A normal digital camera can take snaps of objects not directly visible to its lens, US researchers have shown. The “ghost imaging” technique could help satellites take snapshots through clouds or smoke.
Physicists have known for more than a decade that ghost imaging is possible. But, until now, experiments had only imaged the holes in stencil-like masks, which limited its potential applications.
Now Yanhua Shih of the University of Maryland, Baltimore, and colleagues at the US Army Research Laboratory, also in Maryland, have now taken the first ghost images of an opaque object – a toy soldier …
Ghost imaging works a bit like taking a flash-lit photo of an object using a normal camera. There the image forms from photons that come out of the flash, bounce off an object and into the lens.
The new technique also uses a light source to illuminate an object. However, the image is not formed from light that hits the object and bounces back. Instead, the camera collects photons that do not hit the object, but are paired through a quantum effect with others that did.
In Shih’s experiments a toy soldier was placed 45 centimetres away from a light source, which was split into two beams. One was pointed at the toy and the other at a digital camera. A photon detector was placed near the soldier, able only to record when a photon bounced off.
Photons from the light source constantly travel down both paths made by the splitter, either towards the soldier and the photon detector, or towards the camera. The detector and camera record a constant stream of those photons, and occasionally record a photon at exactly the same time.
When this happens, there is a direct relationship between where one of the photons hit the soldier, and where the other one hits the camera’s sensor, says Shih, because of a quantum effect called “two-photon interference”.
“If the first photon stops at one point on the object plane, the second photon can only be observed at the corresponding point on the image plane,” he says.
So when the camera records only pixels from photons that hit simultaneously with one reaching the detector, a “ghost image” of the object builds up. The soldier’s image appeared after around 1000 coincidental photons were recorded.
“It is clear that the experimental set-up can be directly applied to sensing applications,” Shih told New Scientist .
The same method could one day be employed to produce satellite images of objects hidden behind clouds or smoke, using the sun’s radiation as the photon source, says Shih. Doing that may require a photon counter beneath the clouds, but could allow a top-down view not possible using conventional methods.
Not everyone agrees that quantum effects are at work in ghost imaging, though. Baris Erkmen and Jeffrey Shapiro of the Massachusetts Institute of Technology, Cambridge, US, point out in a recent paper that classical physics says light sources produce numbers of uncoordinated photons that are not correlated as Shih suggests.
They suspect ghost images might be produced without a quantum link between photon pairs, purely because some photons are just similar. …
Archive for the ‘Physics’ Category
Posted by Anonymous on May 17, 2013
Posted by Anonymous on May 16, 2013
Catching a glimpse of even regular neutrinos – low-energy particles generated in the atmosphere – is difficult enough, but spotting a “cosmic neutrino” left over from the Big Bang has been downright impossible. That is until this cubic kilometer buried under Antartica’s frozen wastes started looking.
Known as the IceCube Neutrino Observatory, this $279 million telescope is located under the Amundsen-Scott South Pole Station in Antarctica. Since its completion in 2010, IceCube has been searching for evidence of the cosmic neutrino via an array of thousands of sensors hung in cascading lines under the ice.
Just as its predecessor, the Antarctic Muon And Neutrino Detector Array (AMANDA), did, IceCube consists of spherical optical sensors called Digital Optical Modules (DOMs), each with a photomultiplier tube (PMT). In all, 86 strings containing 60 DOMs apiece and a total of 5,160 PMTs have been hung a depths ranging from 1,450 to 2,450 meters. IceCube researchers leveraged a unique hot water drill to quickly bore through the ice when installing the array.
When a weakly-interacting neutrino does manage to strike the nucleus of an atom in the ice, the resulting energy release creates a brief flash that is picked up by the DOM and transmitted to a data collection station on the surface. The system detects roughly 100,000 neutrino strikes annually but, until last month, all of them were of the atmospheric variety. In April, IceCube detected a pair of strikes – nicknamed Bert and Ernie – with energy signatures in the TeV range, suggesting an extraterrestrial origin. Since then, the system has spotted an additional 26 potential cosmic neutrino strikes.
The data must still be analyzed and verified by the scientific community but if these really are what researchers think they are, we could soon gain new insight into conditions present mere seconds after the Big Bang.
Posted by Anonymous on May 15, 2013
Scientists hailed CERN’s confirmation of the Higgs Boson in July of 2012, speculating that it could one day make light speed travel possible by “un-massing” objects or allow huge items to be launched into space by “switching off” the Higgs. CERN scientist Albert de Roeck likened it to the discovery of electricity, when he said humanity could never have imagined its future applications.
