Protecting Quantum Spin Coherence of Nanodiamonds in Living Cells
At a Glance
Section titled âAt a Glanceâ| 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 | Hebrew University of Jerusalem, UniversitÀt Ulm |
| Citations | 30 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates a highly efficient method for protecting the quantum spin coherence of Nitrogen-Vacancy (N-V) centers in nanodiamonds (NDs) within living cells, addressing critical limitations for in vivo quantum sensing.
- Coherence Extension: The spin coherence time (T2) of N-V centers in living NIH/3T3 cells was extended by an order of magnitude, reaching up to 29.4 ± 3.6 ”s.
- T1 Limit Achieved: This extended T2 time approaches the fundamental spin relaxation time (T1 limit) of the nanodiamond material (T1 â 87 ”s).
- Energy Efficiency: The Concatenated Continuous Dynamical Decoupling (CCDD) scheme significantly outperforms pulsed schemes (like XY8) given the same average microwave power constraint.
- Reduced Biological Damage: CCDD requires substantially less average microwave power, resulting in an estimated 10 °C less temperature increase in biological tissue compared to pulsed sequences achieving similar T2 times.
- Enhanced Sensitivity: The prolonged coherence time and low-power operation enable high-frequency magnetic field sensing (above 10 MHz) with superior measurement sensitivity compared to pulsed methods under power constraints.
- Methodology: CCDD utilizes a phase-modulated, multi-frequency microwave driving field to suppress both fast environmental noise and microwave power fluctuations effectively.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Nanodiamond Source | HPHT Diamond (Milled) | N/A | Microdiamant source material |
| Nanodiamond Size (Average) | 43 ± 18 | nm | Predominantly 25-61 nm |
| Spin Relaxation Time (T1) | 87.35 ± 7.50 | ”s | Measured in nanodiamond |
| Initial Spin Echo Time (T2) | ~3 | ”s | Average coherence time (unprotected) |
| Max T2 (CCDD, In Air) | 31.22 ± 3.14 | ”s | Extended coherence time |
| Max T2 (CCDD, In Cells) | 29.4 ± 3.6 | ”s | Extended coherence time in NIH/3T3 cells |
| Max T2 (XY8, In Cells) | 17.49 ± 1.43 | ”s | Pulsed decoupling comparison |
| CCDD Main Rabi Frequency (Ω1, In Cells) | 4.6 | MHz | Low-power operation constraint |
| CCDD Modulation Ratio (Ω2/Ω1) | 0.1 | N/A | Ratio of phase modulation |
| XY8 Rabi Frequency (Ω, In Cells) | 9.6 | MHz | Pulsed operation comparison |
| Magnetic Field (B, In Cells) | 25 | Gauss | Applied static external field |
| Temperature Increase Delta (Pulsed vs. CCDD) | ~10 | °C | Pulsed schemes cause higher heating for similar T2 |
| Microwave Wire Distance to N-V | ~30 | ”m | Typical distance in the cell measurement setup |
| CCDD Continuous Drive Duration (Ton) | 30 | ”s | Similar to extended T2 time |
Key Methodologies
Section titled âKey MethodologiesâThe experiment focused on characterizing and protecting N-V spin coherence in nanodiamonds, specifically within NIH/3T3 living cells.
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Nanodiamond Preparation:
- Nanodiamonds were derived from milled High-Pressure/High-Temperature (HPHT) diamond.
- Size statistics were confirmed using Atomic Force Microscopy (AFM), showing an average size of 43 ± 18 nm.
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Cell Culture and Uptake:
- NIH/3T3 cells were cultured in Dulbeccoâs modified Eagleâs medium (DMEM).
- Cells were incubated with the ND suspension for 20 hours to allow adherence and uptake.
- Prior to measurement, the medium was replaced with Phosphate Buffered Saline (PBS) to minimize background fluorescence.
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N-V Center Identification:
- Confocal microscopy was used to image the cells and locate internalized nanodiamonds (confirmed via XZ scans).
- Cell membranes were stained using lipophilic fluorescent dyes (DiIC18(3)) to clearly delineate cell boundaries.
- Optically Detected Magnetic Resonance (ODMR) was performed to confirm the presence and spin properties of the N-V centers.
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Microwave Control Setup:
- Microwave pulses and continuous driving fields were generated using an Arbitrary Waveform Generator (AWG) and amplified.
- The microwave signal was delivered via a copper wire (~20 ”m diameter) positioned ~30 ”m from the N-V center.
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Dynamical Decoupling Implementation:
- Pulsed Scheme (Comparison): XY8-N sequences (up to 96 Ï-pulses) were used to characterize maximum achievable T2 under pulsed constraints.
- CCDD Scheme (Core Method): A microwave driving field with phase modulation was implemented, consisting of a main frequency component (Ω1) and a weaker frequency component (Ω2) to compensate for power fluctuations.
- Coherence Measurement: Spin echo and decoupling sequences were used, followed by a final Ï/2 pulse, mapping coherence information onto the spin state population (P|0>), measured via fluorescence.
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Heating Characterization:
- A thermistor (Thorlabs TH10K) was attached to the coverslip to monitor sample temperature increase caused by microwave absorption during both pulsed (XY8) and continuous (CCDD) sequences.
Commercial Applications
Section titled âCommercial ApplicationsâThe successful implementation of low-power, high-sensitivity quantum sensing in a biological environment opens pathways for several advanced commercial and research applications:
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Nanomedicine and In Vivo Sensing:
- Intracellular Thermometry: High-precision, nanoscale temperature sensing within living cells, critical for monitoring cellular processes or therapeutic efficacy (e.g., hyperthermia treatments).
- Magnetic Field Imaging: Mapping weak magnetic fields generated by biological processes (e.g., neuronal activity, radical pair reactions) with high spatial and temporal resolution.
- Drug Delivery Monitoring: Using NDs as traceable quantum probes to monitor delivery and environmental changes (pH, temperature) at the target site.
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Quantum Sensing and Metrology:
- High-Frequency Spectroscopy: Detection of oscillating magnetic fields (e.g., Larmor frequencies of target spins) above 10 MHz, enabling high-field Magnetic Resonance Spectroscopy (MRS) of electron or nuclear spins in complex samples.
- Low-Power Quantum Control: Development of energy-efficient quantum control sequences for solid-state qubits, particularly relevant for portable or battery-operated quantum devices where power is a constraint.
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Material Science and Characterization:
- ND Material Design: Provides a metric (T2 approaching T1) for evaluating improvements in nanodiamond material quality, specifically targeting the reduction of surface spin noise and charge noise.
- Classical Field Disambiguation: The CCDD scheme can avoid misidentification of frequency components in classical fields or single-molecule spectroscopy due to long pulse durations inherent in power-limited pulsed schemes.
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