In a sense most science and technology news is made up of tidbits, bits and pieces of research. Some of the tidbits are choice morsels, others are insight resistant gristle, and perhaps even more are pure confection. What’s generally missing in the news is how (or if) the tidbit fits into a larger piece or the whole enchilada (to use an expression). This fitting into a whole is difficult, even the experts in a field don’t always know how all the various pieces of research integrate – if they do at all. So consider this piece of news as a tidbit that may be part of a potentially very important whole: Robins use quantum physics for navigation.

First, let’s deal with what robins do. They migrate. They fly thousands of miles from northern lands (Canada, Scandinavia) to warmer winter climes in Africa and southern United States, and then they go back in the spring to breed. Like many other birds, they tend to fly back to places they have been before. How do they do that?

Scientists have long suspected that birds have ‘built-in compasses’ of some kind. Over the years through many experiments, it’s become a fairly sure thing that most birds use the Earth’s magnetic fields to guide them over long distances. It’s called magnetoreception and in many species, including the robin, it takes place in the eyes. It’s known to be a chemical process of some kind but the details have remained murky.

Now a team of researchers from Oxford University (UK) and Singapore University have, at least, put a label onto the murky process: Quantum coherence. In a paper to be published in Physical Review Letters, based on experiments on robins performed by Oxford and Frankfurt scientists, Erik Gauger (Oxford) and Simon Benjamin (Singapore) noted that when the robins were subjected to electromagnetic noise – even at extremely low levels – their navigation system failed to work properly. In fact, the levels of interference were so small that only a quantum level system would be sensitive enough to pick it up.

Gauger and Benjamin believe that molecules in the bird’s eyes use quantum coherence, which in a nutshell is about the ability of electrons to follow paths that interfere with each other, sometimes destructively and sometimes perfectly coherent (a pure state). Normally quantum coherence operates at the subatomic level, but some very important technology is based on larger scale coherent effects such as lasers, superconductivity and superfluidity. Now scientists are beginning to find the effects at the molecular level in biological systems.

‘Progress in this area is proving to be very difficult because the phenomena that must be harnessed are extremely delicate. It would normally be thought almost inconceivable that a living organism could have evolved similar capabilities.’

Co-author Simon Benjamin from Singapore explained: ‘Coherent quantum states decay very rapidly, so that the challenge is to hold on to them for as long as possible. The molecular structures in the bird’s compass can evidently keep these states alive for at least 100 microseconds, probably much longer.’

‘While this sounds like a short time, the best comparable artificial molecules can only manage 80 microseconds at room temperature. And that’s in ideal laboratory conditions.’

[Source: Oxford Science Blog]

This research work, which is still very much in progress, is one of several that involve surprisingly sophisticated use of quantum coherence (or quantum entanglement) in biological processes. Several instances have already been posted here at SciTechStory:

Quantum entanglement helps keep DNA together
Quantum entanglement in photosynthesis
Quantum chemistry: A new world

It’s way too early to evaluate the discoveries of quantum effects in biology, but even the first signs are portentous.

Third in a series of posts inspired by ten topics in ‘Insights of the Decade’ from the December 17, 2010 special issue of Science Magazine The topics are: Inflammation, climatology, tricks of light, alien planets, the microbiome, cell development, Martian water, the DNA time machine, cosmology and epigenetics. The original articles are now behind a paywall; they won’t be reproduced here, but their gist is present. I’ll try to put them in context and specifically within the Impact Areas of SciTechStory.

In this new decade, one of the focal points of science and technology will be light. That is, light in all its daedal forms such as photons, plasmons and electromagnetic waves that are the subject of research in quantum mechanics, laser technology and transformation optics. Now most of this is not your everyday sunlight or lamplight; this is light taken down to its smallest bits (particles) or most fundamental behavior (waves). This is where light becomes, for lack of a scientific word, weird. Or less colorfully, where the properties of light become unfamiliar, unintuitive, and subject to some peculiar manipulation.

Of these manipulations of light, transformation optics is the most interesting and least known. The road to transformation optics began in 1968 with a paper by Russian physicist, Victor Veselago, who looked at standard optics – through glass – and wondered if there might be another sort of material that could defy the limitation of always bending light in a positive (greater than 1) direction. Veselago thought this would be a fine thing, to make light bend ‘backwards’ (like a straw in water only with the refraction going back toward the straw). He could visualize lenses that were flat, which could focus light better than conventional lenses.

