Activation of multipartite quantum non-locality (2009)
Almeida, Mafalda L., Cavalcanti, Daniel, Scarani, Valerio, Acin, Antonio
We consider an Elitzur-Popescu-Rohrlich decomposition for correlations obtained by local measurements performed in multipartite quantum systems. Sufficient conditions for a quantum state to be fully...
Quantum information: primitive notions and quantum correlations (2009)
This series of introductory lectures consists of two parts. In the first part, I rapidly review the basic notions of quantum physics and many primitives of quantum information (i.e. notions that one...
The local content of bipartite qubit correlations (2009)
Branciard, Cyril, Gisin, Nicolas, Scarani, Valerio
One of the last open problems concerning two qubits in a pure state is to find the exact local content of their correlation, in the sense of Elitzur, Popescu and Rohrlich (EPR2) [Phys. Lett. A 162,...
The black paper of quantum cryptography: real implementation problems (2009)
Scarani, Valerio, Kurtsiefer, Christian
The fact that the laws of physics play a role in the security of quantum key distribution (QKD) has often been misunderstood, as if the security of QKD would be based \textit{only} of the laws of...
Recovering part of the quantum boundary from information causality (2009)
Allcock, Jonathan, Brunner, Nicolas, Pawlowski, Marcin, Scarani, Valerio
Recently, the principle of information causality has appeared as a good candidate for an information-theoretic principle that would single out quantum correlations among more general non-signalling...
Phase shift of a weak coherent beam induced by a single atom (2009)
Aljunid, Syed Abdullah, Tey, Meng Khoon, Chng, Brenda, Liew, Timothy, Maslennikov, Gleb, Scarani, Valerio, ...
We report on a direct measurement of a phase shift on a weak coherent beam by a single Rb-87 atom in a Mach-Zehnder interferometer. A maximum phase shift of about 1 degree is observed experimentally.
Device-independent quantum key distribution secure against collective attacks (2009)
Pironio, Stefano, Acin, Antonio, Brunner, Nicolas, Gisin, Nicolas, Massar, Serge, Scarani, Valerio
Device-independent quantum key distribution (DIQKD) represents a relaxation of the security assumptions made in usual quantum key distribution (QKD). As in usual QKD, the security of DIQKD follows...
Valerio Scarani, Antonio Acín, Grégoire Ribordy, Nicolas Gisin
cryptography protocols robust against photon number
Finite-key analysis for practical implementations of quantum key distribution (2008)
Cai, Raymond Y. Q., Scarani, Valerio
The lists of bits processed in quantum key distribution are necessarily of finite length. The need for finite-key unconditional security bounds has been recognized long ago, but the theoretical tools...
How non-local are n noisy Popescu-Rohrlich Machines? (2008)
Fitzi, Matthias, Hänggi, Esther, Scarani, Valerio, Wolf, Stefan
In this paper, we consider the question of how much non-locality there is in n Popescu-Rohrlich Machines with errors epsilon (epsilon-PRMs) - where we quantify non-locality by partitioning the...
Security Bounds for Quantum Cryptography with Finite Resources (2008)
Scarani, Valerio, Renner, Renato
A practical quantum key distribution (QKD) protocol necessarily runs in finite time and, hence, only a finite amount of communication is exchanged. This is in contrast to most of the standard results...
Experimental quantum key distribution based on a Bell test (2008)
Ling, Alexander, Peloso, Matthew P., Marcikic, Ivan, Scarani, Valerio, Lamas-Linares, Antia, Kurtsiefer, Christian
We report on a complete free-space field implementation of a modified Ekert91 protocol for quantum key distribution using entangled photon pairs. For each photon pair we perform a random choice...
Interfacing light and single atoms with a lens (2008)
Tey, Meng Khoon, Maslennikov, Gleb, Liew, Timothy C. H., Aljunid, Syed Abdullah, Huber, Florian, Chng, Brenda, ...
We characterize the interaction between a single atom or similar microscopic system and a light field via the scattering ratio. For that, we first derive the electrical field in a strongly focused...
Simulation of partial entanglement with nonsignaling resources (2008)
Brunner, Nicolas, Gisin, Nicolas, Popescu, Sandu, Scarani, Valerio
With the goal of gaining a deeper understanding of quantum non-locality, we decompose quantum correlations into more elementary non-local correlations. We show that the correlations of all pure...
The Security of Practical Quantum Key Distribution (2008)
Scarani, Valerio, Bechmann-Pasquinucci, Helle, Cerf, Nicolas J., Dusek, Miloslav, Lutkenhaus, Norbert, Peev, Momtchil
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...
Testing the Hilbert space dimension (2008)
Brunner, Nicolas, Pironio, Stefano, Acin, Antonio, Gisin, Nicolas, Methot, Andre Allan, Scarani, Valerio
Given a set of correlations originating from measurements on a quantum state of unknown Hilbert space dimension, what is the minimal dimension d necessary to describes such correlations? We introduce...
