Multimode states in decoy-based quantum-key-distribution protocols
Wolfram Helwig, Wolfgang Mauerer, and Christine Silberhorn
Every security analysis of quantum-key distribution (QKD) relies on a faithful modeling of the employed quantum states. Many photon sources, such as for instance a parametric down-conversion (PDC) source, require a multimode description but are usually only considered in a single-mode representation ... [Phys. Rev. A 80, 052326 (2009)] published Thu Nov 19, 2009.
Unconditional Security of Single-Photon Differential Phase Shift Quantum Key Distribution
Kai Wen, Kiyoshi Tamaki, and Yoshihisa Yamamoto
In this Letter, we prove the unconditional security of the single-photon differential phase shift quantum key distribution (DPS-QKD) protocol, based on the conversion to an equivalent entanglement-based protocol. We estimate the upper bound of the phase error rate from the bit error rate, and show t ... [Phys. Rev. Lett. 103, 170503 (2009)] published Thu Oct 22, 2009.
Can Closed Timelike Curves or Nonlinear Quantum Mechanics Improve Quantum State Discrimination or Help Solve Hard Problems?
Charles H. Bennett, Debbie Leung, Graeme Smith, and John A. Smolin
We study the power of closed timelike curves (CTCs) and other nonlinear extensions of quantum mechanics for distinguishing nonorthogonal states and speeding up hard computations. If a CTC-assisted computer is presented with a labeled mixture of states to be distinguishedthe most natural formulationw ... [Phys. Rev. Lett. 103, 170502 (2009)] published Wed Oct 21, 2009.
Characterization of photon statistics in a single-photon source via variable attenuation
ShengLi Zhang, XuBo Zou, ChuanFeng Li, ChenHui Jin, and GuangCan Guo
We propose a simple but effective scheme for characterizing photon-number statistics of a practical single-photon source. In this scheme, the variable attenuation method which frequently appears in decoy state quantum cryptography is utilized here to enhance the estimation of photon-number statistic ... [Phys. Rev. A 80, 043807 (2009)] published Thu Oct 8, 2009.
Multipartite secret key distillation and bound entanglement
Remigiusz Augusiak and Pawel Horodecki
Recently it has been shown that quantum cryptography beyond pure entanglement distillation is possible and a paradigm for the associated protocols has been established. Here we systematically generalize the whole paradigm to the multipartite scenario. We provide constructions of new classes of multi ... [Phys. Rev. A 80, 042307 (2009)] published Wed Oct 7, 2009.
The security of practical quantum key distribution
Valerio Scarani, Helle Bechmann-Pasquinucci, Nicolas J. Cerf, Miloslav Dusek, Norbert Lutkenhaus et al.
Quantum key distribution (QKD) is the first quantum information task to reach the level of mature technology, already fit for commercialization. It aims at the creation of a secret key between authorized partners connected by a quantum channel and a classical authenticated channel. The security of t ... [Rev. Mod. Phys. 81, 1301 (2009)] published Tue Sep 29, 2009.
Robust unconditionally secure quantum key distribution with two nonorthogonal and uninformative states
Marco Lucamarini, Giovanni Di Giuseppe, and Kiyoshi Tamaki
We present an unconventional form of decoy-state technique to make the single-photon Bennett 1992 protocol robust against losses and noise of a communication channel. Two uninformative states are prepared by the transmitter in order to prevent the unambiguous state discrimination attack and improve ... [Phys. Rev. A 80, 032327 (2009)] published Wed Sep 23, 2009.
Robust variations of the Bennett-Brassard 1984 protocol against collective noise
Ying Sun, Qiao-Yan Wen, Fei Gao, and Fu-Chen Zhu
The security of the decoherence-free version of the Bennett-Brassard 1984 (BB84) protocol [A. Cabello, Phys. Rev. A 75, 020301 (2007)] is analyzed and shown to be vulnerable under the intercept-resend attack. We propose two improved versions of this protocol. Both improvements remain the performance ... [Phys. Rev. A 80, 032321 (2009)] published Tue Sep 22, 2009.
Extensive Nonadditivity of Privacy
Graeme Smith and John A. Smolin
Quantum information theory establishes the ultimate limits on communication and cryptography in terms of channel capacities for various types of information. The private capacity is particularly important because it quantifies achievable rates of quantum key distribution. We study the power of quant ... [Phys. Rev. Lett. 103, 120503 (2009)] published Fri Sep 18, 2009.
Private Capacity of Quantum Channels is Not Additive
Ke Li, Andreas Winter, XuBo Zou, and GuangCan Guo
Recently there has been considerable activity on the subject of the additivity of various quantum channel capacities. Here, we construct a family of channels with a sharply bounded classical and, hence, private capacity. On the other hand, their quantum capacity when combined with a zero private (an ... [Phys. Rev. Lett. 103, 120501 (2009)] published Tue Sep 15, 2009.