What Veselago was wishing for (but did not himself develop) was the advent of metamaterials. Metamaterials are mostly man-made and come in many shapes and sizes, literally. Most of them fall into the category of nanomaterials – little rods, cones, spheres, and pipes only a few nanometers in size (that is, thinner than a few hundred-thousandths of a human hair). Because they are so tiny, the spaces within or formed by these metamaterials affect light in unexpected ways. In short, the spaces can be described with the mathematics of Einstein’s theory of General Relativity, where space and time are warped by gravity. In this case, it’s light or electromagnetic waves that get warped.

Late in the 1990’s John Pendry and colleagues at the Imperial College London (UK) caught on to the ability of carbon nanotubes to absorb radio waves. He went on to discover that certain nanomaterials could be ‘tuned’ to resonate with electric and magnetic fields at precise frequencies. As they resonated, they transformed the electromagnetic waves so that it was possible to create a negative refractive index (i.e. less than 1, or bend light backwards).

Pendry’s work, though controversial, could be put to the test – and many experiments in the early 2000’s started to show that indeed negative refraction was possible and shortly hyperlenses were born. By the end of the decade the experiments had gone much further, almost to the point of showing that metamaterials could bend light any way desired. For example, in 2008 Xiang Zhang and colleagues at the University of California Berkeley (USA) made three-dimensional electromagnetic waves ‘flow’ around an object – making it invisible. No, this is not a Romulan cloaking device; not yet.

Actually the ‘cloaking’ capability of transformation optics is a convenient bit of hype for properties that may have more mundane but potentially important uses. The ability to manipulate light at the wave or particle level means scientists are looking at techniques with thousands of possible applications. For example research is now looking at ways to turn electromagnetic waves that refract at half the normal wavelength of light to produce an ultra-thin high-powered laser called a spaser. [Here’s SciTechStory’s post: Progress report: Plasmon Spasers]

As scientists learn more about the behavior of light at the quantum level, they’re finding that it is not only appropriate for certain man-made applications such as electronics, but that it also exist in nature. There are already the early glimmerings of quantum-level effects with light in photosynthesis and quite possibly within the brain. (More on these topics at a later time.)

Light, the field of photonics, isn’t currently a SciTechStory impact area. It should be. The list already has 40 areas, which is itself a cut-down from many potentially important developments in science and technology. One of these days it would be great to have the readership help determine which impact areas are added (or dropped) and their relative ranking. For now though, I have to pick and choose, and it seems time to put photonics in the list.

Is it time to start investing in Bose-Einstein condensates? They’re not dew drops, of course. Anything with ‘Einstein’ in it has got to be physics. So what kind of condensate is this, and what makes it (potentially) useful?

The concept of Bose-Einstein condensates, often abbreviated BEC, was theorized by Satyendra Nath Bose and Albert Einstein in 1924-1925, but not produced in a laboratory until 1995. Carl Wieman, Eric Cornell, and Wolfgang Ketterle received the 2001 Nobel Prize in Physics for the work. Still, Bose-Einstein condensates are not well known outside the physics community (understatement). To use the colloquial, they’re pretty special.

To begin with, only certain atoms qualify to become a Bose-Einstein condensate. They must be bosons, identical particles with an integer spin (the rotation of each particle is a whole number). Photons qualify as do Helium-4 atoms (sort of) and Rubidium atoms. The key is that boson particles can exist together at the same quantum state, which makes it possible to concentrate them. The first BEC particles were made by cooling a gas of rubidium atoms to 170 nanokelvin. The Kelvin scale of temperature starts at absolute zero (0 degrees Kelvin or -273 degrees Celsius). That is so cold even atoms have no motion, no energy. 170 nanokelvin is just a smidgeon above absolute zero (1.7 x 10-7 to be exact). At that extreme temperature the bosons fall (“condense”) into the lowest quantum state, and as Einstein predicted, a new kind of matter is created – a single ‘super-particle’.

A super-photon is one of these new kinds of matter. It was not considered possible to create them. Although Bose and Einstein stated their theory in terms of photons, physicists were unable to make them in the laboratory because as photons cool toward absolute zero they disappear. They disappear literally and figuratively: As they lose temperature photons change their light frequency until finally they leave the visible spectrum and become infrared light (invisible to the human eye). As photons cool through the infrared spectrum, there are fewer and fewer of them – until there are no more. This disappearing act appears to make a Bose-Einstein condensate of photons seemingly impossible.

