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. …
Archive for the ‘Physics’ Category
Posted by Xeno on May 6, 2013
Posted by Xeno 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 Xeno 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. …
Einstein’s gravity theory passes toughest test yet: Bizarre binary star system pushes study of relativity to new limits
Posted by Xeno on April 26, 2013
A strange stellar pair nearly 7,000 light-years from Earth has provided physicists with a unique cosmic laboratory for studying the nature of gravity. The extremely strong gravity of a massive neutron star in orbit with a companion white dwarf star puts competing theories of gravity to a test more stringent than any available before.
Once again, Albert Einstein’s General Theory of Relativity, published in 1915, comes out on top.
At some point, however, scientists expect Einstein’s model to be invalid under extreme conditions. General Relativity, for example, is incompatible with quantum theory. Physicists hope to find an alternate description of gravity that would eliminate that incompatibility.
A newly-discovered pulsar – a spinning neutron star with twice the mass of the Sun – and its white-dwarf companion, orbiting each other once every two and a half hours, has put gravitational theories to the most extreme test yet. Observations of the system, dubbed PSR J0348+0432, produced results consistent with the predictions of General Relativity. …
Posted by Xeno on April 25, 2013
Researchers at TU Delft in the Netherlands have managed to bring two electrons, three meters from each other, into a quantum- entangled state. This result marks a major step towards realizing a quantum network that can be used to connect future quantum computers and to send information in a completely secure way by means of “teleportation”. The results have been published online on April 24 in Nature .
Entanglement is arguably the most intriguing consequence of the laws of quantum mechanics. When two particles become entangled, their identities merge: their collective state is precisely determined but the individual identity of each of the particles has disappeared. The entangled particles behave as one, even when separated by a large distance. Einstein doubted this prediction, which he called “spooky action at a distance”, but experiments have proven its existance.
Entangled states are interesting for computers as they allow a huge number of calculations to be carried out simultaneously. A quantum computer with 400 basic units (“quantum bits”) could, for example, already process more bits of information simultaneously than there are atoms in the universe. In recent years, scientists have succeeded in entangling quantum bits within a single chip. Now, for the first time, this has been successfully achieved with quantum bits on different chips.
Posted by Xeno on April 24, 2013
A dense sheet of electrons accelerated to close to the speed of light can act as a tuneable mirror that can generate bursts of laser-like radiation in the short wavelength range via reflection.
A team of physicists from the Max-Planck-Institute of Quantum Optics (MPQ) in Garching, the Ludwig-Maximilians-Universität (LMU) München, the Queens University Belfast (QUB) and the Rutherford Appleton Laboratory (RAL) near Oxford created such a mirror in a recent experiment. The scientists used an intense laser pulse to accelerate a dense sheet of electrons from a nanometre-thin foil to close to the speed of light and reflected a counter-propagating laser pulse from this relativistic mirror.
With this experiment, the physicists managed to carry out a Gedankenexperiment (thought experiment) formulated in 1905 by Albert Einstein stating that the reflection from a mirror moving close to the speed of light could in principle result in bright light pulses in the short wavelength range. The researchers report on their results in Nature Communications, 23. April, 2013.
In everyday life, reflections of light are usually observed from surfaces that are at rest such as the reflection from a piece of glass or a smooth surface of water. But, what happens if one creates a mirror moving incredibly fast, close to the speed of light? This question was answered more than a century ago by Albert Einsteins in 1905 in his theory of special relativity. Now, an international team of researchers investigated that question in an experiment. …
Posted by Xeno on April 22, 2013
A typical human eye will respond to wavelengths from about 390 to 700 nm. In terms of frequency, this corresponds to a band in the vicinity of 430–790 THz. A light-adapted eye generally has its maximum sensitivity at around 555 nm (540 THz), in the green region of the optical spectrum (see: luminosity function). The spectrum does not, however, contain all the colors that the human eyes and brain can distinguish. Unsaturated colors such as pink, or purple variations such as magenta, are absent, for example, because they can be made only by a mix of multiple wavelengths.
