I’m setting the stage for one of those quiet pieces of very interesting science. It’s about proteins. Proteins are the building blocks of life. The genetic code in DNA provides the template to manufacture protein into all the cells of an organism. So we’re talking about something fundamental to life as we know it.

Proteins are made by stringing together amino acids. For general purposes there are twenty amino acids in protein and they can be put together in endless combinations, some in short chains (yeast averages 466 amino acids), some long chains (titins have nearly 27,000 amino acids) and everything in-between. The pattern of amino acids determines much of the functionality of the protein. But that’s not all. Proteins also have shape – threads, coils, curves, bends – they are folded. The folding of proteins is just as important to the functionality as the sequence of amino acids. A simple analogy would be fitting together the pieces of a puzzle; only pieces cut a certain way fit into other pieces until finally the whole puzzle can be assembled. To extend the analogy: Proteins are three-dimensional puzzle pieces. They are generally very complicated in shape. Even a small protein of only 100 amino acids can theoretically have 10^100 (ten to the hundredth power) different configurations.

In this bewildering number of possible configuration are some of the great mysteries in biology. How are the configurations of proteins determined, and what makes them fold? With all the possible configurations and the complexity of so many proteins, it should take some time for a protein to take on a final configuration. Yet it is known that most protein reconfigurations occur in nanoseconds; how does this work?

The study of how proteins are manufactured and folded into correct shapes is a vast field of study (loosely called proteomics). In this case, the research by two Mongolian scientists, Liaofu Luo at the Inner Mongolia University and Jun Lu at the Inner Mongolia University of Technology (both in Hohhot, China) and published in arXiv, 18 February 2011, Temperature Dependence of Protein Folding Deduced from Quantum Transition, deals with the problem of how proteins change their configurations almost instantaneously.

As scientists usually do, Luo and Lu started with the research already done. (It’s called “scanning the literature.”) They noticed a particular area of protein behavior that was a real problem to explain. In most chemistry, organic chemistry included, the application of heat increases the speed of reaction. This is called the Arrhenius principle. In research on proteins, it was assumed (given their chemical composition) proteins would uniformly fold as they cool down and unfold as they heat up. (Think of a balloon expanding and shrinking with the temperature of the air inside.) The experiments didn’t bear this out; the rate of folding or unfolding according to temperature change was unequal (asymmetric) and uneven (nonlinear). To try to explain this in a traditional manner, scientists referred, for example, to the way parts of a protein that repel or attract water could react very quickly. Some of these explanations seem to work for particular or limited types of protein configurations, but none of the proposed explanations – which Luo and Lu refer to as ‘classical mechanics’ – fit protein transformation in general.

It seemed obvious to them (and may soon to others) that quantum mechanics could provide a better explanation, or in science-speak – a better fit to the observed data. An important argument in favor of a quantum analysis occurred to them: In recent biochemistry a great deal of work is done with ‘tagging’ or ‘marking’ molecules with fluorescent and phosphorescent materials. It’s well known that fluorescence and phosphorescence are phenomena closely related to protein folding and they can only be understood in terms of quantum transition between molecules. Why shouldn’t protein folding also fit within the framework of quantum theory?

Luo and Lu then set about to demonstrate this relationship through mathematics. What they discovered is something like this: In classical mechanics the transition of a protein molecule from one configuration to another should proceed in a series of steps (transition states), adding time at each step – meaning it should be relatively slow. With a quantum transition, the protein could change configuration by ‘jumping’ – skipping all the transition steps – to the final configuration. They call this quantum folding and they developed a mathematical model that shows how the folding, which is virtually instantaneous, would react to change in temperature.

For verification of what the math was showing them, they used the model with the results of real world experimental data. Their quantum transition model matched the folding curves for 15 different proteins and also provides an explanation for the different rates of folding and unfolding among these proteins.

In short, it looks like their model may work for many, if not all, protein folding. Some reports are jumping the gun and calling this the “first universal law of protein folding.” It’s way too early for that.

Luo and Lu’s paper is short, a mere 16 pdf pages, and the model is unpretentious mathematically. (Luo has several other related papers on arXiv.) It comes from unknown researchers in an unknown corner of the academic world, and it’s published on the open-source arXiv system. The lack of pedigree means that it will take more time than usual for scientists around the world to learn of it, examine it, and possibly test it. So it will be interesting to see what – if any – the reactions will be, and whether the research constitutes real breakthrough or something less.

In any case, their work joins the growing list of research that links quantum phenomena to biological processes. If it holds up (their research, and quantum biology as whole) it’s like discovering a brave new world of complexity in the realm of biology.

