A new record distance has been set for the quantum teleportation of information over optical fibers. Researchers working at the National Institute of Standards and Technology (NIST) claim to have transmitted the quantum information carried in light particles over 100 km (62 miles), four times farther than previously achieved.
Gravity as Quantum Entanglement Force
Authors:
Lee et al
Abstract:
We conjecture that the total quantum entanglement of matter and vacuum in the universe tends to increase with time, like entropy, and that an effective force is associated with this tendency. We also suggest that gravity and dark energy are types of quantum entanglement forces, similar to Verlinde's entropic force, and give holographic dark energy with an equation of state comparable to current observational data. This connection between quantum entanglement and gravity could give some new insights into the origins of gravity, dark energy, and the arrow of time.
Subatomic particles have been found that appear to defy the Standard Model of particle physics. The team working at Cern's Large Hadron Collider have found evidence of leptons decaying at different rates, which could possibly point to some undiscovered forces.
Publishing their findings in the journal Physical Review Letters, the team from the University of Maryland had been searching for conditions and behaviours that do not fit with the Standard Model. The model explains most known behaviours and interactions of fundamental subatomic particles, but it is incomplete – for example it does not adequately explain gravity, dark matter and neutrino masses.
Researchers say the discovery of the non-conforming leptons could provide a big lead in the search for non-standard phenomenon. The Standard Model concept of lepton universality assumes leptons are treated equally by fundamental forces.
They looked at B meson decays including two types of leptons – the tau lepton and the muon, both of which are highly unstable and decay within just a fraction of a second. The tau lepton and muon should decay at the same rate after mass differences are corrected. But the researchers found small but important differences in the predicted rates of decay.
This suggests there are undiscovered forces or particles interfering in the process. Study co-author Hassan Jawahery said: "The Standard Model says the world interacts with all leptons in the same way. There is a democracy there. But there is no guarantee that this will hold true if we discover new particles or new forces. Lepton universality is truly enshrined in the Standard Model. If this universality is broken, we can say that we've found evidence for non-standard physics."
This device can transmit the magnetic field from one point in space to another point, through a path that is magnetically invisible," said study co-author Jordi Prat-Camps, a doctoral candidate in physics at the Autonomous University of Barcelona in Spain. "From a magnetic point of view, this device acts like a wormhole, as if the magnetic field was transferred through an extra special dimension."
Lawrence Livermore National Laboratory (LLNL; Livermore, CA) has installed and commissioned the highest-peak-power laser-diode arrays in the world, which in total produce a peak power of 3.2 MW. The diode arrays, which were developed and fabricated by Lasertel (Tucson, AZ), will act as the primary pump source for the High-Repetition-Rate Advanced Petawatt Laser System (HAPLS), currently under construction at LLNL. When completed, the HAPLS laser system will be installed at the European Union’s Extreme Light Infrastructure (ELI) Beamlines facility, which is under construction in the Czech Republic. The HAPLS is being built and commissioned at LLNL and will be installed and integrated into the ELI Beamlines facility starting in 2017.
HAPLS is designed to be capable of generating 30 fs pulses with peak powers greater than a petawatt at a repetition rate of 10 Hz. The high repetition rate is possible because, unlike existing petawatt lasers, which are flashlamp-pumped, HAPLS is pumped by diode arrays capable of delivering kilojoule pulses at high repetition rates to the final power amplifier.
Each laser-diode array supplied by Lasertel supplied contains multiple 888 nm laser-diode bars mounted on water-cooled stacks (see figure). The array operates at a brightness of 10 kW/cm2, which Lasertel notes is a world record, at a repetition frequency of 10 Hz. Each array operates at a total peak power of 800 kW, with four such arrays combined and used as the primary pump sources for the HAPLS laser. More than 500,000 combined laser diode emitters combine to produce the total diode optical input power of 3.2 MW.
