Single-Spin Magnetomechanics with Levitated Micromagnets
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-04-24 |
| Journal | Physical Review Letters |
| Authors | Jan Gieseler, Aaron Kabcenell, Emma Rosenfeld, J. D. Schaefer, Arthur Safira |
| Institutions | Max Planck Institute of Quantum Optics, UniversitÀt Innsbruck |
| Citations | 90 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research introduces a novel mechanical transduction platform utilizing levitated micro-magnets coupled to Nitrogen Vacancy (NV) centers in diamond, aiming for strong spin-mechanical coupling (magnetomechanics).
- Core Platform: Hard micro-magnets are levitated in free space using the flux trapping properties of a Type-II YBCO (Yttrium Barium Copper Oxide) superconductor, minimizing dissipation sources like clamping losses.
- High Performance: The system demonstrates high mechanical quality factors (Q) of approximately 106 and trapping frequencies in the kHz range, achieved under high vacuum (pressure < 10-5 mBar).
- 3D Trapping Control: Stable three-dimensional trapping is achieved by controlling the relative distance between the magnet and the superconductor during the cooldown process (below Tc â 90K).
- Direct Coupling: The magnetâs stray field provides the strong magnetic field gradient necessary for efficient coupling to the electronic spin of an individual NV center in the nearby diamond slab.
- Measured Coupling: The spin-mechanical coupling strength (λg) was experimentally measured at 48 ± 2 mHz, confirming the thermal character of the driven motional mode.
- Future Potential: Projections indicate that achieving Q-factors of 108 could lead to the ultra-strong coupling regime (λg > Ïj) and high cooperativity (C > 1), enabling coherent quantum effects.
- Applications: The platform is designed for ultra-sensitive metrology, realization of quantum networks, and fundamental tests of quantum mechanics with mesoscopic objects.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Mechanical Q-Factor (Measured) | ~1.0 x 106 | Dimensionless | Center-of-mass translational modes |
| Mechanical Q-Factor (Projected) | 108 | Dimensionless | Required for high cooperativity (C > 1) |
| Superconductor Material | YBCO | Yttrium Barium Copper Oxide | Type-II superconductor |
| Superconductor Critical Temp (Tc) | ~90 | K | Cooldown temperature threshold |
| Operating Pressure | < 10-5 | mBar | High vacuum conditions |
| Magnet Radius (a1) | 23.2 ± 0.7 | ”m | Particle 1 (used for frequency scaling) |
| Magnet Radius (a3) | 15.1 ± 0.1 | ”m | Particle 3 (used for coupling measurement) |
| Maximum Trapping Frequencies (fmax) | 2.3 to 25.2 | kHz | Dependent on particle size and mode (x, y, z) |
| NV Center Zero-Field Splitting (Dzf/2Ï) | ~2.87 | GHz | Electronic ground state S=1 |
| Spin-Mechanical Coupling (λg) | 48 ± 2 | mHz | Measured gradient coupling |
| NV Center Zero Point Motion (xzp) | 24 ± 1 | fm | Calculated for the measured mode |
| NV Implantation Depth (dimpl) | ~40 | nm | Below the diamond surface |
| NV-Magnet Separation (râ) | 99 ± 5 | ”m | Distance between centers during coupling test |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relies on controlled magnetostatic levitation and high-sensitivity optical detection of both mechanical motion and spin state.
- Magnet Levitation Setup: Single hard micro-magnets are placed in microfabricated pockets above a thin film of YBCO (Type-II superconductor).
- Controlled Cooldown: The relative distance (hcool) between the magnet and the YBCO film is precisely adjusted while cooling the YBCO below its critical temperature (Tc â 90K). This freezes the magnetic flux penetrating the film, determining the stable 3D trapping conditions (hlev and trapping frequencies).
- Motion Detection (Camera): The magnetâs center-of-mass motion (x, y, z) is observed through a long working distance microscope objective and recorded using a fast camera. Power Spectral Densities (PSD) are calculated from the video time-traces to identify the three translational modes.
- Dissipation Measurement: Q-factors are determined by ring-down measurements, where one mode is excited using an AC magnetic field, and the exponential decay time (1/Îł) of the energy is observed (Q = Ïj/Îł).
- Spin Qubit Integration: A diamond slab containing implanted NV centers is positioned across the pocket, placing the NV center in the magnetâs stray field.
- Spin State Readout (ODMR): Optically Detected Magnetic Resonance (ODMR) is used to monitor the NV center spin state. A microwave (MW) signal drives the |ms = 0> â |ms = ±1> transition, and the resulting change in Photoluminescence (PL) intensity is measured.
- Coupling Measurement: The magnetâs motion shifts the electron spin resonance frequency (ÎŽÏNV). This motion is measured by observing the peak in the PL count PSD while driving the magnet into a quasi-thermal state with a broadband fluctuating magnetic field.
- Thermal Confirmation: The thermal character of the driven mode is confirmed by analyzing the distribution of the integrated PSD area (variance) over repeated measurements, which fits an exponential distribution P(E) = ÎČexp(-ÎČE).
Commercial Applications
Section titled âCommercial ApplicationsâThe demonstrated platform provides a robust foundation for next-generation quantum technologies requiring high-fidelity coupling between massive mechanical systems and individual spins.
- Ultra-Sensitive Metrology:
- Magnetometers, accelerometers, and gyroscopes utilizing the magnet as the sensor element, read out by the NV center.
- Detection of dark matter candidates.
- Quantum Information Processing:
- Realization of quantum networks and hybrid architectures for engineering magnonic quantum networks.
- Mechanically mediated spin-spin entanglement between distant spin qubits.
- Fundamental Physics and Quantum Mechanics:
- Testing quantum mechanics with mesoscopic objects, including the preparation of non-Gaussian quantum states of motion.
- Exploration of dynamics between a levitated nanomagnet and a single flux vortex in the superconductor.
- Advanced Sensing:
- High-cooperativity spin-phonon systems enabling ground-state cooling of mechanical modes.
- Measurement of the magnetâs internal degrees of freedom (e.g., Kittel magnon zero point magnetization).
- Novel Magnetomechanics:
- Observation of precession due to the intrinsic spin angular momentum of the magnet (Einstein-deHaas frequency).
View Original Abstract
We demonstrate a new mechanical transduction platform for individual spin qubits. In our approach, single micromagnets are trapped using a type-II superconductor in proximity of spin qubits, enabling direct magnetic coupling between the two systems. Controlling the distance between the magnet and the superconductor during cooldown, we demonstrate three-dimensional trapping with quality factors around 1Ă10^{6} and kHz trapping frequencies. We further exploit the large magnetic moment to mass ratio of this mechanical oscillator to couple its motion to the spin degrees of freedom of an individual nitrogen vacancy center in diamond. Our approach provides a new path towards interfacing individual spin qubits with mechanical motion for testing quantum mechanics with mesoscopic objects, realization of quantum networks, and ultrasensitive metrology.