Related SciTechStory posts:
Ephaptic coupling: Could be how brains coordinate]
Quantum entanglement helps keep DNA together
Quantum entanglement in photosynthesis
Quantum chemistry: A new world

One of those ways is the exploration of what is called spintronics. “Spin” in this case is a property of quantum mechanics. It’s about the rotation (angular momentum) of elementary particles (quarks for example), or the composite spin of elementary particles (such as for a proton or neutron). Experiments have discovered that this rotation has a property of uniform direction – spin up, or spin down. It’s not difficult to understand that up or down can be stand-ins for ON or OFF – the binary of digital coding.

The big difference is that in a spintronic device, once the direction of the spin is set, requires no energy (electrical power) to keep it that way. Spintronic devices are also faster than traditional semiconductor devices. The difficulty, no surprise, is how to ‘set’ the spin and in what material. This is where graphene comes in.

Graphene is a sheet of pure carbon one atom thick (making it two-dimensional) with the atoms arranged in a honeycomb pattern. Graphene has the distinction of being something relatively tangible (it can actually be made by ‘peeling’ ordinary graphite, as in a lead pencil, with scotch tape), yet it has some very exotic properties that scientists are hustling to exploit – for example, with spin.

Now normally graphene as a flat sheet has its particles (essentially in this case, electrons) spinning every-which-way (random). However, researchers at the Niels Bohr Institute, Nanoscience Center (University of Copenhagen, Denmark) collaborating with colleagues in Japan discovered that if graphene is shaped into a tube only a few nanometers in diameter (essentially a carbon nanotube with walls one atom thick) the spin of the electrons is strongly influenced by the motion of the electrons as they are forced to move around the nanotube. The electrons all move in one direction around the tube, and the spin synchronizes. The effect is robust, working on any number of electrons and even on graphene that has imperfections. The effect can be controlled, turned on and off, which makes this approach a candidate for using graphene in spintronic computer applications. The results were published in the journal Nature Physics [Gate-dependent spin–orbit coupling in multielectron carbon nanotubes].

A very different approach to controlling the spin of graphene particles was taken by researchers at the City University of Hong Kong and The University of Science and Technology (Hefei, China). The publication, in Applied Physics Letters [Spin current generation by adiabatic pumping in monolayer graphene] is described in no simple terms:

It involves using spin splitting in monolayer graphene generated by ferromagnetic proximity effect and adiabatic (a process that is slow compared to the speed of the electrons in the device) quantum pumping. They can control the degree of polarization of the spin current by varying the Fermi energy (the level in the distribution of electron energies in a solid at which a quantum state is equally likely to be occupied or empty), which they say is very important for meeting various application requirements.

[Source: EurekAlert]

Got that? In short (apologies for oversimplification), they use the magnetic properties of graphene (ferromagnetic) to induce the particles to split direction of movement (spin splitting), which sets up an adiabatic quantum pump, a bit of quantum mechanics that literally ‘pumps’ or forces the particles to spin in a specific direction.

Obviously this is a good deal more complicated than simply ‘rolling a graphene nanotube,’ but as these two approaches go further down the line with experimentation and especially as they gear up for real-world applications, it remains to be seen which is the more reliable, controllable, and cost effective. In either case, it’s a demonstration that graphene can be used to achieve spintronic effects. As the optimistic PR releases always say, this opens the path to many applications.

[Here’s a previous SciTechStory’s post: A First: Spintronics made visible]

It’s a little early to be talking about the ‘field’ of quantum biology, although there is already strong evidence for quantum effects in photosynthesis [SciTechStory: Confirmation of quantum entanglement in photosynthesis] but if the existence of significant quantum effects in DNA can be substantiated (that means with experimental evidence) it would be a foundational discovery. However, at this point the idea is a working hypothesis based on mathematical modeling. It goes something like this…

Quantum effects, in this case quantum entanglement, are among the most counter-intuitive and challenging ideas in physics – ‘spookish’ is the word Einstein used. Scientists know quantum mechanics from many decades of mathematical theorizing and a couple of decades of experimentation with atomic behavior at temperatures close to absolute zero. It comes as an enormous intellectual and theoretical leap to grapple with the idea that natural (biological) phenomenon use quantum effects at or above room temperature. Yet, the evidence is accumulating that quantum entanglement is involved with biology in a very fundamental way – photosynthesis being the first to have experimental evidence.

