Study finds single photons cannot exceed the speed of light

first_img Observing a Photon no Longer a Seek-and-Destroy Mission The experimental set-up used to detect the maximum speed of a single photon. Image credit: Shanchao Zhang, et al. ©2011 American Physical Society The scientists found that the precursor wave front of a single photon always travels at c, like the signal velocity of large groups of photons. The main wave packet of a single photon travels no faster than c in any medium, and can be delayed up to 500 ns in a slow light medium where the group velocity is slower than c. “In the slow light (with a group velocity slower than c) case, the central part of the main wave packet follows the group velocity,” Du explained. “When the medium density increases (with more atoms), the slow group velocity decreases. In the fast light or superluminal (with a group velocity faster than c or negative group velocity) case, the main wave packet seems to get ‘confused’ and does not follow the group velocity. …We are sure that the main wave packet cannot travel faster than the precursor, which travels at c.”The results agree with previous studies that have analyzed single photons whose precursor and main wave form have not been separated, which have reported an oscillatory structure. The interference of the precursor and the slightly delayed main waveform can explain this structure.In addition to bringing some closure to the debate on the true speed of information carried by a single photon, the result that single photons cannot travel faster than the speed of light will also likely have practical applications by giving scientists a better understanding of the transmission of quantum information.“Because the amplitude of the rising front of the optical precursor is lossless in any medium (if the rise time of the edge is infinitely short or zero), optical precursors can be used to carry information for optical communication in a loss or absorptive medium, such as underwater optical communication,” Du said, noting that optical precursors experience some loss in practice.At the moment, as Du explained, optical precursor communication is limited by current technology, so it is not yet practical. However, he thinks that the technology will improve to make the method competitive with current communication techniques.“In the future, when the electro-optical technology gets improved such that a step rising time can be as short as <10 femtoseconds and can also be detected by a high-speed photodetector directly, optical precursors will have big applications in optical communication; of course, the single photon precursors can be used for quantum communication.“One may argue that now we have femtosecond lasers which generate pulses with a length of a few femtoseconds,” he noted. “However, we cannot code information on these pulses and they cannot be directly measured by a photodector with current technology.” More information: Shanchao Zhang, et al. “Optical Precursor of a Single Photon.” Physical Review Letters 106, 243602 (2011). DOI: 10.1103/PhysRevLett.106.243602 Copyright 2011 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. Citation: Study finds single photons cannot exceed the speed of light (2011, June 24) retrieved 18 August 2019 from https://phys.org/news/2011-06-photons.htmlcenter_img Explore further (PhysOrg.com) — The rule that nothing can travel faster than the speed of light, c, is one of the most fundamental laws of nature. But since this speed limit has only been experimentally demonstrated for information carried by large groups of photons, physicists have recently speculated as to whether single photons and the information carried by them may be able to exceed the speed of light. In a new study, physicists have performed the difficult task of producing single photons with controllable waveforms, and have shown that single photons also obey the speed limit c. The physicists, led by Professor Shengwang Du from The Hong Kong University of Science and Technology in Hong Kong, China, have published their study on the ultimate speed of a single photon in a recent issue of Physical Review Letters. The results have implications for the maximum speed of information transmission by confirming that single photons obey causality; that is, an effect cannot occur before its cause.“The greatest significance of our work is that our experimental results bring closure to the debate on the true speed of information carried by a single photon,” Du told PhysOrg.com. “It deepens our understanding of the particle-wave duality of photons and the nature of quantum mechanics. It provides people a clear picture of photons (since the name was invented by Einstein more than 100 years ago) and corrects some ‘wrong’ and confusing pictures from before.”With recent advances in technology over the past several years, many groups of scientists have been investigating exactly how fast light can travel. Although previous studies have found that the “group velocity” of light can travel faster than c, the “signal velocity” – the speed at which information travels – cannot. In light of this finding, scientists have wondered whether single photons travel at the group velocity or the signal velocity.To address this question, Du and his coauthors’ demonstration required not only producing single photons, but separating the optical precursor, which is the wave-like propagation at the front of an optical pulse, from the rest of the photon. Previous experiments based on macroscopic electromagnetic wave propagation (involving lots of photons) have shown that the optical precursor is the fastest part in the propagation of an optical pulse. But this study is the first to experimentally show that optical precursors exist at the single-photon level, and that they are the fastest part of the single-photon wave packet.In order to separate the optical precursor from the rest of the photon, the scientists generated a pair of photons, and then passed one of the photons through a group of cold rubidium atoms, while using an electro-optic modulator to shape the photon’s waveform. The atoms had an effect called electromagnetically induced transparency (EIT), which enabled the scientists to separate the single-photon precursors from the main wave packet. As the optical precursor and main wave packet traveled through a second group of rubidium atoms, the scientists took measurements on the speed of the two photon components. 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.last_img read more

