| 1. |
- Giustina, Marissa, et al.
(författare)
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A Significant-Loophole-Free Test of Bells Theorem with Entangled Photons
- 2017
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Ingår i: QUANTUM INFORMATION SCIENCE AND TECHNOLOGY III. - : SPIE-INT SOC OPTICAL ENGINEERING. - 9781510613492 - 9781510613485
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Konferensbidrag (refereegranskat)abstract
- John Bells theorem of 1964 states that local elements of physical reality, existing independent of measurement, are inconsistent with the predictions of quantum mechanics (Bell, J. S. (1964), Physics (College. Park. Md). 1 (3), 195). Specifically, correlations between measurement results from distant entangled systems would be smaller than predicted by quantum physics. This is expressed in Bells inequalities. Employing modifications of Bells inequalities, many experiments have been performed that convincingly support the quantum predictions. Yet, all experiments rely on assumptions, which provide loopholes for a local realist explanation of the measurement. Here we report an experiment with polarization-entangled photons that simultaneously closes the most significant of these loopholes. We use a highly efficient source of entangled photons, distributed these over a distance of 58.5 meters, and implemented rapid random setting generation and high-efficiency detection to observe a violation of a Bell inequality with high statistical significance. The merely statistical probability of our results to occur under local realism is less than 3.74 . 10(-31), corresponding to an 11.5 standard deviation effect.
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| 2. |
- Giustina, Marissa, et al.
(författare)
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Significant-Loophole-Free Test of Bells Theorem with Entangled Photons
- 2015
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 115:25, s. 250401-
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Tidskriftsartikel (refereegranskat)abstract
- Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bells theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bells inequalities. Previous experiments convincingly supported the quantum predictions. Yet, every experiment requires assumptions that provide loopholes for a local realist explanation. Here, we report a Bell test that closes the most significant of these loopholes simultaneously. Using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors, we observe a violation of a Bell inequality with high statistical significance. The purely statistical probability of our results to occur under local realism does not exceed 3.74 x 10(-31), corresponding to an 11.5 standard deviation effect.
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| 3. |
- Joshi, Siddarth Koduru, et al.
(författare)
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Space QUEST mission proposal : experimentally testing decoherence due to gravity
- 2018
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 20
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Tidskriftsartikel (refereegranskat)abstract
- Models of quantum systems on curved space-times lack sufficient experimental verification. Some speculative theories suggest that quantum correlations, such as entanglement, may exhibit different behavior to purely classical correlations in curved space. By measuring this effect or lack thereof, we can test the hypotheses behind several such models. For instance, as predicted by Ralph et al [5] and Ralph and Pienaar [1], a bipartite entangled system could decohere if each particle traversed through a different gravitational field gradient. We propose to study this effect in a ground to space uplink scenario. We extend the above theoretical predictions of Ralph and coworkers and discuss the scientific consequences of detecting/failing to detect the predicted gravitational decoherence. We present a detailed mission design of the European Space Agency's Space QUEST (Space-Quantum Entanglement Space Test) mission, and study the feasibility of the mission scheme.
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| 4. |
- Kaltenbaek, Rainer, et al.
(författare)
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Macroscopic Quantum Resonators (MAQRO) : 2015 update
- 2016
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Ingår i: EPJ Quantum Technology. - : Springer Berlin/Heidelberg. - 2196-0763. ; 3:1
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Forskningsöversikt (refereegranskat)abstract
- Do the laws of quantum physics still hold for macroscopic objects - this is at the heart of Schrodinger's cat paradox - or do gravitation or yet unknown effects set a limit for massive particles? What is the fundamental relation between quantum physics and gravity? Ground-based experiments addressing these questions may soon face limitations due to limited free-fall times and the quality of vacuum and microgravity. The proposed mission Macroscopic Quantum Resonators (MAQRO) may overcome these limitations and allow addressing such fundamental questions. MAQRO harnesses recent developments in quantum optomechanics, high-mass matter-wave interferometry as well as state-of-the-art space technology to push macroscopic quantum experiments towards their ultimate performance limits and to open new horizons for applying quantum technology in space. The main scientific goal is to probe the vastly unexplored 'quantum-classical' transition for increasingly massive objects, testing the predictions of quantum theory for objects in a size and mass regime unachievable in ground-based experiments. The hardware will largely be based on available space technology. Here, we present the MAQRO proposal submitted in response to the 4th Cosmic Vision call for a medium-sized mission (M4) in 2014 of the European Space Agency (ESA) with a possible launch in 2025, and we review the progress with respect to the original MAQRO proposal for the 3rd Cosmic Vision call for a medium-sized mission (M3) in 2010. In particular, the updated proposal overcomes several critical issues of the original proposal by relying on established experimental techniques from high-mass matter-wave interferometry and by introducing novel ideas for particle loading and manipulation. Moreover, the mission design was improved to better fulfill the stringent environmental requirements for macroscopic quantum experiments.
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| 5. |
- Khrennikov, Andrei, et al.