One of the more exciting ideas in high energy physics is the possibility that our three-dimensional universe is embedded in a much bigger multidimensional cosmos. Physicists call these embedded universes “branes” and say that it should be possible for stuff from our brane to leak into other branes nearby and vice versa.
Today, Michael Sarrazin at the University of Namur in Belgium and a few pals say they have worked out to detect this leakage by measuring whether neutrons can bypass barriers by leaping into another brane and back again.
These guys are proposing to measure this effect by placing a neutron detector close to a nuclear reactor to see whether neutrons appear unexpectedly as a result of being transported out of the reactor via another braneworld.
University of California, Berkeley, scientists have proved a fundamental relationship between energy and time that sets a "quantum speed limit" on processes ranging from quantum computing and tunneling to optical switching.
The energy-time uncertainty relationship is the flip side of the Heisenberg uncertainty principle, which sets limits on how precisely you can measure position and speed, and has been the bedrock of quantum mechanics for nearly 100 years. It has become so well-known that it has infected literature and popular culture with the idea that the act of observing affects what we observe.
Not long after German physicist Werner Heisenberg, one of the pioneers of quantum mechanics, proposed his relationship between position and speed, other scientists deduced that energy and time were related in a similar way, implying limits on the speed with which systems can jump from one energy state to another. The most common application of the energy-time uncertainty relationship has been in understanding the decay of excited states of atoms, where the minimum time it takes for an atom to jump to its ground state and emit light is related to the uncertainty of the energy of the excited state.
"This is the first time the energy-time uncertainty principle has been put on a rigorous basis - our arguments don't appeal to experiment, but come directly from the structure of quantum mechanics," said chemical physicist K. Birgitta Whaley, director of the Berkeley Quantum Information and Computation Center and a UC Berkeley professor of chemistry. "Before, the principle was just kind of thrown into the theory of quantum mechanics."
The new derivation of the energy-time uncertainty has application for any measurement involving time, she said, particularly in estimating the speed with which certain quantum processes - such as calculations in a quantum computer - will occur.
Physicists have simulated a photon interacting with an older version of itself in an experiment that could help reconcile quantum mechanics and relativity
One of the curiosities of general relativity is that it seems to allow time travel. Various physicists have discovered solutions to Einstein’s field equations that contain loops that return to the same point in space and time. Physicists call them closed time-like curves.
At first glance, these kinds of time machines seem to lead to all kinds of problems, such as the grandfather paradox. This is where somebody travels back in time and kills their grandfather meaning they could never have been born and so could not have gone back to kill the grandfather.
That’s just bizarre so physicists have attempted to find ways to prevent these paradoxes. In the early 90s, for example, cosmologists showed that a billiard ball entering a wormhole that leads to a closed time-like curve must always meet its older self coming out of the wormhole. What’s more, the resulting collision always prevents the ball entering the wormhole in the first place. In other words, the billiard ball would simply bounce off the entrance to a closed time-like curve.
So much for classical objects and time travel. But what would happen if a quantum particle entered a closed time-like curve? In the early 90s, the physicist David Deutsch showed that not only is this possible but that it can only happen in a way that does not allow superluminal signalling. So quantum mechanics plays havoc with causality but in a way that is consistent with relativity and so prevents grandfather-type paradoxes.
Deutsch’s result has extraordinary implications. It implies that closed time-like curves can be used to solve NP-complete problems in polynomial time and to violate Heisenberg’s uncertainty principle.
[O]ne theorist has shown that an exotic quantum effect called entanglement has a real and measurable influence on a gravitational field— the first time this kind of link has ever been shown.
David Bruschi at the Hebrew University of Jerusalem in Israel says the new result has important implications for quantum mechanics and relativity and may represent an important step towards a long sought after theory that explains them both.
Bruschi’s idea is simple in principle. Physicists have long known that a single quantum particle can exist in two places at the same time. There is a clear quantum correlation called entanglement between these two locations that is well-defined mathematically in quantum mechanics.
