Hi-fi single photons

A trade-off between photon source settings and detector specific requirements allows the generation of high-fidelity single photons.

Many quantum technologies-such as cryptography, quantum computing and quantum networks-hinge on the use of single photons. While she was at the Kastler Brossel Laboratory (affiliated with the Pierre and Marie Curie University, École Normale Supérieure and CNRS) in Paris, France, Virginia d'Auria and her colleagues identified the extent to which photon detector characteristics shape the preparation of a photon source designed to reliably generate single photons. In a paper about to be published in EPJ D, the French team determined the value of key source parameters that are necessary to generate high-fidelity single photons.

The problem with photon detectors is that they can be noisy or have a limited ability to detect single photons. Some cannot identify the number of photons; they can only detect their presence. Given the influence of these factors, improving the fidelity of single-photon generation is very challenging. But it is also crucial for their subsequent use in quantum information protocols, including quantum communication and computing.

Single photons are typically generated using two laser beams that are correlated at the quantum level. This means that the detection of a single photon in the first beam heralds the generation of a single photon in the second one.

The authors first reviewed how to describe a detector from a mathematical point of view. They then simulated which photons would be obtained from different initial sources. This led the team to outline the conditions under which the heralding detector can deliver good resolution of the number of photons, as a means of improving the reliability in obtaining single photons. They corroborated their findings using two experimental detectors.

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Solar cell consisting of a single molecule: Individual protein complex generates electric current

An team of scientists, led by Joachim Reichert, Johannes Barth, and Alexander Holleitner (Technische Universitaet Muenchen, Clusters of Excellence MAP and NIM), and Itai Carmeli (Tel Aviv University) developed a method to measure photocurrents of a single functionalized photosynthetic protein system. The scientists could demonstrate that such a system can be integrated and selectively addressed in artificial photovoltaic device architectures while retaining their biomolecular functional properties.

The proteins represent light-driven, highly efficient single-molecule electron pumps that can act as current generators in nanoscale electric circuits.

The interdisciplinary team publishes the results in Nature Nanotechnology this week.

The scientist investigated the photosystem-I reaction center which is a chlorophyll protein complex located in membranes of chloroplasts from cyanobacteria. Plants, algae and bacteria use photosynthesis to convert solar energy into chemical energy. The initial stages of this process -- where light is absorbed and energy and electrons are transferred -- are mediated by photosynthetic proteins composed of chlorophyll and carotenoid complexes. Until now, none of the available methods were sensitive enough to measure photocurrents generated by a single protein. Photosystem-I exhibits outstanding optoelectronic properties found only in photosynthetic systems. The nanoscale dimension further makes the photosystem-I a promising unit for applications in molecular optoelectronics.

The first challenge the physicists had to master was the development of a method to electrically contact single molecules in strong optical fields. The central element of the realized nanodevice are photosynthetic proteins self-assembled and covalently bound to a gold electrode via cysteine mutation groups. The photocurrent was measured by means of a gold-covered glass tip employed in a scanning near-field optical microscopy set-up. The photosynthetic proteins are optically excited by a photon flux guided through the tetrahedral tip that at the same time provides the electrical contact. With this technique, the physicists were able to monitor the photocurrent generated in single protein units.

The research was supported by the German Research Foundation (DFG) via the SPP 1243 (grants HO 3324/2 and RE 2592/2), the Clusters of Excellence Munich-Centre for Advanced Photonics and Nanosystems Initiative Munich, as well as ERC Advanced Grant MolArt (no. 47299).

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Rapid gene machines used to find cause of newborn illnesses

U.S. scientists have sequenced the entire genetic code of four gravely ill newborns and identified genetic diseases in three of them in two days, quick enough to help doctors make treatment decisions.

Doctors behind the preliminary study released on Wednesday say it demonstrates a practical use for whole genome sequencing, in which researchers analyze all 3.2 billion chemical "bases" or "letters" that make up the human genetic code.

"It is now feasible to decode an entire genome and provide interim results back to the physician in two days," said Dr. Stephen Kingsmore, director of the Center for Pediatric Genomic Medicine at Children's Mercy medical center in Kansas City, Missouri, whose study was published in the journal Science Translational Medicine.

