| Metadata | Details |
|---|
| Publication Date | 2025-08-11 |
| Journal | Physical review. A/Physical review, A |
| Authors | Guangyu Zhang, Huaijin Zhang, Zhang-qi Yin |
| Analysis | Full AI Review Included |
- Novel Quantum Architecture: A scalable quantum computing platform is proposed utilizing arrays of optically levitated nanodiamonds, each embedding a Nitrogen-Vacancy (NV) center qubit.
- Strong Coherent Coupling: Coherent coupling between distant NV spins is mediated by the dipole-dipole interaction of the nanodiamondsâ torsional mechanical modes.
- Performance Metrics: A torsional coupling strength of 119 kHz was achieved, exceeding typical environmental decoherence rates (~kHz) by two orders of magnitude.
- High-Fidelity Gates: The architecture enables Controlled-Phase (CPHASE) gates with fidelity exceeding 99%, meeting the required thresholds for fault-tolerant quantum computation (e.g., surface codes).
- Design Optimization: Optimal coupling is achieved using ellipsoidal nanodiamonds with an aspect ratio of 1.6, maximizing polarizability anisotropy under optical binding fields.
- Scalability and Reconfigurability: The system supports wavelength-selective addressing of individual NV centers and dynamic array reconfiguration via optical tweezers, overcoming traditional scalability limitations in solid-state platforms.
- Operational Environment: The system leverages the long room-temperature spin coherence of NV centers, offering a viable path toward ambient-condition quantum processing.
| Parameter | Value | Unit | Context |
|---|
| Maximum Torsion-Torsion Coupling (g0/2Ï) | 119 | kHz | Achieved with optimal geometry |
| CPHASE Gate Fidelity (F) | > 99 | % | Achieved using dynamical decoupling |
| Optimal Particle Aspect Ratio (a/b) | 1.6 | Dimensionless | Ellipsoidal nanodiamond shape |
| Long Semiaxis (a) | 300 | nm | Fixed particle volume |
| Short Semiaxis (b) | 180 | nm | Fixed particle volume |
| Nanodiamond Density (Ï) | 3500 | kg/m3 | Material property (Diamond) |
| Relative Permittivity (Δr) | 5.7 | Dimensionless | At operational frequency (1064 nm) |
| Trapping Laser Wavelength (λ) | 1064 | nm | Optical tweezers |
| Beam Waist Radius (w0) | 500 | nm | Optical tweezers |
| Laser Power Range (P0) | 600 to 1000 | mW | Used for tuning coupling strength |
| Interparticle Spacing (R) | 1.06 | ”m | Strongest coupling regime (R/λ = 0.95) |
| External Magnetic Field (B) | 0.1 | T | Required for strong spin-torsion coupling (gi) |
| Minimum Gate Time (tg) | 22.5 | ”s | For integer parameter m=4 |
| NV Spin Coherence Time (T2) | ~1 | ms | Typical experimental value |
| Torsional Mode Rethermalization Rate (Îș) | ~100 | Hz | Environmental decoherence limit |
- Optical Trapping and Environment: Ellipsoidal nanodiamonds, each containing an NV center, are trapped in high vacuum using linearly polarized optical tweezers (λ = 1064 nm).
- Torsional Mode Selection: The anisotropic polarizability of the non-spherical particles is exploited to generate strong optical binding forces, coupling the torsional (rotational) modes in the y-z plane.
- Geometry and Field Optimization: Multipole expansion corrections are applied to the dipole-dipole interaction model. The particle aspect ratio is fixed at 1.6 to maximize polarizability anisotropy (Îα) and coupling strength (g0).
- Spin-Torsion Hybridization: A homogeneous external magnetic field (B ~ 0.1 T) is applied, inducing a strong coupling (gi) between the NV electron spin and the mechanical torsional mode, forming a hybrid quantum system.
- CPHASE Gate Protocol: The controlled-phase gate is implemented using a modified SĂžrensen-MĂžlmer scheme, leveraging the resonant coupling between the two NV centers mediated by the mechanical modes.
- Dynamic Control: Gate speed (tg) and coupling strengths (gi, g0) are dynamically tuned by adjusting the optical tweezersâ power (P0) and the external magnetic field (B).
- Error Mitigation: Dynamical Decoupling (DD) and spin echo techniques are applied to the system Hamiltonian to suppress thermal noise (rethermalization) and spin dephasing, achieving fault-tolerant fidelity.
- Reconfigurable Array Assembly: Optical tweezers networks are used for precise spatial control and repositioning of nanodiamonds, enabling non-local gate operations and dynamic reconfiguration of the quantum network geometry.
- Fault-Tolerant Quantum Computing: Provides a scalable, room-temperature platform for implementing quantum error correction protocols (e.g., qLDPC codes) with gate fidelities > 99%.
- Distributed Quantum Networks: The reconfigurable array geometry and spectrally tunable coupling facilitate the development of modular quantum networks and non-local gate operations.
- High-Precision Quantum Sensing: Potential application in advanced rotational sensing, leveraging the ultralow decoherence rates of the levitated mechanical oscillators.
- Programmable Quantum Simulation: Enables the study of complex quantum phenomena, such as entanglement entropy, quantum phase transitions, and quantum many-body scars, analogous to studies in ultra-cold atom systems but within a solid-state platform.
- Solid-State Qubit Technology: Offers a promising alternative to traditional NV-center architectures (which suffer from short-range dipolar coupling) and cryogenic systems (superconducting circuits).
View Original Abstract
Nitrogen-vacancy (NV) centers in nanodiamond offer a promising platform for quantum information processing due to their room-temperature spin coherence and optical addressability. However, scalable quantum processors remain limited by the challenge of achieving strong, controllable interactions between distant NV spins. Here, we propose a scalable architecture utilizing optically levitated nanodiamond arrays, where torsional vibrations mediate the coherent coupling between the embedded NV centers. By optimizing the shape of ellipsoidal nanoparticles, we achieve a light-induced coupling strength exceeding 119 kHz between torsional modes of the distant levitated nanodiamonds, which are two orders of magnitude larger than the typical decoherence rates in this system. This strong interaction, combined with magnetic-field-enabled spin-torsion coupling, establishes an effective interaction between the spatially separated NV centers in the distant nanodiamonds. Numerical simulations confirm that dynamic decoupling can suppress both thermal noise and spin dephasing, enabling two-qubit gates with fidelity exceeding 99%. This work provides a foundation for reconfigurable quantum hybrid systems, with potential applications in rotational sensing and programmable quantum processing.