Physicists, however, can be clever. Four physicists at Bonn University (Germany), Jan Klaers, Julian Schmitt, Dr. Frank Vewinger, and Professor Dr. Martin Weitz published their successful technique in the November 2010 issue of Science [Bose–Einstein condensation of photons in an optical microcavity]. They created a specialized cold-chamber (actually a miniscule cavity) with two highly reflective mirrors and bounced light (photons) between them. Between the mirrors was a layer of dissolved pigment molecules in a fluid. As the photons passed through the layer, some of them temporarily became engaged with the pigment and cooled to the pigment’s temperature – room temperature. As the temperature dropped, a laser beam was added to excite the pigment molecules so that even more photons were cooled. Eventually the point of condensation was reached, and the photons ‘clumped together’ (condensed) into a super-photon particle.

Remember, this condensate is made of photons – light – so the end product is a new kind of light. In fact, when it was first created, the scientists knew it was there because in the center of the chamber there was a yellow laser-like light.

A ‘photonic Bose-Einstein condensate’ has the characteristics of a laser light source, so at least theoretically it could be used for laser-type applications. Here is where the commercial interest begins. Unlike ordinary lasers, which operate in the visible light spectrum, a BEC super-photon operates at X-ray frequencies. The X-ray frequency (wave length) is much shorter and more powerful than visible light. This could be extremely valuable in the process of etching silicon chips with complex and very, very small circuitry. (Current chips are made with standard lasers.)

The technique could also be used to create solar cells that can focus and capture sunlight even on a cloudy day.

No surprise, however, that these practical applications are potential only. Harnessing photons to make a BEC is considered relatively simple by this method, but that’s in a laboratory. At a commercial scale and in a variety of environments – well let’s say that success is not a given. However, now that a BEC super-photon is no longer theory, there will be many who will push very hard to find practical applications – any of them could revolutionize the making of electronics, or change the game in solar energy.

Wrong, at least in one way.

Granted, quantum mechanics is a tough subject. So is your brain. That doesn’t mean it’s not worth knowing about. As for quantum physicists knowing about such a relationship, well they didn’t – and they certainly do care. That’s why the work of two scientists, Stephanie Wehner, an information theorist (and former hacker) from the National University of Singapore and Jonathan Oppenheim, a physicist, from the department of applied mathematics and theoretical physics at Cambridge University (UK) could be an important frame-changer. Published in the journal Science [The Uncertainty Principle Determines the Nonlocality of Quantum Mechanics] what they propose could change the way quantum physics is understood; it changes the frame of reference.

Oppenheim has published on arXiv (open access) a remarkably informal two page article explaining what he and Wehner are doing. His closing words are telling:

What I hope you find is that there are some very simple and fundamental questions about quantum theory that we don’t know the answer to, and that applying techniques from information theory to our laws of nature, allow us to make some progress in answering these questions, and more importantly, suggests basic and important questions we wouldn’t normally think of.

[Source: The uncertainty principle determines nonlocality]

I think for many people, even those who have pondered quantum mechanics for a while, the approach taken by Oppenheim and Wehner may help to frame quantum mysteries in a way that makes them less…mysterious.

Let’s dive into the deep end of the pool (using water-wings, of course, no math). Wehner and Oppenheim begin with the current understanding of the uncertainty principle and quantum nonlocality.

Two supposedly unrelated principles

Heisenberg uncertainty principle: Few concepts in physics get stretched out of shape more than this one. It’s really a statement about the limits of knowledge. There are certain pairs of physical properties, momentum and position are typically used for examples, that cannot be determined simultaneously to an arbitrary degree of precision. Think of an atom as it travels through the air: The uncertainty principle says the more precisely you try to measure its position, the less precisely you can measure its momentum. Put another way, attempting to measure one property with increasing precision makes the measurement of the other property more uncertain.

Quantum nonlocality: Usually this is described as quantum entanglement. It is a quantum effect on information shared between two objects (usually atoms or atomic particles). The ‘entangled’ relationship means that measuring a property on one object simultaneously changes the properties of the other, even if the objects are separated by an arbitrary distance.

Obviously quantum physics is not easy to understand. Even physicists tie their neurons into knots over it. More than anything there’s a natural tendency to want to think of quantum effects in terms of normal human experience (or what physicists call ‘classical physics’). When someone describes two atoms that are entangled so that they behave as if they were one and the same atom (what happens to one instantaneously happens to the other), our brains try to envision this as two separated objects with some invisible link that coordinates them. This way of thinking is rooted in our ‘real world’ physicality – action, reaction, that sort of thing. It requires a form of what physicists call action at a distance, where the change in one atom happens in the other atom without a mediator, that is, some connecting force. In classical physics, this is considered impossible.