This new theory, which is certain to provoke as many skeptical voices as words of interest, began with wondering what role, if any, might quantum entanglement play in DNA. Quantum entanglement is described, simply, as two separate particles that work together as if they were one particle no matter how far apart they might be. If one particle moves up, the other particle moves down, instantly, as if they were on the ends of a teeter-totter. They are a system that behaves as one particle. In the case of DNA, the ‘particles’ are the molecules of the DNA base pairs, formed by the nucleotides with adenine, guanine, thymine, and cytosine. Each nucleotide is surrounded by a cloud of electrons that behave as if the nucleotide were an atomic nucleus. The cloud shifts relative to the nucleus, perhaps influenced by what are called Van der Waals forces, from side to side so to speak forming a dipole (two poles), and this shifting is regular – a harmonic oscillation. In solid-state physics, the oscillation of molecules within a solid is known as a phonon, a kind of quasi-particle that vibrates at a specific frequency and gives the solid many of its electrical and physical properties. In DNA, when a base pair is formed the clouds of each nucleotide must oscillate in opposite directions if the bond is to hold together.

The key question for the researchers was what influence does the double helical structure of DNA have on this oscillation? To answer the question, they first modeled how the phonons would behave at absolute zero temperature. Here (mathematically) it was clear the phonons would be typical quantum objects, existing as both waves and particles exhibiting the property of quantum entanglement. As it turns out, the size of the DNA helix corresponds rather well to the wavelength (frequency) of the phonons. This correspondence causes the phonons to stay within this frequency, something called ‘phonon trapping.’ Though the nucleotide phonons in each base pair oscillate in opposite directions they do so in a quantum entangled system – they act together and at the same frequency, ensuring the stability of the pair bond and of the helix itself.

At least that’s what the model shows can happen. The model also shows that this configuration can maintain the bond at high temperatures – room temperatures or above (e.g. 20 degrees C or 68 degrees F). The quantum entanglement is vital to making this work, because under classical mechanics the vibration of the particles in the helix would shake it apart, especially at higher temperatures.

Of course, this is all modeling. What must come next is experimental evidence. It won’t come easily. The researchers point to the notion that using classical mechanics to add up the energy necessary to hold the helix together comes out short, and that adding the quantum effects makes up the difference. But this is indirect evidence.

Keep in mind that quantum mechanics existed as mathematical theory long before experimental evidence was provided. The situation may be similar with showing quantum effects in DNA. Or not. As is the case when there are potentially major shifts in scientific understanding – and finding quantum mechanics as a basis for some of the most fundamental aspects of biology certainly qualifies – the demands for evidence will be rigorous. In the meantime, scientists will engage in vigorous debate. It will be interesting to see how argument and evidence changes or nullifies the theoretical insight. The process represents the essence of the scientific method applied to a potentially revolutionary hypothesis.

Now a new collaborative team, including Graham Fleming, has added confirmation that the photosynthetic process uses quantum entanglement to utilize nearly 100% of the sun’s energy in the conversion of sunlight to carbon-based (sugar) energy.

The new study published in the journal Nature Physics in May, provides confirmation of quantum effects in a specific photosynthetic mechanism, and according to Mohan Sarovar, one of the authors:

“…this is the first instance in which entanglement has been examined and quantified in a real biological system.”
…
“We present strong evidence for quantum entanglement in noisy non-equilibrium systems at high temperatures by determining the timescales and temperatures for which entanglement is observable in a protein structure that is central to photosynthesis in certain bacteria.”

[Source: Lawrence Berkeley National Laboratory]

Quantum entanglement is one of the signature effects in the strange-seeming world of quantum physics. It basically involves two atomic particles, which though physically separated, behave as if they were one particle; they are ‘entangled.’ The new study establishes that various pigments in a specific light harvesting protein (called, technically, the Fenna-Matthews-Olson or FMO protein) use quantum entanglement to simultaneously choose the optimum pathway for capturing photons of light – capturing all of them. Such efficiency human engineers can only dream about.

Having demonstrated entanglement in the FMO protein, the researchers believe the same effect will also be found in larger light harvesting proteins and, in fact, there may be multiple instances of the effect to act like a kind of highly adaptive filter, trapping the photons of light as they penetrate into the pigments of the protein.

The researchers remain surprised at much of what they discovered: That the entanglement effect persisted even when the molecules of the protein were not strongly coupled (connected) with electronic and vibrational states, and that temperature has so little impact on the process. It appears that the light harvesting quantum effects in plants are almost immune to heat – especially in comparison to quantum effects that are produced in the laboratory.