The study tested two software programs developed at Children's Mercy that were used in conjunction with a high-speed gene sequencer from Illumina called HiSeq 2500, which can sequence an entire genome in about 25 hours.

The company helped pay for the study and company researchers took part in it.

Next-generation gene sequencing machines have driven down the cost of whole genome sequencing, but making practical use of the data has been more challenging, largely because of the time it takes to analyze all of the data.

As many as a third of babies admitted to a neonatal intensive care unit in the United States have some form of genetic disease. Treatments are currently available for more than 500 diseases, but identifying them quickly has been a problem.

Typically, genetic testing on newborns using conventional methods takes four to six weeks, long enough that the infant has either died or been sent home.

"Up until now, they have really had to practice medicine blindfolded," Kingsmore said in a telephone briefing with reporters.

Dr. Neil Miller, director of informatics at Children's Mercy, said the software programs help doctors identify which genes to test, and analyze the data quickly.

One of these programs, called SSAGA, allows doctors to order this test based on the child's symptoms, without having to know in advance which genes to test for.

The software only maps genes associated with the child's symptoms. SSAGA does this for nearly 600 diseases, but the team is expanding this to include all 3,500 known disease genes, Miller told the briefing.

The team developed a second software program called Runes that helps determine which of the suspected genes was most likely to be the cause of the child's illness.

In the study, the team tested the system on four seriously ill babies whose conditions were suspected of having a genetic cause. Only one of the infants is still alive, a boy born with a rare heart defect that the team discovered is also shared by the child's 6-year-old brother. The infant underwent heart surgery.

The testing also was able to diagnose a rare form of epilepsy in a baby girl, and identify the likely cause of a rare and lethal skin condition in a baby boy, which arose from a new genetic mutation that was not passed down from either parent. The team was unable to find out what caused another boy's heart defect.

"We basically struck out completely, for now anyway," said Dr. Carol Saunders, clinical lab director at the hospital who helped interpreted the study results.

Even though the study did not provide cures for the babies, she said, it could give parents more information about the cause of their child's illness and allow them to make decisions about what kinds of treatments they wanted to pursue.

The test is projected to cost $13,500, but the team believes that may be worth it given the high cost of care in a neonatal intensive care unit, which runs roughly $8,000 per night.

The next move is to broaden the test to include 100 or more babies to determine the benefits, costs and potential problems linked with the testing.

Because the Illumina machine was not available in the United States, the team had to discount the time it took to ship the blood samples to Britain, where the actual sequencing was done.

But Kingsmore said the hospital expects to receive its own HiSeq 2500 machine next month. Eventually, the hospital hopes to have its testing validated, so the researchers can do genetic testing on newborns in hospitals across the United States.

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Sticky paper offers cheap, easy solution for paper-based diagnostics

A current focus in global health research is to make medical tests that are not just cheap, but virtually free. One such strategy is to start with paper -- one of humanity's oldest technologies -- and build a device like a home-based pregnancy test that might work for malaria, diabetes or other diseases.

A University of Washington bioengineer recently developed a way to make regular paper stick to medically interesting molecules. The work produced a chemical trick to make paper-based diagnostics using plain paper, the kind found at office supply stores around the world.

"We wanted to go for the simplest, cheapest starting material, and give it more capability," said Daniel Ratner, a UW assistant professor of bioengineering and lead author of the paper recently published in the American Chemical Society journal Langmuir. "We also wanted to make the system as independent of the end applications as possible, something any researcher could plug into."

Many paper-based diagnostics are made from nitrocellulose, a sticky membrane used in pregnancy tests and by medical researchers to detect proteins, DNA or antibodies in the human immune system.

Ratner hopes to replace that specialized membrane with cheap, ubiquitous paper, and to use it for any type of medical test -- not just the big, biological molecules.

