Atomically-thin single-photon sources for quantum communication
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-01-27 |
| Journal | npj 2D Materials and Applications |
| Authors | Timm Gao, Martin von Helversen, C. AntĂłn, Christian Schneider, Tobias Heindel |
| Institutions | Carl von Ossietzky UniversitÀt Oldenburg, Technische UniversitÀt Berlin |
| Citations | 72 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Atomically-Thin Single-Photon Sources for Quantum Communication
Section titled âTechnical Documentation & Analysis: Atomically-Thin Single-Photon Sources for Quantum CommunicationâReference: Gao et al., npj 2D Materials and Applications (2023)7:4.
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates the successful implementation of a strain-engineered WSeâ monolayer as a deterministic single-photon source (SPS) for Quantum Key Distribution (QKD) using the BB84 protocol.
- Application Validation: Pioneers the practical suitability of atomically-thin Transition Metal Dichalcogenides (TMDCs) for robust quantum communication systems.
- High Purity: Achieved exceptional single-photon purity, with a post-processed antibunching value $g^{(2)}(0)$ down to 0.034 ± 0.002, competitive with leading solid-state emitters.
- Performance Metrics: Demonstrated click rates up to 66.95 kHz at a 5.0 MHz clock rate, resulting in a mean photon number per pulse ($\mu$) of up to 0.024 in the quantum channel.
- Extended Range: Optimization via 2D temporal filtering extended the maximally tolerable transmission loss to 22.59 dB, corresponding to a free-space communication distance extension of 43.9 km.
- Benchmarking Opportunity: The study explicitly benchmarks the WSeâ performance against established solid-state quantum emitters, including color centers in diamond and semiconductor quantum dots, highlighting the critical role of high-purity diamond materials supplied by 6CCVD in this competitive field.
- Future Direction: The work paves the way for highly integrated, low-cost quantum light sources, though further improvements in extraction efficiency (e.g., via microcavities) are required to match the performance potential of optimized diamond-based systems.
Technical Specifications
Section titled âTechnical SpecificationsâThe following table summarizes the key performance metrics and physical parameters extracted from the experimental results.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Emitter Material | WSeâ Monolayer | N/A | Strain-engineered TMDC |
| Operation Wavelength ($\lambda$) | 807.3 | nm | First telecom window |
| Excitation Wavelength | 660 | nm | Pulsed diode laser |
| Optimal Clock Rate | 5.0 | MHz | Used for QKD experiments |
| Saturation Pump Power ($P_{sat}$) | 52.5 | ”W | Power at which click rate saturates |
| Maximum Click Rate (Pulsed) | 66.95 ± 1.07 | kHz | Total signal from four channels |
| Single-Photon Purity ($g^{(2)}(0)$) | 0.17 | N/A | Unfiltered, 5.0 MHz clock rate |
| Minimum $g^{(2)}(0)$ | 0.034 ± 0.002 | N/A | Post-processed (24 ns acceptance window) |
| Mean Photon Number ($\mu$) | Up to 0.024 | N/A | Into the quantum channel |
| QBER (Lower Bound) | 0.52 | % | Set by receiver optics |
| Max Tolerable Loss (Optimized) | 22.59 | dB | Achieved via 2D temporal filtering |
| Substrate Stack | Sapphire / 10 nm Cr / 200 nm Ag | N/A | Nano-structured metallic surface |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized a proof-of-concept QKD testbed emulating the BB84 protocol, focusing on the characterization of the WSeâ single-photon source (SPS).
- TMDC Device Preparation: WSeâ monolayer sheets were mechanically exfoliated and transferred onto a nano-structured metallic surface (Sapphire substrate capped with 10 nm Chromium and 200 nm Silver) to induce strain centers for localized quantum emitters.
- Source Operation (Alice): The WSeâ device was mounted in a closed-cycle cryocooler (4.2 K) and excited using a pulsed diode laser (660 nm) with a variable repetition rate (optimized at 5.0 MHz).
- Collection and Filtering: Emission was collected via an aspheric lens (NA = 0.77), spectrally filtered using two long-pass (LP) filters (750 nm and 800 nm cut-ons), and coupled into a single-mode (SM) optical fiber.
- Polarization Encoding: Single photons were prepared in four BB84 polarization states (H, V, D, A) using a fiber polarization controller and a Glan-Thompson prism (static preparation for proof-of-concept).