(författare)
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On the equivalence of the Clauser-Horne and Eberhard inequality based tests
- 2014
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T163
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Tidskriftsartikel (refereegranskat)abstract
- Recently, the results of the first experimental test for entangled photons closing the detection loophole (also referred to as the fair sampling loophole) were published (Vienna, 2013). From the theoretical viewpoint the main distinguishing feature of this long-aspired to experiment was that the Eberhard inequality was used. Almost simultaneously another experiment closing this loophole was performed (Urbana-Champaign, 2013) and it was based on the Clauser-Horne inequality (for probabilities). The aim of this note is to analyze the mathematical and experimental equivalence of tests based on the Eberhard inequality and various forms of the Clauser-Horne inequality. The structure of the mathematical equivalence is nontrivial. In particular, it is necessary to distinguish between algebraic and statistical equivalence. Although the tests based on these inequalities are algebraically equivalent, they need not be equivalent statistically, i.e., theoretically the level of statistical significance can drop under transition from one test to another (at least for finite samples). Nevertheless, the data collected in the Vienna test implies not only a statistically significant violation of the Eberhard inequality, but also of the Clauser-Horne inequality (in the ratio-rate form): for both a violation > 60 sigma.
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| 6. |
- Larsson, Jan-Åke, et al.
(författare)
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Bell-inequality violation with entangled photons, free of the coincidence-time loophole
- 2014
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 90:3, s. 032107-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Pacher, Christoph, et al.
(författare)
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Attacks on quantum key distribution protocols that employ non-ITS authentication
- 2016
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Ingår i: Quantum Information Processing. - : Springer Publishing Company. - 1570-0755 .- 1573-1332. ; 15:1, s. 327-362
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate how adversaries with unbounded 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 QKDpostprocessing. 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.
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| 8. |
- Sadiq, Muhammad, 1979-
(författare)
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Experiments with Entangled Photons : Bell Inequalities, Non-local Games and Bound Entanglement
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Quantum mechanics is undoubtedly a weird field of science, which violates many deep conceptual tenets of classical physics, requiring reconsideration of the concepts on which classical physics is based. For instance, it permits persistent correlations between classically separated systems, that are termed as entanglement. To circumvent these problems and explain entanglement, hidden variables theories--based on undiscovered parameters--have been devised. However, John S. Bell and others invented inequalities that can distinguish between the predictions of local hidden variable (LHV) theories and quantum mechanics. The CHSH-inequality (formulated by J. Clauser, M. Horne, A. Shimony and R. A. Holt), is one of the most famous among these inequalities. In the present work, we found that this inequality actually contains an even simpler logical structure, which can itself be described by an inequality and will be violated by quantum mechanics. We found 3 simpler inequalities and were able to violate them experimentally.Furthermore, the CHSH inequality can be used to devise games that can outperform classical strategies. We explore CHSH-games for biased and unbiased cases and present their experimental realizations. We also found a remarkable application of CHSH-games in real life, namely in the card game of duplicate Bridge. In this thesis, we have described this application along with its experimental realization. Moreover, non-local games with quantum inputs can be used to certify entanglement in a measurement device independent manner. We implemented this method and detected entanglement in a set of two-photon Werner states. Our results are in good agreement with theory.A peculiar form of entanglement that is not distillable through local operations and classical communication (LOCC) is known as bound entanglement (BE). In the present work, we produced and studied BE in four-partite Smolin states and present an experimental violation of a Bell inequality by such states. Moreover we produced a three-qubit BE state, which is also the first experimental realization of a tripartite BE state. We also present its activation, where we experimentally demonstrate super additivity of quantum information resources.
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| 9. |
- Wengerowsky, Soeren, et al.
(författare)
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Entanglement distribution over a 96-km-long submarine optical fiber
- 2019
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : NATL ACAD SCIENCES. - 0027-8424 .- 1091-6490. ; 116:14, s. 6684-6688
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Tidskriftsartikel (refereegranskat)abstract
- Quantum entanglement is one of the most extraordinary effects in quantum physics, with many applications in the emerging field of quantum information science. In particular, it provides the foundation for quantum key distribution (QKD), which promises a conceptual leap in information security. Entanglement-based QKD holds great promise for future applications owing to the possibility of device-independent security and the potential of establishing global-scale quantum repeater networks. While other approaches to QKD have already reached the level of maturity required for operation in absence of typical laboratory infrastructure, comparable field demonstrations of entanglement-based QKD have not been performed so far. Here, we report on the successful distribution of polarization-entangled photon pairs between Malta and Sicily over 96 km of submarine optical telecommunications fiber. We observe around 257 photon pairs per second, with a polarization visibility above 90%. Our results show that QKD based on polarization entanglement is now indeed viable in long-distance fiber links. This field demonstration marks the longest-distance distribution of entanglement in a deployed telecommunications network and demonstrates an international submarine quantum communication channel. This opens up myriad possibilities for future experiments and technological applications using existing infrastructure.
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| 10. |
- Wengerowsky, Soeren, et al.
(författare)
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Passively stable distribution of polarisation entanglement over 192 km of deployed optical fibre
- 2020
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Ingår i: NPJ QUANTUM INFORMATION. - : NATURE PUBLISHING GROUP. - 2056-6387. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- Quantum key distribution (QKD) based on entangled photon pairs holds the potential for repeater-based quantum networks connecting clients over long distance. We demonstrate long-distance entanglement distribution by means of polarisation-entangled photon pairs through two successive deployed 96 km-long telecommunications fibres in the same submarine cable. One photon of each pair was detected directly after the source, while the other travelled the fibre cable in both directions for a total distance of 192 km and attenuation of 48 dB. The observed two-photon Bell state exhibited a fidelity 85 +/- 2% and was stable over several hours. We employed neither active stabilisation of the quantum state nor chromatic dispersion compensation for the fibre.
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