Spin mechanics with levitating ferromagnetic particles

At a Glance

Metadata	Details
Publication Date	2020-04-13
Journal	Physical review. B./Physical review. B
Authors	Paul Huillery, Tom Delord, L. Nicolas, Mathias van den Bossche, M. Perdriat
Institutions	École Normale Supérieure - PSL, Laboratoire de Physique de l’ENS
Citations	40
Analysis	Full AI Review Included

Technical Analysis and Documentation for 6CCVD

Executive Summary

This research demonstrates foundational steps toward achieving strong quantum spin-mechanical coupling between levitating soft ferromagnets and Nitrogen-Vacancy (NV) centers embedded in MPCVD diamond. The findings pave the way for ultra-sensitive gyroscopy and complex quantum state manipulation.

High Frequency & Quality: Achieved high librational frequencies (up to 170 kHz) and exceptional mechanical Q-factors (up to 10⁴) for levitated soft magnets in a Paul trap under moderate vacuum (10^-2 mbar).
Resolved Sideband Potential: The measured librational frequencies largely exceed the decoherence rate of NV centers in high-purity CVD diamond, enabling the critical resolved sideband operation necessary for efficient quantum cooling.
Hybrid Material Validation: Two hybrid architectures were tested: Fluorescent Nanodiamonds (100 nm FNDs) attached to micromagnets, and microdiamonds (8-12 µm) coated with a 200 nm Nickel (Ni) ferromagnetic layer.
Coherent Control Demonstrated: Successfully demonstrated coherent spin control (Rabi oscillations and Hahn-echo T_2,echo = 825 ns) and used the NV spin to optically read out the mechanical libration of the hybrid particles.
6CCVD Material Requirement: Replication and advancement of Scheme 1 require ultra-pure, isotopically controlled Single Crystal Diamond (SCD) to maximize NV coherence times (target T₂ ~ 500 µs), a core specialization of 6CCVD.

Technical Specifications

The table below summarizes the critical physical and experimental parameters extracted from the research for spin-mechanics applications.

Parameter	Value	Unit	Context
Maximum Measured Librational Frequency ($\omega_\phi/2\pi$)	170	kHz	Soft iron rod, B = 0.1 T
Theoretical Librational Frequency (Soft Magnet)	24	MHz	75 nm x 25 nm ellipsoid, B = 0.1 T
Theoretical Librational Frequency (Hard Magnet)	1.3	GHz	75 nm x 25 nm ellipsoid, B = 0.1 T
Mechanical Quality Factor (Q)	9.3 ± 0.8 x 10³	N/A	Measured at 4.5 x 10^-2 mbar vacuum
Applied External Magnetic Field Range (B)	0 to 0.1	T	Used for librational confinement
Ferromagnetic Coating Thickness	200	nm	Sputtered Nickel (Ni) layer on micro-diamond
Micro-diamond Diameter (Coated)	8-12	µm	MSY micro-diamonds
Nanodiamond Diameter (Attached)	100	nm	Fluorescent Nanodiamonds (FNDs)
NV T_2,echo (Observed)	825	ns	FND attached to magnet hybrid system
NV T₂ (Target for Scheme 1)	~500	µs	Isotopically purified bulk CVD diamond (Cryogenic Temp)
Paul Trap Peak Voltage (V_ac)	100 to 4000	V	Used during particle injection/trapping

Key Methodologies

The experimental procedure involved precise material preparation, specialized levitation techniques, and high-sensitivity optical/microwave read-out.