- QKD Receiver (Bob): The receiver comprised a four-state polarization decoder with passive basis choice (50:50 beamsplitter cube and polarizing beamsplitters) and utilized four silicon-based single-photon counting modules (SPCMs) with 80% efficiency at 810 nm.
- Performance Optimization: The secret key rate was optimized by applying 2D temporal filtering (varying acceptance time window $\Delta t$ and center $t_c$) to maximize the signal-to-noise ratio and reduce the contribution of detector dark counts and background noise.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research highlights the intense competition in deterministic quantum light sources, explicitly comparing TMDCs to diamond color centers. 6CCVD provides the foundational material technology necessary to advance and surpass the performance demonstrated by TMDC systems, particularly in high-stability, high-temperature quantum applications.
Applicable Materials for Quantum Emitters
Section titled âApplicable Materials for Quantum EmittersâWhile this paper focuses on WSeâ, the highest performing solid-state quantum emitters for QKD, such as Nitrogen-Vacancy (NV) and Silicon-Vacancy (SiV) centers, rely on high-purity Single Crystal Diamond (SCD).
| 6CCVD Material | Application Relevance | Key Advantage over TMDCs |
|---|---|---|
| Optical Grade SCD | Hosting NV, SiV, GeV, and SnV color centers for deterministic SPS and quantum memory. | Superior thermal conductivity, high stability, and potential for room-temperature operation (NV centers). |
| High-Purity SCD | Substrates for epitaxial growth or ion implantation of quantum defects. | Extremely low defect density, crucial for achieving high photon indistinguishability and coherence times. |
| Boron-Doped Diamond (BDD) | High-efficiency, radiation-hard single-photon detectors and electrodes for integrated quantum circuits. | Excellent electrical properties and chemical inertness for device integration. |
Customization Potential for Integrated Quantum Devices
Section titled âCustomization Potential for Integrated Quantum DevicesâThe complexity of the WSeâ device (requiring a specialized Cr/Ag metallic surface and cryogenic operation) underscores the need for highly customized material solutions. 6CCVD is uniquely positioned to supply the necessary diamond components for next-generation quantum devices.
| Requirement in Research | 6CCVD Custom Capability | Benefit to Quantum Engineers |
|---|---|---|
| Substrate Integration | Custom SCD/PCD plates and wafers up to 125mm in diameter. Substrate thickness up to 10mm. | Enables large-scale integration of diamond quantum chips and compatibility with standard semiconductor processing. |
| Surface Quality | SCD polishing to Ra < 1 nm; PCD polishing to Ra < 5 nm. | Essential for high-Q microcavity integration (as suggested for TMDC improvement) and minimizing scattering losses in photonic circuits. |
| Metalization Layers | Internal capability for custom metalization (Au, Pt, Pd, Ti, W, Cu). | Allows for direct fabrication of electrical contacts, microwave waveguides, and strain-engineering layers on diamond substrates. |
| Unique Dimensions | Custom laser cutting and shaping services. | Provides precise geometries required for solid-immersion lenses (SILs) and photonic crystal structures necessary for efficient photon extraction. |
Engineering Support
Section titled âEngineering SupportâThe optimization routines discussed in the paper (temporal filtering, material selection, and integration) require deep expertise in solid-state physics and quantum optics.
6CCVDâs in-house PhD engineering team specializes in the material science of diamond quantum systems. We offer consultation services to assist researchers and engineers in selecting the optimal diamond material (SCD purity, BDD doping level, surface termination) for similar deterministic single-photon source and QKD projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract To date, quantum communication widely relies on attenuated lasers for secret key generation. In future quantum networks, fundamental limitations resulting from their probabilistic photon distribution must be overcome by using deterministic quantum light sources. Confined excitons in monolayers of transition metal dichalcogenides (TMDCs) constitute an emerging type of emitter for quantum light generation. These atomically thin solid-state sources show appealing prospects for large-scale and low-cost device integration, meeting the demands of quantum information technologies. Here, we pioneer the practical suitability of TMDC devices in quantum communication. We employ a WSe 2 monolayer single-photon source to emulate the BB84 protocol in a quantum key distribution (QKD) setup and achieve click rates of up to 66.95 kHz and antibunching values down to 0.034âa performance competitive with QKD experiments using semiconductor quantum dots or color centers in diamond. Our work opens the route towards wider applications of quantum information technologies using TMDC single-photon sources.