In normal physics everything happens ‘locally.’ That is, really local: Everything is within one angstrom unit or less of each other (one tenth of a billionth the thickness of a human hair, or 0.0000000001 meter). Of course, this is incomprehensibly small. When physicists say two atoms can be ‘entangled,’ it’s not hard to believe at these tiny distances. We’d have more difficulty believing the same thing can happen when the atoms are a kilometer apart. Fortunately, according to Oppenheim and Wehner it appears there are limits to entanglement (more generally, nonlocality).

They go about explaining it like this: Consider two atoms separated but at some predictably limited distance. If the two atoms are entangled it is possible to describe the properties of one atom accurately more often by observing the properties of the other atom. That is, there is a certain amount of ‘information’ about the atoms that is shared, which helps make guesses as to their status more accurate than any other strategy for guessing.

A quantum game

Wehner explains this by means of a game with cats and boxes (shades of Schrödinger). It’s a fairly simple game, but I’m going to change the objects from cats to atoms so you don’t have to make the mental switch from animals to quantum properties:

There are two scientists, Alice and Bob. Alice has a device that can trap two entangled particles and, if desired, put them in two containers (right and left). Alice has programmed her computer to act like a referee. Her colleague Bob stands at the other end of the room where he can’t see what Alice is doing or communicate with her in any way, although he does have a computer connected to hers.

To start the game, Alice’s computer displays “odd” or “even” (like flipping a coin with heads or tails). If it displays “even,” Alice is to put either one particle in each container or no particles in any container. If it displays “odd,” she is to put one particle in either the right or the left container. Then Bob’s computer displays either “odd” or “even.” If it’s “even” Bob is to guess whether there’s a particle in the left box, and if “odd,” he must guess if there’s a particle in the right box. This is not a collaborative game, so they both get a point if Bob guesses correctly and none if he guesses wrong.

I won’t pick this game apart, but there are enough combinations so that people can strategize on how to make the guesses and improve their chances. Bob and Alice confer on strategy, but after the game starts they can’t communicate. If they can make a note in the computer about their strategy, and refine it over a series of games, the best strategy they can devise will win, on average, 75% of the games.

Now here’s the crucial part: Remember that the two particles are entangled. That means if Alice takes measurements (such as momentum, spin direction, mass) of one particle, it influences the properties of the other particle. This is called steering. If instead of recording their strategy Bob bases his guesses on measurements taken of the second particle – he improves the chances of a correct guess to 85%. The information provided by quantum theory allows Alice and Bob to make guesses better than any strategy they could record.

There is a subtle but important difference to highlight: The entangled particles share information and this relationship is based on the way quantum behavior can be measured. This does not imply some physical connection between them, no “action at a distance.” What Oppenheim and Wehner are exploring is an approach to quantum behavior based on information theory, a branch of computer science and mathematics.

The approach led them to a rich question: Why isn’t quantum behavior even weirder than it is?

Quantum weirdness

Einstein thought of quantum entanglement as ‘spooky action at a distance.’ Wehner and Oppenheim wondered why it wasn’t even spookier. In Oppenheim’s words:

Now, instead of fighting nonlocality, we ask why our description of quantum reality doesn’t require even more nonlocality. We don’t ask why quantum theory is so weird, but rather, why isn’t it weirder? Indeed, there could exist states of matter which are better than entanglement, in the sense that Alice and Bob could use them to win the game more than 85% of the time. These hypothetical objects (called PR-boxes, after Sandu Popescu and Daniel Rohrlich), allow Alice and Bob to win the game all the time, and they do not appear to be pathological, at least in the sense that they don’t allow action at a distance. Why does nature rule them out?

Here’s how Oppenheim and Wehner formulate an answer:

It starts with using computer science concepts for the atom/container game. The placement of the atoms in containers can be coded with two bits (in computer-style binary code: 0 or 1) because there are four possible ways to distribute the atoms (00, 01, 10, 11). Bob can only learn about one of the bits, either the atom is in the left container (one bit) or in the right container (one bit). He can’t learn about both bits to make a complete coding of the particle distribution into containers. This is where uncertainty meets up with entanglement. The two bits for coding are like the problem of momentum and position. The more you know about one, the less you can know about the other. Bob can only guess about one side or the other, left or right, but not both. In terms of quantum information, the more Bob tries to learn from one bit, the less he can learn about the other bit.

The conclusion is that even though two particles are in quantum entanglement, the uncertainty principle prevents deriving enough information from one particle so that the game can be won every time.

The game analogy is not perfect. Wehner and Oppenheim admit that they don’t know what restricts Bob’s ability to retrieve both bits of information. Nor can they answer how –or why– two particles can be affected by measuring one of them (by steering). Nevertheless, by putting the problem into the framework of information, instead of grappling with the weirdness like a metaphysical concept, it becomes a problem with more handles for thinking about it.

