To Poster presenters: A0 size posters can only be mounted in portrait (vertical) orientation; A1 size posters in either orientation. Please hang your poster as soon as you arrive and take them down by the end of the workshop. The necessary material for hanging your poster can be obtained from the registration desk.
Wenye Liang, Shuang Wang, Hongwei Li, Zhenqiang Yin, Wei Chen, Yao Yao, Jingzheng Huang, Guangcan Guo, and Zhengfu Han, University of Science and Technology of China
Chun-Mei Zhang*, Mo Li*, Jing-Zheng Huang*, Patcharapong Treeviriyanupab**, Hong-Wei Li*,
Fang-Yi Li*, Chuan Wang*, Wei Chen*, Zhen-Qiang Yin*, Keattisak Sripimanwat**, Zheng-Fu
*Key Laboratory of Quantum Information, CAS, University of Science and Technology of China, Hefei 230026, China
**Optical and Quantum Communications (OQC) Laboratory, National Electronics and Computer Technology Center (NECTEC), National Science and Technology Development Agency (NSTDA), Thailand
Carlo Ottaviani, University of York
Abstract: We present a detailed analysis of the security and performances at different wavelengths, of the two-way quantum cryptography protocol for Continuous Variables (CV). In first place we analyse the scheme from a general perspective demonstrating its unconditional security in all possible encoding/decoding configurations, and stating in this way an important advantage with respect the one-way communication scheme. The strategy (ON/OFF switching) described in this work, is based on the possibility of randomly opening and closing the communication circuit. This opportunity, absent in one-way communication, allows to show that the two-way scheme is immune to general attacks and that the collective attacks are in fact optimal. In second place we provide a detailed study of the security of two-way quantum cryptography at different wavelengths against collective attacks [arXiv:1309.7973], from the optical range down to the microwave range. We focused on a two-way communication protocol where Gaussian-modulated thermal states are subject to random Gaussian displacements and finally homodyned. We show how its security threshold (in reverse reconciliation) is extremely robust with respect to the preparation noise and able to outperform the security thresholds of one-way protocols at any wavelength. As a result, improved security distances are now accessible for implementing quantum key distribution at the very challenging regime of infrared frequencies.
Romain Alleaume, Telecom ParisTech
Abstract: We are considering a challenge for quantum communication, which consists in sharing the phase reference (usually called local oscillator), in the context coherent quantum communication over a network link. Most quantum optics experiments rely on the same laser source to generate the signal as well as the local oscillator. However, this imply to send the local oscillator along with the quantum signal over the communication link, which may lead to very high power requirements for long and/or high speed links and therefore integration issues. Moreover in the context of CVQKD, sending the local oscillator over the public channel opens security issues such as the possibility of calibration as well as wavelength attacks. We have studied an alternative design, relying on phase locking and will be presenting trade-offs between system excess noise and the total optical power sent along the link in order to permit the sharing of a phase reference. As an extension of this work, we will discuss issues and opportunities related to the design of a quantum communication networks based on quantum coherent optical links. We will also discuss the issue of jointly using this infrastructure for quantum and classical communications.
Rupesh Kumar, Telecom ParisTech
Abstract: Quantum Key Distribution is arguably the most developed quantum information technology, but it is not yet widely deployed. The main challenge in order to widen QKD deployments is to integrate QKD into classical communication networks. Wavelength Division Multiplexing (WDM) architectures allow to share the use of one single optical fiber to transport several data channels at different wavelengths. This allows to linearly reduce the infrastructure costs linked to fiber deployment. We have demonstrated the coexistence of a CV-QKD system with intense classical channels over metropolitan distances. The poster includes the detailed features of the experiment such as shot noise and system noise measurement, leakage from classical channel to quantum channel, noise generated by Raman scattering, etc. In our demonstration we have multiplexed and de-multiplexed the quantum channel to and from 25km classical channel of power 8.5dBm. We have analyzed the performance of our CV-QKD system in terms of excess noise generated by the classical channel and found that it is not fundamentally limited by Raman noise but rather the system own excess noise (0.7 shot noise unit). Current work on reducing the system noise makes us hope to achieve a transmission distance as high as 50 km, with 0 dBm classical channel power, with system noise of 0.2 shot noise unit. We will also discuss the improvements in our systems and its future impacts in its integration into WDM environment.
