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Physicists close two loopholes while violating local realism


first_imgPhysicists performed a Bell experiment between the islands of La Palma and Tenerife at an altitude of 2,400 m. Starting with an entangled pair of photons, one photon was sent 6 km away to Alice, and the other photon was sent 144 km away to Bob. The physicists took several steps to simultaneously close the locality loophole and freedom-of-choice loophole. Image credit: Thomas Scheidl, et al. and Google Earth, ©2008 Google, Map Data ©Tele Atlas. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. (PhysOrg.com) — The latest test in quantum mechanics provides even stronger support than before for the view that nature violates local realism and is thus in contradiction with a classical worldview. By performing an experiment in which photons were sent from one Canary Island to another, physicists have shown that two of three loopholes can be closed simultaneously in a test that violates Bell’s inequality (and therefore local realism) by more than 16 standard deviations. Performing a Bell test that closes all three loopholes still remains a challenge, but the physicists predict that such an experiment might be “on the verge of being possible” with state-of-the-art technology. More information: Thomas Scheidl, et al. “Violation of local realism with freedom of choice.” 19708-19713, PNAS, November 16, 2010, vol. 107, no. 46. DOI:10.1073/pnas.1002780107 The physicists, who belong to the group of Rupert Ursin and Anton Zeilinger and were all at either the Austrian Academy of Sciences in Vienna or the University of Vienna when performing the experiments in 2008, have published their study on the new Bell test in the early edition of PNAS. As they explain in their study, local realism consists of both realism – the view that reality exists with definite properties even when not being observed – and locality – the view that an object can only be influenced by its immediate surroundings. If a Bell test shows that a measurement of one object can influence the state of a second, distant object, then local realism has been violated.”The question of whether nature can be understood in terms of classical concepts and explained by local realism is one of the deepest in physics,” coauthor Johannes Kofler told PhysOrg.com. “Getting Bell tests as loophole-free as possible and confirming quantum mechanics is therefore an extremely important task. From a technological perspective, certain protocols of quantum cryptography (which is entering the market at the moment) are based on entanglement and violation of Bell’s inequality. This so-called ‘unconditional security’ must in practice take care of the loopholes in Bell tests.”The physicists explained that, in experimental tests, there are three loopholes that allow observed violations of local realism to still be explained by local realistic theories. These three loopholes can involve locality (if there is not a large enough distance separating the two objects at the time of measurement), the freedom to choose any measurement settings (so measurement settings may be influenced by hidden variables, or vice versa), and fair sampling (a small fraction of observed objects may not accurately represent all objects due to detection inefficiencies).Previous experiments have closed the first loophole, which was done by ensuring a large spatial separation between the two objects (in this case, two quantum mechanically entangled photons) so that measurements of the objects could not be influenced by each other. Special relativity then ensures that the objects cannot influence each other, since no physical signals can travel faster than the speed of light. In these experiments, classically unexplainable correlations were still observed between the objects, indicating a violation of local realism. (The fair sampling loophole was closed in another earlier experiment using ions, where large detection efficiencies can be reached.) Debunking and closing quantum entanglement ‘loopholes’center_img Citation: Physicists close two loopholes while violating local realism (2010, November 30) retrieved 18 August 2019 from https://phys.org/news/2010-11-physicists-loopholes-violating-local-realism.html Explore further In the current experiment, the physicists simultaneously ruled out both the locality loophole and the freedom-of-choice loophole. They performed a Bell test between the Canary Islands of La Palma and Tenerife, located 144 km apart. On La Palma, they generated pairs of entangled photons using a laser diode. Then they locally delayed one photon in a 6-km-long optical fiber (29.6-microsecond traveling time) and sent it to one measurement station (Alice), and sent the other photon 144 km away (479-microsecond traveling time) through open space to the other measurement station (Bob) on Tenerife. The scientists took several steps to close both loopholes. For ruling out the possibility of local influence, they added a delay in the optical fiber to Alice to ensure that the measurement events there were space-like separated from those on Tenerife such that no physical signal could be interchanged. Also, the measurement settings were randomly determined by quantum random number generators. To close the freedom-of-choice loophole, the scientists spatially separated the setting choice and the photon emission, which ensured that the setting choice and photon emission occurred at distant locations and nearly simultaneously (within 0.5 microseconds of each other). The scientists also added a delay to Bob’s random setting choice. These combined measures eliminated the possibility of the setting choice or photon emission events influencing each other. But again, despite these measures, the scientists still detected correlations between the separated photons that can only be explained by quantum mechanics, violating local realism.By showing that local realism can be violated even when the locality and freedom-of-choice loopholes are closed, the experiment greatly reduces the number of “hidden variable theories” that might explain the correlations while obeying local realism. Further, these theories appear to be beyond the possibility of experimental testing, since they propose such things as allowing actions into the past or assuming a common cause for all events. Now, one of the greatest challenges in quantum mechanics is simultaneously closing the fair-sampling loophole along with the others to demonstrate a completely loophole-free Bell test. Such an experiment will require very high-efficiency detectors and other high-quality components, along with the ability to achieve extremely high transmission. Also, the test would have to operate at a critical distance between Alice and Bob that is not too large, to minimize photon loss, and not too small, to ensure sufficient separation. Although these requirements are beyond the current experimental set-up due to high loss between the islands, the scientists predict that these requirements may be met in the near future. “Performing a loophole-free Bell test is certainly one of the biggest open experimental challenges in the foundations of quantum mechanics,” Kofler said. “Various groups are working towards that goal. It is on the edge of being technologically feasible. Such an experiment will probably be done within the next five years.” Copyright 2010 PhysOrg.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.last_img read more