Perhaps it is at least as important that Oppenheim and Wehner have developed an equation, which not only describes the relationship between the locality principle and the uncertainty principle, but also can be used to calculate how much uncertainty affects a given amount of locality. In short the two effects can be quantified. This opens the door to experiments with measurable results, the key to validating their contribution and expanding beyond it.

Because the principles of quantum mechanics are fundamental to everything in the physical world, advances in our understanding will percolate throughout physics and eventually into the domains of electronics, medicine, and other ‘practical’ technologies. That makes the work of Oppenheim and Wehner worth knowing about, if not caring about it as much as a physicist.

Essentially, a diode conducts an electrical current in only one direction. Like a check valve with water, it won’t allow back flow. However, more sophisticated diodes do more than act like a one-way valve, they also can modify the current, such as converting alternating current to direct current or changing the modulation (phase) of radio signals. In short, diodes are versatile and are one of the keystone components of the modern electronics industry. Most diodes these days are made of silicon, like pretty much everything else electronic. Silicon is relatively inexpensive and relatively easy to use in manufacturing, but it has limits. It’s these limits, especially in performance, that the electronics industry is now pushing.

Diodes made from something other than silicon could be one of the prime pushers. The top candidate, the MIM diode, is constructed like a sandwich with two very thin metal strips separated by an insulating material in the middle. Electric current (in the form of electrons) on one metal strip move through the insulator to the other metal strip not by conduction, which is dependent on the conductivity of the material in the middle (and is slow) but on an effect called quantum tunneling. In this case, electrons from one metal strip should not be able to cross the insulator to the other metal strip because, by the numbers, it should take more energy to cross the insulator barrier than the electrons have to begin with. However, cross it they do. As a gross over-simplification, a certain percentage of electrons derive additional energy within the barrier and manage to ‘tunnel through’ to the other side. This happens very fast, much faster than electrons travel through a semiconductor such as silicon. So, in theory, a MIM diode can be much faster than say a silicon transistor.

However, in practice there are problems; problems decades of research have been unable to solve. Now a team of researchers at Oregon State University (Corvallis, USA) has developed an effective solution, published online October 25, 2010 in Wiley Advanced Materials [Advancing MIM Electronics: Amorphous Metal Electrodes]:

As unfamiliar (non-intuitive) as quantum effects are, they are still affected by physical things that we can understand. What the researchers discovered is that an uneven surface of molecules on the metal strips of a MIM diode makes the quantum tunneling highly unpredictable (a.k.a. uncontrollable). As small as a diode might be (a centimeter or two, for example) at the molecular level the metal strips might as well be football fields. Over such a vast area, it’s not unusual to have irregularities – bumps and distortions – in the molecular surface. The material previously used for the metal strips of the MIM diode was aluminum, which is known to have a comparatively ‘rough’ surface. After much experimentation with different metals and combinations, the team settled on an amalgam of Zirconium, Copper, Aluminum, and Nickel (ZrCuAlNi), which they refer to as an ‘amorphous metal contact,’ the amorphous part meaning shapeless as in smooth.

First and foremost, this quantum tunneling diode is much faster than current silicon-based electronics. It is also practical: Not only does the amorphous (smooth) surface of the metal contacts make the tunneling controllable, but these MIM diodes are also relatively easy to manufacture.

The predictions for success of the MIM diode have an expansive quality:

“Researchers have been trying to do this for decades, until now without success,” said Douglas Keszler, a distinguished professor of chemistry at OSU and one of the nation’s leading material science researchers. “Diodes made previously with other approaches always had poor yield and performance.”

“For a long time, everyone has wanted something that takes us beyond silicon,” Keszler said. “This could be a way to simply print electronics on a huge size scale even less expensively than we can now. And when the products begin to emerge the increase in speed of operation could be enormous.”

[Source: Nanotechnology Today]

In short, a world-beater in electronics. Not tomorrow though. It will take some time for the development of manufacturing techniques. MIM diodes may have many potential uses, but they will have to meet stringent demands for reliability and predictability. They will have to be competitive with the costs and applications already in place for conventional silicon semiconductors. There may be limitations, as yet unknown, in what can be done with this kind of diode. Nevertheless, the MIM diode is well worth tracking.

Not only is graphene one atom thick, its atoms are arranged in a honeycomb pattern (hexagonal shapes). However, that’s it: Carbon atoms, arranged as hexagons on a tiny sheet one atom thick. It sounds like graphene is simple stuff, but what this simplicity does to the physics! Graphene has many unique properties, and scientists continue to find more.

