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arXiv:2509.11889

Quantum Communication with Quantum Dots Beyond Telecom Wavelengths via Hollow-Core Fibers

Lorenzo Carosini, Francesco Giorgino, Patrik Isene Sund, L. M. Hansen, Hamel, Rene R., Lee A. Rozema, Francesco Poletti, Radan Slavı́k, Philip John Walther, Christopher Hilweg

Published Sep 15, 2025• 0 citations
arXivHTMLPDF

Abstract

Quantum dot single-photon sources are promising for quantum communication. Yet, the most advanced devices operate near 900 nm, where standard single-mode fibers experience significant losses. We address this by employing a hollow-core fiber engineered for low-loss transmission at quantum dot wavelengths, with measured loss of 0.65 dB/km and potentially as low as 0.12 dB/km near 934 nm. The fiber also supports strong classical signals at 1550 nm without adding Raman noise. Using this platform, we transmit all four BB84 polarization states from an InAs quantum dot over 340 m with 0.1% QBER, preserving single-photon purity and indistinguishability even in the presence of a strong classical signal. These results highlight how tailored transmission media enable quantum networks beyond the limits of standard telecom fibers.

DOI
10.48550/arxiv.2509.11889

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Quantum dot single-photon sources are promising for quantum communication. Yet, the most advanced devices operate near 900 nm, where standard single-mode fibers experience significant losses. We address this by employing a hollow-core fiber engineered for low-loss transmission at quantum dot wavelengths, with measured loss of 0.65 dB/km and potentially as low as 0.12 dB/km near 934 nm. The fiber also supports strong classical signals at 1550 nm without adding Raman noise. Using this platform, we transmit all four BB84 polarization states from an InAs quantum dot over 340 m with 0.1% QBER, preserving single-photon purity and indistinguishability even in the presence of a strong classical signal. These results highlight how tailored transmission media enable quantum networks beyond the limits of standard telecom fibers.
Quantum-dot single-photon sources are promising for quantum communication. Yet, the most advanced devices operate near 900 nm, where standard single-mode fibers experience significant losses. We address this by employing a hollow-core fiber engineered for low-loss transmission at quantum-dot wavelengths, with measured loss of 0.65 dB/km and potentially as low as 0.13 dB/km near 934 nm. The same fiber also supports strong classical signals at 1550 nm without introducing detectable Raman noise. Using this platform, we transmit all four BB84 polarization states from an InAs quantum dot over 340 m with a quantum bit error rate of 0.1% while preserving single-photon purity and indistinguishability even in the presence of a strong classical signal. These results establish an integrated transmission platform that combines a custom-engineered anti-resonant hollow-core fiber with co-existence of classical and quantum channels, enabling practical quantum-dot-based quantum key distribution beyond the conventional telecom bands.
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Coexistence of classical and quantum light in optical fiber is a key requirement for scalable quantum networks. However, it is fundamentally limited by nonlinear crosstalk from intense classical signals. Hollow-core fiber (HCF), with its intrinsically low optical nonlinearity, offers a promising solution. Here, we experimentally demonstrate the coexistence of polarization-entangled photons with dense wavelength-division multiplexed (DWDM) classical signals with a total launch power of 11.2 dBm, and perform a direct comparison between equal-length single-mode fiber (SMF) and photonic-bandgap-based HCF deployed in a campus network. We observe that HCF suppresses background noise by approximately two orders of magnitude compared to SMF, while preserving high-fidelity entanglement distribution. Our results provide clear experimental evidence of the advantage of HCF and establish its potential as a transmission medium.
Advancements in quantum communication and sensing require improved optical transmission that ensures excellent state purity and reduced losses. While free-space optical communication is often preferred, its use becomes challenging over long distances due to beam divergence, atmospheric absorption, scattering, and turbulence, among other factors. In the case of polarization encoding, traditional silica-core optical fibers, though commonly used, struggle with maintaining state purity due to stress-induced birefringence. Hollow core fibers, and in particular nested antiresonant nodeless fibers (NANF), have recently been shown to possess unparalleled polarization purity with minimal birefringence in the telecom wavelength range using continuous-wave (CW) laser light. Here, we investigate a 1-km NANF designed for wavelengths up to the 2-μm waveband. Our results show a polarization extinction ratio between ~-30 dB and ~-70 dB across the 1520 to 1620 nm range in CW operation, peaking at ~-60 dB at the 2-μm design wavelength. Our study also includes the pulsed regime, providing insights beyond previous CW studies, e.g., on the propagation of broadband quantum states of light in NANF at 2 μm, and corresponding extinction-ratio-limited quantum bit error rates (QBER) for prepare-measure and entanglement-based quantum key distribution (QKD) protocols. Our findings highlight the potential of these fibers in emerging applications such as QKD, pointing towards a new standard in optical quantum technologies.
The co-propagation of quantum and classical signals through shared optical fibers is crucial for scalable quantum networks. However, this coexistence is fundamentally limited by spontaneous Raman scattering (SpRS) from the bright classical light, which generates overwhelming noise that disrupts the single-photon-level quantum signals. Here, we overcome this long-standing challenge by leveraging the inherently ultralow nonlinearity of hollow-core fiber (HCF) to suppress SpRS noise. By operating both the quantum time synchronization (QTS) and classical optical frequency transfer (OFT) signals within the telecom C-band, separated by only ~10 nm, we successfully demonstrate their simultaneous transmission over a 122-km HCF link. With a classical OFT power of 1 mW, the QTS performance shows negligible degradation, maintaining sub-picosecond time stability at 2000 s, while the OFT achieves a fractional frequency instability of 10^-20. Near-sub-picosecond QTS stability is preserved even when the classical power is increased to 3 mW. Furthermore, simulations based on our experimental data indicate that with next-generation low-loss HCF, the platform can tolerate classical powers beyond 10 mW and extend the QTS range to over 500 km. By realizing a unified quantum-classical time-frequency distribution framework, this work establishes HCF as a highly capable and practical platform for future scalable quantum networks.