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 | Technische UniversitÀt Berlin, Carl von Ossietzky UniversitÀt Oldenburg |
| Citations | 72 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis analysis focuses on demonstrating the feasibility and competitive performance of atomically-thin Transition Metal Dichalcogenide (TMDC) single-photon sources (SPS) for Quantum Key Distribution (QKD).
- Core Achievement: Pioneering the use of a strain-engineered WSe2 monolayer SPS to successfully emulate the BB84 QKD protocol, proving TMDCs are viable for practical quantum communication.
- Performance Metrics: Achieved high click rates up to 66.95 kHz and demonstrated excellent single-photon purity, with an optimized antibunching value g(2)(0) down to 0.034.
- Competitive Edge: The WSe2 source performance is competitive with state-of-the-art QKD experiments utilizing semiconductor Quantum Dots (QDs) and diamond Color Centers (e.g., NV centers).
- Loss Tolerance Optimization: Employing 2D temporal filtering routines maximized the secret key rate and extended the maximally tolerable transmission loss to 22.59 dB.
- Distance Capability: The optimized loss budget corresponds to an achievable free-space communication distance of 43.9 km under clear-sky atmospheric conditions.
- Scalability Advantage: TMDC-based sources offer significant benefits due to their relatively simple, low-cost fabrication and high potential for integration into large-scale photonic devices.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Emitter Material | WSe2 Monolayer | - | Strain-engineered TMDC |
| Operating Temperature | 4.2 | K | Closed-cycle cryocooler |
| Excitation Wavelength | 660 | nm | Pulsed diode laser |
| Excitation Clock Rate | 5.0 | MHz | Optimal trade-off for QKD |
| Emission Wavelength | 807.3 | nm | Selected localized emitter line |
| Max Click Rate (Pulsed) | 66.95 ± 1.07 | kHz | Detected at Bob, back-to-back |
| Single-Photon Flux (CW) | 1.15 ± 0.23 | MHz | In Single-Mode (SM) fiber |
| Mean Photon Number (”) | Up to 0.024 | - | Into quantum channel |
| Antibunching g(2)(0) (Unfiltered) | 0.172 | - | Measured at saturation |
| Antibunching g(2)(0) (Temporal Filtered) | 0.034 ± 0.002 | - | Optimized purity (24 ns window) |
| Quantum Bit Error Ratio (QBER) | 0.52 | % | Lower bound set by receiver optics |
| Max Tolerable Loss (Optimized) | 22.59 | dB | Achieved via 2D temporal filtering |
| Equivalent Distance (Free-Space) | 43.9 | km | Assuming 0.08 dB/km atmospheric loss |
| Receiver Detector Efficiency | 80 | % | At 810 nm (SPCMs) |
| Receiver Module Transmission (ηBob) | 0.56 | - | Including optics and detector efficiencies |
Key Methodologies
Section titled âKey Methodologiesâ- TMDC Device Fabrication: WSe2 monolayers were prepared via mechanical exfoliation and transferred onto a nano-structured metallic surface. This surface consisted of 200 nm of silver (Ag) on a 600 ”m sapphire substrate, capped with 10 nm of chromium (Cr).
- Strain Engineering: The metallic surface contained silver nanoparticles which induced localized wrinkles in the overlying WSe2 layer, creating strain centers that trap excitons and localize quantum emitters.
- Source Operation (Alice): The WSe2 device was mounted in a closed-cycle cryocooler and maintained at 4.2 K. It was optically triggered using a 660 nm pulsed diode laser, typically operating at a 5.0 MHz clock rate.
- Spectro-Spatial Filtering: The collected luminescence was filtered using two long-pass (LP) filters (750 nm and 800 nm cut-ons) to isolate the single-photon emission line (807.3 nm) from the broad ensemble background.
- Polarization Encoding: Single photons were coupled into a Single-Mode (SM) fiber. Polarization states (H, V, D, A) required for the BB84 protocol were statically prepared using a fiber polarization controller and a Glan-Thompson prism.
- QKD Receiver (Bob): The receiver utilized a passive four-state polarization decoder based on a 50:50 nonpolarizing beamsplitter cube and polarizing beamsplitters, directing photons to four Single-Photon Counting Modules (SPCMs).
- Performance Optimization: The secret key rate was optimized by simulating and applying 2D temporal filtering. This involved varying both the width (ât) and the center (tc) of the acceptance time window to maximize the signal-to-noise ratio and mitigate dark counts and background noise.
Commercial Applications
Section titled âCommercial ApplicationsâThe successful demonstration of TMDC-based SPS in a QKD testbed opens pathways for several commercial and engineering applications:
- Free-Space Quantum Communication: Ideal for high-loss, long-distance links, such as air-to-ground, ship-to-ship, or satellite-to-ground QKD, leveraging the high brightness and purity of the source.
- Integrated Quantum Photonics: The atomically thin nature of TMDCs facilitates integration into on-chip photonic circuits, microcavities, and waveguides, enabling scalable, compact quantum devices.
- Low-Cost Quantum Networks: TMDCs offer a simpler and lower-cost fabrication route compared to traditional III-V semiconductor Quantum Dots, accelerating the deployment of metropolitan and regional quantum networks.
- Plug-and-Play Quantum Sources: Development of compact, user-friendly quantum light sources by combining fiber-pigtailed TMDC devices with compact Stirling cryocoolers for robust field operation.
- Quantum Repeater Nodes: Potential use in future quantum repeaters, especially if high photon indistinguishability can be achieved, enabling entanglement distribution over ultra-long distances.
- Quantum Sensing and Metrology: High-purity, deterministic single-photon sources are fundamental components for advanced quantum sensing applications requiring non-classical light inputs.
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.