#180      29 min 03 sec
Diamond data mining: Quantum computing and the materials that make it possible

Physicist Professor David Awschalom discusses the powerful potential of quantum computing, and how materials such as diamond play a crucial role in the development of this emerging technology. With host Dr. Shane Huntington.

"So we need to generate a new type of quantum engineer which is sort of a mixture of scientist, engineer, technologist, computer scientist, mathematician, all rolled into one." -- Prof David Awschalom





           



Prof David Awschalom
Professor David Awschalom

Professor David Awschalom is the Peter J. Clarke Professor of Physics, Electrical and Computer Engineering at the University of California, Santa Barbara, and Director of the California NanoSystems Institute and the Center for Spintronics and Quantum Computation. He is a pioneer in the field of semiconductor spintronics, exploring the quantum mechanical behaviour of charges and spins in nanostructures and the foundations of solid-state quantum information processing.

Professor Awschalom has published over 350 papers in his career and is one of the most highly cited scientists within his field. He has received the David Turnbull Award and the Outstanding Investigator Prize from the Materials Research Society; the International Magnetism Prize from the International Union of Pure and Applied Physics; the Oliver Buckley Prize from the American Physical Society; the Europhysics Prize from the European Physical Society; and the Newcomb Cleveland Prize from the American Association for the Advancement of Science. He is a member of the US National Academy of Sciences and National Academy of Engineering, and the American Academy of Arts and Sciences.

The Awschalom Group -- University of California, Santa Barbara

David Awschalom speaking on "Spintronics: Abandoning Perfection for the Quantum Age" at TEDx Caltech (via YouTube)

Credits

Host: Dr Shane Huntington
Producers: Kelvin Param, Eric van Bemmel
Audio Engineer: Gavin Nebauer
Episode Research: Dr Dyani Lewis
Voiceover: Nerissa Hannink
Series Creators: Eric van Bemmel and Kelvin Param

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VOICEOVER

Welcome to Up Close, the research talk show from the University of Melbourne, Australia.


SHANE HUNTINGTON

I'm Shane Huntington, thanks for joining us. The strange effects associated with quantum mechanics are no longer just theoretical concepts. Today, in laboratories around the world, the quantum properties of materials are being studied and utilised and it's widely speculated that we'll one day have outrageously powerful computers based on quantum principles. Unlike conventional computer systems that are based on silicon, quantum computers require specialised materials and very careful control over the properties of these materials.
Today on Up Close we speak to Professor David Awschalom about quantum computing using diamond and why this material is so important. David Awschalom, is the Peter J Clarke Professor of Physics, Electrical and Computer Engineering at the University of California, Santa Barbara and director of the California NanoSystems Institute and the Center for Spintronics and Quantum Computation. Professor Awschalom is in Melbourne as a guest of the Melbourne Materials Institute.
Welcome to Up Close David.


DAVID AWSCHALOM

Thank you very much. It's a pleasure to be here.


SHANE HUNTINGTON

Now before we delve into the quantum world, can you give us an idea of why there's so much concern at the moment over conventional computers and how they will be workable in the future?


DAVID AWSCHALOM

Absolutely. Well present technology's been working remarkably well. But as we make today's technology smaller and smaller, approaching feature lengths and circuits at submicron levels, at the end of the day there's a problem with real materials with heat. I think as all of us use laptops on our lap, you're familiar with the fact that they get warm and as the wires and circuits are made smaller and smaller, at some point they become fuses. So there's limits to scaling now on the horizon and a lot of us, a lot of industry around the world, is concerned about what will happen when we hit those limits.


SHANE HUNTINGTON

How far off do you think those limits are at this point?


DAVID AWSCHALOM

Well it's dangerous to bet on these things and historically, whenever you make predictions like this, you're wrong. So I hesitate to do it, but right now, a common view is that within the decade we'll be hitting these limits.


SHANE HUNTINGTON

Many of our listeners will understand that quantum rules apply when you're at very small scales. Do these traditional computers not already effectively work in the quantum realm?


DAVID AWSCHALOM

Well you're quite right. As you approach the nanometre scale, these quantum mechanical properties begin to emerge. Present machines do not use them because the normal materials and traditional materials, such as metals that are used in today's circuits, you would have to go to rather low temperatures, well below ambient temperatures to see these sorts of effects. So no, they don't.


SHANE HUNTINGTON

Now a normal computer makes use of the charge on and electron to do its work. How does it go about that?


DAVID AWSCHALOM

So when you perform some action on your computer or on your iPhone, you're typically moving electronic charges on and off very tiny electrical gates, moving these electron charges on and off, zeros or ones. Typically at the very smallest devices, thousands of these are being moved rapidly back and forth. That's of course what generates the heat that all of us feel.


