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Sample records for counterfactual quantum key

  1. Counterfactual quantum key distribution with high efficiency

    SciTech Connect

    Sun Ying; Wen Qiaoyan

    2010-11-15

    In a counterfactual quantum key distribution scheme, a secret key can be generated merely by transmitting the split vacuum pulses of single particles. We improve the efficiency of the first quantum key distribution scheme based on the counterfactual phenomenon. This scheme not only achieves the same security level as the original one but also has higher efficiency. We also analyze how to achieve the optimal efficiency under various conditions.

  2. Trojan horse attacks on counterfactual quantum key distribution

    NASA Astrophysics Data System (ADS)

    Yang, Xiuqing; Wei, Kejin; Ma, Haiqiang; Sun, Shihai; Du, Yungang; Wu, Lingan

    2016-04-01

    There has been much interest in "counterfactual quantum cryptography" (T.-G. Noh, 2009 [10]). It seems that the counterfactual quantum key distribution protocol without any photon carrier through the quantum channel provides practical security advantages. However, we show that it is easy to break counterfactual quantum key distribution systems in practical situations. We introduce the two types of Trojan horse attacks that are available for the two-way protocol and become possible for practical counterfactual systems with our eavesdropping schemes.

  3. Private database queries based on counterfactual quantum key distribution

    NASA Astrophysics Data System (ADS)

    Zhang, Jia-Li; Guo, Fen-Zhuo; Gao, Fei; Liu, Bin; Wen, Qiao-Yan

    2013-08-01

    Based on the fundamental concept of quantum counterfactuality, we propose a protocol to achieve quantum private database queries, which is a theoretical study of how counterfactuality can be employed beyond counterfactual quantum key distribution (QKD). By adding crucial detecting apparatus to the device of QKD, the privacy of both the distrustful user and the database owner can be guaranteed. Furthermore, the proposed private-database-query protocol makes full use of the low efficiency in the counterfactual QKD, and by adjusting the relevant parameters, the protocol obtains excellent flexibility and extensibility.

  4. Eavesdropping on counterfactual quantum key distribution with finite resources

    NASA Astrophysics Data System (ADS)

    Liu, Xingtong; Zhang, Bo; Wang, Jian; Tang, Chaojing; Zhao, Jingjing; Zhang, Sheng

    2014-08-01

    A striking scheme called "counterfactual quantum cryptography" gives a conceptually new approach to accomplish the task of key distribution. It allows two legitimate parties to share a secret even though a particle carrying secret information is not, in fact, transmitted through the quantum channel. Since an eavesdropper cannot directly access the entire quantum system of each signal particle, the protocol seems to provide practical security advantages. However, here we propose an eavesdropping method which works on the scheme in a finite key scenario. We show that, for practical systems only generating a finite number of keys, the eavesdropping can obtain all of the secret information without being detected. We also present a improved protocol as a countermeasure against this attack.

  5. Counterfactual quantum certificate authorization

    NASA Astrophysics Data System (ADS)

    Shenoy H., Akshata; Srikanth, R.; Srinivas, T.

    2014-05-01

    We present a multipartite protocol in a counterfactual paradigm. In counterfactual quantum cryptography, secure information is transmitted between two spatially separated parties even when there is no physical travel of particles transferring the information between them. We propose here a tripartite counterfactual quantum protocol for the task of certificate authorization. Here a trusted third party, Alice, authenticates an entity Bob (e.g., a bank) that a client Charlie wishes to securely transact with. The protocol is counterfactual with respect to either Bob or Charlie. We prove its security against a general incoherent attack, where Eve attacks single particles.

  6. Probabilistic direct counterfactual quantum communication

    NASA Astrophysics Data System (ADS)

    Zhang, Sheng

    2017-02-01

    It is striking that the quantum Zeno effect can be used to launch a direct counterfactual communication between two spatially separated parties, Alice and Bob. So far, existing protocols of this type only provide a deterministic counterfactual communication service. However, this counterfactuality should be payed at a price. Firstly, the transmission time is much longer than a classical transmission costs. Secondly, the chained-cycle structure makes them more sensitive to channel noises. Here, we extend the idea of counterfactual communication, and present a probabilistic-counterfactual quantum communication protocol, which is proved to have advantages over the deterministic ones. Moreover, the presented protocol could evolve to a deterministic one solely by adjusting the parameters of the beam splitters. Project supported by the National Natural Science Foundation of China (Grant No. 61300203).

  7. Security of counterfactual quantum cryptography

    SciTech Connect

    Yin Zhenqiang; Li Hongwei; Chen Wei; Han Zhengfu; Guo Guangcan

    2010-10-15

    Recently, a 'counterfactual' quantum-key-distribution scheme was proposed by T.-G. Noh [Phys. Rev. Lett. 103, 230501 (2009)]. In this scheme, two legitimate distant peers may share secret keys even when the information carriers are not traveled in the quantum channel. We find that this protocol is equivalent to an entanglement distillation protocol. According to this equivalence, a strict security proof and the asymptotic key bit rate are both obtained when a perfect single-photon source is applied and a Trojan horse attack can be detected. We also find that the security of this scheme is strongly related to not only the bit error rate but also the yields of photons. And our security proof may shed light on the security of other two-way protocols.

  8. Counterfactual quantum cryptography.

    PubMed

    Noh, Tae-Gon

    2009-12-04

    Quantum cryptography allows one to distribute a secret key between two remote parties using the fundamental principles of quantum mechanics. The well-known established paradigm for the quantum key distribution relies on the actual transmission of signal particle through a quantum channel. In this Letter, we show that the task of a secret key distribution can be accomplished even though a particle carrying secret information is not in fact transmitted through the quantum channel. The proposed protocols can be implemented with current technologies and provide practical security advantages by eliminating the possibility that an eavesdropper can directly access the entire quantum system of each signal particle.

  9. Counterfactual quantum cryptography network with untrusted relay

    NASA Astrophysics Data System (ADS)

    Chen, Yuanyuan; Gu, Xuemei; Jiang, Dong; Xie, Ling; Chen, Lijun

    2015-07-01

    Counterfactual quantum cryptography allows two remote parties to share a secret key even though a physical particle is not in fact transmitted through the quantum channel. In order to extend the scope of counterfactual quantum cryptography, we use an untrusted relay to construct a multi-user network. The implementation issues are discussed to show that the scheme can be realized with current technologies. We also prove the practical security advantages of the scheme by eliminating the probability that an eavesdropper can directly access the signal or an untrusted relay can perform false operations.

  10. Analysis of Counterfactual Quantum Certificate Authorization

    NASA Astrophysics Data System (ADS)

    Wang, Tian-Yin; Li, Yan-Ping; Zhang, Rui-Ling

    2016-12-01

    A counterfactual quantum certificate authorization protocol was proposed recently (Shenoy et al., Phys. Rev. A 89, 052307 (20)), in which a trusted third party, Alice, authenticates an entity Bob (e.g., a bank) that a client Charlie wishes to securely transact with. However, this protocol requires a classical authenticated channel between Bob and Charlie to prevent possible attacks from the third party Alice, which is in conflict with the task of certificate authorization in the sense that Bob and Charlie can establish an unconditionally-secure key by a quantum key distribution protocol if there is a classical authenticated channel between them and hence securely transact with each other even without the assistance of the third party Alice.

  11. Quantum counterfactual communication without a weak trace

    NASA Astrophysics Data System (ADS)

    Arvidsson-Shukur, D. R. M.; Barnes, C. H. W.

    2016-12-01

    The classical theories of communication rely on the assumption that there has to be a flow of particles from Bob to Alice in order for him to send a message to her. We develop a quantum protocol that allows Alice to perceive Bob's message "counterfactually"; that is, without Alice receiving any particles that have interacted with Bob. By utilizing a setup built on results from interaction-free measurements, we outline a communication protocol whereby the information travels in the opposite direction of the emitted particles. In comparison to previous attempts on such protocols, this one is such that a weak measurement at the message source would not leave a weak trace that could be detected by Alice's receiver. While some interaction-free schemes require a large number of carefully aligned beam splitters, our protocol is realizable with two or more beam splitters. We demonstrate this protocol by numerically solving the time-dependent Schrödinger equation for a Hamiltonian that implements this quantum counterfactual phenomenon.

  12. On Replacing "Quantum Thinking" with Counterfactual Reasoning

    NASA Astrophysics Data System (ADS)

    Narens, Louis

    The probability theory used in quantum mechanics is currently being employed by psychologists to model the impact of context on decision. Its event space consists of closed subspaces of a Hilbert space, and its probability function sometimes violate the law of the finite additivity of probabilities. Results from the quantum mechanics literature indicate that such a "Hilbert space probability theory" cannot be extended in a useful way to standard, finitely additive, probability theory by the addition of new events with specific probabilities. This chapter presents a new kind of probability theory that shares many fundamental algebraic characteristics with Hilbert space probability theory but does extend to standard probability theory by adjoining new events with specific probabilities. The new probability theory arises from considerations about how psychological experiments are related through counterfactual reasoning.

  13. Comment on 'Nonlocality, Counterfactuals and Quantum Mechanics'

    SciTech Connect

    Stapp, H.P.

    1999-04-14

    A recent proof [H. P. Stapp, Am. J. Phys. 65, 300 (1997)], formulated in the symbolic language of modal logic, claims to show that contemporary quantum theory, viewed as a set of rules that allow us to calculate statistical predictions among certain kinds of observations, cannot be imbedded in any rational framework that conforms to the principles that (1) the experimenters' choices of which experiments they will perform can be considered to be free choices, (2) outcomes of measurements are unique, and (3) the free choices just mentioned have no backward-in-time effects of any kind. This claim is similar to Bell's theorem, but much stronger, because no reality assumption alien to quantum philosophy is used. The paper being commented on [W. Unruh, Phys. Rev. A 59, 126 (1999)] argues that some such reality assumption has been ''smuggled'' in. That argument is examined here and shown, I believe, to be defective.

  14. Quantum key management

    DOEpatents

    Hughes, Richard John; Thrasher, James Thomas; Nordholt, Jane Elizabeth

    2016-11-29

    Innovations for quantum key management harness quantum communications to form a cryptography system within a public key infrastructure framework. In example implementations, the quantum key management innovations combine quantum key distribution and a quantum identification protocol with a Merkle signature scheme (using Winternitz one-time digital signatures or other one-time digital signatures, and Merkle hash trees) to constitute a cryptography system. More generally, the quantum key management innovations combine quantum key distribution and a quantum identification protocol with a hash-based signature scheme. This provides a secure way to identify, authenticate, verify, and exchange secret cryptographic keys. Features of the quantum key management innovations further include secure enrollment of users with a registration authority, as well as credential checking and revocation with a certificate authority, where the registration authority and/or certificate authority can be part of the same system as a trusted authority for quantum key distribution.

  15. Counterfactual distribution of Schrödinger cat states

    NASA Astrophysics Data System (ADS)

    Shenoy-Hejamadi, Akshata; Srikanth, R.

    2015-12-01

    In the counterfactual cryptography scheme proposed by Noh, the sender Alice probabilistically transmits classical information to the receiver Bob without the physical travel of a particle. Here we generalize this idea to the distribution of quantum entanglement. The key insight is to replace their classical input choices with quantum superpositions. We further show that the scheme can be generalized to counterfactually distribute multipartite cat states.

  16. Limitations on quantum key repeaters.

    PubMed

    Bäuml, Stefan; Christandl, Matthias; Horodecki, Karol; Winter, Andreas

    2015-04-23

    A major application of quantum communication is the distribution of entangled particles for use in quantum key distribution. Owing to noise in the communication line, quantum key distribution is, in practice, limited to a distance of a few hundred kilometres, and can only be extended to longer distances by use of a quantum repeater, a device that performs entanglement distillation and quantum teleportation. The existence of noisy entangled states that are undistillable but nevertheless useful for quantum key distribution raises the question of the feasibility of a quantum key repeater, which would work beyond the limits of entanglement distillation, hence possibly tolerating higher noise levels than existing protocols. Here we exhibit fundamental limits on such a device in the form of bounds on the rate at which it may extract secure key. As a consequence, we give examples of states suitable for quantum key distribution but unsuitable for the most general quantum key repeater protocol.

  17. Limitations on quantum key repeaters

    NASA Astrophysics Data System (ADS)

    Bäuml, Stefan; Christandl, Matthias; Horodecki, Karol; Winter, Andreas

    2015-04-01

    A major application of quantum communication is the distribution of entangled particles for use in quantum key distribution. Owing to noise in the communication line, quantum key distribution is, in practice, limited to a distance of a few hundred kilometres, and can only be extended to longer distances by use of a quantum repeater, a device that performs entanglement distillation and quantum teleportation. The existence of noisy entangled states that are undistillable but nevertheless useful for quantum key distribution raises the question of the feasibility of a quantum key repeater, which would work beyond the limits of entanglement distillation, hence possibly tolerating higher noise levels than existing protocols. Here we exhibit fundamental limits on such a device in the form of bounds on the rate at which it may extract secure key. As a consequence, we give examples of states suitable for quantum key distribution but unsuitable for the most general quantum key repeater protocol.

  18. Quantum Key Distribution

    NASA Astrophysics Data System (ADS)

    Hughes, Richard

    2004-05-01

    Quantum key distribution (QKD) uses single-photon communications to generate the shared, secret random number sequences that are used to encrypt and decrypt secret communications. The unconditional security of QKD is based on the interplay between fundamental principles of quantum physics and information theory. An adversary can neither successfully tap the transmissions, nor evade detection (eavesdropping raises the key error rate above a threshold value). QKD could be particularly attractive for free-space optical communications, both ground-based and for satellites. I will describe a QKD experiment performed over multi-kilometer line-of-sight paths, which serves as a model for a satellite-to-ground key distribution system. The system uses single-photon polarization states, without active polarization switching, and for the first time implements the complete BB84 QKD protocol including, reconciliation, privacy amplification and the all-important authentication stage. It is capable of continuous operation throughout the day and night, achieving the self-sustaining production of error-free, shared, secret bits. I will also report on the results of satellite-to-ground QKD modeling.

  19. Secure quantum key distribution

    NASA Astrophysics Data System (ADS)

    Lo, Hoi-Kwong; Curty, Marcos; Tamaki, Kiyoshi

    2014-08-01

    Secure communication is crucial in the Internet Age, and quantum mechanics stands poised to revolutionize cryptography as we know it today. In this Review, we introduce the motivation and the current state of the art of research in quantum cryptography. In particular, we discuss the present security model together with its assumptions, strengths and weaknesses. After briefly introducing recent experimental progress and challenges, we survey the latest developments in quantum hacking and countermeasures against it.

  20. Quantum entanglement assisted key distribution

    NASA Astrophysics Data System (ADS)

    Tang, Ke; Ji, Ping; Zhang, Xiaowen

    2007-04-01

    Quantum correlations or entanglement is a basic ingredient for many applications of quantum information theory.One important application using quantum entanglement exploits the correlation nature of entangled photon states is quantum key distribution, which is proven unbreakable in principle and provides the highest possible security that is impossible in classical information theory. However, generating entangled photon pairs is not a simple task -- only approximately one out of a million pump photons decay into a signal and idler photon pair. This low rate of entangled photon pairs is further reduced by the overhead required in order for the rectification of the inevitable errors due to channel imperfections or caused by potential eavesdroppers. As a consequence, quantum key distribution suffers from a low bit rate, which is in the order of hundreds to thousands bits per second or below. On the other hand, the classical public key distribution does not impose a tight limit on the transmission rate. However, it is subject to the risks of eavesdroppers sitting in the middle of the insecure channel. In this paper, we propose a hybrid key distribution method which uses public key distribution method to generate a raw key, and then uses entanglement assisted communication to modify the raw key by inserting a number of quantum bits in the raw key. Building upon the foundation of the unconditional security of quantum key distribution, we use the privacy amplification to make the affection of inserted bits expand to a whole key. Our quantum entanglement assisted key distribution scheme greatly improves the efficiency of key distribution while without compromising the level of security achievable by quantum cryptography.

  1. Quantum Public-Key Cryptosystem

    NASA Astrophysics Data System (ADS)

    Luo, Ming-Xing; Chen, Xiu-Bo; Yun, Deng; Yang, Yi-Xian

    2012-03-01

    Quantum one-way functions play a fundamental role in cryptography because of its necessity for the secure encryption schemes taking into account the quantum computer. In this paper our purpose is to establish a theoretical framework for a candidate of the quantum one-way functions and quantum trapdoor functions based on one-parameter unitary groups. The dynamics of parameterized unitary groups ensure the one-wayness and quantum undistinguishability in different levels, and the physical feasibility are derived from the simultaneous approximation of its infinitesimal generators. Moreover, these special functions are used to construct new cryptosystems-the quantum public-key cryptosystems for encrypting both the classical and quantum information.

  2. Causal conditionals and counterfactuals

    PubMed Central

    Frosch, Caren A.; Byrne, Ruth M.J.

    2012-01-01

    Causal counterfactuals e.g., ‘if the ignition key had been turned then the car would have started’ and causal conditionals e.g., ‘if the ignition key was turned then the car started’ are understood by thinking about multiple possibilities of different sorts, as shown in six experiments using converging evidence from three different types of measures. Experiments 1a and 1b showed that conditionals that comprise enabling causes, e.g., ‘if the ignition key was turned then the car started’ primed people to read quickly conjunctions referring to the possibility of the enabler occurring without the outcome, e.g., ‘the ignition key was turned and the car did not start’. Experiments 2a and 2b showed that people paraphrased causal conditionals by using causal or temporal connectives (because, when), whereas they paraphrased causal counterfactuals by using subjunctive constructions (had…would have). Experiments 3a and 3b showed that people made different inferences from counterfactuals presented with enabling conditions compared to none. The implications of the results for alternative theories of conditionals are discussed. PMID:22858874

  3. Post-quantum key exchange protocols

    NASA Astrophysics Data System (ADS)

    Li, Xiangdong; Leung, Lin; Kwan, Andis Chi-Tung; Zhang, Xiaowen; Kahanda, Dammika; Anshel, Michael

    2006-05-01

    If an eavesdropper Eve is equipped with quantum computers, she can easily break the public key exchange protocols used today. In this paper we will discuss the post-quantum Diffie-Hellman key exchange and private key exchange protocols.

  4. Quantum walk public-key cryptographic system

    NASA Astrophysics Data System (ADS)

    Vlachou, C.; Rodrigues, J.; Mateus, P.; Paunković, N.; Souto, A.

    2015-12-01

    Quantum Cryptography is a rapidly developing field of research that benefits from the properties of Quantum Mechanics in performing cryptographic tasks. Quantum walks are a powerful model for quantum computation and very promising for quantum information processing. In this paper, we present a quantum public-key cryptographic system based on quantum walks. In particular, in the proposed protocol the public-key is given by a quantum state generated by performing a quantum walk. We show that the protocol is secure and analyze the complexity of public key generation and encryption/decryption procedures.

  5. Comment on [open quotes]Nonlocality, counterfactuals, and quantum mechanics[close quotes

    SciTech Connect

    Stapp, H.P. )

    1999-09-01

    A recent proof [H. P. Stapp, Am. J. Phys. [bold 65], 300 (1997)], formulated in the symbolic language of modal logic, claims to show that contemporary quantum theory, viewed as a set of rules that allow us to calculate statistical predictions among certain kinds of observations, cannot be imbedded in any rational framework that conforms to the principles that (1) the experimenters[close quote] choices of which experiments they will perform can be considered to be free choices, (2) outcomes of measurements are unique, and (3) the free choices just mentioned have no backward-in-time effects of any kind. This claim is similar to Bell[close quote]s theorem, but much stronger, because no reality assumption alien to quantum philosophy is used. The paper being commented on [W. Unruh, Phys. Rev. A [bold 59], 126 (1999)] argues that some such reality assumption has been [open quotes]smuggled[close quotes] in. That argument is examined here and shown, I believe, to be defective. [copyright] [ital 1999] [ital The American Physical Society

  6. Multiparty Quantum Key Agreement Based on Quantum Search Algorithm

    PubMed Central

    Cao, Hao; Ma, Wenping

    2017-01-01

    Quantum key agreement is an important topic that the shared key must be negotiated equally by all participants, and any nontrivial subset of participants cannot fully determine the shared key. To date, the embed modes of subkey in all the previously proposed quantum key agreement protocols are based on either BB84 or entangled states. The research of the quantum key agreement protocol based on quantum search algorithms is still blank. In this paper, on the basis of investigating the properties of quantum search algorithms, we propose the first quantum key agreement protocol whose embed mode of subkey is based on a quantum search algorithm known as Grover’s algorithm. A novel example of protocols with 5 – party is presented. The efficiency analysis shows that our protocol is prior to existing MQKA protocols. Furthermore it is secure against both external attack and internal attacks. PMID:28332610

  7. Multiparty Quantum Key Agreement Based on Quantum Search Algorithm.

    PubMed

    Cao, Hao; Ma, Wenping

    2017-03-23

    Quantum key agreement is an important topic that the shared key must be negotiated equally by all participants, and any nontrivial subset of participants cannot fully determine the shared key. To date, the embed modes of subkey in all the previously proposed quantum key agreement protocols are based on either BB84 or entangled states. The research of the quantum key agreement protocol based on quantum search algorithms is still blank. In this paper, on the basis of investigating the properties of quantum search algorithms, we propose the first quantum key agreement protocol whose embed mode of subkey is based on a quantum search algorithm known as Grover's algorithm. A novel example of protocols with 5 - party is presented. The efficiency analysis shows that our protocol is prior to existing MQKA protocols. Furthermore it is secure against both external attack and internal attacks.

  8. Multiparty Quantum Key Agreement Based on Quantum Search Algorithm

    NASA Astrophysics Data System (ADS)

    Cao, Hao; Ma, Wenping

    2017-03-01

    Quantum key agreement is an important topic that the shared key must be negotiated equally by all participants, and any nontrivial subset of participants cannot fully determine the shared key. To date, the embed modes of subkey in all the previously proposed quantum key agreement protocols are based on either BB84 or entangled states. The research of the quantum key agreement protocol based on quantum search algorithms is still blank. In this paper, on the basis of investigating the properties of quantum search algorithms, we propose the first quantum key agreement protocol whose embed mode of subkey is based on a quantum search algorithm known as Grover’s algorithm. A novel example of protocols with 5 – party is presented. The efficiency analysis shows that our protocol is prior to existing MQKA protocols. Furthermore it is secure against both external attack and internal attacks.

  9. No signaling and quantum key distribution.

    PubMed

    Barrett, Jonathan; Hardy, Lucien; Kent, Adrian

    2005-07-01

    Standard quantum key distribution protocols are provably secure against eavesdropping attacks, if quantum theory is correct. It is theoretically interesting to know if we need to assume the validity of quantum theory to prove the security of quantum key distribution, or whether its security can be based on other physical principles. The question would also be of practical interest if quantum mechanics were ever to fail in some regime, because a scientifically and technologically advanced eavesdropper could perhaps use postquantum physics to extract information from quantum communications without necessarily causing the quantum state disturbances on which existing security proofs rely. Here we describe a key distribution scheme provably secure against general attacks by a postquantum eavesdropper limited only by the impossibility of superluminal signaling. Its security stems from violation of a Bell inequality.

  10. TASQC Quantum Key Transfer Program

    SciTech Connect

    Billings, Jay J.; Bonior, Jason D.; Evans, Philip G.; McCaskey, Alexander J.

    2016-11-04

    Securely transferring timing information in the electrical grid is a critical component of securing the nation's infrastructure from cyber attacks. One solution to this problem is to use quantum information to securely transfer the timing information across sites. This software provides such an infrastructure using a standard Java webserver that pulls the quantum information from associated hardware.

  11. Finite key analysis for symmetric attacks in quantum key distribution

    SciTech Connect

    Meyer, Tim; Kampermann, Hermann; Kleinmann, Matthias; Bruss, Dagmar

    2006-10-15

    We introduce a constructive method to calculate the achievable secret key rate for a generic class of quantum key distribution protocols, when only a finite number n of signals is given. Our approach is applicable to all scenarios in which the quantum state shared by Alice and Bob is known. In particular, we consider the six state protocol with symmetric eavesdropping attacks, and show that for a small number of signals, i.e., below n{approx}10{sup 4}, the finite key rate differs significantly from the asymptotic value for n{yields}{infinity}. However, for larger n, a good approximation of the asymptotic value is found. We also study secret key rates for protocols using higher-dimensional quantum systems.

  12. Quantum asymmetric cryptography with symmetric keys

    NASA Astrophysics Data System (ADS)

    Gao, Fei; Wen, Qiaoyan; Qin, Sujuan; Zhu, Fuchen

    2009-12-01

    Based on quantum encryption, we present a new idea for quantum public-key cryptography (QPKC) and construct a whole theoretical framework of a QPKC system. We show that the quantum-mechanical nature renders it feasible and reasonable to use symmetric keys in such a scheme, which is quite different from that in conventional public-key cryptography. The security of our scheme is analyzed and some features are discussed. Furthermore, the state-estimation attack to a prior QPKC scheme is demonstrated.

  13. Practical challenges in quantum key distribution

    DOE PAGES

    Diamanti, Eleni; Lo, Hoi -Kwong; Qi, Bing; ...

    2016-11-08

    Here, quantum key distribution (QKD) promises unconditional security in data communication and is currently being deployed in commercial applications. Nonetheless, before QKD can be widely adopted, it faces a number of important challenges such as secret key rate, distance, size, cost and practical security. Here, we survey those key challenges and the approaches that are currently being taken to address them.

  14. All-photonic intercity quantum key distribution

    PubMed Central

    Azuma, Koji; Tamaki, Kiyoshi; Munro, William J.

    2015-01-01

    Recent field demonstrations of quantum key distribution (QKD) networks hold promise for unconditionally secure communication. However, owing to loss in optical fibres, the length of point-to-point links is limited to a hundred kilometers, restricting the QKD networks to intracity. A natural way to expand the QKD network in a secure manner is to connect it to another one in a different city with quantum repeaters. But, this solution is overengineered unless such a backbone connection is intercontinental. Here we present a QKD protocol that could supersede even quantum repeaters for connecting QKD networks in different cities below 800 km distant. Nonetheless, in contrast to quantum repeaters, this protocol uses only a single intermediate node with optical devices, requiring neither quantum memories nor quantum error correction. Our all-photonic ‘intercity' QKD protocol bridges large gaps between the conventional intracity QKD networks and the future intercontinental quantum repeaters, conceptually and technologically. PMID:26671044

  15. All-photonic intercity quantum key distribution

    NASA Astrophysics Data System (ADS)

    Azuma, Koji; Tamaki, Kiyoshi; Munro, William J.

    2015-12-01

    Recent field demonstrations of quantum key distribution (QKD) networks hold promise for unconditionally secure communication. However, owing to loss in optical fibres, the length of point-to-point links is limited to a hundred kilometers, restricting the QKD networks to intracity. A natural way to expand the QKD network in a secure manner is to connect it to another one in a different city with quantum repeaters. But, this solution is overengineered unless such a backbone connection is intercontinental. Here we present a QKD protocol that could supersede even quantum repeaters for connecting QKD networks in different cities below 800 km distant. Nonetheless, in contrast to quantum repeaters, this protocol uses only a single intermediate node with optical devices, requiring neither quantum memories nor quantum error correction. Our all-photonic `intercity' QKD protocol bridges large gaps between the conventional intracity QKD networks and the future intercontinental quantum repeaters, conceptually and technologically.

  16. On quantum key distribution using ququarts

    SciTech Connect

    Kulik, S. P. Shurupov, A. P.

    2007-05-15

    A comparative analysis of quantum key distribution protocols using qubits and ququarts as information carriers is presented. Several schemes of incoherent attacks that can be used by an eavesdropper to obtain secret information are considered. The errors induced by the eavesdropper are analyzed for several key distribution protocols.

  17. Device-independent quantum key distribution

    NASA Astrophysics Data System (ADS)

    Hänggi, Esther

    2010-12-01

    In this thesis, we study two approaches to achieve device-independent quantum key distribution: in the first approach, the adversary can distribute any system to the honest parties that cannot be used to communicate between the three of them, i.e., it must be non-signalling. In the second approach, we limit the adversary to strategies which can be implemented using quantum physics. For both approaches, we show how device-independent quantum key distribution can be achieved when imposing an additional condition. In the non-signalling case this additional requirement is that communication is impossible between all pairwise subsystems of the honest parties, while, in the quantum case, we demand that measurements on different subsystems must commute. We give a generic security proof for device-independent quantum key distribution in these cases and apply it to an existing quantum key distribution protocol, thus proving its security even in this setting. We also show that, without any additional such restriction there always exists a successful joint attack by a non-signalling adversary.

  18. Numerical approach for unstructured quantum key distribution

    PubMed Central

    Coles, Patrick J.; Metodiev, Eric M.; Lütkenhaus, Norbert

    2016-01-01

    Quantum key distribution (QKD) allows for communication with security guaranteed by quantum theory. The main theoretical problem in QKD is to calculate the secret key rate for a given protocol. Analytical formulas are known for protocols with symmetries, since symmetry simplifies the analysis. However, experimental imperfections break symmetries, hence the effect of imperfections on key rates is difficult to estimate. Furthermore, it is an interesting question whether (intentionally) asymmetric protocols could outperform symmetric ones. Here we develop a robust numerical approach for calculating the key rate for arbitrary discrete-variable QKD protocols. Ultimately this will allow researchers to study ‘unstructured' protocols, that is, those that lack symmetry. Our approach relies on transforming the key rate calculation to the dual optimization problem, which markedly reduces the number of parameters and hence the calculation time. We illustrate our method by investigating some unstructured protocols for which the key rate was previously unknown. PMID:27198739

  19. Quantum Key Distribution with Blind Polarization Bases

    NASA Astrophysics Data System (ADS)

    Kye, Won-Ho; Kim, Chil-Min; Kim, M. S.; Park, Young-Jai

    2005-07-01

    We propose a new quantum key distribution scheme that uses the blind polarization basis. In our scheme the sender and the receiver share key information by exchanging qubits with arbitrary polarization angles without basis reconciliation. As only random polarizations are transmitted, our protocol is secure even when a key is embedded in a not-so-weak coherent-state pulse. We show its security against the photon-number splitting attack and the impersonation attack.

  20. Quantum key distribution: theory for application

    NASA Astrophysics Data System (ADS)

    Lütkenhaus, N.

    Quantum key distribution bears the promise to set new standards in secure communication. However, on the way from the theoretical principles to the practical implementation we find many obstacles that need to be taken care of. In this article I show how to obtain a key with a realistic setup such that the security of this key can be proven for an important restricted class of eavesdropping attacks, namely the individual attacks.

  1. Frequency-coded quantum key distribution.

    PubMed

    Bloch, Matthieu; McLaughlin, Steven W; Merolla, Jean-Marc; Patois, Frédéric

    2007-02-01

    We report an intrinsically stable quantum key distribution scheme based on genuine frequency-coded quantum states. The qubits are efficiently processed without fiber interferometers by fully exploiting the nonlinear interaction occurring in electro-optic phase modulators. The system requires only integrated off-the-shelf devices and could be used with a true single-photon source. Preliminary experiments have been performed with weak laser pulses and have demonstrated the feasibility of this new setup.

  2. Fundamental quantitative security in quantum key generation

    SciTech Connect

    Yuen, Horace P.

    2010-12-15

    We analyze the fundamental security significance of the quantitative criteria on the final generated key K in quantum key generation including the quantum criterion d, the attacker's mutual information on K, and the statistical distance between her distribution on K and the uniform distribution. For operational significance a criterion has to produce a guarantee on the attacker's probability of correctly estimating some portions of K from her measurement, in particular her maximum probability of identifying the whole K. We distinguish between the raw security of K when the attacker just gets at K before it is used in a cryptographic context and its composition security when the attacker may gain further information during its actual use to help get at K. We compare both of these securities of K to those obtainable from conventional key expansion with a symmetric key cipher. It is pointed out that a common belief in the superior security of a quantum generated K is based on an incorrect interpretation of d which cannot be true, and the security significance of d is uncertain. Generally, the quantum key distribution key K has no composition security guarantee and its raw security guarantee from concrete protocols is worse than that of conventional ciphers. Furthermore, for both raw and composition security there is an exponential catch-up problem that would make it difficult to quantitatively improve the security of K in a realistic protocol. Some possible ways to deal with the situation are suggested.

  3. Quantum key distribution based on quantum dimension and independent devices

    NASA Astrophysics Data System (ADS)

    Li, Hong-Wei; Yin, Zhen-Qiang; Chen, Wei; Wang, Shuang; Guo, Guang-Can; Han, Zheng-Fu

    2014-03-01

    In this paper, we propose a quantum key distribution (QKD) protocol based on only a two-dimensional Hilbert space encoding a quantum system and independent devices between the equipment for state preparation and measurement. Our protocol is inspired by the fully device-independent quantum key distribution (FDI-QKD) protocol and the measurement-device-independent quantum key distribution (MDI-QKD) protocol. Our protocol only requires the state to be prepared in the two-dimensional Hilbert space, which weakens the state preparation assumption in the original MDI-QKD protocol. More interestingly, our protocol can overcome the detection loophole problem in the FDI-QKD protocol, which greatly limits the application of FDI-QKD. Hence our protocol can be implemented with practical optical components.

  4. Key Reconciliation for High Performance Quantum Key Distribution

    PubMed Central

    Martinez-Mateo, Jesus; Elkouss, David; Martin, Vicente

    2013-01-01

    Quantum Key Distribution is carving its place among the tools used to secure communications. While a difficult technology, it enjoys benefits that set it apart from the rest, the most prominent is its provable security based on the laws of physics. QKD requires not only the mastering of signals at the quantum level, but also a classical processing to extract a secret-key from them. This postprocessing has been customarily studied in terms of the efficiency, a figure of merit that offers a biased view of the performance of real devices. Here we argue that it is the throughput the significant magnitude in practical QKD, specially in the case of high speed devices, where the differences are more marked, and give some examples contrasting the usual postprocessing schemes with new ones from modern coding theory. A good understanding of its implications is very important for the design of modern QKD devices. PMID:23546440

  5. Optimal Device Independent Quantum Key Distribution

    PubMed Central

    Kamaruddin, S.; Shaari, J. S.

    2016-01-01

    We consider an optimal quantum key distribution setup based on minimal number of measurement bases with binary yields used by parties against an eavesdropper limited only by the no-signaling principle. We note that in general, the maximal key rate can be achieved by determining the optimal tradeoff between measurements that attain the maximal Bell violation and those that maximise the bit correlation between the parties. We show that higher correlation between shared raw keys at the expense of maximal Bell violation provide for better key rates for low channel disturbance. PMID:27485160

  6. Finite-key security analysis for multilevel quantum key distribution

    NASA Astrophysics Data System (ADS)

    Brádler, Kamil; Mirhosseini, Mohammad; Fickler, Robert; Broadbent, Anne; Boyd, Robert

    2016-07-01

    We present a detailed security analysis of a d-dimensional quantum key distribution protocol based on two and three mutually unbiased bases (MUBs) both in an asymptotic and finite-key-length scenario. The finite secret key rates (in bits per detected photon) are calculated as a function of the length of the sifted key by (i) generalizing the uncertainly relation-based insight from BB84 to any d-level 2-MUB QKD protocol and (ii) by adopting recent advances in the second-order asymptotics for finite block length quantum coding (for both d-level 2- and 3-MUB QKD protocols). Since the finite and asymptotic secret key rates increase with d and the number of MUBs (together with the tolerable threshold) such QKD schemes could in principle offer an important advantage over BB84. We discuss the possibility of an experimental realization of the 3-MUB QKD protocol with the orbital angular momentum degrees of freedom of photons.

  7. Quantum key distribution device with coherent states

    NASA Astrophysics Data System (ADS)

    Lodewyck, Jérôme; Bloch, Matthieu; García-Patrón, Raúl; Fossier, Simon; Karpov, Evgueni; Diamanti, Eleni; Debuisschert, Thierry; Cerf, Nicolas J.; Tualle-Brouri, Rosa; McLaughlin, Steven W.; Grangier, Philippe

    2007-09-01

    We report on both theoretical and experimental aspects of a fully implemented quantum key distribution device with coherent states. This system features a final key rate of more than 2 kb/s over 25 km of optical fiber. It comprises all required elements for field operation: a compact optical setup, a fast secret bit extraction using efficient LDPC codes, privacy amplification algorithms and a classical channel software. Both hardware and software are operated in real time.

  8. Quantum digital signatures with quantum-key-distribution components

    NASA Astrophysics Data System (ADS)

    Wallden, Petros; Dunjko, Vedran; Kent, Adrian; Andersson, Erika

    2015-04-01

    Digital signatures guarantee the authenticity and transferability of messages and are widely used in modern communication. The security of currently used classical digital signature schemes, however, relies on computational assumptions. In contrast, quantum digital signature (QDS) schemes offer information-theoretic security guaranteed by the laws of quantum mechanics. We present two QDS protocols which have the same experimental requirements as quantum key distribution, which is already commercially available. We also give a security proof for the presented QDS schemes against coherent forging attacks.

  9. Experimental quantum key distribution with source flaws

    NASA Astrophysics Data System (ADS)

    Xu, Feihu; Wei, Kejin; Sajeed, Shihan; Kaiser, Sarah; Sun, Shihai; Tang, Zhiyuan; Qian, Li; Makarov, Vadim; Lo, Hoi-Kwong

    2015-09-01

    Decoy-state quantum key distribution (QKD) is a standard technique in current quantum cryptographic implementations. Unfortunately, existing experiments have two important drawbacks: the state preparation is assumed to be perfect without errors and the employed security proofs do not fully consider the finite-key effects for general attacks. These two drawbacks mean that existing experiments are not guaranteed to be proven to be secure in practice. Here, we perform an experiment that shows secure QKD with imperfect state preparations over long distances and achieves rigorous finite-key security bounds for decoy-state QKD against coherent attacks in the universally composable framework. We quantify the source flaws experimentally and demonstrate a QKD implementation that is tolerant to channel loss despite the source flaws. Our implementation considers more real-world problems than most previous experiments, and our theory can be applied to general discrete-variable QKD systems. These features constitute a step towards secure QKD with imperfect devices.

  10. Causal Responsibility and Counterfactuals

    ERIC Educational Resources Information Center

    Lagnado, David A.; Gerstenberg, Tobias; Zultan, Ro'i

    2013-01-01

    How do people attribute responsibility in situations where the contributions of multiple agents combine to produce a joint outcome? The prevalence of over-determination in such cases makes this a difficult problem for counterfactual theories of causal responsibility. In this article, we explore a general framework for assigning responsibility in…

  11. Causal inference based on counterfactuals

    PubMed Central

    Höfler, M

    2005-01-01

    Background The counterfactual or potential outcome model has become increasingly standard for causal inference in epidemiological and medical studies. Discussion This paper provides an overview on the counterfactual and related approaches. A variety of conceptual as well as practical issues when estimating causal effects are reviewed. These include causal interactions, imperfect experiments, adjustment for confounding, time-varying exposures, competing risks and the probability of causation. It is argued that the counterfactual model of causal effects captures the main aspects of causality in health sciences and relates to many statistical procedures. Summary Counterfactuals are the basis of causal inference in medicine and epidemiology. Nevertheless, the estimation of counterfactual differences pose several difficulties, primarily in observational studies. These problems, however, reflect fundamental barriers only when learning from observations, and this does not invalidate the counterfactual concept. PMID:16159397

  12. Modified Wigner inequality for secure quantum-key distribution

    SciTech Connect

    Castelletto, S.; Degiovanni, I.P.; Rastello, M.L.

    2003-04-01

    In this paper, we discuss the insecurity with present implementations of the Ekert protocol for quantum-key distribution based on the Wigner inequality. We propose a modified version of this inequality which guarantees safe quantum-key distribution.

  13. Reference-frame-independent quantum key distribution

    SciTech Connect

    Laing, Anthony; Rarity, John G.; O'Brien, Jeremy L.; Scarani, Valerio

    2010-07-15

    We describe a quantum key distribution protocol based on pairs of entangled qubits that generates a secure key between two partners in an environment of unknown and slowly varying reference frame. A direction of particle delivery is required, but the phases between the computational basis states need not be known or fixed. The protocol can simplify the operation of existing setups and has immediate applications to emerging scenarios such as earth-to-satellite links and the use of integrated photonic waveguides. We compute the asymptotic secret key rate for a two-qubit source, which coincides with the rate of the six-state protocol for white noise. We give the generalization of the protocol to higher-dimensional systems and detail a scheme for physical implementation in the three-dimensional qutrit case.

  14. Public-key encryption and authentication of quantum information

    NASA Astrophysics Data System (ADS)

    Liang, Min; Yang, Li

    2012-09-01

    Public-key cryptosystems for quantum messages are considered from two aspects: public-key encryption and public-key authentication. Firstly, we propose a general construction of quantum public-key encryption scheme, and then construct an information-theoretic secure instance. Then, we propose a quantum public-key authentication scheme, which can protect the integrity of quantum messages. This scheme can both encrypt and authenticate quantum messages. It is information-theoretic secure with regard to encryption, and the success probability of tampering decreases exponentially with the security parameter with regard to authentication. Compared with classical public-key cryptosystems, one private-key in our schemes corresponds to an exponential number of public-keys, and every quantum public-key used by the sender is an unknown quantum state to the sender.

  15. Quantum hacking on quantum key distribution using homodyne detection

    NASA Astrophysics Data System (ADS)

    Huang, Jing-Zheng; Kunz-Jacques, Sébastien; Jouguet, Paul; Weedbrook, Christian; Yin, Zhen-Qiang; Wang, Shuang; Chen, Wei; Guo, Guang-Can; Han, Zheng-Fu

    2014-03-01

    Imperfect devices in commercial quantum key distribution systems open security loopholes that an eavesdropper may exploit. An example of one such imperfection is the wavelength-dependent coupling ratio of the fiber beam splitter. Utilizing this loophole, the eavesdropper can vary the transmittances of the fiber beam splitter at the receiver's side by inserting lights with wavelengths different from what is normally used. Here, we propose a wavelength attack on a practical continuous-variable quantum key distribution system using homodyne detection. By inserting light pulses at different wavelengths, this attack allows the eavesdropper to bias the shot-noise estimation even if it is done in real time. Based on experimental data, we discuss the feasibility of this attack and suggest a prevention scheme by improving the previously proposed countermeasures.

  16. Quantum key distribution with multi letter alphabets

    NASA Astrophysics Data System (ADS)

    Sych, D.; Leuchs, G.

    2010-03-01

    We present a new protocol for continuous variable quantum key distribution (CV QKD). The novelty of the protocol is a multi letter alphabet represented by coherent states of light with a fixed amplitude and variable phase. Information is encoded in the phase of a coherent state which can be chosen from a regular discrete set consisting, however, of an arbitrary number of letters. We evaluate the security of the protocol against the beam splitting attack. As a result we show the proposed protocol has advantages over the standard two letter coherent state QKD protocol, especially in the case when losses in the communication channel are low.

  17. Semiquantum key distribution with secure delegated quantum computation.

    PubMed

    Li, Qin; Chan, Wai Hong; Zhang, Shengyu

    2016-01-27

    Semiquantum key distribution allows a quantum party to share a random key with a "classical" party who only can prepare and measure qubits in the computational basis or reorder some qubits when he has access to a quantum channel. In this work, we present a protocol where a secret key can be established between a quantum user and an almost classical user who only needs the quantum ability to access quantum channels, by securely delegating quantum computation to a quantum server. We show the proposed protocol is robust even when the delegated quantum server is a powerful adversary, and is experimentally feasible with current technology. As one party of our protocol is the most quantum-resource efficient, it can be more practical and significantly widen the applicability scope of quantum key distribution.

  18. Semiquantum key distribution with secure delegated quantum computation

    PubMed Central

    Li, Qin; Chan, Wai Hong; Zhang, Shengyu

    2016-01-01

    Semiquantum key distribution allows a quantum party to share a random key with a “classical” party who only can prepare and measure qubits in the computational basis or reorder some qubits when he has access to a quantum channel. In this work, we present a protocol where a secret key can be established between a quantum user and an almost classical user who only needs the quantum ability to access quantum channels, by securely delegating quantum computation to a quantum server. We show the proposed protocol is robust even when the delegated quantum server is a powerful adversary, and is experimentally feasible with current technology. As one party of our protocol is the most quantum-resource efficient, it can be more practical and significantly widen the applicability scope of quantum key distribution. PMID:26813384

  19. Detector-device-independent quantum key distribution

    SciTech Connect

    Lim, Charles Ci Wen; Korzh, Boris; Martin, Anthony; Bussières, Félix; Thew, Rob; Zbinden, Hugo

    2014-12-01

    Recently, a quantum key distribution (QKD) scheme based on entanglement swapping, called measurement-device-independent QKD (mdiQKD), was proposed to bypass all measurement side-channel attacks. While mdiQKD is conceptually elegant and offers a supreme level of security, the experimental complexity is challenging for practical systems. For instance, it requires interference between two widely separated independent single-photon sources, and the secret key rates are dependent on detecting two photons—one from each source. Here, we demonstrate a proof-of-principle experiment of a QKD scheme that removes the need for a two-photon system and instead uses the idea of a two-qubit single-photon to significantly simplify the implementation and improve the efficiency of mdiQKD in several aspects.

  20. Completely device-independent quantum key distribution

    NASA Astrophysics Data System (ADS)

    Aguilar, Edgar A.; Ramanathan, Ravishankar; Kofler, Johannes; Pawłowski, Marcin

    2016-08-01

    Quantum key distribution (QKD) is a provably secure way for two distant parties to establish a common secret key, which then can be used in a classical cryptographic scheme. Using quantum entanglement, one can reduce the necessary assumptions that the parties have to make about their devices, giving rise to device-independent QKD (DIQKD). However, in all existing protocols to date the parties need to have an initial (at least partially) random seed as a resource. In this work, we show that this requirement can be dropped. Using recent advances in the fields of randomness amplification and randomness expansion, we demonstrate that it is sufficient for the message the parties want to communicate to be (partially) unknown to the adversaries—an assumption without which any type of cryptography would be pointless to begin with. One party can use her secret message to locally generate a secret sequence of bits, which can then be openly used by herself and the other party in a DIQKD protocol. Hence our work reduces the requirements needed to perform secure DIQKD and establish safe communication.

  1. Structural Counterfactuals: A Brief Introduction

    ERIC Educational Resources Information Center

    Pearl, Judea

    2013-01-01

    Recent advances in causal reasoning have given rise to a computational model that emulates the process by which humans generate, evaluate, and distinguish counterfactual sentences. Contrasted with the "possible worlds" account of counterfactuals, this "structural" model enjoys the advantages of representational economy,…

  2. Quantum state regeneration in entanglement based quantum key distribution protocols

    NASA Astrophysics Data System (ADS)

    Erdmann, Reinhard

    2014-05-01

    Quantum Key Distribution (QKD) has been shown to be provably secure when certain idealized conditions are met in a physical realization. All implementations of QKD to date require non-orthogonal basis measurements to implement it; making it commonly assumed that measurement basis variation is fundamental to making QKD protocols secure from eavesdropping. We show here that in particular physical conditions this assumption is incorrect, and that provable security can be achieved without use of multiple bases. Basis setting information can in fact be shared with all potential eavesdroppers, as they are unable to use it to acquire or influence any part of the encryption key generation. Furthermore the key generation efficiency is limited to 100 % as compared with an inherent 50 % limit for alternating bases in BB84 or Entangled Ekert protocols.

  3. Controlled order rearrangement encryption for quantum key distribution

    SciTech Connect

    Deng Fuguo; Long, G.L.

    2003-10-01

    A technique is devised to perform orthogonal state quantum key distribution. In this scheme, entangled parts of a quantum information carrier are sent from Alice to Bob through two quantum channels. However, before the transmission, the order of the quantum information carrier in one channel is reordered so that Eve cannot steal useful information. At the receiver's end, the order of the quantum information carrier is restored. The order rearrangement operation in both parties is controlled by a prior shared control key which is used repeatedly in a quantum key distribution session.

  4. Seaworthy Quantum Key Distribution Design and Validation (SEAKEY)

    DTIC Science & Technology

    2014-07-25

    Address: 10 Moulton Street, Cambridge, MA 02138 Title of the Project: Seaworthy Quantum Key Distribution Design and Validation (SEAKEY...Technologies Kathryn Carson Program Manager Quantum Information Processing Report Documentation Page Form ApprovedOMB No. 0704-0188 Public...2016 4. TITLE AND SUBTITLE Seaworthy Quantum Key Distribution Design and Validation (SEAKEY) 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM

  5. Counterfactual Volcano Hazard Analysis

    NASA Astrophysics Data System (ADS)

    Woo, Gordon

    2013-04-01

    The historical database of past disasters is a cornerstone of catastrophe risk assessment. Whereas disasters are fortunately comparatively rare, near-misses are quite common for both natural and man-made hazards. The word disaster originally means 'an unfavourable aspect of a star'. Except for astrologists, disasters are no longer perceived fatalistically as pre-determined. Nevertheless, to this day, historical disasters are treated statistically as fixed events, although in reality there is a large luck element involved in converting a near-miss crisis situation into a disaster statistic. It is possible to conceive a stochastic simulation of the past to explore the implications of this chance factor. Counterfactual history is the exercise of hypothesizing alternative paths of history from what actually happened. Exploring history from a counterfactual perspective is instructive for a variety of reasons. First, it is easy to be fooled by randomness and see regularity in event patterns which are illusory. The past is just one realization of a variety of possible evolutions of history, which may be analyzed through a stochastic simulation of an array of counterfactual scenarios. In any hazard context, there is a random component equivalent to dice being rolled to decide whether a near-miss becomes an actual disaster. The fact that there may be no observed disaster over a period of time may belie the occurrence of numerous near-misses. This may be illustrated using the simple dice paradigm. Suppose a dice is rolled every month for a year, and an event is recorded if a six is thrown. There is still an 11% chance of no events occurring during the year. A variety of perils may be used to illustrate the use of near-miss information within a counterfactual disaster analysis. In the domain of natural hazards, near-misses are a notable feature of the threat landscape. Storm surges are an obvious example. Sea defences may protect against most meteorological scenarios. However

  6. Quantum key distribution: vulnerable if imperfectly implemented

    NASA Astrophysics Data System (ADS)

    Leuchs, G.

    2013-10-01

    We report several vulnerabilities found in Clavis2, the flagship quantum key distribution (QKD) system from ID Quantique. We show the hacking of a calibration sequence run by Clavis2 to synchronize the Alice and Bob devices before performing the secret key exchange. This hack induces a temporal detection efficiency mismatch in Bob that can allow Eve to break the security of the cryptosystem using faked states. We also experimentally investigate the superlinear behaviour in the single-photon detectors (SPDs) used by Bob. Due to this superlinearity, the SPDs feature an actual multi-photon detection probability which is generally higher than the theoretically-modelled value. We show how this increases the risk of detector control attacks on QKD systems (including Clavis2) employing such SPDs. Finally, we review the experimental feasibility of Trojan-horse attacks. In the case of Clavis2, the objective is to read Bob's phase modulator to acquire knowledge of his basis choice as this information suffices for constructing the raw key in the Scarani-Acin-Ribordy-Gisin 2004 (SARG04) protocol. We work in close collaboration with ID Quantique and for all these loopholes, we notified them in advance. Wherever possible, we or ID Quantique proposed countermeasures and they implemented suitable patches and upgrade their systems.

  7. Chip-based quantum key distribution

    PubMed Central

    Sibson, P.; Erven, C.; Godfrey, M.; Miki, S.; Yamashita, T.; Fujiwara, M.; Sasaki, M.; Terai, H.; Tanner, M. G.; Natarajan, C. M.; Hadfield, R. H.; O'Brien, J. L.; Thompson, M. G.

    2017-01-01

    Improvement in secure transmission of information is an urgent need for governments, corporations and individuals. Quantum key distribution (QKD) promises security based on the laws of physics and has rapidly grown from proof-of-concept to robust demonstrations and deployment of commercial systems. Despite these advances, QKD has not been widely adopted, and large-scale deployment will likely require chip-based devices for improved performance, miniaturization and enhanced functionality. Here we report low error rate, GHz clocked QKD operation of an indium phosphide transmitter chip and a silicon oxynitride receiver chip—monolithically integrated devices using components and manufacturing processes from the telecommunications industry. We use the reconfigurability of these devices to demonstrate three prominent QKD protocols—BB84, Coherent One Way and Differential Phase Shift—with performance comparable to state-of-the-art. These devices, when combined with integrated single photon detectors, pave the way for successfully integrating QKD into future telecommunications networks. PMID:28181489

  8. Chip-based quantum key distribution.

    PubMed

    Sibson, P; Erven, C; Godfrey, M; Miki, S; Yamashita, T; Fujiwara, M; Sasaki, M; Terai, H; Tanner, M G; Natarajan, C M; Hadfield, R H; O'Brien, J L; Thompson, M G

    2017-02-09

    Improvement in secure transmission of information is an urgent need for governments, corporations and individuals. Quantum key distribution (QKD) promises security based on the laws of physics and has rapidly grown from proof-of-concept to robust demonstrations and deployment of commercial systems. Despite these advances, QKD has not been widely adopted, and large-scale deployment will likely require chip-based devices for improved performance, miniaturization and enhanced functionality. Here we report low error rate, GHz clocked QKD operation of an indium phosphide transmitter chip and a silicon oxynitride receiver chip-monolithically integrated devices using components and manufacturing processes from the telecommunications industry. We use the reconfigurability of these devices to demonstrate three prominent QKD protocols-BB84, Coherent One Way and Differential Phase Shift-with performance comparable to state-of-the-art. These devices, when combined with integrated single photon detectors, pave the way for successfully integrating QKD into future telecommunications networks.

  9. Chip-based quantum key distribution

    NASA Astrophysics Data System (ADS)

    Sibson, P.; Erven, C.; Godfrey, M.; Miki, S.; Yamashita, T.; Fujiwara, M.; Sasaki, M.; Terai, H.; Tanner, M. G.; Natarajan, C. M.; Hadfield, R. H.; O'Brien, J. L.; Thompson, M. G.

    2017-02-01

    Improvement in secure transmission of information is an urgent need for governments, corporations and individuals. Quantum key distribution (QKD) promises security based on the laws of physics and has rapidly grown from proof-of-concept to robust demonstrations and deployment of commercial systems. Despite these advances, QKD has not been widely adopted, and large-scale deployment will likely require chip-based devices for improved performance, miniaturization and enhanced functionality. Here we report low error rate, GHz clocked QKD operation of an indium phosphide transmitter chip and a silicon oxynitride receiver chip--monolithically integrated devices using components and manufacturing processes from the telecommunications industry. We use the reconfigurability of these devices to demonstrate three prominent QKD protocols--BB84, Coherent One Way and Differential Phase Shift--with performance comparable to state-of-the-art. These devices, when combined with integrated single photon detectors, pave the way for successfully integrating QKD into future telecommunications networks.

  10. Seaworthy Quantum Key Distribution Design and Validation (SEAKEY)

    DTIC Science & Technology

    2016-03-10

    Contractor Address: 10 Moulton Street, Cambridge, MA 02138 Title of the Project: Seaworthy Quantum Key Distribution Design and Validation (SEAKEY...Technologies Kathryn Carson Program Manager Quantum Information Processing 2 | P a g e Approved for public release; distribution is

  11. Quantum hacking: attacking practical quantum key distribution systems

    NASA Astrophysics Data System (ADS)

    Qi, Bing; Fung, Chi-Hang Fred; Zhao, Yi; Ma, Xiongfeng; Tamaki, Kiyoshi; Chen, Christine; Lo, Hoi-Kwong

    2007-09-01

    Quantum key distribution (QKD) can, in principle, provide unconditional security based on the fundamental laws of physics. Unfortunately, a practical QKD system may contain overlooked imperfections and violate some of the assumptions in a security proof. Here, we report two types of eavesdropping attacks against a practical QKD system. The first one is "time-shift" attack, which is applicable to QKD systems with gated single photon detectors (SPDs). In this attack, the eavesdropper, Eve, exploits the time mismatch between the open windows of the two SPDs. She can acquire a significant amount of information on the final key by simply shifting the quantum signals forwards or backwards in time domain. Our experimental results in [9] with a commercial QKD system demonstrate that, under this attack, the original QKD system is breakable. This is the first experimental demonstration of a feasible attack against a commercial QKD system. This is a surprising result. The second one is "phase-remapping" attack [10]. Here, Eve exploits the fact that a practical phase modulator has a finite response time. In principle, Eve could change the encoded phase value by time-shifting the signal pulse relative to the reference pulse.

