The Experts below are selected from a list of 12603 Experts worldwide ranked by ideXlab platform
Sven Ramelow - One of the best experts on this subject based on the ideXlab platform.
-
Bell Inequality violation with entangled photons free of the coincidence time loophole
Physical Review A, 2014Co-Authors: Janake Larsson, Johannes Kofler, Marissa Giustina, B Wittmann, Rupert Ursin, Sven RamelowAbstract:In a local realist model, physical properties are defined prior to and independent of measurement and no physical influence can propagate faster than the speed of light. Proper experimental violation of a Bell Inequality would show that the world cannot be described with such a model. Experiments intended to demonstrate a violation usually require additional assumptions that make them vulnerable to a number of ``loopholes.'' In both pulsed and continuously pumped photonic experiments, an experimenter needs to identify which detected photons belong to the same pair, giving rise to the coincidence-time loophole. Here, via two different methods, we derive Clauser-Horne- and Eberhard-type inequalities that are not only free of the fair-sampling assumption (thus not being vulnerable to the detection loophole), but also free of the fair-coincidence assumption (thus not being vulnerable to the coincidence-time loophole). Both approaches can be used for pulsed as well as for continuously pumped experiments. Moreover, as they can also be applied to already existing experimental data, we finally show that a recent experiment [Giustina et al., Nature (London) 497, 227 (2013)] violated local realism without requiring the fair-coincidence assumption.
-
Bell violation using entangled photons without the fair sampling assumption
Nature, 2013Co-Authors: Johannes Kofler, Marissa Giustina, B Wittmann, Sven Ramelow, Alexandra Mech, J BeyerAbstract:The fair-sampling loophole is closed in a Bell Inequality violation experiment with entangled photons, making the photon the first physical system for which all the main loopholes have been closed. So-called Bell experiments are used to discriminate between classical ('local realistic') and quantum models of measurable phenomena. In practice, they are subject to various loopholes (arising from non-ideal experimental conditions) that can render the results inconclusive. These authors used a highly efficient source of photon pairs and superconducting transition-edge sensors in a Bell Inequality experiment that closes the 'fair-sampling' loophole for entangled photons. The results conflict with local realism, while making the photon the first physical system for which each of the main loopholes has been closed, albeit in different experiments. The violation of a Bell Inequality is an experimental observation that forces the abandonment of a local realistic viewpoint—namely, one in which physical properties are (probabilistically) defined before and independently of measurement, and in which no physical influence can propagate faster than the speed of light1,2. All such experimental violations require additional assumptions depending on their specific construction, making them vulnerable to so-called loopholes. Here we use entangled photons to violate a Bell Inequality while closing the fair-sampling loophole, that is, without assuming that the sample of measured photons accurately represents the entire ensemble3. To do this, we use the Eberhard form of Bell’s Inequality, which is not vulnerable to the fair-sampling assumption and which allows a lower collection efficiency than other forms4. Technical improvements of the photon source5,6 and high-efficiency transition-edge sensors7 were crucial for achieving a sufficiently high collection efficiency. Our experiment makes the photon the first physical system for which each of the main loopholes has been closed, albeit in different experiments.
-
Bell violation using entangled photons without the fair sampling assumption
Nature, 2013Co-Authors: Johannes Kofler, Marissa Giustina, B Wittmann, Sven Ramelow, Alexandra Mech, J BeyerAbstract:The fair-sampling loophole is closed in a Bell Inequality violation experiment with entangled photons, making the photon the first physical system for which all the main loopholes have been closed. So-called Bell experiments are used to discriminate between classical ('local realistic') and quantum models of measurable phenomena. In practice, they are subject to various loopholes (arising from non-ideal experimental conditions) that can render the results inconclusive. These authors used a highly efficient source of photon pairs and superconducting transition-edge sensors in a Bell Inequality experiment that closes the 'fair-sampling' loophole for entangled photons. The results conflict with local realism, while making the photon the first physical system for which each of the main loopholes has been closed, albeit in different experiments. The violation of a Bell Inequality is an experimental observation that forces the abandonment of a local realistic viewpoint—namely, one in which physical properties are (probabilistically) defined before and independently of measurement, and in which no physical influence can propagate faster than the speed of light1,2. All such experimental violations require additional assumptions depending on their specific construction, making them vulnerable to so-called loopholes. Here we use entangled photons to violate a Bell Inequality while closing the fair-sampling loophole, that is, without assuming that the sample of measured photons accurately represents the entire ensemble3. To do this, we use the Eberhard form of Bell’s Inequality, which is not vulnerable to the fair-sampling assumption and which allows a lower collection efficiency than other forms4. Technical improvements of the photon source5,6 and high-efficiency transition-edge sensors7 were crucial for achieving a sufficiently high collection efficiency. Our experiment makes the photon the first physical system for which each of the main loopholes has been closed, albeit in different experiments.