SHANE HUNTINGTON

Many of our older listeners would remember the term transistor, because it was shorthand for a portable radio. But what exactly is a transistor in a classical computer? What's actually happening on a small scale?


DAVID AWSCHALOM

Sort of sad that you say it's just the older people, but yes, the transistor is the fundamental device in today's integrated circuit technology and one of the successes of miniaturisation today is that there are literally billions of transistors in say a Pentium chip, the processor of today's computers.
And if you dig deep within this Pentium chip, the individual logical elements, what's really performing this binary logic of zero and one control in today's classical computing are taking puddles of electrons and pushing them on and off devices. That's done by this fundamental device, the transistor, where voltage is applied that acts like a tiny gate to move these things to and fro and it also provides a little bit of gain, so as you move from transistor to transistor, you can have constant amplitude signals, you don’t lose the size of your signal. So it's nice to think about them as a very small electronic gate that shifts electrons from one direction or another.


SHANE HUNTINGTON

With these, you can build up a larger structure that gives you the complexity?


DAVID AWSCHALOM

Absolutely, so you can make complimentary circuits, you can perform additions, subtractions, multiplications, by wiring these little transistors together in different configurations to perform different operations.


SHANE HUNTINGTON

Now as we transition into the quantum world, what's different in that context of the transistor?


DAVID AWSCHALOM

Well as you transition to the quantum world, you have to ask yourself whether you even want to think about transistors, because transistors are elements in classical technology that allow you to shuttle these electrons, the way we've just been mentioning. But as we go into the quantum world, these very new physical properties emerge that we don't see on a daily basis. They're very counter-intuitive but they become very run-of-the-mill in these very small dimensions.


SHANE HUNTINGTON

So if we were to start to build a quantum computer from sort of the basic principles as we do in a classical or a conventional computer, what does that look like? What are the base elements that would make up a quantum computer?


DAVID AWSCHALOM

Well that's a very big question. So that's what a large fraction of researchers now are contemplating, because on one hand it's becoming easier to create, observe and control these quantum states of matter than people had expected, in a variety of materials, in a variety of techniques. So it's a very exciting development in science and engineering. On the flip side, it means we have to stand back and think very differently how you would build the technology based on the quantum mechanical properties of matter and what would that fundamental element be and how would you actually program a quantum machine? What would it do? It's such a different scenario that it's a little daunting, but very exciting.


SHANE HUNTINGTON

What is the need for the quantum computer? Why do we care?


DAVID AWSCHALOM

So there are a number of problems in the world that are difficult to imagine being solved even by making a larger and larger classical machine. Classical computers are unqualified successes at many, many things, but there are some problems, whether it's searching through vast databases, or trying to, for example, completely predict how complicated molecules would behave, from first principles. The amount of space and calculation you would need to do is so complex, it's simply hard to imagine doing this. Maybe designing drugs, for example, for particular disease control or understanding how proteins behave in different environments, there are classes of problems that are just immensely complicated. Even as far as predicting the weather tomorrow, these are hard things to do.
So if you thought about a technology that would give you almost infinite amounts of memory and vast amounts of computing speeds, it would allow you to address things that could have enormous societal impacts, not just in engineering or mathematics.


SHANE HUNTINGTON

At the moment it's very hard to actually look into problems that are quantum problems in themselves. Would quantum computers allow us to instantly solve those sorts of problems?


DAVID AWSCHALOM

Well I'm not sure about instantly, but you're absolutely right. One of the attractions of building a quantum machine is to simulate quantum systems and at the end of the day, one of the powers of quantum physics is it’s a fundamental theory that describes matter. And to be able to simulate that and solve certain classes of quantum problems with quantum machines is one of the short term goals of building quantum computers.


SHANE HUNTINGTON

David, your work has investigated the use of diamond as a potential material for making quantum computer elements. What is special about this form of carbon? Why is diamond so important?


DAVID AWSCHALOM

So historically, in building technologies and building electronics, society and engineers have focused enormously on creating extremely pure materials, very clean materials, whether it's silicon or copper, removing the defects, removing the impurities so as you shrink the dimensions, currents, these electronic charges you asked about earlier, can move uninterrupted, without scattering, without heating, without being destroyed.
The interesting thing about diamond is that it is also a semi conductor, much like silicon or gallium arsenide or the materials that are used in today's solar cells, for example, as well as electronics. But historically has been very expensive to make in large quantities, so it hasn't been used. But if you look at it as a material, it's one of the best thermal conductors on the planet and it has a very unique property which is a little counter intuitive in that if you add defects to diamond or if you pluck out a carbon atom from the lattice, a very unusual thing happens: electrons in that semi conductor, rather than moving freely and uninterrupted, will stick in these locations, in these defects, they'll be trapped. Then they become surprisingly easy to manipulate.
So it's an extremely unusual material that you think about differently; by adding defects or systematically destroying the material you can localise these electrons and control their quantum properties at room temperature.