  12. Security proof for quantum key distribution using qudit systems

    SciTech Connect

    Sheridan, Lana; Scarani, Valerio

    2010-09-15

    We provide security bounds against coherent attacks for two families of quantum key distribution protocols that use d-dimensional quantum systems. In the asymptotic regime, both the secret key rate for fixed noise and the robustness to noise increase with d. The finite key corrections are found to be almost insensitive to d < or approx. 20.

  13. SeaQuaKE: Sea-optimized Quantum Key Exchange

    DTIC Science & Technology

    2014-11-01

    SeaQuaKE: Sea-optimized Quantum Key Exchange Technical Progress Report No. 3 Prepared for: Office...From - To) September 2014  November 2014 4. TITLE AND SUBTITLE SeaQuaKE: Sea-optimized Quantum Key Exchange Technical Progress Report No. 1...ONRBAA13-001 14. ABSTRACT This is the 3rd quarterly Technical Progress Report summarizing progress on the Sea-optimized Quantum Key Exchange (SeaQuaKE

  14. Performance of device-independent quantum key distribution

    NASA Astrophysics Data System (ADS)

    Cao, Zhu; Zhao, Qi; Ma, Xiongfeng

    2016-07-01

    Quantum key distribution provides information-theoretically-secure communication. In practice, device imperfections may jeopardise the system security. Device-independent quantum key distribution solves this problem by providing secure keys even when the quantum devices are untrusted and uncharacterized. Following a recent security proof of the device-independent quantum key distribution, we improve the key rate by tightening the parameter choice in the security proof. In practice where the system is lossy, we further improve the key rate by taking into account the loss position information. From our numerical simulation, our method can outperform existing results. Meanwhile, we outline clear experimental requirements for implementing device-independent quantum key distribution. The maximal tolerable error rate is 1.6%, the minimal required transmittance is 97.3%, and the minimal required visibility is 96.8 % .

  15. A Contextuality Based Quantum Key Distribution Protocol

    NASA Astrophysics Data System (ADS)

    Troupe, James

    In 2005 Spekkens presented a generalization of noncontextuality that applies to imperfect measurements (POVMs) by allowing the underlying hidden variable model to be indeterministic. In addition, unlike traditional Bell-Kochen-Specker noncontextuality, HV models of a single qubit were shown to be contextual under this definition. Thus, not all single qubit POVM measurement outcomes can be modeled classically. Recently M. Pusey showed that, under certain conditions, exhibiting an anomalous weak value (i.e. values outside the eigenspectrum of the observable) implies contextuality. We will present a new single qubit prepare and measure QKD protocol that uses observation of anomalous weak values of particular observables to estimate the quantum channel error rate and certify the security of the channel. We also argue that it is the ``degree'' of contextuality of the noisy qubits exiting the channel that fundamentally determine the secure key rate. A benefit of this approach is that the security does not depend on the fair sampling assumption, and so is not compromised by Eve controlling Bob's measurement devices. Thus, it retains much of the benefit of ``Measurement Device Independent'' QKD protocols while only using single photon preparations and measurements. Supported by the Office of Naval Research under Grant N00014-15-1-2225.

  16. A complete classification of quantum public-key encryption protocols

    NASA Astrophysics Data System (ADS)

    Wu, Chenmiao; Yang, Li

    2015-10-01

    We present a classification of quantum public-key encryption protocols. There are six elements in quantum public-key encryption: plaintext, ciphertext, public-key, private-key, encryption algorithm and decryption algorithm. According to the property of each element which is either quantum or classical, the quantum public-key encryption protocols can be divided into 64 kinds. Among 64 kinds of protocols, 8 kinds have already been constructed, 52 kinds can be proved to be impossible to construct and the remaining 4 kinds have not been presented effectively yet. This indicates that the research on quantum public-key encryption protocol should be focus on the existed kinds and the unproposed kinds.

  17. A System-Level Throughput Model for Quantum Key Distribution

    DTIC Science & Technology

    2015-09-17

    xv Dictionary QKD = Quantum Key Distribution OTP = One-Time Pad cryptographic algorithm DES = Data Encryption Standard 3DES... quantum transmission, classical transmission, algorithmic complexity and execution, various information theory techniques, and performance of specific...research into quantum computers has posed a threat to security by means of mathematical complexity. In fact, an algorithm has already been written for

  18. A public-key cryptosystem for quantum message transmission

    NASA Astrophysics Data System (ADS)

    Yang, Li

    2005-01-01

    We present a quantum public-key cryptography protocol for quantum message transmission. The private key of this protocol includes three classical matrices: a generator matrix of a Goppa code, an invertible matrix and a permutation matrix. The public key is product of these three matrices. The encryption and decryption algorithms are merely quantum computations related with the transformations between bases of the quantum registers. The security of this protocol is based on the hypothesis that there is no effective algorithm of NP-complete problem.

  19. Seaworthy Quantum Key Distribution Design and Validation (SEAKEY)

    DTIC Science & Technology

    2015-08-07

    Contractor Address: 10 Moulton Street, Cambridge, MA 02138 Title of the Project: Seaworthy Quantum Key Distribution Design and Validation (SEAKEY...BBN Technologies Kathryn Carson Program Manager Quantum Information Processing Report Documentation Page Form ApprovedOMB No. 0704-0188...00-00-2015 4. TITLE AND SUBTITLE Seaworthy Quantum Key Distribution Design and Validation (SEAKEY) 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c

  20. Seaworthy Quantum Key Distribution Design and Validation (SEAKEY)

    DTIC Science & Technology

    2015-11-12

    Contractor Address: 10 Moulton Street, Cambridge, MA 02138 Title of the Project: Seaworthy Quantum Key Distribution Design and Validation (SEAKEY...Technologies Kathryn Carson Program Manager Quantum Information Processing Report Documentation Page Form ApprovedOMB No. 0704-0188 Public...Seaworthy Quantum Key Distribution Design and Validation (SEAKEY) 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S

  1. Experimental demonstration of subcarrier multiplexed quantum key distribution system.

    PubMed

    Mora, José; Ruiz-Alba, Antonio; Amaya, Waldimar; Martínez, Alfonso; García-Muñoz, Víctor; Calvo, David; Capmany, José

    2012-06-01

    We provide, to our knowledge, the first experimental demonstration of the feasibility of sending several parallel keys by exploiting the technique of subcarrier multiplexing (SCM) widely employed in microwave photonics. This approach brings several advantages such as high spectral efficiency compatible with the actual secure key rates, the sharing of the optical fainted pulse by all the quantum multiplexed channels reducing the system complexity, and the possibility of upgrading with wavelength division multiplexing in a two-tier scheme, to increase the number of parallel keys. Two independent quantum SCM channels featuring a sifted key rate of 10 Kb/s/channel over a link with quantum bit error rate <2% is reported.

  2. The classification of quantum symmetric-key encryption protocols

    NASA Astrophysics Data System (ADS)

    Xiang, Chong; Yang, Li; Peng, Yong; Chen, Dongqing

    2014-11-01

    The classification of quantum symmetric-key encryption protocol is presented. According to five elements of a quantum symmetric-key encryption protocol: plaintext, ciphertext, key, encryption algorithm and decryption algorithm, there are 32 different kinds of them. Among them, 5 kinds of protocols have already been constructed and studied, and 21 kinds of them are proved to be impossible to construct, the last 6 kinds of them are not yet presented effectively. That means the research on quantum symmetric-key encryption protocol only needs to consider with 5 kinds of them nowadays.

  3. Quantum key distribution with an entangled light emitting diode

    SciTech Connect

    Dzurnak, B.; Stevenson, R. M.; Nilsson, J.; Dynes, J. F.; Yuan, Z. L.; Skiba-Szymanska, J.; Shields, A. J.; Farrer, I.; Ritchie, D. A.

    2015-12-28

    Measurements performed on entangled photon pairs shared between two parties can allow unique quantum cryptographic keys to be formed, creating secure links between users. An advantage of using such entangled photon links is that they can be adapted to propagate entanglement to end users of quantum networks with only untrusted nodes. However, demonstrations of quantum key distribution with entangled photons have so far relied on sources optically excited with lasers. Here, we realize a quantum cryptography system based on an electrically driven entangled-light-emitting diode. Measurement bases are passively chosen and we show formation of an error-free quantum key. Our measurements also simultaneously reveal Bell's parameter for the detected light, which exceeds the threshold for quantum entanglement.

  4. Discourse Updating after Reading a Counterfactual Event

    ERIC Educational Resources Information Center

    de Vega, Manuel; Urrutia, Mabel

    2012-01-01

    This paper explores the temporal course of discourse updating after reading counterfactual events. To test the accessibility to discourse information, readers were asked to identify probes related to initial events in the text, previous to the counterfactual, or probes related to the critical counterfactual events. Experiment 1 showed that 500 ms…

  5. Counterfactual Reasoning: From Childhood to Adulthood

    ERIC Educational Resources Information Center

    Rafetseder, Eva; Schwitalla, Maria; Perner, Josef

    2013-01-01

    The objective of this study was to describe the developmental progression of counterfactual reasoning from childhood to adulthood. In contrast to the traditional view, it was recently reported by Rafetseder and colleagues that even a majority of 6-year-old children do not engage in counterfactual reasoning when asked counterfactual questions…

  6. One Step Quantum Key Distribution Based on EPR Entanglement

    PubMed Central

    Li, Jian; Li, Na; Li, Lei-Lei; Wang, Tao

    2016-01-01

    A novel quantum key distribution protocol is presented, based on entanglement and dense coding and allowing asymptotically secure key distribution. Considering the storage time limit of quantum bits, a grouping quantum key distribution protocol is proposed, which overcomes the vulnerability of first protocol and improves the maneuverability. Moreover, a security analysis is given and a simple type of eavesdropper’s attack would introduce at least an error rate of 46.875%. Compared with the “Ping-pong” protocol involving two steps, the proposed protocol does not need to store the qubit and only involves one step. PMID:27357865

  7. Quantum circuit for optimal eavesdropping in quantum key distribution using phase-time coding

    SciTech Connect

    Kronberg, D. A.; Molotkov, S. N.

    2010-07-15

    A quantum circuit is constructed for optimal eavesdropping on quantum key distribution proto- cols using phase-time coding, and its physical implementation based on linear and nonlinear fiber-optic components is proposed.

  8. Authenticated multi-user quantum key distribution with single particles

    NASA Astrophysics Data System (ADS)

    Lin, Song; Wang, Hui; Guo, Gong-De; Ye, Guo-Hua; Du, Hong-Zhen; Liu, Xiao-Fen

    2016-03-01

    Quantum key distribution (QKD) has been growing rapidly in recent years and becomes one of the hottest issues in quantum information science. During the implementation of QKD on a network, identity authentication has been one main problem. In this paper, an efficient authenticated multi-user quantum key distribution (MQKD) protocol with single particles is proposed. In this protocol, any two users on a quantum network can perform mutual authentication and share a secure session key with the assistance of a semi-honest center. Meanwhile, the particles, which are used as quantum information carriers, are not required to be stored, therefore the proposed protocol is feasible with current technology. Finally, security analysis shows that this protocol is secure in theory.

  9. Quantum Key Distribution Using Polarized Single Photons

    DTIC Science & Technology

    2009-04-01

    Cu-O high-temperature superconducting materials, and ferromagnet /superconductor nano-bilayer structures. 15. SUBJECT TERMS Quantum communications...based on high-temperature superconducting materials and ferromagnet /superconductor NiCu/Nb nano-bilayer structures. Time- resolved photoresponse...NOTES none 20090724231 14. ABSTRACT Exhaustive research, development, and testing studies were performed on novel superconducting single-photon

  10. On the complexity of search for keys in quantum cryptography

    NASA Astrophysics Data System (ADS)

    Molotkov, S. N.

    2016-03-01

    The trace distance is used as a security criterion in proofs of security of keys in quantum cryptography. Some authors doubted that this criterion can be reduced to criteria used in classical cryptography. The following question has been answered in this work. Let a quantum cryptography system provide an ɛ-secure key such that ½‖ρ XE - ρ U ⊗ ρ E ‖1 < ɛ, which will be repeatedly used in classical encryption algorithms. To what extent does the ɛ-secure key reduce the number of search steps (guesswork) as compared to the use of ideal keys? A direct relation has been demonstrated between the complexity of the complete consideration of keys, which is one of the main security criteria in classical systems, and the trace distance used in quantum cryptography. Bounds for the minimum and maximum numbers of search steps for the determination of the actual key have been presented.

  11. Photon nonlinear mixing in subcarrier multiplexed quantum key distribution systems.

    PubMed

    Capmany, José

    2009-04-13

    We provide, for the first time to our knowledge, an analysis of the influence of nonlinear photon mixing on the end to end quantum bit error rate (QBER) performance of subcarrier multiplexed quantum key distribution systems. The results show that negligible impact is to be expected for modulation indexes in the range of 2%.

  12. Fundamental rate-loss tradeoff for optical quantum key distribution

    NASA Astrophysics Data System (ADS)

    Takeoka, Masahiro; Guha, Saikat; Wilde, Mark M.

    2014-10-01

    Since 1984, various optical quantum key distribution (QKD) protocols have been proposed and examined. In all of them, the rate of secret key generation decays exponentially with distance. A natural and fundamental question is then whether there are yet-to-be discovered optical QKD protocols (without quantum repeaters) that could circumvent this rate-distance tradeoff. This paper provides a major step towards answering this question. Here we show that the secret key agreement capacity of a lossy and noisy optical channel assisted by unlimited two-way public classical communication is limited by an upper bound that is solely a function of the channel loss, regardless of how much optical power the protocol may use. Our result has major implications for understanding the secret key agreement capacity of optical channels—a long-standing open problem in optical quantum information theory—and strongly suggests a real need for quantum repeaters to perform QKD at high rates over long distances.

  13. Attacks on fixed-apparatus quantum-key-distribution schemes

    NASA Astrophysics Data System (ADS)

    Boyer, Michel; Gelles, Ran; Mor, Tal

    2014-07-01

    We consider quantum-key-distribution implementations in which the receiver's apparatus is fixed and does not depend on his choice of basis at each qubit transmission. We show that, although theoretical quantum key distribution is proven secure, such implementations are totally insecure against a strong eavesdropper that has one-time (single) access to the receiver's equipment. The attack we present here, the "fixed-apparatus attack," causes a potential risk to the usefulness of several recent implementations.

  14. Practical issues in quantum-key-distribution postprocessing

    SciTech Connect

    Fung, C.-H. Fred; Chau, H. F.; Ma Xiongfeng

    2010-01-15

    Quantum key distribution (QKD) is a secure key generation method between two distant parties by wisely exploiting properties of quantum mechanics. In QKD, experimental measurement outcomes on quantum states are transformed by the two parties to a secret key. This transformation is composed of many logical steps (as guided by security proofs), which together will ultimately determine the length of the final secret key and its security. We detail the procedure for performing such classical postprocessing taking into account practical concerns (including the finite-size effect and authentication and encryption for classical communications). This procedure is directly applicable to realistic QKD experiments and thus serves as a recipe that specifies what postprocessing operations are needed and what the security level is for certain lengths of the keys. Our result is applicable to the BB84 protocol with a single or entangled photon source.

  15. Quantum Transmemetic Intelligence

    NASA Astrophysics Data System (ADS)

    Piotrowski, Edward W.; Sładkowski, Jan

    The following sections are included: * Introduction * A Quantum Model of Free Will * Quantum Acquisition of Knowledge * Thinking as a Quantum Algorithm * Counterfactual Measurement as a Model of Intuition * Quantum Modification of Freud's Model of Consciousness * Conclusion * Acknowledgements * References

  16. Semiquantum-key distribution using less than four quantum states

    SciTech Connect

    Zou Xiangfu; Qiu Daowen; Li Lvzhou; Wu Lihua; Li Lvjun

    2009-05-15

    Recently Boyer et al. [Phys. Rev. Lett. 99, 140501 (2007)] suggested the idea of semiquantum key distribution (SQKD) in which Bob is classical and they also proposed a semiquantum key distribution protocol (BKM2007). To discuss the security of the BKM2007 protocol, they proved that their protocol is completely robust. This means that nonzero information acquired by Eve on the information string implies the nonzero probability that the legitimate participants can find errors on the bits tested by this protocol. The BKM2007 protocol uses four quantum states to distribute a secret key. In this paper, we simplify their protocol by using less than four quantum states. In detail, we present five different SQKD protocols in which Alice sends three quantum states, two quantum states, and one quantum state, respectively. Also, we prove that all the five protocols are completely robust. In particular, we invent two completely robust SQKD protocols in which Alice sends only one quantum state. Alice uses a register in one SQKD protocol, but she does not use any register in the other. The information bit proportion of the SQKD protocol in which Alice sends only one quantum state but uses a register is the double as that in the BKM2007 protocol. Furthermore, the information bit rate of the SQKD protocol in which Alice sends only one quantum state and does not use any register is not lower than that of the BKM2007 protocol.

  17. Security of two-way quantum key distribution

    NASA Astrophysics Data System (ADS)

    Beaudry, Normand J.; Lucamarini, Marco; Mancini, Stefano; Renner, Renato

    2013-12-01

    Quantum key distribution protocols typically make use of a one-way quantum channel to distribute a shared secret string to two distant users. However, protocols exploiting a two-way quantum channel have been proposed as an alternative route to the same goal, with the potential advantage of outperforming one-way protocols. Here we provide a strategy to prove security for two-way quantum key distribution protocols against the most general quantum attack possible by an eavesdropper. We utilize an entropic uncertainty relation, and only a few assumptions need to be made about the devices used in the protocol. We also show that a two-way protocol can outperform comparable one-way protocols.

  18. Quantum key distribution session with 16-dimensional photonic states

    PubMed Central

    Etcheverry, S.; Cañas, G.; Gómez, E. S.; Nogueira, W. A. T.; Saavedra, C.; Xavier, G. B.; Lima, G.

    2013-01-01

    The secure transfer of information is an important problem in modern telecommunications. Quantum key distribution (QKD) provides a solution to this problem by using individual quantum systems to generate correlated bits between remote parties, that can be used to extract a secret key. QKD with D-dimensional quantum channels provides security advantages that grow with increasing D. However, the vast majority of QKD implementations has been restricted to two dimensions. Here we demonstrate the feasibility of using higher dimensions for real-world quantum cryptography by performing, for the first time, a fully automated QKD session based on the BB84 protocol with 16-dimensional quantum states. Information is encoded in the single-photon transverse momentum and the required states are dynamically generated with programmable spatial light modulators. Our setup paves the way for future developments in the field of experimental high-dimensional QKD. PMID:23897033

  19. Implementing Diffie-Hellman key exchange using quantum EPR pairs

    NASA Astrophysics Data System (ADS)

    Mandal, Sayonnha; Parakh, Abhishek

    2015-05-01

    This paper implements the concepts of perfect forward secrecy and the Diffie-Hellman key exchange using EPR pairs to establish and share a secret key between two non-authenticated parties and transfer messages between them without the risk of compromise. Current implementations of quantum cryptography are based on the BB84 protocol, which is susceptible to siphoning attacks on the multiple photons emitted by practical laser sources. This makes BB84-based quantum cryptography protocol unsuitable for network computing environments. Diffie-Hellman does not require the two parties to be mutually authenticated to each other, yet it can provide a basis for a number of authenticated protocols, most notably the concept of perfect forward secrecy. The work proposed in this paper provides a new direction in utilizing quantum EPR pairs in quantum key exchange. Although, classical cryptography boasts of efficient and robust protocols like the Diffie-Hellman key exchange, in the current times, with the advent of quantum computing they are very much vulnerable to eavesdropping and cryptanalytic attacks. Using quantum cryptographic principles, however, these classical encryption algorithms show more promise and a more robust and secure structure for applications. The unique properties of quantum EPR pairs also, on the other hand, go a long way in removing attacks like eavesdropping by their inherent nature of one particle of the pair losing its state if a measurement occurs on the other. The concept of perfect forward secrecy is revisited in this paper to attribute tighter security to the proposed protocol.

  20. Structural Counterfactuals: A Brief Introduction

    DTIC Science & Technology

    2013-06-01

    the enigma of consensus: “What mental representation permits such consensus to emerge from the little knowledge we have about Oswald, Kennedy and 1960’s...parsimoniously in the mind, and hence that it must be highly structured. The theory of structural counterfactuals offers a solution to the consensus enigma . It

  1. Randomness determines practical security of BB84 quantum key distribution

    NASA Astrophysics Data System (ADS)

    Li, Hong-Wei; Yin, Zhen-Qiang; Wang, Shuang; Qian, Yong-Jun; Chen, Wei; Guo, Guang-Can; Han, Zheng-Fu

    2015-11-01

    Unconditional security of the BB84 quantum key distribution protocol has been proved by exploiting the fundamental laws of quantum mechanics, but the practical quantum key distribution system maybe hacked by considering the imperfect state preparation and measurement respectively. Until now, different attacking schemes have been proposed by utilizing imperfect devices, but the general security analysis model against all of the practical attacking schemes has not been proposed. Here, we demonstrate that the general practical attacking schemes can be divided into the Trojan horse attack, strong randomness attack and weak randomness attack respectively. We prove security of BB84 protocol under randomness attacking models, and these results can be applied to guarantee the security of the practical quantum key distribution system.

  2. Randomness determines practical security of BB84 quantum key distribution.

    PubMed

    Li, Hong-Wei; Yin, Zhen-Qiang; Wang, Shuang; Qian, Yong-Jun; Chen, Wei; Guo, Guang-Can; Han, Zheng-Fu

    2015-11-10

    Unconditional security of the BB84 quantum key distribution protocol has been proved by exploiting the fundamental laws of quantum mechanics, but the practical quantum key distribution system maybe hacked by considering the imperfect state preparation and measurement respectively. Until now, different attacking schemes have been proposed by utilizing imperfect devices, but the general security analysis model against all of the practical attacking schemes has not been proposed. Here, we demonstrate that the general practical attacking schemes can be divided into the Trojan horse attack, strong randomness attack and weak randomness attack respectively. We prove security of BB84 protocol under randomness attacking models, and these results can be applied to guarantee the security of the practical quantum key distribution system.

  3. Randomness determines practical security of BB84 quantum key distribution

    PubMed Central

    Li, Hong-Wei; Yin, Zhen-Qiang; Wang, Shuang; Qian, Yong-Jun; Chen, Wei; Guo, Guang-Can; Han, Zheng-Fu

    2015-01-01

    Unconditional security of the BB84 quantum key distribution protocol has been proved by exploiting the fundamental laws of quantum mechanics, but the practical quantum key distribution system maybe hacked by considering the imperfect state preparation and measurement respectively. Until now, different attacking schemes have been proposed by utilizing imperfect devices, but the general security analysis model against all of the practical attacking schemes has not been proposed. Here, we demonstrate that the general practical attacking schemes can be divided into the Trojan horse attack, strong randomness attack and weak randomness attack respectively. We prove security of BB84 protocol under randomness attacking models, and these results can be applied to guarantee the security of the practical quantum key distribution system. PMID:26552359

  4. Multi-party Quantum Key Agreement without Entanglement

    NASA Astrophysics Data System (ADS)

    Cai, Bin-Bin; Guo, Gong-De; Lin, Song

    2016-12-01

    A new efficient quantum key agreement protocol without entanglement is proposed. In this protocol, each user encodes his secret key into the traveling particles by performing one of four rotation operations that one cannot perfectly distinguish. In the end, all users can simultaneously obtain the final shared key. The security of the presented protocol against some common attacks is discussed. It is shown that this protocol can effectively protect the privacy of each user and satisfy the requirement of fairness in theory. Moreover, the quantum carriers and the encoding operations used in the protocol can be achieved in realistic physical devices. Therefore, the presented protocol is feasible with current technology.

  5. Multi-party Quantum Key Agreement without Entanglement

    NASA Astrophysics Data System (ADS)

    Cai, Bin-Bin; Guo, Gong-De; Lin, Song

    2017-04-01

    A new efficient quantum key agreement protocol without entanglement is proposed. In this protocol, each user encodes his secret key into the traveling particles by performing one of four rotation operations that one cannot perfectly distinguish. In the end, all users can simultaneously obtain the final shared key. The security of the presented protocol against some common attacks is discussed. It is shown that this protocol can effectively protect the privacy of each user and satisfy the requirement of fairness in theory. Moreover, the quantum carriers and the encoding operations used in the protocol can be achieved in realistic physical devices. Therefore, the presented protocol is feasible with current technology.

  6. Counterfactual Reasoning Deficits in Schizophrenia Patients

    PubMed Central

    Castellví, Pere; Caño, Agnès; Benejam, Bessy

    2016-01-01

    Background Counterfactual thinking is a specific type of conditional reasoning that enables the generation of mental simulations of alternatives to past factual events. Although it has been broadly studied in the general population, research on schizophrenia is still scarce. The aim of the current study was to further examine counterfactual reasoning in this illness. Methods Forty schizophrenia patients and 40 controls completed a series of tests that assessed the influence of the “causal order effect” on counterfactual thinking, and the ability to generate counterfactual thoughts and counterfactually derive inferences from a hypothetical situation. Socio-demographic and clinical characteristics, as well as neurocognitive variables, were also examined. Results Compared to controls, the schizophrenia patients generated fewer counterfactual thoughts when faced with a simulated scenario. The pattern of response when assessing the causality effect of the order was also different between the groups, with the patients being more frequently unable to attribute any ordering of events than the control subjects. Additionally, the schizophrenia patients showed more difficulties when deriving normative counterfactual inferences from hypothetical social situations. None of the counterfactual reasoning measures was associated to any of the cognitive functions or clinical and socio-demographic variables assessed. Conclusions A global impairment in counterfactual thinking characterizes schizophrenia patients. Because of the potential impact of such deficits on psychosocial functioning, targeting counterfactual reasoning for improvement might be considered in future treatment approaches. PMID:26828931

  7. Finite-key analysis of a practical decoy-state high-dimensional quantum key distribution

    NASA Astrophysics Data System (ADS)

    Bao, Haize; Bao, Wansu; Wang, Yang; Zhou, Chun; Chen, Ruike

    2016-05-01

    Compared with two-level quantum key distribution (QKD), high-dimensional QKD enables two distant parties to share a secret key at a higher rate. We provide a finite-key security analysis for the recently proposed practical high-dimensional decoy-state QKD protocol based on time-energy entanglement. We employ two methods to estimate the statistical fluctuation of the postselection probability and give a tighter bound on the secure-key capacity. By numerical evaluation, we show the finite-key effect on the secure-key capacity in different conditions. Moreover, our approach could be used to optimize parameters in practical implementations of high-dimensional QKD.

  8. High-capacity quantum Fibonacci coding for key distribution

    NASA Astrophysics Data System (ADS)

    Simon, David S.; Lawrence, Nate; Trevino, Jacob; Dal Negro, Luca; Sergienko, Alexander V.

    2013-03-01

    Quantum cryptography and quantum key distribution (QKD) have been the most successful applications of quantum information processing, highlighting the unique capability of quantum mechanics, through the no-cloning theorem, to securely share encryption keys between two parties. Here, we present an approach to high-capacity, high-efficiency QKD by exploiting cross-disciplinary ideas from quantum information theory and the theory of light scattering of aperiodic photonic media. We propose a unique type of entangled-photon source, as well as a physical mechanism for efficiently sharing keys. The key-sharing protocol combines entanglement with the mathematical properties of a recursive sequence to allow a realization of the physical conditions necessary for implementation of the no-cloning principle for QKD, while the source produces entangled photons whose orbital angular momenta (OAM) are in a superposition of Fibonacci numbers. The source is used to implement a particular physical realization of the protocol by randomly encoding the Fibonacci sequence onto entangled OAM states, allowing secure generation of long keys from few photons. Unlike in polarization-based protocols, reference frame alignment is unnecessary, while the required experimental setup is simpler than other OAM-based protocols capable of achieving the same capacity and its complexity grows less rapidly with increasing range of OAM used.

  9. Comment on the "Quantum Public-Key Cryptosystem"

    NASA Astrophysics Data System (ADS)

    Zhou, Ri-gui; Li, Wei; Huan, Tian-tian

    2015-03-01

    In 2012, Luo et al. proposed a new quantum public-key cryptosystems, which can encrypt both the classical and quantum information. (Luo et al. Int. J. Theor. Phys. 51(3), 912-924, 2012). However, it cannot be realized because there are some mistakes in the calculation and design process. This paper points out these failures and proposes an improvement to avoid the loophole.

  10. Practical quantum key distribution protocol without monitoring signal disturbance

    NASA Astrophysics Data System (ADS)

    Sasaki, Toshihiko; Yamamoto, Yoshihisa; Koashi, Masato

    2014-05-01

    Quantum cryptography exploits the fundamental laws of quantum mechanics to provide a secure way to exchange private information. Such an exchange requires a common random bit sequence, called a key, to be shared secretly between the sender and the receiver. The basic idea behind quantum key distribution (QKD) has widely been understood as the property that any attempt to distinguish encoded quantum states causes a disturbance in the signal. As a result, implementation of a QKD protocol involves an estimation of the experimental parameters influenced by the eavesdropper's intervention, which is achieved by randomly sampling the signal. If the estimation of many parameters with high precision is required, the portion of the signal that is sacrificed increases, thus decreasing the efficiency of the protocol. Here we propose a QKD protocol based on an entirely different principle. The sender encodes a bit sequence onto non-orthogonal quantum states and the receiver randomly dictates how a single bit should be calculated from the sequence. The eavesdropper, who is unable to learn the whole of the sequence, cannot guess the bit value correctly. An achievable rate of secure key distribution is calculated by considering complementary choices between quantum measurements of two conjugate observables. We found that a practical implementation using a laser pulse train achieves a key rate comparable to a decoy-state QKD protocol, an often-used technique for lasers. It also has a better tolerance of bit errors and of finite-sized-key effects. We anticipate that this finding will give new insight into how the probabilistic nature of quantum mechanics can be related to secure communication, and will facilitate the simple and efficient use of conventional lasers for QKD.

  11. Weak randomness seriously limits the security of quantum key distribution

    NASA Astrophysics Data System (ADS)

    Bouda, Jan; Pivoluska, Matej; Plesch, Martin; Wilmott, Colin

    2012-12-01

    In usual security proofs of quantum protocols the adversary (Eve) is expected to have full control over any quantum communication between any communicating parties (Alice and Bob). Eve is also expected to have full access to an authenticated classical channel between Alice and Bob. Unconditional security against any attack by Eve can be proved even in the realistic setting of device and channel imperfection. In this paper we show that the security of quantum key distribution protocols is ruined if one allows Eve to possess a very limited access to the random sources used by Alice. Such knowledge should always be expected in realistic experimental conditions via different side channels.

  12. Experimental realization of equiangular three-state quantum key distribution

    NASA Astrophysics Data System (ADS)

    Schiavon, Matteo; Vallone, Giuseppe; Villoresi, Paolo

    2016-07-01

    Quantum key distribution using three states in equiangular configuration combines a security threshold comparable with the one of the Bennett-Brassard 1984 protocol and a quantum bit error rate (QBER) estimation that does not need to reveal part of the key. We implement an entanglement-based version of the Renes 2004 protocol, using only passive optic elements in a linear scheme for the positive-operator valued measure (POVM), generating an asymptotic secure key rate of more than 10 kbit/s, with a mean QBER of 1.6%. We then demonstrate its security in the case of finite key and evaluate the key rate for both collective and general attacks.

  13. Entanglement-Based Free Space Quantum Key Distribution

    NASA Astrophysics Data System (ADS)

    Weihs, Gregor

    2007-06-01

    Free-space optical communication can complement fiber optics, when the latter are not readily available or when transmitting to or from a satellite is the goal. I will report on our free-space quantum key distribution experiment that links a source to receivers in two different buildings with a distance of about 1.8 km. There is no direct line of sight between the endpoints. Our implementation is a complete quantum key distribution system that includes error correction and privacy amplification. It is based on the distribution of polarization-entangled photon pairs via optical telescopes from the source location on the roof of a campus building to the building of the Institute for Quantum Computing and the Perimeter Institute for Theoretical Physics respectively. In the future, we want to achieve daylight operation capability and use brighter sources of entangled photon pairs to increase the achievable key rates.

  14. Secret key rates for an encoded quantum repeater

    NASA Astrophysics Data System (ADS)

    Bratzik, Sylvia; Kampermann, Hermann; Bruß, Dagmar

    2014-03-01

    We investigate secret key rates for the quantum repeater using encoding [L. Jiang et al., Phys. Rev. A 79, 032325 (2009), 10.1103/PhysRevA.79.032325] and compare them to the standard repeater scheme by Briegel, Dür, Cirac, and Zoller. The former scheme has the advantage of a minimal consumption of classical communication. We analyze the trade-off in the secret key rate between the communication time and the required resources. For this purpose we introduce an error model for the repeater using encoding which allows for input Bell states with a fidelity smaller than one, in contrast to the model given by L. Jiang et al. [Phys. Rev. A 79, 032325 (2009), 10.1103/PhysRevA.79.032325]. We show that one can correct additional errors in the encoded connection procedure of this repeater and develop a suitable decoding algorithm. Furthermore, we derive the rate of producing entangled pairs for the quantum repeater using encoding and give the minimal parameter values (gate quality and initial fidelity) for establishing a nonzero secret key. We find that the generic quantum repeater is optimal regarding the secret key rate per memory per second and show that the encoded quantum repeater using the simple three-qubit repetition code can even have an advantage with respect to the resources compared to other recent quantum repeater schemes with encoding.

  15. Quantum key distribution with finite resources: Secret key rates via Renyi entropies

    SciTech Connect

    Abruzzo, Silvestre; Kampermann, Hermann; Mertz, Markus; Bruss, Dagmar

    2011-09-15

    A realistic quantum key distribution (QKD) protocol necessarily deals with finite resources, such as the number of signals exchanged by the two parties. We derive a bound on the secret key rate which is expressed as an optimization problem over Renyi entropies. Under the assumption of collective attacks by an eavesdropper, a computable estimate of our bound for the six-state protocol is provided. This bound leads to improved key rates in comparison to previous results.

  16. Is understanding regret dependent on developments in counterfactual thinking?

    PubMed

    Beck, Sarah R; Crilly, Maria

    2009-06-01

    Children's understanding of counterfactual emotions such as regret and relief develops relatively late compared to their ability to imagine counterfactual worlds. We tested whether a late development in counterfactual thinking: understanding counterfactuals as possibilities, underpinned children's understanding of regret. Thirty 5- and 6-year-olds completed tasks assessing counterfactual thinking and understanding regret. Performance on the counterfactual task was better than that on the regret task. We suggest that thinking about counterfactuals as possibilities is a necessary but not sufficient cognitive development in children's understanding of regret. We discuss how other developments in counterfactual thinking may underpin children's emotional understanding.

  17. Bit-oriented quantum public-key encryption based on quantum perfect encryption

    NASA Astrophysics Data System (ADS)

    Wu, Chenmiao; Yang, Li

    2016-08-01

    A bit-oriented quantum public-key encryption scheme is presented. We use Boolean functions as private-key and randomly changed pairs of quantum state and classical string as public-keys. Following the concept of quantum perfect encryption, we prepare the public-key with Hadamard transformation and Pauli transformation. The quantum part of public-keys is various with different classical strings. In contrast to the typical classical public-key scheme, one private-key in our scheme corresponds to an exponential number of public-keys. We investigate attack to the private-key and prove that the public-key is a totally mixed state. So the adversary cannot acquire any information about private-key from measurement of the public-key. Then, the attack to encryption is analyzed. Since the trace distance between two different ciphertexts is zero, the adversary cannot distinguish between the two ciphertext states and also obtains nothing about plaintext and private-key. Thus, we have the conclusion that the proposed scheme is information-theoretically secure under an attack of the private-key and encryption.

  18. Quantum distribution of Gaussian keys using squeezed states

    NASA Astrophysics Data System (ADS)

    Cerf, N. J.; Lévy, M.; Assche, G. Van

    2001-05-01

    A continuous key-distribution scheme is proposed that relies on a pair of conjugate quantum variables. It allows two remote parties to share a secret Gaussian key by encoding it into one of the two quadrature components of a single-mode electromagnetic field. The resulting quantum cryptographic information versus disturbance trade-off is investigated for an individual attack based on the optimal continuous cloning machine. It is shown that the information gained by the eavesdropper then simply equals the information lost by the receiver.

  19. Free-space quantum key distribution to a moving receiver.

    PubMed

    Bourgoin, Jean-Philippe; Higgins, Brendon L; Gigov, Nikolay; Holloway, Catherine; Pugh, Christopher J; Kaiser, Sarah; Cranmer, Miles; Jennewein, Thomas

    2015-12-28

    Technological realities limit terrestrial quantum key distribution (QKD) to single-link distances of a few hundred kilometers. One promising avenue for global-scale quantum communication networks is to use low-Earth-orbit satellites. Here we report the first demonstration of QKD from a stationary transmitter to a receiver platform traveling at an angular speed equivalent to a 600 km altitude satellite, located on a moving truck. We overcome the challenges of actively correcting beam pointing, photon polarization and time-of-flight. Our system generates an asymptotic secure key at 40 bits/s.

  20. Detector-decoy quantum key distribution without monitoring signal disturbance

    NASA Astrophysics Data System (ADS)

    Yin, Hua-Lei; Fu, Yao; Mao, Yingqiu; Chen, Zeng-Bing

    2016-02-01

    The round-robin differential phase-shift quantum key distribution protocol provides a secure way to exchange private information without monitoring conventional disturbances and still maintains a high tolerance of noise, making it desirable for practical implementations of quantum key distribution. However, photon number resolving detectors are required to ensure that the detected signals are single photons in the original protocol. Here, we adopt the detector-decoy method and give the bounds to the fraction of detected events from single photons. Utilizing the advantages of the protocol, we provide a practical method of performing the protocol with desirable performances requiring only threshold single-photon detectors.

  1. Key-rate enhancement using qutrit states for quantum key distribution with askew aligned sources

    NASA Astrophysics Data System (ADS)

    Jo, Yonggi; Son, Wonmin

    2016-11-01

    It is known that measurement-device-independent quantum key distribution (MDI-QKD) provides ultimate security from all types of side-channel attack on detectors at the expense of low key rate. In the present study, we propose MDI-QKD using three-dimensional quantum states and show that the protocol improves the secret key rate under the analysis of mismatched-basis statistics. Specifically, we analyze security of the 3 d -MDI-QKD protocol with askew aligned sources, meaning that the original sources contain unwanted states instead of the expected one. We evaluate the secret key rate of the protocol and identify the regime in which the key rate is higher than the protocol with the qubit MDI-QKD.

  2. Quantum key distribution using card, base station and trusted authority

    DOEpatents

    Nordholt, Jane Elizabeth; Hughes, Richard John; Newell, Raymond Thorson; Peterson, Charles Glen; Rosenberg, Danna; McCabe, Kevin Peter; Tyagi, Kush T; Dallman, Nicholas

    2015-04-07

    Techniques and tools for quantum key distribution ("QKD") between a quantum communication ("QC") card, base station and trusted authority are described herein. In example implementations, a QC card contains a miniaturized QC transmitter and couples with a base station. The base station provides a network connection with the trusted authority and can also provide electric power to the QC card. When coupled to the base station, after authentication by the trusted authority, the QC card acquires keys through QKD with a trusted authority. The keys can be used to set up secure communication, for authentication, for access control, or for other purposes. The QC card can be implemented as part of a smart phone or other mobile computing device, or the QC card can be used as a fillgun for distribution of the keys.

  3. Free-space quantum key distribution with entangled photons

    NASA Astrophysics Data System (ADS)

    Marcikic, Ivan; Lamas-Linares, Antía; Kurtsiefer, Christian

    2006-09-01

    The authors report on a complete experimental implementation of a quantum key distribution protocol through a free-space link using polarization-entangled photon pairs from a compact parametric downconversion source. Over 10h of uninterrupted communication between sites 1.5km apart, they observe average key generation rates of 630/s after error correction and privacy amplification. Their scheme requires no specific hardware channel for synchronization apart from a classical wireless link, and no explicit random number generator.

  4. Authenticated Quantum Key Distribution with Collective Detection using Single Photons

    NASA Astrophysics Data System (ADS)

    Huang, Wei; Xu, Bing-Jie; Duan, Ji-Tong; Liu, Bin; Su, Qi; He, Yuan-Hang; Jia, Heng-Yue

    2016-10-01

    We present two authenticated quantum key distribution (AQKD) protocols by utilizing the idea of collective (eavesdropping) detection. One is a two-party AQKD protocol, the other is a multiparty AQKD protocol with star network topology. In these protocols, the classical channels need not be assumed to be authenticated and the single photons are used as the quantum information carriers. To achieve mutual identity authentication and establish a random key in each of the proposed protocols, only one participant should be capable of preparing and measuring single photons, and the main quantum ability that the rest of the participants should have is just performing certain unitary operations. Security analysis shows that these protocols are free from various kinds of attacks, especially the impersonation attack and the man-in-the-middle (MITM) attack.

  5. Method for adding nodes to a quantum key distribution system

    DOEpatents

    Grice, Warren P

    2015-02-24

    An improved quantum key distribution (QKD) system and method are provided. The system and method introduce new clients at intermediate points along a quantum channel, where any two clients can establish a secret key without the need for a secret meeting between the clients. The new clients perform operations on photons as they pass through nodes in the quantum channel, and participate in a non-secret protocol that is amended to include the new clients. The system and method significantly increase the number of clients that can be supported by a conventional QKD system, with only a modest increase in cost. The system and method are compatible with a variety of QKD schemes, including polarization, time-bin, continuous variable and entanglement QKD.

  6. Measurement-device-independent entanglement-based quantum key distribution

    NASA Astrophysics Data System (ADS)

    Yang, Xiuqing; Wei, Kejin; Ma, Haiqiang; Sun, Shihai; Liu, Hongwei; Yin, Zhenqiang; Li, Zuohan; Lian, Shibin; Du, Yungang; Wu, Lingan

    2016-05-01

    We present a quantum key distribution protocol in a model in which the legitimate users gather statistics as in the measurement-device-independent entanglement witness to certify the sources and the measurement devices. We show that the task of measurement-device-independent quantum communication can be accomplished based on monogamy of entanglement, and it is fairly loss tolerate including source and detector flaws. We derive a tight bound for collective attacks on the Holevo information between the authorized parties and the eavesdropper. Then with this bound, the final secret key rate with the source flaws can be obtained. The results show that long-distance quantum cryptography over 144 km can be made secure using only standard threshold detectors.

  7. Improved multiparty quantum key agreement in travelling mode

    NASA Astrophysics Data System (ADS)

    Huang, Wei; Su, Qi; Xu, BingJie; Liu, Bin; Fan, Fan; Jia, HengYue; Yang, YingHui

    2016-12-01

    The need to simultaneously balance security and fairness in quantum key agreement (QKA) makes it challenging to design a flawless QKA protocol, especially a multiparty quantum key agreement (MQKA) protocol. When designing an MQKA protocol, two modes can be used to transmit the quantum information carriers: travelling mode and distributed mode. MQKA protocols usually have a higher qubit efficiency in travelling mode than in distributed mode. Thus, several travelling mode MQKA protocols have been proposed. However, almost all of these are vulnerable to collusion attacks from internal betrayers. This paper proposes an improved MQKA protocol that operates in travelling mode with Einstein-Podolsky-Rosen pairs. More importantly, we present a new travelling mode MQKA protocol that uses single photons, which is more feasible than previous methods under current technologies.

  8. Trustworthiness of detectors in quantum key distribution with untrusted detectors

    SciTech Connect

    Qi, Bing

    2015-02-25

    Measurement-device-independent quantum key distribution (MDI-QKD) protocol has been demonstrated as a viable solution to detector side-channel attacks. One of the main advantages of MDI-QKD is that the security can be proved without making any assumptions about how the measurement device works. The price to pay is the relatively low secure key rate comparing with conventional quantum key distribution (QKD), such as the decoy-state BB84 protocol. Recently a new QKD protocol, aiming at bridging the strong security of MDI-QKD with the high e ciency of conventional QKD, has been proposed. In this protocol, the legitimate receiver employs a trusted linear optics network to encode information on photons received from an insecure quantum channel, and then performs a Bell state measurement (BSM) using untrusted detectors. One crucial assumption made in most of these studies is that the untrusted BSM located inside the receiver's laboratory cannot send any unwanted information to the outside. Here in this paper, we show that if the BSM is completely untrusted, a simple scheme would allow the BSM to send information to the outside. Combined with Trojan horse attacks, this scheme could allow Eve to gain information of the quantum key without being detected. Ultimately, to prevent the above attack, either countermeasures to Trojan horse attacks or some trustworthiness to the "untrusted" BSM device is required.

  9. Trustworthiness of detectors in quantum key distribution with untrusted detectors

    DOE PAGES

    Qi, Bing

    2015-02-25

    Measurement-device-independent quantum key distribution (MDI-QKD) protocol has been demonstrated as a viable solution to detector side-channel attacks. One of the main advantages of MDI-QKD is that the security can be proved without making any assumptions about how the measurement device works. The price to pay is the relatively low secure key rate comparing with conventional quantum key distribution (QKD), such as the decoy-state BB84 protocol. Recently a new QKD protocol, aiming at bridging the strong security of MDI-QKD with the high e ciency of conventional QKD, has been proposed. In this protocol, the legitimate receiver employs a trusted linear opticsmore » network to encode information on photons received from an insecure quantum channel, and then performs a Bell state measurement (BSM) using untrusted detectors. One crucial assumption made in most of these studies is that the untrusted BSM located inside the receiver's laboratory cannot send any unwanted information to the outside. Here in this paper, we show that if the BSM is completely untrusted, a simple scheme would allow the BSM to send information to the outside. Combined with Trojan horse attacks, this scheme could allow Eve to gain information of the quantum key without being detected. Ultimately, to prevent the above attack, either countermeasures to Trojan horse attacks or some trustworthiness to the "untrusted" BSM device is required.« less

  10. Post-processing procedure for industrial quantum key distribution systems

    NASA Astrophysics Data System (ADS)

    Kiktenko, Evgeny; Trushechkin, Anton; Kurochkin, Yury; Fedorov, Aleksey

    2016-08-01

    We present algorithmic solutions aimed on post-processing procedure for industrial quantum key distribution systems with hardware sifting. The main steps of the procedure are error correction, parameter estimation, and privacy amplification. Authentication of classical public communication channel is also considered.

  11. Two-way quantum key distribution at telecommunication wavelength

    SciTech Connect

    Kumar, Rupesh; Lucamarini, Marco; Di Giuseppe, Giovanni; Natali, Riccardo; Mancini, Giorgio; Tombesi, Paolo

    2008-02-15

    We report on a quantum key distribution effected with a two-way deterministic protocol over a standard telecommunication fiber. Despite the common belief of a prohibitive loss rate for such a scheme, our results show its feasibility on distances of few tenths of kilometers.

  12. Improvement on "Quantum Key Agreement Protocol with Maximally Entangled States"

    NASA Astrophysics Data System (ADS)

    Chong, Song-Kong; Tsai, Chia-Wei; Hwang, Tzonelih

    2011-06-01

    Recently, Hsueh and Chen [in Proceedings of the 14th Information Security Conference, National Taiwan University of Science and Technology, Taipei, pp. 236-242, 2004] proposed a quantum key agreement (QKA) protocol with maximally entangled states. Their protocol allows two users to negotiate a secret key in such a way that no one can predetermine the shared key alone. This study points out two security flaws in their protocol: (1) a legitimate but malicious user can fully control the shared key alone; (2) an eavesdropper can obtain the shared key without being detected. A possible solution is presented to avoid these attacks and also Tsai et al.'s CNOT attack [in Proceedings of the 20th Cryptology and Information Security Conference, National Chiao Tung University, Hsinchu, pp. 210-213, 2010] on Hsueh and Chen protocol to obtain the shared key without being detected.

  13. Quantum cryptography using coherent states: Randomized encryption and key generation

    NASA Astrophysics Data System (ADS)

    Corndorf, Eric

    With the advent of the global optical-telecommunications infrastructure, an increasing number of individuals, companies, and agencies communicate information with one another over public networks or physically-insecure private networks. While the majority of the traffic flowing through these networks requires little or no assurance of secrecy, the same cannot be said for certain communications between banks, between government agencies, within the military, and between corporations. In these arenas, the need to specify some level of secrecy in communications is a high priority. While the current approaches to securing sensitive information (namely the public-key-cryptography infrastructure and deterministic private-key ciphers like AES and 3DES) seem to be cryptographically strong based on empirical evidence, there exist no mathematical proofs of secrecy for any widely deployed cryptosystem. As an example, the ubiquitous public-key cryptosystems infer all of their secrecy from the assumption that factoring of the product of two large primes is necessarily time consuming---something which has not, and perhaps cannot, be proven. Since the 1980s, the possibility of using quantum-mechanical features of light as a physical mechanism for satisfying particular cryptographic objectives has been explored. This research has been fueled by the hopes that cryptosystems based on quantum systems may provide provable levels of secrecy which are at least as valid as quantum mechanics itself. Unfortunately, the most widely considered quantum-cryptographic protocols (BB84 and the Ekert protocol) have serious implementation problems. Specifically, they require quantum-mechanical states which are not readily available, and they rely on unproven relations between intrusion-level detection and the information available to an attacker. As a result, the secrecy level provided by these experimental implementations is entirely unspecified. In an effort to provably satisfy the cryptographic

  14. Key rate for calibration robust entanglement based BB84 quantum key distribution protocol

    SciTech Connect

    Gittsovich, O.; Moroder, T.

    2014-12-04

    We apply the approach of verifying entanglement, which is based on the sole knowledge of the dimension of the underlying physical system to the entanglement based version of the BB84 quantum key distribution protocol. We show that the familiar one-way key rate formula holds already if one assumes the assumption that one of the parties is measuring a qubit and no further assumptions about the measurement are needed.

  15. Measurement-Device-Independent Quantum Key Distribution over 200 km

    NASA Astrophysics Data System (ADS)

    Tang, Yan-Lin; Yin, Hua-Lei; Chen, Si-Jing; Liu, Yang; Zhang, Wei-Jun; Jiang, Xiao; Zhang, Lu; Wang, Jian; You, Li-Xing; Guan, Jian-Yu; Yang, Dong-Xu; Wang, Zhen; Liang, Hao; Zhang, Zhen; Zhou, Nan; Ma, Xiongfeng; Chen, Teng-Yun; Zhang, Qiang; Pan, Jian-Wei

    2014-11-01

    Measurement-device-independent quantum key distribution (MDIQKD) protocol is immune to all attacks on detection and guarantees the information-theoretical security even with imperfect single-photon detectors. Recently, several proof-of-principle demonstrations of MDIQKD have been achieved. Those experiments, although novel, are implemented through limited distance with a key rate less than 0.1 bit /s . Here, by developing a 75 MHz clock rate fully automatic and highly stable system and superconducting nanowire single-photon detectors with detection efficiencies of more than 40%, we extend the secure transmission distance of MDIQKD to 200 km and achieve a secure key rate 3 orders of magnitude higher. These results pave the way towards a quantum network with measurement-device-independent security.

  16. Secret Key Generation via a Modified Quantum Secret Sharing Protocol

    SciTech Connect

    Smith IV, Amos M; Evans, Philip G; Lawrie, Benjamin J; Legre, Matthieu; Lougovski, Pavel; Ray, William R; Williams, Brian P; Qi, Bing; Grice, Warren P

    2015-01-01

    We present and experimentally show a novel protocol for distributing secret information between two and only two parties in a N-party single-qubit Quantum Secret Sharing (QSS) system. We demonstrate this new algorithm with N = 3 active parties over 6km of telecom. ber. Our experimental device is based on the Clavis2 Quantum Key Distribution (QKD) system built by ID Quantique but is generalizable to any implementation. We show that any two out of the N parties can build secret keys based on partial information from each other and with collaboration from the remaining N > 2 parties. This algorithm allows for the creation of two-party secret keys were standard QSS does not and signicantly reduces the number of resources needed to implement QKD on a highly connected network such as the electrical grid.

  17. Long-distance quantum key distribution with imperfect devices

    SciTech Connect

    Lo Piparo, Nicoló; Razavi, Mohsen

    2014-12-04

    Quantum key distribution over probabilistic quantum repeaters is addressed. We compare, under practical assumptions, two such schemes in terms of their secure key generation rate per memory, R{sub QKD}. The two schemes under investigation are the one proposed by Duan et al. in [Nat. 414, 413 (2001)] and that of Sangouard et al. proposed in [Phys. Rev. A 76, 050301 (2007)]. We consider various sources of imperfections in the latter protocol, such as a nonzero double-photon probability for the source, dark count per pulse, channel loss and inefficiencies in photodetectors and memories, to find the rate for different nesting levels. We determine the maximum value of the double-photon probability beyond which it is not possible to share a secret key anymore. We find the crossover distance for up to three nesting levels. We finally compare the two protocols.

  18. High-efficiency reconciliation for continuous variable quantum key distribution

    NASA Astrophysics Data System (ADS)

    Bai, Zengliang; Yang, Shenshen; Li, Yongmin

    2017-04-01

    Quantum key distribution (QKD) is the most mature application of quantum information technology. Information reconciliation is a crucial step in QKD and significantly affects the final secret key rates shared between two legitimate parties. We analyze and compare various construction methods of low-density parity-check (LDPC) codes and design high-performance irregular LDPC codes with a block length of 106. Starting from these good codes and exploiting the slice reconciliation technique based on multilevel coding and multistage decoding, we realize high-efficiency Gaussian key reconciliation with efficiency higher than 95% for signal-to-noise ratios above 1. Our demonstrated method can be readily applied in continuous variable QKD.

  19. Secret key generation via a modified quantum secret sharing protocol

    NASA Astrophysics Data System (ADS)

    Smith, A. M.; Evans, P. G.; Lawrie, B.; Legré, M.; Lougovski, P.; Ray, W.; Williams, B. P.; Qi, B.; Grice, W. P.

    2015-05-01

    We present and experimentally show a novel protocol for distributing secret information between two and only two parties in a N-party single-qubit Quantum Secret Sharing (QSS) system. We demonstrate this new algorithm with N = 3 active parties over ~6km of telecom. fiber. Our experimental device is based on the Clavis2 Quantum Key Distribution (QKD) system built by ID Quantique but is generalizable to any implementation. We show that any two out of the N parties can build secret keys based on partial information from each other and with collaboration from the remaining N - 2 parties. This algorithm allows for the creation of two-party secret keys were standard QSS does not and significantly reduces the number of resources needed to implement QKD on a highly connected network such as the electrical grid.

  20. Quantum key distribution with prepare-and-measure Bell test.

    PubMed

    Tan, Yong-Gang

    2016-10-13

    The prepare-and-measure quantum key distribution (QKD) has the merits of fast speed, high key generation rate, and easy implementation. However, the detector side channel attacks greatly undermine the security of the key bits. The eavesdropper, Eve, exploits the flaws of the detectors to obtain illegal information without violating quantum principles. It means that she can intervene in the communication without being detected. A prepare-and-measure Bell test protocol will be proposed. By randomly carrying out Bell test at the side of the information receiver, Bob, Eve's illegal information gain within the detector side channel attack can be well bounded. This protocol does not require any improvement on the detectors used in available prepare-and-measure QKD. Though we only illustrate its application in the BB84 protocol, it is applicable for any prepare-and-measure QKD.

  1. Quantum key distribution with prepare-and-measure Bell test

    NASA Astrophysics Data System (ADS)

    Tan, Yong-Gang

    2016-10-01

    The prepare-and-measure quantum key distribution (QKD) has the merits of fast speed, high key generation rate, and easy implementation. However, the detector side channel attacks greatly undermine the security of the key bits. The eavesdropper, Eve, exploits the flaws of the detectors to obtain illegal information without violating quantum principles. It means that she can intervene in the communication without being detected. A prepare-and-measure Bell test protocol will be proposed. By randomly carrying out Bell test at the side of the information receiver, Bob, Eve’s illegal information gain within the detector side channel attack can be well bounded. This protocol does not require any improvement on the detectors used in available prepare-and-measure QKD. Though we only illustrate its application in the BB84 protocol, it is applicable for any prepare-and-measure QKD.