Nicolas Gisin - One of the best experts on this subject based on the ideXlab platform.
-
correlations in star networks from Bell inequalities to network inequalities
arXiv: Quantum Physics, 2017Co-Authors: Armin Tavakoli, Nicolas Gisin, Marcolivier Renou, Nicolas BrunnerAbstract:The problem of characterizing classical and quantum correlations in networks is considered. Contrary to the usual Bell scenario, where distant observers share a physical system emitted by one common source, a network features several independent sources, each distributing a physical system to a subset of observers. In the quantum setting, the observers can perform joint measurements on initially independent systems, which may lead to strong correlations across the whole network. In this work, we introduce a technique to systematically map a Bell Inequality to a family of Bell-type inequalities bounding classical correlations on networks in a star-configuration. Also, we show that whenever a given Bell Inequality can be violated by some entangled state $\rho$, then all the corresponding network inequalities can be violated by considering many copies of $\rho$ distributed in the star network. The relevance of these ideas is illustrated by applying our method to a specific multi-setting Bell Inequality. We derive the corresponding network inequalities, and study their quantum violations.
-
Bell Inequality tests with macroscopic entangled states of light
Physical Review A, 2011Co-Authors: Magdalena Stobinska, Nicolas Gisin, Pavel Sekatski, Adam Buraczewski, Gerd LeuchsAbstract:Quantum correlations may violate the Bell inequalities. Most experimental schemes confirming this prediction have been realized in all-optical Bell tests suffering from the detection loophole. Experiments which simultaneously close this loophole and the locality loophole are highly desirable and remain challenging. An approach to loophole-free Bell tests is based on amplification of the entangled photons (i.e., on macroscopic entanglement), for which an optical signal should be easy to detect. However, the macroscopic states are partially indistinguishable by classical detectors. An interesting idea to overcome these limitations is to replace the postselection by an appropriate preselection immediately after the amplification. This is in the spirit of state preprocessing revealing hidden nonlocality. Here, we examine one of the possible preselections, but the presented tools can be used for analysis of other schemes. Filtering methods making the macroscopic entanglement useful for Bell tests and quantum protocols are the subject of an intensive study in the field nowadays.
-
from Bell s theorem to secure quantum key distribution
Physical Review Letters, 2006Co-Authors: Antonio Acin, Nicolas Gisin, Lluis MasanesAbstract:Any Quantum Key Distribution (QKD) protocol consists first of sequences of measurements that produce some correlation between classical data. We show that these correlation data must violate some Bell Inequality in order to contain distillable secrecy, if not they could be produced by quantum measurements performed on a separable state of larger dimension. We introduce a new QKD protocol and prove its security against any individual attack by an adversary only limited by the no-signaling condition.
-
from Bell s theorem to secure quantum key distribution
Physical Review Letters, 2006Co-Authors: Antonio Acin, Nicolas Gisin, Lluis MasanesAbstract:The first step in any quantum key distribution (QKD) protocol consists of sequences of measurements that produce correlated classical data. We show that these correlation data must violate some Bell Inequality in order to contain distillable secrecy, if not they could be produced by quantum measurements performed on a separable state of larger dimension. We introduce a new QKD protocol and prove its security against any individual attack by an adversary only limited by the no-signaling condition.