Stanford Lab developing new kinds of robot aircraft w Video

first_img(Phys.org) —Researchers at Stanford’s Biometrics and Dexterous Manipulation Laboratory just south of San Francisco, have come up with two new innovations in robotic aircraft design. One is an improvement on jumping robots that mimic the actions of natural flying fish, while the other is a plane that can land on the side of a building. Solar plane aims for new world distance record More information: Project page: bdml.stanford.edu/Main/PerchingHomeResearch paper: Efficient Jumpgliding: Theory and Design Considerations (PDF) Citation: Stanford Lab developing new kinds of robot aircraft (w/ Video) (2013, May 30) retrieved 18 August 2019 from https://phys.org/news/2013-05-stanford-lab-kinds-robot-aircraft.html More impressive perhaps, is the perching Unmanned Aerial Vehicle (UAV) the lab has developed. It’s a plane that flies straight at a building, but prior to crashing into it, pulls up into a stall that allows it to neatly perch against its side. Currently the plane has a very small motor—it gains flight by being tossed by a person standing several yards away from a building. The plane flies in a normal slightly arced horizontal trajectory, but just before reaching the building points its nose straight up at the sky so as to “land” its belly against the side of the building—where it remains hanging until taking off again. The UAV utilizes sensors and processors to gauge the proper time for going nose up, then relies on special hooked metal toes to help it cling to various surfaces. To take off, the hooked toes are pulled back like a cat retracting its claws while the propeller activates. The plane flies upside down as it leaves the wall then spins itself upright once stable. The UAV uses very little power, makes little noise and can use its perching ability to spare its battery. For that reason the research team sees the plane as a means of conducting surveillance. In the future, the plane may have solar cells on its wings to allow for recharging as it perches.center_img © 2013 Phys.org Explore further Robots that can jump as their means of locomotion are useful in situations that are difficult to traverse and also require extreme energy efficiency. To make such robots, researchers tend to look to nature—flying squirrels, snakes and fish all get from one location to another by hurling themselves through the air. In studying nature’s examples, it’s become apparent that wings help a lot, both to extend a jump, and to help ease the landing. To that end, the researchers with this new effort have designed a jumping glider that works in similar ways to flying fish.The plane is made of lightweight material and uses a carbon fiber spring to launch itself. To increase distance, the wings are kept pulled back when launching and extend during the glide back to Earth. This approach allows the plane to sail much farther than simple jumping robots, though it can’t match them in achieving vertical heights. 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.last_img read more

These Days Its Not About the Polar Bears

first_imgClimate science has struggled mightily with a messaging problem. — In Europe, Sander van der Linden, a social psychologist at the University of Cambridge, codesigned an inoculation-based online game with doctoral researcher Jon Roozenbeek. Dr. Cook has designed a high school curriculum as well as a popular online course that presents students first with facts and then a myth about climate change; the students are then asked to resolve the conflict. The well-worn tactic of hitting people over the head with scary climate change facts has proved inadequate at changing behavior or policies in ways big enough to alter the course of global warming. The game was designed to help its hundreds of thousands of players become better consumers of climate-related information. “We’re trying,” Dr. van der Linden said, “to help people help themselves and navigate this post-truth environment.” Read the whole story: The New York Timeslast_img read more