The UW technique uses minimal equipment or know-how. The researchers used a cheap, industrial solvent called divinyl sulfone that can be bought by the gallon and has been used for decades as an adhesive. Ratner's group discovered they could dilute the chemical in water, carefully control the acidity, then pour it into a Ziploc bag and add a stack of paper, shake for a couple of hours, and finally rinse the paper and let it dry.

The dried paper feels smooth to the touch but is sticky to all kinds of chemicals that could be of medical interest: proteins, antibodies and DNA, for example, as well as sugars and the small-molecule drugs used to treat most medical conditions.

"We want to develop something to not just ask a single question but ask many personal health questions," Ratner said. "'Is there protein in the urine? Is this person diabetic? Do they have malaria or influenza?'"

To test their idea, the researchers ran the treated paper through an inkjet printer where the cartridge ink had been replaced with biomolecules, in this case a small sugar called galactose that attaches to human cells. They printed the biomolecules onto the sticky paper in an invisible pattern. Exposing that paper to fluorescent ricin, a poison that sticks to galactose, showed that the poison was present.

Now that they have proven their concept, Ratner said, they hope other groups will use the paper to develop actual diagnostic tests.

Leading proponents of paper-based diagnostics include the UW's Paul Yager, a professor of bioengineering who leads the Microfluidics 2.0 initiative, and George Whitesides, a chemistry professor at Harvard University. Ratner's group is working with a graduate student in Yager's lab to use the paper to print patterns of switchable networks.

Co-authors are Arthur Yu, Jing Shang at the UW; Fang Cheng, a former UW doctoral student now at China's Dalian University of Technology; Bradford Paik at the University of Minnesota; and Justin Kaplan and Rodrigo Andrade at Temple University in Philadelphia. The study was funded by the Washington Research Foundation and the UW's Royalty Research Fund.

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Japan author, "spooky" science up for cut-price Nobels

A Japanese author who writes of love and isolation, researchers into "spooky" quantum physics and experts on economic inequality have all been tipped as possible Nobel Prize-winners ahead of the start to the annual awards on Monday.

Medicine, physics and chemistry laureates will receive their Nobels first in Stockholm next week, followed later by economics. But for many outside the world of science, the literature and peace prizes are the most widely discussed at the dinner table.

Odds at British bookmaker Ladbrokes and Sweden's Unibet put Japanese author Haruki Murakami and Chinese writer Mo Yan in the top two places for the literature prize. An American advocate of non-violent struggle and a Coptic Christian who runs a children's mission in Egypt are favored for the peace prize.

Murakami is very popular in Japan, but has also become well known abroad for his works which deal with isolation and love and bring the surreal into everyday life. Mo's works are rooted in his native China, its history and people.

Other literary names bandied about include Ireland's William Trevor, Syrian poet Adonis, South Korean poet Ko Un, U.S. novelist Philip Roth and singer/songwriter Bob Dylan.

Culture columnist Maria Schottenius of Swedish newspaper Dagens Nyheter said that despite the odds, the choice of the Nobel committee was always unpredictable.

"Last year we had a poet, now it could be a storyteller like Philip Roth," Schottenius said. Swedish poet Thomas Transtromer won the prize in 2011.

For the peace prize, betting agencies favour Gene Sharp, an American advocate of non-violent struggle and Maggie Gobran, a Coptic Christian who runs a children's mission in Egypt, but there is no clear candidate.

TELEPORTATION

Researchers who wrote the rulebook for quantum teleportation, described as "spooky" by Albert Einstein, are among the 2012 Thomson Reuters tips for science.

Research into the inner workings of the cell could be in line for the medicine prize, according to Nobel prediction expert David Pendlebury. His annual forecasts are based on the company's "Web of Knowledge" data on how often a scientist's published papers are cited as a basis for further investigation.

For economics, Thomson Reuters has predicted U.S. and British experts on pricing financial assets, how to measure inequality or how to understand market volatility, as possible winners.

In chemistry, Akira Fujishima at Tokyo University of Science, could be in the running for discoveries of new uses for titanium dioxide, long used mainly as an ingredient for paint.