-
a relevant two qubit Bell Inequality inequivalent to the chsh Inequality
Journal of Physics A, 2004Co-Authors: Daniel Collins, Nicolas GisinAbstract:We computationally investigate the complete polytope of Bell inequalities for two particles with small numbers of possible measurements and outcomes. Our approach is limited by Pitowsky's connection of this problem to the computationally hard NP problem. Despite this, we find that there are very few relevant inequivalent inequalities for small numbers. For example, in the case with three possible 2-outcome measurements on each particle, there is just one new Inequality. We describe mixed 2-qubit states which violate this Inequality but not the CHSH. The new Inequality also illustrates a sharing of bi-partite non-locality between three qubits: something not seen using the CHSH Inequality. It also inspires us to discover a class of Bell inequalities with m possible n-outcome measurements on each particle.
Marissa Giustina - One of the best experts on this subject based on the ideXlab platform.
-
Bell Inequality violation with entangled photons free of the coincidence time loophole
Physical Review A, 2014Co-Authors: Janake Larsson, Johannes Kofler, Marissa Giustina, B Wittmann, Rupert Ursin, Sven RamelowAbstract:In a local realist model, physical properties are defined prior to and independent of measurement and no physical influence can propagate faster than the speed of light. Proper experimental violation of a Bell Inequality would show that the world cannot be described with such a model. Experiments intended to demonstrate a violation usually require additional assumptions that make them vulnerable to a number of ``loopholes.'' In both pulsed and continuously pumped photonic experiments, an experimenter needs to identify which detected photons belong to the same pair, giving rise to the coincidence-time loophole. Here, via two different methods, we derive Clauser-Horne- and Eberhard-type inequalities that are not only free of the fair-sampling assumption (thus not being vulnerable to the detection loophole), but also free of the fair-coincidence assumption (thus not being vulnerable to the coincidence-time loophole). Both approaches can be used for pulsed as well as for continuously pumped experiments. Moreover, as they can also be applied to already existing experimental data, we finally show that a recent experiment [Giustina et al., Nature (London) 497, 227 (2013)] violated local realism without requiring the fair-coincidence assumption.
-
Bell violation using entangled photons without the fair sampling assumption
Nature, 2013Co-Authors: Johannes Kofler, Marissa Giustina, B Wittmann, Sven Ramelow, Alexandra Mech, J BeyerAbstract:The fair-sampling loophole is closed in a Bell Inequality violation experiment with entangled photons, making the photon the first physical system for which all the main loopholes have been closed. So-called Bell experiments are used to discriminate between classical ('local realistic') and quantum models of measurable phenomena. In practice, they are subject to various loopholes (arising from non-ideal experimental conditions) that can render the results inconclusive. These authors used a highly efficient source of photon pairs and superconducting transition-edge sensors in a Bell Inequality experiment that closes the 'fair-sampling' loophole for entangled photons. The results conflict with local realism, while making the photon the first physical system for which each of the main loopholes has been closed, albeit in different experiments. The violation of a Bell Inequality is an experimental observation that forces the abandonment of a local realistic viewpoint—namely, one in which physical properties are (probabilistically) defined before and independently of measurement, and in which no physical influence can propagate faster than the speed of light1,2. All such experimental violations require additional assumptions depending on their specific construction, making them vulnerable to so-called loopholes. Here we use entangled photons to violate a Bell Inequality while closing the fair-sampling loophole, that is, without assuming that the sample of measured photons accurately represents the entire ensemble3. To do this, we use the Eberhard form of Bell’s Inequality, which is not vulnerable to the fair-sampling assumption and which allows a lower collection efficiency than other forms4. Technical improvements of the photon source5,6 and high-efficiency transition-edge sensors7 were crucial for achieving a sufficiently high collection efficiency. Our experiment makes the photon the first physical system for which each of the main loopholes has been closed, albeit in different experiments.