Material Preparation:
- Ferromagnet Rods: Micron-sized soft iron particles (98% purity, 0.5 to 3 µm diameter) were injected into a Paul trap. Multiple particles were bound together via applied magnetic fields (tens of Gauss) to form elongated, quasi-ellipsoidal rods, benefiting from shape anisotropy.
- Hybrid Diamond (Scheme 2): Micro-diamonds (MSY 8-12 µm) were coated with a 200 nm thin film of ferromagnetic Nickel (Ni) via sputtering.
- Hybrid FND (Scheme 2): 100 nm Fluorescent Nanodiamonds (FNDs) were attached to iron micro-particles using nebulization onto a quartz coverslip before loading.
Levitation and Confinement:
- Particles were levitated in a ring Paul trap (25 µm tungsten wire, 200 µm radius) operating in the kHz range, under moderate vacuum (10^-2 mbar).
- A homogeneous magnetic field (up to 0.1 T) was applied using permanent magnets for angular confinement and to confine the librational mode ($\omega_\phi$).
Librational Excitation:
- External coils in Helmholtz configuration generated a transverse magnetic field (B_exc) perpendicular to the confining field, used to parametrically excite the librational mode.
Spin Control and Read-Out:
- Librational frequency was detected both via direct optical measurement (green laser speckle pattern reflection) and indirectly by monitoring the Photo-Luminescence (PL) signal of the NV centers.
- Spin control involved applying resonant microwave fields to drive Rabi oscillations and performing Hahn-echo sequences.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials and custom engineering required to replicate and scale the results demonstrated in this spin-mechanics research.

Paper Requirement	6CCVD Capability	Material Recommendation	Value Proposition for Engineers
High Coherence Times (Target T₂ ~500 µs)	Ultra-High Purity MPCVD Growth: Specialized low-nitrogen growth recipes and isotopic purification (¹²C enrichment). SCD wafers available up to 500 µm thick.	Optical Grade Single Crystal Diamond (SCD)	Guarantees the necessary long electronic spin coherence required for resolved sideband operations and quantum protocols.
Hybrid Ferromagnetic Coating (200 nm Ni)	In-House Custom Metalization: Capability to deposit thin films of various metals, including Nickel (Ni), Platinum (Pt), Gold (Au), Titanium (Ti), and Tungsten (W).	Custom Metalized SCD/PCD	Ensures precise, uniform deposition of the magnetic layer on the diamond surface, optimizing magnetic anisotropy and coupling strength ($\lambda_\phi$).
Micro- & Nano-Particle Sizing (e.g., 8-12 µm)	Precision Laser Cutting and Etching: Customization of dimensions from large wafers down to micron-scale plates/wafers.	Micro-Sized SCD or PCD	Provides perfectly shaped, low-mass diamond oscillators engineered for maximum stable levitation and high predicted librational frequencies (up to 1.3 GHz theoretical).
Minimized Surface Defects/Charge Patches	Ultra-High Quality Polishing: Achieving roughness Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD.	Polished SCD Substrates	Low surface roughness minimizes charge fluctuations and surface noise, which were cited as factors that degrade shallow NV coherence and potentially impact magnetic interaction stability.
BDD Sensors (Future Extension)	Boron-Doped Diamond (BDD) Films: Customizable doping levels for electrochemical sensing or integrated conductive pathways.	Heavy Boron-Doped PCD	Enables future integration of diamond materials for electric field control or quantum sensing extensions based on the demonstrated levitation platform.

Engineering Support

6CCVD’s in-house team of PhD material scientists and engineers can provide consultative support for projects focused on spin-mechanics, quantum metrology, and ultra-sensitive gyroscopy. We assist researchers in selecting the optimal MPCVD diamond specifications (purity, thickness, doping, and metalization) required to push the limits of coherence and coupling strength in levitating hybrid systems.

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

View Original Abstract

We propose and demonstrate first steps towards schemes where the librational\nmode of levitating ferromagnets is strongly coupled to the electronic spin of\nNitrogen-Vacancy (NV) centers in diamond. Experimentally, we levitate\nferromagnets in a Paul trap and employ magnetic fields to attain oscillation\nfrequencies in the hundreds of kHz range with Q factors close to $10^4$. These\nlibrational frequencies largely exceed the decoherence rate of NV centers in\ntypical CVD grown diamonds offering prospects for sideband resolved operation.\nWe also prepare and levitate composite diamond-ferromagnet particles and\ndemonstrate both coherent spin control of the NV centers and read-out of the\nparticle libration using the NV spin. Our results will find applications in\nultra-sensitive gyroscopy and bring levitating objects a step closer to\nspin-mechanical experiments at the quantum level.\n

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevb.101.134415