Protecting Quantum Spin Coherence of Nanodiamonds in Living Cells

At a Glance

Metadata	Details
Publication Date	2020-02-10
Journal	Physical Review Applied
Authors	Q Y Cao, P.C. Yang, M S Gong, M. Yu, A. Retzker
Institutions	Universität Ulm, Huazhong University of Science and Technology
Citations	30
Analysis	Full AI Review Included

Technical Documentation & Analysis: Protecting Quantum Spin Coherence in Nanodiamonds

Executive Summary

This research demonstrates a significant advancement in quantum sensing for biological applications by stabilizing Nitrogen-Vacancy (N-V) spin coherence in nanodiamonds (NDs) within living cells.

Core Achievement: Implementation of Concatenated Continuous Dynamical Decoupling (CCDD) successfully protected N-V spin coherence in NIH/3T3 cells.
Coherence Extension: CCDD extended the in vivo spin coherence time ($T_2$) to $29.4 \pm 3.6 \mu\text{s}$, an order of magnitude improvement over standard spin echo and significantly exceeding pulsed dynamical decoupling (XY8) schemes ($17.49 \pm 1.43 \mu\text{s}$).
Power Efficiency: CCDD achieved superior performance while requiring substantially lower average microwave power than XY8 sequences, reducing the risk of thermal damage (heating difference estimated at $\sim 10$ °C) to biological tissue.
Sensing Capability: The methodology enables high-sensitivity detection of oscillating magnetic fields, particularly effective for signal frequencies above 10 MHz where pulsed schemes are limited by power constraints.
Material Limitation & Opportunity: The achieved $T_2$ time is now predominantly limited by the spin relaxation time ($T_1$) of the nanodiamonds, highlighting that further sensitivity gains require improved material design (i.e., higher purity diamond precursors).
Application: Provides a critical step toward efficient, high-sensitivity quantum sensing protocols for in vivo biology and nanomedicine.

Technical Specifications

Parameter	Value	Unit	Context
Nanodiamond Precursor Material	HPHT Diamond	N/A	Milled to produce NDs
Nanodiamond Size (Average)	$43 \pm 18$	nm	Measured via AFM
Bulk $T_2$ Coherence (CCDD)	$31.22 \pm 3.14$	$\mu\text{s}$	Maximum achieved coherence time in bulk NDs
In Vivo $T_2$ Coherence (CCDD)	$29.4 \pm 3.6$	$\mu\text{s}$	Achieved in NIH/3T3 living cells
Bulk $T_1$ Relaxation Time	$87.35 \pm 7.50$	$\mu\text{s}$	Material limit for coherence
CCDD Rabi Frequency ($\Omega_1$)	$8.06$	MHz	Used for bulk $T_2$ measurement
XY8 Rabi Frequency ($\Omega$)	$8.5$	MHz	Used for bulk $T_2$ measurement
Magnetic Field ($B$)	$508$	Gauss	Applied during bulk measurements
Estimated $\Delta T$ (Pulse vs. CCDD)	$\sim 10$	°C	Temperature difference for similar $T_2$ performance
CCDD Sensitivity Advantage	Superior	N/A	For signal frequencies $\omega_s$ > 10 MHz

Key Methodologies

The experiment utilized advanced quantum control techniques and specialized biological sample preparation:

Nanodiamond Preparation: Nanodiamonds (average $43 \pm 18 \text{ nm}$) were milled from HPHT diamond and spin-coated onto mica or introduced to NIH/3T3 cell cultures.
N-V Characterization: Optically Detected Magnetic Resonance (ODMR) was used to identify and characterize N-V centers and their spin transitions ($m_s = 0 \leftrightarrow m_s = \pm 1$).
Microwave Control Generation: Microwave pulses and continuous driving fields were generated using an Arbitrary Waveform Generator (AWG) and amplified, then delivered via a copper wire ($\sim 20 \mu\text{m}$ diameter) positioned $\sim 30 \mu\text{m}$ from the N-V center.
Pulsed Dynamical Decoupling (XY8): Standard XY8-N sequences (up to 96 $\pi$-pulses) were applied to characterize and extend $T_2$ coherence time for comparison.
Concatenated Continuous Dynamical Decoupling (CCDD): CCDD was implemented using a phase-modulated microwave driving field consisting of suitably engineered multi-frequency components ($\Omega_1$ and $\Omega_2$) to suppress both environmental noise and microwave power fluctuations.
In Vivo Measurement: NIH/3T3 cells were cultured, incubated with NDs, and washed with Phosphate Buffered Saline (PBS). Measurements were performed at $22^\circ$C.
Thermal Monitoring: A thermistor was used to monitor sample temperature increase, confirming that CCDD caused less severe heating than pulsed schemes for equivalent coherence performance.

