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Posts Tagged ‘quantum physics’

The team, from the Tyndall National Institute at University College Cork in Ireland, has demonstrated in a new paper how qubits--the basic blocks of quantum computing--can travel over standard fiber optics networks. This has been shown before, but not in a real-world kind of way. In other words, you can move qubits over fiber optics in theory, sure. But to feasibly do so--especially alongside traditional data streams--is a huge step forward.

The problem has always been one of interference. Qubits are carried by single photons, while traditional data packets are carried by strong laser pulses. Those pulses flying throughout a network result in spontaneous Raman scattering of photons within the optical fiber, and that in turn interferes with the quantum channels, causing a rate of error that’s high enough to be prohibitive.

So the Cork team figured out how to squeeze the qubits in there in between the Raman scattering. When the pulses of laser light are moving through the optical fiber, the interference pulses along with it--that is, there are quiet moments in between bursts of Raman scattering that lead to interference or crosstalk on the network. By carefully controlling the timing and wavelength of the quantum data, the researchers showed that they could slip quantum data generated by a QKD scheme in between the noise areas, where they can travel untouched by the interference.

All that is key if we’re ever going to practically begin a shift over to widespread quantum computing (first we’ll need some good quantum computers of course, but it never hurts to be prepared). It would be really expensive to build a second quantum network alongside our existing classical data networks. Using this scheme, it appears you could get classical and quantum streams running alongside each another, making quantum IT more commercially viable.

[PhysOrg]

As Technology Review’s KFC cleverly points out, “getting eight photons exactly where you want them at the same time is the quantum mechanical equivalent of herding cats (clearly of the Schrodinger variety).” Manipulating individual particles at this level is difficult enough, and that’s before you create that quantum link. Once you’ve entangled two or more particles, manipulating the entangled system without breaking the link is even more daunting.

How do you entangle this many photons? You start with one photon from a high energy beam, and you split it with a nonlinear crystal. You now have two weaker photons that are entangled--any exertion on one will affect the other. You put one photon aside in an apparatus and you then split the other, put one of those aside and split the other, etc.

But each split weakens the beam, and previously it was difficult--and time consuming--to produce to a manipulable eight-photon entangled system, so difficult that it hadn’t been achieved. The Chinese team, from the University of Science and Technology of China in Hefei, used a much brighter UV laser capable of churning out more entangled pairs much faster than smaller lasers. Then they figured out how to manipulate them.

That’s significant on a variety of fronts, not least of which is quantum computing. An eight-photon system would allow researchers to probe the quantum world at higher resolutions than was previously possible, demonstrating key pieces of the technology puzzle that should someday enable quantum computers to work as we’ve envisioned them.

For more, check the arXiv.

[Technology Review]

Quantum tunneling is the same mechanism that allows flash memory to store charge and scanning tunneling microscopes to form images. Simply put, tunneling is a well-defined process that lets a particle “tunnel” through a barrier even when its kinetic energy is less than the potential energy of the barrier. In the case of electrons, that means moving through non-conductive areas that, classically speaking, they shouldn’t be able to.

As it pertains to smell, the idea is that receptors in the nose can distinguish between two molecules of essentially identical shape by pumping current through them and identifying them via the resulting vibration rather than molecular shape. Further, when the receptor lacks a direct hookup to the odorant molecule it delivers electrons to it via quantum tunneling.

Using a series of molecules and their nearly-identical dueterated variants (deuterium is a heavier isotope of hydrogen--two molecules, one containing hydrogen and another containing deuterium in its place, are extremely similar in shape), the scientists ran several experiments using fruit flies. With significant regularity, the flies were able to distinguish between the molecules, suggesting that there’s more to smell than the shape of odorant molecules.

This vibrational theory goes beyond proving that fruit flies have a keener sense of smell than once thought. The finding could lead to a rethinking in the way scientists really understand our senses of smell. It could also lead to new kinds of artificial scents and better artificial noses. The latter, of course, can be used for everything from food inspection to national security to medical diagnostics.

[IEEE Spectrum]

Quantum entanglement is that “spooky action” (Einstein’s words, not ours) that links two particles such that a measurement on one immediately influences the state of the other, even if the two particles are separated by miles, or even light years. Entanglement defies the intuitive way we understand the universe to work (as does most of quantum mechanics). The idea of “time teleportation,” as described by S. Jay Olson and Timothy Ralph, doesn’t add clarity but it does introduce some interesting questions about the fundamentals of the universe.

In a sense, everyone and everything is time traveling, moving forward in time at a given rate. What Olson and Ralph propose is that it’s possible to take a shortcut into the future without being present in the interim. How? Tech Review’s KFC explains:

The idea is that a detector acts on a qubit and then generates a classical message describing how this particle can be detected. Then, at some point in the future, another detector at the same position in space, receives this message and carries out the required measurement, thereby reconstructing the qubit.

But here’s the thing: said qubit doesn’t have to exist in the time between it’s initial detection and its reconstruction, though it is the exact same qubit. But there is a wrinkle, in that the initial creation of the qubit and its detection in the future must be symmetrical. "If the past detector was active at a quarter to 12:00, then the future detector must wait to become active at precisely a quarter past 12:00 in order to achieve entanglement," they say in their paper.

How does all this work? Admittedly, we’re not sure. But researchers have already achieved teleportation across space in the lab, so if time teleportation is truly as simple as space teleportation, we’ll likely be shown how it works sometime soon enough.

