Design of an Integrated Bell-State Analyzer on a Thin-Film Lithium Niobate Platform
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-12-17 |
| Journal | IEEE photonics journal |
| Authors | Uday Saha, Edo Waks |
| Institutions | University of Maryland, College Park, Joint Quantum Institute |
| Citations | 4 |
| Analysis | Full AI Review Included |
Integrated Photonic Bell-State Analyzer: Material Science Analysis and 6CCVD Quantum Solutions
Section titled âIntegrated Photonic Bell-State Analyzer: Material Science Analysis and 6CCVD Quantum SolutionsâThis technical documentation analyzes the design of an integrated Bell-State Analyzer (BSA) on a thin-film Lithium Niobate (TFLN) platform, focusing on its implications for scalable quantum computing and its direct relevance to diamond-based spin qubit systems, a core market for 6CCVD.
Executive Summary
Section titled âExecutive SummaryâThe research presents a highly optimized design for a photonic Bell-State Analyzer (BSA) on a thin-film lithium niobate (TFLN) platform, crucial for scaling quantum networks.
- High Fidelity Entanglement: The device achieves entanglement fidelity exceeding 99% between two remote trapped ion qubit systems.
- Polarization Insensitivity: The design successfully overcomes the inherent polarization anisotropy of TFLN waveguides by optimizing etch depth, width, and gap distance, achieving near-identical coupling efficiencies for TE (66.16%) and TM (65.52%) modes.
- Arbitrary Splitting Ratios: By adjusting the coupling length (L$_{c}$), the directional coupler can achieve any desired polarization-independent power splitting ratio, enabling realization of various photonic quantum gates.
- Broad Applicability: While optimized for Barium ions (493.55 nm), the design is explicitly applicable to other optically active spin qubits, including color centers in diamond, quantum dots, and rare-earth ions.
- Fabrication Tolerance: The optimized structure exhibits high tolerance to fabrication imperfections (±10 nm variation in width/etch depth maintains >98% fidelity), crucial for manufacturability.
- 6CCVD Relevance: This BSA technology provides the necessary quantum interconnect for scaling diamond-based quantum processors, requiring high-purity, low-roughness Single Crystal Diamond (SCD) materials provided by 6CCVD.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the optimized Bell-State Analyzer design:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Operating Wavelength ($\lambda_{0}$) | 493.55 | nm | Main transition of trapped Barium ions (Ba+) |
| Entanglement Fidelity | >99 | % | Achieved at optimal coupling length (L$_{c}$) |
| Minimum Entanglement Error | 2.48 x 10-4 | N/A | Achieved at L$_{c}$ = 13.95 ”m |
| Waveguide Width (w) | 475 | nm | Optimized for polarization insensitivity |
| Etch Depth (h$_{e}$) | 110 | nm | Optimized for polarization insensitivity |
| Slab Thickness (h$_{slab}$) | 190 | nm | Total TFLN thickness is 300 nm (h${e}$ + h${slab}$) |
| Gap Distance (g) | 40 | nm | Optimized for full device polarization insensitivity |
| Coupling Length (L$_{c}$) | 13.95 | ”m | Optimal length for 50/50 power splitting |
| Bending Length (L$_{s}$) | 30 | ”m | Optimized for minimal bending loss |
| TE Coupling Efficiency | 66.16 | % | Fiber-to-chip coupling via lensed fiber (NA 0.6) |
| TM Coupling Efficiency | 65.52 | % | Fiber-to-chip coupling via lensed fiber (NA 0.6) |
| Fabrication Tolerance (w, h$_{e}$) | ±10 | nm | Maintains >98% fidelity |
| Fabrication Tolerance (h$_{slab}$) | ±30 | nm | Maintains >96.36% fidelity |
Key Methodologies
Section titled âKey MethodologiesâThe integrated Bell-State Analyzer was designed using a directional coupler structure on a thin-film Lithium Niobate (TFLN) platform, optimized for polarization independence.
- Material Platform: Thin-Film X-cut Lithium Niobate (300 nm thick) on a 2 ”m Silicon Dioxide (SiO$_{2}$) buffer layer.
- Waveguide Geometry: Partially etched rib waveguide structure with 75° sidewall angles, designed to support both Transverse Electric (TE) and Transverse Magnetic (TM) modes.
- Initial Polarization Optimization ($\xi$ = 1): Finite difference eigenmode solver was used to optimize the waveguide width (w = 475 nm) and etch depth (h$_{e}$ = 110 nm) to minimize the disparity between the TE and TM coupling factors ($\Delta\eta$).