  2. Insecurity of Detector-Device-Independent Quantum Key Distribution

    NASA Astrophysics Data System (ADS)

    Sajeed, Shihan; Huang, Anqi; Sun, Shihai; Xu, Feihu; Makarov, Vadim; Curty, Marcos

    2016-12-01

    Detector-device-independent quantum key distribution (DDI-QKD) held the promise of being robust to detector side channels, a major security loophole in quantum key distribution (QKD) implementations. In contrast to what has been claimed, however, we demonstrate that the security of DDI-QKD is not based on postselected entanglement, and we introduce various eavesdropping strategies that show that DDI-QKD is in fact insecure against detector side-channel attacks as well as against other attacks that exploit devices' imperfections of the receiver. Our attacks are valid even when the QKD apparatuses are built by the legitimate users of the system themselves, and thus, free of malicious modifications, which is a key assumption in DDI-QKD.

  3. Quantum key distribution with prepare-and-measure Bell test

    PubMed Central

    Tan, Yong-gang

    2016-01-01

    The prepare-and-measure quantum key distribution (QKD) has the merits of fast speed, high key generation rate, and easy implementation. However, the detector side channel attacks greatly undermine the security of the key bits. The eavesdropper, Eve, exploits the flaws of the detectors to obtain illegal information without violating quantum principles. It means that she can intervene in the communication without being detected. A prepare-and-measure Bell test protocol will be proposed. By randomly carrying out Bell test at the side of the information receiver, Bob, Eve’s illegal information gain within the detector side channel attack can be well bounded. This protocol does not require any improvement on the detectors used in available prepare-and-measure QKD. Though we only illustrate its application in the BB84 protocol, it is applicable for any prepare-and-measure QKD. PMID:27733771

  4. Long-distance quantum key distribution with imperfect devices

    NASA Astrophysics Data System (ADS)

    Lo Piparo, Nicoló; Razavi, Mohsen

    2014-12-01

    Quantum key distribution over probabilistic quantum repeaters is addressed. We compare, under practical assumptions, two such schemes in terms of their secure key generation rate per memory, RQKD. The two schemes under investigation are the one proposed by Duan et al. in [Nat. 414, 413 (2001)] and that of Sangouard et al. proposed in [Phys. Rev. A 76, 050301 (2007)]. We consider various sources of imperfections in the latter protocol, such as a nonzero double-photon probability for the source, dark count per pulse, channel loss and inefficiencies in photodetectors and memories, to find the rate for different nesting levels. We determine the maximum value of the double-photon probability beyond which it is not possible to share a secret key anymore. We find the crossover distance for up to three nesting levels. We finally compare the two protocols.

  5. Experimental Measurement-Device-Independent Quantum Key Distribution

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Chen, Teng-Yun; Wang, Liu-Jun; Liang, Hao; Shentu, Guo-Liang; Wang, Jian; Cui, Ke; Yin, Hua-Lei; Liu, Nai-Le; Li, Li; Ma, Xiongfeng; Pelc, Jason S.; Fejer, M. M.; Peng, Cheng-Zhi; Zhang, Qiang; Pan, Jian-Wei

    2013-09-01

    Quantum key distribution is proven to offer unconditional security in communication between two remote users with ideal source and detection. Unfortunately, ideal devices never exist in practice and device imperfections have become the targets of various attacks. By developing up-conversion single-photon detectors with high efficiency and low noise, we faithfully demonstrate the measurement-device-independent quantum-key-distribution protocol, which is immune to all hacking strategies on detection. Meanwhile, we employ the decoy-state method to defend attacks on a nonideal source. By assuming a trusted source scenario, our practical system, which generates more than a 25 kbit secure key over a 50 km fiber link, serves as a stepping stone in the quest for unconditionally secure communications with realistic devices.

  6. Polarization-basis tracking scheme for quantum key distribution using revealed sifted key bits.

    PubMed

    Ding, Yu-Yang; Chen, Wei; Chen, Hua; Wang, Chao; Li, Ya-Ping; Wang, Shuang; Yin, Zhen-Qiang; Guo, Guang-Can; Han, Zheng-Fu

    2017-03-15

    The calibration of the polarization basis between the transmitter and receiver is an important task in quantum key distribution. A continuously working polarization-basis tracking scheme (PBTS) will effectively promote the efficiency of the system and reduce the potential security risk when switching between the transmission and calibration modes. Here, we proposed a single-photon level continuously working PBTS using only sifted key bits revealed during an error correction procedure, without introducing additional reference light or interrupting the transmission of quantum signals. We applied the scheme to a polarization-encoding BB84 QKD system in a 50 km fiber channel, and obtained an average quantum bit error rate (QBER) of 2.32% and a standard derivation of 0.87% during 24 h of continuous operation. The stable and relatively low QBER validates the effectiveness of the scheme.

  7. Min-entropy and quantum key distribution: Nonzero key rates for ''small'' numbers of signals

    SciTech Connect

    Bratzik, Sylvia; Mertz, Markus; Kampermann, Hermann; Bruss, Dagmar

    2011-02-15

    We calculate an achievable secret key rate for quantum key distribution with a finite number of signals by evaluating the quantum conditional min-entropy explicitly. The min-entropy for a classical random variable is the negative logarithm of the maximal value in its probability distribution. The quantum conditional min-entropy can be expressed in terms of the guessing probability, which we calculate for d-dimensional systems. We compare these key rates to previous approaches using the von Neumann entropy and find nonzero key rates for a smaller number of signals. Furthermore, we improve the secret key rates by modifying the parameter estimation step. Both improvements taken together lead to nonzero key rates for only 10{sup 4}-10{sup 5} signals. An interesting conclusion can also be drawn from the additivity of the min-entropy and its relation to the guessing probability: for a set of symmetric tensor product states, the optimal minimum-error discrimination (MED) measurement is the optimal MED measurement on each subsystem.

  8. Security of quantum key distribution using d-level systems.

    PubMed

    Cerf, Nicolas J; Bourennane, Mohamed; Karlsson, Anders; Gisin, Nicolas

    2002-03-25

    We consider two quantum cryptographic schemes relying on encoding the key into qudits, i.e., quantum states in a d-dimensional Hilbert space. The first cryptosystem uses two mutually unbiased bases (thereby extending the BB84 scheme), while the second exploits all d+1 available such bases (extending the six-state protocol for qubits). We derive the information gained by a potential eavesdropper applying a cloning-based individual attack, along with an upper bound on the error rate that ensures unconditional security against coherent attacks.

  9. Two Quantum Key Agreement Protocols Immune to Collective Noise

    NASA Astrophysics Data System (ADS)

    He, Ye-Feng; Ma, Wen-Ping

    2016-10-01

    In this paper, two quantum key agreement protocols are proposed, which can resist against the collective-dephasing noise and the collective-rotation noise, respectively. These two protocols mainly utilize logical quantum states, the measurement correlation property of multi-particle entangled states and the delayed measurement technique. Moreover, they have no information leakage and are congenitally free from the Trojan horse attacks. The use of the decoy state technology and the delayed measurement technique makes them secure against both participant and outsider attacks. The efficiency analysis shows that the two protocols are very efficient.

  10. Two Quantum Key Agreement Protocols Immune to Collective Noise

    NASA Astrophysics Data System (ADS)

    He, Ye-Feng; Ma, Wen-Ping

    2017-02-01

    In this paper, two quantum key agreement protocols are proposed, which can resist against the collective-dephasing noise and the collective-rotation noise, respectively. These two protocols mainly utilize logical quantum states, the measurement correlation property of multi-particle entangled states and the delayed measurement technique. Moreover, they have no information leakage and are congenitally free from the Trojan horse attacks. The use of the decoy state technology and the delayed measurement technique makes them secure against both participant and outsider attacks. The efficiency analysis shows that the two protocols are very efficient.

  11. The theory research of multi-user quantum access network with Measurement Device Independent quantum key distribution

    NASA Astrophysics Data System (ADS)

    Ji, Yi-Ming; Li, Yun-Xia; Shi, Lei; Meng, Wen; Cui, Shu-Min; Xu, Zhen-Yu

    2015-10-01

    Quantum access network can't guarantee the absolute security of multi-user detector and eavesdropper can get access to key information through time-shift attack and other ways. Measurement-device-independent quantum key distribution is immune from all the detection attacks, and accomplishes the safe sharing of quantum key. In this paper, that Measurement-device-independent quantum key distribution is used in the application of multi-user quantum access to the network is on the research. By adopting time-division multiplexing technology to achieve the sharing of multiuser detector, the system structure is simplified and the security of quantum key sharing is acquired.

  12. Upconversion-based receivers for quantum hacking-resistant quantum key distribution

    NASA Astrophysics Data System (ADS)

    Jain, Nitin; Kanter, Gregory S.

    2016-07-01

    We propose a novel upconversion (sum frequency generation)-based quantum-optical system design that can be employed as a receiver (Bob) in practical quantum key distribution systems. The pump governing the upconversion process is produced and utilized inside the physical receiver, making its access or control unrealistic for an external adversary (Eve). This pump facilitates several properties which permit Bob to define and control the modes that can participate in the quantum measurement. Furthermore, by manipulating and monitoring the characteristics of the pump pulses, Bob can detect a wide range of quantum hacking attacks launched by Eve.

  13. Is Understanding Regret Dependent on Developments in Counterfactual Thinking?

    ERIC Educational Resources Information Center

    Beck, Sarah R.; Crilly, Maria

    2009-01-01

    Children's understanding of counterfactual emotions such as regret and relief develops relatively late compared to their ability to imagine counterfactual worlds. We tested whether a late development in counterfactual thinking: understanding counterfactuals as possibilities, underpinned children's understanding of regret. Thirty 5- and 6-year-olds…

  14. Subcarrier multiplexing multiple-input multiple-output quantum key distribution scheme with orthogonal quantum states

    NASA Astrophysics Data System (ADS)

    Xiao, Hailin; Zhang, Zhongshan

    2017-01-01

    Quantum key distribution (QKD) system is presently being developed for providing high-security transmission in future free-space optical communication links. However, current QKD technique restricts quantum secure communication to a low bit rate. To improve the QKD bit rate, we propose a subcarrier multiplexing multiple-input multiple-output quantum key distribution (SCM-MQKD) scheme with orthogonal quantum states. Specifically, we firstly present SCM-MQKD system model and drive symmetrical SCM-MQKD system into decoherence-free subspaces. We then utilize bipartite Werner and isotropic states to construct multiple parallel single photon with orthogonal quantum states that are invariant for unitary operations. Finally, we derive the density matrix and the capacity of SCM-MQKD system, respectively. Theoretical analysis and numerical results show that the capacity of SCM-MQKD system will increase {log _2}(N^2+1) times than that of single-photon QKD system.

  15. Understanding Counterfactuality: A Review of Experimental Evidence for the Dual Meaning of Counterfactuals

    PubMed Central

    Nieuwland, Mante S.

    2016-01-01

    Abstract Cognitive and linguistic theories of counterfactual language comprehension assume that counterfactuals convey a dual meaning. Subjunctive‐counterfactual conditionals (e.g., ‘If Tom had studied hard, he would have passed the test’) express a supposition while implying the factual state of affairs (Tom has not studied hard and failed). The question of how counterfactual dual meaning plays out during language processing is currently gaining interest in psycholinguistics. Whereas numerous studies using offline measures of language processing consistently support counterfactual dual meaning, evidence coming from online studies is less conclusive. Here, we review the available studies that examine online counterfactual language comprehension through behavioural measurement (self‐paced reading times, eye‐tracking) and neuroimaging (electroencephalography, functional magnetic resonance imaging). While we argue that these studies do not offer direct evidence for the online computation of counterfactual dual meaning, they provide valuable information about the way counterfactual meaning unfolds in time and influences successive information processing. Further advances in research on counterfactual comprehension require more specific predictions about how counterfactual dual meaning impacts incremental sentence processing. PMID:27512408

  16. One-way quantum key distribution: Simple upper bound on the secret key rate

    SciTech Connect

    Moroder, Tobias; Luetkenhaus, Norbert; Curty, Marcos

    2006-11-15

    We present a simple method to obtain an upper bound on the achievable secret key rate in quantum key distribution (QKD) protocols that use only unidirectional classical communication during the public-discussion phase. This method is based on a necessary precondition for one-way secret key distillation; the legitimate users need to prove that there exists no quantum state having a symmetric extension that is compatible with the available measurements results. The main advantage of the obtained upper bound is that it can be formulated as a semidefinite program, which can be efficiently solved. We illustrate our results by analyzing two well-known qubit-based QKD protocols: the four-state protocol and the six-state protocol.

  17. Towards communication-efficient quantum oblivious key distribution

    NASA Astrophysics Data System (ADS)

    Panduranga Rao, M. V.; Jakobi, M.

    2013-01-01

    Symmetrically private information retrieval, a fundamental problem in the field of secure multiparty computation, is defined as follows: A database D of N bits held by Bob is queried by a user Alice who is interested in the bit Db in such a way that (1) Alice learns Db and only Db and (2) Bob does not learn anything about Alice's choice b. While solutions to this problem in the classical domain rely largely on unproven computational complexity theoretic assumptions, it is also known that perfect solutions that guarantee both database and user privacy are impossible in the quantum domain. Jakobi [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.83.022301 83, 022301 (2011)] proposed a protocol for oblivious transfer using well-known quantum key device (QKD) techniques to establish an oblivious key to solve this problem. Their solution provided a good degree of database and user privacy (using physical principles like the impossibility of perfectly distinguishing nonorthogonal quantum states and the impossibility of superluminal communication) while being loss-resistant and implementable with commercial QKD devices (due to the use of the Scarani-Acin-Ribordy-Gisin 2004 protocol). However, their quantum oblivious key distribution (QOKD) protocol requires a communication complexity of O(NlogN). Since modern databases can be extremely large, it is important to reduce this communication as much as possible. In this paper, we first suggest a modification of their protocol wherein the number of qubits that need to be exchanged is reduced to O(N). A subsequent generalization reduces the quantum communication complexity even further in such a way that only a few hundred qubits are needed to be transferred even for very large databases.

  18. Experimental quantum key distribution without monitoring signal disturbance

    NASA Astrophysics Data System (ADS)

    Takesue, Hiroki; Sasaki, Toshihiko; Tamaki, Kiyoshi; Koashi, Masato

    2015-12-01

    Quantum key distribution (QKD) is a method of realizing private communication securely against an adversary with unlimited power. The QKD protocols proposed and demonstrated over the past 30 years relied on the monitoring of signal disturbance to set an upper limit to the amount of leaked information. Here, we report an experimental realization of the recently proposed round-robin differential-phase-shift protocol. We used a receiver set-up in which photons are randomly routed to one of four interferometers with different delays so that the phase difference is measured uniformly over all pair combinations among five pulses comprising the quantum signal. The amount of leak can be bounded from this randomness alone, and a secure key was extracted even when a finite communication time and the threshold nature of photon detectors were taken into account. This demonstrates the first QKD experiment without signal disturbance monitoring, thus opening up a new direction towards secure communication.

  19. Seaworthy Quantum Key Distribution Design and Validation (SEAKEY)

    DTIC Science & Technology

    2015-02-06

    atmospheric absorption and scattering (a numerical model taken from MODTRAN), while employing a single spatial mode . 3. A quantitative trade study of...using multiple spatial modes and finding up to how many spatial modes may yield a perceivable key rate benefit. 4. Development of a quantum-secure...and water vapor, and any coupling efficiency loss at the receiver—for instance the free-space to fiber mode coupling efficiency in a fiber -coupled

  20. Continuous-variable quantum key distribution with Gaussian source noise

    SciTech Connect

    Shen Yujie; Peng Xiang; Yang Jian; Guo Hong

    2011-05-15

    Source noise affects the security of continuous-variable quantum key distribution (CV QKD) and is difficult to analyze. We propose a model to characterize Gaussian source noise through introducing a neutral party (Fred) who induces the noise with a general unitary transformation. Without knowing Fred's exact state, we derive the security bounds for both reverse and direct reconciliations and show that the bound for reverse reconciliation is tight.

  1. Quantum Versus Classical Advantages in Secret Key Distillation (and Their Links to Quantum Entanglement

    NASA Astrophysics Data System (ADS)

    Chitambar, Eric; Fortescue, Benjamin; Hsieh, Min-Hsiu

    We consider the extraction of shared secret key from correlations that are generated by either a classical or quantum source. In the classical setting, two honest parties (Alice and Bob) use public discussion and local operations to distill secret key from some distribution pXYZ that is shared with an unwanted eavesdropper (Eve). In the quantum settings, the correlations pXYZ are delivered to the parties as either an incoherent mixture of orthogonal quantum states or as coherent superposition of such states. Here we demonstrate that the classical and quantum key rates are equivalent when the correlations are generated incoherently in the quantum setting. For coherent sources, we next show that the rates are incomparable, and in fact, their difference can be arbitrarily large in either direction. However, we identify a large class of non-trivial distributions that possess the following properties: (i) Eve's advantage is always greater in the quantum source than classically, and (ii) for the entanglement shared in the coherent source, the so-called entanglement cost/squashed entanglement/relative entropy of entanglement can all be computed. We thus present a rare instance in which various entropic entanglement measures of a quantum state can be explicitly computed.

  2. Long-distance practical quantum key distribution by entanglement swapping.

    PubMed

    Scherer, Artur; Sanders, Barry C; Tittel, Wolfgang

    2011-02-14

    We develop a model for practical, entanglement-based long-distance quantum key distribution employing entanglement swapping as a key building block. Relying only on existing off-the-shelf technology, we show how to optimize resources so as to maximize secret key distribution rates. The tools comprise lossy transmission links, such as telecom optical fibers or free space, parametric down-conversion sources of entangled photon pairs, and threshold detectors that are inefficient and have dark counts. Our analysis provides the optimal trade-off between detector efficiency and dark counts, which are usually competing, as well as the optimal source brightness that maximizes the secret key rate for specified distances (i.e. loss) between sender and receiver.

  3. Efficient multiparty quantum key agreement protocol based on commutative encryption

    NASA Astrophysics Data System (ADS)

    Sun, Zhiwei; Huang, Jiwu; Wang, Ping

    2016-05-01

    A secure multiparty quantum key agreement protocol using single-qubit states is proposed. The agreement key is computed by performing exclusive-OR operation on all the participants' secret keys. Based on the commutative property of the commutative encryption, the exclusive-OR operation can be performed on the plaintext in the encrypted state without decrypting it. Thus, it not only protects the final shared key, but also reduces the complexity of the computation. The efficiency of the proposed protocol, compared with previous multiparty QKA protocols, is also improved. In the presented protocol, entanglement states, joint measurement and even the unitary operations are not needed, and only rotation operations and single-state measurement are required, which are easier to be realized with current technology.

  4. Two-party quantum key agreement against collective noise

    NASA Astrophysics Data System (ADS)

    He, Ye-Feng; Ma, Wen-Ping

    2016-12-01

    In this paper, two two-party quantum key agreement protocols are proposed with logical χ -states and logical Bell states. These two protocols can be immune to the collective-dephasing noise and the collective-rotation noise, respectively. They make full use of the measurement correlation property of multi-particle entangled states and the delayed measurement technique. This ensures that two participants can exchange the secret keys of each other and fairly establishes a shared key. There is no information leakage problem when establishing a shared key. The use of the delayed measurement technique and the decoy state technology makes the two protocols resist against both participant and outsider attacks. Furthermore, the two protocols are congenitally free from the Trojan horse attacks and have high qubit efficiency.

  5. Quantum key agreement protocols with four-qubit cluster states

    NASA Astrophysics Data System (ADS)

    He, Ye-Feng; Ma, Wen-Ping

    2015-09-01

    Based on unitary operations and four-qubit cluster states, a two-party and a three-party quantum key agreement protocols are proposed, respectively, in this paper. The two-party protocol allows that each participant contributes equally to the agreement key by one party performing the unitary operations on two photons of a cluster state and another party performing the delayed measurement on the transformed cluster state. In the three-party scheme, each party can extract the other two parties' secret keys, respectively, encoded in the different photons of the same cluster state by performing the measurement with cluster basis and fairly generates the shared key. The security analysis shows that the two protocols can resist against both participant and outsider attacks. Furthermore, the two protocols also achieve high qubit efficiency.

  6. Statistical Quadrature Evolution for Continuous-Variable Quantum Key Distribution

    NASA Astrophysics Data System (ADS)

    Gyongyosi, Laszlo; Imre, Sandor

    2016-05-01

    We propose a statistical quadrature evolution (SQE) method for multicarrier continuous-variable quantum key distribution (CVQKD). A multicarrier CVQKD protocol utilizes Gaussian subcarrier quantum continuous variables (CV) for information transmission. The SQE framework provides a minimal error estimate of the quadratures of the CV quantum states from the discrete, measured noisy subcarrier variables. We define a method for the statistical modeling and processing of noisy Gaussian subcarrier quadratures. We introduce the terms statistical secret key rate and statistical private classical information, which quantities are derived purely by the statistical functions of our method. We prove the secret key rate formulas for a multiple access multicarrier CVQKD. The framework can be established in an arbitrary CVQKD protocol and measurement setting, and are implementable by standard low-complexity statistical functions, which is particularly convenient for an experimental CVQKD scenario. This work was partially supported by the GOP-1.1.1-11-2012-0092 project sponsored by the EU and European Structural Fund, by the Hungarian Scientific Research Fund - OTKA K-112125, and by the COST Action MP1006.

  7. Side Channel Passive Quantum Key Distribution with One Uninformative State

    NASA Astrophysics Data System (ADS)

    Kang, Guo-Dong; Zhou, Qing-Ping; Fang, Mao-Fa

    2016-12-01

    In most of quantum key distribution schemes, real random number generators are required on both sides for preparation and measurement bases choice. In this paper, via entangled photon pairs, we present a side channel passive quantum key distribution scheme, in which random number generator is unneeded on the receiver side. On the sender Alice side, along with massive of signal photons, small amount of uninformative photons are randomly sent to her partner Bob for eavesdropper-presence testing and error estimation. While on the other side channel, without using random number generator Bob do not actively measure the income signals randomly in two non-orthogonal bases. Instead, he just passively register photon click events, in two settled symmetric (i.e.X) bases, and the raw key(click events) is the probable outcomes of a special quantum measurement module constructed by Alice and Bob. Further, security analysis and formulas of security bounds for this scheme is also investigated under reasonable assumptions. Our work shows that the uninformative state employed in this paper is powerful to fight against eavesdropper Eve.

  8. Side Channel Passive Quantum Key Distribution with One Uninformative State

    NASA Astrophysics Data System (ADS)

    Kang, Guo-Dong; Zhou, Qing-Ping; Fang, Mao-Fa

    2017-03-01

    In most of quantum key distribution schemes, real random number generators are required on both sides for preparation and measurement bases choice. In this paper, via entangled photon pairs, we present a side channel passive quantum key distribution scheme, in which random number generator is unneeded on the receiver side. On the sender Alice side, along with massive of signal photons, small amount of uninformative photons are randomly sent to her partner Bob for eavesdropper-presence testing and error estimation. While on the other side channel, without using random number generator Bob do not actively measure the income signals randomly in two non-orthogonal bases. Instead, he just passively register photon click events, in two settled symmetric (i.e. X) bases, and the raw key(click events) is the probable outcomes of a special quantum measurement module constructed by Alice and Bob. Further, security analysis and formulas of security bounds for this scheme is also investigated under reasonable assumptions. Our work shows that the uninformative state employed in this paper is powerful to fight against eavesdropper Eve.

  9. The physical underpinning of security proofs for quantum key distribution

    NASA Astrophysics Data System (ADS)

    Boileau, Jean Christian

    The dawn of quantum technology unveils a plethora of new possibilities and challenges in the world of information technology, one of which is the quest for secure information transmission. A breakthrough in classical algorithm or the development of a quantum computer could threaten the security of messages encoded using public key cryptosystems based on one-way function such as RSA. Quantum key distribution (QKD) offers an unconditionally secure alternative to such schemes, even in the advent of a quantum computer, as it does not rely on mathematical or technological assumptions, but rather on the universality of the laws of quantum mechanics. Physical concepts associated with quantum mechanics, like the uncertainty principle or entanglement, paved the way to the first successful security proof for QKD. Ever since, further development in security proofs for QKD has been remarkable. But the connection between entanglement distillation and the uncertainty principle has remained hidden under a pile of mathematical burden. Our main goal is to dig the physics out of the new advances in security proofs for QKD. By introducing an alternative definition of private state, which elaborates the ideas of Mayers and Koashi, we explain how the security of all QKD protocols follows from an entropic uncertainty principle. We show explicitly how privacy amplification protocol can be reduced to a private state distillation protocol constructed from our observations about the uncertainty principle. We also derive a generic security proof for one-way permutation-invariant QKD protocols. Considering collective attack, we achieve the same secret key generation rate as the Devetak-Winter's bound. Generalizing an observation from Kraus, Branciard and Renner, we have provided an improved version of the secret key generation rates by considering a different symmetrization. In certain situations, we argue that Azuma's inequality can simplify the security proof considerably, and we explain

  10. Floodlight quantum key distribution: A practical route to gigabit-per-second secret-key rates

    NASA Astrophysics Data System (ADS)

    Zhuang, Quntao; Zhang, Zheshen; Dove, Justin; Wong, Franco N. C.; Shapiro, Jeffrey H.

    2016-07-01

    The channel loss incurred in long-distance transmission places a significant burden on quantum key distribution (QKD) systems: they must defeat a passive eavesdropper who detects all the light lost in the quantum channel and does so without disturbing the light that reaches the intended destination. The current QKD implementation with the highest long-distance secret-key rate meets this challenge by transmitting no more than one photon per bit [M. Lucamarini et al., Opt. Express 21, 24550 (2013), 10.1364/OE.21.024550]. As a result, it cannot achieve the Gbps secret-key rate needed for one-time pad encryption of large data files unless an impractically large amount of multiplexing is employed. We introduce floodlight QKD (FL-QKD), which floods the quantum channel with a high number of photons per bit distributed over a much greater number of optical modes. FL-QKD offers security against the optimum frequency-domain collective attack by transmitting less than one photon per mode and using photon-coincidence channel monitoring, and it is completely immune to passive eavesdropping. More importantly, FL-QKD is capable of a 2-Gbps secret-key rate over a 50-km fiber link, without any multiplexing, using available equipment, i.e., no new technology need be developed. FL-QKD achieves this extraordinary secret-key rate by virtue of its unprecedented secret-key efficiency, in bits per channel use, which exceeds those of state-of-the-art systems by two orders of magnitude.

  11. Feasible attack on detector-device-independent quantum key distribution.

    PubMed

    Wei, Kejin; Liu, Hongwei; Ma, Haiqiang; Yang, Xiuqing; Zhang, Yong; Sun, Yongmei; Xiao, Jinghua; Ji, Yuefeng

    2017-03-27

    Recently, to bridge the gap between security of Measurement-device-independent quantum key distribution (MDI-QKD) and a high key rate, a novel protocol, the so-called detector-device-independent QKD (DDI-QKD), has been independently proposed by several groups and has attracted great interest. A higher key rate is obtained, since a single photon bell state measurement (BSM) setup is applied to DDI-QKD. Subsequently, Qi has proposed two attacks for this protocol. However, the first attack, in which Bob's BSM setup is assumed to be completely a "black box", is easily prevented by using some additional monitoring devices or by specifically characterizing the BSM. The second attack, which combines the blinding attack and the detector wavelength-dependent efficiency, is not explicitly discussed, and its feasibility is not experimentally confirmed. Here, we show that the second attack is not technically viable because of an intrinsically wavelength-dependent property of a realistic beam splitter, which is an essential component in DDI-QKD. Moreover, we propose a feasible attack that combines a well-known attack-detector blinding attack with intrinsic imperfections of single-photon detectors. The experimental measurement and proof-of-principle test results confirm that our attack can allow Eve to get a copy of quantum keys without being detected and that it is feasible with current technology.

  12. Multi-client quantum key distribution using wavelength division multiplexing

    SciTech Connect

    Grice, Warren P; Bennink, Ryan S; Earl, Dennis Duncan; Evans, Philip G; Humble, Travis S; Pooser, Raphael C; Schaake, Jason; Williams, Brian P

    2011-01-01

    Quantum Key Distribution (QKD) exploits the rules of quantum mechanics to generate and securely distribute a random sequence of bits to two spatially separated clients. Typically a QKD system can support only a single pair of clients at a time, and so a separate quantum link is required for every pair of users. We overcome this limitation with the design and characterization of a multi-client entangled-photon QKD system with the capacity for up to 100 clients simultaneously. The time-bin entangled QKD system includes a broadband down-conversion source with two unique features that enable the multi-user capability. First, the photons are emitted across a very large portion of the telecom spectrum. Second, and more importantly, the photons are strongly correlated in their energy degree of freedom. Using standard wavelength division multiplexing (WDM) hardware, the photons can be routed to different parties on a quantum communication network, while the strong spectral correlations ensure that each client is linked only to the client receiving the conjugate wavelength. In this way, a single down-conversion source can support dozens of channels simultaneously--and to the extent that the WDM hardware can send different spectral channels to different clients, the system can support multiple client pairings. We will describe the design and characterization of the down-conversion source, as well as the client stations, which must be tunable across the emission spectrum.

  13. Establishing security of quantum key distribution without monitoring disturbance

    NASA Astrophysics Data System (ADS)

    Koashi, Masato

    2015-10-01

    In conventional quantum key distribution (QKD) protocols, the information leak to an eavesdropper is estimated through the basic principle of quantum mechanics dictated in the original version of Heisenberg's uncertainty principle. The amount of leaked information on a shared sifted key is bounded from above essentially by using information-disturbance trade-off relations, based on the amount of signal disturbance measured via randomly sampled or inserted probe signals. Here we discuss an entirely different avenue toward the private communication, which does not rely on the information disturbance trade-off relations and hence does not require a monitoring of signal disturbance. The independence of the amount of privacy amplification from that of disturbance tends to give it a high tolerance on the channel noises. The lifting of the burden of precise statistical estimation of disturbance leads to a favorable finite-key-size effect. A protocol based on the novel principle can be implemented by only using photon detectors and classical optics tools: a laser, a phase modulator, and an interferometer. The protocol resembles the differential-phase-shift QKD protocol in that both share a simple binary phase shift keying on a coherent train of weak pulses from a laser. The difference lies in the use of a variable-delay interferometer in the new protocol, which randomly changes the combination of pulse pairs to be superposed. This extra randomness has turned out to be enough to upper-bound the information extracted by the eavesdropper, regardless of how they have disturbed the quantum signal.

  14. The countermeasures against the blinding attack in quantum key distribution

    NASA Astrophysics Data System (ADS)

    Wang, Jindong; Wang, Hong; Qin, Xiaojuan; Wei, Zhengjun; Zhang, Zhiming

    2016-01-01

    It has been shown that the single photon detectors (SPDs) based on the avalanche photodiode (APD) can be blinded and controlled by the bright light and short trigger pulses. Eavesdropper can get the full information without causing additional quantum bit error rate. Hence, in order to guarantee the security of the quantum key distribution (QKD) systems, some countermeasures, by changing the characteristic of the SPD or monitoring the parameters of the detector, are presented by some research groups. In this paper, we provide a new and effective countermeasure against the blinding attack based on improving the optical scheme of the decoding unit in the QKD system rather than only considering the characteristic of the SPD. In our proposal we use a coupler with asymmetric splitting ratio to distinguish the detection characteristic of the SPD with blinding attack from that without blinding attack. The detailed analysis shows that the proposed scheme is feasible to defense the blinding attack.

  15. Trojan-horse attacks on quantum-key-distribution systems

    SciTech Connect

    Gisin, N.; Fasel, S.; Kraus, B.; Zbinden, H.; Ribordy, G.

    2006-02-15

    General Trojan-horse attacks on quantum-key-distribution systems, i.e., attacks on Alice or Bob's system via the quantum channel, are analyzed. We illustrate the power of such attacks with today's technology and conclude that all systems must implement active counter measures. In particular, all systems must include an auxiliary detector that monitors any incoming light. We show that such counter measures can be efficient, provided that enough additional privacy amplification is applied to the data. We present a practical way to reduce the maximal information gain that an adversary can gain using Trojan-horse attacks. This does reduce the security analysis of the two-way plug-and-play implementation to those of the standard one-way systems.

  16. Bell's inequality, random sequence, and quantum key distribution

    SciTech Connect

    Hwang, Won-Young

    2005-05-15

    The Ekert 1991 quantum key distribution (QKD) protocol appears to be secure regardless of whatever devices legitimate users adopt for the protocol, as long as the devices give a result that violates Bell's inequality. However, this is not the case if they ignore nondetection events because Eve can make use of the detection loophole, as Larrson showed [Quantum Inf. Comput. 2, 434 (2002)]. We show that even when legitimate users take into account nondetection events Eve can successfully eavesdrop if the QKD system has been appropriately designed by the manufacturer. A loophole utilized here is that of 'free choice' (or 'real randomness'). Local QKD devices with a pseudorandom sequence generator installed in them can apparently violate Bell's inequality.

  17. The Functional Theory of Counterfactual Thinking

    PubMed Central

    Epstude, Kai; Roese, Neal J.

    2008-01-01

    Counterfactuals are thoughts about alternatives to past events, that is, thoughts of what might have been. This article provides an updated account of the functional theory of counterfactual thinking, suggesting that such thoughts are best explained in terms of their role in behavior regulation and performance improvement. The article reviews a wide range of cognitive experiments indicating that counterfactual thoughts may influence behavior by either of two routes: a content-specific pathway (which involves specific informational effects on behavioral intentions, which then influence behavior) and a content-neutral pathway (which involves indirect effects via affect, mind-sets, or motivation). The functional theory is particularly useful in organizing recent findings regarding counterfactual thinking and mental health. The article concludes by considering the connections to other theoretical conceptions, especially recent advances in goal cognition. PMID:18453477

  18. Key-leakage evaluation of authentication in quantum key distribution with finite resources

    NASA Astrophysics Data System (ADS)

    Zhou, Chun; Bao, Wan-Su; Li, Hong-Wei; Wang, Yang; Fu, Xiang-Qun

    2014-04-01

    Partial information leakages of generation key undoubtedly influence the security of practical Quantum Key Distribution (QKD) system. In this paper, based on finite-key analysis and deep investigation on privacy amplification, we present a method for characterizing information leakages gained by adversary in each authentication round and therefore take the theory derived by Cederlöf and Larsson (IEEE Trans Inf Theory 54:1735-1741, 2008) into practical case. As the authentication key is fed from one round of generation keys to the next except the first round, by considering its security weakness due to information leakages and finite size effect, we further propose a universal formula for calculating the lifetime of initial authentication key used in QKD with finite resources. Numerical simulations indicate that our bound for estimating information leakages strictly characterizes the stability of practical QKD against information-leakage-based attacks, and our calculation formula in terms of lifetime can precisely evaluate the usage time of initial authentication key. Our work provides a practical solution for evaluating authentication security of QKD.

  19. Counterfactuals,

    DTIC Science & Technology

    1984-12-01

    pushed too far, however. Suppose that after a MYCIN run, we want to know why the machine asked that a certain clinical test be taken. The response is...assumptions corresponding to the observed misbehavior of the device. The conclusion (10) that one of the two exclusive-or gates must be faulty is in

  20. Cognitive neuroscience of human counterfactual reasoning

    PubMed Central

    Van Hoeck, Nicole; Watson, Patrick D.; Barbey, Aron K.

    2015-01-01

    Counterfactual reasoning is a hallmark of human thought, enabling the capacity to shift from perceiving the immediate environment to an alternative, imagined perspective. Mental representations of counterfactual possibilities (e.g., imagined past events or future outcomes not yet at hand) provide the basis for learning from past experience, enable planning and prediction, support creativity and insight, and give rise to emotions and social attributions (e.g., regret and blame). Yet remarkably little is known about the psychological and neural foundations of counterfactual reasoning. In this review, we survey recent findings from psychology and neuroscience indicating that counterfactual thought depends on an integrative network of systems for affective processing, mental simulation, and cognitive control. We review evidence to elucidate how these mechanisms are systematically altered through psychiatric illness and neurological disease. We propose that counterfactual thinking depends on the coordination of multiple information processing systems that together enable adaptive behavior and goal-directed decision making and make recommendations for the study of counterfactual inference in health, aging, and disease. PMID:26257633

  1. Cognitive neuroscience of human counterfactual reasoning.

    PubMed

    Van Hoeck, Nicole; Watson, Patrick D; Barbey, Aron K

    2015-01-01

    Counterfactual reasoning is a hallmark of human thought, enabling the capacity to shift from perceiving the immediate environment to an alternative, imagined perspective. Mental representations of counterfactual possibilities (e.g., imagined past events or future outcomes not yet at hand) provide the basis for learning from past experience, enable planning and prediction, support creativity and insight, and give rise to emotions and social attributions (e.g., regret and blame). Yet remarkably little is known about the psychological and neural foundations of counterfactual reasoning. In this review, we survey recent findings from psychology and neuroscience indicating that counterfactual thought depends on an integrative network of systems for affective processing, mental simulation, and cognitive control. We review evidence to elucidate how these mechanisms are systematically altered through psychiatric illness and neurological disease. We propose that counterfactual thinking depends on the coordination of multiple information processing systems that together enable adaptive behavior and goal-directed decision making and make recommendations for the study of counterfactual inference in health, aging, and disease.

  2. Verifiable Quantum ( k, n)-threshold Secret Key Sharing

    NASA Astrophysics Data System (ADS)

    Yang, Yu-Guang; Teng, Yi-Wei; Chai, Hai-Ping; Wen, Qiao-Yan

    2011-03-01

    Based on Lagrange interpolation formula and the post-verification mechanism, we show how to construct a verifiable quantum ( k, n) threshold secret key sharing scheme. Compared with the previous secret sharing protocols, ours has the merits: (i) it can resist the fraud of the dealer who generates and distributes fake shares among the participants during the secret distribution phase; Most importantly, (ii) It can check the cheating of the dishonest participant who provides a false share during the secret reconstruction phase such that the authorized group cannot recover the correct secret.

  3. Numerical analysis of decoy state quantum key distribution protocols

    SciTech Connect

    Harrington, Jim W; Rice, Patrick R

    2008-01-01

    Decoy state protocols are a useful tool for many quantum key distribution systems implemented with weak coherent pulses, allowing significantly better secret bit rates and longer maximum distances. In this paper we present a method to numerically find optimal three-level protocols, and we examine how the secret bit rate and the optimized parameters are dependent on various system properties, such as session length, transmission loss, and visibility. Additionally, we show how to modify the decoy state analysis to handle partially distinguishable decoy states as well as uncertainty in the prepared intensities.

  4. Quantum Key Distribution with Multi Letter Continuous Variable Alphabets

    NASA Astrophysics Data System (ADS)

    Sych, Denis; Leuchs, Gerd

    2009-04-01

    We present a new protocol for continuous variable quantum key distribution. The novelty of the protocol is a multi letter alphabet represented by coherent states of light with a fixed amplitude and variable phase. Information is encoded in the phase of a coherent state which can be chosen from a regular discrete set consisting, however, of an arbitrary number of letters. We evaluate the security of the protocol against the beam splitting attack. As a result we show the proposed protocol has advantages over the standard two letter coherent state protocol, especially in the case when losses in the communication channel are low.

  5. Self-referenced continuous-variable quantum key distribution

    DOEpatents

    Soh, Daniel B. S.; Sarovar, Mohan; Camacho, Ryan

    2017-01-24

    Various technologies for continuous-variable quantum key distribution without transmitting a transmitter's local oscillator are described herein. A receiver on an optical transmission channel uses an oscillator signal generated by a light source at the receiver's location to perform interferometric detection on received signals. An optical reference pulse is sent by the transmitter on the transmission channel and the receiver computes a phase offset of the transmission based on quadrature measurements of the reference pulse. The receiver can then compensate for the phase offset between the transmitter's reference and the receiver's reference when measuring quadratures of received data pulses.

  6. Security of quantum key distribution with multiphoton components

    PubMed Central

    Yin, Hua-Lei; Fu, Yao; Mao, Yingqiu; Chen, Zeng-Bing

    2016-01-01

    Most qubit-based quantum key distribution (QKD) protocols extract the secure key merely from single-photon component of the attenuated lasers. However, with the Scarani-Acin-Ribordy-Gisin 2004 (SARG04) QKD protocol, the unconditionally secure key can be extracted from the two-photon component by modifying the classical post-processing procedure in the BB84 protocol. Employing the merits of SARG04 QKD protocol and six-state preparation, one can extract secure key from the components of single photon up to four photons. In this paper, we provide the exact relations between the secure key rate and the bit error rate in a six-state SARG04 protocol with single-photon, two-photon, three-photon, and four-photon sources. By restricting the mutual information between the phase error and bit error, we obtain a higher secure bit error rate threshold of the multiphoton components than previous works. Besides, we compare the performances of the six-state SARG04 with other prepare-and-measure QKD protocols using decoy states. PMID:27383014

  7. Improved key-rate bounds for practical decoy-state quantum-key-distribution systems

    NASA Astrophysics Data System (ADS)

    Zhang, Zhen; Zhao, Qi; Razavi, Mohsen; Ma, Xiongfeng

    2017-01-01

    The decoy-state scheme is the most widely implemented quantum-key-distribution protocol in practice. In order to account for the finite-size key effects on the achievable secret key generation rate, a rigorous statistical fluctuation analysis is required. Originally, a heuristic Gaussian-approximation technique was used for this purpose, which, despite its analytical convenience, was not sufficiently rigorous. The fluctuation analysis has recently been made rigorous by using the Chernoff bound. There is a considerable gap, however, between the key-rate bounds obtained from these techniques and that obtained from the Gaussian assumption. Here we develop a tighter bound for the decoy-state method, which yields a smaller failure probability. This improvement results in a higher key rate and increases the maximum distance over which secure key exchange is possible. By optimizing the system parameters, our simulation results show that our method almost closes the gap between the two previously proposed techniques and achieves a performance similar to that of conventional Gaussian approximations.

  8. Simultaneous classical communication and quantum key distribution using continuous variables*

    NASA Astrophysics Data System (ADS)

    Qi, Bing

    2016-10-01

    Presently, classical optical communication systems employing strong laser pulses and quantum key distribution (QKD) systems working at single-photon levels are very different communication modalities. Dedicated devices are commonly required to implement QKD. In this paper, we propose a scheme which allows classical communication and QKD to be implemented simultaneously using the same communication infrastructure. More specially, we propose a coherent communication scheme where both the bits for classical communication and the Gaussian distributed random numbers for QKD are encoded on the same weak coherent pulse and decoded by the same coherent receiver. Simulation results based on practical system parameters show that both deterministic classical communication with a bit error rate of 10-9 and secure key distribution could be achieved over tens of kilometers of single-mode fibers. It is conceivable that in the future coherent optical communication network, QKD will be operated in the background of classical communication at a minimal cost.

  9. Decoy-state quantum key distribution with biased basis choice

    PubMed Central

    Wei, Zhengchao; Wang, Weilong; Zhang, Zhen; Gao, Ming; Ma, Zhi; Ma, Xiongfeng

    2013-01-01

    We propose a quantum key distribution scheme that combines a biased basis choice with the decoy-state method. In this scheme, Alice sends all signal states in the Z basis and decoy states in the X and Z basis with certain probabilities, and Bob measures received pulses with optimal basis choice. This scheme simplifies the system and reduces the random number consumption. From the simulation result taking into account of statistical fluctuations, we find that in a typical experimental setup, the proposed scheme can increase the key rate by at least 45% comparing to the standard decoy-state scheme. In the postprocessing, we also apply a rigorous method to upper bound the phase error rate of the single-photon components of signal states. PMID:23948999

  10. Simultaneous classical communication and quantum key distribution using continuous variables

    SciTech Connect

    Qi, Bing

    2016-10-26

    Currently, classical optical communication systems employing strong laser pulses and quantum key distribution (QKD) systems working at single-photon levels are very different communication modalities. Dedicated devices are commonly required to implement QKD. In this paper, we propose a scheme which allows classical communication and QKD to be implemented simultaneously using the same communication infrastructure. More specially, we propose a coherent communication scheme where both the bits for classical communication and the Gaussian distributed random numbers for QKD are encoded on the same weak coherent pulse and decoded by the same coherent receiver. Simulation results based on practical system parameters show that both deterministic classical communication with a bit error rate of 10–9 and secure key distribution could be achieved over tens of kilometers of single-mode fibers. It is conceivable that in the future coherent optical communication network, QKD will be operated in the background of classical communication at a minimal cost.

  11. Experimental multiplexing of quantum key distribution with classical optical communication

    SciTech Connect

    Wang, Liu-Jun; Chen, Luo-Kan; Ju, Lei; Xu, Mu-Lan; Zhao, Yong; Chen, Kai; Chen, Zeng-Bing; Chen, Teng-Yun Pan, Jian-Wei

    2015-02-23

    We demonstrate the realization of quantum key distribution (QKD) when combined with classical optical communication, and synchronous signals within a single optical fiber. In the experiment, the classical communication sources use Fabry-Pérot (FP) lasers, which are implemented extensively in optical access networks. To perform QKD, multistage band-stop filtering techniques are developed, and a wavelength-division multiplexing scheme is designed for the multi-longitudinal-mode FP lasers. We have managed to maintain sufficient isolation among the quantum channel, the synchronous channel and the classical channels to guarantee good QKD performance. Finally, the quantum bit error rate remains below a level of 2% across the entire practical application range. The proposed multiplexing scheme can ensure low classical light loss, and enables QKD over fiber lengths of up to 45 km simultaneously when the fibers are populated with bidirectional FP laser communications. Our demonstration paves the way for application of QKD to current optical access networks, where FP lasers are widely used by the end users.

  12. Experimental multiplexing of quantum key distribution with classical optical communication

    NASA Astrophysics Data System (ADS)

    Wang, Liu-Jun; Chen, Luo-Kan; Ju, Lei; Xu, Mu-Lan; Zhao, Yong; Chen, Kai; Chen, Zeng-Bing; Chen, Teng-Yun; Pan, Jian-Wei

    2015-02-01

    We demonstrate the realization of quantum key distribution (QKD) when combined with classical optical communication, and synchronous signals within a single optical fiber. In the experiment, the classical communication sources use Fabry-Pérot (FP) lasers, which are implemented extensively in optical access networks. To perform QKD, multistage band-stop filtering techniques are developed, and a wavelength-division multiplexing scheme is designed for the multi-longitudinal-mode FP lasers. We have managed to maintain sufficient isolation among the quantum channel, the synchronous channel and the classical channels to guarantee good QKD performance. Finally, the quantum bit error rate remains below a level of 2% across the entire practical application range. The proposed multiplexing scheme can ensure low classical light loss, and enables QKD over fiber lengths of up to 45 km simultaneously when the fibers are populated with bidirectional FP laser communications. Our demonstration paves the way for application of QKD to current optical access networks, where FP lasers are widely used by the end users.

  13. Eigenchannel decomposition for continuous-variable quantum key distribution

    NASA Astrophysics Data System (ADS)

    Gyongyosi, L.; Imre, S.

    2015-03-01

    We develop a singular layer transmission model for continuous-variable quantum key distribution (CVQKD). In CVQKD, the transmit information is carried by continuous-variable (CV) quantum states, particularly by Gaussian random distributed position and momentum quadratures. The reliable transmission of the quadrature components over a noisy link is a cornerstone of CVQKD protocols. The proposed singular layer uses the singular value decomposition of the Gaussian quantum channel, which yields an additional degree of freedom for the phase space transmission. This additional degree of freedom can further be exploited in a multiple-access scenario. The singular layer defines the eigenchannels of the Gaussian physical link, which can be used for the simultaneous reliable transmission of multiple user data streams. We demonstrate the results through the adaptive multicarrier quadrature division-multiuser quadrature allocation (AMQD-MQA) CVQKD multiple-access scheme. We define the singular model of AMQD-MQA and characterize the properties of the eigenchannel interference. The singular layer transmission provides improved simultaneous transmission rates for the users with unconditional security in a multiple-access scenario, particularly in crucial low signal-to-noise ratio regimes.

  14. Decoy-state quantum key distribution with a leaky source

    NASA Astrophysics Data System (ADS)

    Tamaki, Kiyoshi; Curty, Marcos; Lucamarini, Marco

    2016-06-01

    In recent years, there has been a great effort to prove the security of quantum key distribution (QKD) with a minimum number of assumptions. Besides its intrinsic theoretical interest, this would allow for larger tolerance against device imperfections in the actual implementations. However, even in this device-independent scenario, one assumption seems unavoidable, that is, the presence of a protected space devoid of any unwanted information leakage in which the legitimate parties can privately generate, process and store their classical data. In this paper we relax this unrealistic and hardly feasible assumption and introduce a general formalism to tackle the information leakage problem in most of existing QKD systems. More specifically, we prove the security of optical QKD systems using phase and intensity modulators in their transmitters, which leak the setting information in an arbitrary manner. We apply our security proof to cases of practical interest and show key rates similar to those obtained in a perfectly shielded environment. Our work constitutes a fundamental step forward in guaranteeing implementation security of quantum communication systems.

  15. FPGA based digital phase-coding quantum key distribution system

    NASA Astrophysics Data System (ADS)

    Lu, XiaoMing; Zhang, LiJun; Wang, YongGang; Chen, Wei; Huang, DaJun; Li, Deng; Wang, Shuang; He, DeYong; Yin, ZhenQiang; Zhou, Yu; Hui, Cong; Han, ZhengFu

    2015-12-01

    Quantum key distribution (QKD) is a technology with the potential capability to achieve information-theoretic security. Phasecoding is an important approach to develop practical QKD systems in fiber channel. In order to improve the phase-coding modulation rate, we proposed a new digital-modulation method in this paper and constructed a compact and robust prototype of QKD system using currently available components in our lab to demonstrate the effectiveness of the method. The system was deployed in laboratory environment over a 50 km fiber and continuously operated during 87 h without manual interaction. The quantum bit error rate (QBER) of the system was stable with an average value of 3.22% and the secure key generation rate is 8.91 kbps. Although the modulation rate of the photon in the demo system was only 200 MHz, which was limited by the Faraday-Michelson interferometer (FMI) structure, the proposed method and the field programmable gate array (FPGA) based electronics scheme have a great potential for high speed QKD systems with Giga-bits/second modulation rate.

  16. Device-independent quantum key distribution based on measurement inputs

    NASA Astrophysics Data System (ADS)

    Rahaman, Ramij; Parker, Matthew G.; Mironowicz, Piotr; Pawłowski, Marcin

    2015-12-01

    We provide an analysis of a family of device-independent quantum key distribution (QKD) protocols that has the following features. (a) The bits used for the secret key do not come from the results of the measurements on an entangled state but from the choices of settings. (b) Instead of a single security parameter (a violation of some Bell inequality) a set of them is used to estimate the level of trust in the secrecy of the key. The main advantage of these protocols is a smaller vulnerability to imperfect random number generators made possible by feature (a). We prove the security and the robustness of such protocols. We show that using our method it is possible to construct a QKD protocol which retains its security even if the source of randomness used by communicating parties is strongly biased. As a proof of principle, an explicit example of a protocol based on the Hardy's paradox is presented. Moreover, in the noiseless case, the protocol is secure in a natural way against any type of memory attack, and thus allows one to reuse the device in subsequent rounds. We also analyze the robustness of the protocol using semidefinite programming methods. Finally, we present a postprocessing method, and observe a paradoxical property that rejecting some random part of the private data can increase the key rate of the protocol.

  17. Finite-key analysis for time-energy high-dimensional quantum key distribution

    NASA Astrophysics Data System (ADS)

    Niu, Murphy Yuezhen; Xu, Feihu; Shapiro, Jeffrey H.; Furrer, Fabian

    2016-11-01

    Time-energy high-dimensional quantum key distribution (HD-QKD) leverages the high-dimensional nature of time-energy entangled biphotons and the loss tolerance of single-photon detection to achieve long-distance key distribution with high photon information efficiency. To date, the general-attack security of HD-QKD has only been proven in the asymptotic regime, while HD-QKD's finite-key security has only been established for a limited set of attacks. Here we fill this gap by providing a rigorous HD-QKD security proof for general attacks in the finite-key regime. Our proof relies on an entropic uncertainty relation that we derive for time and conjugate-time measurements that use dispersive optics, and our analysis includes an efficient decoy-state protocol in its parameter estimation. We present numerically evaluated secret-key rates illustrating the feasibility of secure and composable HD-QKD over metropolitan-area distances when the system is subjected to the most powerful eavesdropping attack.

  18. Architecture of multicast centralized key management scheme using quantum key distribution and classical symmetric encryption

    NASA Astrophysics Data System (ADS)

    Metwaly, A. F.; Rashad, M. Z.; Omara, F. A.; Megahed, A. A.

    2014-06-01

    Multicasting refers to the transmission of a message or information from one sender to multiple receivers simultaneously. Although encryption algorithms can be used to secure transmitted messages among group members, still there are many security aspects for designing a secured multicast cryptosystem. The most important aspects of Multicasting are key generation and management. The researchers have proposed several approaches for solving problems of multicast key distribution and management. In this paper, a secure key generation and distribution solution has been proposed for a single host sending to two or more (N) receivers using centralized Quantum Multicast Key Distribution Centre "QMKDC" and classical symmetric encryption. The proposed scheme uses symmetric classical algorithms for encryption and decryption transmitted messages among multicast group members, but the generated keys which are used for authentication, encryption and decryption also play an important role for designing a secured multicast cryptosystem come from QKD protocols. Authentication verified using EPR entangled Photons and controlled-NOT gate. Multiple requests for initialization as well for transmitting sensitive information handled through priority and sensitivity levels. Multiple members' communication is achieved with full or partial support of QMKDC.

  19. Quantum hacking of a continuous-variable quantum-key-distribution system using a wavelength attack

    NASA Astrophysics Data System (ADS)

    Huang, Jing-Zheng; Weedbrook, Christian; Yin, Zhen-Qiang; Wang, Shuang; Li, Hong-Wei; Chen, Wei; Guo, Guang-Can; Han, Zheng-Fu

    2013-06-01

    The security proofs of continuous-variable quantum key distribution are based on the assumptions that the eavesdropper can neither act on the local oscillator nor control Bob's beam splitter. These assumptions may be invalid in practice due to potential imperfections in the implementations of such protocols. In this paper, we consider the problem of transmitting the local oscillator in a public channel and propose a wavelength attack which allows the eavesdropper to control the intensity transmission of Bob's beam splitter by switching the wavelength of the input light. Specifically we target continuous-variable quantum key distribution systems that use the heterodyne detection protocol using either direct or reverse reconciliation. Our attack is proved to be feasible and renders all of the final keys shared between the legitimate parties insecure, even if they have monitored the intensity of the local oscillator. To prevent our attack on commercial systems, a simple wavelength filter should be randomly added before performing monitoring detection.

  20. Sifting attacks in finite-size quantum key distribution

    NASA Astrophysics Data System (ADS)

    Pfister, Corsin; Lütkenhaus, Norbert; Wehner, Stephanie; Coles, Patrick J.

    2016-05-01

    A central assumption in quantum key distribution (QKD) is that Eve has no knowledge about which rounds will be used for parameter estimation or key distillation. Here we show that this assumption is violated for iterative sifting, a sifting procedure that has been employed in some (but not all) of the recently suggested QKD protocols in order to increase their efficiency. We show that iterative sifting leads to two security issues: (1) some rounds are more likely to be key rounds than others, (2) the public communication of past measurement choices changes this bias round by round. We analyze these two previously unnoticed problems, present eavesdropping strategies that exploit them, and find that the two problems are independent. We discuss some sifting protocols in the literature that are immune to these problems. While some of these would be inefficient replacements for iterative sifting, we find that the sifting subroutine of an asymptotically secure protocol suggested by Lo et al (2005 J. Cryptol. 18 133-65), which we call LCA sifting, has an efficiency on par with that of iterative sifting. One of our main results is to show that LCA sifting can be adapted to achieve secure sifting in the finite-key regime. More precisely, we combine LCA sifting with a certain parameter estimation protocol, and we prove the finite-key security of this combination. Hence we propose that LCA sifting should replace iterative sifting in future QKD implementations. More generally, we present two formal criteria for a sifting protocol that guarantee its finite-key security. Our criteria may guide the design of future protocols and inspire a more rigorous QKD analysis, which has neglected sifting-related attacks so far.

  1. Reinforcement learning and counterfactual reasoning explain adaptive behavior in a changing environment.

    PubMed

    Zhang, Yunfeng; Paik, Jaehyon; Pirolli, Peter

    2015-04-01

    Animals routinely adapt to changes in the environment in order to survive. Though reinforcement learning may play a role in such adaptation, it is not clear that it is the only mechanism involved, as it is not well suited to producing rapid, relatively immediate changes in strategies in response to environmental changes. This research proposes that counterfactual reasoning might be an additional mechanism that facilitates change detection. An experiment is conducted in which a task state changes over time and the participants had to detect the changes in order to perform well and gain monetary rewards. A cognitive model is constructed that incorporates reinforcement learning with counterfactual reasoning to help quickly adjust the utility of task strategies in response to changes. The results show that the model can accurately explain human data and that counterfactual reasoning is key to reproducing the various effects observed in this change detection paradigm.