Christiana Panayi, University of Leeds
Abstract: Quantum memories are used to improve the rate-versus-distance behavior in measurement-device-independent quantum key distribution (MDI-QKD) systems. The required specifications in terms of reading and writing times for such memories are obtained. We show that the faster the access times are, the higher the repetition rates and the lower the required coherence times would be. Additionally this protocol offers an immense security by removing side-attack channels over protocols such as the standard decoy-state BB84 protocol. We compare our protocol with the original MDI-QKD in terms of secret key generation rate under practical assumptions. We consider various sources of imperfection such as reading and writing efficiencies of the memories, channel and detector efficiencies and dark count rates. We determine the crossover distance after which our protocol outperforms the efficiencies and dark count rates. We determine the crossover distance after which our protocol outperforms the MDI-QKD.
Nicolo Lo Piparo, University of Leeds
Abstract: Quantum key distribution (QKD) promises unconditional security for sharing secret keys by relying on the laws of quantum physics. Its practical implementation, however, faces some challenges. For instance, that we need to trust some of the equipment used by our legitimate users poses a threat that has partly been remedied by recently proposed measurement-device-independent QKD (MDI-QKD) schemes. In such schemes, the end users encode (decoy) BB84 signals and transmit them to a middle station at which entanglement swapping operation is performed. At the same time, channel loss will impose an exponential decay of the key rate with distance. This can in principle be avoided by using (probabilistic) quantum repeater (QR) setups, which also rely on entanglement swapping. The combination of the two systems, MDI-QKD and QRs, will then provide us with a system that while offers easy affordable access for the end users, will enable them to exchange secret keys over long distances. Here, we present such a hybrid system and find its secret key generation rate.
H. Kampermann, University of Dusseldorf,
T. M. Barlow, University of Leeds
Abstract: This paper introduces a cavity Hamiltonian which can be used to model fiber connections in coherent cavity networks . When describing a laser-driven two-sided optical cavity, our Hamiltonian allows us to assign different decay channels to photons traveling in different directions and guarantees that reflected and transmitted photons have the same frequency as any incoming light. The corresponding master equation yields the same predictions as Maxwell's equations but for near-resonant cavities, it reduces to the quantum optical standard single-mode description of optical cavities , as it should. Using our methodology, we argue that it should be possible to mediate effective cavity-cavity interactions in a huge variety of configurations by coupling distant cavities via medium length fiber connections and linear optics elements. One can even create coherent cavity networks with complete connectivity with potential applications in quantum computing and the simulation of the complex interaction Hamiltonians of biological systems.
David E. Bruschi, University of Jerusalem
Lajos Hanzo, University of Southhampton
Electra Eleftheriadou, University of Strathclyde
Abstract: It is a fundamental principle of quantum theory that an unknown state cannot be copied or, as a consequence, an unknown optical signal cannot be amplified deterministically and perfectly. In my poster I will describe a protocol that provides nondeterministic quantum optical amplification in the coherent state basis with high gain, high fidelity and which does not use quantum resources. The scheme is based on two mature quantum optical technologies, coherent state comparison and photon subtraction. The method compares favourably with all previous nondeterministic amplifiers in terms of fidelity and success probability.
Gaetana Spedalieri, University of York
Abstract: Quantum hypothesis testing is a central task in quantum information theory. Its simplest formulation is represented by the statistical discrimination of two quantum states, which is typically formulated as a symmetric testing problem whose performance is quantified in terms of minimum error probability. Here we consider the asymmetric formulation of this problem where the two hypotheses have different weights. In this case the optimal performance consists of minimizing the probability of false negatives which can be estimated using the quantum Hoeffding bound. In this poster, we discuss this bound in the framework of multimode Gaussian states.
Fei Gao, Beijing University of Posts and Telecommunications
Sinan Bugu, Okan University
Abstract: Revisiting our recent setup [Bugu et. al., Phys. Rev. A, 87, 032331 (2013)] for enhancing the basic W-state fusion gate [Ozdemir et al., New J. Phys. 13, 103003 (2011)], we study the resource cost analysis of our setup for the strategy that fuses similar size W states, including the recycle process where applicable. We also compare the resource cost of our enhanced setup with the basic fusion setup for various fusion scenarios.
Firat Diker, Bogazici University
Abstract: We revisit the enhanced optical setup for fusing W states [Bugu et al., Phys. Rev. A 87 032331 (2013)] which integrates a single Fredkin gate to the basic fusion setup. We show that it is possible to achieve the same enhancement by replacing the Fredkin gate with two Toffoli gates. Via this replacement, the enhanced setup for creating large-scaleWwebs becomes realizable with current photonics technology.
Nabil Romero Zurita, University of Leeds