Dad is very possessive about me Alia Bhatt

first_imgLike every father, Mahesh Bhatt is extremely possessive when it comes to daughter Alia but the actor does not mind it as he never intrudes in her space and gives her enough freedom.The 22-year-old star says there are times when her father get irked reading about her dating rumours in the media but he does not force his opinions on her.“I have a beautiful relationship with my father and it is only getting better with each passing year. But yes dad is, not little, but very possessive about me though in a cute way. He is a whiner. Also Read – A fresh blend of fame“But he is not intruding. He will never say, ‘Don’t do this’ but he does get disturbed here and there. He once read something in the paper and called me, saying, ‘Are you dating this guy?’ and I told him had I been dating, he would have known,” Alia told a media person.The “Highway” star feels as her father has been in the industry for a long time now and dealt with such stories about step-sister Pooja, he is better with handling rumours about the actress. “This is not new for him at all, he has been in the industry from such a long time. Having Pooja in his life much before I entered Bollywood has made him experienced at all this…,” she said. Also Read – Martin Freeman confirms ‘Black Panther’ returnDespite being from a filmy family, Alia does not discuss work at home, intentionally.“Right now, all conversations about work at home are banned. After working the whole day, that’s not something I like discussing with my family. I like to talk about other things.” Alia wishes to be directed by her mother Soni Razdan, who is currently working on her project “Love Affair”. “I want to work with her. It is everyone’s wish to work with his/her mother. We worked together as actors in an advertisement and that was cherishable for me. I would love to be directed by her but there has to be the right time and script for it,” Alia said. The young star is geared up for her next release Shaandaar, which is extra special for her as she got a chance to work with seniors like Pankaj Kapur and his actor son Shahid Kapoor. “I am hungry to learn. Opportunities like these are a huge deal for me becasue whenever I see someone senior, that moment becomes one to steal or take away from that person something, which I don’t have. Working with phenomenal actors like Pankaj sir and Shahid was an amazing experience for me.” Working with superstar Shah Rukh Khan in Gauri Shinde’s film and opposite Ranbir Kapoor in director Ayan Mukherjee’s next is “very important” for the actor.“I will start working on Ayan’s project next year. As I said I am hungry as an actor, one can imagine what all I can learn from Ranbir. I have heard he is a great co-star and is amazing to have on sets. So, I am excited to start the film.”last_img read more

Speciallyabled to express themselves through art

first_imgPhysically and mentally challenged artists from across the world have got together to put up an international event of inclusive arts aimed at showcasing their talents and proving that disability is not an obstacle to achieving their dreams.The three-day festival being held at India International Centre from November 14, includes events like an international seminar on ‘Challenges of working with persons with disability for inclusive growth with special focus on inclusive arts’. Also Read – ‘Playing Jojo was emotionally exhausting’‘Sambhav 2015,’ organised by A.L.P.A.N.A, (Association for Learning Performing Arts and Normative Action) a Delhi-based NGO includes a workshop of yoga, an exhibition of paintings, sculptures and artifacts made by challenged artists. Persons with disability from over 24 countries are participating in the annual festival, now in its 10th edition.Chief Minister Arvind Kejriwal in a letter to the NGO said, “I am happy to know A.L.P.A.N.A is organising an international event with performances by challenged artists from different parts of the globe and different regions of India.”  Also Read – Leslie doing new comedy special with NetflixThe NGO was instituted by dancer Alpana Nayak in 2006. Nayak said that unlike western countries, in India work done for the betterment of persons who are challenged is negligible. “The west is working in this field since 1940 but in our country we have recognised it in only towards the late 1990s. Even then after 25 years we can see only 10 per cent to 15 per cent development,” Nayak said.“I don’t want to say that this is only the work of our government but others should also came forward for such a noble cause,” she said. The NGO is being assisted by the ministries of Culture, External Affairs besides Ministry of Social Justice and Empowerment. “We don’t charge any participation fee but we give prizes to those who perform well,” she said. “Challenges which we faced while organising an event like this is the identification of the group of participants worldwide,” she said.“I suffered a major accident at the age of eight in which I lost my left leg. Since, childhood I liked dancing. I used to switch on the television set in a locked room and start dancing. Soon it became my passion and I have performed in 21 countries,” Roma Naupane from Nepal, who was a participant at the event said.Taraneh, a 30-year-old artist from Iran said he was inspired by the soft Indian music.” I have played piano since the age of seven. I have never been to any institute to learn but started myself and soft music has always been my interest area,” he said.last_img read more