It should be emphasized that this is pioneer work. Only a few years ago, most scientists did not consider the possibility that natural processes might use quantum effects. Now we are nearly sure that quantum effects lie at the heart of one of the most important natural processes of all. Photosynthesis is the basis of most life as we know it (including our own, since we must eat energy produced by photosynthesis). Eventually, some of the knowledge gained in this area will contribute to human-made artificial photosynthesis. It may also be a path that leads to other fundamental discoveries about the nature of quantum physics, which are now almost totally unsuspected. Great stuff for both biologists and physicists.

At another level, this is the story of more than a decade of grappling with an intuition. Professor Carter, an expert in the materials of aerospace (yes, she’s a rocket scientist…), knew that computer modeling of materials used in jet engines were based on ‘perfect’ samples, for example, materials with perfect crystalline structure. The problem is that in the real world it’s the imperfections of materials that establish their most important properties. The existing computer models couldn’t handle that imperfection. As it was, only by cranking through the model molecule by molecule could perhaps a few hundred molecules be modeled. Capturing imperfections would require modeling tens of thousands or more molecules at a time. Carter’s challenge was to figure out how to bridge that gap.

In the social sciences, including economics, computer models don’t always sport a good reputation. This is to say, they’ve often been wrong; sometimes very wrong. This tends to give computer modeling a bad image. (Not that people usually think highly of computer models.) Sometimes this animosity spills over into computer modeling of any kind. It shouldn’t. Computer models in the physical sciences are another thing altogether. They tend to work. Yes, there are poor models and better ones, but the models do some very useful things – like predict that certain chemical configuration will or won’t work. These days many of the most important innovations in materials science, chemistry, and biology involve creating or improving computer models and simulations.

Professor Carter’s intuition involved trying to incorporate into modeling a well-known conundrum: Measuring the distribution of electrons in a material was relatively easy, but not always useful. Knowing the energy levels of electrons in a material was vital for predicting their behavior, but difficult to measure. Could these two measurements be solved together in some way?

In 1927 Llewellyn Thomas and Nobel laureate Enrico Fermi developed an equation to express the idea that electron kinetic energy – the energy electrons have as a result of their motion – could be calculated on how the electrons are distributed within the material. Electrons crammed into a small space have higher kinetic energy. Spread over a larger space, they have less energy. The equation captured the distribution of electrons to solve how much energy they have. But there was a hitch: Thomas and Fermi used a theoretical gas as the basis of their equation, a gas with perfect distribution of electrons. It couldn’t predict the properties of ‘flawed’ materials (with uneven electron distribution) in the real world.

Later work, developed in 1964 by Pierre Hohenberg and Nobelist Walter Kohn, showed that the Thomas-Fermi equation could be applied to non-perfect materials; but they did not work out the equations to express this finding. In 1996 Professor Carter began her own work on the problem. By 1999 she was able to offer useful extensions to the Hohenberg-Kohn work. She realized that a solution to the Thomas-Fermi approach would make it possible to work out the electron energy of a material by knowing its electron distribution, and she had worked this out for simple metals. However, when she turned to semiconductors (the basic material of digital electronics), it no longer worked.

During this period of head-scratching, she and doctoral candidate in physics Chen Huang began to wonder what was different between metals and semiconductors that the results were so different. (Working backward from results sounds a bit presumptive but can be very useful.) In this case, they realized there was something different – the behavior of metals and semiconductors in the presence of an electrical field. When they incorporated these properties into the model – it worked for both. In fact, the new model works for a wide range of materials and extends the ability of computer modeling by speeding up calculation as much as a factor of 100,000. The new approach and the greater efficiency makes it possible to model up to a million molecules.

It would be wonderful if a perfect equation that explains all of this would just fall from the sky,” she said. “But that isn’t going to happen, so we’ve kept searching for a practical solution that helps us study materials.”
…
The researchers hope that by moving beyond the concepts introduced by Thomas and Fermi more than 80 years ago, their work will speed future innovations. “Before people could only look at small bits of materials and perfect crystals,” Carter said. “Now we can accurately apply quantum mechanics at scales of matter never possible before.”

[Source: Nanotechnology Today]

So on one level, this advance in computer modeling is an exercise in quantum mechanics and about as abstruse a mathematical process as science can offer. On another level, this is a major advance in the practicality of using computers to model the behavior of materials that don’t exist yet – to determine their properties, or usefulness, or safety. It was also a demonstration of gritty collaborative investigation over a period of many years; just the thing that makes real modern science.

