Quantum control of nuclear-spin qubits in a rapidly rotating diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-12-13 |
| Journal | Physical Review Research |
| Authors | A. A. Wood, R. M. Goldblatt, R. E. Scholten, A. Martin |
| Institutions | The University of Melbourne |
| Citations | 12 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Quantum Control in Rotating Diamond
Section titled âTechnical Documentation & Analysis: Quantum Control in Rotating DiamondâReference Paper: Quantum control of nuclear spin qubits in a rapidly rotating diamond (Wood et al., 2021)
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates robust quantum control over 14N nuclear spin qubits embedded in Nitrogen-Vacancy (NV) centers within a diamond rotating at 1 kHz, overcoming significant magnetic and mechanical perturbations. This work validates the use of MPCVD diamond in highly dynamic quantum sensing applications, such as gyroscopes and inertial sensors.
- Core Achievement: Coherent quantum control (Ramsey/Spin-Echo) of 14N nuclear spins maintained in a diamond rotating at 1 kHz, exceeding the quantum decoherence rate.
- Material Requirement: High-purity, electronic-grade Single Crystal Diamond (SCD) with controlled NV ensemble density, cut to a precise (100) orientation.
- Key Innovation: Implementation of feed-forward quantum control using an Arbitrary Waveform Generator (AWG) to dynamically modulate RF frequency, maintaining resonance despite rotation-induced shifts (up to 20% modulation).
- Coherence Preservation: Continuous dynamical decoupling (spin-locking) successfully eliminated the detrimental effects of motor period jitter (standard deviation of 323 ns), preserving nuclear spin coherence (Tâ = 5.0 ms).
- Sensing Regime Unlocked: The experiment accesses a previously inaccessible regime where the NV axis and magnetic field are free to assume any relative orientation, opening new avenues for probing electron-nuclear spin mixing and geometric phases.
- 6CCVD Value Proposition: 6CCVD specializes in providing the high-purity, custom-cut, and precisely polished SCD substrates necessary to replicate and advance this dynamic quantum sensing platform.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research paper, highlighting the critical parameters achieved or required for the experiment:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Material Grade | Electronic Grade | ppb N | Required for high-coherence NV ensemble. |
| Diamond Cut Orientation | (100) | Plane | Mounted face, setting the 54.7° NV angle to the rotation axis. |
| Rotation Frequency (f) | 1 | kHz | Equivalent to 60,000 rpm; faster than Tâ* of electron spin (~100 ”s). |
| Applied Magnetic Field (Bâ) | 480 - 500 | G | Used for ESLAC (Excited State Level Anti-Crossing) polarization. |
| NV Electron Spin Polarization Time | 1 | ”s | Time to achieve almost 100% polarization. |
| Nuclear Spin Polarization Window | ~4 | ”s | Angular window of 1.2° where polarization is possible during rotation. |
| Stationary 14N Tâ Coherence Time | 6.5 (4) | ms | Reference coherence time (held stationary). |
| Rotating 14N Tâ Coherence Time (Spin-Lock) | 5.0 (1) | ms | Achieved coherence time under 1 kHz rotation and dynamical decoupling. |
| Motor Period Jitter (Standard Deviation) | 323 | ns | Primary source of noise overcome by dynamical decoupling. |
| Nuclear Spin Transition Frequency Modulation | ~20 | % | Modulation induced by rotation, countered by feed-forward control. |
| NV Zero-Field Splitting (Dzfs/2Ï) | 2.870 | GHz | Intrinsic property of the NV center. |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relied on precise material preparation and advanced quantum control techniques to maintain coherence in a highly dynamic environment.
- Material Preparation and Mounting:
- Electronic grade diamond containing an ensemble of NV centers was mounted on its (100) face to a high-speed electric motor shaft.
- A 480 G permanent magnetic field was applied at a 54.7° angle relative to the rotation axis.
- Synchronous Optical Polarization:
- The motor controller generated a timing signal fed to a delay generator to trigger laser (532 nm) and RF/microwave pulses synchronous with the diamond rotation.
- The laser pulse was timed to activate only during the narrow 4 ”s window when the NV axis and magnetic field were aligned (via ESLAC) to polarize the 14N nuclear spin into the $|m_{s} = 0, m_{I} = +1\rangle$ state.
- Feed-Forward Quantum Control:
- An Arbitrary Waveform Generator (AWG) was used to synthesize a frequency-modulated (FM) RF signal.
- This FM profile was calculated by diagonalizing the NV Hamiltonian (H) across the rotation angle, ensuring the RF drive remained resonant with the nuclear spin transition despite the rotation-induced frequency shifts.
- Coherence Measurement:
- Standard quantum sensing protocols (Ramsey interferometry and Spin-Echo) were performed using tailored RF Ï/2 and Ï pulses, adjusted in duration based on the instantaneous Rabi frequency (which varied significantly due to rotation).
