Archive for the ‘physics’ Category


This diagram represents the the light of a neutron star passing through an area of space where vacuum birefringence, a theory of quantum electrodynamics, is occurring. The light’s magnetic and electric fields (red and blue arrows) are altered and aligned as they pass through the empty space near a neutron star, suggesting the intense magnetic field there creates virtual particles that affect the light.

About 400 light-years from here, in the area surrounding a neutron star, the electromagnetic field of this unbelievably dense object appears to be creating an area where matter spontaneously appears and then vanishes.

Quantum electrodynamics (QED) describes the relationships between particles of light, or photons, and electrically charged particles such as electrons and protons. The theories of QED suggest that the universe is full of “virtual particles,” which are not really particles at all. They are fluctuations in quantum fields that have most of the same properties as particles, except they appear and vanish all the time. Scientists predicted the existence of virtual particles some 80 years ago, but we have never had experimental evidence of this process until now.


SEEING THE INVISIBLE

How can we possibly see such a thing? One of the properties virtual particles have in common with actual particles is that they both affect light. In addition, intense magnetic fields are thought to excite the activity of virtual particles, affecting any light that passes through that space more dramatically.

So a team of astronomers pointed our most advanced ground-based telescope, the European Southern Observatory’s Very Large Telescope (VLT), at one of the densest objects we know of: a neutron star.

Neutron stars have magnetic fields that are billions of times stronger than our sun’s. Using the VLT, Roberto Mignani from the Italian National Institute for Astrophysics (INAF) and his team observed visible light around the neutron star RX J1856.5-3754 and detected linear polarization—or the alignment of light waves according to external electromagnetic influences—in the empty space around the star. This is rather odd, because conventional relativity says that light should pass freely through a vacuum, such as space, without being altered. The linear polarization was to such a degree (16 degrees to be precise) that the only known explanations are theories of QED and the influence of virtual particles.

“According to QED, a highly magnetized vacuum behaves as a prism for the propagation of light, an effect known as vacuum birefringence,” Mignani says. “The high linear polarization that we measured with the VLT can’t be easily explained by our models unless the vacuum birefringence effects predicted by QED are included.”


HOW DO YOU MEASURE SOMETHING THAT DOESN’T ALWAYS EXIST?

Vacuum birefringence was first predicted in the 1930s by Werner Heisenberg and Hans Heinrich Euler. It was an exciting time for the development of quantum mechanics, when many of the advanced theories still studied today were developed.

In the quantum realm, matter behaves very strangely to say the least. It violates both Newton’s classical laws of physics and Einstein’s theories of relativity and gravity. Matter can exist in two separate places at once. Entangled particles, separated by miles, can influence each other instantaneously. As far as we can tell, the smallest building blocks of matter exist with multiple, or even infinite properties, known as quantum states, until they are observed or measured.

Fortunately, we can model and even predict some quantum phenomena, and we do this using wave functions. A wave, such as a sine curve, is represented by an equation that has multiple correct values to make it a true mathematical statement. This same basic principle can be applied to physical models of particles that exist in different locations, or with different properties, or sometimes don’t exist at all. When the particles are measured, the wave function collapses, and the matter only exists with one set of properties like you would expect. The researchers were able to measure the virtual particles around a neutron star indirectly, by measuring the light that passes through them.

These concepts are so profound that Einstein and Niels Bohr famously debated, at length, whether the universe even exists as a tangible smattering of matter across the void, or if it is a fluid conglomerate of infinite possible realities until we observe it. The first experimental evidence of vacuum birefringence—absurdly strong electromagnetic forces tugging at the very foundations of matter—reminds us that this is still an open-ended question.

http://www.popularmechanics.com/space/a24076/neutron-star-particles-spring-into-existence/


Physicists are putting themselves out of a job, using artificial intelligence to run a complex experiment. The experiment created an extremely cold gas trapped in a laser beam, known as a Bose-Einstein condensate, replicating the experiment that won the 2001 Nobel Prize.

Physicists are putting themselves out of a job, using artificial intelligence to run a complex experiment.

The experiment, developed by physicists from The Australian National University (ANU) and UNSW ADFA, created an extremely cold gas trapped in a laser beam, known as a Bose-Einstein condensate, replicating the experiment that won the 2001 Nobel Prize.

“I didn’t expect the machine could learn to do the experiment itself, from scratch, in under an hour,” said co-lead researcher Paul Wigley from the ANU Research School of Physics and Engineering.

“A simple computer program would have taken longer than the age of the Universe to run through all the combinations and work this out.”

Bose-Einstein condensates are some of the coldest places in the Universe, far colder than outer space, typically less than a billionth of a degree above absolute zero.

They could be used for mineral exploration or navigation systems as they are extremely sensitive to external disturbances, which allows them to make very precise measurements such as tiny changes in the Earth’s magnetic field or gravity.