Bruschi’s new approach is to formulate the mathematics in the context of relativity. He first makes the mathematical assumption that some perturbation of a gravitational field is possible in these circumstances.
He then goes on to formulate the mathematical properties of this perturbation and how they evolve when the two locations are maximally entangled and when they are not, a state known as maximally mixed.
He finds that the perturbation is zero when the states are maximally mixed. But in the other case— when the two locations are maximally entangled— the perturbation spreads through space over a scale related to the energy of the particle and the coherence time of the entanglement.
This kind of perturbation is mathematically similar to a gravitational wave, albeit on a much smaller scale. It is essentially equivalent to the particle having some additional weight. And that is what makes it potentially detectable.
For certain physics experiments, deeper is better. Since it opened in 2010, the China Jinping Underground Laboratory (CJPL)—in a hollowed-out cavern along a tunnel in Sichuan province—has been the world's deepest underground laboratory. Two thousand four hundred meters of rock have shielded its experimental chambers from background radiation that might mask the extremely subtle traces of dark matter, the universe's postulated missing mass. CJPL's observational capabilities were limited by its mere 4000-cubic-meter size. It is about to grow to 120,000 cubic meters, making it the world's second largest underground lab and positioning it to make breakthrough contributions to fundamental investigations into dark matter, neutrinos, and conditions in the early universe.
Back in 1997, physicists performed an extraordinary experiment that will be forever remembered by researchers and Star Trek fans alike. In this demonstration, the team transported photons from one point in the universe to another without sending them through the space in between — the first successful teleportation in history.
Teleportation is the transfer of the information that describes one object to another object elsewhere in space. In effect, this second object takes on the identity of the first. A more precise description of the team’s experiment with photons is that they transferred the quantum information that describes the polarisation state of one photon to another photon.
Still impressive but not quite the teleportation of the entire photon, which has multiple quantum properties. All of these need to be teleported to recreate it exactly.
Since then, this kind of teleportation has become routine in quantum optics labs all over the world but always with the same limitation. All these experiments involve the transfer of a single quantum property. Nobody has ever found a way to transmit the multiple quantum properties of a single object at the same time and thereby truly teleport it.
Until now. Today, Xi-Lin Wang and buddies at the University of Science and Technology of China in Hefei say they have done just that. The team have worked out how to teleport two quantum properties of a single photon to another photon at the same time — the first time this has ever been done. The work is an important stepping stone towards the ultimate goal of teleporting complex objects such as atoms and small molecules in their entirety.
For decades, Europe and the United States have led the way when it comes to high-energy particle colliders. But a proposal by China that is quietly gathering momentum has raised the possibility that the country could soon position itself at the forefront of particle physics.
Scientists at the Institute of High Energy Physics (IHEP) in Beijing, working with international collaborators, are planning to build a ‘Higgs factory’ by 2028 — a 52-kilometre underground ring that would smash together electrons and positrons. Collisions of these fundamental particles would allow the Higgs boson to be studied with greater precision than at the much smaller Large Hadron Collider (LHC) at CERN, Europe’s particle-physics laboratory near Geneva, Switzerland.
Physicists say that the proposed US$3-billion machine is within technological grasp and is considered conservative in scope and cost. But China hopes that it would also be a stepping stone to a next-generation collider — a super proton–proton collider — in the same tunnel.
European and US teams have both shown interest in building their own super collider (see Nature 503, 177; 2013), but the huge amount of research needed before such a machine could be built means that the earliest date either can aim for is 2035. China would like to build its electron–positron collider in the meantime, unaided by international funding if needs be, and follow it up as fast as technologically possible with the super proton collider. Because only one super collider is likely to be built, China’s momentum puts it firmly in the driving seat.
