Deterministic Bell state measurement with a single quantum memory
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-10-16 |
| Journal | npj Quantum Information |
| Authors | Akira Kamimaki, Keidai Wakamatsu, Kosuke Mikata, Yuhei Sekiguchi, Hideo Kosaka |
| Institutions | Yokohama National University |
| Citations | 7 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Deterministic Bell State Measurement in NV Diamond
Section titled âTechnical Documentation & Analysis: Deterministic Bell State Measurement in NV DiamondâExecutive Summary
Section titled âExecutive SummaryâThis research demonstrates a critical advancement in solid-state quantum computing: the deterministic and complete Bell State Measurement (BSM) using only a single Nitrogen-Vacancy (NV) center in diamond as the quantum memory.
- Core Achievement: Deterministic and complete BSM achieved by exploiting the inherent double qutrit nature of the electron and nitrogen ($^{14}$N) nuclear spins within the NV center.
- Resource Minimization: The scheme operates at a zero magnetic field and eliminates the need for auxiliary carbon isotopes, significantly reducing the physical resources required for quantum memory.
- Material Platform: The experiment relies on high-purity, Chemical Vapor Deposition (CVD) grown diamond with a <100> crystalline orientation, underscoring the necessity of high-quality MPCVD substrates.
- High-Fidelity Control: Universal holonomic quantum gates were implemented using Gradient Ascent Pulse Engineering (GRAPE)-optimized Microwave (MW) and Radiofrequency (RF) pulses, achieving intermediate gate fidelities exceeding 90%.
- Application Relevance: This demonstration paves the way for realizing high-fidelity quantum repeaters for long-haul quantum networks and simplified quantum interfaces for large-scale distributed quantum computers.
- 6CCVD Relevance: The success of this work is fundamentally dependent on the quality and customization potential of the CVD diamond substrate, a core offering of 6CCVD.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research paper, detailing the physical and operational parameters of the NV center system.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Material Type | High-Purity Type IIa | N/A | CVD-grown, low defect density |
| Crystal Orientation | <100> | N/A | Used for NV alignment |
| Operating Temperature | Below 5 | K | Required for coherent electron orbital control |
| Electron Spin Zero-Field Splitting (D0/2Ï) | 2.88 | GHz | Energy separation of electron spin states |
| Nitrogen Quadrupole Splitting (Q/2Ï) | 4.95 | MHz | Energy separation of nitrogen nuclear spin states |
| Hyperfine Coupling (A/2Ï) | 2.17 | MHz | Interaction between electron and nitrogen spins |
| Green Laser Wavelength | 515 | nm | Nonresonant excitation/charge state initialization |
| Red Laser Wavelength | 637 | nm | Resonant excitation/electron spin readout |
| Intermediate Gate Fidelity (F) | > 90 | % | Achieved during CNOT and Hadamard operations (QST) |
| Final BSM Fidelity (FBSM) | 68 | % | Average fidelity of the complete BSM |
| Readout Repetition Count | 30 | Times | Repetitions used for single-shot measurement sub-sequence |
| Photon Count Threshold (nc) | 1 | N/A | Used for Bell state discrimination |
Key Methodologies
Section titled âKey MethodologiesâThe deterministic BSM relies on precise material engineering and advanced quantum control techniques:
- Material Selection: The experiment utilized a high-purity, Type IIa CVD diamond substrate with a <100> crystalline orientation, essential for minimizing strain and maximizing spin coherence.
- Zero-Field Operation: Measurements were conducted below 5 K and under a suppressed geomagnetic field (zero magnetic field), simplifying the Hamiltonian and exploiting the inherent degeneracy of the qutrits.
- Quantum Control Setup: Electron and nitrogen nuclear spins were individually manipulated using arbitrarily polarized Microwave (MW) and Radiofrequency (RF) pulses delivered via a crossed-wire antenna structure integrated onto the diamond surface.
- Pulse Optimization: High-fidelity unitary operations (CNOT, Hadamard) were implemented using the GRadient Ascent Pulse Engineering (GRAPE) algorithm, enabling holonomic quantum gates on the geometric spin qubits.