CERN physicists hope that the “new physics” will provide a more straightforward explanation for the characteristics of the Higgs boson than that derived from the current Standard Model. This new physics is sorely needed to find solutions to a series of yet unresolved problems, as presently only the visible universe is explained, which constitutes just four percent of total matter.”The Standard Model has no explanation for the so-called dark matter, so it does not describe the entire universe – there is a lot that remains to be understood,” says Dr. Volker Büscher of Johannes Gutenberg University Mainz (JGU).
The discovery of the long-sought Higgs boson, an elusive particle thought to help explain why matter has mass, was hailed as a huge moment for science by physicists. In July of 2012, CERN, the European Organization for Nuclear Research in Geneva, announced the discovery of a new particle that could be the long sought-after Higgs boson. The particle has a mass of about 126 gigaelectron volts (GeV), roughly that of 126 protons.
The new evidence came from an enormously large volume of data that has been more than doubled since December 2011. According to CERN, the LHC collected more data in the months between April and June 2012 than in the whole of 2011. In addition, the efficiency has been improved to such an extent that it is now much easier to filter out Higgs-like events from the several hundred million particle collisions that occur every second.
The existence of the Higgs boson was predicted in 1964 and it is named after the British physicist Peter Higgs. It is the last piece of the puzzle that has been missing from the Standard Model of physics and its function is to give other elementary particles their mass. According to the theory, the so-called Higgs field extends throughout the entire universe. The mass of individual elementary particles is determined by the extent to which they interact with the Higgs bosons.
“The discovery of the Higgs boson represents a milestone in the exploration of the fundamental interactions of elementary particles,” said Professor Dr. Matthias Neubert, Professor for Theoretical Elementary Particle Physics and spokesman for the Cluster of Excellence PRISMA at JGU. .,,
Cool. Demassing could be a combination warp drive and transporter. Perfect timing for the new Star Trek movie tomorrow!
Posted by Anonymous on May 12, 2013
Researchers at Cern in Switzerland have tested a novel way to find out if antimatter is the source of a force termed “antigravity”.
Antimatter particles are the “mirror image” of normal matter, but with opposite electric charge.
How antimatter responds to gravity remains a mystery, however; it may “fall up” rather than down.
Now researchers reporting in Nature Communications have made strides toward finally resolving that notion.
Antimatter presents one of the biggest mysteries in physics, in that equal amounts of matter and antimatter should have been created at the Universe’s beginning.
Yet when the two meet, they destroy each other in what is called annihilation, turning into pure light.
Why the Universe we see today is made overwhelmingly of matter, with only tiny amounts of antimatter, has prompted a number of studies to try to find some difference between the two.
Tests at Cern’s LHCb experiment and elsewhere, for example, have been looking for evidence that exotic particles decay more often into matter than antimatter.
Last week, the LHCb team reported a slight difference in the decay of particles called Bs mesons – but still not nearly enough to explain the matter mystery.
One significant difference between the two may be the way they interact with gravity – antimatter may be repelled by matter, rather than attracted to it.
But it is a difference that no one has been able to test – until the advent of Cern’s Alpha experiment.
Alpha is an acronym for Antihydrogen Laser Physics Apparatus – an experiment designed to build and trap antimatter “atoms”.
Just as hydrogen is made of a proton and an electron, antihydrogen is an atom made of their antimatter counterparts antiprotons and positrons.
The trick is not just in making it, but in making it hang around long enough to study it – before it bumps into any matter and annihilates. …
The team has now gone back to their existing data on 434 antihydrogen atoms, with the antigravity question in mind.
“In the course of all the experiments, we release (the antihydrogen atoms) and look for their annihilation,” said Jeffrey Hangst, spokesperson for the experiment.
“We’ve gone through those data to see if we can see any influence of gravity on the positions at which they annihilate – looking for atoms to fall for the short amount of time they exist before they hit the wall,” he told BBC News.
The team has made a statistical study of which antihydrogen atoms went where – up or down – and they are able to put a first set of constraints on how the anti-atoms respond to gravity.
The best limits they can suggest is that they are less than 110 times more susceptible to gravity than normal atoms, and less than 65 times that strength, but in the opposite direction: antigravity. In short, the question remains unanswered – so far.
In other words, the data so far says that antihydrogen atoms have a gravity somewhere between -65 and +110 of normal atoms. More tests needed. Perhaps antihydrogen behaves capriciously, sometimes stronger than normal gravity, sometimes anti-gravity, depending on what color shirt the lead experimenter is wearing.
