Mapping a 50-spin-qubit network through correlated sensing
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-03-05 |
| Journal | Nature Communications |
| Authors | G. L. van de Stolpe, Damian Kwiatkowski, C. E. Bradley, J. Randall, M. H. Abobeih |
| Institutions | Element Six (United Kingdom), University of Pennsylvania |
| Citations | 27 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Record Spin Network Mapping: Successfully mapped a network of 50 coupled 13C nuclear spins surrounding a single Nitrogen-Vacancy (NV) center in diamond, a significant increase over previous state-of-the-art systems (up to 27 spins).
- High-Resolution Correlated Sensing: Developed and applied concatenated double-resonance sequences to measure connected spin chains, directly resolving network connectivity and overcoming spectral crowding.
- Spectral Resolution Breakthrough: Achieved T2-limited spectral resolution for spin frequencies (Ai) by integrating electron-nuclear double resonance, improving distinction by approximately 75 times compared to T2*-limited methods.
- Comprehensive Characterization: The mapping characterized 1225 spin-spin interactions, providing a complete connectivity graph and a validated 3D spatial reconstruction of the 50-qubit register.
- Enabling Quantum Simulation: The results provide a basis for universal quantum control and readout of a large, programmable solid-state spin register for quantum simulation and computation.
- Advanced Nano-MRI: The correlated sensing methods are applicable to high-resolution nano-scale magnetic resonance imaging (nano-MRI) of complex spin systems external to the diamond host crystal.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Mapped Spin Count | 50 | spins | 13C nuclear spin network around a single NV center. |
| Spin Interactions Mapped | 1225 | interactions | Total spin-spin couplings characterized. |
| Operating Temperature | 3.7 | K | Performed using a Montana S50 Cryostation setup. |
| External Magnetic Field (Bz) | 403.553 | G | Applied along the NV symmetry axis. |
| Diamond Material | Homo-epitaxially grown | N/A | Sample has a natural abundance of 1.1% 13C. |
| NV Electron T2 (Hahn Echo) | 1.182(5) | ms | Electron spin coherence time. |
| Nuclear Spin T2 (Max) | 0.77(4) | s | Hahn-echo coherence time for isolated nuclear spins. |
| Nuclear Spin T2* (Inhomog.) | ~5 | ms | Typical inhomogeneous dephasing time. |
| High-Resolution Linewidth | 1.8 | Hz | Achieved for a specific nuclear spin (Ai = 14549.91(5) Hz). |
| Spectral Resolution Improvement | ~75 | times | Improvement over T2*-limited methods (e.g., 135 Hz to 1.8 Hz). |
| NV Readout Fidelity (Avg) | 0.938(2) | N/A | Average fidelity for the electronic spin state readout. |
| MW Pulse Frequency | 1.746666 (4.008650) | GHz | Used for driving electronic ms = 0 â ms = ±1 transitions. |
Key Methodologies
Section titled âKey Methodologiesâ- Sample Environment Control: Experiments were conducted on a naturally occurring NV center in a 1.1% 13C diamond sample at 3.7 K, utilizing a gold stripline for applying microwave (MW) and radio-frequency (RF) pulses, and a solid immersion lens (SIL) for enhanced optical readout.
- Spin Polarization: The nuclear spin bath was polarized using the PulsePol dynamical-nuclear-polarization (DNP) sequence, transferring polarization from the electron spin to the nuclear spins to maximize the measurable signal.
- Spin-Chain Sensing (Correlated SEDOR): Developed concatenated double-resonance sequences (extending the standard SEDOR protocol) to measure chains of coupled spins (up to 5 spins). This technique correlates multiple spin frequencies (Ai) and couplings (Cij) in a single measurement, directly revealing network connectivity and reducing ambiguity from spectral overlap.
- T2-Limited Frequency Spectroscopy: Implemented an electron-nuclear double-resonance block within the sensing sequence. By controlling the electron spin state, the hyperfine shift (Ai) was recoupled while decoupling the nuclear spin from quasi-static noise, achieving a high spectral resolution limited by the nuclear T2 time.
- Network Reconstruction Algorithm: The network was mapped using a graph search procedure (breadth-first-like search, rooted at the NV electron spin). Measured spin chains were iteratively fused based on overlapping vertices and edges, generating a hypothesis for the network connectivity.
- 3D Spatial Validation: The connectivity map was validated and refined using a positioning algorithm that models nuclear-nuclear couplings as dipolar interactions and constrains spin positions based on the measured hyperfine shifts (Ai) and the diamond lattice structure.
Commercial Applications
Section titled âCommercial Applicationsâ- Quantum Computing and Simulation: The 50-qubit register provides a robust, scalable platform for developing and testing quantum algorithms, particularly for simulating complex many-body physics and quantum chemistry.
- Quantum Memory and Networks: The characterized nuclear spin network serves as a high-coherence quantum memory register (T2 up to 0.77 s), essential for building long-distance quantum communication networks and performing entanglement distillation.
- Nano-Scale Magnetic Resonance Imaging (Nano-MRI): The high-resolution, correlated sensing techniques are directly applicable to next-generation nano-MRI, enabling the magnetic imaging and spectroscopy of complex biological samples (e.g., single proteins) and quantum materials with high spatial and spectral precision.
- Advanced Quantum Sensing: Provides a precise understanding of the local noise environment and hyperfine tensor, which is critical for optimizing the fidelity of quantum control gates (e.g., CNOT gates) in solid-state spin registers.
- Defect Physics and Materials Science: Offers a testbed for studying the coherence of solid-state spins on a microscopic level, allowing for quantitative tests of open quantum systems and theoretical predictions for defect spin systems (like the NV center).