For a change, U.S. particle physicists are savoring some good news about government funding. The Department of Energy (DOE) and the National Science Foundation (NSF) announced on Friday that they will try to fund two major experiments to detect particles of the mysterious dark matter whose gravity binds the galaxies instead of just one. The decision allays fears that the funding agencies could afford only one experiment to continue the search for so-called weakly interacting massive particles, or WIMPs. It also averts having to choose between the two leading WIMP-search teams in the United States.link.
"We have the opportunity right now for the U.S. experiments to push further in sensitivity and possibly make a discovery," says Richard Gaitskell, a physicist at Brown University and a member of the team developing a WIMP detector called LZ, one of the two leading projects. "There's a real commitment from the community and the funding agencies." Blas Cabrera, a physicist at Stanford University in Palo Alto, California, and spokesman for the rival SuperCDMS experiment, says that having to pick only one team “would have been a grave mistake."
For decades, astronomers and astrophysicists have reasoned that some sort of otherwise unobservable dark matter provides most of the gravity that keeps the galaxies from flying apart. Physicists hope to identify that stuff by detecting particles of it floating around us. For example, dark matter could consist of WIMPs, hypothetical particles that would barely interact with ordinary matter and weigh much more than protons.
Press the start button, switch on the monitor, grab a cup of coffee and off you go. That is pretty much how most us experience booting up a computer. But with a quantum computer the situation is very different. So far, researchers have had to spend hours making dozens of adjustments and fine calibrations in order to set up a chip with just five quantum bits so that it can be used for experimental work. (One quantum bit or 'qubit' is the quantum physical equivalent of a single bit in a conventional computer). Any small errors in the adjustment and calibration procedure and the chip would not work.
The problem is that, not unlike musical instruments, quantum computers react to small changes in the local environment. If, for example, it is a little warmer or a little colder or if the ambient air pressure is a little higher or a little lower than the day before then the complex network of qubits will no longer function – the computer is detuned and has to be readjusted before it can be used. 'Up until now, experimental quantum physicists have had to sit down each day and see how conditions have changed compared to the day before. They then had to remeasure each parameter and carefully recalibrate the chip,' explains Professor Wilhelm-Mauch, Professor for Theoretical Quantum and Solid-State Physics at Saarland University. Only a very small error rate of less than 0.1 percent is permissible when measuring ambient conditions. Frank Wilhelm-Mauch explains this sensitivity thus: 'That means that an error can occur in only one in a thousand measurements. If just two in a thousand measurements are in error, the software will be unable to correct for the errors and the quantum computer will not operate correctly.' With around 50 different parameters involved in the calibration process, one begins to get an idea of the sheer effort involved in calibrating a quantum computer.
Working together with his doctoral student, Wilhelm-Mauch began to consider a fundamentally new approach to the problem. 'We asked ourselves the question: Why is it necessary each and every day to understand how conditions differ from those of the day before?' The answer we eventually came up with was that it isn't necessary. What's important is that the setup procedure produces the right results. Why it produces the right results is not so relevant.' It was this pragmatic approach that underlay the work carried out by Wilhelm-Mauch and Egger. 'For the calibration procedure we used an algorithm from engineering mathematics, strictly speaking from the field of civil and structural engineering, as that's another area in which experiments are costly,' explains Professor Wilhelm-Mauch.
Using this technique, the two theoreticians were able to reduce the calibration error rate to below the required 0.1 percent threshold, while at the same time speeding up the calibration process from six hours to five minutes. The Saarbrücken methodology, which goes under the name Ad-HOC (Adaptive Hybrid Optimal Control), has now been subjected to rigorous testing by a group of experimental physicists from the University of California in Santa Barbara. Their experimental work is published in the issue of Physical Review Letters that also contains the Saarbrücken paper.
In the science-fiction classic, Terminator 2: Judgement Day, the T-1000 is a robotic assassin with a liquid metal endoskeleton that can assume the form of any object or person. Its liquid nature makes it immune to attack by bullets and impervious to mechanical damage in general.
