Citation: Single-photon source may meet the needs of quantum communication systems (2006, November 9) retrieved 18 August 2019 from https://phys.org/news/2006-11-single-photon-source-quantum.html Further, powerful quantum computers could solve problems that are impossible for today’s computers, and quantum cryptography could potentially provide absolute security for these systems.In the past few years, scientists have developed single-photon sources using innovative tools: quantum dots, single atoms and ions, and color centers are a few possibilities. However, all of these potential sources have shortcomings, in either complicated setups or insufficient production. Now, scientists Shuai Chen et al. have developed a controllable single-photon source using atomic quantum memory for generating and storing single photons to be used at a predetermined time. As they report in a recent issue of Physical Review Letters, “such a single-photon source is well-suited for future large-scale realization of quantum communication and linear optical quantum computation.” “Single-photon sources guarantee the absolute security in quantum communication networks,” co-author Zhen-Sheng Yuan told PhysOrg.com. “While developing this single-photon source, we focused on how to obtain a long memory time of the single excitations in the atomic ensemble, and how to convert the single excitations into single photons with a high efficiency.”In the experimental setup, the scientists used Raman scattering, shining a laser pulse at an ensemble of cold rubidium atoms. As the laser light hits the atoms, single excitations in the atomic ensemble can either be generated or they can be converted into single photons. Detecting the newly created photons can generate single spin excitations in the cold atomic ensemble, which makes up the quantum memory—so-called because light-based information is being stored in matter. The single spin excitations can in turn be converted into single photons at a predetermined time, resulting in a controllable single-photon source. Chen et al.’s setup could produce 600 single spin excitations per second, translating to 15 single-photon detections per second.One of the most significant advantages of this quantum memory-based single-photon source is the ability to increase the number of single photons available. With the help of a feed-back circuit, Chen et al. could significantly enhance the production rate of single photons, as their properties align with those of the laser (spatial mode, bandwidth/intensity, frequency). “Compared with the other single-photon source without quantum memory, the greatest advantage here is that one can construct a quantum communication network with a much lower cost of resources because of the scalable property,” said Yuan.In principle, the spin excitation can be stored for up to 300 microseconds, and generate a single photon at any time. Because of the feedback circuit, this quantum memory-based photon source could likely provide enough single photons for a large number of quantum repeaters, a requirement for long-distance quantum communication networks.Citation: Chen, Shuai, Chen, Yu-Ao, Strassel, Thorsten, Yuan, Zhen-Sheng, Zhao, Bo, Schmiedmayer, Jorg, and Pan, Jian-Wei. “Deterministic and Storable Single-Photon Source Based on a Quantum Memory.” Physical Review Letters 97, 173004 (2006).By Lisa Zyga, Copyright 2006 PhysOrg.com One of the largest challenges for building quantum communications networks involves having single photons, which are needed to ensure the security and efficiency of quantum systems. With an adequate supply of single photons, quantum communications systems could send information at nearly the speed of light, compared with the electron speed (and resistance) in classical systems. This icon demonstrates the single photon source: When a laser beam (called Write, shown in green) hits the cold atomic cloud, a single spin excitation can be generated accompanying a Raman photon (shown in blue). Now the single spin excitation is ready for being retrieved to a single photon by another classical laser (called Read). The blue part at bottom right indicates the wavepacket of photons. Credit: Shuai Chen et al. 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.