  2. The SECOQC quantum key distribution network in Vienna

    NASA Astrophysics Data System (ADS)

    Peev, M.; Pacher, C.; Alléaume, R.; Barreiro, C.; Bouda, J.; Boxleitner, W.; Debuisschert, T.; Diamanti, E.; Dianati, M.; Dynes, J. F.; Fasel, S.; Fossier, S.; Fürst, M.; Gautier, J.-D.; Gay, O.; Gisin, N.; Grangier, P.; Happe, A.; Hasani, Y.; Hentschel, M.; Hübel, H.; Humer, G.; Länger, T.; Legré, M.; Lieger, R.; Lodewyck, J.; Lorünser, T.; Lütkenhaus, N.; Marhold, A.; Matyus, T.; Maurhart, O.; Monat, L.; Nauerth, S.; Page, J.-B.; Poppe, A.; Querasser, E.; Ribordy, G.; Robyr, S.; Salvail, L.; Sharpe, A. W.; Shields, A. J.; Stucki, D.; Suda, M.; Tamas, C.; Themel, T.; Thew, R. T.; Thoma, Y.; Treiber, A.; Trinkler, P.; Tualle-Brouri, R.; Vannel, F.; Walenta, N.; Weier, H.; Weinfurter, H.; Wimberger, I.; Yuan, Z. L.; Zbinden, H.; Zeilinger, A.

    2009-07-01

    In this paper, we present the quantum key distribution (QKD) network designed and implemented by the European project SEcure COmmunication based on Quantum Cryptography (SECOQC) (2004-2008), unifying the efforts of 41 research and industrial organizations. The paper summarizes the SECOQC approach to QKD networks with a focus on the trusted repeater paradigm. It discusses the architecture and functionality of the SECOQC trusted repeater prototype, which has been put into operation in Vienna in 2008 and publicly demonstrated in the framework of a SECOQC QKD conference held from October 8 to 10, 2008. The demonstration involved one-time pad encrypted telephone communication, a secure (AES encryption protected) video-conference with all deployed nodes and a number of rerouting experiments, highlighting basic mechanisms of the SECOQC network functionality. The paper gives an overview of the eight point-to-point network links in the prototype and their underlying technology: three plug and play systems by id Quantique, a one way weak pulse system from Toshiba Research in the UK, a coherent one-way system by GAP Optique with the participation of id Quantique and the AIT Austrian Institute of Technology (formerly ARCAustrian Research Centers GmbH—ARC is now operating under the new name AIT Austrian Institute of Technology GmbH following a restructuring initiative.), an entangled photons system by the University of Vienna and the AIT, a continuous-variables system by Centre National de la Recherche Scientifique (CNRS) and THALES Research and Technology with the participation of Université Libre de Bruxelles, and a free space link by the Ludwig Maximillians University in Munich connecting two nodes situated in adjacent buildings (line of sight 80 m). The average link length is between 20 and 30 km, the longest link being 83 km. The paper presents the architecture and functionality of the principal networking agent—the SECOQC node module, which enables the authentic

  3. Finite-key security analysis of quantum key distribution with imperfect light sources

    DOE PAGES

    Mizutani, Akihiro; Curty, Marcos; Lim, Charles Ci Wen; ...

    2015-09-09

    In recent years, the gap between theory and practice in quantum key distribution (QKD) has been significantly narrowed, particularly for QKD systems with arbitrarily flawed optical receivers. The status for QKD systems with imperfect light sources is however less satisfactory, in the sense that the resulting secure key rates are often overly dependent on the quality of state preparation. This is especially the case when the channel loss is high. Very recently, to overcome this limitation, Tamaki et al proposed a QKD protocol based on the so-called 'rejected data analysis', and showed that its security in the limit of infinitelymore » long keys is almost independent of any encoding flaw in the qubit space, being this protocol compatible with the decoy state method. Here, as a step towards practical QKD, we show that a similar conclusion is reached in the finite-key regime, even when the intensity of the light source is unstable. More concretely, we derive security bounds for a wide class of realistic light sources and show that the bounds are also efficient in the presence of high channel loss. Our results strongly suggest the feasibility of long distance provably secure communication with imperfect light sources.« less

  4. Finite-key security analysis of quantum key distribution with imperfect light sources

    SciTech Connect

    Mizutani, Akihiro; Curty, Marcos; Lim, Charles Ci Wen; Imoto, Nobuyuki; Tamaki, Kiyoshi

    2015-09-09

    In recent years, the gap between theory and practice in quantum key distribution (QKD) has been significantly narrowed, particularly for QKD systems with arbitrarily flawed optical receivers. The status for QKD systems with imperfect light sources is however less satisfactory, in the sense that the resulting secure key rates are often overly dependent on the quality of state preparation. This is especially the case when the channel loss is high. Very recently, to overcome this limitation, Tamaki et al proposed a QKD protocol based on the so-called 'rejected data analysis', and showed that its security in the limit of infinitely long keys is almost independent of any encoding flaw in the qubit space, being this protocol compatible with the decoy state method. Here, as a step towards practical QKD, we show that a similar conclusion is reached in the finite-key regime, even when the intensity of the light source is unstable. More concretely, we derive security bounds for a wide class of realistic light sources and show that the bounds are also efficient in the presence of high channel loss. Our results strongly suggest the feasibility of long distance provably secure communication with imperfect light sources.

  5. Counterfactual reasoning: From childhood to adulthood

    PubMed Central

    Rafetseder, Eva; Schwitalla, Maria; Perner, Josef

    2013-01-01

    The objective of this study was to describe the developmental progression of counterfactual reasoning from childhood to adulthood. In contrast to the traditional view, it was recently reported by Rafetseder and colleagues that even a majority of 6-year-old children do not engage in counterfactual reasoning when asked counterfactual questions (Child Development, 2010, Vol. 81, pp. 376–389). By continuing to use the same method, the main result of the current Study 1 was that performance of the 9- to 11-year-olds was comparable to that of the 6-year-olds, whereas the 12- to 14-year-olds approximated adult performance. Study 2, using an intuitively simpler task based on Harris and colleagues (Cognition, 1996, Vol. 61, pp. 233–259), resulted in a similar conclusion, specifically that the ability to apply counterfactual reasoning is not fully developed in all children before 12 years of age. We conclude that children who failed our tasks seem to lack an understanding of what needs to be changed (events that are causally dependent on the counterfactual assumption) and what needs to be left unchanged and so needs to be kept as it actually happened. Alternative explanations, particularly executive functioning, are discussed in detail. PMID:23219156

  6. Counterfactual Thinking in the History of Psychology Course

    ERIC Educational Resources Information Center

    Carroll, David W.

    2013-01-01

    History of psychology students wrote essays about historical figures and counterfactual events. A linguistic analysis of the essays revealed that counterfactual assignments included more auxiliary verbs and more references to tentativeness and the future. More important, scores on the counterfactual assignments but not the historical figure…

  7. Free-space quantum key distribution at night

    SciTech Connect

    Buttler, W.T.; Hughes, R.J.; Kwiat, P.G.; Lamoreaux, S.K.; Luther, G.G.; Morgan, G.L.; Nordholt, J.E.; Peterson, C.G.; Simmons, C.M.

    1998-09-01

    An experimental free-space quantum key distribution (QKD) system has been tested over an outdoor optical path of {approximately} 1 km under nighttime conditions at Los Alamos National Laboratory. This system employs the Bennett 92 protocol; in this paper, the authors give a brief overview of this protocol, and describe the experimental implementation of it. An analysis of the system efficiency is presented, as well as a description of the error detection protocol which employs a two-dimensional parity check scheme. Finally, the susceptibility of this system to eavesdropping by various techniques is determined, and the effectiveness of privacy amplification procedures is discussed. The conclusions are that free-space QKD is both effective and secure; possible applications include the rekeying of satellites in low earth orbit.

  8. Quantum hacking: Experimental demonstration of time-shift attack against practical quantum-key-distribution systems

    NASA Astrophysics Data System (ADS)

    Zhao, Yi; Fung, Chi-Hang Fred; Qi, Bing; Chen, Christine; Lo, Hoi-Kwong

    2008-10-01

    Quantum-key-distribution (QKD) systems can send quantum signals over more than 100km standard optical fiber and are widely believed to be secure. Here, we show experimentally a technologically feasible attack—namely, the time-shift attack—against a commercial QKD system. Our result shows that, contrary to popular belief, an eavesdropper, Eve, has a non-negligible probability (˜4%) to break the security of the system. Eve’s success is due to the well-known detection efficiency loophole in the experimental testing of Bell’s inequalities. Therefore, the detection efficiency loophole plays a key role not only in fundamental physics, but also in technological applications such as QKD systems.

  9. If the real world were irrelevant, so to speak: The role of propositional truth-value in counterfactual sentence comprehension.

    PubMed

    Nieuwland, Mante S; Martin, Andrea E

    2012-01-01

    Propositional truth-value can be a defining feature of a sentence's relevance to the unfolding discourse, and establishing propositional truth-value in context can be key to successful interpretation. In the current study, we investigate its role in the comprehension of counterfactual conditionals, which describe imaginary consequences of hypothetical events, and are thought to require keeping in mind both what is true and what is false. Pre-stored real-world knowledge may therefore intrude upon and delay counterfactual comprehension, which is predicted by some accounts of discourse comprehension, and has been observed during online comprehension. The impact of propositional truth-value may thus be delayed in counterfactual conditionals, as also claimed for sentences containing other types of logical operators (e.g., negation, scalar quantifiers). In an event-related potential (ERP) experiment, we investigated the impact of propositional truth-value when described consequences are both true and predictable given the counterfactual premise. False words elicited larger N400 ERPs than true words, in negated counterfactual sentences (e.g., "If N.A.S.A. had not developed its Apollo Project, the first country to land on the moon would have been Russia/America") and real-world sentences (e.g., "Because N.A.S.A. developed its Apollo Project, the first country to land on the moon was America/Russia") alike. These indistinguishable N400 effects of propositional truth-value, elicited by opposite word pairs, argue against disruptions by real-world knowledge during counterfactual comprehension, and suggest that incoming words are mapped onto the counterfactual context without any delay. Thus, provided a sufficiently constraining context, propositional truth-value rapidly impacts ongoing semantic processing, be the proposition factual or counterfactual.

  10. Finite-size key in the Bennett 1992 quantum-key-distribution protocol for Rényi entropies

    NASA Astrophysics Data System (ADS)

    Mafu, Mhlambululi; Garapo, Kevin; Petruccione, Francesco

    2013-12-01

    A realistic quantum-key-distribution protocol necessarily runs with finite resources. Usually, security proofs for existing quantum key distribution are asymptotic in the sense that certain parameters are exceedingly large compared to practical realistic values. In this paper, we derive bounds on the secret key rates for the Bennett 1992 protocol, which includes a preprocessing step. The derivation for a finite-size key is expressed as an optimization problem by using results from the uncertainty relations and the smooth Rényi entropies.

  11. Simultaneous classical communication and quantum key distribution using continuous variables

    DOE PAGES

    Qi, Bing

    2016-10-26

    Currently, classical optical communication systems employing strong laser pulses and quantum key distribution (QKD) systems working at single-photon levels are very different communication modalities. Dedicated devices are commonly required to implement QKD. In this paper, we propose a scheme which allows classical communication and QKD to be implemented simultaneously using the same communication infrastructure. More specially, we propose a coherent communication scheme where both the bits for classical communication and the Gaussian distributed random numbers for QKD are encoded on the same weak coherent pulse and decoded by the same coherent receiver. Simulation results based on practical system parameters showmore » that both deterministic classical communication with a bit error rate of 10–9 and secure key distribution could be achieved over tens of kilometers of single-mode fibers. It is conceivable that in the future coherent optical communication network, QKD will be operated in the background of classical communication at a minimal cost.« less

  12. A quantum key distribution system for optical fiber networks

    NASA Astrophysics Data System (ADS)

    Hughes, Richard J.; Chapuran, Thomas E.; Dallmann, Nicholas; Hiskett, Philip A.; McCabe, Kevin P.; Montano, Paul M.; Nordholt, Jane E.; Peterson, Charles G.; Runser, Robert J.; Sedillo, Robert; Tyagi, Kush; Wipf, Christopher C.

    2005-08-01

    A novel, user-friendly quantum key distribution (QKD) system operating at a wavelength of 1550nm and at a clock rate of 10MHz was constructed to explore the compatibility of this emerging technology with the optical fiber network environment. Custom circuit boards providing the low-level control and sensing functions for both the transmitter and receiver were developed, allowing software-based system reconfiguration via USB interface to personal computers. The computer control allowed the user to change operating parameters such as detector bias voltages and pulse delays and also allowed for self-tuning of the system. Epitaxx avalanche photodiodes, operated in Geiger mode, were used to detect the single photons. A complete QKD protocol stack incorporating the "sifting", reconciliation, privacy amplification, authentication and key confirmation functions was implemented in software. The system was tested over twenty five kilometers of dark underground fiber, producing 18.6 million sifted bits, with a sifted bit error rate of 4.9% at an average number of photons per pulse of 0.2, during a continuous 12-hour period of self-sustaining operation: a small portion of the secret bits distilled from each session's sifted bits were used to authenticate the next session. A total of 6.8 million shared secret bits were produced.

  13. Symptomatic Remission and Counterfactual Reasoning in Schizophrenia

    PubMed Central

    Albacete, Auria; Contreras, Fernando; Bosque, Clara; Gilabert, Ester; Albiach, Ángela; Menchón, José M.

    2017-01-01

    Counterfactual thinking (CFT) is a type of conditional reasoning involving mental representations of alternatives to past factual events that previous preliminary research has suggested to be impaired in schizophrenia. However, despite the potential impact of these deficits on the functional outcome of these patients, studies examining the role of CFT in this disorder are still few in number. The present study aimed to extent previous results by evaluating CFT in the largest sample to date of schizophrenia patients in symptomatic remission and healthy controls. The relationship with symptomatology, illness duration, and sociodemographic characteristics was also explored. Methods: Seventy-eight schizophrenia patients and 84 healthy controls completed a series of tests that examined the generation of counterfactual thoughts, the influence of the “causal order effect,” and the ability to counterfactually derive inferences by using de Counterfactual Inference Test. Results: Compared with controls, patients generated fewer counterfactual thoughts when faced with a simulated scenario. This deficit was negatively related to scores on all dimensions of the Positive and Negative Syndrome Scale-PANNS, as well as to longer illness duration. The results also showed that schizophrenia patients deviated significantly from the normative pattern when generating inferences from CFT. Conclusions: These findings reveal CFT impairment to be present in schizophrenia even when patients are in symptomatic remission. However, symptomatology and illness duration may have a negative influence on these patients' ability to generate counterfactual thoughts. The results might support the relevance of targeting CFT in future treatment approaches, although further research is needed to better describe the relationship between CFT and both symptomatology and functional outcome. PMID:28111561

  14. Symptomatic Remission and Counterfactual Reasoning in Schizophrenia.

    PubMed

    Albacete, Auria; Contreras, Fernando; Bosque, Clara; Gilabert, Ester; Albiach, Ángela; Menchón, José M

    2016-01-01

    Counterfactual thinking (CFT) is a type of conditional reasoning involving mental representations of alternatives to past factual events that previous preliminary research has suggested to be impaired in schizophrenia. However, despite the potential impact of these deficits on the functional outcome of these patients, studies examining the role of CFT in this disorder are still few in number. The present study aimed to extent previous results by evaluating CFT in the largest sample to date of schizophrenia patients in symptomatic remission and healthy controls. The relationship with symptomatology, illness duration, and sociodemographic characteristics was also explored. Methods: Seventy-eight schizophrenia patients and 84 healthy controls completed a series of tests that examined the generation of counterfactual thoughts, the influence of the "causal order effect," and the ability to counterfactually derive inferences by using de Counterfactual Inference Test. Results: Compared with controls, patients generated fewer counterfactual thoughts when faced with a simulated scenario. This deficit was negatively related to scores on all dimensions of the Positive and Negative Syndrome Scale-PANNS, as well as to longer illness duration. The results also showed that schizophrenia patients deviated significantly from the normative pattern when generating inferences from CFT. Conclusions: These findings reveal CFT impairment to be present in schizophrenia even when patients are in symptomatic remission. However, symptomatology and illness duration may have a negative influence on these patients' ability to generate counterfactual thoughts. The results might support the relevance of targeting CFT in future treatment approaches, although further research is needed to better describe the relationship between CFT and both symptomatology and functional outcome.

  15. Counterfactual thinking affects the excitability of the motor cortex.

    PubMed

    Vicario, Carmelo M; Rafal, Robert D; Avenanti, Alessio

    2015-04-01

    Evidence suggests that monetary reward and affective experiences induce activity in the cortical motor system. Nevertheless, it is unclear whether counterfactual thinking related to wrong choices that lead to monetary loss and regret affects motor excitability. Using transcranial magnetic stimulation (TMS) of the motor cortex, we measured corticospinal excitability of 2 groups of healthy humans asked to actively guess the winning key among two possible alternatives (choice group); or passively assist to monetary outcomes randomly selected by the computer program (follow group). Results document a selective increment of the corticospinal excitability when a monetary loss outcome followed the key selection (i.e., in the choice group). On the other hand, no change in corticospinal excitability was found when participants passively assisted to a monetary loss randomly selected by the computer program (i.e., follow group). These findings suggest that counterfactual thinking and the negative emotional experiences arising from choices causing monetary loss--i.e., "I would have won instead of lost money if I'd made a different choice"--are mapped in the motor system.

  16. Emotional intensity in episodic autobiographical memory and counterfactual thinking.

    PubMed

    Stanley, Matthew L; Parikh, Natasha; Stewart, Gregory W; De Brigard, Felipe

    2017-02-01

    Episodic counterfactual thoughts-imagined alternative ways in which personal past events might have occurred-are frequently accompanied by intense emotions. Here, participants recollected positive and negative autobiographical memories and then generated better and worse episodic counterfactual events from those memories. Our results suggest that the projected emotional intensity during the simulated remembered/imagined event is significantly higher than but typically positively related to the emotional intensity while remembering/imagining the event. Furthermore, repeatedly simulating counterfactual events heightened the emotional intensity felt while simulating the counterfactual event. Finally, for both the emotional intensity accompanying the experience of remembering/imagining and the projected emotional intensity during the simulated remembered/imagined event, the emotional intensity of negative memories was greater than the emotional intensity of upward counterfactuals generated from them but lower than the emotional intensity of downward counterfactuals generated from them. These findings are discussed in relation to clinical work and functional theories of counterfactual thinking.

  17. Quantum exhaustive key search with simplified-DES as a case study.

    PubMed

    Almazrooie, Mishal; Samsudin, Azman; Abdullah, Rosni; Mutter, Kussay N

    2016-01-01

    To evaluate the security of a symmetric cryptosystem against any quantum attack, the symmetric algorithm must be first implemented on a quantum platform. In this study, a quantum implementation of a classical block cipher is presented. A quantum circuit for a classical block cipher of a polynomial size of quantum gates is proposed. The entire work has been tested on a quantum mechanics simulator called libquantum. First, the functionality of the proposed quantum cipher is verified and the experimental results are compared with those of the original classical version. Then, quantum attacks are conducted by using Grover's algorithm to recover the secret key. The proposed quantum cipher is used as a black box for the quantum search. The quantum oracle is then queried over the produced ciphertext to mark the quantum state, which consists of plaintext and key qubits. The experimental results show that for a key of n-bit size and key space of N such that [Formula: see text], the key can be recovered in [Formula: see text] computational steps.

  18. Counterfactual and Semifactual Conditionals Prime Alternative Possibilities

    ERIC Educational Resources Information Center

    Santamaria, Carlos; Espino, Orlando; Byrne, Ruth M. J.

    2005-01-01

    The authors examined in 3 experiments the comprehension of counterfactuals, such as "If it had rained, the plants would have bloomed," and semifactuals, such as "Even if it had rained, the plants would have bloomed," compared with indicative conditionals, "If it rained, the plants bloomed." The first experiment showed that people read the negative…

  19. Inference and Explanation in Counterfactual Reasoning

    ERIC Educational Resources Information Center

    Rips, Lance J.; Edwards, Brian J.

    2013-01-01

    This article reports results from two studies of how people answer counterfactual questions about simple machines. Participants learned about devices that have a specific configuration of components, and they answered questions of the form "If component X had not operated [failed], would component Y have operated?" The data from these…

  20. Quantum hacking: Saturation attack on practical continuous-variable quantum key distribution

    NASA Astrophysics Data System (ADS)

    Qin, Hao; Kumar, Rupesh; Alléaume, Romain

    2016-07-01

    We identify and study a security loophole in continuous-variable quantum key distribution (CVQKD) implementations, related to the imperfect linearity of the homodyne detector. By exploiting this loophole, we propose an active side-channel attack on the Gaussian-modulated coherent-state CVQKD protocol combining an intercept-resend attack with an induced saturation of the homodyne detection on the receiver side (Bob). We show that an attacker can bias the excess noise estimation by displacing the quadratures of the coherent states received by Bob. We propose a saturation model that matches experimental measurements on the homodyne detection and use this model to study the impact of the saturation attack on parameter estimation in CVQKD. We demonstrate that this attack can bias the excess noise estimation beyond the null key threshold for any system parameter, thus leading to a full security break. If we consider an additional criterion imposing that the channel transmission estimation should not be affected by the attack, then the saturation attack can only be launched if the attenuation on the quantum channel is sufficient, corresponding to attenuations larger than approximately 6 dB. We moreover discuss the possible countermeasures against the saturation attack and propose a countermeasure based on Gaussian postselection that can be implemented by classical postprocessing and may allow one to distill the secret key when the raw measurement data are partly saturated.

  1. Fault tolerant quantum key distribution protocol with collective random unitary noise

    NASA Astrophysics Data System (ADS)

    Wang, Xiang-Bin

    2005-11-01

    We propose an easy implementable prepare-and-measure protocol for robust quantum key distribution with photon polarization. The protocol is fault tolerant against collective random unitary channel noise. The protocol does not need any collective quantum measurement or quantum memory. A security proof and a specific linear optical realization using spontaneous parametric down conversion are given.

  2. Implementation of decoy states in a subcarrier wave quantum key distribution system

    NASA Astrophysics Data System (ADS)

    Gaidash, A.; Kozubov, A.; Egorov, V.; Gleim, A.

    2016-08-01

    Subcarrier wave quantum key distribution systems demonstrate promising capabilities for secure quantum networking. However for this class of devices no implementation of secure decoy states protocol was developed. It leaves them potentially vulnerable to photon-number splitting attacks on quantum channel and limiting the key distribution distance. We propose a practical solution to this problem by calculating the required parameters of light source and modulation indices for signal and decoy states in a subcarrier wave system and describing the corresponding experimental scheme.

  3. Quantum hacking: Experimental demonstration of time-shift attack against practical quantum-key-distribution systems

    NASA Astrophysics Data System (ADS)

    Zhao, Yi; Fung, Chi-Hang F.; Qi, Bing; Chen, Christine; Lo, Hoi-Kwong

    2009-03-01

    Quantum key distribution (QKD) systems can send signals over more than 100 km standard optical fiber and are widely believed to be secure. Here, we show experimentally for the first time a technologically feasible attack, namely the time-shift attack, against a commercial QKD system. Our result shows that, contrary to popular belief, an eavesdropper, Eve, has a non-negligible probability (˜4%) to break the security of the system. Eve's success is due to the well-known detection efficiency loophole in the experimental testing of Bell inequalities. Therefore, the detection efficiency loophole plays a key role not only in fundamental physics, but also in technological applications such as QKD. Our work is published in [1]. [4pt] [1] Y. Zhao, C.-H. F. Fung, B. Qi, C. Chen, and H.-K. Lo, Phys. Rev. A, 78:042333 (2008).

  4. Generalized decoding, effective channels, and simplified security proofs in quantum key distribution

    SciTech Connect

    Renes, Joseph M.; Grassl, Markus

    2006-08-15

    Prepare and measure quantum key distribution protocols can be decomposed into two basic steps: delivery of the signals over a quantum channel and distillation of a secret key from the signal and measurement records by classical processing and public communication. Here we formalize the distillation process for a general protocol in a purely quantum-mechanical framework and demonstrate that it can be viewed as creating an 'effective' quantum channel between the legitimate users Alice and Bob. The process of secret key generation can then be viewed as entanglement distribution using this channel, which enables application of entanglement-based security proofs to essentially any prepare and measure protocol. To ensure secrecy of the key, Alice and Bob must be able to estimate the channel noise from errors in the key, and we further show how symmetries of the distillation process simplify this task. Applying this method, we prove the security of several key distribution protocols based on equiangular spherical codes.

  5. Temporal steering and security of quantum key distribution with mutually unbiased bases against individual attacks

    NASA Astrophysics Data System (ADS)

    Bartkiewicz, Karol; Černoch, Antonín; Lemr, Karel; Miranowicz, Adam; Nori, Franco

    2016-06-01

    Temporal steering, which is a temporal analog of Einstein-Podolsky-Rosen steering, refers to temporal quantum correlations between the initial and final state of a quantum system. Our analysis of temporal steering inequalities in relation to the average quantum bit error rates reveals the interplay between temporal steering and quantum cloning, which guarantees the security of quantum key distribution based on mutually unbiased bases against individual attacks. The key distributions analyzed here include the Bennett-Brassard 1984 protocol and the six-state 1998 protocol by Bruss. Moreover, we define a temporal steerable weight, which enables us to identify a kind of monogamy of temporal correlation that is essential to quantum cryptography and useful for analyzing various scenarios of quantum causality.

  6. SeaQuaKE: Sea-optimized Quantum Key Exchange

    DTIC Science & Technology

    2015-01-01

    absorption and scattering, (ii) introduction of additional background noise from sources such as blackbody radiation , and (iii) beam impairments from...SWIR ~1.4-3 m), mid- wave infrared (MWIR ~3-8 m), and long-wavelength infrared (LWIR ~8-15 m). 3.2 Quantum Transmitter: Source Architecture and...Absorption Turbulence Quantum channel (free-space) Scattered light Noise Scattering Background noise (e.g. sun , blackbody) Protocols Spectral filtering

  7. Critical error rate of quantum-key-distribution protocols versus the size and dimensionality of the quantum alphabet

    NASA Astrophysics Data System (ADS)

    Sych, Denis V.; Grishanin, Boris A.; Zadkov, Victor N.

    2004-11-01

    A quantum-information analysis of how the size and dimensionality of the quantum alphabet affect the critical error rate of the quantum-key-distribution (QKD) protocols is given on an example of two QKD protocols—the six-state and ∞-state (i.e., a protocol with continuous alphabet) ones. In the case of a two-dimensional Hilbert space, it is shown that, under certain assumptions, increasing the number of letters in the quantum alphabet up to infinity slightly increases the critical error rate. Increasing additionally the dimensionality of the Hilbert space leads to a further increase in the critical error rate.

  8. Applications of single-qubit rotations in quantum public-key cryptography

    NASA Astrophysics Data System (ADS)

    Nikolopoulos, Georgios M.

    2008-03-01

    We discuss cryptographic applications of single-qubit rotations from the perspective of trapdoor one-way functions and public-key encryption. In particular, we present an asymmetric cryptosystem whose security relies on fundamental principles of quantum physics. A quantum public key is used for the encryption of messages while decryption is possible by means of a classical private key only. The trapdoor one-way function underlying the proposed cryptosystem maps integer numbers to quantum states of a qubit and its inversion can be infeasible by virtue of the Holevo’s theorem.

  9. Deterministic Quantum Key Distribution Using Two Non-orthogonal Entangled States

    NASA Astrophysics Data System (ADS)

    Guo, Ying; Zeng, Gui-Hua

    2007-03-01

    A deterministic quantum key distribution scheme using two non-orthogonal entangled states is proposed. In the proposed scheme, communicators share key information by exchanging one travelling photon with two random and secret polarization angles. The security of the distributed key is guaranteed by three checking phases in three-way channel and the communicators' secret polarization angles.

  10. Preservation of a lower bound of quantum secret key rate in the presence of decoherence

    NASA Astrophysics Data System (ADS)

    Datta, Shounak; Goswami, Suchetana; Pramanik, Tanumoy; Majumdar, A. S.

    2017-03-01

    It is well known that the interaction of quantum systems with the environment reduces the inherent quantum correlations. Under special circumstances the effect of decoherence can be reversed, for example, the interaction modelled by an amplitude damping channel can boost the teleportation fidelity from the classical to the quantum region for a bipartite quantum state. Here, we first show that this phenomenon fails to preserve the quantum secret key rate derived under individual attack. We further show that the technique of weak measurement can be used to slow down the process of decoherence, thereby helping to preserve the quantum secret key rate when one or both systems are interacting with the environment via an amplitude damping channel. Most interestingly, in certain cases weak measurement with post-selection where one considers both success and failure of the technique is shown to be more useful than without it when both systems interact with the environment.

  11. Long-distance continuous-variable quantum key distribution by controlling excess noise

    PubMed Central

    Huang, Duan; Huang, Peng; Lin, Dakai; Zeng, Guihua

    2016-01-01

    Quantum cryptography founded on the laws of physics could revolutionize the way in which communication information is protected. Significant progresses in long-distance quantum key distribution based on discrete variables have led to the secure quantum communication in real-world conditions being available. However, the alternative approach implemented with continuous variables has not yet reached the secure distance beyond 100 km. Here, we overcome the previous range limitation by controlling system excess noise and report such a long distance continuous-variable quantum key distribution experiment. Our result paves the road to the large-scale secure quantum communication with continuous variables and serves as a stepping stone in the quest for quantum network. PMID:26758727

  12. Long-distance continuous-variable quantum key distribution by controlling excess noise

    NASA Astrophysics Data System (ADS)

    Huang, Duan; Huang, Peng; Lin, Dakai; Zeng, Guihua

    2016-01-01

    Quantum cryptography founded on the laws of physics could revolutionize the way in which communication information is protected. Significant progresses in long-distance quantum key distribution based on discrete variables have led to the secure quantum communication in real-world conditions being available. However, the alternative approach implemented with continuous variables has not yet reached the secure distance beyond 100 km. Here, we overcome the previous range limitation by controlling system excess noise and report such a long distance continuous-variable quantum key distribution experiment. Our result paves the road to the large-scale secure quantum communication with continuous variables and serves as a stepping stone in the quest for quantum network.

  13. Quantum Hash function and its application to privacy amplification in quantum key distribution, pseudo-random number generation and image encryption

    PubMed Central

    Yang, Yu-Guang; Xu, Peng; Yang, Rui; Zhou, Yi-Hua; Shi, Wei-Min

    2016-01-01

    Quantum information and quantum computation have achieved a huge success during the last years. In this paper, we investigate the capability of quantum Hash function, which can be constructed by subtly modifying quantum walks, a famous quantum computation model. It is found that quantum Hash function can act as a hash function for the privacy amplification process of quantum key distribution systems with higher security. As a byproduct, quantum Hash function can also be used for pseudo-random number generation due to its inherent chaotic dynamics. Further we discuss the application of quantum Hash function to image encryption and propose a novel image encryption algorithm. Numerical simulations and performance comparisons show that quantum Hash function is eligible for privacy amplification in quantum key distribution, pseudo-random number generation and image encryption in terms of various hash tests and randomness tests. It extends the scope of application of quantum computation and quantum information. PMID:26823196

  14. Quantum Hash function and its application to privacy amplification in quantum key distribution, pseudo-random number generation and image encryption.

    PubMed

    Yang, Yu-Guang; Xu, Peng; Yang, Rui; Zhou, Yi-Hua; Shi, Wei-Min

    2016-01-29

    Quantum information and quantum computation have achieved a huge success during the last years. In this paper, we investigate the capability of quantum Hash function, which can be constructed by subtly modifying quantum walks, a famous quantum computation model. It is found that quantum Hash function can act as a hash function for the privacy amplification process of quantum key distribution systems with higher security. As a byproduct, quantum Hash function can also be used for pseudo-random number generation due to its inherent chaotic dynamics. Further we discuss the application of quantum Hash function to image encryption and propose a novel image encryption algorithm. Numerical simulations and performance comparisons show that quantum Hash function is eligible for privacy amplification in quantum key distribution, pseudo-random number generation and image encryption in terms of various hash tests and randomness tests. It extends the scope of application of quantum computation and quantum information.

  15. Quantum Hash function and its application to privacy amplification in quantum key distribution, pseudo-random number generation and image encryption

    NASA Astrophysics Data System (ADS)

    Yang, Yu-Guang; Xu, Peng; Yang, Rui; Zhou, Yi-Hua; Shi, Wei-Min

    2016-01-01

    Quantum information and quantum computation have achieved a huge success during the last years. In this paper, we investigate the capability of quantum Hash function, which can be constructed by subtly modifying quantum walks, a famous quantum computation model. It is found that quantum Hash function can act as a hash function for the privacy amplification process of quantum key distribution systems with higher security. As a byproduct, quantum Hash function can also be used for pseudo-random number generation due to its inherent chaotic dynamics. Further we discuss the application of quantum Hash function to image encryption and propose a novel image encryption algorithm. Numerical simulations and performance comparisons show that quantum Hash function is eligible for privacy amplification in quantum key distribution, pseudo-random number generation and image encryption in terms of various hash tests and randomness tests. It extends the scope of application of quantum computation and quantum information.

  16. Two-party quantum key agreement based on four-particle GHZ states

    NASA Astrophysics Data System (ADS)

    He, Ye-Feng; Ma, Wen-Ping

    2016-04-01

    Based on four-particle GHZ states, the double CNOT operation and the delayed measurement technique, a two-party quantum key agreement (QKA) protocols is proposed. The double CNOT operation makes each four-particle GHZ state collapse into two independent quantum states without any entanglement. Furthermore, one party can directly know the two quantum states and the other party can be aware of the two quantum states by using the corresponding measurement. According to the initial states of the two quantum states, two parties can extract the secret keys of each other by using the publicly announced value or by performing the delayed measurement, respectively. Then the protocol achieves the fair establishment of a shared key. The security analysis shows that the new protocol can resist against participant attacks, the Trojan horse attacks and other outsider attacks. Furthermore, the new protocol also has no information leakage problem and has high qubit efficiency.

  17. Modeling, Simulation, and Analysis of a Decoy State Enabled Quantum Key Distribution System

    DTIC Science & Technology

    2015-03-26

    perform error reconciliation where quantum communication errors are counted and corrected for using bi-directional error correction algorithms over the...configured to control communications on the quantum channel. QKD systems can be paired with traditional symmetric encryption algorithms (e.g., DES, 3DES, or...Error reconciliation algorithms perform bi-directional error correction of the shared sifted keys to correct for quantum communication errors, while

  18. Secure multi-party communication with quantum key distribution managed by trusted authority

    DOEpatents

    Hughes, Richard John; Nordholt, Jane Elizabeth; Peterson, Charles Glen

    2015-01-06

    Techniques and tools for implementing protocols for secure multi-party communication after quantum key distribution ("QKD") are described herein. In example implementations, a trusted authority facilitates secure communication between multiple user devices. The trusted authority distributes different quantum keys by QKD under trust relationships with different users. The trusted authority determines combination keys using the quantum keys and makes the combination keys available for distribution (e.g., for non-secret distribution over a public channel). The combination keys facilitate secure communication between two user devices even in the absence of QKD between the two user devices. With the protocols, benefits of QKD are extended to multi-party communication scenarios. In addition, the protocols can retain benefit of QKD even when a trusted authority is offline or a large group seeks to establish secure communication within the group.

  19. Secure multi-party communication with quantum key distribution managed by trusted authority

    DOEpatents

    Nordholt, Jane Elizabeth; Hughes, Richard John; Peterson, Charles Glen

    2013-07-09

    Techniques and tools for implementing protocols for secure multi-party communication after quantum key distribution ("QKD") are described herein. In example implementations, a trusted authority facilitates secure communication between multiple user devices. The trusted authority distributes different quantum keys by QKD under trust relationships with different users. The trusted authority determines combination keys using the quantum keys and makes the combination keys available for distribution (e.g., for non-secret distribution over a public channel). The combination keys facilitate secure communication between two user devices even in the absence of QKD between the two user devices. With the protocols, benefits of QKD are extended to multi-party communication scenarios. In addition, the protocols can retain benefit of QKD even when a trusted authority is offline or a large group seeks to establish secure communication within the group.

  20. Quantum displacement receiver for M-ary phase-shift-keyed coherent states

    SciTech Connect

    Izumi, Shuro; Takeoka, Masahiro; Fujiwara, Mikio; Sasaki, Masahide; Pozza, Nicola Dalla; Assalini, Antonio

    2014-12-04

    We propose quantum receivers for 3- and 4-ary phase-shift-keyed (PSK) coherent state signals to overcome the standard quantum limit (SQL). Our receiver, consisting of a displacement operation and on-off detectors with or without feedforward, provides an error probability performance beyond the SQL. We show feedforward operations can tolerate the requirement for the detector specifications.

  1. Quantum displacement receiver for M-ary phase-shift-keyed coherent states

    NASA Astrophysics Data System (ADS)

    Izumi, Shuro; Takeoka, Masahiro; Fujiwara, Mikio; Pozza, Nicola Dalla; Assalini, Antonio; Ema, Kazuhiro; Sasaki, Masahide

    2014-12-01

    We propose quantum receivers for 3- and 4-ary phase-shift-keyed (PSK) coherent state signals to overcome the standard quantum limit (SQL). Our receiver, consisting of a displacement operation and on-off detectors with or without feedforward, provides an error probability performance beyond the SQL. We show feedforward operations can tolerate the requirement for the detector specifications.

  2. A Secure Key Distribution System of Quantum Cryptography Based on the Coherent State

    NASA Technical Reports Server (NTRS)

    Guo, Guang-Can; Zhang, Xiao-Yu

    1996-01-01

    The cryptographic communication has a lot of important applications, particularly in the magnificent prospects of private communication. As one knows, the security of cryptographic channel depends crucially on the secrecy of the key. The Vernam cipher is the only cipher system which has guaranteed security. In that system the key must be as long as the message and most be used only once. Quantum cryptography is a method whereby key secrecy can be guaranteed by a physical law. So it is impossible, even in principle, to eavesdrop on such channels. Quantum cryptography has been developed in recent years. Up to now, many schemes of quantum cryptography have been proposed. Now one of the main problems in this field is how to increase transmission distance. In order to use quantum nature of light, up to now proposed schemes all use very dim light pulses. The average photon number is about 0.1. Because of the loss of the optical fiber, it is difficult for the quantum cryptography based on one photon level or on dim light to realize quantum key-distribution over long distance. A quantum key distribution based on coherent state is introduced in this paper. Here we discuss the feasibility and security of this scheme.

  3. Towards secure quantum key distribution protocol for wireless LANs: a hybrid approach

    NASA Astrophysics Data System (ADS)

    Naik, R. Lalu; Reddy, P. Chenna

    2015-12-01

    The primary goals of security such as authentication, confidentiality, integrity and non-repudiation in communication networks can be achieved with secure key distribution. Quantum mechanisms are highly secure means of distributing secret keys as they are unconditionally secure. Quantum key distribution protocols can effectively prevent various attacks in the quantum channel, while classical cryptography is efficient in authentication and verification of secret keys. By combining both quantum cryptography and classical cryptography, security of communications over networks can be leveraged. Hwang, Lee and Li exploited the merits of both cryptographic paradigms for provably secure communications to prevent replay, man-in-the-middle, and passive attacks. In this paper, we propose a new scheme with the combination of quantum cryptography and classical cryptography for 802.11i wireless LANs. Since quantum cryptography is premature in wireless networks, our work is a significant step forward toward securing communications in wireless networks. Our scheme is known as hybrid quantum key distribution protocol. Our analytical results revealed that the proposed scheme is provably secure for wireless networks.

  4. If the Real World Were Irrelevant, so to Speak: The role of propositional truth-value in counterfactual sentence comprehension

    ERIC Educational Resources Information Center

    Nieuwland, Mante S.; Martin, Andrea E.

    2012-01-01

    Propositional truth-value can be a defining feature of a sentence's relevance to the unfolding discourse, and establishing propositional truth-value in context can be key to successful interpretation. In the current study, we investigate its role in the comprehension of counterfactual conditionals, which describe imaginary consequences of…

  5. The day after an electoral defeat: counterfactuals and collective action.

    PubMed

    Milesi, Patrizia; Catellani, Patrizia

    2011-12-01

    An intriguing question for scholars of collective action is how participants of unsuccessful actions become re-engaged in future collective activities. At an individual level, previous research has shown that after negative outcomes counterfactual thoughts ('if only … ') may serve to prepare for future action. In the current research, we investigated whether counterfactuals may also prepare for future action at a collective level. After a defeat of their party at the regional elections, 163 political activists rated their agreement with abstract (as opposed to concrete) and party-focused (as opposed to other-focused) counterfactuals about how the elections outcome might have been better. Results showed that abstract counterfactuals, dealing with the core elements of the elections, supported collective action intention better than concrete ones. Consistent with the recent developments of dual-pathway models of collective action, counterfactuals predicted collective action intention through the mediation of group efficacy and group identification. In particular, while both party- and other-focused abstract counterfactuals increased group efficacy, only other-focused abstract counterfactuals increased group identification. Discussion focuses on how the investigation of counterfactuals can enlarge our knowledge of the socio-cognitive antecedents of collective action.

  6. Counterfactual Thinking as a Mechanism in Narrative Persuasion

    ERIC Educational Resources Information Center

    Tal-Or, Nurit; Boninger, David S.; Poran, Amir; Gleicher, Faith

    2004-01-01

    Two experiments examined the impact of counterfactual thinking on persuasion. Participants in both experiments were exposed to short video clips in which an actor described a car accident that resulted in serious injury. In the narrative description, the salience of a counterfactual was manipulated by either explicitly including the counterfactual…

  7. Procrastination and counterfactual thinking: avoiding what might have been.

    PubMed

    Sirois, Fuschia M

    2004-06-01

    The possible negative consequences of counterfactuals were explored in the current study by examining the relationship between counterfactual direction and trait procrastination, a self-defeating behavioural style. Eighty participants generated counterfactuals in response to two experimental anxiety inductions. Trait procrastination was overall related to avoiding thoughts about how things could have been better (making more downward and relatively fewer upward counterfactuals) in response to the two anxiety-provoking scenarios, suggesting the involvement of a self-enhancement motive (mood repair). Evidence for the involvement of this self-motive in procrastinating behaviour also emerged, as procrastination was more related to making more downward counterfactuals for a delay-specific anxiety scenario than for a general anxiety scenario. The pattern of results supports the proposal that downward counterfactuals may be associated with negative behavioural styles such as procrastination and implicates self-enhancement motives in this relationship. The behavioural and motivational consequences of downward counterfactuals are discussed and possible connections between downward counterfactuals and other self-defeating behaviours are presented.

  8. Supporting Children's Counterfactual Thinking with Alternative Modes of Responding

    ERIC Educational Resources Information Center

    Beck, Sarah R.; Carroll, Daniel J.; Brunsdon, Victoria E. A.; Gryg, Charlotte K.

    2011-01-01

    To speculate about counterfactual worlds, children need to ignore what they know to be true about the real world. Prior studies yielding individual differences data suggested that counterfactual thinking may be related to overcoming prepotent responses. In two experiments, we manipulated how 3- to 5-year-olds responded to counterfactual…

  9. Entanglement-based quantum key distribution with biased basis choice via free space.

    PubMed

    Cao, Yuan; Liang, Hao; Yin, Juan; Yong, Hai-Lin; Zhou, Fei; Wu, Yu-Ping; Ren, Ji-Gang; Li, Yu-Huai; Pan, Ge-Sheng; Yang, Tao; Ma, Xiongfeng; Peng, Cheng-Zhi; Pan, Jian-Wei

    2013-11-04

    We report a free-space entanglement-based quantum key distribution experiment, implementing the biased basis protocol between two sites which are 15.3 km apart. Photon pairs from a polarization-entangled source are distributed through two 7.8-km free-space optical links. An optimal bias 20:80 between the X and Z basis is used. A post-processing scheme with finite-key analysis is applied to extract the final secure key. After three-hour continuous operation at night, a 4293-bit secure key is obtained, with a final key rate of 0.124 bit per raw key bit which increases the final key rate by 14.8% comparing to the standard BB84 case. Our results experimentally demonstrate that the efficient BB84 protocol, which increases key generation efficiency by biasing Alice and Bob's basis choices, is potentially useful for the ground-satellite quantum communication.

  10. SeaQuaKE: Sea-optimized Quantum Key Exchange

    DTIC Science & Technology

    2014-06-01

    waveguide. Higher order spatial modes (e.g. orbital angular momentum), on the other hand, will not be considered, at least initially, due to the...broken down further into three smaller subsystems, including the pump source, time-bin multiplexer , polarization entanglement & pair generation...technologies, including conventional DFB and mode-locked laser technologies as well as longer wavelength sources, including quantum cascade lasers (QCLs

  11. Counterfactuals in Action: An fMRI Study of Counterfactual Sentences Describing Physical Effort

    ERIC Educational Resources Information Center

    Urrutia, Mabel; Gennari, Silvia P.; de Vega, Manuel

    2012-01-01

    Counterfactual statements such as "if Mary had cleaned the room, she would have moved the sofa" convey both actual and hypothetical actions, namely, that Mary did not clean the room or move the sofa, but she would have done so in some possible past situation. Such statements are ubiquitous in daily life and are involved in critical cognitive…

  12. Depressive states amplify both upward and downward counterfactual thinking.

    PubMed

    Feng, Xue; Gu, Ruolei; Liang, Fucheng; Broster, Lucas S; Liu, Yunzhe; Zhang, Dandan; Luo, Yue-jia

    2015-08-01

    Depression has been linked to counterfactual thinking in many behavioral studies, but the direction of this effect remains disputed. In the current study, the relationship between depression and counterfactual thinking was examined using the event-related potential (ERP) technique. In a binary choice gambling task, outcome feedback of the chosen option and that of the alternative option were both provided, so as to elicit the process of counterfactual comparison. By investigating ERP signals in response to outcome presentation, we discovered that when the fictive outcome was better or worse than the factual outcome, the amplitude of the P3 component was positively correlated with individual levels of depression, but not levels of anxiety. These results indicate that depression strengthens both upward counterfactual thinking and downward counterfactual thinking. The implication of this finding to clinical research is discussed.

  13. Robust shot-noise measurement for continuous-variable quantum key distribution

    NASA Astrophysics Data System (ADS)

    Kunz-Jacques, Sébastien; Jouguet, Paul

    2015-02-01

    We study a practical method to measure the shot noise in real time in continuous-variable quantum key distribution systems. The amount of secret key that can be extracted from the raw statistics depends strongly on this quantity since it affects in particular the computation of the excess noise (i.e., noise in excess of the shot noise) added by an eavesdropper on the quantum channel. Some powerful quantum hacking attacks relying on faking the estimated value of the shot noise to hide an intercept and resend strategy were proposed. Here, we provide experimental evidence that our method can defeat the saturation attack and the wavelength attack.

  14. Continuous-variable quantum authentication of physical unclonable keys

    PubMed Central

    Nikolopoulos, Georgios M.; Diamanti, Eleni

    2017-01-01

    We propose a scheme for authentication of physical keys that are materialized by optical multiple-scattering media. The authentication relies on the optical response of the key when probed by randomly selected coherent states of light, and the use of standard wavefront-shaping techniques that direct the scattered photons coherently to a specific target mode at the output. The quadratures of the electromagnetic field of the scattered light at the target mode are analysed using a homodyne detection scheme, and the acceptance or rejection of the key is decided upon the outcomes of the measurements. The proposed scheme can be implemented with current technology and offers collision resistance and robustness against key cloning. PMID:28393853

  15. Finite-key-size security of the Phoenix-Barnett-Chefles 2000 quantum-key-distribution protocol

    NASA Astrophysics Data System (ADS)

    Mafu, Mhlambululi; Garapo, Kevin; Petruccione, Francesco

    2014-09-01

    The postselection technique was introduced by Christandl, König, and Renner [Phys. Rev. Lett. 102, 020504 (2009), 10.1103/PhysRevLett.102.020504] in order to simplify the security of quantum-key-distribution schemes. Here, we present how it can be applied to study the security of the Phoenix-Barnett-Chefles 2000 trine-state protocol, a symmetric version of the Bennett 1992 protocol.

  16. Two-party quantum key agreement protocol with four-particle entangled states

    NASA Astrophysics Data System (ADS)

    He, Yefeng; Ma, Wenping

    2016-09-01

    Based on four-particle entangled states and the delayed measurement technique, a two-party quantum key agreement protocol is proposed in this paper. In the protocol, two participants can deduce the measurement results of each other’s initial quantum states in terms of the measurement correlation property of four-particle entangled states. According to the corresponding initial quantum states deduced by themselves, two parties can extract the secret keys of each other by using the publicly announced value or by performing the delayed measurement, respectively. This guarantees the fair establishment of a shared key. Since each particle in quantum channel is transmitted only once, the protocol is congenitally free from the Trojan horse attacks. The security analysis shows that the protocol not only can resist against both participant and outsider attacks but also has no information leakage problem. Moreover, it has high qubit efficiency.

  17. Quantum-locked key distribution at nearly the classical capacity rate.

    PubMed

    Lupo, Cosmo; Lloyd, Seth

    2014-10-17

    Quantum data locking is a protocol that allows for a small secret key to (un)lock an exponentially larger amount of information, hence yielding the strongest violation of the classical one-time pad encryption in the quantum setting. This violation mirrors a large gap existing between two security criteria for quantum cryptography quantified by two entropic quantities: the Holevo information and the accessible information. We show that the latter becomes a sensible security criterion if an upper bound on the coherence time of the eavesdropper's quantum memory is known. Under this condition, we introduce a protocol for secret key generation through a memoryless qudit channel. For channels with enough symmetry, such as the d-dimensional erasure and depolarizing channels, this protocol allows secret key generation at an asymptotic rate as high as the classical capacity minus one bit.

  18. Quantum-Locked Key Distribution at Nearly the Classical Capacity Rate

    NASA Astrophysics Data System (ADS)

    Lupo, Cosmo; Lloyd, Seth

    2014-10-01

    Quantum data locking is a protocol that allows for a small secret key to (un)lock an exponentially larger amount of information, hence yielding the strongest violation of the classical one-time pad encryption in the quantum setting. This violation mirrors a large gap existing between two security criteria for quantum cryptography quantified by two entropic quantities: the Holevo information and the accessible information. We show that the latter becomes a sensible security criterion if an upper bound on the coherence time of the eavesdropper's quantum memory is known. Under this condition, we introduce a protocol for secret key generation through a memoryless qudit channel. For channels with enough symmetry, such as the d-dimensional erasure and depolarizing channels, this protocol allows secret key generation at an asymptotic rate as high as the classical capacity minus one bit.

  19. Security Bounds for Continuous Variables Quantum Key Distribution

    NASA Astrophysics Data System (ADS)

    Navascués, Miguel; Acín, Antonio

    2005-01-01

    Security bounds for key distribution protocols using coherent and squeezed states and homodyne measurements are presented. These bounds refer to (i)general attacks and (ii)collective attacks where Eve applies the optimal individual interaction to the sent states, but delays her measurement until the end of the reconciliation process. For the case of a lossy line and coherent states, it is first proven that a secure key distribution is possible up to 1.9dB of losses. For the second scenario, the security bounds are the same as for the completely incoherent attack.

  20. One-time pad, complexity of verification of keys, and practical security of quantum cryptography

    NASA Astrophysics Data System (ADS)

    Molotkov, S. N.

    2016-11-01

    A direct relation between the complexity of the complete verification of keys, which is one of the main criteria of security in classical systems, and a trace distance used in quantum cryptography is demonstrated. Bounds for the minimum and maximum numbers of verification steps required to determine the actual key are obtained.

  1. Quantum key distribution using entangled-photon trains with no basis selection

    SciTech Connect

    Inoue, Kyo; Takesue, Hiroki

    2006-03-15

    Conventional quantum key distribution (QKD) protocols include a basis selection process for providing a secure secret key. In contrast, this paper proposes an entanglement-based QKD with no basis selection procedure. Entangled-photon pulse trains with an average photon number less than one per pulse are sent to two legitimate parties, from which a secret key is created utilizing the entanglement nature. Eavesdropping on a transmission line is prevented by a condition of less than one photon per pulse, and sending classically correlated coherent pulses instead of quantum correlated ones is revealed by monitoring coincident count rate000.

  2. Simulating of the measurement-device independent quantum key distribution with phase randomized general sources

    PubMed Central

    Wang, Qin; Wang, Xiang-Bin

    2014-01-01

    We present a model on the simulation of the measurement-device independent quantum key distribution (MDI-QKD) with phase randomized general sources. It can be used to predict experimental observations of a MDI-QKD with linear channel loss, simulating corresponding values for the gains, the error rates in different basis, and also the final key rates. Our model can be applicable to the MDI-QKDs with arbitrary probabilistic mixture of different photon states or using any coding schemes. Therefore, it is useful in characterizing and evaluating the performance of the MDI-QKD protocol, making it a valuable tool in studying the quantum key distributions. PMID:24728000

  3. Cryptanalysis on authenticated semi-quantum key distribution protocol using Bell states

    NASA Astrophysics Data System (ADS)

    Meslouhi, A.; Hassouni, Y.

    2017-01-01

    Recently, Yu et al. (Quantum Inf Process 13(6):1457-1465, 2014) proposed the first semi-quantum scheme without the need of a classical channel to generate a secret key, while employing a "master key" and the entanglement properties of Bell states. This study points out a vulnerability that allows a malicious person to recover a partial master key and to launch a successful Man-In-The-Middle attack. Accordingly, we present the most likely leakage information scenarios where an outside attacker affects the security of the proposed protocol.

  4. Adiabatic pipelining: a key to ternary computing with quantum dots.

    PubMed

    Pečar, P; Ramšak, A; Zimic, N; Mraz, M; Lebar Bajec, I

    2008-12-10

    The quantum-dot cellular automaton (QCA), a processing platform based on interacting quantum dots, was introduced by Lent in the mid-1990s. What followed was an exhilarating period with the development of the line, the functionally complete set of logic functions, as well as more complex processing structures, however all in the realm of binary logic. Regardless of these achievements, it has to be acknowledged that the use of binary logic is in computing systems mainly the end result of the technological limitations, which the designers had to cope with in the early days of their design. The first advancement of QCAs to multi-valued (ternary) processing was performed by Lebar Bajec et al, with the argument that processing platforms of the future should not disregard the clear advantages of multi-valued logic. Some of the elementary ternary QCAs, necessary for the construction of more complex processing entities, however, lead to a remarkable increase in size when compared to their binary counterparts. This somewhat negates the advantages gained by entering the ternary computing domain. As it turned out, even the binary QCA had its initial hiccups, which have been solved by the introduction of adiabatic switching and the application of adiabatic pipeline approaches. We present here a study that introduces adiabatic switching into the ternary QCA and employs the adiabatic pipeline approach to successfully solve the issues of elementary ternary QCAs. What is more, the ternary QCAs presented here are sizewise comparable to binary QCAs. This in our view might serve towards their faster adoption.

  5. Unconditionally secure device-independent quantum key distribution with only two devices

    NASA Astrophysics Data System (ADS)

    Barrett, Jonathan; Colbeck, Roger; Kent, Adrian

    2012-12-01

    Device-independent quantum key distribution is the task of using uncharacterized quantum devices to establish a shared key between two users. If a protocol is secure, regardless of the device behavior, it can be used to generate a shared key even if the supplier of the devices is malicious. To date, all device-independent quantum key distribution protocols that are known to be secure require separate isolated devices for each entangled pair, which is a significant practical limitation. We introduce a protocol that requires Alice and Bob to have only one device each. Although inefficient and unable to tolerate reasonable levels of noise, our protocol is unconditionally secure against an adversarial supplier limited only by locally enforced signaling constraints.

  6. Implementation of polarization-coded free-space BB84 quantum key distribution

    NASA Astrophysics Data System (ADS)

    Kim, Y.-S.; Jeong, Y.-C.; Kim, Y.-H.