One new finding, which is still a matter of mathematical theory, describes a unique property of graphene that may provide a more convenient way to study something currently approachable only with a massive atomic particle accelerator. A group of physicists led by Abdulaziz Alhaidari at the Saudi Center for Theoretical Physics (Dhahran, Saudi Arabia) have published a paper at arXiv [Dynamical mass generation via space compactification in graphene] showing mathematically that the fundamental particles in graphene (fermions), which have no mass in two dimensions, will effectively have mass if the graphene is simply rolled into a tube.

How, you may ask, does an obviously three-dimensional figure (a tube) have only one dimension for moving fermions? This is where the unique properties of graphene come in: Electrons flowing through the special structure of graphene (hexagons in a one atom thick layer) behave like electrons travelling in a vacuum close to the speed of light. This behavior is not described by the traditional mathematics (Schrodinger equation) but by the mass-less Dirac equation. How then can these electrons acquire mass?

What constitutes and creates mass is a subject of debate in physics, but a commonly held theory is that matter at the smallest scale (nanoscale or below) has compacted dimensions. Describing these compactified spaces in quantum mechanics uses equations that include mass – voila, that’s how mass arises. Alhaidari and colleagues looked at these equations and wondered how they would apply to graphene. What if the space dimensions of two dimensional graphene were compactified into one dimension? Looking at various forms for graphene, they decided that when a sheet of graphene is rolled (essentially this makes a carbon nanotube), the fermions travelling down the tube would behave as if they were in a single dimension.

Remember, this is all mathematics. The Saudi physicists are not writing about creating mass ‘out of nothing.’ They’re saying that a two-dimensional condition that can be described with a massless Dirac equation can be effectively turned into a somewhat simpler one-dimensional equation with a term for mass. They believe this is the condition of a graphene sheet rolled into a tube. Mathematically the approach could provide a somewhat easier to use framework for looking at some very difficult problems in relativistic physics.

The math and the physics are tantalizing for the specialists. For most of us, the take-away is how graphene is providing the stimulus for theorizing and experimentation on a very broad front. From electronics to quantum physics this seemingly simple substance is opening fresh pathways for enquiring minds.

While it probably won’t be easy, there is hope that graphene as a physical substance can be involved in experiments that provide verification (or not) for mathematical predictions. The hope comes from the combination of graphene’s unusual properties and the fact that anybody in any lab anywhere can acquire graphene, attach electrodes to it, and go to work. While it’s not exactly the old ‘500 monkeys typing eventually create Shakespeare,’ easy accessibility to experimental procedures increases the chance that somebody will do breakthrough work.

Of course, there’s also hope that insights gained from the mathematical and physical knowledge of graphene will have practical applications. Even physicists smile at that happy thought. Engineers are more likely to be skeptical about the leap from quantum and relativistic effects at the nanoscale to finding useful applications at the macro scale (human visible size). I suppose this means that it will be a while (if ever) before graphene becomes a household word. On the other hand, the possible applications of graphene are already real enough to attract investment. In the end it may not matter so much if graphene is truly a ‘wonder material’ but that it was the material which caused so many people in science and technology to wonder.

But wait. This is the reported result of one paper, based on one type of (novel) experiment. True, the scientists representing a large collegium of institutions and publishing in the journal Nature put the size uncertainty at 0.00067 femtometers, whereas the old uncertainty size was 0.0069. The new one is an order of magnitude better. Nevertheless, whenever something this, well, the word is shocking, comes along the reaction of most scientists is to ask questions: What is the integrity of the experimental setup? Is it possible that mistakes in measurement or calculation were made? Is it possible that while this may seem to contradict or invalidate many theoretical constructs, a small tweak here or there might explain this result? In short, the basic reaction is not “This must be wrong!” It is, “We must question, test, and validate (or invalidate) this result as thoroughly as possible because it is extremely important.” That it is.

Not as important for me and thee as discovering the sun is going to explode, but for the many theories in quantum electrodynamics (QED) and nuclear particle science that are based on the way a proton of a specific size interacts with the orbits of electrons – a fundamental notion of how the physical world is constructed – it’s very important indeed. (To trivialize for an example, what would happen if you discovered your name was Smit instead of Smith? If you wanted to be correct, how many documents would need to change?)

