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arXiv:2006.12713 · Photonics Research

High-fidelity, low-latency polarization quantum state transmissions over a hollow-core conjoined-tube fiber at around 800 nm

Xinyu Chen, Wei Ding, Yingying Wang, Shoufei Gao, Feixiang Xu, Huichao Xu, Yifeng Hong, Yizhi Sun, Wang Pu, Yanqing Lu, Lijian Zhang

Published Jan 25, 2021• 38 citations
arXivHTMLPDF

Abstract

Hollow-core fiber (HCF) promises to unify air-borne light propagation and non-line-of-sight transmission, thus holding great potential for versatile photonics-based quantum information applications. The early version of HCF based on photonic-bandgap guidance has not proven itself a reliable quantum channel because of the poor modal purity in both spatial and polarization domains, as well as significant difficulty in fabrication when the wavelength shifts to the visible region. In this work, based on the polarization degree of freedom, we demonstrate high-fidelity ( ∼ 0.98 ) single-photon transmission and distribution of entangled photons over a 36.4 m hollow-core conjoined-tube fiber (CTF) by using commercial silicon single-photon avalanche photodiodes. Our CTF realizes the combined merits of low loss, high spatial modal purity, low polarization degradation, and low chromatic dispersion. We also demonstrate single-photon low-latency ( ∼ 99.96 % speed of light in vacuum) transmission, paving the way for extensive uses of HCF links in versatile photonics-based quantum information processing.

DOI
10.1364/prj.409521

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Hollow-core fiber (HCF) promises to unify air-borne light propagation and non-line-of-sight transmission, thus holding great potential for versatile photonics-based quantum information applications. The early version of HCF based on photonic-bandgap guidance has not proven itself a reliable quantum channel because of the poor modal purity in both spatial and polarization domains, as well as significant difficulty in fabrication when the wavelength shifts to the visible region. In this work, based on the polarization degree of freedom, we demonstrate high-fidelity ( ∼ 0.98 ) single-photon transmission and distribution of entangled photons over a 36.4 m hollow-core conjoined-tube fiber (CTF) by using commercial silicon single-photon avalanche photodiodes. Our CTF realizes the combined merits of low loss, high spatial modal purity, low polarization degradation, and low chromatic dispersion. We also demonstrate single-photon low-latency ( ∼ 99.96 % speed of light in vacuum) transmission, paving the way for extensive uses of HCF links in versatile photonics-based quantum information processing.
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.
State of the art classical and quantum communications rely on standard optical fibers with solid cores to transmit light over long distances. However, recent advances have led to the emergence of antiresonant hollow-core optical fibers (AR-HCFs), which, due to the novel fiber geometry, show remarkable optical guiding properties, which are not as limited by the material properties as solid-core fibers. In this paper, we explore the transmission of entangled photons through a novel 7.7 km AR-HCF in a laboratory environment at 1550 nm, presenting the first successful demonstration of entanglement distribution via a long AR-HCF. In addition to showing these novel fibers are compatible with long distance quantum communication, we highlight the low latency and low chromatic dispersion intrinsic to AR-HCF, which can increase the secure key rate in time-bin-based quantum key distribution protocols.
Antiresonant hollow-core fibers are a novel type of optical fiber with unparalleled characteristics, unattainable with solid-core fibers. In particular, antiresonant hollow-core fibers are characterized by vacuum-like propagation speed, suppressed dispersion and nonlinear optical effects and, recently, even ultra-low propagation loss. In recent years, the development of a type of antiresonant hollow-core fiber, called Nested Antiresonant Nodeless Fiber (NANF) has seen tremendous improvements, and applications in both classical and quantum communications have been suggested. While encouraging results over meter long distances have been shown, the distribution of polarized entangled photons over inner-city distances through antiresonant hollow-core fibers has not been demonstrated yet. This could be a game changer for the development of quantum networks, which leverage entanglement for the distribution of secret keys, and more in the long term, in a quantum internet scenario. In this work, an experimental investigation of entanglement distribution through a NANF with an overall length of 7.72 km is presented. Remarkably, substantial reduction of latency (about 13μs) and suppressed chromatic dispersion (about one order of magnitude) of the studied NANF compared to a telecom single-mode fiber (Corning's SMF28) of equal length are measured for different bandwidths of the distributed entangled photons. Moreover, by encoding entanglement in polarization, high fidelity (>95%) distribution of narrow-bandwidth entangled photons is demonstrated. This result paves the way to the exploitation of NANF as a superior transmitting medium for quantum technology applications relying on the distribution of entanglement encoded in polarization over inner-city distances.
The coexistence of quantum information and classical signals in a single fiber is essential for future quantum networks that leverage the well-established optical fiber infrastructure. Although multiplexing technologies can separate quantum and classical signals, pure silica core fibers (PSCFs) remain fundamentally limited by the high nonlinearity, which generates substantial Raman scattering and four-wave mixing noise. Hollow-core fibers (HCFs), guiding light predominantly in air, offer an attractive solution with intrinsically ultra-low nonlinearity and strongly suppressed nonlinear noise. In this work, we demonstrate the entanglement-based key coexisting with data over an 18-km HCF link. We achieve time-encoded high-dimensional quantum key distribution (HD-QKD) carrying 0 dBm of bidirectional received power, corresponding to a theoretical data capacity of up to 2.3 Tbps. During 24 hours of continuous operation, an average secret key rate (SKR) of 10.56 kbps is obtained. Theoretical analysis further predicts SKRs above 135 kbps over transmission distances exceeding 200 km using state-of-the-art low-loss HCFs. These results show significantly improved performance compared with PSCF-based systems and highlight the potential of HCFs for scalable quantum-classical coexistence compatible with the architectures of established fiber-optic networks.
Quantum key distribution (QKD) is approaching industrial maturity, but its integration with high-power classical signals in shared optical fiber is hindered by noise from nonlinear effects like spontaneous Raman scattering and four-wave mixing. Hollow-core fiber (HCF) offers a promising solution by inherently suppressing these nonlinearities. However, a comprehensive noise analysis for pure HCF or standard single-mode-fiber–HCF hybrid links, validated experimentally under realistic high-power conditions, remains unavailable. This work bridges that gap through a thorough theoretical and experimental investigation of an HCF-featured coexistence system. We demonstrate a silicon-photonics-based QKD system operating with an optical transport network (OTN). The system achieves multiplexed launch powers of 20 dBm for counter-propagation and 14 dBm for co-propagation, meeting the highest requirements of modern OTNs. Over a 10 km HCF link, it simultaneously supports 12×583 Gbps classical channels across the C-band and achieves secure key rates of 5.7 kbps (counter-propagation) and 2.5 kbps (co-propagation) over a 1550 nm quantum channel. Our results provide critical benchmarks and a practical framework for deploying HCF-based quantum-classical networks, paving the way for future inherently secure telecommunications.