Ultracoherent Gigahertz Diamond Spin-Mechanical Lamb Wave Resonators
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-08-22 |
| Journal | Nano Letters |
| Authors | Xinzhu Li, Ignas Lekavicius, Jens U. Noeckel, Hailin Wang |
| Institutions | University of Oregon |
| Citations | 4 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Ultracoherent GHz Performance: Demonstrated diamond Lamb Wave Resonators (LWRs) operating at a fundamental compression mode frequency (fm) of 0.977 GHz.
- Record Quality Factor (Q): Achieved an ultrahigh Quality factor (Q) of 1.2 x 107 at temperatures near 7 K, surpassing previously reported diamond optomechanical crystals and rivaling state-of-the-art silicon devices.
- Phononic Protection: The LWR is embedded in a square phononic crystal lattice, utilizing a large phononic band gap to shield the compression mode, significantly reducing structural and intrinsic material loss.
- All-Optical Excitation and Detection: An all-optical approach was developed, using a temporally modulated optical gradient force (1550 nm laser) to excite the in-plane compression mode.
- Strain-Mediated Detection: Mechanical vibrations were detected via strain coupling to an embedded silicon vacancy (SiV) center, observed through strong phonon sidebands in the SiV optical excitation spectrum.
- High-Sensitivity Measurement: Sideband optical interferometry was successfully employed to detect picometer-scale in-plane mechanical vibrations, a method effective where conventional optical interferometry fails.
- Quantum Platform: This ultracoherent platform provides a promising foundation for reaching the quantum regime of spin mechanics, particularly for phononic cavity QED of electron spins.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Resonator Material | Diamond | N/A | Electronic grade bulk film |
| Resonance Frequency (fm) | 0.977 | GHz | Fundamental compression mode |
| Quality Factor (Q) | 1.2 x 107 | N/A | Measured near 7 K |
| Mechanical Linewidth (Îłm/2Ï) | 83 | Hz | Corresponding to Q=1.2 x 107 |
| Operating Temperature | Near 7 | K | Closed cycle cryostat |
| Estimated Vibration Amplitude (Am) | 3 x 10-12 | m | Detected via SiV coupling (3 picometers) |
| LWR Thickness (d) | 1.5 | ”m | Fabricated sample thickness |
| LWR Dimensions | 9.5 x 4.5 | ”m | Length and width of the plate |
| Phononic Lattice Period | 8 | ”m | Square phononic crystal lattice |
| Excitation Laser Wavelength | 1550 | nm | Modulated optical gradient force drive |
| Excitation Laser Beam Waist | 2.3 | ”m | Radius at the center of the resonator |
| SiV Transition Wavelength (C-transition) | 737.0983 | nm | Optical detection wavelength |
| SiV Implantation Depth | 45 | nm | 28Si ions below the diamond surface |
| Diamond Youngâs Modulus | 1200 | GPa | Simulation parameter |
| Diamond Mass Density | 3500 | kg/m3 | Simulation parameter |
Key Methodologies
Section titled âKey MethodologiesâThe experiment involved advanced nanofabrication of diamond phononic structures and a specialized all-optical cryogenic measurement setup.
Fabrication Process
Section titled âFabrication Processâ- Starting Material: Electronic grade bulk diamond film was used.
- SiV Precursor Implantation: 28Si ions were implanted approximately 45 nm below the diamond surface to create silicon vacancy centers.
- Layer Deposition:
- A 280 nm layer of Si3N4 was deposited via Plasma-Enhanced Chemical Vapor Deposition (PECVD).
- A 500 nm layer of polymethyl methacrylate (PMMA) was deposited for lithography.
- Patterning: Electron beam lithography defined the phononic crystal pattern.
- Front-Side Etching:
- The pattern was transferred from PMMA to Si3N4 using CHF3 plasma etching.
- The diamond was etched using O2 plasma Reactive Ion Etching (RIE) at a rate of 100 nm/minute, achieving a depth of 1.6 ”m.
- Back-Side Release: The diamond film was thinned down from the backside using alternating Ar/Cl2 and O2 plasma RIE until the LWRs were released. A U-shaped shadow mask ensured the released structure remained attached to the bulk diamond film.
Measurement and Excitation
Section titled âMeasurement and Excitationâ- Cryogenic Environment: The sample was mounted on a cold-finger and maintained at temperatures near 7 K.
- Mechanical Drive: The fundamental compression mode was excited using a temporally modulated 1550 nm laser beam (average power typically 2 mW) focused onto the LWR center, leveraging the optical gradient force.
- Optical Detection (PLE): Photoluminescence Excitation (PLE) experiments used a 737 nm laser pulse for resonant excitation of the SiV C-transition.
- Strain Detection: The induced mechanical vibrations were detected via strain coupling to the SiV center, manifesting as strong phonon sidebands in the PLE spectrum.
- Interferometry: Sideband optical interferometry, utilizing a phase electro-optic modulator (EOM), was used to detect the in-plane mechanical vibrations coherently, enabling measurement of amplitudes as small as 3 picometers.
Commercial Applications
Section titled âCommercial ApplicationsâThe development of ultracoherent, GHz-frequency diamond spin-mechanical resonators is highly relevant to emerging quantum technologies and high-performance classical systems:
- Quantum Information Processing (QIP):
- Spin-Based Quantum Computers: Provides a robust platform for mechanical quantum networks, enabling phonon-mediated entanglement and coupling between distant electron spins (e.g., SiV centers).
- Phononic Cavity QED: The high Q-factor and strong coupling potential (estimated cooperativity C > 10) are crucial for realizing phononic cavity QED of electron spins, a key step toward quantum transduction and memory.
- Quantum Sensing: High-Q diamond resonators coupled to spin qubits are ideal for developing ultra-sensitive sensors for force, acceleration, and magnetic fields.
- Quantum Transduction: Phonons serve as an interface between solid-state qubits and optical photons, necessary for linking quantum processors across different physical domains.
- High-Frequency Electronics: The ultrahigh Q-factor (107) at GHz frequencies is valuable for developing extremely low-loss filters, oscillators, and timing references in classical radio frequency (RF) and microwave systems.
- Advanced Materials Science: The methodology for creating and shielding these structures (phononic band gaps in diamond) can be extended to other materials (e.g., silicon carbide) that host suitable spin qubits.
View Original Abstract
We report the development of an all-optical approach that excites the fundamental compression mode in a diamond Lamb wave resonator with an optical gradient force and detects the induced vibrations via strain coupling to a silicon vacancy center, specifically, via phonon sidebands in the optical excitation spectrum of the silicon vacancy. Sideband optical interferometry has also been used for the detection of in-plane mechanical vibrations, for which conventional optical interferometry is not effective. These experiments demonstrate a gigahertz fundamental compression mode with a <i>Q</i> factor of >10<sup>7</sup> at temperatures near 7 K, providing a promising platform for reaching the quantum regime of spin mechanics, especially phononic cavity quantum electrodynamics of electron spins.