-
Bell violation using entangled photons without the fair sampling assumption
Nature, 2013Co-Authors: Johannes Kofler, Marissa Giustina, B Wittmann, Sven Ramelow, Alexandra Mech, J BeyerAbstract:The fair-sampling loophole is closed in a Bell Inequality violation experiment with entangled photons, making the photon the first physical system for which all the main loopholes have been closed. So-called Bell experiments are used to discriminate between classical ('local realistic') and quantum models of measurable phenomena. In practice, they are subject to various loopholes (arising from non-ideal experimental conditions) that can render the results inconclusive. These authors used a highly efficient source of photon pairs and superconducting transition-edge sensors in a Bell Inequality experiment that closes the 'fair-sampling' loophole for entangled photons. The results conflict with local realism, while making the photon the first physical system for which each of the main loopholes has been closed, albeit in different experiments. The violation of a Bell Inequality is an experimental observation that forces the abandonment of a local realistic viewpoint—namely, one in which physical properties are (probabilistically) defined before and independently of measurement, and in which no physical influence can propagate faster than the speed of light1,2. All such experimental violations require additional assumptions depending on their specific construction, making them vulnerable to so-called loopholes. Here we use entangled photons to violate a Bell Inequality while closing the fair-sampling loophole, that is, without assuming that the sample of measured photons accurately represents the entire ensemble3. To do this, we use the Eberhard form of Bell’s Inequality, which is not vulnerable to the fair-sampling assumption and which allows a lower collection efficiency than other forms4. Technical improvements of the photon source5,6 and high-efficiency transition-edge sensors7 were crucial for achieving a sufficiently high collection efficiency. Our experiment makes the photon the first physical system for which each of the main loopholes has been closed, albeit in different experiments.
Anton Zeilinger - One of the best experts on this subject based on the ideXlab platform.
-
experimental violation of a Bell Inequality with two different degrees of freedom of entangled particle pairs
Physical Review A, 2009Co-Authors: Angie Qarry, Thomas Jennewein, Anton Zeilinger, Johannes KoflerAbstract:We demonstrate hybrid entanglement of photon pairs via the experimental violation of a Bell Inequality with two different degrees of freedom (DOF), namely, the path (linear momentum) of one photon and the polarization of the other photon. Hybrid entangled photon pairs are created by spontaneous parametric down conversion and coherent polarization to path conversion for one photon. For that photon, path superposition is analyzed, and polarization superposition for its twin photon. The correlations between these two measurements give an $S$ parameter of $S=2.653\ifmmode\pm\else\textpm\fi{}0.027$ in a Clauser-Horne-Shimony-Holt Inequality and thus violate local realism for two different DOF by more than 24 standard deviations. This experimentally supports the idea that entanglement is a fundamental concept which is indifferent to the specific physical realization of Hilbert space.
-
Experimental violation of a cluster state Bell Inequality.
Physical review letters, 2005Co-Authors: Philip Walther, Markus Aspelmeyer, Kevin J. Resch, Anton ZeilingerAbstract:Cluster states are a new type of multiqubit entangled states with entanglement properties exceptionally well suited for quantum computation. In the present work, we experimentally demonstrate that correlations in a four-qubit linear cluster state cannot be described by local realism. This exploration is based on a recently derived Bell-type Inequality [V. Scarani et al., Phys. Rev. A 71, 042325 (2005)] which is tailored, by using a combination of three- and four-particle correlations, to be maximally violated by cluster states but not violated at all by GHZ states. We observe a cluster-state Bell parameter of $2.59\ifmmode\pm\else\textpm\fi{}0.08$, which is more than $7\ensuremath{\sigma}$ larger than the threshold of 2 imposed by local realism.
-
Experimental Two-Photon, Three-Dimensional Entanglement for Quantum Communication
Physical Review Letters, 2002Co-Authors: Ali Vaziri, Gregor Weihs, Anton ZeilingerAbstract:Orbital angular momentum entangled photons emitted by a down-conversion source are in higher dimensional entangled states. Here we report the experimental confirmation by demonstrating a violation of a generalized Clauser-Horne-Shimony-Holt-type Bell Inequality in three dimensions by more than 18 standard deviations. Higher dimensional entangled states allow the realization of new types of quantum communication protocols. They also provide a more secure quantum cryptography scheme. Therefore our experimental results are likely to have applications in future quantum communication technology.
B Wittmann - One of the best experts on this subject based on the ideXlab platform.