Posted by Anonymous on May 8, 2013
Russian physicists Alex Gurevich and Anatoly Karashtin claim, in a paper published in the journal Physical Review Letters, they have found more evidence to support their idea that lightning is caused by cosmic rays. The notion was first proposed by Gurevich back in 1992, and has been a source of debate ever since.
No one really knows what causes lightning to form and strike—the prevailing view is that it comes about as a result of collisions between ice crystals in clouds and hail stones. But because clouds and the lightning they produce are unpredictable and hard to pin down, no one has been able to prove this theory. Another theory, proposed by Gurevich twenty years ago, says that lightning is formed from the collisions between cosmic rays and water droplets present in thunderclouds. Now he and a colleague claim to have found evidence to support this idea.
Gurevich suggests that cosmic rays entering thunder clouds cause the air in them to be ionized, resulting in a lot of free electrons floating around. The electronic field already present in the cloud, he continues, leads to the free electrons being boosted to higher energies. When the electrons present in the air collide with water atoms, more electrons are released, setting off what he describes as an avalanche of high-energy particles that eventually give way to a “runaway breakdown”—a discharge that is witnessed as a lightning strike.
As with other theories regarding the origins of lightning, Gurevich’s ideas haven’t been proved. But he hasn’t been sitting still. In this new effort, he along with Karashtin have been measuring and analyzing radio waves in storm clouds as lightning occurs. The idea is that if such strikes are due to interactions with cosmic rays, there should be measurable amounts of radio waves given off.
Gurevich and Karashtin set up equipment to monitor storm clouds over Russia and Kazakhstan—recording radio waves emitted during 3,800 lightning strikes. In analyzing the data, they found that hundreds, and perhaps even thousands of short radio wave pulses occurred just as a bolt of lightning was about to form. Perhaps more importantly, they matched the models Gurevich had built years before. There was on hitch however, the amount of energy delivered by the cosmic rays in the model don’t happen often enough in the real world to cause lightning strikes in most every thunderstorm.
Gurevich and Karashtin say the discrepancy can be explained by the addition of energy into the system by free electrons passing near hydrometeors (bits of hail or water droplets). When that happens, very small discharges result, adding to the total charge. Taken together they say, enough energy is added to cause the cascade that leads to lightning formation.
Posted by Anonymous on May 8, 2013
Seven years ago, Duke University engineers demonstrated the first working invisibility cloak in complex laboratory experiments. Now it appears creating a simple cloak has become a lot simpler.
“I would argue that essentially anyone who can spend a couple thousand dollars on a non-industry grade 3-D printer can literally make a plastic cloak overnight,” said Yaroslav Urzhumov, assistant research professor in electrical and computer engineering at Duke’s Pratt School of Engineering.
Three-dimensional printing, technically known as stereolithographic fabrication, has become increasingly popular, not only among industry, but for personal use. It involves a moving nozzle guided by a computer program laying down successive thin layers of a material—usually a polymer plastic—until a three-dimensional object is produced.
Urzhumov said that producing a cloak in this fashion is inexpensive and easy. He and his team made a small one at Duke which looks like a Frisbee™ disc made out of Swiss cheese. Algorithms determined the location, size and shape of the holes to deflect microwave beams. The fabrication process takes from three to seven hours.
The results of Urzhumov’s experiments were published online in the journal Optics Letters, and the team’s research was supported by the U.S. Army Research Office through a Multidisciplinary University Research Initiative grant.
Just like the 2006 cloak, the newer version deflects microwave beams, but researchers feel confident that in the not-so-distant future, the cloak can work for higher wavelengths, including visible light.
“We believe this approach is a way towards optical cloaking, including visible and infrared,” Urzhumov said. “And nanotechnology is available to make these cloaks from transparent polymers or glass. The properties of transparent polymers and glasses are not that different from what we have in our polymer at microwave frequencies.”
The disk-like cloak has an open area in its center where the researchers placed an opaque object. When microwave beams were aimed at the object through the side of the disk, the cloak made it appear that the object was not there.
“The design of the cloak eliminates the ‘shadow’ that would be cast, and suppresses the scattering from the object that would be expected,” said Urzhumov. “In effect, the bright, highly reflective object, like a metal cylinder, is made invisible. The microwaves are carefully guided by a thin dielectric shell and then re-radiated back into free space on the shadow side of the cloak.”
Urzhumov said that theoretically, the technique can be used to create much larger devices.