6CCVD Solutions & Capabilities

The research explicitly identifies that the ultimate limit to $T_2$ coherence time is the material’s $T_1$ relaxation time, which can be improved by “nanodiamond material design.” 6CCVD specializes in providing the ultra-high purity MPCVD diamond required to push these limits for next-generation quantum sensors.

Applicable Materials for Replication and Extension

To replicate this research or extend the coherence time beyond the current $T_1$ limit, researchers require diamond material with extremely low concentrations of P1 centers and ¹³C isotopes.

Research Requirement	6CCVD Material Solution	Technical Advantage
Ultra-High Purity Precursor	Optical Grade Single Crystal Diamond (SCD)	SCD with P1 center concentration < 1 ppb for maximum $T_1$ and $T_2$ coherence. Ideal for milling into high-purity nanodiamonds.
Isotopic Engineering	Isotopically Purified SCD	SCD with ¹²C enrichment (> 99.99%) to eliminate nuclear spin bath noise, crucial for achieving solid-state electronic spin coherence times approaching one second (as cited in Ref. [45]).
High-Volume Sensing	High-Purity Polycrystalline Diamond (PCD)	MPCVD PCD wafers up to 125mm in diameter, offering scalable, cost-effective precursors for large-batch nanodiamond production.
Integrated Sensing Platforms	Boron-Doped Diamond (BDD)	For electrochemical or integrated sensor applications requiring conductive diamond substrates.

Customization Potential for Integrated Devices

The experiment utilized a copper wire for microwave delivery, requiring precise alignment and proximity to the N-V centers. 6CCVD offers comprehensive fabrication services to integrate microwave delivery structures directly onto or adjacent to the diamond material.

Custom Dimensions and Thickness: We provide SCD and PCD plates/wafers in custom dimensions up to 125mm, with thicknesses ranging from $0.1 \mu\text{m}$ (for thin films) up to $10 \text{ mm}$ (for robust substrates).
Advanced Metalization: 6CCVD offers in-house metalization services (Au, Pt, Pd, Ti, W, Cu) for creating integrated microwave waveguides, coplanar waveguides (CPW), or antennas directly on the diamond surface, ensuring optimal Rabi frequency control and minimizing power loss.
Surface Quality: We guarantee ultra-smooth polishing (Ra < 1 nm for SCD, Ra < 5 nm for inch-size PCD), essential for minimizing surface spin noise and electric charge noise that degrade nanodiamond $T_2$ coherence.
Laser Cutting and Shaping: Custom laser cutting services are available to produce specific geometries required for complex quantum sensing setups or microfluidic integration.

Engineering Support

6CCVD’s in-house team of PhD material scientists and quantum engineers are experts in MPCVD growth parameters necessary to optimize N-V center density, location, and material purity. We can assist researchers in selecting the optimal diamond material (SCD vs. PCD, isotopic purity, doping levels) for similar in vivo quantum sensing and biosensing projects.

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

View Original Abstract

Due to its superior coherent and optical properties at room temperature, the\nnitrogen-vacancy (N-V ) center in diamond has become a promising quantum probe\nfor nanoscale quantum sensing. However, the application of N-V containing\nnanodiamonds to quantum sensing suffers from their relatively poor spin\ncoherence times. Here we demonstrate energy efficient protection of N-V spin\ncoherence in nanodiamonds using concatenated continuous dynamical decoupling,\nwhich exhibits excellent performance with less stringent microwave power\nrequirement. When applied to nanodiamonds in living cells we are able to extend\nthe spin coherence time by an order of magnitude to the $T_1$-limit of up to\n$30\mu$s. Further analysis demonstrates concomitant improvements of sensing\nperformance which shows that our results provide an important step towards in\nvivo quantum sensing using N-V centers in nanodiamond.\n

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevapplied.13.024021