Continuous dynamical decoupling of a single diamond nitrogen-vacancy center spin with a mechanical resonator

At a Glance

Metadata	Details
Publication Date	2015-12-14
Journal	Physical Review B
Authors	E. R. MacQuarrie, Tanay A. Gosavi, Sunil A. Bhave, Gregory D. Fuchs
Institutions	Cornell University, Purdue University West Lafayette
Citations	66
Analysis	Full AI Review Included

Technical Documentation & Analysis: Continuous Dynamical Decoupling in NV Centers

Executive Summary

This research demonstrates a critical advancement in solid-state quantum technology by using continuous dynamical decoupling (CDD) via a mechanical resonator (HBAR) to significantly enhance the coherence time (T₂) of a single Nitrogen-Vacancy (NV) center spin qubit in diamond.

Core Achievement: Prolongation of the NV center spin dephasing time (T₂) from $2.7 \pm 0.1$ µs (undressed) to $15 \pm 1$ µs (dressed) by engineering a protected spin basis.
Methodology: Application of AC lattice strain generated by a High-Overtone Bulk Acoustic Resonator (HBAR) to coherently drive the magnetically forbidden $|+1\rangle \leftrightarrow |-1\rangle$ spin transition.
Material Requirement: The experiment required ultra-low nitrogen concentration (< 5 ppb) “electronic grade” (100)-oriented Single Crystal Diamond (SCD) to minimize environmental magnetic noise.
Noise Mitigation: Mechanical CDD successfully isolates the qubit from magnetic field fluctuations and thermal drift, which typically dominate dephasing in NV systems.
Device Integration: The HBAR structure required complex thin-film metalization (Ti/Pt ground plane, Al top contact) and piezoelectric material (ZnO) integration onto the diamond substrate.
6CCVD Value Proposition: 6CCVD provides the necessary ultra-high purity SCD substrates (Optical/Quantum Grade) and custom metalization services required to replicate and scale this advanced quantum device architecture.

Technical Specifications

Parameter	Value	Unit	Context
Undressed T₂ Coherence Time	2.7 ± 0.1	µs	Bare $
Dressed T₂ Coherence Time (Max)	15 ± 1	µs	Protected $
T₂ Improvement Factor	$\ge$ 5.5	Ratio	Achieved via Mechanical CDD
Mechanical Rabi Frequency ($\Omega/2\pi$)	581 ± 2	kHz	Optimal dressing field
HBAR Resonance Mode ($\omega_{mech}/2\pi$)	586	MHz	High-overtone bulk acoustic resonator frequency
HBAR Quality Factor (Q)	2700	Dimensionless	Used for noise filtering
Diamond Orientation	(100)	Crystal Plane	Substrate orientation
Nitrogen Impurity Specification	< 5	ppb	Electronic grade diamond requirement
NV Center Depth	~47	µm	Post-irradiation/annealing depth
Annealing Temperature	850	°C	NV creation process
Zero-Field Splitting (D₀/2$\pi$)	2.87	GHz	Intrinsic NV property

Key Methodologies

The successful implementation of mechanical CDD relied on precise material preparation and advanced resonator fabrication techniques:

Substrate Selection and Preparation:
- Use of ultra-low nitrogen, (100)-oriented Single Crystal Diamond (SCD) to minimize paramagnetic noise sources.
- NV centers were created via 2 MeV electron irradiation ($1.2 \times 10^{14}$ cm^-2 fluence) followed by high-temperature annealing at 850 °C.
Mechanical Resonator (HBAR) Fabrication:
- A 3 µm thick (002)-oriented piezoelectric ZnO film was deposited.
- The ZnO film was sandwiched between a Ti/Pt (25 nm/200 nm) ground plane and an Al (250 nm) top contact.
Resonator Operation and Noise Filtering:
- The HBAR was operated at a specific high-overtone mode ($\omega_{mech}/2\pi = 586$ MHz) exhibiting a high quality factor (Q = 2700).
- This high Q factor provides passive noise filtering above a cutoff frequency ($\omega_c/2\pi = 110$ kHz), crucial for stabilizing the mechanical driving field.
Continuous Dynamical Decoupling (CDD):
- The HBAR generated AC lattice strain, providing a mechanical Rabi field ($\Omega$) to continuously drive the $|+1\rangle \leftrightarrow |-1\rangle$ transition.
- This created a dressed basis (eigenstates $|m\rangle$ and $|p\rangle$) that is robust against magnetic field fluctuations ($\delta b$).
Coherence Quantification:
- Ramsey measurements were performed within the dressed basis to quantify T₂ protection as a function of the mechanical driving field ($\Omega$).
- The study confirmed that while magnetic noise limits coherence at low $\Omega$, amplitude noise ($\delta\Omega$) in the mechanical driving field becomes the dominant dephasing source at larger driving fields.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the foundational materials and advanced fabrication services necessary to replicate and extend this high-coherence NV center research.

