Euk Jin Alexander Ling
Email Address
phyalej@nus.edu.sg
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Publication Temperature insensitive type II quasi-phasematched spontaneous parametric downconversion(American Institute of Physics Inc., 2021-07-12) Pan, Xin-Yi; Kurtsiefer, Christian; Ling, Alexander; Grieve, James A.; CENTRE FOR QUANTUM TECHNOLOGIES; PHYSICSThe temperature dependence of the refractive indices of potassium titanyl phosphate (KTP) is shown to enable quasi-phasematched type II spontaneous parametric downconversion (SPDC) with low temperature sensitivity. Calculations show the effect to be maximized for emission of photons at around 1165 nm, as well as producing similar plateaus for wavelengths throughout the telecommunications bands. We experimentally demonstrate the effect, observing temperature-insensitive degenerate emission between 20 °C and 100 °C at 1327 nm, within the telecommunications O band. This result has practical implications for the development of entangled photon sources for resource-constrained environments, and we demonstrate a simple polarization entangled source as a proof of concept. © 2021 Author(s).Publication Fibre polarisation state compensation in entanglement-based quantum key distribution(The Optical Society, 2021-10-18) Shi, Yicheng; Poh, Hou Shun; Ling, Alexander; Kurtsiefer, Christian; CENTRE FOR QUANTUM TECHNOLOGIES; PHYSICSQuantum key distribution (QKD) using polarisation encoding can be hard to implement over deployed telecom fibres because the routing geometry and the birefringence of the fibre link can alter the polarisation states of the propagating photons. These alterations cause a basis mismatch, leading to an increased quantum bit error rate (QBER). In this work we demonstrate a technique for a dynamically compensating fibre-induced state alteration in a QKD system. This compensation scheme includes a feedback loop that minimizes the QBER using a stochastic optimization algorithm. The effectiveness of this technique is implemented and verified in a polarisation entanglement QKD system over a deployed telecom fibre. © 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.Publication CubeSat quantum communications mission(2017) Oi, D.K.L; Ling, A; Vallone, G; Villoresi, P; Greenland, S; Kerr, E; Macdonald, M; Weinfurter, H; Kuiper, H; Charbon, E; Ursin, R; PHYSICSQuantum communication is a prime space technology application and offers near-term possibilities for long-distance quantum key distribution (QKD) and experimental tests of quantum entanglement. However, there exists considerable developmental risks and subsequent costs and time required to raise the technological readiness level of terrestrial quantum technologies and to adapt them for space operations. The small-space revolution is a promising route by which synergistic advances in miniaturization of both satellite systems and quantum technologies can be combined to leap-frog conventional space systems development. Here, we outline a recent proposal to perform orbit-to-ground transmission of entanglement and QKD using a CubeSat platform deployed from the International Space Station (ISS). This ambitious mission exploits advances in nanosatellite attitude determination and control systems (ADCS), miniaturised target acquisition and tracking sensors, compact and robust sources of single and entangled photons, and high-speed classical communications systems, all to be incorporated within a 10 kg 6 litre mass-volume envelope. The CubeSat Quantum Communications Mission (CQuCoM) would be a pathfinder for advanced nanosatellite payloads and operations, and would establish the basis for a constellation of low-Earth orbit trusted-nodes for QKD service provision. © The Author(s) 2017.Publication The photon pair source that survived a rocket explosion(2016) Tang, Z; Chandrasekara, R; Tan, Y.C; Cheng, C; Durak, K; Ling, A; CENTRE FOR QUANTUM TECHNOLOGIES; PHYSICSWe report on the performance of a compact photon pair source that was recovered intact from a failed space launch. The source had been embedded in a nanosatellite and was designed to perform pathfinder experiments leading to global quantum communication networks using spacecraft. Despite the launch vehicle explosion soon after takeoff, the nanosatellite was successfully retrieved from the accident site and the source within it was found to be fully operational. We describe the assembly technique for the rugged source. Post-recovery data is