Antiresonant hollow-core fibres for quantum communications
23 July 2024
Hollow core fibres (HCFs) are emerging as a revolutionary technology for quantum communications, particularly in the distribution of single-photon-based quantum keys. Recent demonstrations have highlighted several advantages of HCFs over traditional glass-guiding fibres.
Quantum communications have seen many advancements recently, leading to the development of large-scale quantum networks. These networks require the transmission of quantum states of light, or “flying qubits,” between distant nodes using optical fibres. The telecom C-band (1530–1565 nm) is optimal for low-loss transmission, essential for quantum protocols like quantum key distribution (QKD), quantum money, and quantum coin-flipping.
Traditionally, solid-core telecom single-mode fibres have been used for these protocols due to their minimal absorption, at telecom wavelengths. However, they face technical challenges, such as relatively large latency, chromatic dispersion and optical nonlinearity. Moreover, single-photon receivers in the C-band are expensive, as opposed to more affordable Si-avalanche photodiodes in the visible. Additionally, modifying quantum technologies like quantum dots and quantum memories is often necessary for them to operate in the C-band, or shifting their output using inefficient processes becomes required.
A promising solution to these challenges has emerged with antiresonant hollow-core fibres (HCF). These fibres guide light through a central hole surrounded by microstructures, minimizing light-glass interaction and offering significant advantages. Firstly, HCFs show almost non-existent optical nonlinearity, enabling the coexistence of single photons and classical signals within the same transmission band, such as the C-band. This is not possible with standard glass fibres, which suffer from higher nonlinearity issues that interfere with quantum signals. Secondly, HCFs can be effectively single-moded at both 1550nm and 850nm wavelengths, a unique feature among optical fibres. This dual-modality would allow the transmission of classical signals in the C-band and single-photon signals at 850nm. The latter wavelength benefits from the availability of cost-effective and efficient sources and detectors.
Moreover, HCFs have shown potential for achieving ultra-low loss transmission. Recent reports indicate losses as low as 0.11 dB/km at 1550 nm, which would extend the reach of non-regenerated quantum transmissions. Additionally, HCFs could provide low-loss transmission at wavelengths where efficient sources, detectors, and quantum memories operate. Another advantage is the 30% lower latency of HCFs compared to traditional fibres. This is crucial for extending the geographical range of quantum communications, as it addresses the limitations posed by the processing and storage lifetimes of quantum repeaters.
Antiresonant HCFs have already entered the commercial market, with deployments in the UK achieving 40 km links. For quantum communication, they offer latency benefits crucial for establishing remote entanglement between matter-based systems, like nitrogen vacancy centres or trapped ion qubits. In their experiment, QSNP partners from AIT (Austrian Institute of Technology) and University of Vienna and ICCS (Institute of Communications and Computer Systems) successfully transmitted telecom entangled-photon states through a 7.7 km AR-HCF, achieving a 13 μs latency advantage, which can extend the distance and rate of entanglement distribution.
In summary, anti-resonant HCFs hold huge potential for enhancing quantum networks by supporting various quantum technologies at their natural wavelengths, promising advancements in both distance and performance for future quantum communications. This research marks a step forward in quantum communications, showcasing the potential of HCFs to overcome existing limitations and enable more sophisticated quantum networks. Further research and optimization of HCFs will be crucial in realizing their full potential in this rapidly evolving field.
Source
Alessandro Trenti, Costin Luchian, Francesco Poletti, Radan Slavík, Periklis Petropoulos, Obada Alia, George T. Kanellos, George T. and Hannes Hübel.
Distribution of telecom entangled photons through a 7.7 km antiresonant hollow-core fiber