Color Frequency Wavelength violet 668–789 THz 380–450 nm blue 606–668 THz 450–495 nm green 526–606 THz 495–570 nm yellow 508–526 THz 570–590 nm orange 484–508 THz 590–620 nm red 400–484 THz 620–750 nm
Is there any device to shift the spectrum of what is seen so red becomes orange, orange becomes yellow, yellow becomes green and so on, smoothly? I haven’t found any substance that will do this but I did find this interesting paper:
Gravitational Blueshift and Redshift generated at Laboratory Scale
… it is possible to produce gravitational blueshift and redshift at laboratory scale by means of a device that can strongly intensify the local gravitational potential… Thus, by using this device, it is
possible to generate electromagnetic radiation of any frequency, from ELF radiation (f < 10Hz) up to high energy gamma-rays. In this case, several uses, such as in medical imaging, radiotherapy and radioisotope production for PET (positron emission tomography) scanning and others, could be devised. The device is smaller and less costly than conventional sources of gamma rays.
A lens can filter out colors, but I’m asking a different question, how to change one color into another. X-ray film seems to red-shift x-rays into the visible spectrum. How does it do that? Answer: It doesn’t. There is no shift, but x-rays hitting some substances can cause light to be emitted.
… the conversion of a relatively small number of X-ray photons of high energy to a large number of light photons of low energy is due predominantly to X-ray absorption via the photoelectric effect in the high Z components of the phosphor. … – link
What is the photoelectric effect?
Heinrich Hertz in 1887  discovered that electrodes illuminated with ultraviolet light create electric sparks more easily. In 1905 Albert Einstein published a paper that explained experimental data from the photoelectric effect as being the result of light energy being carried in discrete quantized packets. Einstein was awarded the Nobel Prize in 1921 for “his discovery of the law of the photoelectric effect”.
Just use photo editing software? Here is an original image I took hiking at table mountain this weekend:
In this next photo, I used the free Paint.net program to shift the hue by a value of 100 positive. As you can see, yellow is green, green is blue, and blue is now purple. This is a blueshift, shortening the color wavelengths, moving reds toward the blue. That’s not obvious because the blue sky now looks more red, but the blue is actually now violet and the yellow is green. If my camera picked up infrared outside of human vision, assuming the photo format kept and could manipulate that data, this shift would show it. Similarly, if my camera picked up x-rays, a redshift would move it into the visible spectrum.
Here is the original image redshifted. The blue sky becomes green with a redshift, the yellow flowers become red:
Next, here is a more dramatic blueshift, moving the yellow flowers all the way to blue:
What I was really curious about is if my iPhone camera includes any information outside of the visible spectrum. Unfortunately, Paint.net’s hue feature just cycles the visible colors. You can’t move things into the red and just keep going more and more red until you move into infrared. This makes complete sense as computers are designed only to work with the visible spectrum.
Still, I wonder if what I’m envisioning could be done with software: Shift colors up to the point where only certain colors would be visible after a big enough shift in one direction. In other words, when the colors move out of the visible range, I just want them to become invisible, not to cycle around. The color spectrum is not a circle.
In infrared photography, the film or image sensor used is sensitive to infrared light. The part of the spectrum used is referred to as near-infrared to distinguish it from far-infrared, which is the domain of thermal imaging. Wavelengths used for photography range from about 700 nm to about 900 nm. Film is usually sensitive to visible light too, so an infrared-passing filter is used; this lets infrared (IR) light pass through to the camera, but blocks all or most of the visible light spectrum (the filter thus looks black or deep red). (“Infrared filter” may refer either to this type of filter or to one that blocks infrared but passes other wavelengths.)
When these filters are used together with infrared-sensitive film or sensors, very interesting “in-camera effects” can be obtained; false-color or black-and-white images with a dreamlike or sometimes lurid appearance known as the “Wood Effect,” an effect mainly caused by foliage (such as tree leaves and grass) strongly reflecting in the same way visible light is reflected from snow. There is a small contribution from chlorophyll fluorescence, but this is marginal and is not the real cause of the brightness seen in infrared photographs. The effect is named after the infrared photography pioneer Robert W. Wood, and not after the material wood, which does not strongly reflect infrared.