One of the reasons there are no phonon devices is fundamental difference between light and sound. While they both can be thought of as waves and both have units defined by quantum mechanics (the photon and phonon), the problem is that sound travels much more slowly than light – meaning that at any given frequency the wavelength of sound is much shorter than light. To work in a laser, sound would have to be in the range of terahertz (trillions of hertz) frequencies; but because of the tiny wavelengths high-frequency sounds tend to result not in orderly laser-like focus but a more random emission like a light bulb.

Two different approaches to this problem have recently been announced. One by researchers at the California Institute of Technology (USA) overcame the problem by using a pair of microscopic cavities that permit only specific frequencies of phonons to be emitted. This approach allows for precise tuning of frequencies.

Another approach, coming from the University of Nottingham (UK), constructed a device using quantum wells (typically a semiconductor that forces electrons into a two-dimensional plane) so that electrons hopping from one well to another emit phonons. They have not built a true laser, but can demonstrate a system that amplifies high-frequency sounds to a level that could be used in sonic lasers.

Physicists have taken major step forward in the development of practical phonon lasers, which emit sound in much the same way that optical lasers emit light. The development should lead to new, high-resolution imaging devices and medical applications. Just as optical lasers have been incorporated into countless, ubiquitous devices, a phonon laser is likely to be critical to a host of as yet unimaginable applications.

Two separate research groups, one located in the US and the other in the UK, are reporting dramatic advances in the development of phonon lasers in the current issue of Physical Review Letters. The papers are highlighted with a Viewpoint by Jacob Khurgin of Johns Hopkins University in the February 22 issue of Physics.

[Source: EurekAlert]

Scientists have long known how to control the internal states of molecules, such as their rotational and vibrational energy levels. In addition, the field of quantum chemistry has existed for decades to study the effects of the quantum behavior of electrons and nuclei—constituents of molecules. But until now scientists have been unable to observe direct consequences of quantum mechanical motions of whole molecules on the chemical reaction process. Creating simple molecules and chilling them almost to a standstill makes this possible by presenting a simpler and more placid environment that can reveal subtle, previously unobserved chemical phenomena.

[Source: EurekAlert]

The new research started with the premise that in extreme cold – a few hundred billionths of a Kelvin (nanokelvins) above absolute zero (minus 273 degrees Celsius or minus 459 degrees Fahrenheit – no chemical reactions should occur.

The physicists at JILA (formerly the Joint Institute for Laboratory Astrophysics, now just JILA, a joint venture of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder, USA) cooled a gas of potassium and rubidium molecules to this temperature and subjected them to manipulation with electric fields. Then they observed the unexpected – heat – a few billionths of a degree to be sure, but measurable proof that chemical reactions were taking place and, in fact, taking place very quickly.

Taking the experiments further, the researchers worked with the gas as a 50/50 mix of molecules with two different ‘spins’ (that’s spin in the quantum sense, the angular momentum) and found that this increased the speed of reaction up to a hundred-fold. This is indicative that manipulating quantum properties (electronic, vibrational and rotational states) changes the chemical reaction.

How this works is still very much up for more research. These are ‘toe in the water’ experiments that only hint at what’s happening. Outside of masses of equations for the highly trained few, an intuition for molecular quantum chemistry are difficult to explain. I’ll try.

Here’s a crude analogy to work with: Consider two magnets, tiny bars with polar ends. We know that putting to unlike poles together and the bars attract each other. They repel each other when two like poles are put together. Simple magnetic properties. Now visualize these bars having unequal magnetic energy, one bar is more strongly magnetized than the other; that they are rotating very fast; spinning (with different total angles of momentum) so that the orientation of the poles continually changes, and that each bar is vibrating at different rates. What happens to the magnetic properties? How would these two bars react to each other? The quantum mechanics of molecules isn’t the same as this kind of magnetism, but perhaps this helps visualize how differently the magnets might behave when the extra conditions are added. That complex behavior is analogous to what it’s like for molecules undergoing quantum chemistry, and why, when scientists get their first glimpses of such behavior, they realize that underlying all that we think we know about chemistry, is another, more subtle but nevertheless decisive set of behaviors that governs how molecules react to each other.

