers (50 mW to 200 mW).
Thermal Stability: Internal temperatures of the levitated nanodiamond were confirmed to remain near room temperature (300.3 K extracted at 2.5 kPa) despite continuous laser exposure in low vacuum.
Platform Enablement: This work establishes the levitated nanodiamond system as a viable platform for fundamental quantum superposition tests, mechanical squeezing, and next-generation nanoscale sensing protocols.
Material Implications: Although current nanodiamonds showed $T_2$ values consistent with Type Ib HPHT diamond, the research points toward the necessity of high-purity, low-nitrogen MPCVD diamond (Type II) to achieve microsecond or millisecond coherence times necessary for practical quantum applications.

Technical Specifications

Parameter	Value	Unit	Context
Nanodiamond Size	40	nm	Nominal largest dimension
Trapped Qubit	Single NV- center	N/A	Negatively charged Nitrogen-Vacancy center
Trapping Laser Wavelength	1064	nm	Continuous Wave (CW)
Excitation Laser Wavelength	532	nm	Confocal Alignment
Trapping Power Range	0 to 200	mW	Measured before focusing objective
Vacuum Pressure	2.5 to 101	kPa	Low vacuum to atmospheric pressure
Trapping Objective NA	0.8	N/A	Numerical Aperture
Internal Temperature	300.32	K	Calculated from ESR spectrum shift at 2.5 kPa
Ground State Splitting (D)	2.87	GHz	Zero-field splitting (NV- center)
Transverse Coherence (T₂)	101.4 ± 15.7	ns	Mean value across trapping powers
PL Zero-Phonon Line	637	nm	Spin state readout indicator
Microwave Loop Diameter	25	µm	Bare-wire loop used for spin manipulation

Key Methodologies

The experiment successfully combined optical trapping, magnetic spin manipulation, and high-sensitivity photoluminescence (PL) detection, leveraging the unique spin-selective intersystem crossing mechanism of the NV- center.

Optical Dipole Trapping: Nanodiamonds were optically trapped via the tight focusing of a continuous wave 1064 nm laser beam through a high Numerical Aperture (NA) objective (NA = 0.8).
Fluorescence Excitation & Collection: A 532 nm laser beam was confocally aligned for NV- excitation. Collected photoluminescence (PL) was broadband (637 nm to 800 nm) and directed to a single avalanche photodiode (APD) or Hanbury-Brown and Twiss correlator for g⁽²⁾(∆t) measurement to confirm single NV- status (g⁽²⁾(0) = 0.08).
Spin State Preparation and Readout: Polarization and readout of the ground state spin triplet (³A₂) utilized spin-selective intersystem crossing to the singlet states (¹A₁ and ¹E). A reduction in collected PL indicates preparation in the m_s = ±1 sublevels.
Microwave Spin Manipulation (ESR): Electron spin resonance (ESR) was driven using microwave frequency currents through a 25 µm bare-wire loop placed adjacent to the trapped particle. Pulse sequences were synchronized by a 500 MHz clock source.
Coherence Time Extraction: Time-resolved ESR scans were fitted using a model based on damped optical Bloch equations, allowing for the extraction of the transverse coherence time (T₂).
Thermal Monitoring: Internal temperature was inferred by monitoring the shift of the ground state ESR resonance frequency (D) as pressure and trapping conditions changed.

6CCVD Solutions & Capabilities

The findings in this research underscore the limitations of standard commercial nanodiamonds (typically high-nitrogen Type Ib) and highlight the need for advanced, low-defect diamond materials achievable through specialized MPCVD synthesis. 6CCVD is uniquely positioned to supply the materials required to replicate, extend, and commercialize this quantum technology.

Applicable Materials for Quantum Advancement

To push T₂ coherence times from the currently measured 101 ns toward the microsecond or millisecond regimes—necessary for scalable quantum protocols—researchers require ultra-low-defect, isotopically pure diamond.

Recommended Material: Optical Grade SCD, Low-Nitrogen (Type IIa/IIb) Diamond Substrates.
- The paper notes that Type II CVD diamond can achieve T₂ times ranging from several µs to several hundred µs. 6CCVD specializes in high-purity MPCVD SCD, offering exceptional crystal quality and low paramagnetic impurity concentration (below 1 ppb N).
Recommended Extension: Isotopically Enriched SCD (e.g., ¹²C > 99.99%) Precursors.
- To suppress decoherence caused by surrounding nuclear spins, isotopically purified diamond precursors are mandatory. 6CCVD offers custom-grown SCD substrates suitable for implantation and subsequent formation of high-coherence NV centers.
Nanoscale Precursors: While the experiment used 40 nm nanodiamonds, high-quality bulk SCD plates are required for generating the highest purity nanodiamonds (via crushing/milling) or for fabricating deterministic NV sources. 6CCVD provides SCD material up to 500 µm thickness.

Customization Potential and Engineering Support

Replicating or scaling this levitated nanodiamond experiment requires specialized engineering capabilities that 6CCVD offers in-house.

Requirement Area	6CCVD Solution	Technical Advantage
Precursor Geometry	Custom Dimensions and Thickness	Plates/wafers up to 125mm (PCD) and SCD substrates up to 10mm thickness, ensuring flexibility for micro-machining.
Microwave Coupling/ESR	Custom Metalization Services	We offer in-house deposition of Au, Pt, Pd, Ti, W, and Cu layers, ideal for integrating micro-antennae or microwave delivery circuits directly onto a diamond platform (as an alternative to the bare-wire loop used here).
Optical Interface Quality	High-Precision Polishing	We provide industry-leading polishing, achieving surface roughness Ra < 1 nm for SCD, critical for minimizing scattering losses and stabilizing optical traps in related experiments.
Material Sourcing	Global Logistics & Support	Standard global shipping (DDU default) with DDP availability ensures reliable delivery of sensitive materials to international research institutions.

Engineering Support

6CCVD’s in-house PhD team can assist researchers and engineers with material selection, defect engineering (NV center creation via implantation planning), and custom material preparation (polishing, cleaning, metalization) for optically levitated quantum sensing and diamond-based quantum information projects.

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

View Original Abstract

Here, we report the first observation, to the best of our knowledge, of electron spin transients in single negatively charged nitrogen-vacancy (NV-) centers, contained within optically trapped nanodiamonds, in both atmospheric pressure and low vacuum. It is shown that, after an initial exposure to low vacuum, the trapped nanodiamonds remain at temperatures near room temperature even in low vacuum. Furthermore, the transverse coherence time of the NV- center spin, measured to be T2=101.4 ns, is robust over the range of trapping powers considered in this study.

Tech Support

Original Source

DOI: https://doi.org/10.1364/josab.34.000c31