Spin dynamical decoupling for generating macroscopic superpositions of a free-falling nanodiamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-01-31 |
| Journal | Physical review. A/Physical review, A |
| Authors | Benjamin D. Wood, Sougato Bose, Gavin W. Morley |
| Institutions | University College London, University of Warwick |
| Citations | 22 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Spin Dynamical Decoupling for Macroscopic Superpositions
Section titled âTechnical Documentation & Analysis: Spin Dynamical Decoupling for Macroscopic SuperpositionsâThis document analyzes the requirements for generating macroscopic spatial superpositions using NV- centers in nanodiamonds, as proposed in the attached research. It outlines how 6CCVDâs specialized MPCVD diamond materials and fabrication services directly enable the replication and advancement of this critical quantum research.
Executive Summary
Section titled âExecutive SummaryâThe research proposes a scheme utilizing Nitrogen-Vacancy (NV-) centers in levitated nanodiamonds to generate macroscopic spatial superpositions, probing the limits of quantum mechanics.
- Core Achievement: Proposal to place a 250 nm diameter diamond in a spatial superposition with separation exceeding 250 nm (estimated 276 nm).
- Critical Material Requirement: Ultra-long NV spin coherence time (T2 > 1 s) is mandatory to maintain coherence throughout the 190 ms drop duration in the inhomogeneous field.
- Material Solution: Achieving the required T2 necessitates the use of high-purity, isotopically enriched Carbon-12 (12C) diamond material to suppress spin bath decoherence.
- Methodology: Dynamical decoupling is implemented via a free-fall drop (2.4 m total) through a magnetic structure featuring 1.13 m of alternating inhomogeneous magnetic field gradients (âmagnetic teethâ).
- Fabrication Complexity: The scheme requires precise nanodiamond fabrication (250 nm spheres or etched pillars) and integration with complex microwave pulsing infrastructure.
- 6CCVD Value Proposition: 6CCVD provides the necessary high-purity Single Crystal Diamond (SCD) substrates, custom fabrication support (etching, polishing), and metalization services required for the magnetic and microwave components of the experiment.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points are extracted from the proposed experimental scheme:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Nanodiamond Diameter | 250 | nm | Target particle size for superposition |
| Nanodiamond Mass (m) | 2.9 x 10-17 | kg | Used in Hamiltonian calculations |
| Maximum Spatial Separation (s) | 276 | nm | Estimated maximum superposition distance |
| Required NV- T2 Coherence Time | > 1 | s | Necessary for coherence throughout the drop |
| Longest Reported T2 (12C Nanodiamond) | 708 | ”s | Achieved in isotopically pure 12C etched pillars |
| Total Drop Distance | 2.4 | m | Total length of the free-fall experiment |
| Inhomogeneous Field Region Length | 1.13 | m | Region where dynamical decoupling occurs |
| Drop Time in Inhomogeneous Region | 190 | ms | Duration of superposition evolution |
| Alternating Gradient Magnitude | ±1.45 | T mm-1 | Generated by magnetic teeth structure |
| Bias Magnetic Field (B0) | 420 | mT | Applied at the center of the magnetic structure |
| Required Microwave Pulses | ~9800 | N/A | For dynamical decoupling (e.g., modified XY8) |
| Required Tilt Stability | < 350 | nrad | For active stabilization of the optical table |
Key Methodologies
Section titled âKey MethodologiesâThe proposed experiment relies on precise material preparation, environmental control, and synchronized microwave pulsing:
- Nanodiamond Preparation: The diamond must be cryogenically cooled (5K) and levitated in ultrahigh vacuum (UHV) using a magnetic or Paul trap. Mass, NV- presence, and single-spin occupancy must be confirmed.
- NV- Alignment and Neutralization: The NV- axis must be aligned to the external magnetic field (x-axis). The nanodiamond must be electrically neutralized (radioactive source/UV light) to ensure stable trapping.
- Spin Polarization and Initial Drop: The NV spin is polarized to |0), flipped to |-1), and dropped through the initial 1.27 m homogeneous magnetic field region to build speed.
- Superposition Initialization: A microwave Ï/2 pulse is applied to create the spin superposition state: (|0) + |-1))/â2.
- Dynamical Decoupling (DD): The diamond falls through the 1.13 m inhomogeneous region generated by magnetic teeth. Repeated microwave Ï pulses (e.g., modified XY8 sequence) are applied, synchronized to the magnetic field gradient changes, to maintain spin coherence (T2) and increase spatial separation.