- Dynamical Decoupling (Spin-Locking):
- Continuous dynamical decoupling (spin-locking) was applied over multiple rotation periods (up to 2 ms) to eliminate the effects of mechanical noise (period jitter) and preserve the long Tâ coherence time.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials required to replicate, optimize, and extend this groundbreaking research into dynamic quantum sensing and gyroscopy.
Applicable Materials
Section titled âApplicable Materialsâ| Research Requirement | 6CCVD Material Recommendation | Technical Justification |
|---|---|---|
| High-Purity Substrate (Electronic Grade, low ppb N) | Optical Grade Single Crystal Diamond (SCD) | Provides the necessary low defect density and high Tâ coherence required for quantum memory and sensing applications. We control the NV precursor concentration for optimal ensemble performance. |
| Future Isotope Studies (e.g., 15N, 13C) | Custom Isotope-Doped SCD | Enables exploration of alternative spin systems (e.g., 15N, which lacks the quadrupole interaction of 14N) as discussed in the paper, simplifying control and potentially increasing coherence. |
| High-Power/High-Field Applications | Polycrystalline Diamond (PCD) Substrates | For applications requiring larger area (up to 125 mm) or thick substrates (up to 10 mm) to support stronger magnetic fields or higher mechanical loads. |
Customization Potential
Section titled âCustomization PotentialâThe success of this experiment hinges on the precise preparation and integration of the diamond substrate. 6CCVD offers critical customization services to meet these demands:
- Custom Dimensions and Geometry: The rotating diamond must be small and precisely balanced. 6CCVD provides laser cutting services to produce custom plates and wafers up to 125 mm in size, cut to specific geometries required for high-speed motor mounting and minimal mechanical jitter.
- Crystallographic Precision: We guarantee custom orientation cuts (e.g., (100) as used here, or (111) for alternative NV alignment) with high angular accuracy, essential for optimizing the ESLAC polarization window.
- Surface Quality: The optical readout relies on collecting red fluorescence (PL). 6CCVD provides ultra-smooth polishing (Ra < 1 nm for SCD, Ra < 5 nm for inch-size PCD) to minimize scattering and maximize the photon collection efficiency, crucial for detecting the low fluorescence contrast (2.5%) observed during rotation.
- Metalization for Integration: While not explicitly detailed in the paper, future integration may require on-chip RF coils or contacts. 6CCVD offers internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu) for creating custom contact pads or microstructures directly on the diamond surface.
Engineering Support
Section titled âEngineering SupportâThe complexity of dynamic quantum control requires deep material expertise. 6CCVDâs in-house PhD team specializes in the material science of NV centers and can assist researchers with:
- Material Selection: Guidance on optimizing NV ensemble density and purity specifications (e.g., nitrogen concentration) to maximize Tâ coherence for similar rotating quantum sensing projects.
- Integration Challenges: Consultation on mechanical mounting, thermal management, and optical alignment strategies for high-speed rotation environments.
- Global Logistics: We offer global shipping (DDU default, DDP available) to ensure rapid and reliable delivery of custom materials worldwide.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Nuclear spins in certain solids couple weakly to their environment, making\nthem attractive candidates for quantum information processing and inertial\nsensing. When coupled to the spin of an optically-active electron, nuclear\nspins can be rapidly polarized, controlled and read via lasers and\nradiofrequency fields. Possessing coherence times of several milliseconds at\nroom temperature, nuclear spins hosted by a nitrogen-vacancy center in diamond\nare thus intriguing systems to observe how classical physical rotation at\nquantum timescales affects a quantum system. Unlocking this potential is\nhampered by precise and inflexible constraints on magnetic field strength and\nalignment in order to optically induce nuclear polarization, which restricts\nthe scope for further study and applications. In this work, we demonstrate\noptical nuclear spin polarization and rapid quantum control of nuclear spins in\na diamond physically rotating at $1\,$kHz, faster than the nuclear spin\ncoherence time. Free from the need to maintain strict field alignment, we are\nable to measure and control nuclear spins in hitherto inaccessible regimes,\nsuch as in the presence of a large, time-varying magnetic field that makes an\nangle of more than $100^\circ$ to the nitrogen-lattice vacancy axis. The field\ninduces spin mixing between the electron and nuclear states of the qubits,\ndecoupling them from oscillating rf fields. We are able to demonstrate that\ncoherent spin state control is possible at any point of the rotation, and even\nfor up to six rotation periods. We combine continuous dynamical decoupling with\nquantum feedforward control to eliminate decoherence induced by imperfect\nmechanical rotation. Our work liberates a previously inaccessible degree of\nfreedom of the NV nuclear spin, unlocking new approaches to quantum control and\nrotation sensing.\n