-
Bell Inequality violation with entangled photons free of the coincidence time loophole
Physical Review A, 2014Co-Authors: Janake Larsson, Johannes Kofler, Marissa Giustina, B Wittmann, Rupert Ursin, Sven RamelowAbstract:In a local realist model, physical properties are defined prior to and independent of measurement and no physical influence can propagate faster than the speed of light. Proper experimental violation of a Bell Inequality would show that the world cannot be described with such a model. Experiments intended to demonstrate a violation usually require additional assumptions that make them vulnerable to a number of ``loopholes.'' In both pulsed and continuously pumped photonic experiments, an experimenter needs to identify which detected photons belong to the same pair, giving rise to the coincidence-time loophole. Here, via two different methods, we derive Clauser-Horne- and Eberhard-type inequalities that are not only free of the fair-sampling assumption (thus not being vulnerable to the detection loophole), but also free of the fair-coincidence assumption (thus not being vulnerable to the coincidence-time loophole). Both approaches can be used for pulsed as well as for continuously pumped experiments. Moreover, as they can also be applied to already existing experimental data, we finally show that a recent experiment [Giustina et al., Nature (London) 497, 227 (2013)] violated local realism without requiring the fair-coincidence assumption.
-
Bell violation using entangled photons without the fair sampling assumption
Nature, 2013Co-Authors: Johannes Kofler, Marissa Giustina, B Wittmann, Sven Ramelow, Alexandra Mech, J BeyerAbstract:The fair-sampling loophole is closed in a Bell Inequality violation experiment with entangled photons, making the photon the first physical system for which all the main loopholes have been closed. So-called Bell experiments are used to discriminate between classical ('local realistic') and quantum models of measurable phenomena. In practice, they are subject to various loopholes (arising from non-ideal experimental conditions) that can render the results inconclusive. These authors used a highly efficient source of photon pairs and superconducting transition-edge sensors in a Bell Inequality experiment that closes the 'fair-sampling' loophole for entangled photons. The results conflict with local realism, while making the photon the first physical system for which each of the main loopholes has been closed, albeit in different experiments. The violation of a Bell Inequality is an experimental observation that forces the abandonment of a local realistic viewpoint—namely, one in which physical properties are (probabilistically) defined before and independently of measurement, and in which no physical influence can propagate faster than the speed of light1,2. All such experimental violations require additional assumptions depending on their specific construction, making them vulnerable to so-called loopholes. Here we use entangled photons to violate a Bell Inequality while closing the fair-sampling loophole, that is, without assuming that the sample of measured photons accurately represents the entire ensemble3. To do this, we use the Eberhard form of Bell’s Inequality, which is not vulnerable to the fair-sampling assumption and which allows a lower collection efficiency than other forms4. Technical improvements of the photon source5,6 and high-efficiency transition-edge sensors7 were crucial for achieving a sufficiently high collection efficiency. Our experiment makes the photon the first physical system for which each of the main loopholes has been closed, albeit in different experiments.
-
Bell violation using entangled photons without the fair sampling assumption
Nature, 2013Co-Authors: Johannes Kofler, Marissa Giustina, B Wittmann, Sven Ramelow, Alexandra Mech, J BeyerAbstract:The fair-sampling loophole is closed in a Bell Inequality violation experiment with entangled photons, making the photon the first physical system for which all the main loopholes have been closed. So-called Bell experiments are used to discriminate between classical ('local realistic') and quantum models of measurable phenomena. In practice, they are subject to various loopholes (arising from non-ideal experimental conditions) that can render the results inconclusive. These authors used a highly efficient source of photon pairs and superconducting transition-edge sensors in a Bell Inequality experiment that closes the 'fair-sampling' loophole for entangled photons. The results conflict with local realism, while making the photon the first physical system for which each of the main loopholes has been closed, albeit in different experiments. The violation of a Bell Inequality is an experimental observation that forces the abandonment of a local realistic viewpoint—namely, one in which physical properties are (probabilistically) defined before and independently of measurement, and in which no physical influence can propagate faster than the speed of light1,2. All such experimental violations require additional assumptions depending on their specific construction, making them vulnerable to so-called loopholes. Here we use entangled photons to violate a Bell Inequality while closing the fair-sampling loophole, that is, without assuming that the sample of measured photons accurately represents the entire ensemble3. To do this, we use the Eberhard form of Bell’s Inequality, which is not vulnerable to the fair-sampling assumption and which allows a lower collection efficiency than other forms4. Technical improvements of the photon source5,6 and high-efficiency transition-edge sensors7 were crucial for achieving a sufficiently high collection efficiency. Our experiment makes the photon the first physical system for which each of the main loopholes has been closed, albeit in different experiments.