The new study suggests that the universe that came before our own universe was its identical twin. Image credit: NASA and ESA. Satellites assisting look into hurricanes Until very recently, asking what happened at or before the Big Bang was considered by physicists to be a religious question. General relativity theory just doesn’t go there – at T=0, it spews out zeros, infinities, and errors – and so the question didn’t make sense from a scientific view. Explore further That means that our universe today, roughly 13.7 billion years after the bounce, would share many of the same properties of the pre-bounce universe at 13.7 billion years before the bounce. In a sense, our universe has a mirror image of itself, with the Big Bang (or bounce) as the line of symmetry. “In the universe before the bounce, all the general features will be the same,” said Singh. “It will follow the same dynamical equations, the Einstein’s equations when the universe is large. Our model predicts that this happens when the universe becomes of the order 100 times larger than the Planck size. Further, the matter content will be the same, and it will have the same evolution. Since the pre-bounce universe is contracting, it will look as if we were looking at ours backward in time.”Specifically, Corichi and Singh calculate that the change in relative fluctuations across the bounce is less than 10-56, a number which becomes even smaller for universes that grow larger than 1 megaparsec (our universe is somewhere between 3,000 and 6,000 megaparsecs). As the researchers explain, having an identical twin universe would not necessarily mean that every single feature of both universes would be identical. For instance, it doesn’t imply that there was another you that existed at some point, a person who has already lived your life. “If one were able to look at certain microscopic properties with a very strong microscope – a very high-energy experiment probing the Planck scale – one might see differences in some quantities, just as one might see that twins have different fingerprints or one has a mole and the other does not, or a different DNA,” Singh said.As Singh explained, there are still many questions regarding the details of the possible pre-bounce universe. “The biggest question is whether these features survive when we consider more complex situations,” he said. “For example, one would like to know whether some structures present in the previous universe – like galaxies – will leave some imprint in the new expanding one that will give rise to identical structure or just ‘similar.’ For instance, it could happen that, in the previous universe, galaxies formed in a different way, so one might have a different distribution of galaxies on the other side. We will be able to answer this question when we understand these models.” Ultimately, Corichi and Singh’s model might even tell us what a future universe would look like. Depending on how fast our present universe is accelerating – which will ultimately determine its fate – there’s a possibility that a generalization of the model would predict a re-collapse of our own universe.“Such a universe will have many bounces from one branch to another,” Singh said. “It is also possible that universes in different branches will be identical.”More information: Corichi, Alejandro, and Singh, Parampreet. “Quantum bounce and cosmic recall.” Arxiv:0710.4543v2. Accepted for publication in Physical Review Letters.Copyright 2008 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. But in the past few years, a new theory called Loop Quantum Gravity (LQG) has emerged. The theory suggests the possibility of a “quantum bounce,” where our universe stems from the collapse of a previous universe. Yet what that previous universe looked like was still beyond answering.Now, physicists Alejandro Corichi from Universidad Nacional Autónoma de México and Parampreet Singh from the Perimeter Institute for Theoretical Physics in Ontario have developed a simplified LQG model that gives an intriguing answer: a pre-Big Bang universe might have looked a lot like ours. Their study will appear in an upcoming issue of Physical Review Letters.“The significance of this concept is that it answers what happened to the universe before the Big Bang,” Singh told PhysOrg.com. “It has remained a mystery, for models that could resolve the Big Bang singularity, whether it is a quantum foam or a classical space-time on the other side. For instance, if it were a quantum foam, we could not speak about a space-time, a notion of time, etc. Our study shows that the universe on the other side is very classical as ours.”The finding builds on previous research, with some important differences. Last year, Penn State physicist Martin Bojowald used a simplified version of LQG to show that a universe “on the other side” of the bounce could have existed. However, although that model produced valid math, no observations of our current universe could have lead to any understanding of the state of the pre-bounce universe, as nothing was preserved across the bounce. Bojowald described this as a sort of “cosmic amnesia.”But Corichi and Singh have modified the simplified LQG theory further by approximating a key equation called the quantum constraint. Using their version, called sLQG, the researchers show that the relative fluctuations of volume and momentum in the pre-bounce universe are conserved across the bounce. “This means that the twin universe will have the same laws of physics and, in particular, the same notion of time as in ours,” Singh said. “The laws of physics will not change because the evolution is always unitary, which is the nicest way a quantum system can evolve. In our analogy, it will look identical to its twin when seen from afar; one could not distinguish them.” Citation: Before the Big Bang: A Twin Universe? (2008, April 9) retrieved 18 August 2019 from https://phys.org/news/2008-04-big-twin-universe.html 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.