The artificial intelligence system’s ability to set itself up quickly every morning and compensate for any overnight fluctuations would make this fragile technology much more useful for field measurements, said co-lead researcher Dr Michael Hush from UNSW ADFA.

“You could make a working device to measure gravity that you could take in the back of a car, and the artificial intelligence would recalibrate and fix itself no matter what,” he said.

“It’s cheaper than taking a physicist everywhere with you.”

The team cooled the gas to around 1 microkelvin, and then handed control of the three laser beams over to the artificial intelligence to cool the trapped gas down to nanokelvin.

Researchers were surprised by the methods the system came up with to ramp down the power of the lasers.

“It did things a person wouldn’t guess, such as changing one laser’s power up and down, and compensating with another,” said Mr Wigley.

“It may be able to come up with complicated ways humans haven’t thought of to get experiments colder and make measurements more precise.

The new technique will lead to bigger and better experiments, said Dr Hush.

“Next we plan to employ the artificial intelligence to build an even larger Bose-Einstein condensate faster than we’ve seen ever before,” he said.

The research is published in the Nature group journal Scientific Reports.

https://www.sciencedaily.com/releases/2016/05/160516091544.htm

schrodinger-cat-two-boxes

By Tia Ghose

Bizarrely behaving light particles show that the famous Schrödinger’s cat thought experiment, meant to reveal the strange nature of subatomic particles, can get even weirder than physicists thought.

Not only can the quantum cat be alive and dead at the same time — but it can also be in two places at once, new research shows.

“We are showing an analogy to Schrödinger’s cat that is made out of an electromagnetic field that is confined in two cavities,” said study lead author Chen Wang, a physicist at Yale University. “The interesting thing here is the cat is in two boxes at once.”

The findings could have implications for cracking unsolvable mathematicalproblems using quantum computing, which relies on the ability of subatomic particles to be in multiple states at once, Wang said.

Cat experiment

The famous paradox was laid out by physicist Erwin Schrödinger in 1935 to elucidate the notion of quantum superposition, the phenomenon in which tiny subatomic particles can be in multiple states at once.

In the paradox, a cat is trapped in a box with a deadly radioactive atom. If the radioactive atom decayed, the cat was a goner, but if it had not yet decayed, the cat was still alive. Because, according to the dominant interpretation of quantum mechanics, particles can exist in multiple states until they are measured, logic dictated that the cat would be both alive and dead at the same time until the radioactive atom was measured.

Cat in two boxes

The setup for the new study was deceptively simple: The team created two aluminum cavities about 1 inch (2.5 centimeters) across, and then used a sapphire chip to produce a standing wave of light in those cavities. They used a special electronic element, called a Josephson Junction, to superimpose a standing wave of two separate wavelengths of light in each cavity. The end result was that the cat, or the group of about 80 photons in the cavities, was oscillating at two different wavelengths at once — in two different places. Figuring out whether the cat is dead or alive, so to speak, requires opening both boxes.

Though conceptually simple, the physical setup required ultrapure aluminum and highly precise chips and electromagnetic devices to ensure that the photons were as isolated from the environment as possible, Wang said.

That’s because at large scales, quantum superposition tends to disappear almost instantaneously, as soon as these superimposed subatomic particles whose fates are linked interact with the environment. Most of the time, this so-called decoherence would happen so quickly that researchers would have no time to observe the superposition, Wang said. So devices that keep coherence (or keep the particles in superposition) for long periods of time, known as the quality factor, is extremely important, Wang added.

“The quality of these things determines once you put a single excitation into the system, how long does it live, or does it die away,” Wang told Live Science.

If the excitation of the system — the production of the electromagnetic standing wave — is similar to the swing of a pendulum, then “our pendulum swings essentially tens of billions of times before it stops.”

The new findings could make for easier error correction in quantum computing, Wang said. In quantum computing, bits of information are encoded in the fragile superposition states of particles, and once that superposition is lost or corrupted, the data is also corrupted. So most quantum computing concepts involve a lot of redundancy.

“It’s well understood that 99 percent of computation or more will be done to correct for errors, rather than computation itself,” Wang said.

Their system could conceivably get around this problem by encoding the redundancy in the size of the cavity itself rather than in separate, calculated bits, Wang said.

“Demonstrating this cat in a ‘two boxes state’ is basically the first step in our architecture,” Wang said.

See more at: http://www.livescience.com/54890-schrodinger-cat-can-be-in-two-places.html#sthash.X4gB2Mc1.dpuf

Here is the perfect example of how any two objects will fall at the same rate in a vacuum, brought to us by physicist Brian Cox. He checked out NASA’s Space Simulation Chamber located at the Space Power Facility in Ohio. With a volume of 22,653 cubic meters, it’s the largest vacuum chamber in the world.