A simple approach to test Leggett's model of nonlocal quantum correlations (2008)
Branciard, Cyril, Brunner, Nicolas, Gisin, Nicolas, Kurtsiefer, Christian, Lamas-Linares, Antia, Ling, Alexander, ...
We present new inequalities for testing Leggett's model [Found. Phys. 33, 1469 (2003)] of non-local quantum correlations. Remarkably these inequalities can be derived in a very simple way, assuming...
On the local and non-local content of bipartite qubit and qutrit correlations (2007)
The local and non-local contents of non-local probability distributions are studied using the approach of Elitzur, Popescu and Rohrlich [Phys. Lett. A \textbf{162}, 25 (1992)]. This work focuses on...
The main features of quantum computing are described in the framework of spin resonance methods. Stress is put on the fact that quantum computing is in itself nothing but a re-interpretation...
Branciard, Cyril, Gisin, Nicolas, Scarani, Valerio
The Differential-Phase-Shift (DPS) and the Coherent-One-Way (COW) are among the most practical protocols for quantum cryptography, and are therefore the object of fast-paced experimental...
Experimental Falsification of Leggett's Non-Local Variable Model (2007)
Branciard, Cyril, Ling, Alexander, Gisin, Nicolas, Kurtsiefer, Christian, Lamas-Linares, Antia, Scarani, Valerio
Bell's theorem guarantees that no model based on local variables can reproduce quantum correlations. Also some models based on non-local variables, if subject to apparently "reasonable" constraints,...
Scarani, Valerio, Renner, Renato
We derive a bound for the security of QKD with finite resources under one-way post-processing, based on a definition of security that is composable and has an operational meaning. While our proof...
Entanglement and Irreversibility in the Approach to Thermal Equilibrium (2007)
When a physical system is put in contact with a very large thermal bath, it undergoes a dissipative (i.e., an apparently irreversible) process that leads to thermal equilibrium. This dynamical...
Entangling Independent Photons by Time Measurement (2007)
Halder, Matthaeus, Beveratos, Alexios, Gisin, Nicolas, Scarani, Valerio, Simon, Christoph, Zbinden, Hugo
A quantum system composed of two or more subsystems can be in an entangled state, i.e. a state in which the properties of the global system are well defined but the properties of each subsystem are...
Device-independent security of quantum cryptography against collective attacks (2007)
Acin, Antonio, Brunner, Nicolas, Gisin, Nicolas, Massar, Serge, Pironio, Stefano, Scarani, Valerio
We present the optimal collective attack on a Quantum Key Distribution (QKD) protocol in the "device-independent" security scenario, where no assumptions are made about the way the QKD devices work...
Detection loophole in asymmetric Bell experiments (2007)
Brunner, Nicolas, Gisin, Nicolas, Scarani, Valerio, Simon, Christoph
The problem of closing the detection loophole with asymmetric systems, such as entangled atom-photon pairs, is addressed. We show that, for the Bell inequality I_3322, a minimal detection efficiency...
Branciard, Cyril, Gisin, Nicolas, Lutkenhaus, Norbert, Scarani, Valerio
This is a study of the security of the Coherent One-Way (COW) protocol for quantum cryptography, proposed recently as a simple and fast experimental scheme. In the zero-error regime, the eavesdropper...
Secrecy extraction from no-signalling correlations (2006)
Scarani, Valerio, Gisin, Nicolas, Brunner, Nicolas, Masanes, Lluis, Pino, Sergi, Acin, Antonio
Quantum cryptography shows that one can guarantee the secrecy of correlation on the sole basis of the laws of physics, that is without limiting the computational power of the eavesdropper. The usual...
Valerio Scarani, Nicolas Gisin
Superluminal hidden communication as the underlying mechanism for quantum correlations: Constraining models
Bell-type inequalities for non-local resources (2006)
Brunner, Nicolas, Scarani, Valerio, Gisin, Nicolas
We present bipartite Bell-type inequalities which allow the two partners to use some non-local resource. Such inequality can only be violated if the parties use a resource which is more non-local...
Feats, Features and Failures of the PR-box (2006)
One of the most intriguing features of quantum physics is the non-locality of correlations that can be obtained by measuring entangled particles. Recently, it has been noticed that non-locality can...
Oblivious transfer and quantum channels (2006)
Gisin, Nicolas, Popescu, Sandu, Scarani, Valerio, Wolf, Stefan, Wullschleger, Jürg
We show that oblivious transfer can be seen as the classical analogue to a quantum channel in the same sense as non-local boxes are for maximally entangled qubits.