Cataclysmic variables (CVs) are binary star systems consisting of a white dwarf and a normal star companion. They irregularly increase in brightness by a large factor, then drop back down to a quiescent state. Polars are a subclass of cataclysmic variables, distinguished from other CVs by the presence of a very strong magnetic field in their white dwarfs.Although over 140 polars have been detected to date, only 33 of them have been identified as eclipsing systems. Hence, every new addition to the still relatively short list of eclipsing polars is very important for creating a reliable sample of such objects. Building a larger database of these systems would offer astronomers more opportunities to study magnetic accretion in binaries.Now, a group of astronomers led by Hannes Breytenbach of South African Astronomical Observatory (SAAO) in Cape Town, South Africa, reports the finding of a new magnetic CV, which they believe is a synchronized polar. The discovery was made using the recently commissioned MASTER-SAAO telescope, which identified the new object as a transient source. Follow-up observations provided more insights into the nature of this source.”Here, we report on the discovery of a new eclipsing cataclysmic variable from the MASTER-SAAO optical transient survey, MASTER OT J061451.70–272535.5 (hereafter J0614–27),” the researchers wrote in the paper.The astronomers found that MASTER OT J061451.70–272535.5 eclipses with a period of 2.08 hours. The eclipse light curve of this system showcases a peculiar morphology as observations show an initial dip, where the object’s brightness drops to about 50 percent of the pre-eclipse level before gradually increasing again in brightness. Afterward, the second rapid ingress is observed, where the brightness drops by around 60 to 80 percent, what is followed by a more gradual decrease to zero flux.The authors of the paper concluded that a light curve with such characteristics is result of an initial obscuration of the accretion hot-spot on the magnetic white dwarf by the accretion stream. This is followed by an eclipse of both the hot spot and the partially illuminated stream by the red dwarf donor star.According to the study, the white dwarf in the system has a radius of about 0.012 solar radii, and a mass between 0.5 and 0.86 solar masses. The red dwarf donor star is approximately five times smaller and six times less massive than our sun. The stars are separated from each other by about 3.25 AU.All in all, the researchers note that the properties of MASTER OT J061451.70–272535.5 suggest that it is a synchronized polar. “The spectral features, along with the structure of the light curve, suggest MASTER OT J061451.70–272535.5 is a new magnetic cataclysmic variable, most likely of the synchronized polar subclass,” the paper reads.Given that many aspects of the nature of MASTER OT J061451.70–272535.5 remain to be investigated, especially its evolutionary status, magnetic field structure and accretion flow, the authors of the study propose further multi-wavelength observations of this system. Explore further Using the Mobile Astronomical System of Telescope-Robots (MASTER), an international team of astronomers has detected a new eclipsing cataclysmic variable. The newfound object, designated MASTER OT J061451.70–272535.5, is most likely of the polar subclass. The finding is detailed in a paper published January 9 on arXiv.org. © 2019 Science X Network Astronomers identify new asynchronous short period polar The on-sky instrument field-of-view in equatorial J2000 coordinates for the photometric data collected on MASTER OT J061451.70–272535.5 from the SAAO. Image credit: Breytenbach et al., 2019. More information: H. Breytenbach et al. Discovery, observations and modelling of a new eclipsing polar: MASTER OT J061451.70-272535.5. arXiv:1901.02669 [astro-ph.SR]. arxiv.org/abs/1901.02669 Citation: New eclipsing cataclysmic variable discovered (2019, January 21) retrieved 18 August 2019 from https://phys.org/news/2019-01-eclipsing-cataclysmic-variable.html 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.
Citation: Student gives possible explanation for female mating preferences that decrease male survival chances (2019, June 6) retrieved 18 August 2019 from https://phys.org/news/2019-06-student-explanation-female-decrease-male.html Having an STI could benefit male animals Pavitra Muralidhar, a Ph.D. student in the Department of Organismic and Evolutionary Biology at Harvard University, has developed a theory to explain why females of some species are more attracted to some males who have a lesser chance of survival. In her paper published in the journal Nature, she outlines her theory of selfish sex chromosomes and how it might work in nature. Mark Kirkpatrick, with the University of Texas has published a News and Views piece in the same journal issue, outlining the work done by Muralidhar. 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. Journal information: Nature More information: Pavitra Muralidhar. Mating preferences of selfish sex chromosomes, Nature (2019). DOI: 10.1038/s41586-019-1271-7 Explore further © 2019 Science X Network Prior research has shown that females of some species are more attracted to males who posses certain impressive features, such as bright plumage. But such research has also shown that males who sport brighter plumage are more likely to be seen and eaten by a predator—so why do the females prefer them? Scientists have been unable to answer this question. But Kirkpatrick notes that there are two main theories. The first is called direct selection, and it is what it sounds like—genes that affect mating preferences are direct targets of selection. An example might be a male that is good at helping tend a nest, and is therefore highly prized by females looking for a mate. The other theory, quite naturally, is called indirect selection, and it involves females choosing mates who have one trait, but get another trait as part of the deal. A female who chooses a male based on plumage, for example, might wind up with a male that also has a good immune system, which is responsible for his great plumage. Unfortunately, neither of these theories explains why a female would go for a male that is clearly less likely to survive; doing so will decrease her male offspring’s chances of survival. Muralidhar suggests this phenomenon is due to what she describes as “selfish sex chromosomes.”Muralidhar’s theory is based on the indirect selection theory, and also sexually antagonistic selection, in which a gene benefits one gender, but could mean harm to the other. She also considers the possibility of an exception in situations where one gender has a pair of same chromosomes and the other has two that are different. She suggests that in cases in which a gene involved in mating is located on the chromosome that is present in only one gender, it can result in only offspring of the same gender carrying that gene, which could benefit them, but it could also bring harm to the offspring of the other gender. She has also carried out a mathematical analysis of her ideas to prove her theory and carried out a study of 36 species, half of which aligned with her “selfish sex chromosome” hypothesis expectations. Human chromosomes during metaphase. Credit: Steffen Dietzel/Wikipedia
Jindal Steel and Power Ltd (JSPL) on Wednesday commissioned the country’s largest billet caster plant at Angul in Odisha.The billet caster plant, which would cast molten steel into semis of various sizes and shapes, would help the company to produce various long products used in construction sector. “We have commissioned India’s largest capacity billet caster plant in Angul within a record time of one year; setting yet another benchmark in the country,” JSPL’s Managing Director and Group CEO Ravi Uppal said in a statement.JSPL has a 2.5 mtpa steel making capacity at Angul and the company plans to raise it to six mtpa.Commissioning of the billet caster plant would enable JSPL to produce long products in addition to flat products already produced at the Angul plant.
