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[en] Quantum cryptography enables two parties to perform private communication. Crucial for the security are the assumptions, which have to be made about the practical implementation of the theoretical protocol. In the device independent scenario one tries to consider only as few assumptions as possible, while still guaranteeing security even against the most general, i.e. coherent, attacks. We present results on the problem in a black-box scenario
Journal
Verhandlungen der Deutschen Physikalischen Gesellschaft; ISSN 0420-0195; 
; CODEN VDPEAZ; (Hamburg 2009 issue); [1 p.]
; CODEN VDPEAZ; (Hamburg 2009 issue); [1 p.]
[en] The subcarrier domain of multicarrier continuous-variable quantum key distribution (CVQKD) is defined. In a multicarrier CVQKD scheme, the information is granulated into Gaussian subcarrier CVs and the physical Gaussian link is divided into Gaussian sub-channels. The subcarrier domain injects physical attributes to the description of the subcarrier transmission. We prove that the subcarrier domain is a natural representation of the subcarrier-level transmission in a multicarrier CVQKD scheme. We also extend the subcarrier domain to a multiple-access multicarrier CVQKD setting. We demonstrate the results through the adaptive multicarrier quadrature-division (AMQD) CVQKD scheme and the AMQD-MQA (multiuser quadrature allocation) multiple-access multicarrier scheme. The subcarrier domain representation provides a general apparatus that can be utilized for an arbitrary multicarrier CVQKD scenario.
Journal
[en] In a deterministic quantum key distribution (DQKD) protocol with a two-way quantum channel, Bob sends a qubit to Alice who then encodes a key bit onto the qubit and sends it back to Bob. After measuring the returned qubit, Bob can obtain Alice's key bit immediately, without basis reconciliation. Since an eavesdropper may attack the qubits traveling on either the Bob-Alice channel or the Alice-Bob channel, the security analysis of DQKD protocol with a two-way quantum channel is complicated and its unconditional security has been controversial. This paper presents a security proof of a single-photon four-state DQKD protocol against general attacks.
Journal
[en] We propose a novel type of composite light–matter magnetometer based on a transversely driven multi-component Bose–Einstein condensate coupled to two distinct electromagnetic modes of a linear cavity. Above the critical pump strength, the change of the population imbalance of the condensate caused by an external magnetic field entails the change of relative photon number of the two cavity modes. Monitoring the cavity output fields thus allows for nondestructive measurement of the magnetic field in real time and we show that the sensitivity of the proposed magnetometer exhibits Heisenberg-like scaling with respect to the atom number. For state-of-the-art experimental parameters, we calculate the lower bound on the sensitivity of such a system to be of the order of fT –pT for a condensate of 104 atoms with coherence times on the order of several ms. (paper)
Journal
New Journal of Physics; ISSN 1367-2630; ; v. 23(4); [12 p.]
; v. 23(4); [12 p.]
[en] A quantum channel is a physical media able to carry quantum signals. Quantum key distribution (QKD) requires direct quantum channels between every pair of prepare-and-measure modules. This requirement heavily compromises the scalability of networks of directly connected QKD modules. A way to avoid this problem is to introduce switches that can dynamically reconfigure the set of connections. The reconfiguration of a quantum channel implies that the modules using it can adapt to the new channel and peer. The maturity and flexibility of continuous-variable QKD (CV-QKD) qualifies it as a strong contender for integration into optical communication networks. Here we present the implementation of a switched CV-QKD network embedded in the Madrid quantum testbed. The optical switching of the quantum paths significantly reduces the amount of required QKD modules and facilitates the scalability of the network. This demonstration highlights the flexibility and ease of integration of this emerging technology.
Journal
EPJ Quantum Technology; ISSN 2196-0763; ; v. 10(1); vp
; v. 10(1); vp
[en] Recently, Zou and Qiu (Sci China Phys Mech Astron 57:1696–1702, 2014) proposed a three-step semi-quantum secure direct communication protocol allowing a classical participant who does not have a quantum register to securely send his/her secret message to a quantum participant. However, this study points out that an eavesdropper can use the double C-NOT attack to obtain the secret message. To solve this problem, a modification is proposed.
Journal
Quantum Information Processing (Print); ISSN 1570-0755; ; v. 17(7); p. 1-8
; v. 17(7); p. 1-8
[en] Based on locally indistinguishable orthogonal product states, we propose a novel multiparty quantum key agreement (QKA) protocol. In this protocol, the private key information of each party is encoded as some orthogonal product states that cannot be perfectly distinguished by local operations and classical communications. To ensure the security of the protocol with small amount of decoy particles, the different particles of each product state are transmitted separately. This protocol not only can make each participant fairly negotiate a shared key, but also can avoid information leakage in the maximum extent. We give a detailed security proof of this protocol. From comparison result with the existing QKA protocols, we can know that the new protocol is more efficient.
Journal
Quantum Information Processing (Print); ISSN 1570-0755; ; v. 17(7); p. 1-17
; v. 17(7); p. 1-17
[en] Recently, Wang et al (2008 Phys. Lett. A 373 65) proposed an attack on Zhang et al's (2007 Opt. Commun. 269 418) multiparty quantum secret sharing scheme, in which the first and the last agent are reported to be able to cooperatively eavesdrop on all the secret messages without being detected. In this paper, we show that in Wang et al's attack, on average no more than half the secret messages can be eavesdropped. (paper)
Journal
Physica Scripta (Online); ISSN 1402-4896; ; v. 86(2); [3 p.]
; v. 86(2); [3 p.]
No abstract available
Journal
Verhandlungen der Deutschen Physikalischen Gesellschaft; ISSN 0420-0195; ; CODEN VDPEAZ; v. 43(1); [1 p.]
; CODEN VDPEAZ; v. 43(1); [1 p.]
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