Govt puts cork on plying of very heavy trucks on flyovers

first_imgKolkata: With 20 flyovers and bridges in and around the city identified as “weak”, the state government has imposed restrictions on plying of very heavy trucks that cause heavy damage to roads and bridges.This comes on the heels of the incident in which the middle portion of Majerhat Bridge caved in on Tuesday, claiming 3 lives and leaving 24 injured.After holding a high level meeting at Nabanna, Chief Minister Mamata Banerjee said: “There are around 20 flyovers and bridges whose life has expired. We are taking opinions of the experts in this connection. If needed, opinions of technical persons from outside will also be taken.” Also Read – Rain batters Kolkata, cripples normal lifeBesides taking the steps for maintenance of the “old” and “weak” flyovers to avert incidents like the collapse of Majerhat Bridge, the state government is also taking necessary steps to check plying of overloaded vehicles and there will also be restriction on plying of very heavy vehicles. However, there will be no restrictions on plying of the essential goods vehicles.The Chief Minister said: “Very heavy vehicles including the trucks with 20 wheels, cause damage to roads and bridges. Police have been directed not to allow them to ply. Heavy containers from the port can be transported using ro-ro service or through the route of the inland waterways.” Also Read – Speeding Jaguar crashes into Mercedes car in Kolkata, 2 pedestrians killedCiting an example she said: “It will not be tolerated if a vehicle that is supposed to carry a load of 9 tonnes, transports goods weighing 15 tonnes.”The bridges that have been identified as “weak” include Santragachi Bridge, Ultadanga Bridge, Sealdah Flyover, Dhakuria Flyover, Chingrighata Flyover and Belgachia Flyover. While speaking about the repairing of Sealdah Flyover, the Chief Minister said: “Attempts were made for repairing the flyover. But it had not become possible as many vendors have set up their shops under the flyover. I would urge officials of the Kolkata Municipal Corporation (KMC) and Kolkata Police to speak to the people who have set up their stalls, so that repair work can be carried out.” She further said that all public vehicles will be allowed on Santragachi Flyover, but there will be restriction on movement of heavy goods vehicles.She has also directed to remove the flower tubs from Vidyasagar Setu to reduce load on it. At the same time, she gave strict direction that repairing of roads on bridges has to be done by removing the existing layer of asphalt, so that the load on the bridge doesn’t go up.She further said that encroachment of the spaces under flyovers and bridges will not be allowed. “I would direct the police to take steps in this connection. If required, alternate place will be given to the people who reside under the flyovers, as much as possible,” Banerjee said, adding that explosives could also be stored by some people at such places. So, the police have been directed to take necessary steps. There are some places where the help of the Indian Army would also be taken and Chief Secretary Malay De will speak to the army in this connection.Meanwhile, in connection with Vidyasagar Flyover which had collapsed in 2016, opinion of experts has been sought to take the final decision on its fate.IIT Kharagpur and Jadavpur University experts had given their opinions in this regard, but no concrete decision has been taken in the past 2 years, because as per the reports, the buildings in the area would get affected if the remaining portion of the flyover is brought down. There has also been no suggestion for the scenario where it is rebuilt.last_img read more