Though their prestige remains undiminished, the cash element for the annual prizes created in dynamite tycoon Alfred Nobel's will to recognize achievements in medicine, physics, chemistry, literature and peace -- economics was added in the 1960s at the behest of the Swedish central bank -- have been cut by 20 percent to 8 million crowns ($1.20 million).

The Nobel Foundation which oversees the wealth left by the businessman said it was worried about future returns and that it had been hit by overspending in previous years' prize seasons.

The deliberations on all the prizes are wrapped in secrecy. For literature, the 18 members of the Swedish Academy who award the Nobel prize for literature, are only allowed to discuss the prize within the walls of the Academy itself.

It is extremely rare for the name of any winner to leak out, though 2010 was an exception when newspaper Svenska Dagbladet got a tip that test tube baby pioneer Robert Edwards had won.

The prize for medicine will begin the Nobel season on Monday, followed by physics and chemistry over the next two days. The literature prize will likely be handed out on Thursday October 11 or 18th, while the peace prize will be awarded in Oslo on Friday October 12th and the prize for economics on October 15th.

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Researchers create most detailed, 3-D rendering of key region of mammal lung

Amidst the extraordinarily dense network of pathways in a mammal lung is a common destination. There, any road leads to a cul-de-sac of sorts called the pulmonary acinus. This place looks like a bunch of grapes attached to a stem (acinus means "berry" in Latin).

Scientists have struggled to understand more specifically what happens in this microscopic, labyrinthine intersection of alleys and dead ends. To find out, a research team led by the University of Iowa created the most detailed, three-dimensional rendering of the pulmonary acinus. The computerized model, derived from mice, faithfully mimics each twist and turn in this region, including the length, direction and angles of the respiratory branches that lead to the all-important air sacs called alveoli.

"The imaging and image analysis methods described here provide for branch morphometry at the acinar level that has not been available previously," the researchers write in the paper, published this week in the online early edition of the Proceedings of the National Academy of Sciences.

The model is important, because it can help scientists understand where and how lung diseases emerge as well as the role the pulmonary acinus plays in the delivery of drugs, such as those commonly administered with inhalers.

"These methods allow us to understand where in the lung periphery disease begins and how it progresses," says Eric Hoffman, professor in the departments of radiology, medicine, and biomedical engineering at the UI and corresponding author on the paper. "How do gases and inhaled substances get there and do they accumulate in one or another acinus? How do they swirl around and clear out? We just don't have a complete understanding how that happens."

As an example, Hoffman said the model could be used to determine how smoking-induced emphysema originates. "It has been hypothesized recently that it begins with the loss of peripheral airways rather than the lung air sacs," he says, citing ongoing research by James Hogg at the University of British Columbia, who was not involved in this study. It also could shed light and lead to more effective treatment of chronic obstructive pulmonary disease, which causes irreversible damage to the lung, says Dragos Vasilescu, first author on the paper who based his thesis on the research while a graduate student at the UI.

For years, the best that lung anatomy pioneers such as study co-corresponding author Ewald Weibel, professor emeritus of anatomy at the University of Bern, could do to study specific areas of a lung was to make measurements in two dimensions or create 3D casts of a lung's air spaces. The techniques, while giving the earliest insights into a lungs's makeup and functioning, had their limitations. For one, they did not directly replicate a lung's structure in real life, and they could not convey how various parts act together as a whole. Yet advances in imaging and computation have enabled researchers to more fully explore how gases and other inhaled substances act in the lung's furthest recesses.

In this study, the team worked with 22 pulmonary acini culled from young and old mice. They then set to "reconstruct" the acini based on micro computed tomography imaging of scanned lungs in mice and extracted from them. The extracted lungs were preserved in a way that kept the anatomy intact -- including the tiny air spaces required for successful imaging. From that, the researchers were able to measure an acinus, estimate the number of acini for each mouse lung and even count the alveoli and measure their surface area. The mouse lung, in its structure and function, is remarkably similar to the human lung. That means researchers can alter the genetics of a mouse and see how those changes affect the peripheral structure of the lung and its performance.