- S-Bend Integration: S-bend regions were introduced to connect the input ports to the coupling region. The bending length (L$_{s}$) was optimized to 30 ”m to ensure high transmission (>99%) and a compact footprint.
- Full Device Re-optimization: The gap distance (g) was re-optimized to 40 nm to compensate for the polarization anisotropy introduced by the S-bends, achieving polarization-independent power splitting for the complete device.
- Entanglement Calculation: Entanglement error (E = 1 - F) was calculated based on the transmission and reflection coefficients of the beam splitter, yielding a minimum error at the optimal coupling length (L$_{c}$ = 13.95 ”m).
- Light Coupling Interface: Coupling efficiency was optimized using a lensed fiber edge-coupled approach (NA 0.6) to achieve polarization-insensitive light injection into the chip.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research demonstrates a critical component for scalable quantum interconnects. While the platform is TFLN, the application extends directly to diamond-based spin qubits (e.g., NV, SiV, GeV centers), which require high-quality CVD diamond materials for integration. 6CCVD is uniquely positioned to supply the necessary diamond substrates and specialized processing required to replicate or extend this quantum research.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research using diamond-based spin qubits, researchers require materials with exceptional purity, low strain, and precise surface quality:
- Optical Grade Single Crystal Diamond (SCD): Essential for hosting high-coherence color centers (NV$^{-}$, SiV$^{-}$, GeV$^{-}$). 6CCVD provides SCD with ultra-low nitrogen content necessary for maximizing qubit coherence times and optical properties.
- Polycrystalline Diamond (PCD) Substrates: For large-scale integrated photonic circuits where the active quantum material (SCD) is bonded or grown locally. 6CCVD offers PCD plates/wafers up to 125mm in diameter, enabling high-throughput manufacturing and complex circuit integration.
- Custom Thickness Control: We provide precise thickness control for both SCD and PCD, ranging from 0.1”m to 500”m for active layers, and substrates up to 10mm thick, supporting complex device architectures and thermal management.
Customization Potential
Section titled âCustomization PotentialâThe TFLN design relies on highly precise nanophotonic fabrication (475 nm width, 110 nm etch depth). Diamond-based quantum photonics requires similar precision, which 6CCVD supports through advanced processing:
| Requirement from Research | 6CCVD Capability | Technical Advantage |
|---|---|---|
| Ultra-Low Loss Interface | Polishing (Ra < 1nm for SCD) | Ensures minimal scattering loss for visible-spectrum quantum photons (493.55 nm and typical color center wavelengths). |
| Integrated Components | Custom Metalization | We offer in-house deposition of Au, Pt, Pd, Ti, W, and Cu, necessary for creating electrical contacts, micro-heaters, or bonding layers required for hybrid integration with TFLN or ion traps. |
| Precise Dimensions | Custom Dimensions & Laser Cutting | We supply custom-sized plates and wafers, ensuring compatibility with existing lithography and etching tools used for nanophophotonic fabrication. |
| Scalability | Inch-Size PCD Polishing | Our capability to polish inch-size PCD wafers to Ra < 5nm supports the development of large-scale quantum integrated circuits. |
Engineering Support
Section titled âEngineering SupportâThe successful implementation of a Bell-State Analyzer is critical for establishing quantum interconnects. 6CCVDâs in-house PhD team specializes in material selection and optimization for quantum applications.
- Material Selection for Spin Qubits: We assist engineers and scientists in selecting the optimal SCD grade, orientation, and thickness for specific color center applications (e.g., NV centers in the visible range, SiV/GeV centers in the telecom range).
- Hybrid Integration Consultation: Our expertise supports projects involving the integration of diamond quantum emitters with external photonic platforms, such as TFLN or silicon nitride, ensuring optimal optical coupling and thermal performance.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Trapped ions are excellent candidates for quantum computing and quantum networks because of their long coherence times, ability to generate entangled photons as well as high fidelity single- and two-qubit gates. To scale up trapped ion quantum computing, we need a Bell-state analyzer on a reconfigurable platform that can herald high fidelity entanglement between ions. In this work, we design a photonic Bell-state analyzer on a reconfigurable thin-film lithium niobate platform for polarization-encoded qubits. We optimize the device to achieve high fidelity entanglement between two trapped ions and find >99% fidelity. Apart from that, the directional coupler used in our design can achieve any polarization-independent power splitting ratio which can have a rich variety of applications in the integrated photonic technology. The proposed device can scale up trapped ion quantum computing as well as other optically active spin qubits, such as color centers in diamond, quantum dots, and rare-earth ions.