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The Smaller the Particles the Bigger the Questions Vice President Research, Office of the 2006-12-31

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THE SMALLER THE PARTICLES THE BIGGER THE QUESTIONS  JOSH FOLK EXPLAINS HOW THE TRADITIONAL RULES OF PHYSICS DON’T MAKE SENSE AT THE QUANTUM-MECHANICAL LEVEL – AND HOW THOSE DISCREPANCIES CAN BE TURNED INTO OPPORTUNITIES Josh Folk is an assistant professor in the department of physics and astronomy at UBC Vancouver; he studies physics on the nanometer scale – a world that exists between the subatomic scale of quantum mechanics and the world that is described by classical Newtonian physics. As Folk describes it, the nanometer scale is the place where the two meet: “Quantum mechanics is a theory in physics that describes atoms and smaller. But if you go up the scale, quantum mechanics doesn’t make sense at all. That’s why the nanometer scale is a particularly interesting one, because it’s where quantum mechanics stops working so well, but at the same time Newtonian classical physics stops working also.” Although the nanometer scale is larger than the subatomic scale, it’s still pretty darn small. The word refers to one billionth of a meter; a human hair is about 10,000 nanometers wide. The technological developments from the nanometer scale, called nanotechnology, give rise, potentially, to new devices that put quantum mechanics to work. In quantum mechanics, it’s possible for one object to have two apparently contradictory characteristics at the same time. When this concept is applied to computing, it’s referred to as “quantum computing.” This is still at a theoretical stage, but it’s the closest device application for quantum mechanics and the implications are enormous. Folk explains: “Imagine a computer processor that works based on zeros and ones. Let’s say your input to the processor, your data going in, could be many things at the same time; instead of being either a zero or a one, it could be both a zero and a one. For example, if you were to write the binary number four, it would be ‘one one.’ If both of those bits could be either zero or one at the same time, then this input string of two bits could be four possible things at the same time. And this scales exponentially, so if you had one hundred bits it would be two to the power of one hundred things at the same time. That’s a very large number – about a one-with-thirty-zeros-after-it things that it could be at the same time. It means you could run your computer program once, yet do one-with-thirty-zeros-after-it operations at the same time.” Quantum computing is of enormous  interest to the military – security codes are based on factoring large numbers. It’s also critically relevant to banks with similar encryption schemes. The fundamental element is called the qubit, which stands for quantum bit: the element that can be zero and one at the same time. A qubit could be made in many different ways. For example, atoms have different energy levels, and therefore a single atom could have two of those energy levels describe zero and one. It’s possible for an atom to be at two of those energy levels at the same time. And that would be an atom functioning as a qubit.  The word “nanometer” refers to one billionth of a meter; a human hair is about 10,000 nanometers wide At the nanometer scale, superconducting rings – rings with electrical resistance – could have the current running both clockwise and counterclockwise at the same time. As Folk says, it’s a very strange thing to imagine, but it’s a way in which current direction can also function as a qubit – clockwise could mean zero, counterclockwise could mean one. Folk’s research is focused on using electron spin as zero and one. That means whether the spin is pointing up or pointing down, or doing both at the same time. Electron spin is what gives rise to magnetism. For example, a refrigerator magnet has a huge number of spins all pointing in the same direction and produces a big magnetic field. Isolate a single one of those spins and it could serve as a qubit. By confining and controlling a single electron spin, each spin could be like a qubit and also like a normal computing bit. Folk explains that information on a computer hard drive is stored as tiny regions of magnetic field, pointing either up or down. Each element on the hard drive is also at the nanometer scale, but it contains many more than one spin. As a result it acts classically instead of quantum mechanically; it acts as a normal bit, where it’s either up  or down, and not as a quantum mechanical bit. The point at which it acts as a quantum mechanical bit is the point at which it’s doing both simultaneously: up and down at the same time. Folk compares spin to an arrow, which classically moves in two directions: up or down. Think about that scenario in quantum mechanics and the whole sphere becomes possible – up, down, left, right, in, out. It’s got a different dimensionality. Folk works to turn the spin information (which is hard to detect) into information that is more detectable, such as electron charge. “Charge is a very powerful, detectable force, with a lot of energy stored in it. If I can turn spin information into charge information, it becomes much easier to read out. One way of doing this would be by creating a device where an electron can move away only if its spin is up; if the spin is down, it’s trapped where it is. And so if I give the spin an option to flow away and then I measure where it is, that’s a way of turning spin info into charge info, because then I can measure the location of the charge, and that will tell me what the spin is.” Another potential application for the enormous power of nanotechnology lies in medical science. And that’s where the spins come in. Folk explains: “One of the limitations with MRI (Magnetic Resonance Imaging) is resolution – you can’t look at any thing much smaller than a millimeter, because you need a very large number of nuclear spins to measure something using MRI. I’m very interested in the possibility of measuring just a few nuclear spins by using the same kind of techniques – turning that spin information into something more detectable. That would make an MRI a much more powerful medical tool. It would mean that the type of measurement that could tell you now if you have a broken bone, could tell you if in a single cell or just a few cells there’s something going wrong.” The behaviour of physical objects on the nanometer scale is slowly revealing itself. Folk’s research helps to clarify a fundamental part of the physical world. As he puts it: “This is an underlying type of behaviour that is always with us, always going on in everything around us. I’m involved in understanding that behaviour and harnessing its power.”  December 2006  7  


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