One-Way Quantum Repeater Based on Near-Deterministic Photon-Emitter Interfaces
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-06-30 |
| Journal | Physical Review X |
| Authors | Johannes Borregaard, Hannes Pichler, Tim Schröder, Mikhail D. Lukin, Peter Lodahl |
| Institutions | Center for Astrophysics Harvard & Smithsonian, QuTech |
| Citations | 141 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: One-Way Quantum Repeater using MPCVD Diamond
Section titled âTechnical Documentation & Analysis: One-Way Quantum Repeater using MPCVD DiamondâThis document analyzes the requirements and findings of the research paper âOne-way quantum repeater based on near-deterministic photon-emitter interfacesâ (arXiv:1907.05101v4) and aligns them with the advanced material capabilities offered by 6CCVD.
Executive Summary
Section titled âExecutive SummaryâThe proposed one-way quantum repeater architecture leverages photonic tree-cluster states and near-deterministic photon-emitter interfaces to achieve high-rate, long-distance quantum communication.
- High-Rate Performance: Achieves secret bit rates up to 70 kHz over 1000 km, significantly surpassing conventional two-way repeater protocols by relying on fast local processing rather than two-way communication time limits.
- Resource Efficiency: Requires substantially fewer resources per repeater station, utilizing only two stationary memory qubits and one quantum emitter (e.g., Diamond NV/SiV defect centers).
- Material Requirements: Implementation relies on solid-state quantum emitters strongly coupled to nanophotonic structures, demanding high material purity, high cooperativity ($C \sim 100$), and efficient photon collection ($\eta_d \ge 95%$).
- Operational Speed: Requires ultra-fast spin-spin CZ gates ($\tau_{CZ} \sim 10$ ns) and high-speed optical switching (> 2 GHz) for time-bin encoding and decoding.
- Diamond Relevance: Diamond defect centers (NV and SiV) are identified as key physical systems capable of meeting the required coherence times and fast gate operations necessary for the stationary spin qubits.
- 6CCVD Value Proposition: 6CCVD provides the necessary Optical Grade Single Crystal Diamond (SCD) substrates with custom dimensions, ultra-low surface roughness (Ra < 1 nm), and custom metalization required for scalable, integrated hybrid photonic platforms.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points are extracted from the analysis of the optimized repeater performance and required hardware parameters:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Maximum Transmission Distance (L) | 1000 | km | Achieved with optimal parameters. |
| Maximum Secret Bit Rate | ~70 | kHz | At 1000 km, assuming fast gates ($\tau_{CZ}$ = 10 ns). |
| Repeater Station Spacing ($L_0$) | 2.6 | km | Optimized spacing for 70 kHz rate. |
| Required Re-encoding Error ($\epsilon_r$) | 0.1 to 0.5 | % | Tolerable range for high performance. |
| Photon Detection Efficiency ($\eta_d$) | 95 | % | Assumed minimum for resource analysis. |
| Spin-Spin CZ Gate Time ($\tau_{CZ}$) | 10 or 100 | ns | Required for fast/modest rates. |
| Purcell-Enhanced Lifetime | ~100 | ps | Feasible for solid-state emitters (Diamond/QD). |
| Required Cooperativity (C) | ~100 | - | Necessary to ensure spin-photon CZ gate error $\le 10^{-4}$. |
| Optical Switching Rate | > 2 | GHz | Required for time-bin qubit generation and detection. |
| Required Delay Line Length ($l_{del}$) | 68 to 374 | m | Depending on gate time, needed for detection order. |
| Stationary Qubits per Station | 2 | - | Memory spins ($S_1, S_2$). |
| Quantum Emitters per Station | 1 | - | Coupled to light field ($E$). |
Key Methodologies
Section titled âKey MethodologiesâThe experimental protocol relies on advanced solid-state quantum optics techniques and high-speed integrated photonics:
- Deterministic Tree-Cluster Generation: Photonic tree-cluster states (optimally depth 3) are generated sequentially using two stationary memory spins and one quantum emitter coupled to a one-sided cavity.
