Angle Locking of a Levitating Diamond Using Spin Diamagnetism
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-03-18 |
| Journal | Physical Review Letters |
| Authors | M. Perdriat, Paul Huillery, Clément Pellet-Mary, G. Hétet |
| Institutions | Centre National de la Recherche Scientifique, Ăcole Normale SupĂ©rieure - PSL |
| Citations | 11 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThe research demonstrates a novel method for achieving stable angular alignment of levitating micro-diamonds containing Nitrogen-Vacancy (NV) centers, leveraging induced spin-diamagnetism.
- Core Achievement: Successful realization of âangle locking,â stabilizing the diamondâs [111] crystalline axis along an external magnetic field (B).
- Mechanism: Strong, tunable diamagnetism is induced in the NV-doped diamond by achieving population inversion near the Ground State Level Anti-Crossing (GSLAC, B â 105 mT) using optical pumping.
- Susceptibility: The induced magnetic susceptibility (Xâ„) reaches a maximum magnitude of approximately 10-2, two orders of magnitude larger than the off-resonance paramagnetic response.
- Value Proposition: Overcomes the major limitation of untethered NV diamondsârandom orientation and loss of polarizationâenabling stable coherent control and high-fidelity sensing.
- Applications: Crucial for advancing in vivo hyperpolarization (NMR), nanoscale magnetometry in biological environments, and spin-mechanics experiments with levitating particles.
- Tunability: The magnetic response (paramagnetic or diamagnetic) and the resulting torque are optically tunable via green laser power, controlling the spin polarization state.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Center Concentration | 3-5 | ppm | Density in micro-diamond sample. |
| Zero-Field Splitting (D) | 2.87 | GHz | NV center electronic ground state triplet. |
| GSLAC Critical Field (Bc) | â 105 | mT | Observed transition point (paramagnetic to diamagnetic). |
| Maximum Susceptibility (Xâ„) | â 10-2 | N/A | Induced spin-diamagnetism near GSLAC. |
| Orbital Diamagnetism (Xorb) | â 10-5 | N/A | Background diamond diamagnetism (negligible). |
| Longitudinal Spin Relaxation (T1) | â 500 | ”s | Measured rate for NV spins. |
| Spin Dephasing Rate (Î/2Ï) | â 5 | MHz | Primarily due to coupling with P1 nitrogen spins. |
| Paul Trap Type | Ring Paul-Straubel | N/A | Used for levitation and as a microwave antenna. |
| Paul Trap Diameter | â 200 | ”m | Physical dimension of the trap. |
| Paul Trap Angular Frequencies | 100 to 1 | KHz | Range of librational confinement frequencies. |
| Magnetic Potential Depth (U) | â 10-15 | J | Estimated confinement depth for 109 NV centers at 0.11 T. |
| Laser Polarization Rate (Îlas) | 10 to 1000 | KHz | Dependent on NV density and optical alignment. |
| Microwave Power | -10 to 0 | dBm | Power used for MDMR measurements. |
Key Methodologies
Section titled âKey Methodologiesâ- Levitation and Confinement: Micro-diamonds were loaded into an electrostatic ring Paul-Straubel trap, providing both levitation and angular confinement (librational frequencies 100 Hz to 1 KHz).
- Spin Polarization: Green laser light (532 nm) was applied to optically pump the NV electronic spin into the |ms = 0> state via intersystem crossing in the 3E excited state.
- Magnetism Induction: The external magnetic field (B) was tuned close to the GSLAC (B â 105 mT). Optical pumping maintains polarization even after the GSLAC, resulting in a population inversion and strong, tunable Van Vleck diamagnetism.
- Torque Measurement (MDMR): The NV-induced magnetization (M) creates a magnetic torque (Ï = VM(B) Ă B) on the diamond. This torque shifts the diamondâs equilibrium angular position (Ξ).
- Motion Detection: Mechanically-Detected Magnetic Resonance (MDMR) was used to track the angle (Ξ) of the four NV orientations relative to B. This involved scanning a microwave signal and detecting changes in the back-reflected laser light (speckle detection) due to slight angular shifts.
- Angle Locking Demonstration: By increasing the magnetic field past the GSLAC (Region 3, Fig. 2), the NV axis was observed to align almost perfectly (angles less than 2°) with the applied magnetic field, demonstrating angle locking.
Commercial Applications
Section titled âCommercial ApplicationsâThe demonstrated spin-diamagnetism and angle locking technique are critical enabling technologies for several advanced fields:
- Quantum Sensing and Magnetometry:
- Untethered Nano-Magnetometry: Enables stable, high-coherence magnetic field sensing in complex environments, particularly in vivo sensing within living cells, where random diamond rotation is typically prohibitive.
- Nuclear Magnetic Resonance (NMR) and Hyperpolarization:
- Enhanced NMR Efficiency: By aligning the NV axis with the external B field, the technique boosts the efficiency of hyperpolarizing adjacent nuclear spins (e.g., 13C atoms in solution), opening a path toward more efficient NMR spectroscopy.
- Spin-Mechanics and Quantum Physics:
- Stable Quantum Experiments: Provides a microwave-free solution for stabilizing the angle of nanodiamonds in optical tweezers, which is essential for future spin-mechanical experiments aimed at matter-wave interferometry and tests of quantum gravity.
- Material Science and Levitation:
- Magnetic Expulsion: If NV spin density is increased (e.g., 10x), the induced diamagnetism could become strong enough to expel magnetic field lines, potentially enabling magnetic levitation of the diamond, similar to superconductor behavior.
- Micro- and Nanorobotics:
- Remote Control: The magneto-optical tunability of the torque offers a mechanism for local, remote control and steering of the motion of microscopic objects in liquid or vacuum environments.
View Original Abstract
Nanodiamonds with embedded nitrogen-vacancy (NV) centers have emerged as promising magnetic field sensors, as hyperpolarizing agents in biological environments, as well as efficient tools for spin mechanics with levitating particles. These applications currently suffer from random environmental interactions with the diamond which implies poor control of the N-V direction. Here, we predict and report on a strong diamagnetism of a pure spin origin mediated by a population inversion close to a level crossing in the NV center electronic ground state. We show control of the sign of the magnetic susceptibility as well as angle locking of the crystalline axis of a microdiamond along an external magnetic field, with bright perspectives for these applications.