In this clip from the BBC, Cox drops a bowling ball and a feather together, first in normal conditions, and then after virtually all the air has been sucked out of the chamber. We know what happens, but that doesn’t stop it from being awesome, especially with the team’s ecstatic faces.

http://www.iflscience.com/physics/dropping-bowling-ball-and-feather-vacuum

Thanks to Kebmodee for bringing this to the attention of the It’s Interesting community.

Academics are challenging the foundations of quantum science with a radical new theory on parallel universes. Scientists now propose that parallel universes really exist, and that they interact. They show that such an interaction could explain everything that is bizarre about quantum mechanics.

Griffith University academics are challenging the foundations of quantum science with a radical new theory based on the existence of, and interactions between, parallel universes.

In a paper published in the journal Physical Review X, Professor Howard Wiseman and Dr Michael Hall from Griffith’s Centre for Quantum Dynamics, and Dr Dirk-Andre Deckert from the University of California, take interacting parallel worlds out of the realm of science fiction and into that of hard science.
The team proposes that parallel universes really exist, and that they interact. That is, rather than evolving independently, nearby worlds influence one another by a subtle force of repulsion. They show that such an interaction could explain everything that is bizarre about quantum mechanics.

Quantum theory is needed to explain how the universe works at the microscopic scale, and is believed to apply to all matter. But it is notoriously difficult to fathom, exhibiting weird phenomena which seem to violate the laws of cause and effect.

As the eminent American theoretical physicist Richard Feynman once noted: “I think I can safely say that nobody understands quantum mechanics.”

However, the “Many-Interacting Worlds” approach developed at Griffith University provides a new and daring perspective on this baffling field.

“The idea of parallel universes in quantum mechanics has been around since 1957,” says Professor Wiseman.

“In the well-known “Many-Worlds Interpretation,” each universe branches into a bunch of new universes every time a quantum measurement is made. All possibilities are therefore realised — in some universes the dinosaur-killing asteroid missed Earth. In others, Australia was colonised by the Portuguese.

“But critics question the reality of these other universes, since they do not influence our universe at all. On this score, our “Many Interacting Worlds” approach is completely different, as its name implies.”

Professor Wiseman and his colleagues propose that:

•The universe we experience is just one of a gigantic number of worlds. Some are almost identical to ours while most are very different;
•All of these worlds are equally real, exist continuously through time, and possess precisely defined properties;
•All quantum phenomena arise from a universal force of repulsion between ‘nearby’ (i.e. similar) worlds which tends to make them more dissimilar.
Dr Hall says the “Many-Interacting Worlds” theory may even create the extraordinary possibility of testing for the existence of other worlds.

“The beauty of our approach is that if there is just one world our theory reduces to Newtonian mechanics, while if there is a gigantic number of worlds it reproduces quantum mechanics,” he says.

“In between it predicts something new that is neither Newton’s theory nor quantum theory.

“We also believe that, in providing a new mental picture of quantum effects, it will be useful in planning experiments to test and exploit quantum phenomena.”

The ability to approximate quantum evolution using a finite number of worlds could have significant ramifications in molecular dynamics, which is important for understanding chemical reactions and the action of drugs.

Professor Bill Poirier, Distinguished Professor of Chemistry at Texas Tech University, has observed: “These are great ideas, not only conceptually, but also with regard to the new numerical breakthroughs they are almost certain to engender.”

Journal Reference:

1.Michael J. W. Hall, Dirk-André Deckert, Howard M. Wiseman. Quantum Phenomena Modeled by Interactions between Many Classical Worlds. Physical Review X, 2014; 4 (4) DOI: 10.1103/PhysRevX.4.041013

http://www.sciencedaily.com/releases/2014/10/141030101654.htm

Since the 1930s scientists have been searching for particles that are simultaneously matter and antimatter. Now physicists have found strong evidence for one such entity inside a superconducting material. The discovery could represent the first so-called Majorana particle, and may help researchers encode information for quantum computers.

Physicists think that every particle of matter has an antimatter counterpart with equal mass but opposite charge. When matter meets its antimatter equivalent, the two annihilate one another. But some particles might be their own antimatter partners, according to a 1937 prediction by Italian physicist Ettore Majorana. For the first time researchers say they have imaged one of these Majorana particles, and report their findings in the October 3 Science.

The new Majorana particle showed up inside a superconductor, a material in which the free movement of electrons allows electricity to flow without resistance. The research team, led by Ali Yazdani of Princeton University, placed a long chain of iron atoms, which are magnetic, on top of a superconductor made of lead. Normally, magnetism disrupts superconductors, which depend on a lack of magnetic fields for their electrons to flow unimpeded. But in this case the magnetic chain turned into a special type of superconductor in which electrons next to one another in the chain coordinated their spins to simultaneously satisfy the requirements of magnetism and superconductivity. Each of these pairs can be thought of as an electron and an antielectron, with a negative and a positive charge, respectively. That arrangement, however, leaves one electron at each end of the chain without a neighbor to pair with, causing them to take on the properties of both electrons and antielectrons—in other words, Majorana particles.