    2008-06-01

    We report on the implementation of a Bennett-Brassard 1984 quantum key distribution protocol over a free-space optical path on an optical table. Attenuated laser pulses and Pockels cells driven by a pseudorandom number generator are employed to prepare polarization-encoded photons. The sifted key generation rate of 23.6 kbits per second and the quantum bit error rate (QBER) of 3% have been demonstrated at the average photon number per pulse μ = 0.16. This QBER is sufficiently low to extract final secret keys from shared sifted keys via error correction and privacy amplification. We also tested the long-distance capability of our system by adding optical losses to the quantum channel and found that the QBER remains the same regardless of the loss.

  7. Quantum key distribution for security guarantees over QoS-driven 3D satellite networks

    NASA Astrophysics Data System (ADS)

    Wang, Ping; Zhang, Xi; Chen, Genshe; Pham, Khanh; Blasch, Erik

    2014-06-01

    In recent years, quantum-based communication is emerging as a new technique for ensuring secured communications because it can guarantee absolute security between two different remote entities. Quantum communication performs the transmission and exchange of quantum information among distant nodes within a network. Quantum key distribution (QKD) is a methodology for generating and distributing random encryption keys using the principles of quantum physics. In this paper, we investigate the techniques on how to efficiently use QKD in 3D satellite networks and propose an effective method to overcome its communications-distance limitations. In order to implement secured and reliable communications over wireless satellite links, we develop a free-space quantum channel model in satellite communication networks. To enlarge the communications distances over 3D satellite networks, we propose to employ the intermediate nodes to relay the unconditional keys and guarantee the Quantum Bit Error Rate (QBER) for security requirement over 3D satellite networks. We also propose the communication model for QKD security-Quality of Service (QoS) guarantee and an adaptive cooperative routing selection scheme to optimize the throughput performance of QKD-based satellite communications networks. The obtained simulation results verify our proposed schemes.

  8. Family of finite geometry low-density parity-check codes for quantum key expansion

    NASA Astrophysics Data System (ADS)

    Hsu, Kung-Chuan; Brun, Todd A.

    2013-06-01

    We consider a quantum key expansion (QKE) protocol based on entanglement-assisted quantum error-correcting codes (EAQECCs). In these protocols, a seed of a previously shared secret key is used in the postprocessing stage of a standard quantum key distribution protocol like the Bennett-Brassard 1984 protocol, in order to produce a larger secret key. This protocol was proposed by Luo and Devetak, but codes leading to good performance have not been investigated. We look into a family of EAQECCs generated by classical finite geometry (FG) low-density parity-check (LDPC) codes, for which very efficient iterative decoders exist. A critical observation is that almost all errors in the resulting secret key result from uncorrectable block errors that can be detected by an additional syndrome check and an additional sampling step. Bad blocks can then be discarded. We make some changes to the original protocol to avoid the consumption of the preshared key when the protocol fails. This allows us to greatly reduce the bit error rate of the key at the cost of a minor reduction in the key production rate, but without increasing the consumption rate of the preshared key. We present numerical simulations for the family of FG LDPC codes, and show that this improved QKE protocol has a good net key production rate even at relatively high error rates, for appropriate choices of these codes.

  9. Security analysis on some experimental quantum key distribution systems with imperfect optical and electrical devices

    NASA Astrophysics Data System (ADS)

    Liang, Lin-Mei; Sun, Shi-Hai; Jiang, Mu-Sheng; Li, Chun-Yan

    2014-10-01

    In general, quantum key distribution (QKD) has been proved unconditionally secure for perfect devices due to quantum uncertainty principle, quantum noncloning theorem and quantum nondividing principle which means that a quantum cannot be divided further. However, the practical optical and electrical devices used in the system are imperfect, which can be exploited by the eavesdropper to partially or totally spy the secret key between the legitimate parties. In this article, we first briefly review the recent work on quantum hacking on some experimental QKD systems with respect to imperfect devices carried out internationally, then we will present our recent hacking works in details, including passive faraday mirror attack, partially random phase attack, wavelength-selected photon-number-splitting attack, frequency shift attack, and single-photon-detector attack. Those quantum attack reminds people to improve the security existed in practical QKD systems due to imperfect devices by simply adding countermeasure or adopting a totally different protocol such as measurement-device independent protocol to avoid quantum hacking on the imperfection of measurement devices [Lo, et al., Phys. Rev. Lett., 2012, 108: 130503].

  10. Improved key integrity checking for high-speed quantum key distribution using combinatorial group testing with strongly selective family design

    NASA Astrophysics Data System (ADS)

    Fang, Junbin; Jiang, Zoe L.; Ren, Kexin; Luo, Yunhan; Chen, Zhe; Liu, Weiping; Wang, Xuan; Niu, Xiamu; Yiu, S. M.; Hui, Lucas C. K.

    2014-06-01

    Key integrity checking is a necessary process in practical quantum key distribution (QKD) to check whether there is any error bit escaped from the previous error correction procedure. The traditional single-hash method may become a bottleneck in high-speed QKD since it has to discard all the key bits even if just one error bit exists. In this paper, we propose an improved scheme using combinatorial group testing (CGT) based on strong selective family design to verify key integrity in fine granularity and consequently improve the total efficiency of key generation after the error correction procedure. Code shortening technique and parallel computing are also applied to enhance the scheme's flexibility and to accelerate the computation. Experimental results show that the scheme can identify the rare error bits precisely and thus avoid dropping the great majority of correct bits, while the overhead is reasonable. For a -bit key, the disclosed information for public comparison is 800 bits (about 0.076 % of the key bits), reducing 256 bits when compared with the previous CGT scheme. Besides, with an Intel® quad-cores CPU at 3.40 GHz and 8 GB RAM, the computational times are 3.0 and 6.3 ms for hashing and decoding, respectively, which are reasonable in real applications and will not cause significant latency in practical QKD systems.

  11. Counterfactual cognitive deficit in persons with Parkinson's disease

    PubMed Central

    McNamara, P; Durso, R; Brown, A; Lynch, A

    2003-01-01

    Background: Counterfactuals are mental representations of alternatives to past events. Recent research has shown them to be important for other cognitive processes, such as planning, causal reasoning, problem solving, and decision making—all processes independently linked to the frontal lobes. Objective: To test the hypothesis that counterfactual thinking is impaired in some patients with Parkinson's disease and is linked to frontal dysfunction in these patients. Methods. Measures of counterfactual processing and frontal lobe functioning were administered to 24 persons with Parkinson's disease and 15 age matched healthy controls. Results. Patients with Parkinson's disease spontaneously generated significantly fewer counterfactuals than controls despite showing no differences from controls on a semantic fluency test; they also performed at chance levels on a counterfactual inference test, while age matched controls performed above chance levels on this test. Performance on both the counterfactual generation and inference tests correlated significantly with performance on two tests traditionally linked to frontal lobe functioning (Stroop colour–word interference and Tower of London planning tasks) and one test of pragmatic social communication skills. Conclusions: Counterfactual thinking is impaired in Parkinson's disease. This impairment may be related to frontal lobe dysfunction. PMID:12876235

  12. Practical Quantum Private Database Queries Based on Passive Round-Robin Differential Phase-shift Quantum Key Distribution

    NASA Astrophysics Data System (ADS)

    Li, Jian; Yang, Yu-Guang; Chen, Xiu-Bo; Zhou, Yi-Hua; Shi, Wei-Min

    2016-08-01

    A novel quantum private database query protocol is proposed, based on passive round-robin differential phase-shift quantum key distribution. Compared with previous quantum private database query protocols, the present protocol has the following unique merits: (i) the user Alice can obtain one and only one key bit so that both the efficiency and security of the present protocol can be ensured, and (ii) it does not require to change the length difference of the two arms in a Mach-Zehnder interferometer and just chooses two pulses passively to interfere with so that it is much simpler and more practical. The present protocol is also proved to be secure in terms of the user security and database security.

  13. Practical Quantum Private Database Queries Based on Passive Round-Robin Differential Phase-shift Quantum Key Distribution.

    PubMed

    Li, Jian; Yang, Yu-Guang; Chen, Xiu-Bo; Zhou, Yi-Hua; Shi, Wei-Min

    2016-08-19

    A novel quantum private database query protocol is proposed, based on passive round-robin differential phase-shift quantum key distribution. Compared with previous quantum private database query protocols, the present protocol has the following unique merits: (i) the user Alice can obtain one and only one key bit so that both the efficiency and security of the present protocol can be ensured, and (ii) it does not require to change the length difference of the two arms in a Mach-Zehnder interferometer and just chooses two pulses passively to interfere with so that it is much simpler and more practical. The present protocol is also proved to be secure in terms of the user security and database security.

  14. Practical Quantum Private Database Queries Based on Passive Round-Robin Differential Phase-shift Quantum Key Distribution

    PubMed Central

    Li, Jian; Yang, Yu-Guang; Chen, Xiu-Bo; Zhou, Yi-Hua; Shi, Wei-Min

    2016-01-01

    A novel quantum private database query protocol is proposed, based on passive round-robin differential phase-shift quantum key distribution. Compared with previous quantum private database query protocols, the present protocol has the following unique merits: (i) the user Alice can obtain one and only one key bit so that both the efficiency and security of the present protocol can be ensured, and (ii) it does not require to change the length difference of the two arms in a Mach-Zehnder interferometer and just chooses two pulses passively to interfere with so that it is much simpler and more practical. The present protocol is also proved to be secure in terms of the user security and database security. PMID:27539654

  15. Molecular thermodynamics of metabolism: quantum thermochemical calculations for key metabolites.

    PubMed

    Hadadi, N; Ataman, M; Hatzimanikatis, V; Panayiotou, C

    2015-04-28

    The present work is the first of a series of papers aiming at a coherent and unified development of the thermodynamics of metabolism and the rationalization of feasibility analysis of metabolic pathways. The focus in this part is on high-level quantum chemical calculations of the thermochemical quantities of relatively heavy metabolites such as amino acids/oligopeptides, nucleosides, saccharides and their derivatives in the ideal gas state. The results of this study will be combined with the corresponding hydration/solvation results in subsequent parts of this work in order to derive the desired thermochemical quantities in aqueous solutions. The above metabolites exist in a vast conformational/isomerization space including rotational conformers, tautomers or anomers exhibiting often multiple or cooperative intramolecular hydrogen bonding. We examine the challenges posed by these features for the reliable estimation of thermochemical quantities. We discuss conformer search, conformer distribution and averaging processes. We further consider neutral metabolites as well as protonated and deprotonated metabolites. In addition to the traditional presentation of gas-phase acidities, basicities and proton affinities, we also examine heats and free energies of ionic species. We obtain simple linear relations between the thermochemical quantities of ions and the formation quantities of their neutral counterparts. Furthermore, we compare our calculations with reliable experimental measurements and predictive calculations from the literature, when available. Finally, we discuss the next steps and perspectives for this work.

  16. High-speed free-space quantum key distribution system for urban daylight applications.

    PubMed

    García-Martínez, M J; Denisenko, N; Soto, D; Arroyo, D; Orue, A B; Fernandez, V

    2013-05-10

    We report a free-space quantum key distribution system designed for high-speed key transmission in urban areas. Clocking the system at gigahertz frequencies and efficiently filtering background enables higher secure key rates than those previously achieved by similar systems. The transmitter and receiver are located in two separate buildings 300 m apart in downtown Madrid and they exchange secure keys at rates up to 1 Mbps. The system operates in full bright daylight conditions with an average secure key rate of 0.5 Mbps and 24 h stability without human intervention.

  17. Plug-and-play measurement-device-independent quantum key distribution

    NASA Astrophysics Data System (ADS)

    Choi, Yujun; Kwon, Osung; Woo, Minki; Oh, Kyunghwan; Han, Sang-Wook; Kim, Yong-Su; Moon, Sung

    2016-03-01

    Quantum key distribution (QKD) guarantees unconditional communication security based on the laws of quantum physics. However, practical QKD suffers from a number of quantum hackings due to the device imperfections. From the security standpoint, measurement-device-independent quantum key distribution (MDI-QKD) is in the limelight since it eliminates all the possible loopholes in detection. Due to active control units for mode matching between the photons from remote parties, however, the implementation of MDI-QKD is highly impractical. In this paper, we propose a method to resolve the mode matching problem while minimizing the use of active control units. By introducing the plug-and-play (P&P) concept into MDI-QKD, the indistinguishability in spectral and polarization modes between photons can naturally be guaranteed. We show the feasibility of P&P MDI-QKD with a proof-of-principle experiment.

  18. Continuous-variable quantum enigma machines for long-distance key distribution

    NASA Astrophysics Data System (ADS)

    Lupo, Cosmo; Lloyd, Seth

    2015-12-01

    Quantum physics allows for unconditionally secure communication through insecure communication channels. The achievable rates of quantum-secured communication are fundamentally limited by the laws of quantum physics and in particular by the properties of entanglement. For a lossy communication line, this implies that the secret-key generation rate vanishes at least exponentially with the communication distance. We show that this fundamental limitation can be violated in a realistic scenario where the eavesdropper can store quantum information for only a finite, yet arbitrarily long, time. We consider communication through a lossy bononic channel (modeling linear loss in optical fibers) and we show that it is in principle possible to achieve a constant rate of key generation of one bit per optical mode over arbitrarily long communication distances.

  19. Multiplexing scheme for simplified entanglement-based large-alphabet quantum key distribution

    NASA Astrophysics Data System (ADS)

    Dada, Adetunmise C.

    2015-05-01

    We propose a practical quantum cryptographic scheme which combines high information capacity, such as provided by high-dimensional quantum entanglement, with the simplicity of a two-dimensional Clauser-Horne-Shimony-Holt (CHSH) Bell test for security verification. By applying a state combining entanglement in a two-dimensional degree of freedom, such as photon polarization, with high-dimensional correlations in another degree of freedom, such as photon orbital angular momentum (OAM) or path, the scheme provides a considerably simplified route towards security verification in quantum key distribution (QKD) aimed at exploiting high-dimensional quantum systems for increased secure key rates. It also benefits from security against collective attacks and is feasible using currently available technologies.

  20. High Speed Quantum Key Distribution Over Optical Fiber Network System1

    PubMed Central

    Ma, Lijun; Mink, Alan; Tang, Xiao

    2009-01-01

    The National Institute of Standards and Technology (NIST) has developed a number of complete fiber-based high-speed quantum key distribution (QKD) systems that includes an 850 nm QKD system for a local area network (LAN), a 1310 nm QKD system for a metropolitan area network (MAN), and a 3-node quantum network controlled by a network manager. This paper discusses the key techniques used to implement these systems, which include polarization recovery, noise reduction, frequency up-conversion detection based on a periodically polled lithium nitrate (PPLN) waveguide, custom high-speed data handling boards and quantum network management. Using our quantum network, a QKD secured video surveillance application has been demonstrated. Our intention is to show the feasibility and sophistication of QKD systems based on current technology. PMID:27504218

  1. An improved arbitrated quantum signature protocol based on the key-controlled chained CNOT encryption

    NASA Astrophysics Data System (ADS)

    Zhang, Long; Sun, Hong-Wei; Zhang, Ke-Jia; Jia, Heng-Yue

    2017-03-01

    In this paper, a new quantum encryption based on the key-controlled chained CNOT operations, which is named KCCC encryption, is proposed. With the KCCC encryption, an improved arbitrated quantum signature (AQS) protocol is presented. Compared with the existing protocols, our protocol can effectively prevent forgery attacks and disavowal attacks. Moreover, only single state is required in the protocol. We hope it is helpful to further research in the design of AQS protocols in future.

  2. The excess choice effect: The role of outcome valence and counterfactual thinking.

    PubMed

    Hafner, Rebecca J; White, Mathew P; Handley, Simon J

    2016-02-01

    Contrary to economic theory, psychological research has demonstrated increased choice can undermine satisfaction. When and why this 'excess choice effect' (ECE) occurs remains unclear. Building on theories of counterfactual thinking we argue the ECE is more likely to occur when people experience counterfactual thought or emotion and that a key trigger is a negative versus positive task outcome. Participants either selected a drink (Experiment 1) or chocolate (Experiment 2) from a limited (6) versus extensive (24) selection (Experiment 1) or were given no choice versus extensive (24) choice (Experiment 2). In both experiments, however, the choice was illusory: Half the participants tasted a 'good' flavour, half a 'bad' flavour. As predicted, extensive choice was only detrimental to satisfaction when participants tasted the 'bad' drink or chocolate, and this was mediated by the experience of counterfactual thought (Experiment 1) or emotion (Experiment 2). When outcomes were positive, participants were similarly satisfied with limited versus extensive and no choice versus extensive choice. Implications for our theoretical understanding of the ECE and for the construction of choice architectures aimed at promoting individual satisfaction and well-being are discussed.

  3. Multi-user quantum key distribution with entangled photons from an AlGaAs chip

    NASA Astrophysics Data System (ADS)

    Autebert, C.; Trapateau, J.; Orieux, A.; Lemaître, A.; Gomez-Carbonell, C.; Diamanti, E.; Zaquine, I.; Ducci, S.

    2016-12-01

    In view of real-world applications of quantum information technologies, the combination of miniature quantum resources with existing fibre networks is a crucial issue. Among such resources, on-chip entangled photon sources play a central role for applications spanning quantum communications, computing and metrology. Here, we use a semiconductor source of entangled photons operating at room temperature in conjunction with standard telecom components to demonstrate multi-user quantum key distribution, a core protocol for securing communications in quantum networks. The source consists of an AlGaAs chip-emitting polarisation entangled photon pairs over a large bandwidth in the main telecom band around 1550 nm without the use of any off-chip compensation or interferometric scheme; the photon pairs are directly launched into a dense wavelength division multiplexer (DWDM) and secret keys are distributed between several pairs of users communicating through different channels. We achieve a visibility measured after the DWDM of 87% and show long-distance key distribution using a 50-km standard telecom fibre link between two network users. These results illustrate a promising route to practical, resource-efficient implementations adapted to quantum network infrastructures.

  4. Practical private database queries based on a quantum-key-distribution protocol

    SciTech Connect

    Jakobi, Markus; Simon, Christoph; Gisin, Nicolas; Bancal, Jean-Daniel; Branciard, Cyril; Walenta, Nino; Zbinden, Hugo

    2011-02-15

    Private queries allow a user, Alice, to learn an element of a database held by a provider, Bob, without revealing which element she is interested in, while limiting her information about the other elements. We propose to implement private queries based on a quantum-key-distribution protocol, with changes only in the classical postprocessing of the key. This approach makes our scheme both easy to implement and loss tolerant. While unconditionally secure private queries are known to be impossible, we argue that an interesting degree of security can be achieved by relying on fundamental physical principles instead of unverifiable security assumptions in order to protect both the user and the database. We think that the scope exists for such practical private queries to become another remarkable application of quantum information in the footsteps of quantum key distribution.

  5. Measurement-device-independent quantum key distribution with q-plate

    NASA Astrophysics Data System (ADS)

    Chen, Dong; Shang-Hong, Zhao; Ying, Sun

    2015-12-01

    The original measurement-device-independent quantum key distribution is reviewed and a modified protocol using rotation invariant photonic state is proposed. A hybrid encoding approach combined polarization qubit with orbit angular momentum qubit is adopted to overcome the polarization misalignment associated with random rotations in long-distance quantum key distribution. The initial encoding and final decoding of information in our MDI-QKD implementation protocol can be conveniently performed in the polarization space, while the transmission is done in the rotation invariant hybrid space. Our analysis indicates that both the secure key rate and transmission distance can be improved with our modified protocol owing to the lower quantum bit error rate. Furthermore, our hybrid encoding approach only needs to insert four q-plates in practical experiment and to overcome the polarization misalignment problem mentioned above without including any feedback control.

  6. Faked state attacks on realistic round robin DPS quantum key distribution systems and countermeasure

    NASA Astrophysics Data System (ADS)

    Iwakoshi, T.

    2015-05-01

    In May 2014, a new quantum key distribution protocol named "Round Robin Differential-Phase-Shift Quantum Key Distribution (RR DPS QKD)" was proposed. It has a special feature that the key consumption via privacy amplification is a small constant because RR DPS QKD guarantees its security by information causality, not by information-disturbance trade-off. Therefore, the authors claimed that RR DPS QKD systems does not need to monitor the disturbance by an attacker in the quantum channel. However, this study shows that a modified Faked-State Attack (or so-called bright illumination attack) can hack a RR DPS QKD system almost perfectly if it is implemented with realistic detectors even information-causality guarantees the security of RR DPS QKD protocol. Therefore, this study also proposes a possible Measurement-Device-Independent RR DPS QKD system to avoid the modified Faked-State Attack.

  7. Heralded-qubit amplifiers for practical device-independent quantum key distribution

    SciTech Connect

    Curty, Marcos; Moroder, Tobias

    2011-07-15

    Device-independent quantum key distribution does not need a precise quantum mechanical model of employed devices to guarantee security. Despite its beauty, it is still a very challenging experimental task. We compare a recent proposal by Gisin et al.[Phys. Rev. Lett. 105, 070501 (2010)] to close the detection loophole problem with that of a simpler quantum relay based on entanglement swapping with linear optics. Our full-mode analysis for both schemes confirms that, in contrast to recent beliefs, the second scheme can indeed provide a positive key rate which is even considerably higher than that of the first alternative. The resulting key rates and required detection efficiencies of approximately 95% for both schemes, however, strongly depend on the underlying security proof.

  8. Long-distance measurement-device-independent quantum key distribution with coherent-state superpositions.

    PubMed

    Yin, H-L; Cao, W-F; Fu, Y; Tang, Y-L; Liu, Y; Chen, T-Y; Chen, Z-B

    2014-09-15

    Measurement-device-independent quantum key distribution (MDI-QKD) with decoy-state method is believed to be securely applied to defeat various hacking attacks in practical quantum key distribution systems. Recently, the coherent-state superpositions (CSS) have emerged as an alternative to single-photon qubits for quantum information processing and metrology. Here, in this Letter, CSS are exploited as the source in MDI-QKD. We present an analytical method that gives two tight formulas to estimate the lower bound of yield and the upper bound of bit error rate. We exploit the standard statistical analysis and Chernoff bound to perform the parameter estimation. Chernoff bound can provide good bounds in the long-distance MDI-QKD. Our results show that with CSS, both the security transmission distance and secure key rate are significantly improved compared with those of the weak coherent states in the finite-data case.

  9. Quantum hacking of two-way continuous-variable quantum key distribution using Trojan-horse attack

    NASA Astrophysics Data System (ADS)

    Ma, Hong-Xin; Bao, Wan-Su; Li, Hong-Wei; Chou, Chun

    2016-08-01

    We present a Trojan-horse attack on the practical two-way continuous-variable quantum key distribution system. Our attack mainly focuses on the imperfection of the practical system that the modulator has a redundancy of modulation pulse-width, which leaves a loophole for the eavesdropper inserting a Trojan-horse pulse. Utilizing the unique characteristics of two-way continuous-variable quantum key distribution that Alice only takes modulation operation on the received mode without any measurement, this attack allows the eavesdropper to render all of the final keys shared between the legitimate parties insecure without being detected. After analyzing the feasibility of the attack, the corresponding countermeasures are put forward. Project supported by the National Basic Research Program of China (Grant No. 2013CB338002) and the National Natural Science Foundation of China (Grant Nos. 11304397 and 61505261).

  10. Misinterpretation of statistical distance in security of quantum key distribution shown by simulation

    NASA Astrophysics Data System (ADS)

    Iwakoshi, Takehisa; Hirota, Osamu

    2014-10-01

    This study will test an interpretation in quantum key distribution (QKD) that trace distance between the distributed quantum state and the ideal mixed state is a maximum failure probability of the protocol. Around 2004, this interpretation was proposed and standardized to satisfy both of the key uniformity in the context of universal composability and operational meaning of the failure probability of the key extraction. However, this proposal has not been verified concretely yet for many years while H. P. Yuen and O. Hirota have thrown doubt on this interpretation since 2009. To ascertain this interpretation, a physical random number generator was employed to evaluate key uniformity in QKD. In this way, we calculated statistical distance which correspond to trace distance in quantum theory after a quantum measurement is done, then we compared it with the failure probability whether universal composability was obtained. As a result, the degree of statistical distance of the probability distribution of the physical random numbers and the ideal uniformity was very large. It is also explained why trace distance is not suitable to guarantee the security in QKD from the view point of quantum binary decision theory.

  11. Differential-phase-shift quantum key distribution using heralded narrow-band single photons.

    PubMed

    Liu, Chang; Zhang, Shanchao; Zhao, Luwei; Chen, Peng; Fung, C-H F; Chau, H F; Loy, M M T; Du, Shengwang

    2013-04-22

    We demonstrate the first proof of principle differential phase shift (DPS) quantum key distribution (QKD) using narrow-band heralded single photons with amplitude-phase modulations. In the 3-pulse case, we obtain a quantum bit error rate (QBER) as low as 3.06% which meets the unconditional security requirement. As we increase the pulse number up to 15, the key creation efficiency approaches 93.4%, but with a cost of increasing the QBER. Our result suggests that narrow-band single photons maybe a promising source for the DPS-QKD protocol.

  12. High performance frame synchronization for continuous variable quantum key distribution systems.

    PubMed

    Lin, Dakai; Huang, Peng; Huang, Duan; Wang, Chao; Peng, Jinye; Zeng, Guihua

    2015-08-24

    Considering a practical continuous variable quantum key distribution(CVQKD) system, synchronization is of significant importance as it is hardly possible to extract secret keys from unsynchronized strings. In this paper, we proposed a high performance frame synchronization method for CVQKD systems which is capable to operate under low signal-to-noise(SNR) ratios and is compatible with random phase shift induced by quantum channel. A practical implementation of this method with low complexity is presented and its performance is analysed. By adjusting the length of synchronization frame, this method can work well with large range of SNR values which paves the way for longer distance CVQKD.

  13. Large-Alphabet Quantum Key Distribution Using Energy-Time Entangled Bipartite States

    NASA Astrophysics Data System (ADS)

    Ali-Khan, Irfan; Broadbent, Curtis J.; Howell, John C.

    2007-02-01

    We present a protocol for large-alphabet quantum key distribution (QKD) using energy-time entangled biphotons. Binned, high-resolution timing measurements are used to generate a large-alphabet key with over 10 bits of information per photon pair, albeit with large noise. QKD with 5% bit error rate is demonstrated with 4 bits of information per photon pair, where the security of the quantum channel is determined by the visibility of Franson interference fringes. The protocol is easily generalizable to even larger alphabets, and utilizes energy-time entanglement which is robust to transmission over large distances in fiber.

  14. Secure quantum key distribution with a single not-so-weak coherent pulse

    NASA Astrophysics Data System (ADS)

    Kim, Chil-Min; Kim, Yong-Wan; Park, Young-Jai

    2007-04-01

    We propose a secure quantum key distribution (QKD) protocol using a single not-so-weak coherent qubit. With two preprocesses for random rotation and compensation, a key bit is encoded to a randomly polarized not-so-weak coherent qubit. We analyze the security of the QKD protocol, which counters the photon number splitting and the impersonation attacks. The estimated mean number of photon, which is less than 6.0, guarantees security. Additionally, we discuss the possibility of quantum secure direct communication.

  15. Quantum cryptography: Theoretical protocols for quantum key distribution and tests of selected commercial QKD systems in commercial fiber networks

    NASA Astrophysics Data System (ADS)

    Jacak, Monika; Jacak, Janusz; Jóźwiak, Piotr; Jóźwiak, Ireneusz

    2016-06-01

    The overview of the current status of quantum cryptography is given in regard to quantum key distribution (QKD) protocols, implemented both on nonentangled and entangled flying qubits. Two commercial R&D platforms of QKD systems are described (the Clavis II platform by idQuantique implemented on nonentangled photons and the EPR S405 Quelle platform by AIT based on entangled photons) and tested for feasibility of their usage in commercial TELECOM fiber metropolitan networks. The comparison of systems efficiency, stability and resistivity against noise and hacker attacks is given with some suggestion toward system improvement, along with assessment of two models of QKD.

  16. Basic Conditional Reasoning: How Children Mimic Counterfactual Reasoning

    PubMed Central

    Leahy, Brian; Rafetseder, Eva; Perner, Josef

    2014-01-01

    Children approach counterfactual questions about stories with a reasoning strategy that falls short of adults’ Counterfactual Reasoning (CFR). It was dubbed “Basic Conditional Reasoning” (BCR) in Rafetseder et al. (Child Dev 81(1):376-389, 2010). In this paper we provide a characterisation of the differences between BCR and CFR using a distinction between permanent and nonpermanent features of stories and Lewis/Stalnaker counterfactual logic. The critical difference pertains to how consistency between a story and a conditional antecedent incompatible with a nonpermanent feature of the story is achieved. Basic conditional reasoners simply drop all nonpermanent features of the story. Counterfactual reasoners preserve as much of the story as possible while accommodating the antecedent. PMID:25729114

  17. Basic Conditional Reasoning: How Children Mimic Counterfactual Reasoning.

    PubMed

    Leahy, Brian; Rafetseder, Eva; Perner, Josef

    2014-08-01

    Children approach counterfactual questions about stories with a reasoning strategy that falls short of adults' Counterfactual Reasoning (CFR). It was dubbed "Basic Conditional Reasoning" (BCR) in Rafetseder et al. (Child Dev 81(1):376-389, 2010). In this paper we provide a characterisation of the differences between BCR and CFR using a distinction between permanent and nonpermanent features of stories and Lewis/Stalnaker counterfactual logic. The critical difference pertains to how consistency between a story and a conditional antecedent incompatible with a nonpermanent feature of the story is achieved. Basic conditional reasoners simply drop all nonpermanent features of the story. Counterfactual reasoners preserve as much of the story as possible while accommodating the antecedent.

  18. Phase-remapping attack in practical quantum-key-distribution systems

    NASA Astrophysics Data System (ADS)

    Fung, Chi-Hang Fred; Qi, Bing; Tamaki, Kiyoshi; Lo, Hoi-Kwong

    2007-03-01

    Quantum key distribution (QKD) can be used to generate secret keys between two distant parties. Even though QKD has been proven unconditionally secure against eavesdroppers with unlimited computation power, practical implementations of QKD may contain loopholes that may lead to the generated secret keys being compromised. In this paper, we propose a phase-remapping attack targeting two practical bidirectional QKD systems (the “plug-and-play” system and the Sagnac system). We showed that if the users of the systems are unaware of our attack, the final key shared between them can be compromised in some situations. Specifically, we showed that, in the case of the Bennett-Brassard 1984 (BB84) protocol with ideal single-photon sources, when the quantum bit error rate (QBER) is between 14.6% and 20%, our attack renders the final key insecure, whereas the same range of QBER values has been proved secure if the two users are unaware of our attack; also, we demonstrated three situations with realistic devices where positive key rates are obtained without the consideration of Trojan horse attacks but in fact no key can be distilled. We remark that our attack is feasible with only current technology. Therefore, it is very important to be aware of our attack in order to ensure absolute security. In finding our attack, we minimize the QBER over individual measurements described by a general POVM, which has some similarity with the standard quantum state discrimination problem.

  19. Making the decoy-state measurement-device-independent quantum key distribution practically useful

    NASA Astrophysics Data System (ADS)

    Zhou, Yi-Heng; Yu, Zong-Wen; Wang, Xiang-Bin

    2016-04-01

    The relatively low key rate seems to be the major barrier to its practical use for the decoy-state measurement-device-independent quantum key distribution (MDI-QKD). We present a four-intensity protocol for the decoy-state MDI-QKD that hugely raises the key rate, especially in the case in which the total data size is not large. Also, calculations show that our method makes it possible for secure private communication with fresh keys generated from MDI-QKD with a delay time of only a few seconds.

  20. Polarization recovery and auto-compensation in quantum key distribution network

    NASA Astrophysics Data System (ADS)

    Ma, Lijun; Xu, Hai; Tang, Xiao

    2006-08-01

    A Quantum Key Distribution (QKD) network can allow multi-user communication via secure key. Moreover, by actively switching communication nodes, one can achieve high key transmission rate for the selected nodes. However, the polarization properties of different fiber path are different and these properties also randomly drift over time. Therefore, polarization recovery after the switching and auto-compensation during key transmission are critical for the QKD network. In this work, we use programmable polarization controllers to implement polarization recovery and auto-compensation in the QKD network. We will also discuss its time limitation and future improvement.

  1. Secure coherent-state quantum key distribution protocols with efficient reconciliation

    SciTech Connect

    Assche, G. van; Cerf, N.J.

    2005-05-15

    We study the equivalence of a realistic quantum key distribution protocol using coherent states and homodyne detection with a formal entanglement purification protocol. Maximally entangled qubit pairs that one can extract in the formal protocol correspond to secret key bits in the realistic protocol. More specifically, we define a qubit encoding scheme that allows the formal protocol to produce more than one entangled qubit pair per entangled oscillator pair or, equivalently for the realistic protocol, more than one secret key bit per coherent state. The entanglement parameters are estimated using quantum tomography. We analyze the properties of the encoding scheme and investigate the resulting secret key rate in the important case of the attenuation channel.

  2. Hacking on decoy-state quantum key distribution system with partial phase randomization

    PubMed Central

    Sun, Shi-Hai; Jiang, Mu-Sheng; Ma, Xiang-Chun; Li, Chun-Yan; Liang, Lin-Mei

    2014-01-01

    Quantum key distribution (QKD) provides means for unconditional secure key transmission between two distant parties. However, in practical implementations, it suffers from quantum hacking due to device imperfections. Here we propose a hybrid measurement attack, with only linear optics, homodyne detection, and single photon detection, to the widely used vacuum + weak decoy state QKD system when the phase of source is partially randomized. Our analysis shows that, in some parameter regimes, the proposed attack would result in an entanglement breaking channel but still be able to trick the legitimate users to believe they have transmitted secure keys. That is, the eavesdropper is able to steal all the key information without discovered by the users. Thus, our proposal reveals that partial phase randomization is not sufficient to guarantee the security of phase-encoding QKD systems with weak coherent states. PMID:24755767

  3. Security of a practical semi-device-independent quantum key distribution protocol against collective attacks

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Bao, Wan-Su; Li, Hong-Wei; Zhou, Chun; Li, Yuan

    2014-08-01

    Similar to device-independent quantum key distribution (DI-QKD), semi-device-independent quantum key distribution (SDI-QKD) provides secure key distribution without any assumptions about the internal workings of the QKD devices. The only assumption is that the dimension of the Hilbert space is bounded. But SDI-QKD can be implemented in a one-way prepare-and-measure configuration without entanglement compared with DI-QKD. We propose a practical SDI-QKD protocol with four preparation states and three measurement bases by considering the maximal violation of dimension witnesses and specific processes of a QKD protocol. Moreover, we prove the security of the SDI-QKD protocol against collective attacks based on the min-entropy and dimension witnesses. We also show a comparison of the secret key rate between the SDI-QKD protocol and the standard QKD.

  4. Improving the security of protocols of quantum key agreement solely using Bell states and Bell measurement

    NASA Astrophysics Data System (ADS)

    Zhu, Zhen-Chao; Hu, Ai-Qun; Fu, An-Min

    2015-11-01

    In a recent study, Shukla et al. (Quantum Inf Process 13:2391-2405, 2014) proposed two quantum key agreement protocols based on Bell state and Bell measurement, and they claimed that their two protocols were secure. However, in this study, we will show that the three-party protocol they proposed is not secure. Any participant in the protocol can directly obtain other two participants' secret keys. More seriously, two dishonest participants in the protocol can conclude to determine the shared key alone. Furthermore, we will show that there is another minor flaw in their two protocols; that is, eavesdroppers can flip any bit of the final key without introducing any error. In the end, some possible improvements are proposed to avoid these flaws.

  5. Hacking on decoy-state quantum key distribution system with partial phase randomization

    NASA Astrophysics Data System (ADS)

    Sun, Shi-Hai; Jiang, Mu-Sheng; Ma, Xiang-Chun; Li, Chun-Yan; Liang, Lin-Mei

    2014-04-01

    Quantum key distribution (QKD) provides means for unconditional secure key transmission between two distant parties. However, in practical implementations, it suffers from quantum hacking due to device imperfections. Here we propose a hybrid measurement attack, with only linear optics, homodyne detection, and single photon detection, to the widely used vacuum + weak decoy state QKD system when the phase of source is partially randomized. Our analysis shows that, in some parameter regimes, the proposed attack would result in an entanglement breaking channel but still be able to trick the legitimate users to believe they have transmitted secure keys. That is, the eavesdropper is able to steal all the key information without discovered by the users. Thus, our proposal reveals that partial phase randomization is not sufficient to guarantee the security of phase-encoding QKD systems with weak coherent states.

  6. Hacking on decoy-state quantum key distribution system with partial phase randomization.

    PubMed

    Sun, Shi-Hai; Jiang, Mu-Sheng; Ma, Xiang-Chun; Li, Chun-Yan; Liang, Lin-Mei

    2014-04-23

    Quantum key distribution (QKD) provides means for unconditional secure key transmission between two distant parties. However, in practical implementations, it suffers from quantum hacking due to device imperfections. Here we propose a hybrid measurement attack, with only linear optics, homodyne detection, and single photon detection, to the widely used vacuum + weak decoy state QKD system when the phase of source is partially randomized. Our analysis shows that, in some parameter regimes, the proposed attack would result in an entanglement breaking channel but still be able to trick the legitimate users to believe they have transmitted secure keys. That is, the eavesdropper is able to steal all the key information without discovered by the users. Thus, our proposal reveals that partial phase randomization is not sufficient to guarantee the security of phase-encoding QKD systems with weak coherent states.

  7. Improving Physical Task Performance with Counterfactual and Prefactual Thinking

    PubMed Central

    Hammell, Cecilia; Chan, Amy Y. C.

    2016-01-01

    Counterfactual thinking (reflecting on “what might have been”) has been shown to enhance future performance by translating information about past mistakes into plans for future action. Prefactual thinking (imagining “what might be if…”) may serve a greater preparative function than counterfactual thinking as it is future-orientated and focuses on more controllable features, thus providing a practical script to prime future behaviour. However, whether or not this difference in hypothetical thought content may translate into a difference in actual task performance has been largely unexamined. In Experiment 1 (n = 42), participants performed trials of a computer-simulated physical task, in between which they engaged in either task-related hypothetical thinking (counterfactual or prefactual) or an unrelated filler task (control). As hypothesised, prefactuals contained more controllable features than counterfactuals. Moreover, participants who engaged in either form of hypothetical thinking improved significantly in task performance over trials compared to participants in the control group. The difference in thought content between counterfactuals and prefactuals, however, did not yield a significant difference in performance improvement. Experiment 2 (n = 42) replicated these findings in a dynamic balance task environment. Together, these findings provide further evidence for the preparatory function of counterfactuals, and demonstrate that prefactuals share this same functional characteristic. PMID:27942041

  8. Measurement-device-independent quantum key distribution with source state errors and statistical fluctuation

    NASA Astrophysics Data System (ADS)

    Jiang, Cong; Yu, Zong-Wen; Wang, Xiang-Bin

    2017-03-01

    We show how to calculate the secure final key rate in the four-intensity decoy-state measurement-device-independent quantum key distribution protocol with both source errors and statistical fluctuations with a certain failure probability. Our results rely only on the range of only a few parameters in the source state. All imperfections in this protocol have been taken into consideration without assuming any specific error patterns of the source.

  9. Optimal pair-generation rate for entanglement-based quantum key distribution

    NASA Astrophysics Data System (ADS)

    Holloway, Catherine; Doucette, John A.; Erven, Christopher; Bourgoin, Jean-Philippe; Jennewein, Thomas

    2013-02-01

    In entanglement-based quantum key distribution (QKD), the generation and detection of multiphoton modes leads to a trade-off between entanglement visibility and twofold coincidence events when maximizing the secure key rate. We produce a predictive model for the optimal twofold coincidence probability per coincidence window given the channel efficiency and detector dark count rate of a given system. This model is experimentally validated and used in simulations for QKD with satellites as well as optical fibers.

  10. Upper bound on the secret key rate distillable from effective quantum correlations with imperfect detectors

    SciTech Connect

    Moroder, Tobias; Curty, Marcos; Luetkenhaus, Norbert

    2006-01-15

    We provide a simple method to obtain an upper bound on the secret key rate that is particularly suited to analyze practical realizations of quantum key distribution protocols with imperfect devices. We consider the so-called trusted device scenario where Eve cannot modify the actual detection devices employed by Alice and Bob. The upper bound obtained is based on the available measurements results, but it includes the effect of the noise and losses present in the detectors of the legitimate users.

  11. W-state Analyzer and Multi-party Measurement-device-independent Quantum Key Distribution.

    PubMed

    Zhu, Changhua; Xu, Feihu; Pei, Changxing

    2015-12-08

    W-state is an important resource for many quantum information processing tasks. In this paper, we for the first time propose a multi-party measurement-device-independent quantum key distribution (MDI-QKD) protocol based on W-state. With linear optics, we design a W-state analyzer in order to distinguish the four-qubit W-state. This analyzer constructs the measurement device for four-party MDI-QKD. Moreover, we derived a complete security proof of the four-party MDI-QKD, and performed a numerical simulation to study its performance. The results show that four-party MDI-QKD is feasible over 150 km standard telecom fiber with off-the-shelf single photon detectors. This work takes an important step towards multi-party quantum communication and a quantum network.

  12. W-state Analyzer and Multi-party Measurement-device-independent Quantum Key Distribution

    PubMed Central

    Zhu, Changhua; Xu, Feihu; Pei, Changxing

    2015-01-01

    W-state is an important resource for many quantum information processing tasks. In this paper, we for the first time propose a multi-party measurement-device-independent quantum key distribution (MDI-QKD) protocol based on W-state. With linear optics, we design a W-state analyzer in order to distinguish the four-qubit W-state. This analyzer constructs the measurement device for four-party MDI-QKD. Moreover, we derived a complete security proof of the four-party MDI-QKD, and performed a numerical simulation to study its performance. The results show that four-party MDI-QKD is feasible over 150 km standard telecom fiber with off-the-shelf single photon detectors. This work takes an important step towards multi-party quantum communication and a quantum network. PMID:26644289

  13. Device-independent quantum key distribution using single-photon entanglement

    NASA Astrophysics Data System (ADS)

    Kamaruddin, S.; Shaari, J. S.

    2015-04-01

    Quantum key distribution (QKD) with security features based on the notion of nonlocality has provided valuable insights into the possibility of device-independent scenarios. The essential resource for nonlocality in Nature described by quantum physics has been mainly associated with entanglement of two particles or more, although it has been shown that nonlocality of a single particle is indeed possible. Here, we consider a quantum key distribution scheme based on Phys. Rev. A, 68 (2003) 012324 exploiting single-particle nonlocality testing to demonstrate its security. We present our analysis of security against individual attack within a device-independent scenario where Eve is constrained only by the no-signaling principle. We further consider a family of QKD protocols based on binary measurements and discuss the possibility of optimal scenarios.

  14. 2 GHz clock quantum key distribution over 260 km of standard telecom fiber.

    PubMed

    Wang, Shuang; Chen, Wei; Guo, Jun-Fu; Yin, Zhen-Qiang; Li, Hong-Wei; Zhou, Zheng; Guo, Guang-Can; Han, Zheng-Fu

    2012-03-15

    We report a demonstration of quantum key distribution (QKD) over a standard telecom fiber exceeding 50 dB in loss and 250 km in length. The differential phase shift QKD protocol was chosen and implemented with a 2 GHz system clock rate. By careful optimization of the 1 bit delayed Faraday-Michelson interferometer and the use of the superconducting single photon detector (SSPD), we achieved a quantum bit error rate below 2% when the fiber length was no more than 205 km, and of 3.45% for a 260 km fiber with 52.9 dB loss. We also improved the quantum efficiency of SSPD to obtain a high key rate for 50 km length.

  15. Kochen-Specker theorem as a precondition for secure quantum key distribution

    SciTech Connect

    Nagata, Koji

    2005-07-15

    We show that (1) the violation of the Ekert 1991 inequality is a sufficient condition for certification of the Kochen-Specker (KS) theorem, and (2) the violation of the Bennett-Brassard-Mermin 1992 (BBM92) inequality is, also, a sufficient condition for certification of the KS theorem. Therefore the success in each quantum key distribution protocol reveals the nonclassical feature of quantum theory, in the sense that the KS realism is violated. Further, it turned out that the Ekert inequality and the BBM inequality are depictured by distillable entanglement witness inequalities. Here, we connect the success in these two key distribution processes into the no-hidden-variables theorem and into witness on distillable entanglement. We also discuss the explicit difference between the KS realism and Bell's local realism in the Hilbert space formalism of quantum theory.

  16. Measurement-Device-Independent Quantum Key Distribution over Untrustful Metropolitan Network

    NASA Astrophysics Data System (ADS)

    Tang, Yan-Lin; Yin, Hua-Lei; Zhao, Qi; Liu, Hui; Sun, Xiang-Xiang; Huang, Ming-Qi; Zhang, Wei-Jun; Chen, Si-Jing; Zhang, Lu; You, Li-Xing; Wang, Zhen; Liu, Yang; Lu, Chao-Yang; Jiang, Xiao; Ma, Xiongfeng; Zhang, Qiang; Chen, Teng-Yun; Pan, Jian-Wei

    2016-01-01

    Quantum cryptography holds the promise to establish an information-theoretically secure global network. All field tests of metropolitan-scale quantum networks to date are based on trusted relays. The security critically relies on the accountability of the trusted relays, which will break down if the relay is dishonest or compromised. Here, we construct a measurement-device-independent quantum key distribution (MDIQKD) network in a star topology over a 200-square-kilometer metropolitan area, which is secure against untrustful relays and against all detection attacks. In the field test, our system continuously runs through one week with a secure key rate 10 times larger than previous results. Our results demonstrate that the MDIQKD network, combining the best of both worlds—security and practicality, constitutes an appealing solution to secure metropolitan communications.

  17. Multi-user quantum key distribution with collective eavesdropping detection over collective-noise channels

    NASA Astrophysics Data System (ADS)

    Huang, Wei; Wen, Qiao-Yan; Liu, Bin; Gao, Fei

    2015-07-01

    A multi-user quantum key distribution protocol is proposed with single particles and the collective eavesdropping detection strategy on a star network. By utilizing this protocol, any two users of the network can accomplish quantum key distribution with the help of a serving center. Due to the utilization of the collective eavesdropping detection strategy, the users of the protocol just need to have the ability of performing certain unitary operations. Furthermore, we present three fault-tolerant versions of the proposed protocol, which can combat with the errors over different collective-noise channels. The security of all the proposed protocols is guaranteed by the theorems on quantum operation discrimination. Project supported by the National Natural Science Foundation of China (Grant Nos. 61272057, 61170270, and 61309029), Beijing Higher Education Young Elite Teacher Project, China (Grant Nos. YETP0475 and YETP0477), and BUPT Excellent Ph.D. Students Foundation, China (Grant No. CX201441).

  18. Free-space quantum key distribution by rotation-invariant twisted photons.

    PubMed

    Vallone, Giuseppe; D'Ambrosio, Vincenzo; Sponselli, Anna; Slussarenko, Sergei; Marrucci, Lorenzo; Sciarrino, Fabio; Villoresi, Paolo

    2014-08-08

    "Twisted photons" are photons carrying a well-defined nonzero value of orbital angular momentum (OAM). The associated optical wave exhibits a helical shape of the wavefront (hence the name) and an optical vortex at the beam axis. The OAM of light is attracting a growing interest for its potential in photonic applications ranging from particle manipulation, microscopy, and nanotechnologies to fundamental tests of quantum mechanics, classical data multiplexing, and quantum communication. Hitherto, however, all results obtained with optical OAM were limited to laboratory scale. Here, we report the experimental demonstration of a link for free-space quantum communication with OAM operating over a distance of 210 m. Our method exploits OAM in combination with optical polarization to encode the information in rotation-invariant photonic states, so as to guarantee full independence of the communication from the local reference frames of the transmitting and receiving units. In particular, we implement quantum key distribution, a protocol exploiting the features of quantum mechanics to guarantee unconditional security in cryptographic communication, demonstrating error-rate performances that are fully compatible with real-world application requirements. Our results extend previous achievements of OAM-based quantum communication by over 2 orders of magnitude in the link scale, providing an important step forward in achieving the vision of a worldwide quantum network.

  19. Quantum circuit for the proof of the security of quantum key distribution without encryption of error syndrome and noisy processing

    NASA Astrophysics Data System (ADS)

    Tamaki, Kiyoshi; Kato, Go

    2010-02-01

    One of the simplest security proofs of quantum key distribution is based on the so-called complementarity scenario, which involves the complementarity control of an actual protocol and a virtual protocol [M. Koashi, e-print arXiv:0704.3661 (2007)]. The existing virtual protocol has a limitation in classical postprocessing, i.e., the syndrome for the error-correction step has to be encrypted. In this paper, we remove this limitation by constructing a quantum circuit for the virtual protocol. Moreover, our circuit with a shield system gives an intuitive proof of why adding noise to the sifted key increases the bit error rate threshold in the general case in which one of the parties does not possess a qubit. Thus, our circuit bridges the simple proof and the use of wider classes of classical postprocessing.

  20. Quantum circuit for the proof of the security of quantum key distribution without encryption of error syndrome and noisy processing

    SciTech Connect

    Tamaki, Kiyoshi; Kato, Go

    2010-02-15

    One of the simplest security proofs of quantum key distribution is based on the so-called complementarity scenario, which involves the complementarity control of an actual protocol and a virtual protocol [M. Koashi, e-print arXiv:0704.3661 (2007)]. The existing virtual protocol has a limitation in classical postprocessing, i.e., the syndrome for the error-correction step has to be encrypted. In this paper, we remove this limitation by constructing a quantum circuit for the virtual protocol. Moreover, our circuit with a shield system gives an intuitive proof of why adding noise to the sifted key increases the bit error rate threshold in the general case in which one of the parties does not possess a qubit. Thus, our circuit bridges the simple proof and the use of wider classes of classical postprocessing.

  1. A linear optical protocol of random quantum key distribution by using polarization entangled photons

    NASA Astrophysics Data System (ADS)

    Cao, Wen-Zhen; Wu, Yan-Hua; Jiang, Hui-Juan; Li, Chong

    2010-02-01

    Utilized polarization entangled photons, a linear optical protocol for generating random quantum key distribution (QKD) is proposed, which is made up of EPR-source, linear optical elements, and conventional photon detectors. It is shown that total efficiency of QKD η=100% in theory.

  2. High-dimensional quantum key distribution with the entangled single-photon-added coherent state

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Bao, Wan-Su; Bao, Hai-Ze; Zhou, Chun; Jiang, Mu-Sheng; Li, Hong-Wei

    2017-04-01

    High-dimensional quantum key distribution (HD-QKD) can generate more secure bits for one detection event so that it can achieve long distance key distribution with a high secret key capacity. In this Letter, we present a decoy state HD-QKD scheme with the entangled single-photon-added coherent state (ESPACS) source. We present two tight formulas to estimate the single-photon fraction of postselected events and Eve's Holevo information and derive lower bounds on the secret key capacity and the secret key rate of our protocol. We also present finite-key analysis for our protocol by using the Chernoff bound. Our numerical results show that our protocol using one decoy state can perform better than that of previous HD-QKD protocol with the spontaneous parametric down conversion (SPDC) using two decoy states. Moreover, when considering finite resources, the advantage is more obvious.

  3. Efficient bit sifting scheme of post-processing in quantum key distribution

    NASA Astrophysics Data System (ADS)

    Li, Qiong; Le, Dan; Wu, Xianyan; Niu, Xiamu; Guo, Hong

    2015-10-01

    Bit sifting is an important step in the post-processing of quantum key distribution (QKD). Its function is to sift out the undetected original keys. The communication traffic of bit sifting has essential impact on the net secure key rate of a practical QKD system. In this paper, an efficient bit sifting scheme is presented, of which the core is a lossless source coding algorithm. Both theoretical analysis and experimental results demonstrate that the performance of the scheme is approaching the Shannon limit. The proposed scheme can greatly decrease the communication traffic of the post-processing of a QKD system, which means the proposed scheme can decrease the secure key consumption for classical channel authentication and increase the net secure key rate of the QKD system, as demonstrated by analyzing the improvement on the net secure key rate. Meanwhile, some recommendations on the application of the proposed scheme to some representative practical QKD systems are also provided.

  4. A Large-alphabet Quantum Key Distribution Protocol Using Orbital Angular Momentum Entanglement

    NASA Astrophysics Data System (ADS)

    Zhao, Sheng-Mei; Gong, Long-Yan; Li, Yong-Qiang; Yang, Hua; Sheng, Yu-Bo; Cheng, Wei-Wen

    2013-06-01

    We experimentally demonstrate a quantum key distribution protocol using entangled photon pairs in orbital angular momentum (OAM). Here Alice uses a fixed phase hologram to modulate her OAM state on one photon with a spatial light modulator (SLM), while Bob uses the designed N different phase holograms for his N-based keys on the other photon with his SLM. With coincidences, Alice can fully retrieve the keys sent by Bob without reconciliation. We report the experiment results with N = 3 and OAM eigenmodes |l = ±1>, and discuss the security from the light path and typical attacks.

  5. Experimental demonstration of free-space decoy-state quantum key distribution over 144 km.

    PubMed

    Schmitt-Manderbach, Tobias; Weier, Henning; Fürst, Martin; Ursin, Rupert; Tiefenbacher, Felix; Scheidl, Thomas; Perdigues, Josep; Sodnik, Zoran; Kurtsiefer, Christian; Rarity, John G; Zeilinger, Anton; Weinfurter, Harald

    2007-01-05

    We report on the experimental implementation of a Bennett-Brassard 1984 (BB84) protocol type quantum key distribution over a 144 km free-space link using weak coherent laser pulses. Optimization of the link transmission was achieved with bidirectional active telescope tracking, and the security was ensured by employing decoy-state analysis. This enabled us to distribute a secure key at a rate of 12.8 bit/s at an attenuation of about 35 dB. Utilizing a simple transmitter setup and an optical ground station capable of tracking a spacecraft in low earth orbit, this outdoor experiment demonstrates the feasibility of global key distribution via satellites.

  6. Experimental Demonstration of Free-Space Decoy-State Quantum Key Distribution over 144km

    NASA Astrophysics Data System (ADS)

    Schmitt-Manderbach, Tobias; Weier, Henning; Fürst, Martin; Ursin, Rupert; Tiefenbacher, Felix; Scheidl, Thomas; Perdigues, Josep; Sodnik, Zoran; Kurtsiefer, Christian; Rarity, John G.; Zeilinger, Anton; Weinfurter, Harald

    2007-01-01

    We report on the experimental implementation of a Bennett-Brassard 1984 (BB84) protocol type quantum key distribution over a 144 km free-space link using weak coherent laser pulses. Optimization of the link transmission was achieved with bidirectional active telescope tracking, and the security was ensured by employing decoy-state analysis. This enabled us to distribute a secure key at a rate of 12.8bit/s at an attenuation of about 35 dB. Utilizing a simple transmitter setup and an optical ground station capable of tracking a spacecraft in low earth orbit, this outdoor experiment demonstrates the feasibility of global key distribution via satellites.

  7. Entangled quantum key distribution over two free-space optical links.

    PubMed

    Erven, C; Couteau, C; Laflamme, R; Weihs, G

    2008-10-13

    We report on the first real-time implementation of a quantum key distribution (QKD) system using entangled photon pairs that are sent over two free-space optical telescope links. The entangled photon pairs are produced with a type-II spontaneous parametric down-conversion source placed in a central, potentially untrusted, location. The two free-space links cover a distance of 435 m and 1,325 m respectively, producing a total separation of 1,575 m. The system relies on passive polarization analysis units, GPS timing receivers for synchronization, and custom written software to perform the complete QKD protocol including error correction and privacy amplification. Over 6.5 hours during the night, we observed an average raw key generation rate of 565 bits/s, an average quantum bit error rate (QBER) of 4.92%, and an average secure key generation rate of 85 bits/s.

  8. Deterministic quantum-public-key encryption: Forward search attack and randomization

    NASA Astrophysics Data System (ADS)

    Nikolopoulos, Georgios M.; Ioannou, Lawrence M.

    2009-04-01

    In the classical setting, public-key encryption requires randomness in order to be secure against a forward search attack, whereby an adversary compares the encryption of a guess of the secret message with the encryption of the actual secret message. We show that this is also true in the information-theoretic setting—where the public keys are quantum systems—by defining and giving an example of a forward search attack for any deterministic quantum-public-key bit-encryption scheme. However, unlike in the classical setting, we show that any such deterministic scheme can be used as a black box to build a randomized bit-encryption scheme that is no longer susceptible to this attack.