compared to baseline measurements collected before the launch attempt and no degradation in brightness or polarization correlation was observed. The survival of the source through an extreme environment provides strong evidence that it is possible to engineer rugged quantum optical systems.Publication Manipulation and measurement of quantum states with liquid crystal devices(OSA - The Optical Society, 2019) Lohrmann, A.; Perumgatt, C.; Ling, A.; CENTRE FOR QUANTUM TECHNOLOGIES; PHYSICSWe present the use of liquid crystal retarders (LCR) as phase control elements in optical quantum technologies. We show that an entangled photon pair state can be actively controlled using an LCR without introducing state mixing or polarization drifts. Similarly, we demonstrate that the entanglement quality can be conveniently analyzed using liquid crystal polarization retarders. © 2019 Optical Society of America.Publication Breakdown flash at telecom wavelengths in InGaAs avalanche photodiodes(OPTICAL SOC AMER, 2017-11-27) Shi, Yicheng; Lim, Janet Zheng Jie; Poh, Hou Shun; Tan, Peng Kian; Tan, Peiyu Amelia; Ling, Alexander; Kurtsiefer, Christian; Dr Peng Kian Tan; CENTRE FOR QUANTUM TECHNOLOGIES; PHYSICS; DEAN'S OFFICE (SCHOOL OF COMPUTING)Quantum key distribution (QKD) at telecom wavelengths (1260 − 1625 nm) has the potential for fast deployment due to existing optical fibre infrastructure and mature telecom technologies. At these wavelengths, Indium Gallium Arsenide (InGaAs) avalanche photodiode (APD) based detectors are the preferred choice for photon detection. Similar to their Silicon counterparts used at shorter wavelengths, they exhibit fluorescence from recombination of electron-hole pairs generated in the avalanche breakdown process. This fluorescence may open side channels for attacks on QKD systems. Here, we characterize the breakdown fluorescence from two commercial InGaAs single photon counting modules, and find a spectral distribution between 1000 nm and 1600 nm. We also show that by spectral filtering, this side channel can be e ciently suppressed.Publication Nanosatellite experiments to enable future space-based QKD missions(2016) Bedington, R; Bai, X; Truong-Cao, E; Tan, Y.C; Durak, K; Zafra, A.V; Grieve, J.A; Oi, D.K.L; Ling, A; CENTRE FOR QUANTUM TECHNOLOGIES; PHYSICSWe present a programme for establishing the space worthiness of highly-miniaturised, polarisation-entangled, photon pair sources using CubeSat nanosatellites. Once demonstrated, the photon pair sources can be deployed on more advanced satellites that are equipped with optical links to establish a global space-based quantum key distribution network. In doing so, this work will also bring experimental tests of the overlap between quantum and relativistic regimes closer to realisation. © 2016 Bedington et al.Publication Satellite quantum communications when man-in-the-middle attacks are excluded(MDPI AG, 2019) Vergoossen, T.; Bedington, R.; Grieve, J.A.; Ling, A.; CENTRE FOR QUANTUM TECHNOLOGIES; PHYSICSAn application of quantum communications is the transmission of qubits to create shared symmetric encryption keys in a process called quantum key distribution (QKD). Contrary to public-private key encryption, symmetric encryption is considered safe from (quantum) computing attacks, i.e. it provides forward security and is thus attractive for secure communications. In this paper we argue that for free-space quantum communications, especially with satellites, if one assumes that man-in-the-middle attacks can be detected by classical channel monitoring techniques, simplified quantum communications protocols and hardware systems can be implemented that offer improved key rates. We term these protocols photon key distribution (PKD) to differentiate them from the standard QKD protocols. We identify three types of photon sources and calculate asymptotic secret key rates for PKD protocols and compare them to their QKD counterparts. PKD protocols use only one measurement basis which we show roughly doubles the key rates. Furthermore, with the relaxed security assumptions one can establish keys at very high losses, in contrast to QKD where at the same losses privacy amplification would make key generation impossible. © 2019 by the authors.Publication Nanosatellites for quantum science and technology(Taylor & Francis, 2016-11-15) Daniel K. L. Oi; Alex Ling; James A. Grieve; Thomas Jennewein; Aline N. Dinkelaker; Markus Krutzik; CENTRE FOR QUANTUM TECHNOLOGIES; PHYSICS