As opposed to particles found in a vacuum, unattached to other matter, these Majoranas are what’s called “emergent particles.” They emerge from the collective properties of the surrounding matter and could not exist outside the superconductor.

The new study shows a convincing signature of Majorana particles, says Leo Kouwenhoven of the Delft University of Technology in the Netherlands who was not involved in the research but previously found signs of Majorana particles in a different superconductor arrangement. “But to really speak of full proof, unambiguous evidence, I think you have to do a DNA test.” Such a test, he says, must show the particles do not obey the normal laws of the two known classes of particles in nature—fermions (protons, electrons and most other particles we are familiar with) and bosons (photons and other force-carrying particles, including the Higgs boson). “The great thing about Majoranas is that they are potentially a new class of particle,” Kouwenhoven adds. “If you find a new class of particles, that really would add a new chapter to physics.”

Physicist Jason Alicea of California Institute of Technology, who also did not participate in the research, said the study offers “compelling evidence” for Majorana particles but that “we should keep in mind possible alternative explanations—even if there are no immediately obvious candidates.” He praised the experimental setup for its apparent ability to easily produce the elusive Majoranas. “One of the great virtues of their platform relative to earlier works is that it allowed the researchers to apply a new type of microscope to probe the detailed anatomy of the physics.”

The discovery could have implications for searches for free Majorana particles outside of superconducting materials. Many physicists suspect neutrinos—very lightweight particles with the strange ability to alter their identities, or flavors—are Majorana particles, and experiments are ongoing to investigate whether this is the case. Now that we know Majorana particles can exist inside superconductors, it might not be surprising to find them in nature, Yazdani says. “Once you find the concept to be correct, it’s very likely that it shows up in another layer of physics. That’s what’s exciting.”

The finding could also be useful for constructing quantum computers that harness the laws of quantum mechanics to make calculations many times faster than conventional computers. One of the main issues in building a quantum computer is the susceptibility of quantum properties such as entanglement (a connection between two particles such that an action on one affects the other) to collapse due to outside interference. A particle chain with Majoranas capping each end would be somewhat immune to this danger, because damage would have to be done to both ends simultaneously to destroy any information encoded there. “You could build a quantum bit based on these Majoranas,” Yazdani says. ”The idea is that such a bit would be much more robust to the environment than the types of bits people have tried to make so far.”

http://www.scientificamerican.com/article/majorana-particle-matter-and-antimatter/


Doctoral student Joseph Choi demonstrates a multidirectional ‘perfect paraxial’ cloak using 4 lenses.


Choi uses his hand to further demonstrate his device.


A laser shows the paths that light rays travel through the system, showing regions that can be used for cloaking an object.

Scientists at the University of Rochester have discovered a way to hide large objects from sight using inexpensive and readily available lenses.

Cloaking is the process by which an object becomes hidden from view, while everything else around the cloaked object appears undisturbed.

“A lot of people have worked on a lot of different aspects of optical cloaking for years,” John Howell, a professor of physics at the upstate New York school, said on Friday.

The so-called Rochester Cloak is not really a tangible cloak at all. Rather the device looks like equipment used by an optometrist. When an object is placed behind the layered lenses it seems to disappear.

Previous cloaking methods have been complicated, expensive, and not able to hide objects in three dimensions when viewed at varying angles, they say.

“From what, we know this is the first cloaking device that provides three-dimensional, continuously multidirectional cloaking,” said Joseph Choi, a graduate student who helped develop the method at Rochester, which is renowned for its optical research.

In their tests, the researchers have cloaked a hand, a face, and a ruler – making each object appear “invisible” while the image behind the hidden object remains in view. The implications for the discovery are endless, they say.

“I imagine this could be used to cloak a trailer on the back of a semi-truck so the driver can see directly behind him,” Choi said. “It can be used for surgery, in the military, in interior design, art.”

Howell said the Rochester Cloak, like the fictitious cloak described in the pages of the Harry Potter series, causes no distortion of the background object.

Building the device does not break the bank either. It cost Howell and Choi a little over $US1000 ($1140) in materials to create it and they believe it can be done even cheaper.

Although a patent is pending, they have released simple instructions on how to create a Rochester Cloak at home for under $US100 (114).

There is also a one-minute video about the project on YouTube.

http://www.smh.com.au/technology/sci-tech/scientists-unveil-invisibility-cloak-to-rival-harry-potters-20140927-10n1dp.html