  9. Long-distance entanglement-based quantum key distribution over optical fiber.

    PubMed

    Honjo, T; Nam, S W; Takesue, H; Zhang, Q; Kamada, H; Nishida, Y; Tadanaga, O; Asobe, M; Baek, B; Hadfield, R; Miki, S; Fujiwara, M; Sasaki, M; Wang, Z; Inoue, K; Yamamoto, Y

    2008-11-10

    We report the first entanglement-based quantum key distribution (QKD) experiment over a 100-km optical fiber. We used superconducting single photon detectors based on NbN nanowires that provide high-speed single photon detection for the 1.5-mum telecom band, an efficient entangled photon pair source that consists of a fiber coupled periodically poled lithium niobate waveguide and ultra low loss filters, and planar lightwave circuit Mach-Zehnder interferometers (MZIs) with ultra stable operation. These characteristics enabled us to perform an entanglement-based QKD experiment over a 100-km optical fiber. In the experiment, which lasted approximately 8 hours, we successfully generated a 16 kbit sifted key with a quantum bit error rate of 6.9 % at a rate of 0.59 bits per second, from which we were able to distill a 3.9 kbit secure key.

  10. Measurement-Device-Independent Quantum Key Distribution Over a 404 km Optical Fiber

    NASA Astrophysics Data System (ADS)

    Yin, Hua-Lei; Chen, Teng-Yun; Yu, Zong-Wen; Liu, Hui; You, Li-Xing; Zhou, Yi-Heng; Chen, Si-Jing; Mao, Yingqiu; Huang, Ming-Qi; Zhang, Wei-Jun; Chen, Hao; Li, Ming Jun; Nolan, Daniel; Zhou, Fei; Jiang, Xiao; Wang, Zhen; Zhang, Qiang; Wang, Xiang-Bin; Pan, Jian-Wei

    2016-11-01

    Measurement-device-independent quantum key distribution (MDIQKD) with the decoy-state method negates security threats of both the imperfect single-photon source and detection losses. Lengthening the distance and improving the key rate of quantum key distribution (QKD) are vital issues in practical applications of QKD. Herein, we report the results of MDIQKD over 404 km of ultralow-loss optical fiber and 311 km of a standard optical fiber while employing an optimized four-intensity decoy-state method. This record-breaking implementation of the MDIQKD method not only provides a new distance record for both MDIQKD and all types of QKD systems but also, more significantly, achieves a distance that the traditional Bennett-Brassard 1984 QKD would not be able to achieve with the same detection devices even with ideal single-photon sources. This work represents a significant step toward proving and developing feasible long-distance QKD.

  11. Measurement-device-independent quantum key distribution with nitrogen vacancy centers in diamond

    NASA Astrophysics Data System (ADS)

    Lo Piparo, Nicoló; Razavi, Mohsen; Munro, William J.

    2017-02-01

    Memory-assisted measurement-device-independent quantum key distribution (MA-MDI-QKD) has recently been proposed as a possible intermediate step towards the realization of quantum repeaters. Despite its relaxing some of the requirements on quantum memories, the choice of memory in relation to the layout of the setup and the protocol has a stark effect on our ability to beat existing no-memory systems. Here, we investigate the suitability of nitrogen vacancy (NV) centers, as quantum memories, in MA-MDI-QKD. We particularly show that moderate cavity enhancement is required for NV centers if we want to outperform no-memory QKD systems. Using system parameters mostly achievable by today's state of the art, we then anticipate some total key rate advantage in the distance range between 300 and 500 km for cavity-enhanced NV centers. Our analysis accounts for major sources of error including the dark current, the channel loss, and the decoherence of the quantum memories.

  12. Tight finite-key analysis of a practical decoy-state quantum key distribution with unstable sources

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Bao, Wan-Su; Zhou, Chun; Jiang, Mu-Sheng; Li, Hong-Wei

    2016-09-01

    The decoy-state quantum key distribution (QKD) protocol has been widely used in commercial QKD systems. Several QKD field networks show its practicability and commercial prospects. Importantly, practical decoy-state QKD systems should be characterized with device imperfections. In this paper, for the case without intensity fluctuations, we present the parameter estimation based on the Chernoff bound for a practical decoy-state QKD protocol and compare performances of that based on Hoeffding's inequality and the Chernoff bound, respectively. Taking intensity fluctuations into consideration, we present the finite-key analysis with composable security against general attacks based on Azuma's inequality. Our numerical results show that the finite-key analysis based on the Chernoff bound is tighter than Hoeffding's inequality when the total number of transmitting signals N <1 ×1012 . Moreover, the intensity fluctuations' influence is more obvious when the data size of total transmitting signals is small. Our results emphasize the importance of the stability of the intensity modulator as well as the accurate estimation of emitted pulse's intensity.

  13. Unconditional security of time-energy entanglement quantum key distribution using dual-basis interferometry.

    PubMed

    Zhang, Zheshen; Mower, Jacob; Englund, Dirk; Wong, Franco N C; Shapiro, Jeffrey H

    2014-03-28

    High-dimensional quantum key distribution (HDQKD) offers the possibility of high secure-key rate with high photon-information efficiency. We consider HDQKD based on the time-energy entanglement produced by spontaneous parametric down-conversion and show that it is secure against collective attacks. Its security rests upon visibility data-obtained from Franson and conjugate-Franson interferometers-that probe photon-pair frequency correlations and arrival-time correlations. From these measurements, an upper bound can be established on the eavesdropper's Holevo information by translating the Gaussian-state security analysis for continuous-variable quantum key distribution so that it applies to our protocol. We show that visibility data from just the Franson interferometer provides a weaker, but nonetheless useful, secure-key rate lower bound. To handle multiple-pair emissions, we incorporate the decoy-state approach into our protocol. Our results show that over a 200-km transmission distance in optical fiber, time-energy entanglement HDQKD could permit a 700-bit/sec secure-key rate and a photon information efficiency of 2 secure-key bits per photon coincidence in the key-generation phase using receivers with a 15% system efficiency.

  14. Experimental quantum key distribution with simulated ground-to-satellite photon losses and processing limitations

    NASA Astrophysics Data System (ADS)

    Bourgoin, Jean-Philippe; Gigov, Nikolay; Higgins, Brendon L.; Yan, Zhizhong; Meyer-Scott, Evan; Khandani, Amir K.; Lütkenhaus, Norbert; Jennewein, Thomas

    2015-11-01

    Quantum key distribution (QKD) has the potential to improve communications security by offering cryptographic keys whose security relies on the fundamental properties of quantum physics. The use of a trusted quantum receiver on an orbiting satellite is the most practical near-term solution to the challenge of achieving long-distance (global-scale) QKD, currently limited to a few hundred kilometers on the ground. This scenario presents unique challenges, such as high photon losses and restricted classical data transmission and processing power due to the limitations of a typical satellite platform. Here we demonstrate the feasibility of such a system by implementing a QKD protocol, with optical transmission and full post-processing, in the high-loss regime using minimized computing hardware at the receiver. Employing weak coherent pulses with decoy states, we demonstrate the production of secure key bits at up to 56.5 dB of photon loss. We further illustrate the feasibility of a satellite uplink by generating a secure key while experimentally emulating the varying losses predicted for realistic low-Earth-orbit satellite passes at 600 km altitude. With a 76 MHz source and including finite-size analysis, we extract 3374 bits of a secure key from the best pass. We also illustrate the potential benefit of combining multiple passes together: while one suboptimal "upper-quartile" pass produces no finite-sized key with our source, the combination of three such passes allows us to extract 165 bits of a secure key. Alternatively, we find that by increasing the signal rate to 300 MHz it would be possible to extract 21 570 bits of a secure finite-sized key in just a single upper-quartile pass.

  15. High speed and adaptable error correction for megabit/s rate quantum key distribution

    PubMed Central

    Dixon, A. R.; Sato, H.

    2014-01-01

    Quantum Key Distribution is moving from its theoretical foundation of unconditional security to rapidly approaching real world installations. A significant part of this move is the orders of magnitude increases in the rate at which secure key bits are distributed. However, these advances have mostly been confined to the physical hardware stage of QKD, with software post-processing often being unable to support the high raw bit rates. In a complete implementation this leads to a bottleneck limiting the final secure key rate of the system unnecessarily. Here we report details of equally high rate error correction which is further adaptable to maximise the secure key rate under a range of different operating conditions. The error correction is implemented both in CPU and GPU using a bi-directional LDPC approach and can provide 90–94% of the ideal secure key rate over all fibre distances from 0–80 km. PMID:25450416

  16. Experimental passive round-robin differential phase-shift quantum key distribution.

    PubMed

    Guan, Jian-Yu; Cao, Zhu; Liu, Yang; Shen-Tu, Guo-Liang; Pelc, Jason S; Fejer, M M; Peng, Cheng-Zhi; Ma, Xiongfeng; Zhang, Qiang; Pan, Jian-Wei

    2015-05-08

    In quantum key distribution (QKD), the bit error rate is used to estimate the information leakage and hence determines the amount of privacy amplification-making the final key private by shortening the key. In general, there exists a threshold of the error rate for each scheme, above which no secure key can be generated. This threshold puts a restriction on the environment noises. For example, a widely used QKD protocol, the Bennett-Brassard protocol, cannot tolerate error rates beyond 25%. A new protocol, round-robin differential phase-shifted (RRDPS) QKD, essentially removes this restriction and can in principle tolerate more environment disturbance. Here, we propose and experimentally demonstrate a passive RRDPS QKD scheme. In particular, our 500 MHz passive RRDPS QKD system is able to generate a secure key over 50 km with a bit error rate as high as 29%. This scheme should find its applications in noisy environment conditions.

  17. Experimental Passive Round-Robin Differential Phase-Shift Quantum Key Distribution

    NASA Astrophysics Data System (ADS)

    Guan, Jian-Yu; Cao, Zhu; Liu, Yang; Shen-Tu, Guo-Liang; Pelc, Jason S.; Fejer, M. M.; Peng, Cheng-Zhi; Ma, Xiongfeng; Zhang, Qiang; Pan, Jian-Wei

    2015-05-01

    In quantum key distribution (QKD), the bit error rate is used to estimate the information leakage and hence determines the amount of privacy amplification—making the final key private by shortening the key. In general, there exists a threshold of the error rate for each scheme, above which no secure key can be generated. This threshold puts a restriction on the environment noises. For example, a widely used QKD protocol, the Bennett-Brassard protocol, cannot tolerate error rates beyond 25%. A new protocol, round-robin differential phase-shifted (RRDPS) QKD, essentially removes this restriction and can in principle tolerate more environment disturbance. Here, we propose and experimentally demonstrate a passive RRDPS QKD scheme. In particular, our 500 MHz passive RRDPS QKD system is able to generate a secure key over 50 km with a bit error rate as high as 29%. This scheme should find its applications in noisy environment conditions.

  18. High speed and adaptable error correction for megabit/s rate quantum key distribution.

    PubMed

    Dixon, A R; Sato, H

    2014-12-02

    Quantum Key Distribution is moving from its theoretical foundation of unconditional security to rapidly approaching real world installations. A significant part of this move is the orders of magnitude increases in the rate at which secure key bits are distributed. However, these advances have mostly been confined to the physical hardware stage of QKD, with software post-processing often being unable to support the high raw bit rates. In a complete implementation this leads to a bottleneck limiting the final secure key rate of the system unnecessarily. Here we report details of equally high rate error correction which is further adaptable to maximise the secure key rate under a range of different operating conditions. The error correction is implemented both in CPU and GPU using a bi-directional LDPC approach and can provide 90-94% of the ideal secure key rate over all fibre distances from 0-80 km.

  19. On the vulnerability of basic quantum key distribution protocols and three protocols stable to attack with 'blinding' of avalanche photodetectors

    SciTech Connect

    Molotkov, S. N.

    2012-05-15

    The fundamental quantum mechanics prohibitions on the measurability of quantum states allow secure key distribution between spatially remote users to be performed. Experimental and commercial implementations of quantum cryptography systems, however, use components that exist at the current technology level, in particular, one-photon avalanche photodetectors. These detectors are subject to the blinding effect. It was shown that all the known basic quantum key distribution protocols and systems based on them are vulnerable to attacks with blinding of photodetectors. In such attacks, an eavesdropper knows all the key transferred, does not produce errors at the reception side, and remains undetected. Three protocols of quantum key distribution stable toward such attacks are suggested. The security of keys and detection of eavesdropping attempts are guaranteed by the internal structure of protocols themselves rather than additional technical improvements.

  20. On the vulnerability of basic quantum key distribution protocols and three protocols stable to attack with "blinding" of avalanche photodetectors

    NASA Astrophysics Data System (ADS)

    Molotkov, S. N.

    2012-05-01

    The fundamental quantum mechanics prohibitions on the measurability of quantum states allow secure key distribution between spatially remote users to be performed. Experimental and commercial implementations of quantum cryptography systems, however, use components that exist at the current technology level, in particular, one-photon avalanche photodetectors. These detectors are subject to the blinding effect. It was shown that all the known basic quantum key distribution protocols and systems based on them are vulnerable to attacks with blinding of photodetectors. In such attacks, an eavesdropper knows all the key transferred, does not produce errors at the reception side, and remains undetected. Three protocols of quantum key distribution stable toward such attacks are suggested. The security of keys and detection of eavesdropping attempts are guaranteed by the internal structure of protocols themselves rather than additional technical improvements.

  1. Spontaneous Parametric Down-Conversion to Create a Quantum Key Distribution System

    NASA Astrophysics Data System (ADS)

    Salgado, Erik; Aragoneses, Andres, , Dr.

    Quantum Key Distribution (QKD) aims to share a secret key between two parties in a secure manner. It provides security benefits over classical communication systems. We have constructed a QKD system that uses quantum entanglement to ensure security against eavesdroppers. We use polarization to encode the binary information of an encryption key. This key is secure due to the quantum properties of light. We use the process of spontaneous parametric down-conversion (SPDC) to create entangled photon pairs. Experimentally, we fire pump (laser) photons through a nonlinear crystal, where there exists a probability of them being annihilated and spontaneously generating two entangled photons of lower energies. A coincidence measurement between two entangled photons indicates the successful transfer of one bit of information, and a coincidence measurement between two disparate photons indicates an error in data transfer. We aim to optimize data transfer rate and reduce error rate. The project is still in development and we look forward to collecting data in the near future.

  2. Security of a semi-quantum protocol where reflections contribute to the secret key

    NASA Astrophysics Data System (ADS)

    Krawec, Walter O.

    2016-05-01

    In this paper, we provide a proof of unconditional security for a semi-quantum key distribution protocol introduced in a previous work. This particular protocol demonstrated the possibility of using X basis states to contribute to the raw key of the two users (as opposed to using only direct measurement results) even though a semi-quantum participant cannot directly manipulate such states. In this work, we provide a complete proof of security by deriving a lower bound of the protocol's key rate in the asymptotic scenario. Using this bound, we are able to find an error threshold value such that for all error rates less than this threshold, it is guaranteed that A and B may distill a secure secret key; for error rates larger than this threshold, A and B should abort. We demonstrate that this error threshold compares favorably to several fully quantum protocols. We also comment on some interesting observations about the behavior of this protocol under certain noise scenarios.

  3. Practical round-robin differential-phase-shift quantum key distribution

    NASA Astrophysics Data System (ADS)

    Zhang, Zhen; Yuan, Xiao; Cao, Zhu; Ma, Xiongfeng

    2017-03-01

    The security of quantum key distribution (QKD) relies on the Heisenberg uncertainty principle, with which legitimate users are able to estimate information leakage by monitoring the disturbance of the transmitted quantum signals. Normally, the disturbance is reflected as bit flip errors in the sifted key; thus, privacy amplification, which removes any leaked information from the key, generally depends on the bit error rate. Recently, a round-robin differential-phase-shift QKD protocol for which privacy amplification does not rely on the bit error rate (Sasaki et al 2014 Nature 509 475) was proposed. The amount of leaked information can be bounded by the sender during the state-preparation stage and hence, is independent of the behavior of the unreliable quantum channel. In our work, we apply the tagging technique to the protocol and present a tight bound on the key rate and employ a decoy-state method. The effects of background noise and misalignment are taken into account under practical conditions. Our simulation results show that the protocol can tolerate channel error rates close to 50% within a typical experiment setting. That is, there is a negligible restriction on the error rate in practice.

  4. Phase-Reference-Free Experiment of Measurement-Device-Independent Quantum Key Distribution

    NASA Astrophysics Data System (ADS)

    Wang, Chao; Song, Xiao-Tian; Yin, Zhen-Qiang; Wang, Shuang; Chen, Wei; Zhang, Chun-Mei; Guo, Guang-Can; Han, Zheng-Fu

    2015-10-01

    Measurement-device-independent quantum key distribution (MDI QKD) is a substantial step toward practical information-theoretic security for key sharing between remote legitimate users (Alice and Bob). As with other standard device-dependent quantum key distribution protocols, such as BB84, MDI QKD assumes that the reference frames have been shared between Alice and Bob. In practice, a nontrivial alignment procedure is often necessary, which requires system resources and may significantly reduce the secure key generation rate. Here, we propose a phase-coding reference-frame-independent MDI QKD scheme that requires no phase alignment between the interferometers of two distant legitimate parties. As a demonstration, a proof-of-principle experiment using Faraday-Michelson interferometers is presented. The experimental system worked at 1 MHz, and an average secure key rate of 8.309 bps was obtained at a fiber length of 20 km between Alice and Bob. The system can maintain a positive key generation rate without phase compensation under normal conditions. The results exhibit the feasibility of our system for use in mature MDI QKD devices and its value for network scenarios.

  5. Preschoolers' Generation of Different Types of Counterfactual Statements and Theory of Mind Understanding

    ERIC Educational Resources Information Center

    Guajardo, Nicole R.; Turley-Ames, Kandi Jo

    2004-01-01

    Two studies examined associations between theory of mind performance and counterfactual thinking using both antecedent and consequent counterfactual tasks. Moreover, the studies examined children's abilities to generate different types of counterfactual statements in terms of direction and structure. Participants were 3-, 4-, and 5-year-old…

  6. Counterfactual thinking in patients with amnesia.

    PubMed

    Mullally, Sinéad L; Maguire, Eleanor A

    2014-11-01

    We often engage in counterfactual (CF) thinking, which involves reflecting on "what might have been." Creating alternative versions of reality seems to have parallels with recollecting the past and imagining the future in requiring the simulation of internally generated models of complex events. Given that episodic memory and imagining the future are impaired in patients with hippocampal damage and amnesia, we wondered whether successful CF thinking also depends upon the integrity of the hippocampus. Here using two nonepisodic CF thinking tasks, we found that patients with bilateral hippocampal damage and amnesia performed comparably with matched controls. They could deconstruct reality, add in and recombine elements, change relations between temporal sequences of events, enabling them to determine plausible alternatives of complex episodes. A difference between the patients and control participants was evident, however, in the patients' subtle avoidance of CF simulations that required the construction of an internal spatial representation. Overall, our findings suggest that mental simulation in the form of nonepisodic CF thinking does not seem to depend upon the hippocampus unless there is the added requirement for construction of a coherent spatial scene within which to play out scenarios.

  7. Efficient quantum key distribution with trines of reference-frame-free qubits

    NASA Astrophysics Data System (ADS)

    Tabia, Gelo; Englert, Berthold-Georg

    2011-01-01

    We propose a rotationally-invariant quantum key distribution scheme that uses a pair of orthogonal qubit trines, realized as mixed states of three physical qubits. The measurement outcomes do not depend on how Alice and Bob choose their individual reference frames. The efficient key generation by two-way communication produces two independent raw keys, a bit key and a trit key. For a noiseless channel, Alice and Bob get a total of 0.573 key bits per trine state sent (98% of the Shannon limit). This exceeds by a considerable amount the yield of standard trine schemes, which ideally attain half a key bit per trine state. Eavesdropping introduces an ɛ-fraction of unbiased noise, ensured by twirling if necessary. The security analysis reveals an asymmetry in Eve's conditioned ancillas for Alice and Bob resulting from their inequivalent roles in the key generation. Upon simplifying the analysis by a plausible symmetry assumption, we find that a secret key can be generated if the noise is below the threshold set by ɛ=0.197.

  8. Space-bound optical source for satellite-ground decoy-state quantum key distribution.

    PubMed

    Li, Yang; Liao, Sheng-Kai; Chen, Xie-Le; Chen, Wei; Cheng, Kun; Cao, Yuan; Yong, Hai-Lin; Wang, Tao; Yang, Hua-Qiang; Liu, Wei-Yue; Yin, Juan; Liang, Hao; Peng, Cheng-Zhi; Pan, Jian-Wei

    2014-11-03

    Satellite-ground quantum key distribution has embarked on the stage of engineering implementation, and a global quantum-secured network is imminent in the foreseeable future. As one payload of the quantum-science satellite which will be ready before the end of 2015, we report our recent work of the space-bound decoy-state optical source. Specialized 850 nm laser diodes have been manufactured and the integrated optical source has gotten accomplished based on these LDs. The weak coherent pulses produced by our optical source feature a high clock rate of 100 MHz, intensity stability of 99.5%, high polarization fidelity of 99.7% and phase randomization. A series of space environment tests have been conducted to verify the optical source's performance and the results are satisfactory. The emulated final secure keys are about 120 kbits during one usable pass of the low Earth orbit satellite. This work takes a significant step forward towards satellite-ground QKD and the global quantum-secured network.

  9. Two-dimensional distributed-phase-reference protocol for quantum key distribution

    NASA Astrophysics Data System (ADS)

    Bacco, Davide; Christensen, Jesper Bjerge; Castaneda, Mario A. Usuga; Ding, Yunhong; Forchhammer, Søren; Rottwitt, Karsten; Oxenløwe, Leif Katsuo

    2016-12-01

    Quantum key distribution (QKD) and quantum communication enable the secure exchange of information between remote parties. Currently, the distributed-phase-reference (DPR) protocols, which are based on weak coherent pulses, are among the most practical solutions for long-range QKD. During the last 10 years, long-distance fiber-based DPR systems have been successfully demonstrated, although fundamental obstacles such as intrinsic channel losses limit their performance. Here, we introduce the first two-dimensional DPR-QKD protocol in which information is encoded in the time and phase of weak coherent pulses. The ability of extracting two bits of information per detection event, enables a higher secret key rate in specific realistic network scenarios. Moreover, despite the use of more dimensions, the proposed protocol remains simple, practical, and fully integrable.

  10. Two-dimensional distributed-phase-reference protocol for quantum key distribution

    PubMed Central

    Bacco, Davide; Christensen, Jesper Bjerge; Castaneda, Mario A. Usuga; Ding, Yunhong; Forchhammer, Søren; Rottwitt, Karsten; Oxenløwe, Leif Katsuo

    2016-01-01

    Quantum key distribution (QKD) and quantum communication enable the secure exchange of information between remote parties. Currently, the distributed-phase-reference (DPR) protocols, which are based on weak coherent pulses, are among the most practical solutions for long-range QKD. During the last 10 years, long-distance fiber-based DPR systems have been successfully demonstrated, although fundamental obstacles such as intrinsic channel losses limit their performance. Here, we introduce the first two-dimensional DPR-QKD protocol in which information is encoded in the time and phase of weak coherent pulses. The ability of extracting two bits of information per detection event, enables a higher secret key rate in specific realistic network scenarios. Moreover, despite the use of more dimensions, the proposed protocol remains simple, practical, and fully integrable. PMID:28004821

  11. Composable Security Proof for Continuous-Variable Quantum Key Distribution with Coherent States

    NASA Astrophysics Data System (ADS)

    Leverrier, Anthony

    2015-02-01

    We give the first composable security proof for continuous-variable quantum key distribution with coherent states against collective attacks. Crucially, in the limit of large blocks the secret key rate converges to the usual value computed from the Holevo bound. Combining our proof with either the de Finetti theorem or the postselection technique then shows the security of the protocol against general attacks, thereby confirming the long-standing conjecture that Gaussian attacks are optimal asymptotically in the composable security framework. We expect that our parameter estimation procedure, which does not rely on any assumption about the quantum state being measured, will find applications elsewhere, for instance, for the reliable quantification of continuous-variable entanglement in finite-size settings.

  12. Multi-partite squash operation and its application to device-independent quantum key distribution

    NASA Astrophysics Data System (ADS)

    Tsurumaru, Toyohiro; Ichikawa, Tsubasa

    2016-10-01

    The squash operation, or the squashing model, is a useful mathematical tool for proving the security of quantum key distribution systems using practical (i.e., non-ideal) detectors. At the present, however, this method can only be applied to a limited class of detectors, such as the threshold detector of the Bennett-Brassard 1984 type. In this paper we generalize this method to include multi-partite measurements, such that it can be applied to a wider class of detectors. We demonstrate the effectiveness of this generalization by applying it to the device-independent security proof of the Ekert 1991 protocol, and by improving the associated key generation rate. For proving this result we use two physical assumptions, namely, that quantum mechanics is valid, and that Alice’s and Bob’s detectors are memoryless.

  13. High-Speed Large-Alphabet Quantum Key Distribution Using Photonic Integrated Circuits

    DTIC Science & Technology

    2014-01-28

    interaction in graphene coupled to a photonic crystal nanocavity. Nano Letters, 12(11):5626-5631, 2012. 7. High-dimensional quantum key distribution...Chip- integrated ultrafast graphene photodetector with high responsivity, , Nature Photonics (03 2013) Tian Zhong, Franco N. C. Wong. Nonlocal... GRAPHENE PHOTONICS FOR RESONATOR-ENHANCED ELECTRO-OPTIC DEVICES AND ALL-OPTICAL INTERACTIONS SYSTEMS AND METHODS FOR COUPLING ELECTROMAGNETIC

  14. Noiseless Linear Amplifiers in Entanglement-Based Continuous-Variable Quantum Key Distribution

    NASA Astrophysics Data System (ADS)

    Zhang, Yichen; Li, Zhengyu; Weedbrook, Christian; Marshall, Kevin; Pirandola, Stefano; Yu, Song; Guo, Hong

    2015-06-01

    We propose a method to improve the performance of two entanglement-based continuous-variable quantum key distribution protocols using noiseless linear amplifiers. The two entanglement-based schemes consist of an entanglement distribution protocol with an untrusted source and an entanglement swapping protocol with an untrusted relay. Simulation results show that the noiseless linear amplifiers can improve the performance of these two protocols, in terms of maximal transmission distances, when we consider small amounts of entanglement, as typical in realistic setups.

  15. Conceptual Modeling of a Quantum Key Distribution Simulation Framework Using the Discrete Event System Specification

    DTIC Science & Technology

    2014-09-18

    www.ijetae.com (ISSN 2250-2459, ISO 9001 :2008 Certified Journal, Volume 4, Issue 2, February 2014) 829 Towards the Modeling and Simulation of Quantum Key...ISSN 2250-2459, ISO 9001 :2008 Certified Journal, Volume 4, Issue 2, February 2014) 830 Such a simulation capability needs to address many ―concerns...www.ijetae.com (ISSN 2250-2459, ISO 9001 :2008 Certified Journal, Volume 4, Issue 2, February 2014) 831 TABLE II END USER CAPABILITY REQUIREMENTS

  16. Quantum Key Distribution with Higher-Order Alphabets Using Spatially Encoded Qudits

    NASA Astrophysics Data System (ADS)

    Walborn, S. P.; Lemelle, D. S.; Almeida, M. P.; Ribeiro, P. H. Souto

    2006-03-01

    We present a proof of principle demonstration of a quantum key distribution scheme in higher-order d-dimensional alphabets using spatial degrees of freedom of photons. Our implementation allows for the transmission of 4.56 bits per sifted photon, while providing improved security: an intercept-resend attack on all photons would induce an average error rate of 0.47. Using our system, it should be possible to send more than a byte of information per sifted photon.

  17. Single-Event Correlation Analysis of Quantum Key Distribution with Single-Photon Sources

    NASA Astrophysics Data System (ADS)

    Shangli Dong,; Xiaobo Wang,; Guofeng Zhang,; Liantuan Xiao,; Suotang Jia,

    2010-04-01

    Multiple photons exist that allow efficient eavesdropping strategies that threaten the security of quantum key distribution. In this paper, we theoretically discuss the photon correlations between authorized partners in the case of practical single-photon sources including a multiple-photon background. To investigate the feasibility of intercept-resend attacks, the cross correlations and the maximum intercept-resend ratio caused by the background signal are determined using single-event correlation analysis based on single-event detection.

  18. New passive decoy-state quantum key distribution with thermal distributed parametric down-conversion source

    NASA Astrophysics Data System (ADS)

    Wei, Jie; Zhang, Chun-Hui; Wang, Qin

    2017-02-01

    We present a new scheme on implementing the passive quantum key distribution with thermal distributed parametric down-conversion source. In this scheme, only one-intensity decoy state is employed, but we can achieve very precise estimation on the single-photon-pulse contribution by utilizing those built-in decoy states. Moreover, we compare the new scheme with other practical methods, i.e., the standard three-intensity decoy-state BB84 protocol using either weak coherent states or parametric down-conversion source. Through numerical simulations, we demonstrate that our new scheme can drastically improve both the secure transmission distance and the key generation rate.

  19. Improving the maximum transmission distance of continuous-variable quantum key distribution using a noiseless amplifier

    SciTech Connect

    Blandino, Rémi; Etesse, Jean; Grangier, Philippe; Leverrier, Anthony; Barbieri, Marco; Tualle-Brouri, Rosa

    2014-12-04

    We show that the maximum transmission distance of continuous-variable quantum key distribution in presence of a Gaussian noisy lossy channel can be arbitrarily increased using a heralded noiseless linear amplifier. We explicitly consider a protocol using amplitude and phase modulated coherent states with reverse reconciliation. Assuming that the secret key rate drops to zero for a line transmittance T{sub lim}, we find that a noiseless amplifier with amplitude gain g can improve this value to T{sub lim}/g{sup 2}, corresponding to an increase in distance proportional to log g. We also show that the tolerance against noise is increased.

  20. Field test of classical symmetric encryption with continuous variables quantum key distribution.

    PubMed

    Jouguet, Paul; Kunz-Jacques, Sébastien; Debuisschert, Thierry; Fossier, Simon; Diamanti, Eleni; Alléaume, Romain; Tualle-Brouri, Rosa; Grangier, Philippe; Leverrier, Anthony; Pache, Philippe; Painchault, Philippe

    2012-06-18

    We report on the design and performance of a point-to-point classical symmetric encryption link with fast key renewal provided by a Continuous Variable Quantum Key Distribution (CVQKD) system. Our system was operational and able to encrypt point-to-point communications during more than six months, from the end of July 2010 until the beginning of February 2011. This field test was the first demonstration of the reliability of a CVQKD system over a long period of time in a server room environment. This strengthens the potential of CVQKD for information technology security infrastructure deployments.

  1. Symmetries and security of a quantum-public-key encryption based on single-qubit rotations

    NASA Astrophysics Data System (ADS)

    Seyfarth, U.; Nikolopoulos, G. M.; Alber, G.

    2012-02-01

    Exploring the symmetries underlying a previously proposed encryption scheme that relies on single-qubit rotations, we derive an improved upper bound on the maximum information that an eavesdropper might extract from all the available copies of the public key. Subsequently, the robustness of the scheme is investigated in the context of attacks that address each public-key qubit independently. The attacks under consideration make use of projective measurements on single qubits and their efficiency is compared to attacks that address many qubits collectively and require complicated quantum operations.

  2. Two robust quantum key agreement protocols based on logical GHZ states

    NASA Astrophysics Data System (ADS)

    He, Yefeng; Ma, Wenping

    2017-01-01

    Based on logical GHZ states and logical Bell states, two robust quantum key agreement protocols are proposed, which can be immune to the collective-dephasing noise and the collective-rotation noise, respectively. The delayed measurement technique ensures that two participants can fairly negotiate a shared key and any one of them cannot successfully perform the participant attacks. The two protocols are congenitally free from the Trojan horse attacks and they can resist against other outsider attacks with the help of the decoy state technology. Moreover, they have no information leakage problem and achieve high qubit efficiency.

  3. Long-distance decoy-state quantum key distribution in optical fiber.

    PubMed

    Rosenberg, Danna; Harrington, Jim W; Rice, Patrick R; Hiskett, Philip A; Peterson, Charles G; Hughes, Richard J; Lita, Adriana E; Nam, Sae Woo; Nordholt, Jane E

    2007-01-05

    The theoretical existence of photon-number-splitting attacks creates a security loophole for most quantum key distribution (QKD) demonstrations that use a highly attenuated laser source. Using ultralow-noise, high-efficiency transition-edge sensor photodetectors, we have implemented the first version of a decoy-state protocol that incorporates finite statistics without the use of Gaussian approximations in a one-way QKD system, enabling the creation of secure keys immune to photon-number-splitting attacks and highly resistant to Trojan horse attacks over 107 km of optical fiber.

  4. Practical security of continuous-variable quantum key distribution with finite sampling bandwidth effects

    NASA Astrophysics Data System (ADS)

    Wang, Chao; Huang, Peng; Huang, Duan; Lin, Dakai; Zeng, Guihua

    2016-02-01

    Practical security of the continuous-variable quantum key distribution (CVQKD) system with finite sampling bandwidth of analog-to-digital converter (ADC) at the receiver's side is investigated. We find that the finite sampling bandwidth effects may decrease the lower bound of secret key rate without awareness of the legitimate communicators. This leaves security loopholes for Eve to attack the system. In addition, this effect may restrains the linear relationship of secret key bit rate with repetition rate of the system; subsequently, there is a saturation value for the secret key bit rate with the repetition rate. To resist such kind of effects, we propose a dual sampling detection approach in which two ADCs are employed so that the finite sampling bandwidth effects are removed.

  5. Balancing continuous-variable quantum key distribution with source-tunable linear optics cloning machine

    NASA Astrophysics Data System (ADS)

    Guo, Ying; Lv, Geli; Zeng, Guihua

    2015-11-01

    We show that the tolerable excess noise can be dynamically balanced in source preparation while inserting a tunable linear optics cloning machine (LOCM) for balancing the secret key rate and the maximal transmission distance of continuous-variable quantum key distribution (CVQKD). The intensities of source noise are sensitive to the tunable LOCM and can be stabilized to the suitable values to eliminate the impact of channel noise and defeat the potential attacks even in the case of the degenerated linear optics amplifier (LOA). The LOCM-additional noise can be elegantly employed by the reference partner of reconciliation to regulate the secret key rate and the transmission distance. Simulation results show that there is a considerable improvement in the secret key rate of the LOCM-based CVQKD while providing a tunable LOCM for source preparation with the specified parameters in suitable ranges.

  6. Long-distance copropagation of quantum key distribution and terabit classical optical data channels

    NASA Astrophysics Data System (ADS)

    Wang, Liu-Jun; Zou, Kai-Heng; Sun, Wei; Mao, Yingqiu; Zhu, Yi-Xiao; Yin, Hua-Lei; Chen, Qing; Zhao, Yong; Zhang, Fan; Chen, Teng-Yun; Pan, Jian-Wei

    2017-01-01

    Quantum key distribution (QKD) generates symmetric keys between two remote parties and guarantees the keys are not accessible to any third party. Wavelength-division multiplexing between QKD and classical optical communications by sharing the existing fiber-optics infrastructure is highly desired in order to reduce the cost of QKD applications. However, comparing to the light for classical transmission, quantum signals are very weak and easily affected by impairments from classical light, such as the spontaneous Raman-scattering effect. Here, by selecting an optimal wavelength of quantum signals, we significantly reduce the influence of the Raman-scattering effect. In addition, through coherent optical communication technology, we achieve high-speed classical data transmission with relatively low launch powers, thereby further reducing the impairments from classical light. As a result, we realize the multiplexing and long-distance copropagation of QKD and terabit classical data transmission up to 80 km. The data capacity is two orders of magnitude larger than the existing results. Our demonstration verifies the feasibility of QKD and classical communication to share the resources of backbone fiber links and thus taking the utility of QKD a great step forward.

  7. Integrated quantum key distribution sender unit for daily-life implementations

    NASA Astrophysics Data System (ADS)

    Mélen, Gwenaelle; Vogl, Tobias; Rau, Markus; Corrielli, Giacomo; Crespi, Andrea; Osellame, Roberto; Weinfurter, Harald

    2016-03-01

    Unlike currently implemented encryption schemes, Quantum Key Distribution provides a secure way of generating and distributing a key among two parties. Although a multitude of research platforms has been developed, the integration of QKD units within classical communication systems remains a tremendous challenge. The recently achieved maturity of integrated photonic technologies could be exploited to create miniature QKD add-ons that could extend the primary function of various existing systems such as mobile devices or optical stations. In this work we report on an integrated optics module enabling secure short-distance communication for, e.g., quantum access schemes. Using BB84-like protocols, Alice's mobile low-cost device can exchange secure key and information everywhere within a trusted node network. The new optics platform (35×20×8mm) compatible with current smartphone's technology generates NIR faint polarised laser pulses with 100MHz repetition rate. Fully automated beam tracking and live basis-alignment on Bob's side ensure user-friendly operation with a quantum link efficiency as high as 50% stable over a few seconds.

  8. Children's understanding of counterfactual emotions: age differences, individual differences, and the effects of counterfactual-information salience.

    PubMed

    Ferrell, Jennifer M; Guttentag, Robert E; Gredlein, Jeffrey M

    2009-09-01

    The present study investigated developmental trends in the effects of the salience of counterfactual alternatives on judgments of others' counterfactual-thinking-based emotions. We also examined possible correlates of individual differences in the understanding of these emotions. Thirty-four adults and 102 children, 5-8 years of age, were presented scenarios in which characters would be expected to experience regret. In one version of each scenario, the regret-relevant counterfactual alternative was made more salient than was the case with the other version. Adults consistently judged that a character for whom a counterfactual course of events would have resulted in a better outcome would feel worse than a character for whom an alternative course of events would not have resulted in a more positive outcome. The majority of the children's judgments were not affected by the counterfactual alternatives. However, the judgments of the oldest children (the 8-year-olds) were significantly more adult-like in the high-salience than in the low-salience condition. Although the three predictors examined in the present study (verbal ability, working memory capacity, second-order false belief task performance) together accounted for significant variance in performance on the emotions judgment task, no single predictor alone accounted for significant unique variance in performance. The importance of different social cognitive abilities for understanding people's affective responses is discussed.

  9. Counterfactual Reasoning: Sharpening Conceptual Distinctions in Developmental Studies

    PubMed Central

    Rafetseder, Eva; Perner, Josef

    2014-01-01

    Counterfactual reasoning (CFR)—mentally representing what the world would be like now if things had been different in the past—is an important aspect of human cognition and the focus of research in areas such as philosophy, social psychology, and clinical psychology. More recently, it has also gained broad interest in cognitive developmental psychology, mainly focusing on the question of how this kind of reasoning can be characterized. Studies have been inconsistent in identifying when children can use CFR. In this article, we present theoretical positions that may account for this inconsistency and evaluate them in the light of research on counterfactual emotions. PMID:24600482

  10. Practical scheme to share a secret key through a quantum channel with a 27.6% bit error rate

    NASA Astrophysics Data System (ADS)

    Chau, H. F.

    2002-12-01

    A secret key shared through quantum key distribution between two cooperative players is secure against any eavesdropping attack allowed by the laws of physics. Yet, such a key can be established only when the quantum channel error rate due to eavesdropping or imperfect apparatus is low. Here, a practical quantum key distribution scheme by making use of an adaptive privacy amplification procedure with two-way classical communication is reported. Then, it is proven that the scheme generates a secret key whenever the bit error rate of the quantum channel is less than 0.5-0.1(5)≈27.6%, thereby making it the most error resistant scheme known to date.

  11. Practical scheme to share a secret key through a quantum channel with a 27.6% bit error rate

    SciTech Connect

    Chau, H.F.

    2002-12-01

    A secret key shared through quantum key distribution between two cooperative players is secure against any eavesdropping attack allowed by the laws of physics. Yet, such a key can be established only when the quantum channel error rate due to eavesdropping or imperfect apparatus is low. Here, a practical quantum key distribution scheme by making use of an adaptive privacy amplification procedure with two-way classical communication is reported. Then, it is proven that the scheme generates a secret key whenever the bit error rate of the quantum channel is less than 0.5-0.1{radical}(5){approx_equal}27.6%, thereby making it the most error resistant scheme known to date.

  12. N-dimensional measurement-device-independent quantum key distribution with N + 1 un-characterized sources: zero quantum-bit-error-rate case

    PubMed Central

    Hwang, Won-Young; Su, Hong-Yi; Bae, Joonwoo

    2016-01-01

    We study N-dimensional measurement-device-independent quantum-key-distribution protocol where one checking state is used. Only assuming that the checking state is a superposition of other N sources, we show that the protocol is secure in zero quantum-bit-error-rate case, suggesting possibility of the protocol. The method may be applied in other quantum information processing. PMID:27452275

  13. Distillation of secret-key from a class of compound memoryless quantum sources

    NASA Astrophysics Data System (ADS)

    Boche, H.; Janßen, G.

    2016-08-01

    We consider secret-key distillation from tripartite compound classical-quantum-quantum (cqq) sources with free forward public communication under strong security criterion. We design protocols which are universally reliable and secure in this scenario. These are shown to achieve asymptotically optimal rates as long as a certain regularity condition is fulfilled by the set of its generating density matrices. We derive a multi-letter formula which describes the optimal forward secret-key capacity for all compound cqq sources being regular in this sense. We also determine the forward secret-key distillation capacity for situations where the legitimate sending party has perfect knowledge of his/her marginal state deriving from the source statistics. In this case regularity conditions can be dropped. Our results show that the capacities with and without the mentioned kind of state knowledge are equal as long as the source is generated by a regular set of density matrices. We demonstrate that regularity of cqq sources is not only a technical but also an operational issue. For this reason, we give an example of a source which has zero secret-key distillation capacity without sender knowledge, while achieving positive rates is possible if sender marginal knowledge is provided.

  14. Giving Yourself a Good Beating: Appraisal, Attribution, Rumination, and Counterfactual Thinking

    PubMed Central

    Uphill, Mark A.; Dray, Katie

    2009-01-01

    How individuals respond to adversity is one component of mental toughness and athletes may manage the adversity of a defeat in very different ways. In this article we focus on four types of cognition (appraisal, attribution, counterfactual thinking, and rumination) that athletes may exhibit in the immediate aftermath of a competitive defeat. In particular we define each of these terms and present a “caricature ”of each of the respective literatures, focussing on the prevailing trends and substantive findings. These caricatures assist in the identification of several areas in which literature on athletes’ retrospective cognition about defeat may be advanced. We use combat sports as a vehicle to illustrate our propositions. Key Points Please provide 3-5 bullet points of the paper. Little is known about how athletes psychologically manage adversity, a key component of mental toughness. There is a great deal of conceptual overlap between four types of retrospective cognition (appraisal, attribution, rumination and counterfactual thinking) athletes may exhibit after defeat. Rather than continue of examine these retrospective cognitions in isolation, there appears to be value in consideration of these constructs collectively to enhance theoretical parsimony. PMID:24474879

  15. Attacks exploiting deviation of mean photon number in quantum key distribution and coin tossing

    NASA Astrophysics Data System (ADS)

    Sajeed, Shihan; Radchenko, Igor; Kaiser, Sarah; Bourgoin, Jean-Philippe; Pappa, Anna; Monat, Laurent; Legré, Matthieu; Makarov, Vadim

    2015-03-01

    The security of quantum communication using a weak coherent source requires an accurate knowledge of the source's mean photon number. Finite calibration precision or an active manipulation by an attacker may cause the actual emitted photon number to deviate from the known value. We model effects of this deviation on the security of three quantum communication protocols: the Bennett-Brassard 1984 (BB84) quantum key distribution (QKD) protocol without decoy states, Scarani-Acín-Ribordy-Gisin 2004 (SARG04) QKD protocol, and a coin-tossing protocol. For QKD we model both a strong attack using technology possible in principle and a realistic attack bounded by today's technology. To maintain the mean photon number in two-way systems, such as plug-and-play and relativistic quantum cryptography schemes, bright pulse energy incoming from the communication channel must be monitored. Implementation of a monitoring detector has largely been ignored so far, except for ID Quantique's commercial QKD system Clavis2. We scrutinize this implementation for security problems and show that designing a hack-proof pulse-energy-measuring detector is far from trivial. Indeed, the first implementation has three serious flaws confirmed experimentally, each of which may be exploited in a cleverly constructed Trojan-horse attack. We discuss requirements for a loophole-free implementation of the monitoring detector.

  16. Company, country, connections: counterfactual origins increase organizational commitment, patriotism, and social investment.

    PubMed

    Ersner-Hershfield, Hal; Galinsky, Adam D; Kray, Laura J; King, Brayden G

    2010-10-01

    Four studies examined the relationship between counterfactual origins--thoughts about how the beginning of organizations, countries, and social connections might have turned out differently--and increased feelings of commitment to those institutions and connections. Study 1 found that counterfactually reflecting on the origins of one's country increases patriotism. Study 2 extended this finding to organizational commitment and examined the mediating role of poignancy. Study 3 found that counterfactual reflection boosts organizational commitment even beyond the effects of other commitment-enhancing appeals and that perceptions of fate mediate the positive effect of counterfactual origins on commitment. Finally, Study 4 temporally separated the counterfactual manipulation from a behavioral measure of commitment and found that counterfactual reflection predicted whether participants e-mailed social contacts 2 weeks later. The robust relationship between counterfactual origins and commitment was found across a wide range of companies and countries, with undergraduates and M.B.A. students, and for attitudes and behaviors.

  17. On the counterfactual nature of envy: "It could have been me".

    PubMed

    van de Ven, Niels; Zeelenberg, Marcel

    2015-01-01

    We examined whether counterfactual thinking influences the experience of envy. Counterfactual thinking refers to comparing the situation as it is to what it could have been, and these thought processes have been shown to lead to a variety of emotions. We predicted that for envy the counterfactual thought "it could have been me" would be important. In four studies we found a clear link between such counterfactual thoughts and the intensity of envy. Furthermore, Studies 3 and 4 revealed that a manipulation known to affect the extent of counterfactual thinking (the perception of being close to obtaining the desired outcome oneself), had an effect on the intensity of envy via counterfactual thoughts. This relationship between counterfactual thinking and the experience of envy allows for new predictions concerning situations under which envy is likely be more intense.

  18. I could have done otherwise: Availability of counterfactual comparisons informs the sense of agency.

    PubMed

    Kulakova, Eugenia; Khalighinejad, Nima; Haggard, Patrick

    2017-03-01

    Personal control and agency are closely associated with the counterfactual notion that a person could have done otherwise (CDO). In both philosophy and law, this counterfactual evaluation determines responsibility and punishment, yet little is known about its influence on agents' experience during action. We used a risky decision-making task to study how counterfactual evaluations influenced participants' sense of agency. Two factors were manipulated independently: the presence/absence of counterfactual comparisons between actions and the presence/absence of counterfactual comparisons between outcomes of these actions. Perceived agency was highest when both counterfactual comparisons were available. Interestingly, this pattern persisted even when counterfactual information was only revealed after action, suggesting a purely reconstructive evaluation effect. These findings allow a more precise phrasing of the CDO element of personal agency: a person feels most control when she could have performed another action, thereby obtaining another outcome.

  19. The NanoQEY mission: ground to space quantum key and entanglement distribution using a nanosatellite

    NASA Astrophysics Data System (ADS)

    Jennewein, T.; Grant, C.; Choi, E.; Pugh, C.; Holloway, C.; Bourgoin, JP.; Hakima, H.; Higgins, B.; Zee, R.

    2014-10-01

    The NanoQEY (Nano Quantum Encryption) Satellite is a proposed nanosatellite mission concept developed by the Institute for Quantum Computing (IQC) at the University of Waterloo and the Space Flight Laboratory (SFL) at the University of Toronto Institute for Aerospace Studies (UTIAS) that would demonstrate long-distance quantum key distribution (QKD) between two distant ground stations on Earth using an optical uplink. SFL's existing and proven NEMO (Nanosatellite for Earth Monitoring and Observation) bus forms the baseline spacecraft for NanoQEY, with a QKD receiver payload designed by IQC. The primary objective of the NanoQEY mission would be to successfully distribute at least 10 kbit of secure key between two optical ground stations, where the satellite acts as a trusted node. The secondary mission objective would be to perform Bell tests for entangled photons between ground and space. We designed a compact QKD receiver payload that would be compatible with the mass, volume, power and performance constraints of a low-cost nanosatellite platform. The low-cost rapid schedule "microspace" approach of UTIAS/SFL would allow for the proposed NanoQEY mission to be developed in 2.5 years from project kick-off to launch of the spacecraft, followed by a one-year on-orbit mission.

  20. Round-robin differential quadrature phase-shift quantum key distribution

    NASA Astrophysics Data System (ADS)

    Zhou, Chun; Zhang, Ying-Ying; Bao, Wan-Su; Li, Hong-Wei; Wang, Yang; Jiang, Mu-Sheng

    2017-02-01

    Recently, a round-robin differential phase-shift (RRDPS) protocol was proposed [Nature 509, 475 (2014)], in which the amount of leakage is bounded without monitoring the signal disturbance. Introducing states of the phase-encoded Bennett–Brassard 1984 protocol (PE-BB84) to the RRDPS, this paper presents another quantum key distribution protocol called round-robin differential quadrature phase-shift (RRDQPS) quantum key distribution. Regarding a train of many pulses as a single packet, the sender modulates the phase of each pulse by one of {0, π/2, π, 3π/2}, then the receiver measures each packet with a Mach–Zehnder interferometer having a phase basis of 0 or π/2. The RRDQPS protocol can be implemented with essential similar hardware to the PE-BB84, so it has great compatibility with the current quantum system. Here we analyze the security of the RRDQPS protocol against the intercept-resend attack and the beam-splitting attack. Results show that the proposed protocol inherits the advantages arising from the simplicity of the RRDPS protocol and is more robust against these attacks than the original protocol. Project supported by the National Natural Science Foundation of China (Grant Nos. 61505261 and 11304397) and the National Basic Research Program of China (Grant No. 2013CB338002)

  1. High-capacity quantum key distribution using Chebyshev-map values corresponding to Lucas numbers coding

    NASA Astrophysics Data System (ADS)

    Lai, Hong; Orgun, Mehmet A.; Pieprzyk, Josef; Li, Jing; Luo, Mingxing; Xiao, Jinghua; Xiao, Fuyuan

    2016-11-01

    We propose an approach that achieves high-capacity quantum key distribution using Chebyshev-map values corresponding to Lucas numbers coding. In particular, we encode a key with the Chebyshev-map values corresponding to Lucas numbers and then use k-Chebyshev maps to achieve consecutive and flexible key expansion and apply the pre-shared classical information between Alice and Bob and fountain codes for privacy amplification to solve the security of the exchange of classical information via the classical channel. Consequently, our high-capacity protocol does not have the limitations imposed by orbital angular momentum and down-conversion bandwidths, and it meets the requirements for longer distances and lower error rates simultaneously.

  2. Two-way deterministic quantum key distribution against detector-side-channel attacks

    NASA Astrophysics Data System (ADS)

    Lu, Hua; Fung, Chi-Hang Fred; Cai, Qing-yu

    2013-10-01

    In a two-way deterministic quantum key distribution (DQKD) protocol, Bob randomly prepares qubits in one of four states and sends them to Alice. To encode a bit, Alice performs an operation on each received qubit and returns it to Bob. Bob then measures the backward qubits to learn about Alice's operations and hence the key bits. Recently, we proved the unconditional security of the final key of this protocol in the ideal device setting. In this paper, we prove that two-way DQKD protocols are immune to all detector-side-channel attacks at Bob's side, while we assume ideal detectors at Alice's side for error testing. Our result represents a step forward in making DQKD protocols secure against general detector-side-channel attacks.

  3. Continuous-variable quantum key distribution with random intensity fluctuation of the local oscillator

    NASA Astrophysics Data System (ADS)

    Gui, Ming; Huang, Ming-Qiu; Liang, Lin-Mei

    2016-10-01

    In practical continuous-variable quantum key distribution (CVQKD) systems, due to environmental disturbance or some intrinsic imperfections of devices, inevitably the local oscillator (LO) employed in a coherent detection always fluctuates arbitrarily over time, which compromises the security and performance of practical CVQKD systems. In this paper, we investigate the performance of practical CVQKD systems with LO fluctuating randomly. By revising the measurement result of balanced homodyne detection and embedding fluctuation parameters into security analysis, we find that in addition to the average LO intensity, the fluctuation variance also severely affects the secret key rate. No secret key can be obtained if fluctuation variance is relatively large. This indicates that in a practical CVQKD, LO intensity should be well monitored and stabilized. Our research can be directly applied to improve the robustness of a practical CVQKD system as well as be used to optimize CVQKD protocols.

  4. Finite-size analysis of a continuous-variable quantum key distribution

    SciTech Connect

    Leverrier, Anthony; Grangier, Philippe

    2010-06-15

    The goal of this paper is to extend the framework of finite-size analysis recently developed for quantum key distribution to continuous-variable protocols. We do not solve this problem completely here, and we mainly consider the finite-size effects on the parameter estimation procedure. Despite the fact that some questions are left open, we are able to give an estimation of the secret key rate for protocols which do not contain a postselection procedure. As expected, these results are significantly more pessimistic than those obtained in the asymptotic regime. However, we show that recent continuous-variable protocols are able to provide fully secure secret keys in the finite-size scenario, over distances larger than 50 km.

  5. Experimental study on discretely modulated continuous-variable quantum key distribution

    SciTech Connect

    Shen Yong; Zou Hongxin; Chen Pingxing; Yuan Jianmin; Tian Liang

    2010-08-15

    We present a discretely modulated continuous-variable quantum key distribution system in free space by using strong coherent states. The amplitude noise in the laser source is suppressed to the shot-noise limit by using a mode cleaner combined with a frequency shift technique. Also, it is proven that the phase noise in the source has no impact on the final secret key rate. In order to increase the encoding rate, we use broadband homodyne detectors and the no-switching protocol. In a realistic model, we establish a secret key rate of 46.8 kbits/s against collective attacks at an encoding rate of 10 MHz for a 90% channel loss when the modulation variance is optimal.

  6. A fiber-based quasi-continuous-wave quantum key distribution system

    PubMed Central

    Shen, Yong; Chen, Yan; Zou, Hongxin; Yuan, Jianmin

    2014-01-01

    We report a fiber-based quasi-continuous-wave (CW) quantum key distribution (QKD) system with continuous variables (CV). This system employs coherent light pulses and time multiplexing to maximally reduce cross talk in the fiber. No-switching detection scheme is adopted to optimize the repetition rate. Information is encoded on the sideband of the pulsed coherent light to fully exploit the continuous wave nature of laser field. With this configuration, high secret key rate can be achieved. For the 50 MHz detected bandwidth in our experiment, when the multidimensional reconciliation protocol is applied, a secret key rate of 187 kb/s can be achieved over 50 km of optical fiber against collective attacks, which have been shown to be asymptotically optimal. Moreover, recently studied loopholes have been fixed in our system. PMID:24691409

  7. Experimental Demonstration of Polarization Encoding Measurement-Device-Independent Quantum Key Distribution

    NASA Astrophysics Data System (ADS)

    Tang, Zhiyuan; Liao, Zhongfa; Xu, Feihu; Qi, Bing; Qian, Li; Lo, Hoi-Kwong

    2014-05-01

    We demonstrate the first implementation of polarization encoding measurement-device-independent quantum key distribution (MDI-QKD), which is immune to all detector side-channel attacks. Active phase randomization of each individual pulse is implemented to protect against attacks on imperfect sources. By optimizing the parameters in the decoy state protocol, we show that it is feasible to implement polarization encoding MDI-QKD with commercial off-the-shelf devices. A rigorous finite key analysis is applied to estimate the secure key rate. Our work paves the way for the realization of a MDI-QKD network, in which the users only need compact and low-cost state-preparation devices and can share complicated and expensive detectors provided by an untrusted network server.

  8. Long-distance continuous-variable quantum key distribution with a Gaussian modulation

    SciTech Connect

    Jouguet, Paul; Kunz-Jacques, Sebastien; Leverrier, Anthony

    2011-12-15

    We designed high-efficiency error correcting codes allowing us to extract an errorless secret key in a continuous-variable quantum key distribution (CVQKD) protocol using a Gaussian modulation of coherent states and a homodyne detection. These codes are available for a wide range of signal-to-noise ratios on an additive white Gaussian noise channel with a binary modulation and can be combined with a multidimensional reconciliation method proven secure against arbitrary collective attacks. This improved reconciliation procedure considerably extends the secure range of a CVQKD with a Gaussian modulation, giving a secret key rate of about 10{sup -3} bit per pulse at a distance of 120 km for reasonable physical parameters.