How is it that something so fundamental as the size of a proton could be wrongly measured? Simple, scientists didn’t have the right tools to make such an accurate measurement. The idea for the experiment was conceived over forty years ago, but until recently the equipment and the techniques were not available. The essential technique was to use pulsed laser spectroscopy (the new equipment) to look at an atom of hydrogen where the usual single electron has been replaced by a muon, which acts like an electron but is 200 times heavier. Because they’re bigger, muons are more sensitive to the size and pull (electromagnetic) of the proton and this sensitivity is large enough to be measured. By calculating backward (so to speak) from the behavior of the muon, the size of the proton is revealed – and was revealed to be 4% smaller than expected.

At this point, the real impact of the experimental results finding a smaller proton is not to change the world or even the world of physics – it is to excite the activity of scientists who find the possibility of a ‘game changer’ a great challenge or a dreadful possibility. In either case, the chase is on to either confirm or deny the findings through further investigation, experimentation, and theoretical noodling.

For a good backgrounder and commentary, check out the blog Uncertain Principles:

So, protons are way smaller than we thought? Yes and no. This measurement suggests that the size is smaller than that measured in previous experiments, but the difference isn’t all that big in absolute terms. And it’s possible that there’s some effect they haven’t accounted for properly in making this measurement.

What sort of effect? Well, if they knew that, they would’ve accounted for it. There’s a fearsome amount of theory going into the conversion from Lamb shift to proton size, so it’s possible that something there is a little bit off. It’s also possible that there’s something wrong experimentally– this is the first time anybody has ever done laser spectroscopy of muonic hydrogen, so they might’ve overlooked something.

Or it could be completely new physics.

[Source: Uncertain Principles]

Physics this complex and important doesn’t usually come gift-wrapped from the mind of one scientist; it takes a massively collective effort:

Randolf Pohl1, Aldo Antognini1, François Nez2, Fernando D. Amaro3, François Biraben2, João M. R. Cardoso3, Daniel S. Covita3,4, Andreas Dax5, Satish Dhawan5, Luis M. P. Fernandes3, Adolf Giesen6,13, Thomas Graf6, Theodor W. Hänsch1, Paul Indelicato2, Lucile Julien2, Cheng-Yang Kao7, Paul Knowles8, Eric-Olivier Le Bigot2, Yi-Wei Liu7, José A. M. Lopes3, Livia Ludhova8, Cristina M. B. Monteiro3, Françoise Mulhauser8,13, Tobias Nebel1, Paul Rabinowitz9, Joaquim M. F. dos Santos3, Lukas A. Schaller8, Karsten Schuhmann10, Catherine Schwob2, David Taqqu11, João F. C. A. Veloso4 & Franz Kottmann12

1. 1 Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany
2. 2 Laboratoire Kastler Brossel, École Normale Supérieure, CNRS, and Université P. et M. Curie-Paris 6, 75252 Paris, Cedex 05, France
3. 3 Departamento de Física, Universidade de Coimbra, 3004-516 Coimbra, Portugal
4. 4 I3N, Departamento de Física, Universidade de Aveiro, 3810-193 Aveiro, Portugal
5. 5 Physics Department, Yale University, New Haven, Connecticut 06520-8121, USA
6. 6 Institut für Strahlwerkzeuge, Universität Stuttgart, 70569 Stuttgart, Germany
7. 7 Physics Department, National Tsing Hua University, Hsinchu 300, Taiwan
8. 8 Département de Physique, Université de Fribourg, 1700 Fribourg, Switzerland
9. 9 Department of Chemistry, Princeton University, Princeton, New Jersey 08544-1009, USA
10. 10 Dausinger & Giesen GmbH, Rotebühlstr. 87, 70178 Stuttgart, Germany
11. 11 Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland
12. 12 Institut für Teilchenphysik, ETH Zürich, 8093 Zürich, Switzerland
13. 13 Present addresses: Deutsches Zentrum für Luft- und Raumfahrt e.V. in der Helmholtz-Gemeinschaft, 70569 Stuttgart, Germany (A.G.); International Atomic Energy Agency, A-1400 Vienna, Austria (F.M.).

The why question is rather easy to answer: The dark pulse laser uses infrared frequencies, which come in very short wavelengths. The short wavelength produces a pulse with a span of about 90 picoseconds, that is 90 trillionths of a second. This very short pulse has advantages in certain applications; communications, for example, where the ultra-short pulses tend to transmit (propagate) without distortion. It could also be used for ‘exposure’ as in a camera, to capture events happening in extremely short periods of time. Most of the applications will take advantage of the short duration of this laser’s pulse.