The other attributes of infrared photographs include very dark skies and penetration of atmospheric haze, caused by reduced Rayleigh scattering and Mie scattering, respectively, compared to visible light. The dark skies, in turn, result in less infrared light in shadows and dark reflections of those skies from water, and clouds will stand out strongly. These wavelengths also penetrate a few millimeters into skin and give a milky look to portraits, although eyes often look black. – wikipedia
Can the iPhone 4S take photos like these? It seems not and I think there is even a filter to block infrared that the iPhone 4 did not have according to this: http://www.cameratechnica.com/2011/10/31/how-good-is-the-iphone-4s-cameras-ir-filter/
Here is a claimed iPhone infrared photography, probably the iPhone 4?
I have a whole set of genuine infrared photos here, all taken with just an iPhone and a Hoya R72 infrared filter held over the lens: http://www.flickr.com/photos/matt_brock/sets/72157624198109814/
Posted by Xeno on April 19, 2013
… As published in Nature today, my colleagues and I have established a world-first in this area. We’ve demonstrated a quantum bit (or qubit) based on the nucleus of a single atom in silicon, promising dramatic improvements for data processing in the ultra-powerful quantum computers of the future.
…What determines the size of the atom is the orbit of the electron. The core of the atom is the nucleus, which contains the positive charge and is about a million times smaller than the electron orbit.
The nucleus itself has a spin, but its magnetic dipole is a thousand times weaker than that of the electron. Our breakthrough consists in the demonstration of a fully functional, readable and writable, quantum bit based on the nuclear spin of a single phosphorus atom.
This was an extraordinary challenge, but it came with big rewards.
Animation and explanation of how we wrote quantum information into the nucleus of an atom in silicon. Credit: UNSWTV
The nucleus is very well isolated from the outside world, and that means a delicate quantum state – the superposition of 0 and 1 – can remain undisturbed for very long time.
We managed to preserve it for 0.06 seconds, which in the quantum world is an eternity. We were able to read out the state of the nucleus with fidelity better than 99.8% – a result comparable with ions trapped in vacuum.
We even succeeded in observing “quantum jumps” (abrupt changes from one energy level to another) of the nuclear spin, something that even Erwin Schroedinger – one of the founding father of quantum mechanics – was sceptical about.
The electron and the nucleus of an atom represent two independent qubits – and that’s a lot of quantum resources in such a small volume. Since they are naturally coupled to each other, we are currently exploring the option of using the nucleus as a “quantum memory” for the state of the electron, which would otherwise decay more quickly.
There is still a long way to go before a large-scale quantum computer becomes available. But now we know silicon can be used to host coherent and high-fidelity qubits, the future looks rosier than ever.
Andrea Morello receives funding from the Australian Research Council and the U.S. Army Research Office.
It is fun to imagine what we would do with computers millions of times more powerful than today’s supercomputers.
Posted by Xeno on April 18, 2013
Throughout decades of research on solar cells, one formula has been considered an absolute limit to the efficiency of such devices in converting sunlight into electricity: Called the Shockley-Queisser efficiency limit, it posits that the ultimate conversion efficiency can never exceed 34 percent for a single optimized semiconductor junction.
Now, researchers at MIT have shown that there is a way to blow past that limit as easily as today’s jet fighters zoom through the sound barrier — which was also once seen as an ultimate limit. …
in the new technique, each photon can instead knock two electrons loose. This makes the process much more efficient: In a standard cell, any excess energy carried by a photon is wasted as heat, whereas in the new system the extra energy goes into producing two electrons instead of one.
While others have previously “split” a photon’s energy, they have done so using ultraviolet light, a relatively minor component of sunlight at Earth’s surface. The new work represents the first time this feat has been accomplished with visible light, laying a pathway for practical applications in solar PV panels.
This was accomplished using an organic compound called pentacene in an organic solar cell. While that material’s ability to produce two excitons from one photon had been known, nobody had previously been able to incorporate it within a PV device that generated more than one electron per photon.