  9. Tomographic Approach in Reference-Frame-Independent Measurement-Device-Independent Quantum Key Distribution

    NASA Astrophysics Data System (ADS)

    Fang, Xi; Wang, Chao; Han, Yun-Guang; Yin, Zhen-Qiang; Chen, Wei; Han, Zheng-Fu

    2016-11-01

    Recently, a novel reference-frame-independent measurement-device-independent quantum key distribution protocol was proposed, which can remove all detector side channels as well as tolerate unknown and slow variance of reference frame without active alignment. In this paper, we propose a new tomographic method to estimate the key rate in that protocol. We estimate the key rate using conventional method and tomographic method respectively and compare the two methods by numerical simulation. The numerical simulation results show that tomographic approach is equivalent to the conventional approach, which can be used as an alternative method. Supported by the National Basic Research Program of China under Grant Nos. 2011CBA00200 and 2011CB921200, the National Natural Science Foundation of China under Grant Nos. 61475148, 61575183, and the “Strategic Priority Research Program (B)” of the Chinese Academy of Sciences under Grant Nos. XDB01030100, XDB01030300

  10. Improving the performance of continuous variable quantum key distribution using fading effects of free-space channel

    NASA Astrophysics Data System (ADS)

    Zhang, Zeyu; Zhu, Chengrui; He, Guangqiang

    2015-08-01

    Quantum key distribution can be used to share secret keys with information-theoretic security between two legitimate partners for secure communication. In the case of satellite communication, free-space channel is the only way to transmit information, thus research on its properties is of great significance to quantum cryptographic communication. In this paper, we thoroughly analyze the influence of free-space channel fading effects on continuous variable quantum key distribution and for the first time prove that random distribution (such as Rayleigh distribution, Rice distribution and et al.) of free-space channel fading coefficients can be used to increase secret information rates and improve system stability against excess noises. Our results offer academic reference for practical applications of ground-space and space-space quantum communication and global quantum communication network.

  11. Experimental asymmetric plug-and-play measurement-device-independent quantum key distribution

    NASA Astrophysics Data System (ADS)

    Tang, Guang-Zhao; Sun, Shi-Hai; Xu, Feihu; Chen, Huan; Li, Chun-Yan; Liang, Lin-Mei

    2016-09-01

    Measurement-device-independent quantum key distribution (MDI-QKD) is immune to all security loopholes on detection. Previous experiments on MDI-QKD required spatially separated signal lasers and complicated stabilization systems. In this paper, we perform a proof-of-principle experimental demonstration of plug-and-play MDI-QKD over an asymmetric channel setting with a single signal laser in which the whole system is automatically stabilized in spectrum, polarization, arrival time, and phase reference. Both the signal laser and the single-photon detectors are in the possession of a common server. A passive timing-calibration technique is applied to ensure the precise and stable overlap of signal pulses. The results pave the way for the realization of a quantum network in which the users only need the encoding devices.

  12. Security of continuous-variable quantum key distribution against general attacks

    NASA Astrophysics Data System (ADS)

    Leverrier, Anthony

    2013-03-01

    We prove the security of Gaussian continuous-variable quantum key distribution with coherent states against arbitrary attacks in the finite-size regime. In contrast to previously known proofs of principle (based on the de Finetti theorem), our result is applicable in the practically relevant finite-size regime. This is achieved using a novel proof approach, which exploits phase-space symmetries of the protocols as well as the postselection technique introduced by Christandl, Koenig and Renner (Phys. Rev. Lett. 102, 020504 (2009)). This work was supported by the SNF through the National Centre of Competence in Research ``Quantum Science and Technology'' and through Grant No. 200020-135048, the ERC (grant No. 258932), the Humbolt foundation and the F.R.S.-FNRS under project HIPERCOM.

  13. Photon-monitoring attack on continuous-variable quantum key distribution with source in middle

    NASA Astrophysics Data System (ADS)

    Wang, Yijun; Huang, Peng; Guo, Ying; Huang, Dazu

    2014-12-01

    Motivated by a fact that the non-Gaussian operation may increase entanglement of an entangled system, we suggest a photon-monitoring attack strategy in the entanglement-based (EB) continuous-variable quantum key distribution (CVQKD) using the photon subtraction operations, where the entangled source originates from the center instead of one of the legal participants. It shows that an eavesdropper, Eve, can steal large information from participants after intercepting the partial beams with the photon-monitoring attach strategy. The structure of the proposed CVQKD protocol is useful in simply analyzing how quantum loss in imperfect channels can decrease the performance of the CVQKD protocol. The proposed attack strategy can be implemented under current technology, where a newly developed and versatile no-Gaussian operation can be well employed with the entangled source in middle in order to access to mass information in the EB CVQKD protocol, as well as in the prepare-and-measure (PM) CVQKD protocol.

  14. Attacks on practical quantum key distribution systems (and how to prevent them)

    NASA Astrophysics Data System (ADS)

    Jain, Nitin; Stiller, Birgit; Khan, Imran; Elser, Dominique; Marquardt, Christoph; Leuchs, Gerd

    2016-07-01

    With the emergence of an information society, the idea of protecting sensitive data is steadily gaining importance. Conventional encryption methods may not be sufficient to guarantee data protection in the future. Quantum key distribution (QKD) is an emerging technology that exploits fundamental physical properties to guarantee perfect security in theory. However, it is not easy to ensure in practice that the implementations of QKD systems are exactly in line with the theoretical specifications. Such theory-practice deviations can open loopholes and compromise security. Several such loopholes have been discovered and investigated in the last decade. These activities have motivated the proposal and implementation of appropriate countermeasures, thereby preventing future attacks and enhancing the practical security of QKD. This article introduces the so-called field of quantum hacking by summarising a variety of attacks and their prevention mechanisms.

  15. Self-coherent phase reference sharing for continuous-variable quantum key distribution

    NASA Astrophysics Data System (ADS)

    Marie, Adrien; Alléaume, Romain

    2017-01-01

    We develop a comprehensive framework to model and optimize the performance of continuous-variable quantum key distribution (CV-QKD) with a local local oscillator (LLO), when phase reference sharing and QKD are jointly implemented. We first analyze the limitations of the only existing approach, called LLO-sequential, and show that it requires high modulation dynamics and can only tolerate small phase noise. Our main contribution is to introduce two designs to perform LLO CV-QKD, respectively called LLO-delayline and LLO-displacement, and to study their performance. Both designs rely on a self-coherent approach, in which phase reference information and quantum information are coherently obtained from a single optical wavefront. We show that these designs can lift some limitations of the existing LLO-sequential approach. The LLO-delayline design can in particular tolerate much stronger phase noise and thus appears to be an appealing alternative to LLO-sequential in terms of network integrability. We also investigate, with the LLO-displacement design, how phase reference information and quantum information can be multiplexed within a single optical pulse. By studying the trade-off between phase reference recovery and phase noise induced by displacement, we, however, demonstrate that this design can only tolerate low phase noise. On the other hand, the LLO-displacement design has the advantage of minimal hardware requirements and provides a simple approach to multiplex classical and quantum communications, opening a practical path towards the development of ubiquitous coherent classical-quantum communications systems compatible with next-generation network requirements.

  16. Fast optical source for quantum key distribution based on semiconductor optical amplifiers.

    PubMed

    Jofre, M; Gardelein, A; Anzolin, G; Amaya, W; Capmany, J; Ursin, R; Peñate, L; Lopez, D; San Juan, J L; Carrasco, J A; Garcia, F; Torcal-Milla, F J; Sanchez-Brea, L M; Bernabeu, E; Perdigues, J M; Jennewein, T; Torres, J P; Mitchell, M W; Pruneri, V

    2011-02-28

    A novel integrated optical source capable of emitting faint pulses with different polarization states and with different intensity levels at 100 MHz has been developed. The source relies on a single laser diode followed by four semiconductor optical amplifiers and thin film polarizers, connected through a fiber network. The use of a single laser ensures high level of indistinguishability in time and spectrum of the pulses for the four different polarizations and three different levels of intensity. The applicability of the source is demonstrated in the lab through a free space quantum key distribution experiment which makes use of the decoy state BB84 protocol. We achieved a lower bound secure key rate of the order of 3.64 Mbps and a quantum bit error ratio as low as 1.14×10⁻² while the lower bound secure key rate became 187 bps for an equivalent attenuation of 35 dB. To our knowledge, this is the fastest polarization encoded QKD system which has been reported so far. The performance, reduced size, low power consumption and the fact that the components used can be space qualified make the source particularly suitable for secure satellite communication.

  17. Fast optical source for quantum key distribution based on semiconductor optical amplifiers

    NASA Astrophysics Data System (ADS)

    Jofre, M.; Gardelein, A.; Anzolin, G.; Amaya, W.; Campmany, J.; Ursin, R.; Penate, L.; Lopez, D.; San Juan, J. L.; Carrasco, J. A.; Garcia, F.; Torcal-Milla, F. J.; Sanchez-Brea, L. M.; Bernabeu, E.; Perdigues, J. M.; Jennewein, T.; Torres, J. P.; Mitchell, M. W.; Pruneri, V.

    2011-02-01

    A novel integrated optical source capable of emitting faint pulses with different polarization states and with different intensity levels at 100 MHz has been developed. The source relies on a single laser diode followed by four semiconductor optical amplifiers and thin film polarizers, connected through a fiber network. The use of a single laser ensures high level of indistinguishability in time and spectrum of the pulses for the four different polarizations and three different levels of intensity. The applicability of the source is demonstrated in the lab through a free space quantum key distribution experiment which makes use of the decoy state BB84 protocol. We achieved a lower bound secure key rate of the order of 3.64 Mbps and a quantum bit error ratio as low as $1.14\\times 10^{-2}$ while the lower bound secure key rate became 187 bps for an equivalent attenuation of 35 dB. To our knowledge, this is the fastest polarization encoded QKD system which has been reported so far. The performance, reduced size, low power consumption and the fact that the components used can be space qualified make the source particularly suitable for secure satellite communication.

  18. Continuous operation of four-state continuous-variable quantum key distribution system

    NASA Astrophysics Data System (ADS)

    Matsubara, Takuto; Ono, Motoharu; Oguri, Yusuke; Ichikawa, Tsubasa; Hirano, Takuya; Kasai, Kenta; Matsumoto, Ryutaroh; Tsurumaru, Toyohiro

    2016-10-01

    We report on the development of continuous-variable quantum key distribution (CV-QKD) system that are based on discrete quadrature amplitude modulation (QAM) and homodyne detection of coherent states of light. We use a pulsed light source whose wavelength is 1550 nm and repetition rate is 10 MHz. The CV-QKD system can continuously generate secret key which is secure against entangling cloner attack. Key generation rate is 50 kbps when the quantum channel is a 10 km optical fiber. The CV-QKD system we have developed utilizes the four-state and post-selection protocol [T. Hirano, et al., Phys. Rev. A 68, 042331 (2003).]; Alice randomly sends one of four states {|+/-α⟩,|+/-𝑖α⟩}, and Bob randomly performs x- or p- measurement by homodyne detection. A commercially available balanced receiver is used to realize shot-noise-limited pulsed homodyne detection. GPU cards are used to accelerate the software-based post-processing. We use a non-binary LDPC code for error correction (reverse reconciliation) and the Toeplitz matrix multiplication for privacy amplification.

  19. Long-distance continuous-variable quantum key distribution with advanced reconciliation of a Gaussian modulation

    NASA Astrophysics Data System (ADS)

    Gyongyosi, L.; Imre, S.

    2014-02-01

    The two-way continuous-variable quantum key distribution (CVQKD) systems allow higher key rates and improved transmission distances over standard telecommunication networks in comparison to the one-way CVQKD protocols. To exploit the real potential of two-way CVQKD systems a robust reconciliation technique is needed. It is currently unavailable, which makes it impossible to reach the real performance of a two-way CVQKD system. The reconciliation process of correlated Gaussian variables is a complex problem that requires either tomography in the physical layer that is intractable in a practical scenario, or high-cost calculations in the multidimensional spherical space with strict dimensional limitations. To avoid these issues, we propose an efficient logical layer-based reconciliation method for two-way CVQKD to extract binary information from correlated Gaussian variables. We demonstrate that by operating on the raw-data level, the noise of the quantum channel can be corrected in the scalar space and the reconciliation can be extended to arbitrary high dimensions. We prove that the error probability of scalar reconciliation is zero in any practical CVQKD scenario, and provides unconditional security. The results allow to significantly improve the currently available key rates and transmission distances of two-way CVQKD. The proposed scalar reconciliation can also be applied in oneway systems as well, to replace the existing reconciliation schemes.

  20. Practical security analysis of two-way quantum-key-distribution protocols based on nonorthogonal states

    NASA Astrophysics Data System (ADS)

    Henao, C. Ivan; Serra, Roberto M.

    2015-11-01

    Within the broad research scenario of quantum secure communication, two-way quantum key distribution (TWQKD) is a relatively new proposal for sharing secret keys that is not yet fully explored. We analyze the security of TWQKD schemes that use qubits prepared in nonorthogonal states to transmit the key. Investigating protocols that employ an arbitrary number of bases for the channel preparation, we show, in particular, that the security of the LM05 protocol cannot be improved by the use of more than two preparation bases. We also provide an alternative proof of unconditional security for a deterministic TWQKD protocol recently proposed in Beaudry et al., Phys. Rev. A 88, 062302 (2013), 10.1103/PhysRevA.88.062302. In addition, we introduce a deterministic protocol named "TWQKD six-state" and compute an analytical lower bound (which can be tightened) for the maximum amount of information that an eavesdropper could extract in this case. An interesting advantage of our approach to the security analysis of TWQKD is the great simplicity and transparency of the derivations.

  1. Counterfactual Thinking and False Belief: The Role of Executive Function

    ERIC Educational Resources Information Center

    Drayton, Stefane; Turley-Ames, Kandi J.; Guajardo, Nicole R.

    2011-01-01

    The purpose of the current study was to examine further the relationship between counterfactual thinking and false belief (FB) as examined by Guajardo and Turley-Ames ("Cognitive Development, 19" (2004) 53-80). More specifically, the current research examined the importance of working memory and inhibitory control in understanding the relationship…

  2. Associations among False Belief Understanding, Counterfactual Reasoning, and Executive Function

    ERIC Educational Resources Information Center

    Guajardo, Nicole R.; Parker, Jessica; Turley-Ames, Kandi

    2009-01-01

    The primary purposes of the present study were to clarify previous work on the association between counterfactual thinking and false belief performance to determine (1) whether these two variables are related and (2) if so, whether executive function skills mediate the relationship. A total of 92 3-, 4-, and 5-year-olds completed false belief,…

  3. False belief and counterfactual reasoning in a social environment.

    PubMed

    Van Hoeck, Nicole; Begtas, Elizabet; Steen, Johan; Kestemont, Jenny; Vandekerckhove, Marie; Van Overwalle, Frank

    2014-04-15

    Behavioral studies indicate that theory of mind and counterfactual reasoning are strongly related cognitive processes. In a neuroimaging study, we explored the common and distinct regions underlying these inference processes. We directly compared false belief reasoning (inferring an agent's false belief about an object's location or content) and counterfactual reasoning (inferring what the object's location or content would be if an agent had acted differently), both in contrast with a baseline condition of conditional reasoning (inferring what the true location or content of an object is). Results indicate that these three types of reasoning about social scenarios are supported by activations in the mentalizing network (left temporo-parietal junction and precuneus) and the executive control network (bilateral prefrontal cortex [PFC] and right inferior parietal lobule). In addition, representing a false belief or counterfactual state (both not directly observable in the external world) recruits additional activity in the executive control network (left dorsolateral PFC and parietal lobe). The results further suggest that counterfactual reasoning is a more complex cognitive process than false belief reasoning, showing stronger activation of the dorsomedial, left dorsolateral PFC, cerebellum and left temporal cortex.

  4. Counterfactual Reasoning: Developing a Sense of "Nearest Possible World"

    ERIC Educational Resources Information Center

    Rafetseder, Eva; Cristi-Vargas, Renate; Perner, Josef

    2010-01-01

    This study investigated at what point in development 3- to 6-year-old children begin to demonstrate counterfactual reasoning by controlling for fortuitously correct answers that result from basic conditional reasoning. "Basic conditional reasoning" occurs when one applies typical regularities (such as "If 'whenever' it doesn't rain the street is…

  5. Counterfactual Thinking and Impact Evaluation in Environmental Policy

    ERIC Educational Resources Information Center

    Ferraro, Paul J.

    2009-01-01

    Impact evaluations assess the degree to which changes in outcomes can be attributed to an intervention rather than to other factors. Such attribution requires knowing what outcomes would have looked like in the absence of the intervention. This counterfactual world can be inferred only indirectly through evaluation designs that control for…

  6. Counterfactuals and Causal Models: Introduction to the Special Issue

    ERIC Educational Resources Information Center

    Sloman, Steven A.

    2013-01-01

    Judea Pearl won the 2010 Rumelhart Prize in computational cognitive science due to his seminal contributions to the development of Bayes nets and causal Bayes nets, frameworks that are central to multiple domains of the computational study of mind. At the heart of the causal Bayes nets formalism is the notion of a counterfactual, a representation…

  7. Expectations in Counterfactual and Theory of Mind Reasoning

    ERIC Educational Resources Information Center

    Ferguson, Heather J.; Scheepers, Christoph; Sanford, Anthony J.

    2010-01-01

    During language comprehension, information about the world is exchanged and processed. Two essential ingredients of everyday cognition that are employed during language comprehension are the ability to reason counterfactually, and the ability to understand and predict other peoples' behaviour by attributing independent mental states to them…

  8. Counterfactual Thinking Deficit in Huntington’s Disease

    PubMed Central

    Solca, Federica; Poletti, Barbara; Zago, Stefano; Crespi, Chiara; Sassone, Francesca; Lafronza, Annalisa; Maraschi, Anna Maria; Sassone, Jenny; Silani, Vincenzo; Ciammola, Andrea

    2015-01-01

    Background and Objective Counterfactual thinking (CFT) refers to the generation of mental simulations of alternatives to past events, actions and outcomes. CFT is a pervasive cognitive feature in every-day life and is closely related to decision-making, planning and problem-solving – all of which are cognitive processes linked to unimpaired frontal lobe functioning. Huntington’s Disease (HD) is a neurodegenerative disorder characterised by motor, behavioral and cognitive dysfunctions. Because an impairment in frontal and executive functions has been described in HD, we hypothesised that HD patients may have a CFT impairment. Methods Tests of spontaneous counterfactual thoughts and counterfactual-derived inferences were administered to 24 symptomatic HD patients and 24 age- and sex-matched healthy subjects. Results Our results show a significant impairment in the spontaneous generation of CFT and low performance on the Counterfactual Inference Test (CIT) in HD patients. Low performance on the spontaneous CFT test significantly correlates with impaired attention abilities, verbal fluency and frontal lobe efficiency, as measured by Trail Making Test – Part A, Phonemic Verbal Fluency Test and FAB. Conclusions Spontaneous CFT and the use of this type of reasoning are impaired in HD patients. This deficit may be related to frontal lobe dysfunction, which is a hallmark of HD. Because CFT has a pervasive role in patients’ daily lives regarding their planning, decision making and problem solving skills, cognitive rehabilitation may improve HD patients’ ability to analyse current behaviors and future actions. PMID:26070155

  9. Using Counterfactual History to Enhance Students' Historical Understanding

    ERIC Educational Resources Information Center

    Roberts, Scott L.

    2011-01-01

    The question "what if?" has been asked by historians for generations. This article explains how history teachers can use students' own what-if questions to enhance their historical knowledge and understanding by offering educators a step-by-step plan for utilizing counterfactual history into their classrooms. Additionally, the author offers a…

  10. Finding Fault: Causality and Counterfactuals in Group Attributions

    ERIC Educational Resources Information Center

    Zultan, Ro'i; Gerstenberg, Tobias; Lagnado, David A.

    2012-01-01

    Attributions of responsibility play a critical role in many group interactions. This paper explores the role of causal and counterfactual reasoning in blame attributions in groups. We develop a general framework that builds on the notion of pivotality: an agent is pivotal if she could have changed the group outcome by acting differently. In three…

  11. Experimental transmission of quantum digital signatures over 90 km of installed optical fiber using a differential phase shift quantum key distribution system

    NASA Astrophysics Data System (ADS)

    Collins, Robert J.; Amiri, Ryan; Fujiwara, Mikio; Honjo, Toshimori; Shimizu, Kaoru; Tamaki, Kiyoshi; Takeoka, Masahiro; Andersson, Erika; Buller, Gerald S.; Sasaki, Masahide

    2016-11-01

    Quantum digital signatures apply quantum mechanics to the problem of guaranteeing message integrity and non-repudiation with information-theoretical security, which are complementary to the confidentiality realized by quantum key distribution. Previous experimental demonstrations have been limited to transmission distances of less than 5-km of optical fiber in a laboratory setting. Here we report the first demonstration of quantum digital signatures over installed optical fiber as well as the longest transmission link reported to date. This demonstration used a 90-km long differential phase shift quantum key distribution system to achieve approximately one signed bit per second - an increase in the signature generation rate of several orders of magnitude over previous optical fiber demonstrations.

  12. Security of continuous-variable quantum key distribution against general attacks.

    PubMed

    Leverrier, Anthony; García-Patrón, Raúl; Renner, Renato; Cerf, Nicolas J

    2013-01-18

    We prove the security of Gaussian continuous-variable quantum key distribution with coherent states against arbitrary attacks in the finite-size regime. In contrast to previously known proofs of principle (based on the de Finetti theorem), our result is applicable in the practically relevant finite-size regime. This is achieved using a novel proof approach, which exploits phase-space symmetries of the protocols as well as the postselection technique introduced by Christandl, Koenig, and Renner [Phys. Rev. Lett. 102, 020504 (2009)].

  13. Continuous-variable quantum key distribution under the local oscillator intensity attack with noiseless linear amplifier

    NASA Astrophysics Data System (ADS)

    Yang, Fangli; Shi, Ronghua; Guo, Ying; Shi, JinJing; Zeng, Guihua

    2015-08-01

    An improved continuous-variable quantum key distribution (CVQKD) protocol is proposed to improve the performance of CVQKD system under the local oscillator intensity attack by using a suitable noiseless linear amplifier (NLA) at the destination. This method can enhance the efficiency of the CVQKD scheme in terms of the maximum transmission distance, no matter whether the direct or reverse reconciliation is used. Simulation results show that there is a considerable increase in the transmission distance for the NLA-based CVQKD by adjusting the values of the parameters.

  14. Room temperature single-photon detectors for high bit rate quantum key distribution

    SciTech Connect

    Comandar, L. C.; Patel, K. A.; Fröhlich, B. Lucamarini, M.; Sharpe, A. W.; Dynes, J. F.; Yuan, Z. L.; Shields, A. J.; Penty, R. V.

    2014-01-13

    We report room temperature operation of telecom wavelength single-photon detectors for high bit rate quantum key distribution (QKD). Room temperature operation is achieved using InGaAs avalanche photodiodes integrated with electronics based on the self-differencing technique that increases avalanche discrimination sensitivity. Despite using room temperature detectors, we demonstrate QKD with record secure bit rates over a range of fiber lengths (e.g., 1.26 Mbit/s over 50 km). Furthermore, our results indicate that operating the detectors at room temperature increases the secure bit rate for short distances.

  15. Trustworthiness of measurement devices in round-robin differential-phase-shift quantum key distribution

    NASA Astrophysics Data System (ADS)

    Cao, Zhu; Yin, Zhen-Qiang; Han, Zheng-Fu

    2016-02-01

    Round-robin differential-phase-shift quantum key distribution (RRDPS QKD) has been proposed to raise the noise tolerability of the channel. However, in practice, the measurement device in RRDPS QKD may be imperfect. Here, we show that, with these imperfections, the security of RRDPS may be damaged by proposing two attacks for RRDPS systems with uncharacterized measurement devices. One is valid even for a system with unit total efficiency, while the other is valid even when a single-photon state is sent. To prevent these attacks, either security arguments need to be fundamentally revised or further practical assumptions on the measurement device should be put.

  16. Security of Continuous-Variable Quantum Key Distribution Against General Attacks

    NASA Astrophysics Data System (ADS)

    Leverrier, Anthony; García-Patrón, Raúl; Renner, Renato; Cerf, Nicolas J.

    2013-01-01

    We prove the security of Gaussian continuous-variable quantum key distribution with coherent states against arbitrary attacks in the finite-size regime. In contrast to previously known proofs of principle (based on the de Finetti theorem), our result is applicable in the practically relevant finite-size regime. This is achieved using a novel proof approach, which exploits phase-space symmetries of the protocols as well as the postselection technique introduced by Christandl, Koenig, and Renner [Phys. Rev. Lett. 102, 020504 (2009)PRLTAO0031-9007].

  17. Trojan horse attack free fault-tolerant quantum key distribution protocols

    NASA Astrophysics Data System (ADS)

    Yang, Chun-Wei; Hwang, Tzonelih

    2013-11-01

    This work proposes two quantum key distribution (QKD) protocols—each of which is robust under one kind of collective noises—collective-dephasing noise and collective-rotation noise. Due to the use of a new coding function which produces error-robust codewords allowing one-time transmission of quanta, the proposed QKD schemes are fault-tolerant and congenitally free from Trojan horse attacks without having to use any extra hardware. Moreover, by adopting two Bell state measurements instead of a 4-GHZ state joint measurement for decoding, the proposed protocols are practical in combating collective noises.

  18. Practical quantum private query of blocks based on unbalanced-state Bennett-Brassard-1984 quantum-key-distribution protocol

    PubMed Central

    Wei, Chun-Yan; Gao, Fei; Wen, Qiao-Yan; Wang, Tian-Yin

    2014-01-01

    Until now, the only kind of practical quantum private query (QPQ), quantum-key-distribution (QKD)-based QPQ, focuses on the retrieval of a single bit. In fact, meaningful message is generally composed of multiple adjacent bits (i.e., a multi-bit block). To obtain a message from database, the user Alice has to query l times to get each ai. In this condition, the server Bob could gain Alice's privacy once he obtains the address she queried in any of the l queries, since each ai contributes to the message Alice retrieves. Apparently, the longer the retrieved message is, the worse the user privacy becomes. To solve this problem, via an unbalanced-state technique and based on a variant of multi-level BB84 protocol, we present a protocol for QPQ of blocks, which allows the user to retrieve a multi-bit block from database in one query. Our protocol is somewhat like the high-dimension version of the first QKD-based QPQ protocol proposed by Jacobi et al., but some nontrivial modifications are necessary. PMID:25518810

  19. Measurement-device-independent quantum key distribution for Scarani-Acin-Ribordy-Gisin 04 protocol

    PubMed Central

    Mizutani, Akihiro; Tamaki, Kiyoshi; Ikuta, Rikizo; Yamamoto, Takashi; Imoto, Nobuyuki

    2014-01-01

    The measurement-device-independent quantum key distribution (MDI QKD) was proposed to make BB84 completely free from any side-channel in detectors. Like in prepare & measure QKD, the use of other protocols in MDI setting would be advantageous in some practical situations. In this paper, we consider SARG04 protocol in MDI setting. The prepare & measure SARG04 is proven to be able to generate a key up to two-photon emission events. In MDI setting we show that the key generation is possible from the event with single or two-photon emission by a party and single-photon emission by the other party, but the two-photon emission event by both parties cannot contribute to the key generation. On the contrary to prepare & measure SARG04 protocol where the experimental setup is exactly the same as BB84, the measurement setup for SARG04 in MDI setting cannot be the same as that for BB84 since the measurement setup for BB84 in MDI setting induces too many bit errors. To overcome this problem, we propose two alternative experimental setups, and we simulate the resulting key rate. Our study highlights the requirements that MDI QKD poses on us regarding with the implementation of a variety of QKD protocols. PMID:24913431

  20. Statistical-fluctuation analysis for quantum key distribution with consideration of after-pulse contributions

    NASA Astrophysics Data System (ADS)

    Li, Hongxin; Jiang, Haodong; Gao, Ming; Ma, Zhi; Ma, Chuangui; Wang, Wei

    2015-12-01

    The statistical fluctuation problem is a critical factor in all quantum key distribution (QKD) protocols under finite-key conditions. The current statistical fluctuation analysis is mainly based on independent random samples, however, the precondition cannot always be satisfied because of different choices of samples and actual parameters. As a result, proper statistical fluctuation methods are required to solve this problem. Taking the after-pulse contributions into consideration, this paper gives the expression for the secure key rate and the mathematical model for statistical fluctuations, focusing on a decoy-state QKD protocol [Z.-C. Wei et al., Sci. Rep. 3, 2453 (2013), 10.1038/srep02453] with a biased basis choice. On this basis, a classified analysis of statistical fluctuation is represented according to the mutual relationship between random samples. First, for independent identical relations, a deviation comparison is made between the law of large numbers and standard error analysis. Second, a sufficient condition is given that the Chernoff bound achieves a better result than Hoeffding's inequality based on only independent relations. Third, by constructing the proper martingale, a stringent way is proposed to deal issues based on dependent random samples through making use of Azuma's inequality. In numerical optimization, the impact on the secure key rate, the comparison of secure key rates, and the respective deviations under various kinds of statistical fluctuation analyses are depicted.

  1. Long distance measurement-device-independent quantum key distribution with entangled photon sources

    SciTech Connect

    Xu, Feihu; Qi, Bing; Liao, Zhongfa; Lo, Hoi-Kwong

    2013-08-05

    We present a feasible method that can make quantum key distribution (QKD), both ultra-long-distance and immune, to all attacks in the detection system. This method is called measurement-device-independent QKD (MDI-QKD) with entangled photon sources in the middle. By proposing a model and simulating a QKD experiment, we find that MDI-QKD with one entangled photon source can tolerate 77 dB loss (367 km standard fiber) in the asymptotic limit and 60 dB loss (286 km standard fiber) in the finite-key case with state-of-the-art detectors. Our general model can also be applied to other non-QKD experiments involving entanglement and Bell state measurements.

  2. Two-party secret key distribution via a modified quantum secret sharing protocol.

    PubMed

    Grice, W P; Evans, P G; Lawrie, B; Legré, M; Lougovski, P; Ray, W; Williams, B P; Qi, B; Smith, A M

    2015-03-23

    We present and demonstrate a novel protocol for distributing secret keys between two and only two parties based on N-party single-qubit Quantum Secret Sharing (QSS). We demonstrate our new protocol with N = 3 parties using phase-encoded photons. We show that any two out of N parties can build a secret key based on partial information from each other and with collaboration from the remaining N - 2 parties. Our implementation allows for an accessible transition between N-party QSS and arbitrary two party QKD without modification of hardware. In addition, our approach significantly reduces the number of resources such as single photon detectors, lasers and dark fiber connections needed to implement QKD.

  3. Proof-of-principle experiment of reference-frame-independent quantum key distribution with phase coding

    PubMed Central

    Liang, Wen-Ye; Wang, Shuang; Li, Hong-Wei; Yin, Zhen-Qiang; Chen, Wei; Yao, Yao; Huang, Jing-Zheng; Guo, Guang-Can; Han, Zheng-Fu

    2014-01-01

    We have demonstrated a proof-of-principle experiment of reference-frame-independent phase coding quantum key distribution (RFI-QKD) over an 80-km optical fiber. After considering the finite-key bound, we still achieve a distance of 50 km. In this scenario, the phases of the basis states are related by a slowly time-varying transformation. Furthermore, we developed and realized a new decoy state method for RFI-QKD systems with weak coherent sources to counteract the photon-number-splitting attack. With the help of a reference-frame-independent protocol and a Michelson interferometer with Faraday rotator mirrors, our system is rendered immune to the slow phase changes of the interferometer and the polarization disturbances of the channel, making the procedure very robust. PMID:24402550

  4. The enhanced measurement-device-independent quantum key distribution with two-intensity decoy states

    NASA Astrophysics Data System (ADS)

    Zhu, Jian-Rong; Zhu, Feng; Zhou, Xing-Yu; Wang, Qin

    2016-09-01

    We put forward a new scheme for implementing the measurement-device-independent quantum key distribution (QKD) with weak coherent source, while using only two different intensities. In the new scheme, we insert a beam splitter and a local detector at both Alice's and Bob's side, and then all the triggering and non-triggering signals could be employed to process parameter estimations, resulting in very precise estimations for the two-single-photon contributions. Besides, we compare its behavior with two other often used methods, i.e., the conventional standard three-intensity decoy-state measurement-device-independent QKD and the passive measurement-device-independent QKD. Through numerical simulations, we demonstrate that our new approach can exhibit outstanding characteristics not only in the secure transmission distance, but also in the final key generation rate.

  5. Proof-of-principle experiment of reference-frame-independent quantum key distribution with phase coding.

    PubMed

    Liang, Wen-Ye; Wang, Shuang; Li, Hong-Wei; Yin, Zhen-Qiang; Chen, Wei; Yao, Yao; Huang, Jing-Zheng; Guo, Guang-Can; Han, Zheng-Fu

    2014-01-09

    We have demonstrated a proof-of-principle experiment of reference-frame-independent phase coding quantum key distribution (RFI-QKD) over an 80-km optical fiber. After considering the finite-key bound, we still achieve a distance of 50 km. In this scenario, the phases of the basis states are related by a slowly time-varying transformation. Furthermore, we developed and realized a new decoy state method for RFI-QKD systems with weak coherent sources to counteract the photon-number-splitting attack. With the help of a reference-frame-independent protocol and a Michelson interferometer with Faraday rotator mirrors, our system is rendered immune to the slow phase changes of the interferometer and the polarization disturbances of the channel, making the procedure very robust.

  6. Proof-of-principle experiment of reference-frame-independent quantum key distribution with phase coding

    NASA Astrophysics Data System (ADS)

    Liang, Wen-Ye; Wang, Shuang; Li, Hong-Wei; Yin, Zhen-Qiang; Chen, Wei; Yao, Yao; Huang, Jing-Zheng; Guo, Guang-Can; Han, Zheng-Fu

    2014-01-01

    We have demonstrated a proof-of-principle experiment of reference-frame-independent phase coding quantum key distribution (RFI-QKD) over an 80-km optical fiber. After considering the finite-key bound, we still achieve a distance of 50 km. In this scenario, the phases of the basis states are related by a slowly time-varying transformation. Furthermore, we developed and realized a new decoy state method for RFI-QKD systems with weak coherent sources to counteract the photon-number-splitting attack. With the help of a reference-frame-independent protocol and a Michelson interferometer with Faraday rotator mirrors, our system is rendered immune to the slow phase changes of the interferometer and the polarization disturbances of the channel, making the procedure very robust.

  7. Experimental measurement-device-independent quantum key distribution with uncharacterized encoding.

    PubMed

    Wang, Chao; Wang, Shuang; Yin, Zhen-Qiang; Chen, Wei; Li, Hong-Wei; Zhang, Chun-Mei; Ding, Yu-Yang; Guo, Guang-Can; Han, Zheng-Fu

    2016-12-01

    Measurement-device-independent quantum key distribution (MDI QKD) is an efficient way to share secrets using untrusted measurement devices. However, the assumption on the characterizations of encoding states is still necessary in this promising protocol, which may lead to unnecessary complexity and potential loopholes in realistic implementations. Here, by using the mismatched-basis statistics, we present the first proof-of-principle experiment of MDI QKD with uncharacterized encoding sources. In this demonstration, the encoded states are only required to be constrained in a two-dimensional Hilbert space, and two distant parties (Alice and Bob) are resistant to state preparation flaws even if they have no idea about the detailed information of their encoding states. The positive final secure key rates of our system exhibit the feasibility of this novel protocol, and demonstrate its value for the application of secure communication with uncharacterized devices.

  8. Practical round-robin differential phase-shift quantum key distribution.

    PubMed

    Zhang, Ying-Ying; Bao, Wan-Su; Zhou, Chun; Li, Hong-Wei; Wang, Yang; Jiang, Mu-Sheng

    2016-09-05

    Recently, a novel protocol named round-robin differential phase-shift (RRDPS) quantum key distribution [Nature 509, 475(2014)] has been proposed. It can estimate information leakage without monitoring bit error rate. In this paper, we study the performance of RRDPS using heralded single photon source (HSPS) without and with decoy-state method, then compare it with the performance of weak coherent pulses (WCPs). From numerical simulation, we can see that HSPS performs better especially for shorter packet and higher bit error rate. Moreover, we propose a general theory of decoy-state method for RRDPS protocol based on only three decoy states and one signal state. Taking WCPs as an example, the three-intensity decoy-state protocol can distribute secret keys over a distance of 128 km when the length of pulses packet is 32, which confirms great practical interest of our method.

  9. Practical round-robin differential phase-shift quantum key distribution

    NASA Astrophysics Data System (ADS)

    Zhang, Ying-Ying; Bao, Wan-Su; Zhou, Chun; Li, Hong-Wei; Wang, Yang; Jiang, Mu-Sheng

    2016-09-01

    To overcome the signal disturbance from the transmission process, recently, a new type of protocol named round-robin differential-phase-shift(RRDPS) quantum key distribution[Nature 509, 475(2014)] is proposed. It can estimate how much information has leaked to eavesdropper without monitoring bit error rates. In this paper, we compare the performance of RRDPS using different sources without and with decoy-state method, such as weak coherent pulses(WCPs) and heralded single photon source(HSPS). For practical implementations, we propose finite decoy-state method for RRDPS, the performance of which is close to the infinite one. Taking WCPs as an example, the three-intensity decoystate protocol can distribute secret keys over a distance of 128 km when the length of pulses packet is 32, which confirms the great practical interest of our method.

  10. Experimental demonstration of a quantum key distribution without signal disturbance monitoring

    NASA Astrophysics Data System (ADS)

    Wang, Shuang; Yin, Zhen-Qiang; Chen, Wei; He, De-Yong; Song, Xiao-Tian; Li, Hong-Wei; Zhang, Li-Jun; Zhou, Zheng; Guo, Guang-Can; Han, Zheng-Fu

    2015-12-01

    In existing quantum key distribution protocols, two legitimate peers, Alice and Bob, must monitor the signal disturbance to place a bound on the potential information leakage. However, in the round-robin differential phase shift (RRDPS) protocol, monitoring of the signal disturbance is unnecessary. Here, we present the first active implementation of the RRDPS protocol. In our experiment, Alice prepares packets of pulses, where each packet is a train with 65 pulses and the global phase of each packet is randomized. Bob uses a novel actively controlled variable-delay interferometer to realize the random switching of different delays. Benefiting from the large pulse number of each packet, and the high stability and low insertion loss of the interferometer, the system can distribute a secret key over a distance of 90 km. Our experimental demonstration and results confirm the feasibility of the RRDPS protocol, particularly in high-error situations.

  11. Preventing side-channel effects in continuous-variable quantum key distribution

    NASA Astrophysics Data System (ADS)

    Derkach, Ivan; Usenko, Vladyslav C.; Filip, Radim

    2016-03-01

    The role of the side channels in the continuous-variable quantum key distribution is studied. It is shown how the information leakage through a side channel from the trusted sender station increases the vulnerability of the protocols to the eavesdropping in the main quantum communication channel. Moreover, the untrusted noise infusion by an eavesdropper on the trusted receiving side breaks the security even for a purely attenuating main quantum channel. As a method to compensate for the effect of the side-channel leakage on the sender side, we suggest several types of manipulations on the side-channel input. It is shown that by applying the modulated coherent light on the input of the side channel that is optimally correlated to the modulation on the main signal and optionally introducing additional squeezing in the case of the squeezed-state protocol, the negative influence of the lossy side channel on the sender side can be completely removed. For the trusted receiving side, the method of optimal monitoring of the residual noise from the side-channel noise infusion is suggested and shown to be able to completely eliminate the presence of the noisy side channel. We therefore prove that the side-channel effects can be completely removed using feasible operations if the trusted parties access the respective parts of the side channels.

  12. Real-world two-photon interference and proof-of-principle quantum key distribution immune to detector attacks.

    PubMed

    Rubenok, A; Slater, J A; Chan, P; Lucio-Martinez, I; Tittel, W

    2013-09-27

    Several vulnerabilities of single-photon detectors have recently been exploited to compromise the security of quantum-key-distribution (QKD) systems. In this Letter, we report the first proof-of-principle implementation of a new quantum-key-distribution protocol that is immune to any such attack. More precisely, we demonstrated this new approach to QKD in the laboratory over more than 80 km of spooled fiber, as well as across different locations within the city of Calgary. The robustness of our fiber-based implementation, together with the enhanced level of security offered by the protocol, confirms QKD as a realistic technology for safeguarding secrets in transmission. Furthermore, our demonstration establishes the feasibility of controlled two-photon interference in a real-world environment and thereby removes a remaining obstacle to realizing future applications of quantum communication, such as quantum repeaters and, more generally, quantum networks.

  13. Real-World Two-Photon Interference and Proof-of-Principle Quantum Key Distribution Immune to Detector Attacks

    NASA Astrophysics Data System (ADS)

    Rubenok, A.; Slater, J. A.; Chan, P.; Lucio-Martinez, I.; Tittel, W.

    2013-09-01

    Several vulnerabilities of single-photon detectors have recently been exploited to compromise the security of quantum-key-distribution (QKD) systems. In this Letter, we report the first proof-of-principle implementation of a new quantum-key-distribution protocol that is immune to any such attack. More precisely, we demonstrated this new approach to QKD in the laboratory over more than 80 km of spooled fiber, as well as across different locations within the city of Calgary. The robustness of our fiber-based implementation, together with the enhanced level of security offered by the protocol, confirms QKD as a realistic technology for safeguarding secrets in transmission. Furthermore, our demonstration establishes the feasibility of controlled two-photon interference in a real-world environment and thereby removes a remaining obstacle to realizing future applications of quantum communication, such as quantum repeaters and, more generally, quantum networks.

  14. Information-theoretic security proof for quantum-key-distribution protocols

    NASA Astrophysics Data System (ADS)

    Renner, Renato; Gisin, Nicolas; Kraus, Barbara

    2005-07-01

    We present a technique for proving the security of quantum-key-distribution (QKD) protocols. It is based on direct information-theoretic arguments and thus also applies if no equivalent entanglement purification scheme can be found. Using this technique, we investigate a general class of QKD protocols with one-way classical post-processing. We show that, in order to analyze the full security of these protocols, it suffices to consider collective attacks. Indeed, we give new lower and upper bounds on the secret-key rate which only involve entropies of two-qubit density operators and which are thus easy to compute. As an illustration of our results, we analyze the Bennett-Brassard 1984, the six-state, and the Bennett 1992 protocols with one-way error correction and privacy amplification. Surprisingly, the performance of these protocols is increased if one of the parties adds noise to the measurement data before the error correction. In particular, this additional noise makes the protocols more robust against noise in the quantum channel.

  15. Source attack of decoy-state quantum key distribution using phase information

    NASA Astrophysics Data System (ADS)

    Tang, Yan-Lin; Yin, Hua-Lei; Ma, Xiongfeng; Fung, Chi-Hang Fred; Liu, Yang; Yong, Hai-Lin; Chen, Teng-Yun; Peng, Cheng-Zhi; Chen, Zeng-Bing; Pan, Jian-Wei

    2013-08-01

    Quantum key distribution (QKD) utilizes the laws of quantum mechanics to achieve information-theoretically secure key generation. This field is now approaching the stage of commercialization, but many practical QKD systems still suffer from security loopholes due to imperfect devices. In fact, practical attacks have successfully been demonstrated. Fortunately, most of them only exploit detection-side loopholes, which are now closed by the recent idea of measurement-device-independent QKD. On the other hand, little attention is paid to the source, which may still leave QKD systems insecure. In this work, we propose and demonstrate an attack that exploits a source-side loophole existing in qubit-based QKD systems using a weak coherent state source and decoy states. Specifically, by implementing a linear-optics unambiguous state discrimination measurement, we show that the security of a system without phase randomization—which is a step assumed in conventional security analyses but sometimes neglected in practice—can be compromised. We conclude that implementing phase randomization is essential to the security of decoy-state QKD systems under current security analyses.

  16. Passive Faraday-mirror attack in a practical two-way quantum-key-distribution system

    SciTech Connect

    Sun Shihai; Jiang Musheng; Liang Linmei

    2011-06-15

    The Faraday mirror (FM) plays a very important role in maintaining the stability of two-way plug-and-play quantum key distribution (QKD) systems. However, the practical FM is imperfect, which will not only introduce an additional quantum bit error rate (QBER) but also leave a loophole for Eve to spy the secret key. In this paper we propose a passive Faraday mirror attack in two-way QKD system based on the imperfection of FM. Our analysis shows that if the FM is imperfect, the dimension of Hilbert space spanned by the four states sent by Alice is three instead of two. Thus Eve can distinguish these states with a set of Positive Operator Valued Measure (POVM) operators belonging to three-dimension space, which will reduce the QBER induced by her attack. Furthermore, a relationship between the degree of the imperfection of FM and the transmittance of the practical QKD system is obtained. The results show that the probability that Eve loads her attack successfully depends on the degree of the imperfection of FM rapidly, but the QBER induced by Eve's attack changes slightly with the degree of the FM imperfection.

  17. Device-dependent and device-independent quantum key distribution without a shared reference frame

    NASA Astrophysics Data System (ADS)

    Slater, Joshua A.; Branciard, Cyril; Brunner, Nicolas; Tittel, Wolfgang

    2014-04-01

    Standard quantum key distribution (QKD) protocols typically assume that the distant parties share a common reference frame. In practice, however, establishing and maintaining a good alignment between distant observers is rarely a trivial issue, which may significantly restrain the implementation of long-distance quantum communication protocols. Here we propose simple QKD protocols that do not require the parties to share any reference frame, and study their security and feasibility in both the usual device-dependent (DD) case—in which the two parties use well characterized measurement devices—as well as in the device-independent (DI) case—in which the measurement devices can be untrusted, and the security relies on the violation of a Bell inequality. To illustrate the practical relevance of these ideas, we present a proof-of-principle demonstration of our protocols using polarization entangled photons distributed over a coiled 10-km long optical fiber. We consider two situations, in which either the fiber spool's polarization transformation freely drifts, or randomly chosen polarization transformations are applied. The correlations obtained from measurements allow, with high probability, to generate positive asymptotic secret key rates in both the DD and DI scenarios (under the fair-sampling assumption for the latter case).

  18. Apply current exponential de Finetti theorem to realistic quantum key distribution

    NASA Astrophysics Data System (ADS)

    Zhao, Yi-Bo; Yin, Zhen-Qiang

    2014-09-01

    In the realistic quantum key distribution (QKD), Alice and Bob respectively get a quantum state from an unknown channel, whose dimension may be unknown. However, while discussing the security, sometime we need to know exact dimension, since current exponential de Finetti theorem, crucial to the information-theoretical security proof, is deeply related with the dimension and can only be applied to finite dimensional case. Here we address this problem in detail. We show that if POVM elements corresponding to Alice and Bob's measured results can be well described in a finite dimensional subspace with sufficiently small error, then dimensions of Alice and Bob's states can be almost regarded as finite. Since the security is well defined by the smooth entropy, which is continuous with the density matrix, the small error of state actually means small change of security. Then the security of unknown-dimensional system can be solved. Finally we prove that for heterodyne detection continuous variable QKD and differential phase shift QKD, the collective attack is optimal under the infinite key size case.

  19. Information-theoretic security proof for quantum-key-distribution protocols

    SciTech Connect

    Renner, Renato; Gisin, Nicolas; Kraus, Barbara

    2005-07-15

    We present a technique for proving the security of quantum-key-distribution (QKD) protocols. It is based on direct information-theoretic arguments and thus also applies if no equivalent entanglement purification scheme can be found. Using this technique, we investigate a general class of QKD protocols with one-way classical post-processing. We show that, in order to analyze the full security of these protocols, it suffices to consider collective attacks. Indeed, we give new lower and upper bounds on the secret-key rate which only involve entropies of two-qubit density operators and which are thus easy to compute. As an illustration of our results, we analyze the Bennett-Brassard 1984, the six-state, and the Bennett 1992 protocols with one-way error correction and privacy amplification. Surprisingly, the performance of these protocols is increased if one of the parties adds noise to the measurement data before the error correction. In particular, this additional noise makes the protocols more robust against noise in the quantum channel.

  20. Necessary detection efficiencies for secure quantum key distribution and bound randomness

    NASA Astrophysics Data System (ADS)

    Acín, Antonio; Cavalcanti, Daniel; Passaro, Elsa; Pironio, Stefano; Skrzypczyk, Paul

    2016-01-01

    In recent years, several hacking attacks have broken the security of quantum cryptography implementations by exploiting the presence of losses and the ability of the eavesdropper to tune detection efficiencies. We present a simple attack of this form that applies to any protocol in which the key is constructed from the results of untrusted measurements performed on particles coming from an insecure source or channel. Because of its generality, the attack applies to a large class of protocols, from standard prepare-and-measure to device-independent schemes. Our attack gives bounds on the critical detection efficiencies necessary for secure quantum key distribution, which show that the implementation of most partly device-independent solutions is, from the point of view of detection efficiency, almost as demanding as fully device-independent ones. We also show how our attack implies the existence of a form of bound randomness, namely nonlocal correlations in which a nonsignalling eavesdropper can find out a posteriori the result of any implemented measurement.

  1. Implementation of continuous-variable quantum key distribution with composable and one-sided-device-independent security against coherent attacks.

    PubMed

    Gehring, Tobias; Händchen, Vitus; Duhme, Jörg; Furrer, Fabian; Franz, Torsten; Pacher, Christoph; Werner, Reinhard F; Schnabel, Roman

    2015-10-30

    Secret communication over public channels is one of the central pillars of a modern information society. Using quantum key distribution this is achieved without relying on the hardness of mathematical problems, which might be compromised by improved algorithms or by future quantum computers. State-of-the-art quantum key distribution requires composable security against coherent attacks for a finite number of distributed quantum states as well as robustness against implementation side channels. Here we present an implementation of continuous-variable quantum key distribution satisfying these requirements. Our implementation is based on the distribution of continuous-variable Einstein-Podolsky-Rosen entangled light. It is one-sided device independent, which means the security of the generated key is independent of any memoryfree attacks on the remote detector. Since continuous-variable encoding is compatible with conventional optical communication technology, our work is a step towards practical implementations of quantum key distribution with state-of-the-art security based solely on telecom components.

  2. Implementation of continuous-variable quantum key distribution with composable and one-sided-device-independent security against coherent attacks

    NASA Astrophysics Data System (ADS)

    Gehring, Tobias; Händchen, Vitus; Duhme, Jörg; Furrer, Fabian; Franz, Torsten; Pacher, Christoph; Werner, Reinhard F.; Schnabel, Roman

    2015-10-01

    Secret communication over public channels is one of the central pillars of a modern information society. Using quantum key distribution this is achieved without relying on the hardness of mathematical problems, which might be compromised by improved algorithms or by future quantum computers. State-of-the-art quantum key distribution requires composable security against coherent attacks for a finite number of distributed quantum states as well as robustness against implementation side channels. Here we present an implementation of continuous-variable quantum key distribution satisfying these requirements. Our implementation is based on the distribution of continuous-variable Einstein-Podolsky-Rosen entangled light. It is one-sided device independent, which means the security of the generated key is independent of any memoryfree attacks on the remote detector. Since continuous-variable encoding is compatible with conventional optical communication technology, our work is a step towards practical implementations of quantum key distribution with state-of-the-art security based solely on telecom components.

  3. Implementation of continuous-variable quantum key distribution with composable and one-sided-device-independent security against coherent attacks

    PubMed Central

    Gehring, Tobias; Händchen, Vitus; Duhme, Jörg; Furrer, Fabian; Franz, Torsten; Pacher, Christoph; Werner, Reinhard F.; Schnabel, Roman

    2015-01-01

    Secret communication over public channels is one of the central pillars of a modern information society. Using quantum key distribution this is achieved without relying on the hardness of mathematical problems, which might be compromised by improved algorithms or by future quantum computers. State-of-the-art quantum key distribution requires composable security against coherent attacks for a finite number of distributed quantum states as well as robustness against implementation side channels. Here we present an implementation of continuous-variable quantum key distribution satisfying these requirements. Our implementation is based on the distribution of continuous-variable Einstein–Podolsky–Rosen entangled light. It is one-sided device independent, which means the security of the generated key is independent of any memoryfree attacks on the remote detector. Since continuous-variable encoding is compatible with conventional optical communication technology, our work is a step towards practical implementations of quantum key distribution with state-of-the-art security based solely on telecom components. PMID:26514280

  4. Measurement-device-independent quantum key distribution: from idea towards application

    NASA Astrophysics Data System (ADS)

    Valivarthi, Raju; Lucio-Martinez, Itzel; Chan, Philip; Rubenok, Allison; John, Caleb; Korchinski, Daniel; Duffin, Cooper; Marsili, Francesco; Verma, Varun; Shaw, Mathew D.; Stern, Jeffrey A.; Nam, Sae Woo; Oblak, Daniel; Zhou, Qiang; Slater, Joshua A.; Tittel, Wolfgang

    2015-08-01

    We assess the overall performance of our quantum key distribution (QKD) system implementing the measurement-device-independent (MDI) protocol using components with varying capabilities such as different single-photon detectors and qubit preparation hardware. We experimentally show that superconducting nanowire single-photon detectors allow QKD over a channel featuring 60 dB loss, and QKD with more than 600 bits of secret key per second (not considering finite key effects) over a 16 dB loss channel. This corresponds to 300 and 80 km of standard telecommunication fiber, respectively. We also demonstrate that the integration of our QKD system into FPGA-based hardware (instead of state-of-the-art arbitrary waveform generators) does not impact on its performance. Our investigation allows us to acquire an improved understanding of the trade-offs between complexity, cost and system performance, which is required for future customization of MDI-QKD. Given that our system can be operated outside the laboratory over deployed fiber, we conclude that MDI-QKD is a promising approach to information-theoretic secure key distribution.

  5. Floodlight quantum key distribution: Demonstrating a framework for high-rate secure communication

    NASA Astrophysics Data System (ADS)

    Zhang, Zheshen; Zhuang, Quntao; Wong, Franco N. C.; Shapiro, Jeffrey H.

    2017-01-01

    Floodlight quantum key distribution (FL-QKD) is a radically different QKD paradigm that can achieve gigabit-per-second secret-key rates over metropolitan area distances without multiplexing [Q. Zhuang et al., Phys. Rev. A 94, 012322 (2016), 10.1103/PhysRevA.94.012322]. It is a two-way protocol that transmits many photons per bit duration and employs a high-gain optical amplifier, neither of which can be utilized by existing QKD protocols, to mitigate channel loss. FL-QKD uses an optical bandwidth that is substantially larger than the modulation rate and performs decoding with a unique broadband homodyne receiver. Essential to FL-QKD is Alice's injection of photons from a photon-pair source—in addition to the light used for key generation—into the light she sends to Bob. This injection enables Alice and Bob to quantify Eve's intrusion and thus secure FL-QKD against collective attacks. Our proof-of-concept experiment included 10 dB propagation loss—equivalent to 50 km of low-loss fiber—and achieved a 55 Mbit/s secret-key rate (SKR) for a 100 Mbit/s modulation rate, as compared to the state-of-the-art system's 1 Mbit/s SKR for a 1 Gbit/s modulation rate [M. Lucamarini et al., Opt. Express 21, 24550 (2013), 10.1364/OE.21.024550], representing ˜500 -fold and ˜50 -fold improvements in secret-key efficiency (bits per channel use) and SKR (bits per second), respectively.

  6. Passive decoy-state quantum key distribution with practical light sources

    SciTech Connect

    Curty, Marcos; Ma, Xiongfeng; Qi, Bing; Moroder, Tobias

    2010-02-15

    Decoy states have been proven to be a very useful method for significantly enhancing the performance of quantum key distribution systems with practical light sources. Although active modulation of the intensity of the laser pulses is an effective way of preparing decoy states in principle, in practice passive preparation might be desirable in some scenarios. Typical passive schemes involve parametric down-conversion. More recently, it has been shown that phase-randomized weak coherent pulses (WCP) can also be used for the same purpose [M. Curty et al., Opt. Lett. 34, 3238 (2009).] This proposal requires only linear optics together with a simple threshold photon detector, which shows the practical feasibility of the method. Most importantly, the resulting secret key rate is comparable to the one delivered by an active decoy-state setup with an infinite number of decoy settings. In this article we extend these results, now showing specifically the analysis for other practical scenarios with different light sources and photodetectors. In particular, we consider sources emitting thermal states, phase-randomized WCP, and strong coherent light in combination with several types of photodetectors, like, for instance, threshold photon detectors, photon number resolving detectors, and classical photodetectors. Our analysis includes as well the effect that detection inefficiencies and noise in the form of dark counts shown by current threshold detectors might have on the final secret key rate. Moreover, we provide estimations on the effects that statistical fluctuations due to a finite data size can have in practical implementations.