“Computer simulations make me believe that it is possible to create a similar polymer-based cloaking layer as thin as one inch wrapped around a massive object several meters in diameter,” he said. “I have run some simulations that seem to confirm this point.”
Posted by Anonymous on May 6, 2013
By using light, researchers at UC Santa Barbara have manipulated the quantum state of a single atomic-sized defect in diamond — the nitrogen-vacancy center — in a method that allows for more unified control than conventional processes.
The method is also more versatile, and opens up the possibility of exploring new solid-state quantum systems.
“In contrast to conventional electronics, we developed an all-optical scheme for controlling individual quantum bits in semiconductors using pulses of light,” said David Awschalom, director of UCSB’s Center for Spintronics & Quantum Computation, professor of physics and of electrical and computer engineering, and the Peter J. Clarke director of the California NanoSystems Institute.
“This finding offers an intriguing opportunity for processing and communicating quantum information with photonic chips.
“The nitrogen-vacancy (NV) center is a defect in the atomic structure of a diamond where one carbon atom in the diamond lattice is replaced by a nitrogen atom, and an adjacent site in the lattice is vacant. The resulting electronic spin around the defect forms a quantum bit — “qubit” — which is the basic unit of a quantum computer.
Current processes require this qubit be initialized into a well-defined energy state before interfacing with it. Unlike classical computers, where the basic unit of information, the bit, is either 0 or 1, qubits can be 0, 1, or any mathematical superposition of both, allowing for more complex operations.
“The initial problem we were trying to solve was to figure out a way that we could place our qubit into any possible superposition of its state in a single step,” said the paper’s first author, physics graduate student Christopher Yale. “It turns out that in addition to being able to do that just by adjusting the laser light interacting with our spin, we discovered that we could generate coherent rotations of that spin state and read out its state relative to any other state of our choosing using only optical processes.”
The all-optical control allows for greater versatility in manipulating the NV center over disparate conventional methods that use microwave fields and exploit defect-specific properties. While the NV center in diamond is a promising qubit that has been studied extensively for the past decade, diamonds are challenging to engineer and grow.
This all-optical methodology, say the researchers, may allow for the exploration of quantum systems in other materials that are more technologically mature. “Compared to how the NV center is usually studied, these techniques in some ways are more general and could potentially enable the study of unexplored quantum systems,” said UCSB physics graduate student Bob Buckley.
Additionally, the all-optical method also has the potential to be more scalable, noted physics graduate student David Christle. “If you have an array of these qubits in order, and if you’re applying conventional microwave fields, it becomes difficult to talk to one of them without talking to the others. In principle, with our technique in an idealized optical system, you would be able focus the light down onto a single qubit and only talk to it.”
While practical quantum computers are still years and years away, the research opens up new paths toward their eventual creation. According to the group, these devices would be capable of performing certain sophisticated calculations and functions far more efficiently than today’s computers can — leading to advances in fields as diverse as encryption and quantum simulation.
Posted by Anonymous on May 6, 2013
One of the dreams for security experts is the creation of a quantum internet that allows perfectly secure communication based on the powerful laws of quantum mechanics.
The basic idea here is that the act of measuring a quantum object, such as a photon, always changes it. So any attempt to eavesdrop on a quantum message cannot fail to leave telltale signs of snooping that the receiver can detect. That allows anybody to send a “one-time pad” over a quantum network which can then be used for secure communication using conventional classical communication.
That sets things up nicely for perfectly secure messaging known as quantum cryptography and this is actually a fairly straightforward technique for any half decent quantum optics lab. Indeed, a company called ID Quantique sells an off-the-shelf system that has begun to attract banks and other organisations interested in perfect security.
These systems have an important limitation, however. The current generation of quantum cryptography systems are point-to-point connections over a single length of fibre, So they can send secure messages from A to B but cannot route this information onwards to C, D, E or F. That’s because the act of routing a message means reading the part of it that indicates where it has to be routed. And this inevitably changes it, at least with conventional routers. This makes a quantum internet impossible with today’s technology
Various teams are racing to develop quantum routers that will fix this problem by steering quantum messages without destroying them. We looked at one of the first last year. But the truth is that these devices are still some way from commercial reality.
Today, Richard Hughes and pals at Los Alamos National Labs in New Mexico reveal an alternative quantum internet, which they say they’ve been running for two and half years. Their approach is to create a quantum network based around a hub and spoke-type network. All messages get routed from any point in the network to another via this central hub.