Already, the researchers found in the current study that mouse alveoli increase in number long past the two weeks that at least one previous study had indicated. Hoffman adds that a separate study is needed to determine whether humans, too, increase the number of air sacs past a certain, predetermined age.

The researchers next aim to use the model to more fully understand how gases interact with the bloodstream within the acini and the alveoli.

"Our imaging and image-analysis methodologies enable new ways to investigate the lung's structure and can now be used to further investigate the normal healthy-lung anatomy in humans and be used to visualize and assess the pathological changes in animal models of specific structural diseases," says Vasilescu, who is a postdoctoral researchfellow at the University of British Columbia.

Contributing authors include Zhiyun Gao, post-doctoral researcher in the department of electrical engineering at the UI; Punam Saha, associate professor in the department of electrical engineering at the UI; Leilei Yin, at the University of Illinois; Ge Wang, former radiology professor at the UI and now at Virginia Polytechnic Institute and State University; Beatrice Haefeli-Bleuer, of the University of Bern; and Matthias Ochs, of Hannover Medical School in Germany.

The National Institutes of Health, the National Science Foundation and the Swiss National Science Foundation funded the research.

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Switching cause and effect in quantum world? A causes B causes A

One of the most deeply rooted concepts in science and in our everyday life is causality; the idea that events in the present are caused by events in the past and, in turn, act as causes for what happens in the future. If an event A is a cause of an effect B, then B cannot be a cause of A. Now theoretical physicists from the University of Vienna and the Université Libre de Bruxelles have shown that in quantum mechanics it is possible to conceive situations in which a single event can be both, a cause and an effect of another one.The findings will be published this week in Nature Communications.Although it is still not known if such situations can be actually found in nature, the sheer possibility that they could exist may have far-reaching implications for the foundations of quantum mechanics, quantum gravity and quantum computing.Causal relations: who influences whomIn everyday life and in classical physics, events are ordered in time: a cause can only influence an effect in its future not in its past. As a simple example, imagine a person, Alice, walking into a room and finding there a piece of paper. After reading what is written on the paper Alice erases the message and leaves her own message on the piece of paper. Another person, Bob, walks into the same room at some other time and does the same: he reads, erases and re-writes some message on the paper. If Bob enters the room after Alice, he will be able to read what she wrote; however Alice will not have a chance to know Bob's message. In this case, Alice's writing is the "cause" and what Bob reads the "effect." Each time the two repeat the procedure, only one will be able to read what the other wrote. Even if they don't have watches and don't know who enters the room first, they can deduce it by what they write and read on the paper. For example, Alice might write "Alice was here today," such that if Bob reads the message, he will know that he came to the room after her.Quantum violation of causal orderAs long as only the laws of classical physics are allowed, the order of events is fixed: either Bob or Alice is first to enter the room and leave a message for the other person. When quantum mechanics enters into play, however, the picture may change drastically. According to quantum mechanics, objects can lose their well-defined classical properties, such as e.g. a particle that can be at two different locations at the same time. In quantum physics this is called a "superposition."Now an international team of physicists led by Caslav Brukner from the University of Vienna have shown that even the causal order of events could be in such a superposition. If -- in our example -- Alice and Bob have a quantum system instead of an ordinary piece of paper to write their messages on, they can end up in a situation where each of them can read a part of the message written by the other. Effectively, one has a superposition of two situations: "Alice enters the room first and leaves a message before Bob" and "Bob enters the room first and leaves a message before Alice.""Such a superposition, however, has not been considered in the standard formulation of quantum mechanics since the theory always assumes a definite causal order between events," says Ognyan Oreshkov from the Université Libre de Bruxelles (formerly University of Vienna). "But if we believe that quantum mechanics governs all phenomena, it is natural to expect that the order of events could also be indefinite, similarly to the location of a particle or its velocity," adds Fabio Costa from the University of Vienna.The work provides an important step towards understanding that definite causal order might not be a mandatory property of nature. "The real challenge is finding out where in nature we should look for superpositions of causal orders," explains Caslav Brukner from the Quantum Optics, Quantum Nanophysics, Quantum Information group of the University of Vienna.View the original article here

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