Applicable Materials

To achieve the demonstrated coherence times, the research requires diamond with extremely low paramagnetic impurities. 6CCVD offers the following materials:

6CCVD Material	Specification Match	Relevance to Research
Optical Grade SCD	Ultra-low N (< 1 ppb), High Purity	Essential for minimizing magnetic noise and achieving long T₂ coherence times. Directly replaces the “electronic grade” material used.
(100) Oriented SCD	Custom Orientation	Available in (100) orientation, matching the substrate used for optimal device integration.
Custom Thickness SCD	0.1 µm to 500 µm	Provides flexibility for optimizing NV center depth and integration with HBAR structures.
Polished SCD	Ra < 1 nm	Ultra-smooth surfaces are critical for high-quality thin-film deposition (ZnO, metal layers) required for the HBAR.

Customization Potential for HBAR Integration

The HBAR device architecture requires precise material deposition and patterning. 6CCVD offers comprehensive in-house capabilities to meet these needs:

Custom Metalization Stacks: The paper utilized Ti/Pt (ground plane) and Al (top contact). 6CCVD offers internal metalization capabilities including Ti, Pt, Au, Pd, W, and Cu, allowing researchers to optimize electrode performance and adhesion layers for piezoelectric films (like ZnO).
Custom Dimensions: While the paper used small samples, 6CCVD can supply SCD plates up to 10mm thick and PCD wafers up to 125mm in diameter, enabling scaling and integration of large-area HBAR arrays.
Substrate Engineering: 6CCVD can provide substrates pre-processed with specific features (e.g., laser cutting, edge polishing) to facilitate subsequent steps like electron irradiation and HBAR bonding/deposition.

Engineering Support

The transition from fundamental research to scalable quantum devices requires deep material science expertise. 6CCVD’s in-house PhD team specializes in NV center physics and diamond integration:

Material Selection Consultation: Assistance in selecting the optimal SCD grade (e.g., balancing N concentration for NV creation vs. ¹³C concentration for hyperfine noise) for specific Continuous Dynamical Decoupling (CDD) or Quantum Metrology projects.
Fabrication Recipe Optimization: Guidance on surface preparation and metalization recipes to ensure robust adhesion and high performance of piezoelectric films (like ZnO) used in mechanical resonators.
Global Logistics: Global shipping (DDU default, DDP available) ensures rapid and reliable delivery of high-value diamond substrates worldwide, minimizing project delays.

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

View Original Abstract

Inhomogeneous dephasing from uncontrolled environmental noise can limit the\ncoherence of a quantum sensor or qubit. For solid state spin qubits such as the\nnitrogen-vacancy (NV) center in diamond, a dominant source of environmental\nnoise is magnetic field fluctuations due to nearby paramagnetic impurities and\ninstabilities in a magnetic bias field. In this work, we use ac stress\ngenerated by a diamond mechanical resonator to engineer a dressed spin basis in\nwhich a single NV center qubit is less sensitive to its magnetic environment.\nFor a qubit in the thermally isolated subspace of this protected basis, we\nprolong the dephasing time $T_2^$ from $2.7\pm0.1$ $\mu$s to $15\pm1$ $\mu$s\nby dressing with a $\Omega=581\pm2$ kHz mechanical Rabi field. Furthermore, we\ndevelop a model that quantitatively predicts the relationship between $\Omega$\nand $T_2^$ in the dressed basis. Our model suggests that a combination of\nmagnetic field fluctuations and hyperfine coupling to nearby nuclear spins\nlimits the protected coherence time over the range of $\Omega$ accessed here.\nWe show that amplitude noise in $\Omega$ will dominate the dephasing for larger\ndriving fields.\n

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevb.92.224419