This is not the first time this kind of approach has been tried. The idea is that messages to the hub rely on the usual level of quantum security. However, once at the hub, they are converted to conventional classical bits and then reconverted into quantum bits to be sent on the second leg of their journey.
So as long as the hub is secure, then the network should also be secure.
The problem with this approach is scalability. As the number of links to the hub increases, it becomes increasingly difficult to handle all the possible connections that can be made between one point in the network and another.
Hughes and co say they’ve solved this with their unique approach which equips each node in the network with quantum transmitters-ie lasers-but not with photon detectors which are expensive and bulky. Only the hub is capable of receiving a quantum message (although all nodes can send and receiving conventional messages in the normal way).
That may sound limiting but it still allows each node to send a one-time pad to the hub which it then uses to communicate securely over a classical link. The hub can then route this message to another node using another one time pad that it has set up with this second node. So the entire network is secure, provided that the central hub is also secure.
The big advantage of this system is that it makes the technology required at each node extremely simple-essentially little more
than a laser. In fact, Los Alamos has already designed and built plug-and-play type modules that are about the size of a box of matches. “Our next-generation [module] will be an order of magnitude smaller in each linear dimension,” they say.
Their ultimate goal is to have one of these modules built in to almost any device connected to a fibre optic network, such as set top TV boxes, home computers and so on, to allow perfectly secure messaging.
Having run this system now for over two years, Los Alamos are now highly confident in its efficacy.
Of course, the network can never be more secure than the hub at the middle of it and this is an important limitation of this approach. By contrast, a pure quantum internet should allow perfectly secure communication from any point in the network to any other. …
Posted by Anonymous on May 2, 2013
Researchers used a scanning tunnelling microscope to move thousands of carbon monoxide molecules to make an animated short film depicting a stick boy playing with his pet atom.
In the one-minute video, individual molecules are repeatedly rearranged to show a boy dancing, throwing a ball and bouncing on a trampoline.
The film, called A Boy and His Atom, is so small it can be seen only when magnified 100 million times.
The ability to move single atoms — the smallest particles of any element in the universe — is crucial to IBM’s research in the field of atomic memory.
The company has honed atomic-manipulation technique after years of researching atomic data storage.
Posted by Anonymous on May 2, 2013
The existence of gravitational waves, or ripples in space and time, has long been predicted, but the elusive phenomenon has eluded scientists for decades. Now researchers are proposing a new method to detect these cosmic wrinkles that relies on the quantum nature of atoms.
Gravitational waves are a consequence of Einstein’s general theory of relativity, which posits that massive objects warp the space-time around them, causing other objects, and even light, to travel along curved paths when they pass nearby. Objects with very strong gravitational fields, such as black holes or dense stars orbiting in binary pairs, should create gravitational waves so powerful they are detectable here on Earth.
However, no experiment has yet found definitive proof that gravity waves exist. A group of physicists led by Stanford University’s Peter Graham hopes to change that, though, with a new detection method they call “atom interferometry.” [The Search for Gravity Waves (Gallery)]
“No one’s yet seen a gravitational wave, but that’s not the reason most of us are really excited about it,” Graham told SPACE.com. “We’re all basically certain gravitational waves are there. But you could build a gravitational wave telescope and use gravitational waves to look at the whole universe.”…
To get around the problem of laser noise, Graham and his colleagues want to use atoms instead of lasers. Instead of splitting a laser beam in two, the scientists plan to essentially split an atom — a prospect made possible by quantum mechanics. According to this theory, particles are less like tiny marbles and more like hazy clouds of probability described by equations called wave functions. They don’t definitively exist in a certain place at a certain time unless pinned down by direct measurements.
Splitting the atom
For atom interferometry, the wave function of an atom is split. “The atom is in a weird quantum mechanical combination of here and there,” Graham said. “If a gravity wave flies through this interferometer, then the two halves of the atom will accelerate with respect to each other because of this gravity wave.”
To measure this acceleration, the experiment would use lasers, potentially introducing the laser noise problem all over again. To avoid this difficulty, the researchers want to launch two atom interferometers on two satellites that would orbit a set distance apart. “If you shine the same laser beam simultaneously on the two atom interferometers, then you get the same noise read into both of the atoms, but the gravitational wave signal is not the same at the two spots, so that’s the key,” Graham said, adding that the laser noise can be compared and subtracted out of the signal.
The experiment works best on spacecraft, rather than on the ground, because the normal vibrations and shaking of the Earth could contaminate measurements made in ground-based detectors. …