The how question is a little more involved, mainly because it involves quantum mechanics. Anything quantum tends to become somewhat murky, even though with laser technology it is a relatively standard phenomenon. In any case, the dark pulse laser uses quantum dots (or qdots). Quantum dots are a type of semiconductor (think of semiconductors in computer chips), which are crystals that ‘excited’ by an electric current store energy until, in a burst, they emit the energy at a specific wavelength (usually within the spectrum of light). The size and electrical properties of the quantum dot crystals can be controlled with great precision.

In the dark pulse laser millions of quantum dots (all about the same size of 10 nanometers, that is, billionths of a meter) in a ‘laser cavity’ are subjected to a small electric current until they begin to emit light. Since there are millions of them, all emitting at the same frequency and voila – laser light. Now comes the interesting part: After emitting light the qdots ‘rest’ (recover energy) for all of 1 picosecond, but recover more slowly from their energy loss as a group in the laser cavity (about 200 picoseconds). This sets up a cycle of energy gain and loss increasingly dominated by the loss period, until the laser reaches a steady state of repeating dips in intensity of about 70%, a very substantial drop or ‘darkness’ against a background of the emitted laser light. Hence, the name ‘dark pulse.’

The NIST/JILA dark pulse laser, using all ‘homegrown’ quantum dots, is the first to produce the pulses without needing post emission electrical or optical shaping – in short, a simpler, purer form of quantum dot crystal that produces more precise pulses.

The results, as described in the journal Optics Express represent just a step in developing the dark pulse laser technology. Like all laser technologies, the path leads down the trials of production – attempting to take instrumentation and procedures that work under the extreme control of a laboratory, and make them work in ‘other locations.’ Eventually, if all goes well, this leads to commercial production.

The imagery was captured with a highly customized microscope with an iron-coated tip to manipulate cobalt atoms on a plate of manganese. The type of microscope, scanning tunneling microscopy (STM), produces images down to the atomic level. In this case, the ‘scope was used to position individual cobalt atoms on the manganese surface in order to change their electrons’ direction of spin. The images they captured showed that the atoms would appear as a single protrusion (bump) if the spin was upward and as a double protrusion if the spun was downward.

The images provide the first visual evidence of the spin property (although it’s not video and you don’t see the actual electrons turning). Equally as important, the techniques used demonstrate the ability to manipulate spin, which will be necessary for future development in quantum computing or other spintronics devices.

“Different directions in spin can mean different states for data storage,” said Saw-Wai Hla, an associate professor of physics and astronomy in Ohio University’s Nanoscale and Quantum Phenomena Institute and one of the primary investigators on the study. “The memory devices of current computers involve tens of thousands of atoms. In the future, we may be able to use one atom and change the power of the computer by the thousands.”

[Source: Ohio University]

The future is ‘down the road a bit’ for spintronics. For instance, in this case the experiments were conducted with materials cooled to 10 degrees Kelvin. That’s just ten degrees above absolute zero. The same techniques will need to work at room temperatures before computers and other real-world electronics can be built with spintronics.

By ‘higher temperatures’ this does not mean room temperature, but it does mean up to 50 degrees Kelvin, which is substantially warmer than 4 degrees Kelvin. They accomplished this by doing what physicists call “squeezing.” In quantum physics, the more accurately positions (of atomic particles) are measured, the less can be determined about their momentum. Similarly, measuring time decreases the measurement of energy, or phase amplitude. (This is remindful of the old bromide: You want quick, easy, and cheap? Pick any two.) The effect is called the Heisenberg uncertainty principle, which places limits on how well pairs of complementary properties can be observed.

Physicists have learned how to juggle the measurements to optimize one measurement or another. This is “squeezing.” What the Spanish team wanted to know was could squeezing be applied to a quantum situation where everything was changing (that is, in disequilibrium – whereas most such research is done in an equilibrium state). To test this, they used a pair of driven (by magnetic fields) quantum oscillators that are entangled in a ‘hot’ environment. Because they could control temperature and the driving force of the oscillators, they could constantly squeeze the system, and the entanglement was retained at higher temperatures. How high could this go?

Galve and co say this depends on the coupling between the oscillators. But they calculate that entanglement between a pair of calcium ions in an rf trap–a standard set up in many labs–and show how it could be sustained at 50K. That’s significantly better than the sub-4K systems that experimenters have to manage with today. “We believe this to be a huge experimental step,” they say.

What about room temperature experiments? That would require a very strong coupling and may cause other problems. The squeezing causes the quantum states to become more delocalised, in other words they become smeared out in space. That could be a problem if the ions end up largely outside the trap in which they are supposed to be confined.

[Source: Technology Review]

This new approach – exploring quantum entanglement in non-equilibrium systems – is not only an important step for quantum physics, but apparently it’s also a step in the direction already taken by Nature.