Scarani, Valerio, Iblisdir, Sofyan, Gisin, Nicolas, Acin, Antonio
The impossibility of perfectly copying (or cloning) an arbitrary quantum state is one of the basic rules governing the physics of quantum systems. The processes that perform the optimal approximate...
Fast and simple one-way Quantum Key Distribution (2005)
Stucki, Damien, Brunner, Nicolas, Gisin, Nicolas, Scarani, Valerio, Zbinden, Hugo
We present and demonstrate a new protocol for practical quantum cryptography, tailored for an implementation with weak coherent pulses to obtain a high key generation rate. The key is obtained by a...
Scarani,Valerio, Gisin,Nicolas
Since Bell's theorem, it is known that quantum correlations cannot be described by local variables (LV) alone: if one does not want to abandon classical mechanisms for correlations, a superluminal...
Security of two quantum cryptography protocols using the same four qubit states (2005)
Branciard, Cyril, Gisin, Nicolas, Kraus, Barbara, Scarani, Valerio
The first quantum cryptography protocol, proposed by Bennett and Brassard in 1984 (BB84), has been widely studied in the last years. This protocol uses four states (more precisely, two complementary...
Entanglement and non-locality are different resources (2004)
Brunner, Nicolas, Gisin, Nicolas, Scarani, Valerio
Bell's theorem states that, to simulate the correlations created by measurement on pure entangled quantum states, shared randomness is not enough: some "non-local" resources are required. It has been...
Towards practical and fast Quantum Cryptography (2004)
Gisin, Nicolas, Ribordy, Gregoire, Zbinden, Hugo, Stucki, Damien, Brunner, Nicolas, Scarani, Valerio
We present a new protocol for practical quantum cryptography, tailored for an implementation with weak coherent pulses. The key is obtained by a very simple time-of-arrival measurement on the data...
Scarani, Valerio, Gisin, Nicolas
Since Bell's theorem, it is known that quantum correlations cannot be described by local variables (LV) alone: if one does not want to abandon classical mechanisms for correlations, a superluminal...
Niederberger, Armand, Scarani, Valerio, Gisin, Nicolas
In practical quantum cryptography, the source sometimes produces multi-photon pulses, thus enabling the eavesdropper Eve to perform the powerful photon-number-splitting (PNS) attack. Recently, it was...
Four-photon correction in two-photon Bell experiments (2004)
Scarani, Valerio, De Riedmatten, Hugues, Marcikic, Ivan, Zbinden, Hugo, Gisin, Nicolas
Correlated photons produced by spontaneous parametric down-conversion are an essential tool for quantum communication, especially suited for long-distance connections. To have a reasonable count rate...
Direct measurement of superluminal group velocity and of signal velocity in an optical fiber (2004)
Brunner, Nicolas, Scarani, Valerio, Wegmuller, Mark, Legre, Matthieu, Gisin, Nicolas
We present an easy way of observing superluminal group velocities using a birefringent optical fiber and other standard devices. In the theoretical analysis, we show that the optical properties of...
Nonlocality of cluster states of qubits (2004)
Scarani, Valerio, Acin, Antonio, Schenck, Emmanuel, Aspelmeyer, Markus
We investigate cluster states of qubits with respect to their non-local properties. We demonstrate that a Greenberger-Horne-Zeilinger (GHZ) argument holds for any cluster state: more precisely, it...
Bell's inequalities detect efficient entanglement (2003)
Acin, Antonio, Gisin, Nicolas, Masanes, Lluis, Scarani, Valerio
We review the status of Bell's inequalities in quantum information, stressing mainly the links with quantum key distribution and distillation of entanglement. We also prove that for all the...
De Riedmatten, Hugues, Scarani, Valerio, Marcikic, Ivan, Acin, Antonio, Tittel, Wolfgang, Zbinden, Hugo, ...
We study the physics of four-photon states generated in spontaneous parametric down-conversion with a pulsed pump field. In the limit where the coherence time of the photons t_c is much shorter than...
Classical and quantum: some mutual clarifications (2003)
This paper presents two unconventional links between quantum and classical physics. The first link appears in the study of quantum cryptography. In the presence of a spy, the quantum correlations...
Tailoring photonic entanglement in high-dimensional Hilbert spaces (2003)
De Riedmatten, Hugues, Marcikic, Ivan, Scarani, Valerio, Tittel, Wolfgang, Zbinden, Hugo, Gisin, Nicolas
We present an experiment where two photonic systems of arbitrary dimensions can be entangled. The method is based on spontaneous parametric down conversion with trains of d pump pulses with a fixed...
Energy-time entanglement of quasi-particles in solid-state devices (2003)
Scarani, Valerio, Gisin, Nicolas, Popescu, Sandu
We present a proposal for the experimental observation of energy-time entanglement of quasi-particles in mesoscopic physics. This type of entanglement arises whenever correlated particles are...