  7. Security of six-state quantum key distribution protocol with threshold detectors

    PubMed Central

    Kato, Go; Tamaki, Kiyoshi

    2016-01-01

    The security of quantum key distribution (QKD) is established by a security proof, and the security proof puts some assumptions on the devices consisting of a QKD system. Among such assumptions, security proofs of the six-state protocol assume the use of photon number resolving (PNR) detector, and as a result the bit error rate threshold for secure key generation for the six-state protocol is higher than that for the BB84 protocol. Unfortunately, however, this type of detector is demanding in terms of technological level compared to the standard threshold detector, and removing the necessity of such a detector enhances the feasibility of the implementation of the six-state protocol. Here, we develop the security proof for the six-state protocol and show that we can use the threshold detector for the six-state protocol. Importantly, the bit error rate threshold for the key generation for the six-state protocol (12.611%) remains almost the same as the one (12.619%) that is derived from the existing security proofs assuming the use of PNR detectors. This clearly demonstrates feasibility of the six-state protocol with practical devices. PMID:27443610

  8. Phase-noise limitations in continuous-variable quantum key distribution with homodyne detection

    NASA Astrophysics Data System (ADS)

    Corvaja, Roberto

    2017-02-01

    In continuous-variables quantum key distribution with coherent states, the advantage of performing the detection by using standard telecoms components is counterbalanced by the lack of a stable phase reference in homodyne detection due to the complexity of optical phase-locking circuits and to the unavoidable phase noise of lasers, which introduces a degradation on the achievable secure key rate. Pilot-assisted phase-noise estimation and postdetection compensation techniques are used to implement a protocol with coherent states where a local laser is employed and it is not locked to the received signal, but a postdetection phase correction is applied. Here the reduction of the secure key rate determined by the laser phase noise, for both individual and collective attacks, is analytically evaluated and a scheme of pilot-assisted phase estimation proposed, outlining the tradeoff in the system design between phase noise and spectral efficiency. The optimal modulation variance as a function of the phase-noise amount is derived.

  9. Attacks on quantum key distribution protocols that employ non-ITS authentication

    NASA Astrophysics Data System (ADS)

    Pacher, C.; Abidin, A.; Lorünser, T.; Peev, M.; Ursin, R.; Zeilinger, A.; Larsson, J.-Å.

    2016-01-01

    We demonstrate how adversaries with large computing resources can break quantum key distribution (QKD) protocols which employ a particular message authentication code suggested previously. This authentication code, featuring low key consumption, is not information-theoretically secure (ITS) since for each message the eavesdropper has intercepted she is able to send a different message from a set of messages that she can calculate by finding collisions of a cryptographic hash function. However, when this authentication code was introduced, it was shown to prevent straightforward man-in-the-middle (MITM) attacks against QKD protocols. In this paper, we prove that the set of messages that collide with any given message under this authentication code contains with high probability a message that has small Hamming distance to any other given message. Based on this fact, we present extended MITM attacks against different versions of BB84 QKD protocols using the addressed authentication code; for three protocols, we describe every single action taken by the adversary. For all protocols, the adversary can obtain complete knowledge of the key, and for most protocols her success probability in doing so approaches unity. Since the attacks work against all authentication methods which allow to calculate colliding messages, the underlying building blocks of the presented attacks expose the potential pitfalls arising as a consequence of non-ITS authentication in QKD post-processing. We propose countermeasures, increasing the eavesdroppers demand for computational power, and also prove necessary and sufficient conditions for upgrading the discussed authentication code to the ITS level.

  10. Round-robin differential-phase-shift quantum key distribution with a passive decoy state method

    NASA Astrophysics Data System (ADS)

    Liu, Li; Guo, Fen-Zhuo; Qin, Su-Juan; Wen, Qiao-Yan

    2017-02-01

    Recently, a new type of protocol named Round-robin differential-phase-shift quantum key distribution (RRDPS QKD) was proposed, where the security can be guaranteed without monitoring conventional signal disturbances. The active decoy state method can be used in this protocol to overcome the imperfections of the source. But, it may lead to side channel attacks and break the security of QKD systems. In this paper, we apply the passive decoy state method to the RRDPS QKD protocol. Not only can the more environment disturbance be tolerated, but in addition it can overcome side channel attacks on the sources. Importantly, we derive a new key generation rate formula for our RRDPS protocol using passive decoy states and enhance the key generation rate. We also compare the performance of our RRDPS QKD to that using the active decoy state method and the original RRDPS QKD without any decoy states. From numerical simulations, the performance improvement of the RRDPS QKD by our new method can be seen.

  11. Round-robin differential-phase-shift quantum key distribution with a passive decoy state method.

    PubMed

    Liu, Li; Guo, Fen-Zhuo; Qin, Su-Juan; Wen, Qiao-Yan

    2017-02-13

    Recently, a new type of protocol named Round-robin differential-phase-shift quantum key distribution (RRDPS QKD) was proposed, where the security can be guaranteed without monitoring conventional signal disturbances. The active decoy state method can be used in this protocol to overcome the imperfections of the source. But, it may lead to side channel attacks and break the security of QKD systems. In this paper, we apply the passive decoy state method to the RRDPS QKD protocol. Not only can the more environment disturbance be tolerated, but in addition it can overcome side channel attacks on the sources. Importantly, we derive a new key generation rate formula for our RRDPS protocol using passive decoy states and enhance the key generation rate. We also compare the performance of our RRDPS QKD to that using the active decoy state method and the original RRDPS QKD without any decoy states. From numerical simulations, the performance improvement of the RRDPS QKD by our new method can be seen.

  12. Experimental round-robin differential phase-shift quantum key distribution

    NASA Astrophysics Data System (ADS)

    Li, Yu-Huai; Cao, Yuan; Dai, Hui; Lin, Jin; Zhang, Zhen; Chen, Wei; Xu, Yu; Guan, Jian-Yu; Liao, Sheng-Kai; Yin, Juan; Zhang, Qiang; Ma, Xiongfeng; Peng, Cheng-Zhi; Pan, Jian-Wei

    2016-03-01

    In conventional quantum key distribution (QKD) protocols, security is guaranteed by estimating the amount of leaked information. Such estimation tends to overrate, leading to a fundamental threshold of the bit error rate, which becomes a bottleneck of practical QKD development. This bottleneck is broken through by the recent work of round-robin differential phase-shift (RRDPS) protocol, which eliminates the fundamental threshold of the bit error rate. The key challenge for the implementation of the RRDPS scheme lies in the realization of a variable-delay Mach-Zehnder interferometer, which requires active and random choice of many delays. By designing an optical system with multiple switches and employing an active phase stabilization technology, we successfully construct a variable-delay interferometer with 127 actively selectable delays. With this measurement, we experimentally demonstrate the RRDPS protocol and obtain a final key rate of 15.54 bps with a total loss of 18 dB and an error rate of 8.9%.

  13. Round-robin differential-phase-shift quantum key distribution with a passive decoy state method

    PubMed Central

    Liu, Li; Guo, Fen-Zhuo; Qin, Su-Juan; Wen, Qiao-Yan

    2017-01-01

    Recently, a new type of protocol named Round-robin differential-phase-shift quantum key distribution (RRDPS QKD) was proposed, where the security can be guaranteed without monitoring conventional signal disturbances. The active decoy state method can be used in this protocol to overcome the imperfections of the source. But, it may lead to side channel attacks and break the security of QKD systems. In this paper, we apply the passive decoy state method to the RRDPS QKD protocol. Not only can the more environment disturbance be tolerated, but in addition it can overcome side channel attacks on the sources. Importantly, we derive a new key generation rate formula for our RRDPS protocol using passive decoy states and enhance the key generation rate. We also compare the performance of our RRDPS QKD to that using the active decoy state method and the original RRDPS QKD without any decoy states. From numerical simulations, the performance improvement of the RRDPS QKD by our new method can be seen. PMID:28198808

  14. Security of six-state quantum key distribution protocol with threshold detectors.

    PubMed

    Kato, Go; Tamaki, Kiyoshi

    2016-07-22

    The security of quantum key distribution (QKD) is established by a security proof, and the security proof puts some assumptions on the devices consisting of a QKD system. Among such assumptions, security proofs of the six-state protocol assume the use of photon number resolving (PNR) detector, and as a result the bit error rate threshold for secure key generation for the six-state protocol is higher than that for the BB84 protocol. Unfortunately, however, this type of detector is demanding in terms of technological level compared to the standard threshold detector, and removing the necessity of such a detector enhances the feasibility of the implementation of the six-state protocol. Here, we develop the security proof for the six-state protocol and show that we can use the threshold detector for the six-state protocol. Importantly, the bit error rate threshold for the key generation for the six-state protocol (12.611%) remains almost the same as the one (12.619%) that is derived from the existing security proofs assuming the use of PNR detectors. This clearly demonstrates feasibility of the six-state protocol with practical devices.

  15. Biased decoy-state measurement-device-independent quantum key distribution with finite resources

    NASA Astrophysics Data System (ADS)

    Zhou, Chun; Bao, Wan-Su; Zhang, Hai-long; Li, Hong-Wei; Wang, Yang; Li, Yuan; Wang, Xiang

    2015-02-01

    Measurement-device-independent quantum key distribution (MDI-QKD) can remove all the side-channel attacks from imperfections in the detection side. However, finite-size resources undoubtedly influence its performance and the achievable finite secret key rates of MDI-QKD are typically lower than that of standard decoy-state QKD. In this paper, we introduce the efficient decoy-state method with biased basis choice into the finite-key analysis and propose a decoy-state protocol for MDI-QKD. By applying vacuum + weak decoy-state method, we analytically derive concise formulas for estimating the lower bound of single-photon yield and the upper bound of phase error rate in the case of finite resources. The simulations show that proper basis choice combined with deliberate intensity choice can substantially enhance the performance of decoy-state MDI-QKD and, without a full optimization program, our protocol can bring a long-distance implementation (168 km on standard optical fiber) of MDI-QKD with a reasonable data size of total transmitting signals (N =1015 ).

  16. Round-robin differential-phase-shift quantum key distribution with heralded pair-coherent sources

    NASA Astrophysics Data System (ADS)

    Wang, Le; Zhao, Shengmei

    2017-04-01

    Round-robin differential-phase-shift (RRDPS) quantum key distribution (QKD) scheme provides an effective way to overcome the signal disturbance from the transmission process. However, most RRDPS-QKD schemes use weak coherent pulses (WCPs) as the replacement of the perfect single-photon source. Considering the heralded pair-coherent source (HPCS) can efficiently remove the shortcomings of WCPs, we propose a RRDPS-QKD scheme with HPCS in this paper. Both infinite-intensity decoy-state method and practical three-intensity decoy-state method are adopted to discuss the tight bound of the key rate of the proposed scheme. The results show that HPCS is a better candidate for the replacement of the perfect single-photon source, and both the key rate and the transmission distance are greatly increased in comparison with those results with WCPs when the length of the pulse trains is small. Simultaneously, the performance of the proposed scheme using three-intensity decoy states is close to that result using infinite-intensity decoy states when the length of pulse trains is small.

  17. Quantum-key-distribution protocols without sifting that are resistant to photon-number-splitting attacks

    NASA Astrophysics Data System (ADS)

    Grazioso, Fabio; Grosshans, Frédéric

    2013-11-01

    We propose a family of sifting-less quantum-key-distribution protocols which use reverse reconciliation, and are based on weak coherent pulses (WCPs) polarized along m different directions. When m=4, the physical part of the protocol is identical to most experimental implementations of BB84 [Bennett and Brassard, in Proceedings of the IEEE International Conference on Computers, Systems, and Signal Processing (IEEE, New York, 1984)] and SARG04 [Scarani, Acín, Ribordy, and Gisin, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.92.057901 92, 057901 (2004); Acín, Gisin, and Scarani, Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.69.012309 69, 012309 (2004)] protocols and they differ only in classical communications and data processing. We compute their total key rate as a function of the channel transmission T, using general information theoretical arguments, and we show that they have a higher key rate than the more standard protocols, both for fixed and optimized average photon number of the WCPs. When no decoy-state protocols (DSPs) [Hwang, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.91.057901 91, 057901 (2003); Lo, Ma, and Chen, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.94.230504 94, 230504 (2005); Wang, Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.72.012322 72, 012322 (2005)] are applied, the scaling of the key rate with transmission is improved from T2 for BB84 to T1+(1)/(m-2). If a DSP is applied, we show how the key rates scale linearly with T, with an improvement of the prefactor by 75.96% for m=4. High values of m allow one to asymptotically approach the key rate obtained with ideal single-photon pulses. The fact that the key rates of these sifting-less protocols are higher compared to those of the aforementioned more standard protocols show that the latter are not optimal, since they do not extract all the available secret keys from the experimental correlations.

  18. On the optimality of individual entangling-probe attacks against BB84 quantum key distribution

    NASA Astrophysics Data System (ADS)

    Herbauts, I. M.; Bettelli, S.; Hã¼bel, H.; Peev, M.

    2008-02-01

    Some MIT researchers [Phys. Rev. A 75, 042327 (2007)] have recently claimed that their implementation of the Slutsky-Brandt attack [Phys. Rev. A 57, 2383 (1998); Phys. Rev. A 71, 042312 (2005)] to the BB84 quantum-key-distribution (QKD) protocol puts the security of this protocol “to the test” by simulating “the most powerful individual-photon attack” [Phys. Rev. A 73, 012315 (2006)]. A related unfortunate news feature by a scientific journal [G. Brumfiel, Quantum cryptography is hacked, News @ Nature (april 2007); Nature 447, 372 (2007)] has spurred some concern in the QKD community and among the general public by misinterpreting the implications of this work. The present article proves the existence of a stronger individual attack on QKD protocols with encrypted error correction, for which tight bounds are shown, and clarifies why the claims of the news feature incorrectly suggest a contradiction with the established “old-style” theory of BB84 individual attacks. The full implementation of a quantum cryptographic protocol includes a reconciliation and a privacy-amplification stage, whose choice alters in general both the maximum extractable secret and the optimal eavesdropping attack. The authors of [Phys. Rev. A 75, 042327 (2007)] are concerned only with the error-free part of the so-called sifted string, and do not consider faulty bits, which, in the version of their protocol, are discarded. When using the provably superior reconciliation approach of encrypted error correction (instead of error discard), the Slutsky-Brandt attack is no more optimal and does not “threaten” the security bound derived by Lütkenhaus [Phys. Rev. A 59, 3301 (1999)]. It is shown that the method of Slutsky and collaborators [Phys. Rev. A 57, 2383 (1998)] can be adapted to reconciliation with error correction, and that the optimal entangling probe can be explicitly found. Moreover, this attack fills Lütkenhaus bound, proving that it is tight (a fact which was not

  19. Effects of message framing in anti-binge drinking PSAs: the moderating role of counterfactual thinking.

    PubMed

    Baek, Tae Hyun; Shen, Lijiang; Reid, Leonard N

    2013-01-01

    This experiment examined the interaction effects of message framing and counterfactual thinking on attitudes toward binge drinking and behavioral intentions. Data from a 2 (message framing: gain vs. loss) × 2 (counterfactual thinking priming: additive vs. subtractive) between-subjects factorial design showed that a gain-framed message resulted in lower binge drinking intentions than did a loss-framed message after subjects engaged in additive counterfactual thinking. The effects of a loss-framed message on binge drinking intentions occurred when subtractive counterfactual thinking was induced. Theoretical and practical implications for anti-binge drinking public service announcements are discussed.

  20. Countermeasure against probabilistic blinding attack in practical quantum key distribution systems

    NASA Astrophysics Data System (ADS)

    Qian, Yong-Jun; Li, Hong-Wei; He, De-Yong; Yin, Zhen-Qiang; Zhang, Chun-Mei; Chen, Wei; Wang, Shuang; Han, Zheng-Fu

    2015-09-01

    In a practical quantum key distribution (QKD) system, imperfect equipment, especially the single-photon detector, can be eavesdropped on by a blinding attack. However, the original blinding attack may be discovered by directly detecting the current. In this paper, we propose a probabilistic blinding attack model, where Eve probabilistically applies a blinding attack without being caught by using only an existing intuitive countermeasure. More precisely, our countermeasure solves the problem of how to define the bound in the limitation of precision of current detection, and then we prove security of the practical system by considering the current parameter. Meanwhile, we discuss the bound of the quantum bit error rate (QBER) introduced by Eve, by which Eve can acquire information without the countermeasure. Project supported by the National Basic Research Program of China (Grant Nos. 2011CBA00200 and 2011CB921200), the National Natural Science Foundation of China (Grant Nos. 61475148, 61201239, 61205118, and 11304397), and the China Postdoctoral Science Foundation (Grant No. 2013M540514).

  1. Research on measurement-device-independent quantum key distribution based on an air-water channel

    NASA Astrophysics Data System (ADS)

    Zhou, Yuan-yuan; Zhou, Xue-jun; Xu, Hua-bin; Cheng, Kang

    2016-11-01

    A measurement-device-independent quantum key distribution (MDI-QKD) method with an air-water channel is researched. In this method, the underwater vehicle and satellite are the legitimate parties, and the third party is at the airwater interface in order to simplify the unilateral quantum channel to water or air. Considering the condition that both unilateral transmission distance and transmission loss coefficient are unequal, a perfect model of the asymmetric channel is built. The influence of asymmetric channel on system loss tolerance and secure transmission distance is analyzed. The simulation results show that with the increase of the channel's asymmetric degree, the system loss tolerance will descend, one transmission distance will be reduced while the other will be increased. When the asymmetric coefficient of channel is between 0.068 and 0.171, MDI-QKD can satisfy the demand of QKD with an air-water channel, namely the underwater transmission distance and atmospheric transmission distance are not less than 60 m and 12 km, respectively.

  2. Security of quantum key distribution with light sources that are not independently and identically distributed

    NASA Astrophysics Data System (ADS)

    Nagamatsu, Yuichi; Mizutani, Akihiro; Ikuta, Rikizo; Yamamoto, Takashi; Imoto, Nobuyuki; Tamaki, Kiyoshi

    2016-04-01

    Although quantum key distribution (QKD) is theoretically secure, there is a gap between the theory and practice. In fact, real-life QKD may not be secure because component devices in QKD systems may deviate from the theoretical models assumed in security proofs. To solve this problem, it is necessary to construct the security proof under realistic assumptions on the source and measurement unit. In this paper, we prove the security of a QKD protocol under practical assumptions on the source that accommodate fluctuation of the phase and intensity modulations. As long as our assumptions hold, it does not matter at all how the phase and intensity distribute or whether or not their distributions over different pulses are independently and identically distributed. Our work shows that practical sources can be safely employed in QKD experiments.

  3. Demonstration of free-space reference frame independent quantum key distribution

    NASA Astrophysics Data System (ADS)

    Wabnig, J.; Bitauld, D.; Li, H. W.; Laing, A.; O'Brien, J. L.; Niskanen, A. O.

    2013-07-01

    Quantum key distribution (QKD) is moving from research laboratories towards applications. As computing becomes more mobile, cashless as well as cardless payment solutions are introduced. A possible route to increase the security of wireless communications is to incorporate QKD in a mobile device. Handheld devices present a particular challenge as the orientation and the phase of a qubit will depend on device motion. This problem is addressed by the reference frame independent (RFI) QKD scheme. The scheme tolerates an unknown phase between logical states that vary slowly compared to the rate of particle repetition. Here we experimentally demonstrate the feasibility of RFI QKD over a free-space link in a prepare and measure scheme using polarization encoding. We extend the security analysis of the RFI QKD scheme to be able to deal with uncalibrated devices and a finite number of measurements. Together these advances are an important step towards mass production of handheld QKD devices.

  4. Continuous-variable quantum key distribution in non-Markovian channels

    SciTech Connect

    Vasile, Ruggero; Olivares, Stefano; Paris, MatteoG. A.; Maniscalco, Sabrina

    2011-04-15

    We address continuous-variable quantum key distribution (QKD) in non-Markovian lossy channels and show how the non-Markovian features may be exploited to enhance security and/or to detect the presence and the position of an eavesdropper along the transmission line. In particular, we suggest a coherent-state QKD protocol which is secure against Gaussian individual attacks based on optimal 1{yields}2 asymmetric cloning machines for arbitrarily low values of the overall transmission line. The scheme relies on specific non-Markovian properties, and cannot be implemented in ordinary Markovian channels characterized by uniform losses. Our results give a clear indication of the potential impact of non-Markovian effects in QKD.

  5. Decoy-state quantum key distribution with large random errors of light intensity

    NASA Astrophysics Data System (ADS)

    Wang, Xiang-Bin

    2007-05-01

    We show how to do decoy-state quantum key distribution efficiently with large random errors in the intensity control. We present a theorem for efficiently calculating the lower bound of single-photon counts with many undetermined parameters. In the calculation of the single-photon counts of our protocol, the linear terms of the intensity fluctuation disappear and only the quadratic terms take effect. Given that the intensity fluctuation is upper bounded by ±5% , ±10% , and ±15% , the verified lower bound of the percentage of untagged bits from our protocol is as large as 99.7%, 99.0%, and 97.9% of that from an ideal protocol where the light intensity is exactly controlled.

  6. Practical continuous-variable quantum key distribution without finite sampling bandwidth effects.

    PubMed

    Li, Huasheng; Wang, Chao; Huang, Peng; Huang, Duan; Wang, Tao; Zeng, Guihua

    2016-09-05

    In a practical continuous-variable quantum key distribution system, finite sampling bandwidth of the employed analog-to-digital converter at the receiver's side may lead to inaccurate results of pulse peak sampling. Then, errors in the parameters estimation resulted. Subsequently, the system performance decreases and security loopholes are exposed to eavesdroppers. In this paper, we propose a novel data acquisition scheme which consists of two parts, i.e., a dynamic delay adjusting module and a statistical power feedback-control algorithm. The proposed scheme may improve dramatically the data acquisition precision of pulse peak sampling and remove the finite sampling bandwidth effects. Moreover, the optimal peak sampling position of a pulse signal can be dynamically calibrated through monitoring the change of the statistical power of the sampled data in the proposed scheme. This helps to resist against some practical attacks, such as the well-known local oscillator calibration attack.

  7. Clinical applications of counterfactual thinking during memory reactivation.

    PubMed

    De Brigard, Felipe; Hanna, Eleanor

    2015-01-01

    The Integrative Memory Model offers a strong foundation upon which to build successful strategies for clinical intervention. The next challenge is to figure out which cognitive strategies are more likely to bring about successful and beneficial modifications of reactivated memories during therapy. In this commentary we suggest that exercising emotional regulation during episodic counterfactual thinking is likely to be a successful therapeutic strategy to bring about beneficial memory modifications.

  8. Attacking a practical quantum-key-distribution system with wavelength-dependent beam-splitter and multiwavelength sources

    SciTech Connect

    Li, Hong-Wei; Wang, Shuang; Huang, Jing-Zheng; Chen, Wei; Yin, Zhen-Qiang; Li, Fang-Yi; Zhou, Zheng; Liu, Dong; Zhang, Yang; Guo, Guang-Can; Han, Zheng-Fu; Bao, Wan-Su

    2011-12-15

    It is well known that the unconditional security of quantum-key distribution (QKD) can be guaranteed by quantum mechanics. However, practical QKD systems have some imperfections, which can be controlled by the eavesdropper to attack the secret key. With current experimental technology, a realistic beam splitter, made by fused biconical technology, has a wavelength-dependent property. Based on this fatal security loophole, we propose a wavelength-dependent attacking protocol, which can be applied to all practical QKD systems with passive state modulation. Moreover, we experimentally attack a practical polarization encoding QKD system to obtain all the secret key information at the cost of only increasing the quantum bit error rate from 1.3 to 1.4%.

  9. Secret information reconciliation based on punctured low-density parity-check codes for continuous-variable quantum key distribution

    NASA Astrophysics Data System (ADS)

    Jiang, Xue-Qin; Huang, Peng; Huang, Duan; Lin, Dakai; Zeng, Guihua

    2017-02-01

    Achieving information theoretic security with practical complexity is of great interest to continuous-variable quantum key distribution in the postprocessing procedure. In this paper, we propose a reconciliation scheme based on the punctured low-density parity-check (LDPC) codes. Compared to the well-known multidimensional reconciliation scheme, the present scheme has lower time complexity. Especially when the chosen punctured LDPC code achieves the Shannon capacity, the proposed reconciliation scheme can remove the information that has been leaked to an eavesdropper in the quantum transmission phase. Therefore, there is no information leaked to the eavesdropper after the reconciliation stage. This indicates that the privacy amplification algorithm of the postprocessing procedure is no more needed after the reconciliation process. These features lead to a higher secret key rate, optimal performance, and availability for the involved quantum key distribution scheme.

  10. Controlled quantum key distribution with three-photon polarization-entangled states via the collective noise channel

    SciTech Connect

    Dong Li; Xiu Xiaoming; Gao Yajun; Yi, X. X.

    2011-10-15

    Using three-photon polarization-entangled GHZ states or W states, we propose controlled quantum key distribution protocols for circumventing two main types of collective noise, collective dephasing noise, or collective rotation noise. Irrespective of the number of controllers, a three-photon state can generate a one-bit secret key. The storage technique of quantum states is dispensable for the controller and the receiver, and it therefore allows performing the process in a more convenient mode. If the photon cost in a security check is disregarded, then the efficiency theoretically approaches unity.

  11. Comparison between Two Practical Methods of Light Source Monitoring in Quantum Key Distribution

    NASA Astrophysics Data System (ADS)

    Wang, Gan; Chen, Ziyang; Xu, Bingjie; Li, Zhengyu; Peng, Xiang; Guo, Hong

    2016-05-01

    The practical security of a quantum key distribution (QKD) is a critical issue due to the loopholes opened by the imperfections of practical devices. The untrusted source problem is a fundamental issue that exists in almost every protocol, including the loss-tolerant protocol and the measurement-device-independent protocol. Two practical light source monitoring methods were proposed, i.e., two-threshold detector scheme and photon-number-resolving (PNR) detector scheme. In this work, we test the fluctuation level of different gain-switched pulsed lasers, i.e., the ratio between the standard deviation and the mean of the pulse energy (noted as γ) changes from 1% to 7%. Moreover, we propose an improved practical PNR detector scheme, and discuss in what circumstances one should use which light source monitoring method, i.e., generally speaking when the fluctuation is large the PNR detector method performs better. This provides an instruction of selecting proper monitoring module for different practical systems. This work is supported by the National Science Fund for Distinguished Young Scholars of China (Grant No. 61225003), the State Key Project of National Natural Science Foundation of China (Grant No. 61531003).

  12. Passive decoy-state quantum key distribution using weak coherent pulses with modulator attenuation

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Bao, Wan-Su; Li, Hong-Wei; Zhou, Chun; Wang, Yang

    2015-11-01

    Passive decoy-state quantum key distribution is more desirable than the active one in some scenarios. It is also affected by the imperfections of the devices. In this paper, the influence of modulator attenuation on the passive decoy-state method is considered. We introduce and analyze the unbalanced Mach-Zehnder interferometer, briefly, and combining with the virtual source and imaginary unitary transformation, we characterize the passive decoy-state method using a weak coherent photon source with modulator attenuation. According to the attenuation parameter δ, the pass efficiencies are given. Then, the key generation rate can be acquired. From numerical simulations, it can be seen that modulator attenuation has a nonnegligible influence on the performance of passive-state QKD protocol. Based on the research, the analysis method of virtual source and imaginary unitary transformation are preferred in analyzing passive decoy state protocol, and the passive decoy-state method is better than the active one and is close to the active vacuum + weak decoy state under the condition of having the same modulator attenuation. Project supported by the National Natural Science Foundation of China (Grant No. 11304397).

  13. Detector-device-independent quantum key distribution: Security analysis and fast implementation

    DOE PAGES

    Boaron, Alberto; Korzh, Boris; Houlmann, Raphael; ...

    2016-08-09

    One of the most pressing issues in quantum key distribution (QKD) is the problem of detector side-channel attacks. To overcome this problem, researchers proposed an elegant “time-reversal” QKD protocol called measurement-device-independent QKD (MDI-QKD), which is based on time-reversed entanglement swapping. But, MDI-QKD is more challenging to implement than standard point-to-point QKD. Recently, we proposed an intermediary QKD protocol called detector-device-independent QKD (DDI-QKD) in order to overcome the drawbacks of MDI-QKD, with the hope that it would eventually lead to a more efficient detector side-channel-free QKD system. We analyze the security of DDI-QKD and elucidate its security assumptions. We find thatmore » DDI-QKD is not equivalent to MDI-QKD, but its security can be demonstrated with reasonable assumptions. On the more practical side, we consider the feasibility of DDI-QKD and present a fast experimental demonstration (clocked at 625 MHz), capable of secret key exchange up to more than 90 km.« less

  14. Detector-device-independent quantum key distribution: Security analysis and fast implementation

    SciTech Connect

    Boaron, Alberto; Korzh, Boris; Houlmann, Raphael; Boso, Gianluca; Lim, Charles Ci Wen; Martin, Anthony; Zbinden, Hugo

    2016-08-09

    One of the most pressing issues in quantum key distribution (QKD) is the problem of detector side-channel attacks. To overcome this problem, researchers proposed an elegant “time-reversal” QKD protocol called measurement-device-independent QKD (MDI-QKD), which is based on time-reversed entanglement swapping. But, MDI-QKD is more challenging to implement than standard point-to-point QKD. Recently, we proposed an intermediary QKD protocol called detector-device-independent QKD (DDI-QKD) in order to overcome the drawbacks of MDI-QKD, with the hope that it would eventually lead to a more efficient detector side-channel-free QKD system. We analyze the security of DDI-QKD and elucidate its security assumptions. We find that DDI-QKD is not equivalent to MDI-QKD, but its security can be demonstrated with reasonable assumptions. On the more practical side, we consider the feasibility of DDI-QKD and present a fast experimental demonstration (clocked at 625 MHz), capable of secret key exchange up to more than 90 km.

  15. Efficient and universal quantum key distribution based on chaos and middleware

    NASA Astrophysics Data System (ADS)

    Jiang, Dong; Chen, Yuanyuan; Gu, Xuemei; Xie, Ling; Chen, Lijun

    2017-01-01

    Quantum key distribution (QKD) promises unconditionally secure communications, however, the low bit rate of QKD cannot meet the requirements of high-speed applications. Despite the many solutions that have been proposed in recent years, they are neither efficient to generate the secret keys nor compatible with other QKD systems. This paper, based on chaotic cryptography and middleware technology, proposes an efficient and universal QKD protocol that can be directly deployed on top of any existing QKD system without modifying the underlying QKD protocol and optical platform. It initially takes the bit string generated by the QKD system as input, periodically updates the chaotic system, and efficiently outputs the bit sequences. Theoretical analysis and simulation results demonstrate that our protocol can efficiently increase the bit rate of the QKD system as well as securely generate bit sequences with perfect statistical properties. Compared with the existing methods, our protocol is more efficient and universal, it can be rapidly deployed on the QKD system to increase the bit rate when the QKD system becomes the bottleneck of its communication system.

  16. Experimental demonstration of passive-decoy-state quantum key distribution with two independent lasers

    NASA Astrophysics Data System (ADS)

    Sun, Shi-Hai; Tang, Guang-Zhao; Li, Chun-Yan; Liang, Lin-Mei

    2016-09-01

    The decoy-state method could effectively enhance the performance of quantum key distribution (QKD) with a practical phase randomized weak coherent source. Although active modulation of the source intensity is effective and has been implemented in many experiments, passive preparation of decoy states is also an important addition to the family of decoy-state QKD protocols. In this paper, following the theory of Curty et al. [Phys. Rev. A 81, 022310 (2010), 10.1103/PhysRevA.81.022310], we experimentally demonstrate the phase-encoding passive-decoy-state QKD with only linear optical setups and threshold single-photon detectors. In our experiment, two homemade independent pulsed lasers, with visibility of Hong-Ou-Mandel interference 0.53 (±0.003 ) , have been implemented and used to passively generate the different decoy states. Finally, a secret key rate of 1.5 ×10-5 /pulse is obtained with 10-km commercial fiber between Alice and Bob.

  17. Security of the differential-quadrature-phase-shift quantum key distribution

    NASA Astrophysics Data System (ADS)

    Kawakami, Shun; Sasaki, Toshihiko; Koashi, Masato

    2016-08-01

    One of the simplest methods for implementing quantum key distribution over fiber-optic communication is the Bennett-Brassard 1984 protocol with phase encoding (PE-BB84 protocol), in which the sender uses phase modulation over double pulses from a laser and the receiver uses a passive delayed interferometer. Using essentially the same setup and by regarding a train of many pulses as a single block, one can carry out the so-called differential-quadrature-phase-shift (DQPS) protocol, which is a variant of differential-phase-shift (DPS) protocols. Here we prove the security of the DQPS protocol based on an adaptation of proof techniques for the BB84 protocol, which inherits the advantages arising from the simplicity of the protocol, such as accommodating the use of threshold detectors and simple off-line calibration methods for the light source. We show that the secure key rate of the DQPS protocol in the proof is eight-thirds as high as the rate of the PE-BB84 protocol.

  18. Aerospace laser communications technology as enabler for worldwide quantum key distribution

    NASA Astrophysics Data System (ADS)

    Moll, Florian; Weinfurter, Harald; Rau, Markus; Schmidt, Christopher; Melén, Gwen; Vogl, Tobias; Nauerth, Sebastian; Fuchs, Christian

    2016-04-01

    A worldwide growing interest in fast and secure data communications pushes technology development along two lines. While fast communications can be realized using laser communications in fiber and free-space, inherently secure communications can be achieved using quantum key distribution (QKD). By combining both technologies in a single device, many synergies can be exploited, therefore reducing size, weight and power of future systems. In recent experiments we demonstrated quantum communications over large distances as well as between an aircraft and a ground station which proved the feasibility of QKD between moving partners. Satellites thus may be used as trusted nodes in combination with QKD receiver stations on ground, thereby enabling fast and secure communications on a global scale. We discuss the previous experiment with emphasis on necessary developments to be done and corresponding ongoing research work of German Aerospace Center (DLR) and Ludwig Maximilians University Munich (LMU). DLR is performing research on satellite and ground terminals for the high-rate laser communication component, which are enabling technologies for the QKD link. We describe the concept and hardware of three generations of OSIRIS (Optical High Speed Infrared Link System) laser communication terminals for low Earth orbiting satellites. The first type applies laser beam pointing solely based on classical satellite control, the second uses an optical feedback to the satellite bus and the third, currently being in design phase, comprises of a special coarse pointing assembly to control beam direction independent of satellite orientation. Ongoing work also targets optical terminals for CubeSats. A further increase of beam pointing accuracy can be achieved with a fine pointing assembly. Two ground stations will be available for future testing, an advanced stationary ground station and a transportable ground station. In parallel the LMU QKD source size will be reduced by more than an

  19. Analysis of the secrecy of the running key in quantum encryption channels using coherent states of light

    NASA Astrophysics Data System (ADS)

    Nikulin, Vladimir V.; Hughes, David H.; Malowicki, John; Bedi, Vijit

    2015-05-01

    Free-space optical communication channels offer secure links with low probability of interception and detection. Despite their point-to-point topology, additional security features may be required in privacy-critical applications. Encryption can be achieved at the physical layer by using quantized values of photons, which makes exploitation of such quantum communication links extremely difficult. One example of such technology is keyed communication in quantum noise, a novel quantum modulation protocol that offers ultra-secure communication with competitive performance characteristics. Its utilization relies on specific coherent measurements to decrypt the signal. The process of measurements is complicated by the inherent and irreducible quantum noise of coherent states. This problem is different from traditional laser communication with coherent detection; therefore continuous efforts are being made to improve the measurement techniques. Quantum-based encryption systems that use the phase of the signal as the information carrier impose aggressive requirements on the accuracy of the measurements when an unauthorized party attempts intercepting the data stream. Therefore, analysis of the secrecy of the data becomes extremely important. In this paper, we present the results of a study that had a goal of assessment of potential vulnerability of the running key. Basic results of the laboratory measurements are combined with simulation studies and statistical analysis that can be used for both conceptual improvement of the encryption approach and for quantitative comparison of secrecy of different quantum communication protocols.

  20. The Influence of Counterfactual Thinking and Regret on Ethical Decision Making

    ERIC Educational Resources Information Center

    Celuch, Kevin; Saxby, Carl; Oeding, Jill

    2015-01-01

    The authors explore the influence of counterfactual thoughts in triggering the emotions of regret and disappointment in ethical decision making. Counterfactual thinking involves examining possible outcomes to events and is often explored in what-if scenarios. Findings support that subjects were able to transfer regret (but not disappointment)…

  1. Anomalies in Real and Counterfactual Worlds: An Eye-Movement Investigation

    ERIC Educational Resources Information Center

    Ferguson, Heather J.; Sanford, Anthony J.

    2008-01-01

    Counterfactual reasoning is valid reasoning arising from premises that are true in a hypothetical model, but false in actuality. Investigations of counterfactuals have concentrated on reasoning and production, but psycholinguistic research has been more limited. We report three eye-movement studies investigating the comprehension of counterfactual…

  2. Data Mining in Finance: Using Counterfactuals To Generate Knowledge from Organizational Information Systems.

    ERIC Educational Resources Information Center

    Dhar, Vasant

    1998-01-01

    Shows how counterfactuals and machine learning methods can be used to guide exploration of large databases that addresses some of the fundamental problems that organizations face in learning from data. Discusses data mining, particularly in the financial arena; generating useful knowledge from data; and the evaluation of counterfactuals. (LRW)

  3. The Qubit as Key to Quantum Physics Part II: Physical Realizations and Applications

    ERIC Educational Resources Information Center

    Dür, Wolfgang; Heusler, Stefan

    2016-01-01

    Using the simplest possible quantum system--the qubit--the fundamental concepts of quantum physics can be introduced. This highlights the common features of many different physical systems, and provides a unifying framework when teaching quantum physics at the high school or introductory level. In a previous "TPT" article and in a…

  4. Device-independent quantum key distribution with generalized two-mode Schrödinger cat states

    NASA Astrophysics Data System (ADS)

    Broadbent, Curtis J.; Marshall, Kevin; Weedbrook, Christian; Howell, John C.

    2015-11-01

    We show how weak nonlinearities can be used in a device-independent quantum key distribution (QKD) protocol using generalized two-mode Schrödinger cat states. The QKD protocol is therefore shown to be secure against collective attacks and for some coherent attacks. We derive analytical formulas for the optimal values of the Bell parameter, the quantum bit error rate, and the device-independent secret key rate in the noiseless lossy bosonic channel. Additionally, we give the filters and measurements which achieve these optimal values. We find that, over any distance in this channel, the quantum bit error rate is identically zero, in principle, and the states in the protocol are always able to violate a Bell inequality. The protocol is found to be superior in some regimes to a device-independent QKD protocol based on polarization entangled states in a depolarizing channel. Finally, we propose an implementation for the optimal filters and measurements.

  5. Cloning and optimal Gaussian individual attacks for a continuous-variable quantum key distribution using coherent states and reverse reconciliation

    SciTech Connect

    Namiki, Ryo; Koashi, Masato; Imoto, Nobuyuki

    2006-03-15

    We investigate the security of continuous-variable quantum key distribution using coherent states and reverse reconciliation against Gaussian individual attacks based on an optimal Gaussian 1{yields}2 cloning machine. We provide an implementation of the optimal Gaussian individual attack. We also find a Bell-measurement attack which works without delayed choice of measurements and has better performance than the cloning attack.

  6. Undoing the past in order to lie in the present: Counterfactual thinking and deceptive communication.

    PubMed

    Briazu, Raluca A; Walsh, Clare R; Deeprose, Catherine; Ganis, Giorgio

    2017-04-01

    This paper explores the proposal that there is a close link between counterfactual thinking and lying. Both require the imagination of alternatives to reality and we describe four studies which explore this link. In Study 1 we measured individual differences in both abilities and found that individuals with a tendency to generate counterfactual thoughts were also more likely to generate potential lies. Studies 2 and 3 showed that counterfactual availability influences people's ability to come up with lies and the extent to which they expect others to lie. Study 4 used a behavioural measure of deception to show that people tend to lie more in situations also known to elicit counterfactual thoughts. Overall, the results show that the imagination of alternatives to the past plays an important role in the generation of lies. We discuss the implications for the fields of counterfactual thinking and deception.

  7. Neural activity associated with self, other, and object-based counterfactual thinking.

    PubMed

    De Brigard, Felipe; Nathan Spreng, R; Mitchell, Jason P; Schacter, Daniel L

    2015-04-01

    Previous research has shown that autobiographical episodic counterfactual thinking-i.e., mental simulations about alternative ways in which one's life experiences could have occurred-engages the brain's default network (DN). However, it remains unknown whether or not the DN is also engaged during impersonal counterfactual thoughts, specifically those involving other people or objects. The current study compares brain activity during counterfactual simulations involving the self, others and objects. In addition, counterfactual thoughts involving others were manipulated in terms of similarity and familiarity with the simulated characters. The results indicate greater involvement of DN during person-based (i.e., self and other) as opposed to object-based counterfactual simulations. However, the involvement of different regions of the DN during other-based counterfactual simulations was modulated by how close and/or similar the simulated character was perceived to be by the participant. Simulations involving unfamiliar characters preferentially recruited dorsomedial prefrontal cortex. Simulations involving unfamiliar similar characters, characters with whom participants identified personality traits, recruited lateral temporal gyrus. Finally, our results also revealed differential coupling of right hippocampus with lateral prefrontal and temporal cortex during counterfactual simulations involving familiar similar others, but with left transverse temporal gyrus and medial frontal and inferior temporal gyri during counterfactual simulations involving either oneself or unfamiliar dissimilar others. These results suggest that different brain mechanisms are involved in the simulation of personal and impersonal counterfactual thoughts, and that the extent to which regions associated with autobiographical memory are recruited during the simulation of counterfactuals involving others depends on the perceived similarity and familiarity with the simulated individuals.

  8. Adaptive Gaussian quadrature detection for continuous-variable quantum key distribution

    NASA Astrophysics Data System (ADS)

    Gyongyosi, L.; Imre, S.

    2016-03-01

    We propose the adaptive quadrature detection for multicarrier continuous-variable quantum key distribution (CVQKD). A multicarrier CVQKD scheme uses Gaussian subcarrier continuous variables for the information conveying and Gaussian sub-channels for the transmission. The proposed multicarrier detection scheme dynamically adapts to the subchannel conditions using a corresponding statistics which is provided by our sophisticated sub-channel estimation procedure. The sub-channel estimation phase determines the transmittance coefficients of the sub-channels, which information are used further in the adaptive quadrature decoding process. We define a technique to estimate the transmittance conditions of the sub-channels. We introduce the terms of single and collective adaptive quadrature detection. We prove the achievable error probabilities, the signal-to-noise ratios, and quantify the attributes of the framework. The adaptive detection scheme allows to utilize the extra resources of multicarrier CVQKD and to maximize the amount of transmittable valuable information in diverse measurement and transmission conditions. The framework is particularly convenient for experimental CVQKD scenarios.

  9. Performance of a quantum key distribution protocol with dual-rail displaced photon states

    SciTech Connect

    Podoshvedov, S. A.

    2010-04-15

    We propose a scheme for a quantum key distribution (QKD) protocol with dual-rail displaced photon states. Displaced single-photon states with different amplitudes carry bit values of code that may be extracted, while coherent states carry nothing and only provide an inconclusive outcome. A real resource of single photons is used, involving imperfections associated with experimental technique that result in a photon state with an admixture of the vacuum state. The protocol is robust against the loss of a single photon and the inefficiency of the detectors. Pulses with large amplitudes, unlike the conventional QKD relying on faint laser pulses, are used that may approximate it to standard telecommunication and may show resistance to eaves-dropping even in settings with high attenuation. Information leakage to the eavesdropper is determined from comparison of the output distributions of the outcomes with ideal ones that are defined by two additional parameters accessible to only those send the pulses. Robustness to some possible eavesdropping attacks is shown.

  10. Scintillation has minimal impact on far-field Bennett-Brassard 1984 protocol quantum key distribution

    SciTech Connect

    Shapiro, Jeffrey H.

    2011-09-15

    The effect of scintillation, arising from propagation through atmospheric turbulence, on the sift and error probabilities of a quantum key distribution (QKD) system that uses the weak-laser-pulse version of the Bennett-Brassard 1984 (BB84) protocol is evaluated. Two earth-space scenarios are examined: satellite-to-ground and ground-to-satellite transmission. Both lie in the far-field power-transfer regime. This work complements previous analysis of turbulence effects in near-field terrestrial BB84 QKD [J. H. Shapiro, Phys. Rev. A 67, 022309 (2003)]. More importantly, it shows that scintillation has virtually no impact on the sift and error probabilities in earth-space BB84 QKD, something that has been implicitly assumed in prior analyses for that application. This result contrasts rather sharply with what is known for high-speed laser communications over such paths, in which deep, long-lived scintillation fades present a major challenge to high-reliability operation.

  11. Method and apparatus for free-space quantum key distribution in daylight

    DOEpatents

    Hughes, Richard J.; Buttler, William T.; Lamoreaux, Steve K.; Morgan, George L.; Nordholt, Jane E.; Peterson, C. Glen; Kwiat, Paul G.

    2004-06-08

    A quantum cryptography apparatus securely generates a key to be used for secure transmission between a sender and a receiver connected by an atmospheric transmission link. A first laser outputs a timing bright light pulse; other lasers output polarized optical data pulses after having been enabled by a random bit generator. Output optics transmit output light from the lasers that is received by receiving optics. A first beam splitter receives light from the receiving optics, where a received timing bright light pulse is directed to a delay circuit for establishing a timing window for receiving light from the lasers and where an optical data pulse from one of the lasers has a probability of being either transmitted by the beam splitter or reflected by the beam splitter. A first polarizer receives transmitted optical data pulses to output one data bit value and a second polarizer receives reflected optical data pulses to output a second data bit value. A computer receives pulses representing receipt of a timing bright timing pulse and the first and second data bit values, where receipt of the first and second data bit values is indexed by the bright timing pulse.

  12. Increasing operational command and control security by the implementation of device independent quantum key distribution

    NASA Astrophysics Data System (ADS)

    Bovino, Fabio Antonio; Messina, Angelo

    2016-10-01

    In a very simplistic way, the Command and Control functions can be summarized as the need to provide the decision makers with an exhaustive, real-time, situation picture and the capability to convey their decisions down to the operational forces. This two-ways data and information flow is vital to the execution of current operations and goes far beyond the border of military operations stretching to Police and disaster recovery as well. The availability of off-the shelf technology has enabled hostile elements to endanger the security of the communication networks by violating the traditional security protocols and devices and hacking sensitive databases. In this paper an innovative approach based to implementing Device Independent Quantum Key Distribution system is presented. The use of this technology would prevent security breaches due to a stolen crypto device placed in an end-to-end communication chain. The system, operating with attenuated laser, is practical and provides the increasing of the distance between the legitimate users.

  13. Unbreakable distributed storage with quantum key distribution network and password-authenticated secret sharing

    PubMed Central

    Fujiwara, M.; Waseda, A.; Nojima, R.; Moriai, S.; Ogata, W.; Sasaki, M.

    2016-01-01

    Distributed storage plays an essential role in realizing robust and secure data storage in a network over long periods of time. A distributed storage system consists of a data owner machine, multiple storage servers and channels to link them. In such a system, secret sharing scheme is widely adopted, in which secret data are split into multiple pieces and stored in each server. To reconstruct them, the data owner should gather plural pieces. Shamir’s (k, n)-threshold scheme, in which the data are split into n pieces (shares) for storage and at least k pieces of them must be gathered for reconstruction, furnishes information theoretic security, that is, even if attackers could collect shares of less than the threshold k, they cannot get any information about the data, even with unlimited computing power. Behind this scenario, however, assumed is that data transmission and authentication must be perfectly secure, which is not trivial in practice. Here we propose a totally information theoretically secure distributed storage system based on a user-friendly single-password-authenticated secret sharing scheme and secure transmission using quantum key distribution, and demonstrate it in the Tokyo metropolitan area (≤90 km). PMID:27363566

  14. Unbreakable distributed storage with quantum key distribution network and password-authenticated secret sharing.

    PubMed

    Fujiwara, M; Waseda, A; Nojima, R; Moriai, S; Ogata, W; Sasaki, M

    2016-07-01

    Distributed storage plays an essential role in realizing robust and secure data storage in a network over long periods of time. A distributed storage system consists of a data owner machine, multiple storage servers and channels to link them. In such a system, secret sharing scheme is widely adopted, in which secret data are split into multiple pieces and stored in each server. To reconstruct them, the data owner should gather plural pieces. Shamir's (k, n)-threshold scheme, in which the data are split into n pieces (shares) for storage and at least k pieces of them must be gathered for reconstruction, furnishes information theoretic security, that is, even if attackers could collect shares of less than the threshold k, they cannot get any information about the data, even with unlimited computing power. Behind this scenario, however, assumed is that data transmission and authentication must be perfectly secure, which is not trivial in practice. Here we propose a totally information theoretically secure distributed storage system based on a user-friendly single-password-authenticated secret sharing scheme and secure transmission using quantum key distribution, and demonstrate it in the Tokyo metropolitan area (≤90 km).

  15. Unbreakable distributed storage with quantum key distribution network and password-authenticated secret sharing

    NASA Astrophysics Data System (ADS)

    Fujiwara, M.; Waseda, A.; Nojima, R.; Moriai, S.; Ogata, W.; Sasaki, M.

    2016-07-01

    Distributed storage plays an essential role in realizing robust and secure data storage in a network over long periods of time. A distributed storage system consists of a data owner machine, multiple storage servers and channels to link them. In such a system, secret sharing scheme is widely adopted, in which secret data are split into multiple pieces and stored in each server. To reconstruct them, the data owner should gather plural pieces. Shamir’s (k, n)-threshold scheme, in which the data are split into n pieces (shares) for storage and at least k pieces of them must be gathered for reconstruction, furnishes information theoretic security, that is, even if attackers could collect shares of less than the threshold k, they cannot get any information about the data, even with unlimited computing power. Behind this scenario, however, assumed is that data transmission and authentication must be perfectly secure, which is not trivial in practice. Here we propose a totally information theoretically secure distributed storage system based on a user-friendly single-password-authenticated secret sharing scheme and secure transmission using quantum key distribution, and demonstrate it in the Tokyo metropolitan area (≤90 km).

  16. Neural systems for choice and valuation with counterfactual learning signals.

    PubMed

    Tobia, M J; Guo, R; Schwarze, U; Boehmer, W; Gläscher, J; Finckh, B; Marschner, A; Büchel, C; Obermayer, K; Sommer, T

    2014-04-01

    The purpose of this experiment was to test a computational model of reinforcement learning with and without fictive prediction error (FPE) signals to investigate how counterfactual consequences contribute to acquired representations of action-specific expected value, and to determine the functional neuroanatomy and neuromodulator systems that are involved. 80 male participants underwent dietary depletion of either tryptophan or tyrosine/phenylalanine to manipulate serotonin (5HT) and dopamine (DA), respectively. They completed 80 rounds (240 trials) of a strategic sequential investment task that required accepting interim losses in order to access a lucrative state and maximize long-term gains, while being scanned. We extended the standard Q-learning model by incorporating both counterfactual gains and losses into separate error signals. The FPE model explained the participants' data significantly better than a model that did not include counterfactual learning signals. Expected value from the FPE model was significantly correlated with BOLD signal change in the ventromedial prefrontal cortex (vmPFC) and posterior orbitofrontal cortex (OFC), whereas expected value from the standard model did not predict changes in neural activity. The depletion procedure revealed significantly different neural responses to expected value in the vmPFC, caudate, and dopaminergic midbrain in the vicinity of the substantia nigra (SN). Differences in neural activity were not evident in the standard Q-learning computational model. These findings demonstrate that FPE signals are an important component of valuation for decision making, and that the neural representation of expected value incorporates cortical and subcortical structures via interactions among serotonergic and dopaminergic modulator systems.

  17. Fault-tolerant high-capacity quantum key distribution over a collective-noise channel using extended unitary operations

    NASA Astrophysics Data System (ADS)

    Lai, Hong; Orgun, Mehmet A.; Xiao, Jinghua; Xue, Liyin

    2014-07-01

    We propose two fault-tolerant high-capacity quantum key distribution schemes, in which an entangled pair over a collective-noise channel consisting of one logical qubit and one physical qubit can carry four bits of key information. The basic idea is to use 2-extended unitary operations from collective noises together with quantum dense coding. The key messages are encoded on logical qubits of two physical qubits with sixteen 2-extended unitary operations based on collective noises. The key can be recovered using Bell-state analysis on the logical qubit and a single-photon measurement on the physical qubit rather than three-qubit GHZ joint measurements. The proposed protocols require a collation table to be shared between Alice and Bob in advance. Consequently, the key messages carried by an entangled state, in our protocol, have doubled at the price of sharing the collation table between Alice and Bob. However, the efficiency of qubits is enhanced because a quantum bit is more expensive to prepare than a classical bit.

  18. Controlling Continuous-Variable Quantum Key Distribution with Entanglement in the Middle Using Tunable Linear Optics Cloning Machines

    NASA Astrophysics Data System (ADS)

    Wu, Xiao Dong; Chen, Feng; Wu, Xiang Hua; Guo, Ying

    2016-11-01

    Continuous-variable quantum key distribution (CVQKD) can provide detection efficiency, as compared to discrete-variable quantum key distribution (DVQKD). In this paper, we demonstrate a controllable CVQKD with the entangled source in the middle, contrast to the traditional point-to-point CVQKD where the entanglement source is usually created by one honest party and the Gaussian noise added on the reference partner of the reconciliation is uncontrollable. In order to harmonize the additive noise that originates in the middle to resist the effect of malicious eavesdropper, we propose a controllable CVQKD protocol by performing a tunable linear optics cloning machine (LOCM) at one participant's side, say Alice. Simulation results show that we can achieve the optimal secret key rates by selecting the parameters of the tuned LOCM in the derived regions.

  19. Revealing of photon-number splitting attack on quantum key distribution system by photon-number resolving devices

    NASA Astrophysics Data System (ADS)

    Gaidash, A. A.; Egorov, V. I.; Gleim, A. V.

    2016-08-01

    Quantum cryptography allows distributing secure keys between two users so that any performed eavesdropping attempt would be immediately discovered. However, in practice an eavesdropper can obtain key information from multi-photon states when attenuated laser radiation is used as a source of quantum states. In order to prevent actions of an eavesdropper, it is generally suggested to implement special cryptographic protocols, like decoy states or SARG04. In this paper, we describe an alternative method based on monitoring photon number statistics after detection. We provide a useful rule of thumb to estimate approximate order of difference of expected distribution and distribution in case of attack. Formula for calculating a minimum value of total pulses or time-gaps to resolve attack is shown. Also formulas for actual fraction of raw key known to Eve were derived. This method can therefore be used with any system and even combining with mentioned special protocols.

  20. Controlling Continuous-Variable Quantum Key Distribution with Entanglement in the Middle Using Tunable Linear Optics Cloning Machines

    NASA Astrophysics Data System (ADS)

    Wu, Xiao Dong; Chen, Feng; Wu, Xiang Hua; Guo, Ying

    2017-02-01

    Continuous-variable quantum key distribution (CVQKD) can provide detection efficiency, as compared to discrete-variable quantum key distribution (DVQKD). In this paper, we demonstrate a controllable CVQKD with the entangled source in the middle, contrast to the traditional point-to-point CVQKD where the entanglement source is usually created by one honest party and the Gaussian noise added on the reference partner of the reconciliation is uncontrollable. In order to harmonize the additive noise that originates in the middle to resist the effect of malicious eavesdropper, we propose a controllable CVQKD protocol by performing a tunable linear optics cloning machine (LOCM) at one participant's side, say Alice. Simulation results show that we can achieve the optimal secret key rates by selecting the parameters of the tuned LOCM in the derived regions.