“Our whole project was directed at showing that this splitting process was effective,” says Baldo, who is also the director of the Center for Excitonics, sponsored by the U.S. Department of Energy. “We showed that we could get through that barrier.”
The theoretical basis for this work was laid long ago, says Congreve, but nobody had been able to realize it in a real, functioning system. “In this system,” he says, “everyone knew you could, they were just waiting for someone to do it.”
Since this was just a first proof of principle, the team has not yet optimized the energy-conversion efficiency of the system, which remains less than 2 percent. But ratcheting up that efficiency through further optimization should be a straightforward process, the researchers say. “There appears to be no fundamental barrier,” Thompson says.
While today’s commercial solar panels typically have an efficiency of at most 25 percent, a silicon solar cell harnessing singlet fission should make it feasible to achieve efficiency of more than 30 percent, Baldo says — a huge leap in a field typically marked by slow, incremental progress. In solar cell research, he notes, people are striving “for an increase of a tenth of a percent.”
Solar panel efficiencies can also be improved by stacking different solar cells together, but combining solar cells is expensive with conventional solar-cell materials. The new technology instead promises to work as an inexpensive coating on solar cells.
The work made use of a known material, but the team is now exploring new materials that might perform the same trick even better. “The field is working on materials that were chanced upon,” Baldo says — but now that the principles are better understood, researchers can begin exploring possible alternatives in a more systematic way. …
Posted by Xeno on April 15, 2013
… Physicists have succeeded in closing the last local realistic loophole for systems of entangled photons.
In everyday life it is only natural that the properties of objects exist independent of being observed or not. The quantum world on the other hand is ruled by other laws: the property of a particle may be not be defined until the instant it is being measured, and two entangled particles seem to be connected in a non-local way over large distances. Various experiments worldwide have demonstrated this fundamental attribute of quantum theory. However, up to now last doubts could not be ruled out completely. Advocates of “local realism” by which the classical world is governed refer to several “loopholes” in order to save their world view. Now physicists from the group of Prof. Anton Zeilinger at the Institute of Quantum Optics and Quantum Information (IQOQI) in Vienna, Austria, have closed an important loophole in photonic experiments which use quantum entanglement to rule out a local realistic explanation of nature.
The results are published this week in Nature .
“Local realism” is a world view in which the properties of physical objects exist independent of whether or not they are observed by anyone (realism) and in which no physical influence can propagate faster than the speed of light (locality). In 1964, in one of the most important works in the history of the foundations of quantum theory, the Irish physicist John Bell proved theoretically that local realism is in contradiction with the predictions of quantum mechanics, and that the decision between these philosophically so radically different world views can be made by experiment. A certain inequality, the now famous “Bell inequality,” can be used for an experimental test. Quantum mechanics can violate the inequality, whereas local realism cannot.
In a Bell test, pairs of particles, e.g. photons, are produced. From every pair, one photon is sent to a party usually called Alice, and the other photon is sent to Bob. They each make a choice which physical property they want to measure, e.g. which direction of their photon’s polarization. For pairs that are quantum entangled, the correlations of Alice’s and Bob’s measurement outcomes can violate Bell’s inequality. Quantum entanglement – a term coined by the Austrian physicist Erwin Schrödinger – means that neither photon taken by itself has a definite polarisation but that, if one party measures the polarisation of its photon and obtains a random result, the other photon will always show a perfectly correlated polarisation. Albert Einstein called this strange effect “spooky action at a distance.”…http://www.sciencedaily.com/releases/2013/04/130415094839.htm
I experienced spooky action at a distance tonight. A bottle of soap began rocking on its own near my kitchen sink. No breeze, no earthquake. I was about 5 ft away. The only thing that makes sense is that the slow moving soap from the top took a while to settle and after a certain balance point was reached, it started rocking.
I’ve had a key fly off of the wall in this very same room. The guy who installed the locks and had that key made had recently died in a car crash. The key was hanging on a sign that says, “life is what happens when you are busy making other plans.”
Soap. Dish soap. Could be a clue to something I’m working on…