Mouth-watering dishes warmed up Delhi’s chilling weather as the annual food festival, Dilli ke Pakwan kicked off in the Capital. The culinary delight of the city saw a large number of visitors pouring from in and around along with foreign tourists. The festival organised by Delhi Tourism was inaugurated by Harsh Vardhan, Union Minister for Science & Technology & Earth Sciences, in the presence of Meenakshi Lekhi, MP, on 24 December at Baba Karag Singh Marg. Ramesh Tiwari, MD & CEO, DTTDC along with Ravi Dadhich, GM, DTTDC were also present at the ocassion. Also Read – ‘Playing Jojo was emotionally exhausting’While speaking on the occasion, Harsh Vardhan congratulated everyone present and expressed his temptation for food at the festival. He said, “Delhi can be termed as mini-India as the city is true example of unity in diversity”. Vardhan also expressed his passion for good health and advised the visitors on eating in a balanced manner. Meenakshi Lekhi feels that cooking is an art and street food vendors should be given at least a three weeks of training to hone their skills, while she also stressed on the role of entrepreneurship for betterment of the nation. Also Read – Leslie doing new comedy special with NetflixNearly 60 food items are being served at this seven-day street food festival to mark the celebration of Delhi’s culinary diversity. From paneer pakoda, aflatooni tikka to chicken lollipop and mouthwatering halwa and gulab jamuns, all popular dishes from the nook and corner of the city are being served with great hospitality.Fifth in the row, Delhi Tourism has been providing an organised platform to food artistes and ensures that festivals alike impact the tourism circuit in the capital. Cuisiniers, halwai, cooks and chefs have specially come to Baba Kharak Singh Marg for giving the city a taste of their best dishes all under one roof. Apart, delicacies of Delhi, the venue witnessed cultural activities like katchi-godi, bhopa-bhopi and a lively puppet show in the evening. A daring fire act was also organised, which left the visitors amazement.Dilli Ke Pakwaan’s colourful and informative souvenir was also launched on the occasion.Cultural evenings which includes blazing bhangra performance, a special food quiz and food talk is also to be held. To mark the celebration of the Christmas, large number of people would be attending the festival to enjoy the festivities.
The National Green Tribunal on Monday flayed Delhi Transport Corporation (DTC) for running its air conditioned buses without passengers for a major part of the day.Irked at improper maintenance of the DTC buses, the green panel also issued notice to the Tata Motors and Ashok Leyland, which supply buses, and directed their senior-most official to be present on next date of hearing.“Unfortunately, we also live in Delhi. Your huge buses ply empty for at least five hours a day. Have you rationalised on this aspect? It is shocking that nobody listens in DTC. Your buses are more than overcrowded. Also Read – Man arrested for making hoax call at IGI airport“We are thinking about afternoon when most of your AC buses, which have a capacity of 60, are empty. After 9.30
With the winter season approaching, we need to take extra care of our lips. Drinking a good amount of water, shuffling your professional lip balm with remedies like butter or ghee, and keeping your tongue in check are critical elements of lip care, says as expert. Abhishek Raj, facial aesthetic expert, has rolled out a few tips to battle the problems:1. Drink water: You know that your skin needs hydration and that happens best with the intake of enough water. The same goes for lips. Though people drink enough water in summers, this intake decreases in winters because we do not sweat in the cold season and feel thirsty. Drinking ample amount of water is necessary to replenish the lost moisture from the skin and the lips. Also Read – Add new books to your shelf2. Hold your tongue: Most of us have a habit of licking our lips now and then with our tongue. This tendency increases whenever the lips feel dry and stretched. You need moisture to keep them soft and hydrated and saliva comes handy for this. But, this proves counter-productive and dries away the lips more.3. Avoid vitamin B deficiency: Insufficient consumption of vitamin B not only affects your digestive system’s functioning but it also affects the health of the lips. Also Read – Over 2 hours screen time daily will make your kids impulsiveThe lips and the corners of the mouth get cracked and deficiency of vitamin B can also cause ulcers in the mouth. Ensure enough intake of vitamin B to keep lips healthy during winters.4. Lip augmentation or hydration procedure: For people who have thin lips and desire a pronounced appearance, dermal fillers like Juvederm are very effective. When administered into the lips, the hyaluronic acid based fillers give volume to the lips.