We provide limits to practical quantum key distribution, taking into account channel losses, a realistic detection process, and imperfections in the "qubits" sent from sender receiver. As we show, even distribution with perfect qubits might not be achievable over long distances when other are taken account. Furthermore, existing experimental schemes (based on weak pulses) currently do offer unconditional security for reported signal strength. Finally show that parametric down-conversion...

We exhibit an orthogonal set of product states two three-state particles that nevertheless cannot be reliably distinguished by a pair separated observers ignorant which the has been presented to them, even if are allowed any sequence local operations and classical communication between separate observers. It is proved there finite gap mutual information obtainable joint measurement on these in only actions permitted. This result implies existence separable superoperators implemented locally....

We apply the full power of modern electronic band-structure engineering and epitaxial heterostructures to design a transistor that can sense control single-donor electron spin. Spin-resonance transistors may form technological basis for quantum information processing. One- two-qubit operations are performed by applying gate bias. The bias electric field pulls wave function away from dopant ion into layers different alloy composition. Owing variation g factor...

An unextendible product basis (UPB) for a multipartite quantum system is an incomplete orthogonal whose complementary subspace contains no state. We give examples of UPBs, and show that the uniform mixed state over to any UPB bound entangled exhibit tripartite 2x2x2 has entanglement but bipartite entanglement, i.e. all three corresponding 2x4 states are unentangled. members not perfectly distinguishable by local POVMs classical communication.

The safety of a quantum key distribution system relies on the fact that any eavesdropping attempt channel creates errors in transmission. For given error rate, amount information may have leaked to eavesdropper depends both particular and strategy. In this work, we discuss cryptographic protocols based transmission weak coherent states present system, symbiosis two existing systems, for which available is significantly reduced. This therefore safer than previous ones. We also suggest...

Secure key distribution among two remote parties is impossible when both are classical, unless some unproven computation-complexity assumptions made, such as the difficulty of factorizing large numbers. On other hand, a secure possible quantum. What only one party (Alice) quantum, yet (Bob) has classical capabilities? We present protocol with this constraint and prove its robustness against attacks: we that any attempt an adversary to obtain information necessarily induces errors legitimate...

Secure key distribution between two remote parties is impossible when both are classical, unless some unproven (and arguably unrealistic) computation-complexity assumptions made, such as the difficulty of factorizing large numbers. On other hand, a secure possible quantum. What only one party (Alice) quantum, yet (Bob) has classical capabilities? Recently, semiquantum protocol was presented [M. Boyer, D. Kenigsberg, and T. Mor, Phys. Rev. Lett. 99, 140501 (2007)], in which yet, proven to be...

Quantum correlations between two particles show non-classical properties which can be used for providing secure transmission of information. We present a quantum cryptographic system, in users store memories kept center. Correlations the stored by are created upon request projecting their product state onto fully entangled state. Our system allows communication any pair who have same Unlike other systems, it work without channels and is suitable building network. also modified with many centers.

We present here algorithmic cooling (via polarization heat bath)-a powerful method for obtaining a large number of highly polarized spins in liquid nuclear-spin systems at finite temperature. Given that spin-half states represent (quantum) bits, cleans dirty bits beyond the Shannon's bound on data compression, by using set rapidly thermal-relaxing bits. Such auxiliary could be implemented get into thermal equilibrium with environment, e.g., electron spins. Interestingly, interaction usually...

Quantum key distribution (QKD) protocols make it possible for two quantum parties to generate a secret shared key. Semiquantum (SQKD) protocols, such as "QKD with classical Bob" and Alice" (that have both been proven robust), achieve this goal even if one of the is classical. However, existing SQKD are not experimentally feasible current technology. Here we suggest new protocol, "Classical Alice controllable mirror", that can be implemented technology (using 4-level systems instead qubits),...

We present strong attacks against quantum key distribution schemes which use memories and gates to attack directly the final key. analyze a specific of this type, for we find density matrices available eavesdropper optimal information can be extracted from them. prove security discuss any allowed by rules mechanics.