Journeys and bonds


first_imgPavitra Bandhan is a journey of two strangers Aashima and Girish, who are not suppose to meet by any means but destiny brings them not only under the same roof but also binds them in a relationship of lifetime. Aashima is a small town girl, born and brought up in a middle class nuclear family. Her father is a mill worker and he had to struggle his entire life to make two ends meet. Aashima loves her family and follows her family values religiously. She is young, kind hearted and generous girl for whom her family is the priority. She wants to share the burden of her father and wants to build a home for him.  Also Read – ‘Playing Jojo was emotionally exhausting’On the other hand Girish Roy Chowdhury is the owner of saree mill in which Aashima’s father is an employee. Girish hails from an influential family in Murshidabad and has built his empire with his own hard work and persistence. His principles are based on the experiences of the life. Though Aashima and Girish belong to different worlds , are different personalities but similarity between them is they live for their families. As the story unfolds we will see the journey of these two strangers, with their share of trials and tribulations , coming from different worlds, different mindsets but as destiny has it but will always be bonded by the thread of love , sacrifice and devotion that is why it will hold the title of being a Pavitra Bandhan- Do Dilon Ka. Yash Tonk, Hritu Dudhani, Yamini Thakur, Shabnam Sayeed, Shailley Kaushik, Munni Jha, Shalini Arora, Rajat Dahiya are main cast in this serial.The serial will be aired every Monday-Friday, 9 September onwards at 8.30 PM only on DD National.last_img read more


CID takes over probe of Kajipara blast


first_imgKolkata: The Criminal Investigation Department (CID) of the state has taken over investigation of the Kajipara blast case. On Wednesday, all the documents and evidences have been handed over to CID by the Barrackpore Police.Immediately after the investigation was handed over, a CID team led by Deputy Inspector General (DIG) Pranav Kumar visited the spot in the afternoon. Apart from CID, a team from the Central Forensic Science Laboratory (CFSL) also visited the spot. Also Read – Rain batters Kolkata, cripples normal lifeSources informed that as per direction from Chief Minister Mamata Banerjee, CID took over investigation of the case. On Wednesday afternoon, investigators visited the flats in the building in front of which the blast took place on Tuesday. The owners and residents of the flats were also questioned.Later, CID officials measured the distance of damaged points from the blast spot. The shutter opposite the blast spot, which was also damaged, was opened. After opening the shutter it was found that a splinter had penetrated the shutter and damaged a showcase inside. Also Read – Speeding Jaguar crashes into Mercedes car in Kolkata, 2 pedestrians killedCID officials also looked for Close Circuit Television (CCTV) cameras present in the locality, to find out what actually happened. As no CCTV camera was available, sleuths turned towards the conventional method of enquiry by questioning the locals. According to CID sources, it is being suspected that the bomb which exploded on Tuesday was bigger than average socket bombs. Ammonium nitrate and acid were also used to intensify the blast. The cap at the bottom of the bomb was tighter than the upper one. As a result, most of the explosion was directed upwards, which cracked the windows inside the blast radius. Experts have collected samples and sent them for necessary examination.last_img read more