I’m searching for a metaphor – a door opening, curtain rising, fog lifting – not really any of these. That there is such a thing as quantum chemistry, scientists have known for quite a while; but this…this is something else. It’s in between what we knew about individual nuclear particles and the much larger world of molecular chemistry (which itself is a smaller world inside the world we see as physical reality). We’re just beginning to get a fix on the existence of this ‘world’ of molecular quantum chemistry, and the minds of scientists boggle at the implications. For example, here’s a typically reserved statement from the research:

…a key to advancing biology, creating new materials, producing energy and other research areas. The new JILA work also will aid studies of quantum gases (in which particles behave like waves) and exotic physics spanning the quantum and macroscopic worlds. It may provide practical tools for “designer chemistry” and other applications such as precision measurements and quantum computing.

Is there anything this doesn’t cover? Not really. Quantum physics underlies everything, so unless its effects are trivial, it affects everything. The ability to manipulate quantum chemistry means that in some way, almost any kind of physical material or process is fair game. Among other things, just the other week scientists announced the discovery that plants are (since long ago) using quantum mechanics in photosynthesis. Where else? What Nature does; science and technology usually try to imitate (hominid see, hominid do).

We can think about this in terms of Feynman’s way of talking about quantum mechanics: rather than a particle taking a unique path between two points, as in classical mechanics, a quantum particle takes every possible path, with simple paths getting a bit more weight than complicated ones. In the case of the protein, different paths for the energy might be more or less efficient at any particular moment, but this bit of quantum trickery allows the energy to find the best possible route at any one time. Imagine at rush hour, if your car could take every possible route from your home to the office, and the time it officially took would be whatever turned out to be the shortest path. How awesome would that be?

[Source: Quantum Photosynthesis; Cosmic Variance]

The pioneering work, done by a team of chemists at the University of Toronto (Canada), started with collecting what are called ‘light-harvesting complexes’ from two species of marine algae. Light-harvesting complexes capture photons from sunlight and use them to excite electrons in protein compounds to higher levels – a transfer of energy. Later that energy can be attached to organic compounds, such as glucose (sugars), for storage. These light-harvesting complexes were stimulated with femtosecond pulses of laser energy to simulate sunlight, and observed with a two-dimensional electronic spectroscope. What they found was that during this conversion the same quanta of energy existed in two places at once (in the photon and in the electrons) – a quantum superposition – which is a hallmark characteristic of quantum mechanics.

This was a surprising and highly suggestive result. As one of the researchers put it:

“There’s been a lot of excitement and speculation that nature may be using quantum mechanical practices,” says chemistry professor Greg Scholes, lead author of a new study published this week in Nature. “Our latest experiments show that normally functioning biological systems have the capacity to use quantum mechanics in order to optimize a process as essential to their survival as photosynthesis.”

“This and other recent discoveries have captured the attention of researchers for several reasons,” says Scholes. “First, it means that quantum mechanical probability laws can prevail over the classical laws of kinetics in this complex biological system, even at normal temperatures. The energy can thereby flow efficiently by—counter intuitively—traversing several alternative paths through the antenna proteins simultaneously. It also raises some other potentially fascinating questions, such as, have these organisms developed quantum-mechanical strategies for light-harvesting to gain an evolutionary advantage? It suggests that algae knew about quantum mechanics nearly two billion years before humans,” says Scholes.

[Source: EurekAlert]

The finding also suggests that if this quantum-based process is correctly identified, that other biological processes may also utilize quantum mechanics in ways that, up to now, science has not even considered. Oh my, goodness.

By ‘solid-state’ is meant metallic electron particles in a super-cold, superconducting environment, an environment similar to that used by some supercomputers. This experiment used carbon nanotubes to split electrons, a significant advantage because the nanotube’s tiny diameter retains the charge of each electron at higher energy than other techniques. As the nanotubes split what are called Cooper pairs (already entangled electrons), the particles that remain entangled are deposited on one or the other of two quantum dots (semiconductors with the capability of quantum confinement). Because the quantum dots are physically separated, it demonstrates that two particles are involved, and the instant communication property of entanglement occurs over a measurable distance.

More work needs to be done to verify the entanglement properties of the particles in the quantum dots, and there are many variations yet to be tried for types and configurations of nanotubes (especially metallic carbon nanotubes). This means that practical applications are speculative, but the potential is enhanced by the solid-state entanglement. This is an environment, such as supercomputing, where the conditions for creating and monitoring super-cold, superconducting particle activity is already part of engineering. As one analyst put it:

…electrons entangled in a superconducting Cooper pair can be spatially separated into different arms of a carbon nanotube, a material thought favorable for the efficient injection and transport of split, entangled pairs. This work may help pave the way for tests of nonlocal effects [quantum entanglement] in solid-state systems, as well as applications such as quantum teleportation and ultrasecure communication.

[Source: American Physical Society]