- Disentanglement Circuit: The four Bell states ($\vert\Phi^{\pm}\rangle_{e,N}$, $\vert\Psi^{\pm}\rangle_{e,N}$) were transformed into four measurable eigenstates ($\vert\pm 1, \pm 1\rangle_{e,N}$) via the CNOT and Hadamard gates.
- Quantum Nondemolition (QND) Readout: The resulting eigenstates were measured using a repetitive single-shot readout sequence, mapping the nuclear spin state into the electron spin state, followed by detection of phonon sideband emission using a red laser (637 nm) and an Avalanche Photodiode (APD).
- Initialization: Electron spin initialization was achieved either through optical spin pumping (515 nm laser) or via GRAPE-optimized MW pulses.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD provides the foundational MPCVD diamond materials and customization services necessary to replicate, optimize, and scale the deterministic BSM demonstrated in this research.
| Research Requirement | 6CCVD Solution & Capability | Technical Advantage & Sales Proposition |
|---|---|---|
| High-Purity Diamond Substrate | Optical Grade Single Crystal Diamond (SCD) | Our SCD material is grown via MPCVD, offering ultra-low nitrogen content (critical for long coherence times, T2 > 1 minute for nuclear spins) and high crystalline quality, essential for stable NV center formation. |
| Specific Crystal Orientation | Custom <100> and <111> Substrates | We supply SCD plates up to 500”m thick (and substrates up to 10mm) with precise <100> orientation, ensuring optimal NV alignment and minimal internal strain, which is crucial for reproducible quantum device performance. |
| Integrated Control Structures | Custom Metalization Services (Ti, Pt, Au, Cu) | The experiment requires a crossed-wire antenna for MW/RF delivery. 6CCVD offers in-house metalization (e.g., Ti/Pt/Au stacks) directly patterned onto the diamond surface, enabling integrated, high-frequency control circuits necessary for GRAPE pulse implementation. |
| Enhanced Photon Extraction | Ultra-Smooth Polishing (Ra < 1nm for SCD) | The Discussion section notes that low photon extraction efficiency limits the final BSM fidelity (68%). Our industry-leading polishing achieves Ra < 1nm on SCD, minimizing surface defects and maximizing the efficiency of integrated Solid Immersion Lenses (SILs), thereby boosting photon collection and readout fidelity. |
| Scalability for Quantum Networks | Large-Area Polycrystalline Diamond (PCD) Wafers | For scaling up distributed quantum networks and interfaces, 6CCVD offers PCD wafers up to 125mm in diameter, providing a cost-effective platform for high-volume fabrication of quantum devices based on NV centers. |
| Custom Dimensions & Thickness | Plates/Wafers up to 125mm (PCD) / SCD (0.1”m - 500”m) | We provide custom dimensions and thicknesses to match specific experimental setups, whether for bulk measurements or thin-film integration into photonic circuits. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in MPCVD diamond growth and post-processing for quantum applications. We offer consultation services to assist researchers and engineers in selecting the optimal material specifications (e.g., nitrogen doping levels, orientation, and metalization schemes) required to replicate or extend high-fidelity quantum repeater and quantum interface projects based on NV centers.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract Entanglements serve as a resource for any quantum information system and are deterministically generated or swapped by a joint measurement called complete Bell state measurement (BSM). The determinism arises from a quantum nondemolition measurement of two coupled qubits with the help of readout ancilla, which inevitably requires extra physical qubits. We here demonstrate a deterministic and complete BSM with only a nitrogen atom in a nitrogen-vacancy (NV) center in diamond as a quantum memory without relying on any carbon isotopes, which are the extra qubits, by exploiting electronânitrogen ( 14 N) double qutrits at a zero magnetic field. The degenerate logical qubits within the subspace of qutrits on the electron and nitrogen spins are holonomically controlled by arbitrarily polarized microwave and radiofrequency pulses via zero-field-split states as the ancilla, thus enabling the complete BSM deterministically. Since the system works under an isotope-free and field-free environment, the demonstration paves the way to realize high-fidelity quantum repeaters for long-haul quantum networks and quantum interfaces for large-scale distributed quantum computers.