Researchers at the Technical University of Denmark have created near-infrared quantum emitters in bilayer MoTe₂ operating at wavelengths of 1090-1200 nm, a range important for long-distance optical quantum communication. The team demonstrated a reproducible method using deterministic strain and defect engineering to overcome limitations in spectral range and single-photon indistinguishability that have previously hindered two-dimensional transition metal dichalcogenides.
Most notably, the work achieves a Hong-Ou-Mandel visibility of up to 60% with temporal filtering, representing the highest reported indistinguishability for this class of quantum emitter and establishing MoTe₂ as a viable platform for advanced quantum photonic technologies.
Deterministic Strain Engineering Creates NIR MoTe₂ Quantum Emitters
Bilayer molybdenum ditelluride quantum emitters fabricated with deterministic strain engineering now demonstrate resolution-limited emission at approximately 150 microelectronvolts, a key characteristic for advanced quantum technologies. This level of spectral precision, achieved through a systematic fabrication process, addresses a longstanding limitation of two-dimensional transition metal dichalcogenides (TMDs) as single-photon sources. The fabrication process combines nanopillar-induced strain with controlled electron beam activation of defects, yielding quantum emitters with radiative lifetimes as short as 130 picoseconds.
This speed is important for minimizing decoherence, a process that destroys the delicate quantum states necessary for reliable information processing. Triggered single-photon purity reached a measured value of 0.01 under p-shell excitation, indicating a highly selective emission of single photons rather than multiple or spurious signals.
As summarized in Supplementary Notes 5, 8, and 9, these emitters consistently exhibit reproducible narrow emission lines, high degree of linear polarization (DOLP), short lifetimes, and high-purity single-photon emission, confirming the robustness of the fabrication method. Efficient quantum emitter generation was observed in 50% of available sites when both strain and defect engineering were applied, demonstrating a significant improvement in yield.
This deterministic approach contrasts with previous methods that relied on random defect formation, offering a path toward scalable manufacturing of these quantum light sources. “These results establish MoTe₂ and TMD quantum emitters in general as a viable platform for tunable, low-noise single-photon sources capable of generating indistinguishable photons for photonic quantum technologies at telecom wavelengths,” the researchers state in their published work.
Reproducible Defect Activation Enhances Emission Purity
Characterization of these emitters reveals fast radiative decays, measured as short as 130 picoseconds, alongside a high degree of linear polarization exceeding 70%. These properties are not isolated incidents. Multiple samples fabricated using this method consistently exhibit similar optical characteristics, including narrow emission lines and high-purity single-photon emission. The observed resolution-limited emission linewidths contribute to the overall fidelity of the emitted photons.
Quasi-resonant and p-shell excitations further suppress spectral diffusion and enhance purity, reducing background emission and improving the signal-to-noise ratio. This systematic approach represents a departure from previous methods reliant on random defect formation, offering a pathway toward predictably creating quantum emitters for complex circuits and networks.
Sub-Nanosecond Radiative Lifetimes and Polarization in MoTe₂
Electrostatic biasing of bilayer molybdenum ditelluride quantum emitters demonstrably shortens radiative lifetimes, yielding emission with experimental to transform-limited linewidth ratios as low as R~55. This level of control surpasses previous demonstrations with similar two-dimensional materials, which often exhibited long radiative lifetimes ranging from 20 nanoseconds to milliseconds. The ability to actively tune these emitters, over a range of approximately 3 meV, also suppresses photon bunching, a critical factor for reliable quantum communication.
The fabrication process relies on combining directional strain engineering with electron beam-induced defect activation to generate stable emitters operating within the 1090-1200 nm spectral range. These characteristics address key limitations previously hindering the development of telecom-wavelength quantum emitters.
Two-photon interference measurements revealed a Hong-Ou-Mandel visibility of ~7.1% (3.6%), and up to ~60% (approximately 40%) with post-selection by temporal filtering under p-shell excitation. The researchers state. It is important to distinguish between slow spectral wandering observed over second-scale integration (~150-200 µeV) and the fast dephasing relevant for two-photon interference, which operates on the ~10 nanosecond timescale set by their Hong-Ou-Mandel delay line.
Electrostatic Biasing Enables 3 meV Emission Tuning
Electrostatic biasing achieves continuous tuning of emission energy by approximately 3 meV, a critical capability for aligning multiple emitters to enable Hong-Ou-Mandel interference, a key process for quantum networking. This level of control surpasses previous limitations in spectral range for bilayer molybdenum ditelluride (MoTe₂) quantum emitters, and significantly reduces unwanted photon bunching. The ability to actively modulate emission characteristics through an external electric field represents a step toward practical, scalable quantum technologies.
Applying an electrical bias not only shifts the emission wavelength but also demonstrably improves emission stability by suppressing long-timescale blinking, a common issue hindering the reliability of these sources. Measurements reveal a reduction in the ratio of experimental to transform-limited linewidths to approximately 55, indicating a significant decrease in charge noise affecting the emitters.
Optimized excitation using photoluminescence excitation (PLE) at p-shell resonances further enhances performance by suppressing background emission and contributing to the high single-photon purity already demonstrated. The combined effect of electrical biasing and resonant excitation yields narrow emission lines, important for minimizing decoherence and maximizing the fidelity of quantum operations. The team notes that this approach offers a pathway toward realizing practical, tunable, low-noise single-photon sources for long-distance quantum communication and information processing.
Triggered g^(2)(0) Values Demonstrate High Single-Photon Purity
Measurements of the pulsed g^(2)(0) revealed an initial value of 0.16, which decreased to 0.010 with p-shell excitation, a result attributed to the effective suppression of background emission. This improvement was consistently observed across multiple emitters, confirming the reliability of the fabrication process and the robustness of the technique. The team verified these results on two additional emitters, solidifying the reproducibility of the approach within hBN-encapsulated MoTe₂.
The ability to generate stable, spectrally narrow emitters operating in the 1090-1200 nm range is particularly noteworthy, as this wavelength band is important for long-distance optical quantum communication. This combination of narrow linewidth, fast decay and high purity positions MoTe₂ as a promising material for advanced quantum applications.
Narrowed Emission Linewidths Approach Transform Limit (R~55)
This achievement directly addresses a key obstacle in developing these two-dimensional materials for long-distance quantum communication, where indistinguishable photons are essential for reliable signal transmission. Electrostatic biasing enables tuning over a ~3 meV range, suppresses photon bunching, and significantly shortens radiative lifetimes, yielding narrow emission with ratios of experimental to transform-limited linewidths as low as R~ 55.
This measurement assesses how well two photons can combine and interfere, a fundamental requirement for quantum gates and entanglement-based communication. The team, based at the Technical University of Denmark, reports that electrostatic biasing enables tuning over a ~3 meV range, suppressing photon bunching and significantly shortening radiative lifetimes.
The research builds on deterministic strain and defect engineering to reproducibly create near-infrared quantum emitters, a significant departure from earlier methods that often yielded inconsistent results. Paweł Wyborski of the Department of Electrical and Photonics Engineering at the Technical University of Denmark, and colleagues, demonstrate a systematic approach for generating these emitters.
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