[arXiv via Technology Review]

Like fiber optic networks, information traveling through quantum networks via entangled particles needs somewhere to live – something akin to computer memory – in order for complex computations to take place or sophisticated networks to be created. This isn’t easy, as the entangled link between two particles is fragile – tamper with it too much, and the link can be fouled. You also have to make the photon or electron sit still, another problem entirely.

But the researchers were able to pull all these tricks off at once using a lithium niobate crystal doped with rare earth ions and chilled to -454 degrees. Here the science gets tricky (New Scientist has a great, concise explanation if you care for it), but essentially the researchers tuned this crystal just right to make it produce an entangled copy of a photon. Those photons, sharing their quantum link, can be separated and remain identical – a change in the measurement of one affects a change in the measurement of the other.

The material properties in these cooled crystals are such that the photons can be stored and retrieved, much as bytes on a computer are squirreled away for later recall. Compared to the complexity with which our conventional computers and networks function, the ability to store and retrieve a single photon might seem rudimentary. But it’s a big first step down a road that could produce unhackable communications schemes and superfast, energy efficient quantum computers.

And if that single proof of concept seems as fragile as the bond between two entangled photons, think again; a separate research team at the University of Geneva in Switzerland has reported similar results using a different kind of crystal.

[Eurekalert]

One confidential diplomatic cable sent from the Beijing Embassy to Washington in February suggests China is doing big things at the small scale. For one, China is aggressively expanding its nuclear energy resources, with plans to open at least 70 nuclear plants in the next decade. More interestingly, the Chinese Academy of Sciences (CAS) is pouring research funding into its Institute of Plasma Physics (IPP) to conduct ongoing research into nuclear fusion.

Apparently China has been hard at work on its Experimental Advanced Superconducting Tokamak (EAST) reactor, which is designed to sustain a controlled fusion reaction that can go on indefinitely at high temperatures. In 2009, researchers apparently sustained a 18-million-degree reaction for 400 seconds, and a 180-million-degree reaction for 60 seconds. Their goal for 2010 was to sustain a 180-million-degree reaction for more than 400 seconds, though it’s unclear if they achieved that. Moreover, IPP is apparently conducting research on hybrid fission-fusion reactors, though details are slim.

Perhaps most interesting: China doubled the IPP budget in 2009 over 2008, and the diplomatic chatter suggests 2010’s budget saw a significant boost as well. Amid choppy economic waters, such funding bumps indicate a real commitment on China’s part to figure out the fusion energy puzzle.

China’s sci-tech ambitions don’t stop there. While the evidence is anecdotal, the embassy seems to think the Chinese are pulling ahead in fields like quantum communications and even teleportation. To quote one diplomat’s description of a trip to the University of Science and Technology of China (USTC) in Hefei: “A cursory walk through their labs seemed to indicate they had already succeeded in single-particle quantum teleportation and are now trying to conduct dual-particle quantum teleportation.”

Then there’s the Big Brother tech that we’ve come to expect from China. The same cable says the CAS’s Institute of Intelligent Machines (IIM) in Hefei has created a biometric system that identifies individuals through their pace and gait. “The device measure weight and two-dimensional sheer forces applied by a person’s foot during walking to create a uniquely identifiable biometrics profile,” the cable says, and can be installed covertly in a floor to surreptitiously collect biometric data.

[Wikileaks]

String theory elegantly reconciles the otherwise competing rules of quantum mechanics and general relativity. It’s the most widely accepted unified field theory, but it remains controversial. It basically posits that electrons and quarks are not objects, but one-dimensional strings, whose oscillation gives them their observed qualities. The most fun element of string theory is the requirement that the universe has about a dozen dimensions, rather than the usual four (length, width, height and time).

M-theory, the dominant version of string theory, holds that the universe is made up of unfathomably small slices of a 2-dimensional membrane, wriggling in 11-dimensional space.

These bizarre ideas are widely accepted by many theoretical physicists, but the problem is that they can’t be tested — how do you examine an 11th dimension? The field has suffered a backlash in recent years partly for this reason, as some scientists say a theory is not a theory if its predictions can’t be studied in a lab.

Well, now they can, according to professor Mike Duff of the theoretical physics department at Imperial College London. He is lead author of a paper to be published tomorrow in Physical Review Letters, which explains how string theory math can be used to predict quantum entanglement.

Duff said he was at a conference in Tasmania when a colleague presented some mathematical formulas describing entanglement of multiple quantum bits. The equations looked familiar. Upon returning home, Duff checked his notebooks from a few years earlier, and realized the formulas were the same as those he developed to use string theory to describe black holes.

This is completely unexpected, he said. There is no obvious reason why the insanely complex mathematics underlying string theory can also be used to predict the behavior of entangled quantum systems.

“This may be telling us something very deep about the world we live in, or it may be no more than a quirky coincidence,” he said.

Either way, it’s useful, he added. Using string theory math, Duff predicted the pattern that would occur when four quantum bits are entangled with each other. This can be measured in a lab, and the results will demonstrate whether string theory actually works.

Right now, the best hope for string theory tests comes from CERN’s Large Hadron Collider, which is designed to find the tiniest elementary particles that make up matter. It’s theoretically possible that LHC experiments will uncover supersymmetric particles — one element of string theory — or bounce a graviton into a higher dimension, which could help prove M-theory. But testing the fuzzy math that predicts these behaviors will be much easier.