GAIL to make Rs 5000 cr investment for construction of natural gas

first_imgKolkata: GAIL (India) Limited, the largest state-owned natural gas processing and distribution company, is all set to make a fresh investment of Rs 5,000 crore for the construction of pipelines to supply gas and CNG in Bengal in the next 5-6 years. The project is being executed as a part of Pradhan Mantri Urja Ganga Pipeline Project. A 555 km long pipeline will pass through eight districts in the state, such as Purulia, Bankura, Burdwan, Nadia, Hooghly, Howrah, East Midnapore and North 24-Parganas. Also Read – 3 injured, flight, train services hit as rains lash BengalS Bairagi, CGM (Marketing), GAIL, was speaking to reporters on the sidelines of an interactive session on ‘Gas Industry in West Bengal’, organised by FICCI at a city hotel on Wednesday. The project is expected to be completed up to Durgapur within July 2019, while it would be done up to Kolkata within July 2020. Gas pipeline will then go up to Haldia in East Midnapore. The projects will be done in various phases. Further project activities for execution of pipeline in Bengal up to Haldia and city gas distribution in Kolkata are also expected to commence shortly. The project will usher industrial development in the eastern part of the country by supplying environmentally clean natural gas to fertiliser and power plants, refineries, steel plants and other industries. Also Read – Speeding Jaguar crashes into Mercedes car in Kolkata, 2 pedestrians killedBengal has significant natural gas reserves, which will boost the state’s economy and provide scope for huge employment generation in the future years, if explored commercially. State Finance and Industry minister Amit Mitra, who attended the programme, said that the city gas network and GAIL’s joint venture project will create more employment in the state. This will create huge employment in producing sector, consuming sector and infrastructure sector, which is the intermediation between producers and consumers.last_img read more

Kol to experience chill again Darjeeling sees sun snow

first_imgKolkata: Despite the temperature going up for the past few days, the Kolkata weather office informed that the city will experience the chill once again from Wednesday. Due to the Western disturbances, the cold air flow was obstructed which will resume again.According to the Alipore weather office, the sky will be clear from Wednesday and as a result the north-westerly will flow over the South Bengal districts. Temperature will go down and will hover around 15 degree Celsius for a few days, which is normal at this time of the year. Also Read – Speeding Jaguar crashes into Mercedes car in Kolkata, 2 pedestrians killedMeanwhile, Darjeeling town experienced rain, hail, sleet, light snow with intermittent sunshine on Tuesday. Not that anybody was complaining as locals and tourists alike went about enjoying all of this in a single day. At around 10:30 am with overcast skies there was a spell of sleet and very light snow. This was followed by hail and rain. Finally, it was sleet again till 2:30 pm followed by sunshine for a brief period. “I haven’t ever experienced such different weather conditions in a single day. It was magnificent. As soon as it started to snow we rushed to the Chowrasta. It was a lovely experience for us,” stated Rajesh Sharma, a tourist from Kanpur. Also Read – Bose & Gandhi: More similar than apart, says Sugata BoseThe day temperature hovered around 3.5 degree Celsius. Tourists and local residents thronged the Darjeeling Chowrasta with busy shutterbugs making the most of the weather. The upper reaches including Sadakphu, Phalut along with neighbouring Sikkim also witnessed snowfall. On December 28, 2018, it had snowed in Darjeeling town after a long gap of 10 years. “The snow in the upper reaches along with rain and hail in other parts was caused by western disturbances. There is a trough in the mid-tropospheric westerly at about 85 degree E 25 degree N. However, it is gradually shifting away,” stated Gopinath Raha, in-charge of the MeT office in Gangtok, Sikkim.last_img read more