Simultaneous near-certain preparation of qubits (quantum bits) in their ground states is a key hurdle quantum computing proposals as varied liquid-state NMR and ion traps. ``Closed-system'' cooling mechanisms are limited applicability due to the need for continual supply ancillas fault tolerance, high initial temperatures some systems. ``Open-system'' therefore required. We describe new, efficient initialization procedure such open With this procedure, an $n$-qubit device that originally...

A novel universal and fault-tolerant basis (set of gates) for quantum computation is described. Such a set necessary to perform in realistic noisy environment. The new consists two single-qubit gates (Hadamard ${σ_z}^{1/4}$), one double-qubit gate (Controlled-NOT). Since the consisting Controlled-NOT Hadamard not universal, achieves universality by including only additional elementary (in sense that it does include angles are irrational multiples $π$) gate, hence, potentially simplest can...

A novel universal and fault-tolerant basis (set of gates) for quantum computation is described. Such a set necessary to perform in realistic noisy environment. The new consists two single-qubit gates (Hadamard /spl sigma//sub z//sup 1/4 /) one double-qubit gate (Controlled-NOT). Since the consisting Controlled-NOT Hadamard not universal, achieves universality by including only additional elementary (in sense that it does include angles are irrational multiples pi/) gate, hence, potentially...

An efficient technique to generate ensembles of spins that are highly polarized by external magnetic fields is the Holy Grail in Nuclear Magnetic Resonance (NMR) spectroscopy. Since spin-half nuclei have steady-state polarization biases increase inversely with temperature, exhibiting high considered cool, even when their environment warm. Existing spin-cooling techniques limited efficiency and usefulness. Algorithmic cooling a promising new approach employs data compression methods open...

Controlled preparation of highly pure quantum states is at the core practical applications information science, from state initialization most algorithms to a reliable supply ancilla qubits that satisfy fault-tolerance threshold for error correction. Heat-bath algorithmic cooling has been shown purify by controlled redistribution entropy and multiple contact with bath, not only ensemble implementations but also technologies strong imperfect measurements. However, an implicit restriction...

In this paper we use properties of quantum mixed states to find bounds on various measures their distinguishability. These are used for analyzing strong joint attacks against key distribution which probes, memories, and gates attack directly the final key. We present a wide class attacks, prove security them.

Article Free Access Share on A proof of the security quantum key distribution (extended abstract) Authors: Eli Biham Computer Science Department, Technion, Haifa 32000, Israel IsraelView Profile , Michel Boyer DIRO, Université de Montréal, Canada CanadaView P. Oscar Boykin Dept. Electrical Engineering, UCLA, Los Angeles, CA CAView Tal Mor and College Judea Samaria, Ariel, Vwani Roychowdhury Authors Info & Claims STOC '00: Proceedings thirty-second annual ACM symposium Theory computingMay...

Secure key distribution among two remote parties is impossible when both are classical, unless some unproven (and arguably unrealistic) computation-complexity assumptions made, such as the difficulty of factorizing large numbers. On other hand, a secure possible quantum. What only one party (Alice) quantum, yet (Bob) has classical capabilities? We present protocols with this constraint, and prove their robustness against attacks: we that any attempt an adversary to obtain information even...

For several decades it was believed that information-secure key distribution requires both the sender and receiver to have ability generate and/or manipulate quantum states. Earlier, we showed in which one party is classical possible [Boyer, Kenigsberg, Mor, Phys. Rev. Lett. 99, 140501 (2007)]. A surprising very nice extension of result suggested by Zou, Qiu, Li, Wu, Li [Phys. 79, 052312 (2009)]. Their paper suggests sufficient for originator states (the person holding technology) just...

We prove the security of quantum key distribution against most general attacks which can be performed on channel, by an eavesdropper who has unlimited computation abilities, and full power allowed rules classical physics. A created that way then used to transmit secure messages in a their is also unaffected future.