- Time-Bin Encoding: Photonic qubits are represented in a time-bin format (presence of a single photon in one of two non-overlapping spatiotemporal modes) to enable loss detection and transmission through optical fibers.
- Cavity-Mediated Spin-Photon CZ Gate: The core re-encoding operation utilizes a controlled-phase (CZ) gate between the spin qubit and the photonic qubit, achieved by reflecting the photon off a cavity strongly coupled to the quantum emitter ($C \sim 100$).
- Loss-Tolerant Re-encoding: A heralded storage mechanism is employed, where the Bell measurement is designed with built-in error detection. If the 1st-level photon is lost, the measurement aborts without perturbing the root qubit of the new tree.
- High-Speed On-Chip Detection: Measurements in the x-basis require fast optical switching (> 2 GHz) using integrated Mach-Zehnder Interferometers (MZIs) based on electro-optic (EO) modulation, necessitating a scalable hybrid photonic platform.
- Material Platform Selection: The protocol is proposed for implementation using solid-state quantum emitters, specifically diamond defect centers (NV, SiV) or semiconductor quantum dots, due to their long spin coherence times and efficient light-matter coupling when integrated into nanophotonic structures.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe successful implementation of this high-performance quantum repeater protocol critically depends on the availability of high-quality diamond materials and precision fabrication services. 6CCVD is uniquely positioned to supply the necessary components for researchers and engineers developing these hybrid quantum systems.
| Research Requirement | 6CCVD Solution & Capability | Technical Advantage for Quantum Repeaters |
|---|---|---|
| High-Purity Diamond Substrates for NV/SiV Qubits. | Optical Grade Single Crystal Diamond (SCD): Custom MPCVD growth ensures ultra-low defect density and high material purity, essential for achieving the required long spin coherence times (up to $\sim 7$ ”s) at low temperatures. | Guarantees stable, high-fidelity stationary memory qubits necessary for tree-cluster generation and re-encoding. |
| Nanophotonic Structure Fabrication (Cavities/Waveguides). | Custom Thickness and Dimensions: SCD plates available from 0.1 ”m up to 500 ”m, and substrates up to 10 mm thick. Plates can be polished to Ra < 1 nm. | Provides ideal starting material for etching high-quality photonic crystal cavities, maximizing Purcell enhancement and collection efficiency ($\beta > 98%$). |
| Integrated Hybrid Photonic Circuits (Fig. 10). | Custom Metalization Services: In-house deposition of Au, Pt, Pd, Ti, W, and Cu. | Enables the integration of fast electrical contacts for EO modulators (> 2 GHz switching) and microwave lines for rapid spin control ($\tau_{CZ} \sim 10$ ns). |
| Scalable Repeater Stations. | Large Area Polycrystalline Diamond (PCD): Wafers up to 125 mm in diameter, polished to Ra < 5 nm. | Offers a cost-effective, scalable platform for integrated photonic circuits and heat management in complex, multi-chip repeater stations. |
| Global Supply Chain. | Global Shipping (DDU default, DDP available). | Ensures reliable, timely delivery of specialized diamond materials to research facilities worldwide. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the material science of diamond for quantum applications. We offer expert consultation on material selection, doping levels (including Boron-Doped Diamond, BDD, for specific electronic applications), and surface preparation techniques to optimize the integration of Diamond Defect Centers into nanophophotonic structures for similar quantum communication projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
We propose a novel one-way quantum repeater architecture based on photonic\ntree-cluster states. Encoding a qubit in a photonic tree-cluster protects the\ninformation from transmission loss and enables long-range quantum communication\nthrough a chain of repeater stations. As opposed to conventional approaches\nthat are limited by the two-way communication time, the overall transmission\nrate of the current quantum repeater protocol is determined by the local\nprocessing time enabling very high communication rates. We further show that\nsuch a repeater can be constructed with as little as two stationary qubits and\none quantum emitter per repeater station, which significantly increases the\nexperimental feasibility. We discuss potential implementations with diamond\ndefect centers and semiconductor quantum dots efficiently coupled to photonic\nnanostructures and outline how such systems may be integrated into repeater\nstations.\n