The T-1000 is an entirely fictional device that might as well be magic as far as conventional manufacturing techniques are concerned. And yet this might be about to change thanks to the pioneering work of Lei Sheng, Jie Zhang and Jing Liu at Tsinghua University in Beijing.
These guys have taken the first tentative steps to making liquid machines that work like the T-1000. Their first attempts can assume various shapes, move around and then transform into other shapes more or less without limit. And they say the work has profound implications for the design of robots, future machines and the nature of manufacturing.
While the most familiar liquid metal is the toxic mercury, there are other metals and alloys that are liquid at room temperature and much more benign. In particular, a gallium-indium-selenium alloy, with a melting point of around 10°C, has received much recent attention because it can be used for cooling microprocessors and even for liquid metal printing techniques.
Now Lei Sheng and co have made this liquid metal assume simple shapes by placing a thin film of it in water and applying an electric field.
With careful arrangement of the voltages and electrode geometries, these guys can make the metal form into a sphere. They say this is the result of the balance between the surface tension in the liquid metal and the electronic forces applied to its surface.
Scientists at Johannes Gutenberg University Mainz (JGU) and the University of Erlangen-Nuremberg are working on a heat engine that consists of just a single ion. Such a nano-heat engine could be far more efficient than, for example, a car engine or a coal-fired power plant. A usual heat engine transforms heat into utilizable mechanical energy with the corresponding efficiency of an Otto engine amounting to only about 25 percent, for instance. The proposed nano-heat engine consisting of a single calcium ion would be much more efficient. The main aim of the research being conducted is to better understand how thermodynamics works on very small scales. A pilot prototype of such a single-ion heat engine is currently being constructed at Mainz University.
In this month's issue of Physics World, Jon Cartwright explains how the revelation that the US National Security Agency (NSA) is developing quantum computers has renewed interest and sparked debate on just how far ahead they are of the world's major labs looking to develop the same technology.
In 2006 the NSA openly announced a partnership with two US institutions to develop quantum computers. However, according to documents leaked by whistle-blower Edward Snowden, and published last month by the Washington Post, the NSA also wishes to develop the technology so that it is capable of breaking modern Internet security.
The $79.7m project, dubbed "Penetrating Hard Targets", could be made possible by the extraordinary potential of quantum computers to factorize large numbers in a short space of time, quickly deciphering encryption keys that are used to protect sensitive information.
For the NSA, this could mean deciphering banking transactions, private messages and government files; however, many physicists are not surprised and believe this is exactly the type of technology that the NSA is expected to develop.
Speaking to Physics World, Raymond Laflamme, a leading quantum information theorist at the University of Waterloo in Canada, said "If you put my level of surprise on a scale from zero to 10, where 10 is very, very surprised, my answer would be zero."
Observation of Dirac monopoles in a synthetic magnetic field
Authors:
Ray et al
Abstract:
Magnetic monopoles—particles that behave as isolated north or south magnetic poles—have been the subject of speculation since the first detailed observations of magnetism several hundred years ago. Numerous theoretical investigations and hitherto unsuccessful experimental searches have followed Dirac’s 1931 development of a theory of monopoles consistent with both quantum mechanics and the gauge invariance of the electromagnetic field3. The existence of even a single Dirac magnetic monopole would have far-reaching physical consequences, most famously explaining the quantization of electric charge. Although analogues of magnetic monopoles have been found in exotic spin ices and other systems there has been no direct experimental observation of Dirac monopoles within a medium described by a quantum field, such as superfluid helium-3. Here we demonstrate the controlled creation of Dirac monopoles in the synthetic magnetic field produced by a spinor Bose–Einstein condensate. Monopoles are identified, in both experiments and matching numerical simulations, at the termini of vortex lines within the condensate. By directly imaging such a vortex line, the presence of a monopole may be discerned from the experimental data alone. These real-space images provide conclusive and long-awaited experimental evidence of the existence of Dirac monopoles. Our result provides an unprecedented opportunity to observe and manipulate these quantum mechanical entities in a controlled environment.