SER plans to run special trains

first_imgKolkata: The South Eastern Railway has decided to run 11 pairs of special trains between Shalimar andMumbai from April 20 to July 1 and another 11 pairs of special trains between Santragachi and New Jalpaiguri from April 21 to June 30 to clear the extra rush of passengers during summer. Trains get more passengers during summer as people plan trips during holidays. A weekly special train will leave Shalimar station at 6.10 am every Monday and will reach Mumbai at 4.05 pm on Tuesday. Also Read – Rs 13,000 crore investment to provide 2 lakh jobs: MamataIn the opposite direction, the special train will leave Mumbai at 11.05 am every Saturday and will arrive at Shalimar at 9.30 pm the next day, Sunday. “The special train consisting of one AC 2 Tier, two AC 3-Tier, seven sleeper Class and three general second class coaches, will have stoppages at Santragachi, Kharagpur, Tatanagar, Chakradharpur, Rourkela, Jharsuguda, Bilaspur, Raipur, Durg, Gondia, Nagpur, Wardha, Badnera, Akola, Bhusawal, Nasik Road, Igatpuri, Kalyan and Dadar between Shalimar and Mumbai CSMT,” a senior SER official said. Also Read – Lightning kills 8, injures 16 in stateSantragachi-New Jalpaiguri weekly AC special will be leaving Santragachi at 10.25 am every Sunday and will reach New Jalpaiguri at 8.55 pm, the same day. In the opposite direction, New Jalpaiguri-Santragachi special will leave New Jalpaiguri at 11.15 pm every Sunday and will arrive Santragachi at 11.15 am , the next day. This train will have sixteen AC 3-tier coaches and will have stoppages at Bardhaman, Rampurhat, Malda Town, Barsoi, Kishanganj and Alubari Road between Santragachi and New Jalpaiguri. Booking will be available for both the trains from Passenger Reservation System (PRS) and internet with immediate effect.last_img read more

Fresh clash at Sandeshkhali adds fuel to TMCBJP fire

first_imgKolkata: Despite two weeks having passed since the results of Lok Sabha Elections 2019 came out, political clashes continue to rage on in the state.On Saturday, a Trinamool Congress worker was allegedly shot dead by BJP-backed miscreants. Following that, workers of both the parties got involved in a clash and two BJP workers were reportedly killed in the scuffle. On Sunday, a delegation of Trinamool Congress visited Bhangipara in Sandeshkhali and alleged that BJP is trying to spark terror across the state. Trinamool Congress secretary general Partha Chatterjee on Sunday alleged that BJP is trying to instigate violence and killing their workers. Also Read – Rs 13,000 crore investment to provide 2 lakh jobs: MamataAccording to sources, on Saturday afternoon local Trinamool leaders had organised an election review meeting at Bhangipara, Nyazat in Sandeshkhali. Following the meeting, Trinamool had arranged a rally in the area. It has been alleged that BJP workers attacked the Trinamool workers when the rally was underway. Within moments, the area nearly turned into a battlefield. During the clash, a Trinamool worker identified as Kayum Mollah was allegedly shot dead by BJP-backed miscreants. Following the alleged attack by BJP workers, Trinamool workers reportedly retaliated. Also Read – Lightning kills 8, injures 16 in stateOn the other hand, BJP workers alleged that Trinamool-backed miscreants had attacked the BJP workers and killed three of them. But till Sunday night, the death of only two BJP workers was confirmed. The BJP workers who were killed on Saturday were identified as Sukanta Mondal and Pradip Mondal. Upon receiving the news, police from Sandeshkhali police station went to the spot but were not able to reach there as the number of personnel was inadequate. Later, a huge police force along with Rapid Action Force (RAF) was called in. After entering the Bhangipara area, police were obstructed while taking away the bodies of the deceased. Later, police dispersed the mob and recovered the bodies. On Sunday, a delegation team of Trinamool Congress lead by the party’s North 24-Parganas President Jyotipriya Mallick went to Sandeshkhali to assess the situation. The other members of the delegation team were MLA Nirmal Ghosh, Sujit Bose and Tapas Roy. They talked with the local residents and police administration regarding Saturday’s clash. Later, Roy alleged that BJP is in a hurry to take over Bengal and for that they are resorting to violence. “The Union Home Ministry has sought a report on Saturday’s incident in Sandeshkhali. Why has it not been done for other areas? Why is the Home Ministry silent about the Nimta Trinamool worker’s murder or the incident of Barrackpore?” Roy questioned. Mallick also alleged that BJP is using contract killers to murder Trinamool workers. On Sunday, a BJP delegation team went to Sandeshkhali as well and interacted with the families of the two workers who were killed on Saturday. Later, party leadership tried to take the bodies to Kolkata, which was not permitted by the police, anticipating a law and order situation. The bodies were later taken back to Sandeshkhali for cremation.last_img read more