Optical telecom networks as weak quantum measurements with post- selection (2003)
Brunner, Nicolas, Acin, Antonio, Collins, Daniel, Gisin, Nicolas, Scarani, Valerio
We show that weak measurements with post-selection, proposed in the context of the quantum theory of measurement, naturally appear in the everyday physics of fiber optics telecom networks through...
Security bounds in Quantum Cryptography using d-level systems (2003)
Acin, Antonio, Gisin, Nicolas, Scarani, Valerio
We analyze the security of quantum cryptography schemes for $d$-level systems using 2 or $d+1$ maximally conjugated bases, under individual eavesdropping attacks based on cloning machines and...
Acin, Antonio, Gisin, Nicolas, Scarani, Valerio
A new class of quantum cryptography (QC) protocols that are robust against the most general photon number splitting attacks in a weak coherent pulse implementation has been recently proposed. In this...
Scarani, Valerio, Acin, Antonio, Ribordy, Gregoire, Gisin, Nicolas
We introduce a new class of quantum quantum key distribution protocols, tailored to be robust against photon number splitting (PNS) attacks. We study one of these protocols, which differs from the...
Bell inequalities and distillability in N-quantum-bit systems (2002)
Acin, Antonio, Scarani, Valerio, Wolf, Michael M.
The relation between Bell inequalities with two two-outcome measurements per site and distillability is analyzed in systems of an arbitrary number of quantum bits. We observe that the violation of...
Femtosecond Time-Bin Entangled Qubits for Quantum Communication (2002)
Marcikic, Ivan, De Riedmatten, Hugues, Tittel, Wolfgang, Scarani, Valerio, Zbinden, Hugo, Gisin, Nicolas
We create pairs of non-degenerate time-bin entangled photons at telecom wavelengths with ultra-short pump pulses. Entanglement is shown by performing Bell kind tests of the Franson type with...
Quantum cloning with an optical fiber amplifier (2002)
Fasel, Sylvain, Gisin, Nicolas, Ribordy, Gregoire, Scarani, Valerio, Zbinden, Hugo
It has been shown theoretically that a light amplifier working on the physical principle of stimulated emission should achieve optimal quantum cloning of the polarization state of light. We...
Bell-type inequalities to detect true n-body non-separability (2002)
Collins, Daniel, Gisin, Nicolas, Popescu, Sandu, Roberts, David, Scarani, Valerio
We analyze the structure of correlations among more than two quantum systems. We introduce a classification of correlations based on the concept of non-separability, which is different {\em a priori}...
Thermalizing Quantum Machines: Dissipation and Entanglement (2001)
Scarani, Valerio, Ziman, Mario, Stelmachovic, Peter, Gisin, Nicolas, Buzek, Vladimir
We study the relaxation of a quantum system towards the thermal equilibrium using tools developed within the context of quantum information theory. We consider a model in which the system is a qubit,...
Superluminal influences, hidden variables, and signaling (2001)
Scarani, Valerio, Gisin, Nicolas
We consider alternative models to quantum mechanics, that have been proposed in the recent years in order to explain the EPR correlations between two particles. These models allow in principle local...
Quantum Key Distribution between N partners: optimal eavesdropping and Bell's inequalities (2001)
Scarani, Valerio, Gisin, Nicolas
Quantum secret-sharing protocols involving N partners (NQSS) are key distribution protocols in which Alice encodes her key into $N-1$ qubits, in such a way that all the other partners must cooperate...
Spectral decomposition of Bell's operators for qubits (2001)
Scarani, Valerio, Gisin, Nicolas
The spectral decomposition is given for the N-qubit Bell operators with two observables per qubit. It is found that the eigenstates (when non-degenerate) are N-qubit GHZ states even for those...
Quantum Communication between N partners and Bell's inequalities (2001)
Scarani, Valerio, Gisin, Nicolas
We consider a family of quantum communication protocols involving $N$ partners. We demonstrate the existence of a link between the security of these protocols against individual attacks by the...
The speed of quantum information and the preferred frame: analysis of experimental data (2000)
Scarani, Valerio, Tittel, Wolfgang, Zbinden, Hugo, Gisin, Nicolas
The results of EPR experiments performed in Geneva are analyzed in the frame of the cosmic microwave background radiation, generally considered as a good candidate for playing the role of preferred...
NMR studies on magnetic nanostructures / (2000)
Thèse no 2146 sciences EPF Lausanne.
The main features of quantum computing are described in the framework of spin resonance methods. Stress is put on the fact that quantum computing is in itself nothing but a re-interpretation...
Does entanglement depend on the timing of the impacts at the beam-splitters? (1997)
Suarez, Antoine, Scarani, Valerio
A new nonlocality experiment with moving beam-splitters is proposed. The experiment is analysed according to conventional quantum mechanics, and to an alternative nonlocal description in which...