Unconditional security of the Bennett 1992 quantum-key-distribution scheme with a strong reference pulse
Kiyoshi Tamaki, Norbert Lutkenhaus, Masato Koashi, and Jamie Batuwantudawe
We prove the unconditional security of the original Bennett 1992 protocol with strong reference pulse. We show that we may place a projection onto suitably defined qubit spaces before the receiver, which makes the analysis as simple as qubit-based protocols. Unlike the single-photon-based qubits, th ... [Phys. Rev. A 80, 032302 (2009)] published Tue Sep 1, 2009.
Quantum repeaters with imperfect memories: Cost and scalability
M. Razavi, M. Piani, and N. Lutkenhaus
Memory dephasing and its impact on the rate of entanglement generation in quantum repeaters is addressed. For systems that rely on probabilistic schemes for entanglement distribution and connection, we estimate the maximum achievable rate per employed memory for our optimized partial nesting protoco ... [Phys. Rev. A 80, 032301 (2009)] published Tue Sep 1, 2009.
Two-way protocols for quantum cryptography with a nonmaximally entangled qubit pair
Kaoru Shimizu, Kiyoshi Tamaki, and Hiroyuki Fukasaka
This paper proposes a scheme for quantum cryptography with a nonmaximally entangled qubit pair. In a two-way configuration similar to quantum super dense coding, a two-bit key can be distributed by a round trip of one particle of the qubit pair and received by an appropriate joint measurement with t ... [Phys. Rev. A 80, 022323 (2009)] published Wed Aug 19, 2009.
Sharing classical secrets with Calderbank-Shor-Steane codes
Pradeep Kiran Sarvepalli and Andreas Klappenecker
In this paper we investigate the use of quantum information to share classical secrets. While every quantum secret sharing scheme is a quantum error-correcting code, the converse is not true. Motivated by this we sought to find quantum codes which can be converted to secret sharing schemes. If we ar ... [Phys. Rev. A 80, 022321 (2009)] published Tue Aug 18, 2009.
Partially unbiased entangled bases
A. Kalev, F. C. Khanna, and M. Revzen
In this contribution we group the operator basis for d-dimensional Hilbert space in a way that enables us to relate bases of entangled states with single-particle mutually unbiased state bases (MUB), each in dimensionality d. We utilize these sets of operators to show that an arbitrary density matri ... [Phys. Rev. A 80, 022112 (2009)] published Mon Aug 17, 2009.
Public and private communication with a quantum channel and a secret key
Min-Hsiu Hsieh and Mark M. Wilde
We consider using a secret key and a noisy quantum channel to generate noiseless public communication and noiseless private communication. The optimal protocol for this setting is the publicly enhanced private father protocol. This protocol exploits random coding techniques and piggybacking of publi ... [Phys. Rev. A 80, 022306 (2009)] published Wed Aug 5, 2009.
Quantum interface to a noisy system through a single kind of arbitrary Gaussian coupling with limited interaction strength
Radim Filip
We propose a continuous-variable quantum interface that transfers an arbitrary unknown quantum state between a well-controllable source oscillator and a weakly controllable noisy target oscillator through an arbitrary Gaussian coupling. The unit fidelity of transfer is achieved by the preprocessing ... [Phys. Rev. A 80, 022304 (2009)] published Tue Aug 4, 2009.
Symmetric extendibility for qudits and tolerable error rates in quantum cryptography
Kedar S. Ranade
Symmetric extendibility of quantum states has recently drawn attention in the context of quantum cryptography to judge whether quantum states shared between two distant parties can be purified by means of one-way error correction protocols. In this paper we study the symmetric extendibility in a spe ... [Phys. Rev. A 80, 022301 (2009)] published Mon Aug 3, 2009.
Decoy-state quantum key distribution using homodyne detection
S. H. Shams Mousavi and P. Gallion
In this paper, we propose to use the decoy-state technique to improve the security of the quantum key distribution (QKD) systems based on homodyne detection against the photon number splitting attack. The decoy-state technique is a powerful tool that can significantly boost the secure transmission r ... [Phys. Rev. A 80, 012327 (2009)] published Fri Jul 24, 2009.
Entanglement enhances security in quantum communication
Rafal Demkowicz-Dobrzanski, Aditi Sen(De), Ujjwal Sen, and Maciej Lewenstein
Secret sharing is a protocol in which a boss wants to send a classical message secretly to two subordinates, such that none of the subordinates is able to know the message alone, while they can find it if they cooperate. Quantum mechanics is known to allow for such a possibility. We analyze tolerabl ... [Phys. Rev. A 80, 012311 (2009)] published Mon Jul 13, 2009.
Conjectured Strong Complementary Information Tradeoff
Joseph M. Renes and Jean-Christian Boileau
We conjecture a new entropic uncertainty principle governing the entropy of complementary observations made on a system given side information in the form of quantum states, generalizing the entropic uncertainty relation of Maassen and Uffink [Phys. Rev. Lett. 60, 1103 (1988)]. We prove a special ca ... [Phys. Rev. Lett. 103, 020402 (2009)] published Thu Jul 9, 2009.