- Recombination and Readout: Diamagnetic forces cause the superposition components to recombine after 190 ms. A final Ï/2 pulse ends the interferometric sequence. The nanodiamond is caught on a 5K glass slide, and the final spin state is read out optically via a confocal microscope setup.
- Environmental Control: Extreme stability is required, including magnet temperature stability (< 1 mK) and drop length monitoring (< 10 nm precision) to suppress induced phases and ensure precise pulse timing (< 1 ns).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the high-specification MPCVD diamond materials and custom fabrication services required for this cutting-edge quantum gravity research.
Applicable Materials
Section titled âApplicable MaterialsâThe success of this experiment hinges on maximizing the NV- spin coherence time (T2), which requires minimizing decoherence from the surrounding spin bath (primarily 13C impurities).
| Research Requirement | 6CCVD Material Solution | Technical Justification |
|---|---|---|
| Ultra-Long T2 Coherence | Optical Grade Single Crystal Diamond (SCD) | Our SCD is grown with extremely low nitrogen content, minimizing paramagnetic defects. |
| Isotopic Purity | Custom Isotopic Enrichment (12C SCD) | We offer custom growth of SCD with isotopic purity > 99.99% 12C, essential for achieving T2 times > 1 second by eliminating the primary source of spin bath noise. |
| Nanodiamond Precursor | SCD Plates up to 125 mm | Provides the high-quality bulk material necessary for subsequent etching into 250 nm nanodiamonds or 300-500 nm pillars, as referenced in the paper. |
| Polishing Requirements | SCD Polishing (Ra < 1 nm) | Ensures high-quality optical surfaces for efficient spin excitation and readout (PL excitation) and minimizes surface defects that can degrade NV- performance. |
Customization Potential
Section titled âCustomization PotentialâThe experimental setup requires precise geometry and integration of microwave delivery systems. 6CCVD offers comprehensive customization capabilities:
- Custom Dimensions: We supply SCD plates up to 125 mm, allowing researchers to select the optimal starting material size for subsequent nanodiamond fabrication (etching, milling).
- Nanodiamond Fabrication Support: While the paper references etching bulk diamond into pillars (300-500 nm diameter), 6CCVD offers consultation and support for creating specific geometries from our high-purity SCD substrates.
- Metalization Services: The dynamical decoupling scheme requires precise microwave pulses. 6CCVD offers in-house metalization (Au, Pt, Pd, Ti, W, Cu) for fabricating high-frequency microwave strip lines directly onto the diamond substrate or adjacent components used for pulse delivery.
- Substrate Thickness: We provide SCD substrates ranging from 0.1 ”m up to 500 ”m, and custom substrates up to 10 mm, offering flexibility for mounting and thermal management in cryogenic environments (5K operation).
Engineering Support
Section titled âEngineering SupportâThe complexity of achieving macroscopic quantum superpositions demands expert material science consultation.
- NV-Center Optimization: 6CCVDâs in-house PhD team specializes in optimizing MPCVD growth recipes to control NV- concentration and maximize T2 performance, critical for similar Quantum Gravity/Macroscopic Superposition projects.
- Thermal and Mechanical Stability: We assist engineers in selecting diamond specifications that provide the necessary thermal conductivity and mechanical stability required for the extreme precision (1 mK temperature stability, 10 nm length precision) needed for the magnetic structure.
- Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) of sensitive, high-value diamond materials to research facilities worldwide.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Levitated nanodiamonds containing negatively charged nitrogen-vacancy centers\n(${\text{NV}}^{-}$) have been proposed as a platform to generate macroscopic\nspatial superpositions. Requirements for this include having a long\n${\text{NV}}^{-}$ spin coherence time, which necessitates formulating a\ndynamical decoupling strategy in which the regular spin flips do not cancel the\ngrowth of the superposition through the Stern-Gerlach effect in an\ninhomogeneous magnetic field. Here, we propose a scheme to place a\n$250$-nm-diameter diamond in a superposition with spatial separation of over\n$250$ nm, while incorporating dynamical decoupling. We achieve this by letting\na diamond fall for $2.4$ m through a magnetic structure, including $1.13$ m in\nan inhomogeneous region generated by magnetic teeth.\n