SHANE HUNTINGTON

David, what's a semi conductor?


DAVID AWSCHALOM

A semi conductor is a type of material that, as the name would imply, is not fully a conductor and is not really an insulator. So copper is a material that conducts electrons very well, a metal. An insulator, like a plastic, is a material that would not conduct electricity. A semi conductor is a material that based on how you manipulate that material, can be either a conductor or an insulator and you can control that material with local electric fields. So that's the type of material that's used, for example, in today's transistors and commonly in today's electronics technology.


SHANE HUNTINGTON

This is Up Close, coming to you from the University of Melbourne, Australia. I'm Shane Huntington and we're venturing into the quantum world today with physicist, Professor David Awschalom.
Now David there are many different forms of carbon that we see, in fact a lot of notoriety in recent years over graphene with the Nobel Prize being awarded for those working in that particular area, are these usable as well as diamond or is there something specific about diamond as a carbon form that we can manipulate?


DAVID AWSCHALOM

Well that's a remarkably astute question because it's something that's being addressed right now in the research community. So for conventional electronics, there's been remarkable headway, as you just mentioned, with grapheme as a material to build conventional electronics. But what's unusual about diamond is the electronic state or the way electrons adjust themselves in this material, when you remove one of its atoms, is rather unusual. You create a type of potential or trap to hold an electron. It does beg the question how unusual is diamond and are there other materials like that.
One material that also involves carbon that's been around for a long time, that people already use today for making high power electronic circuits is silicon carbide. You might think about it as the collision of carbon and silicon and we're all familiar with silicon technology. And a few years ago, working with a group of theorists in Santa Barbara, we posed the question: why do things work so well in diamond and could there be other materials like diamond? Using quite advanced computational materials techniques, trying to simulate electronic materials using today's classical computers, after a year or two of doing simulations, a number of materials popped out, one being silicon carbide.
It turns out that that does work, in many ways, like diamond. These are very recent results, but it does act as a proof of concept that there are other materials in which defects can also act as a type of quantum bit. So we're beginning to think now that maybe with us spending so much effort to purify and make perfect materials, maybe we've missed the opportunities by making defects and damaging materials that there are lots of different quantum material systems that might be available for technology that we simply haven't explored.
So silicon carbide is one. Another, which is in sunscreens, for example, zinc oxide, should be another. Very recently it's our understanding that some groups in Asia have just seen the fact that zinc oxide also can act as a quantum material.


SHANE HUNTINGTON

David, coming back to diamond, when you talk about removing an atom from diamond, can you describe how you go about doing that? It sounds like a phenomenal achievement to remove a single atom.


DAVID AWSCHALOM

Well destroying materials, of course, is something that's a little easier than creating them. So the defects or damages in diamond can either occur naturally when they come out of the ground, or you can induce them by using beams of ions that are shot into the material, dislodging atoms as the ions move through the material. That sounds complicated and in a way it is, but on the flip side, there's a vast corporate infrastructure for implanting materials that's done with traditional semi conductors today to make devices. So these same companies that implant ions to change the electronic properties of conventional semi conductors, can also be used to shoot atoms into diamond, creating these defects in well defined arrays or certain locations in the lattice.


SHANE HUNTINGTON

One of the defects, I understand you use, is called the nitrogen-vacancy center.


DAVID AWSCHALOM

That's correct.


SHANE HUNTINGTON

Tell us about that.


DAVID AWSCHALOM

So the nitrogen-vacancy center, as the name implies, simply creates a vacancy by shooting nitrogen atoms into diamond, knocking out a carbon and this nitrogen atom that resides near this vacancy creates a type of molecule in the solid, a nitrogen vacancy composite. This nitrogen atom sitting next to the absent carbon atom creates this type of molecular state which has an electron and it is that electron that one can use as a basis for quantum bit or quantum technology.


SHANE HUNTINGTON

Nitrogen seems to be everywhere. Do you find there's a contamination problem with producing this sort of material?


DAVID AWSCHALOM

No, there isn't because to get the nitrogen in requires a fair amount of energy. So nitrogen just from air around us does not every easily become absorbed by materials like diamond; you really have to force it in. Once it's in, it's hard to remove.


SHANE HUNTINGTON

Is there something special about nitrogen, or can you use a range of other materials for the defect?


DAVID AWSCHALOM

There are hundreds of defects in diamond and that's what gives diamond its unusual colours. You've probably seen yellow diamond, blue diamond; the type of defect that's put in provides a certain type of colour. The question for us is, it's not so much the charge of the electron we play with for these quantum states of matter, but electrons also have another property called spin. They spin about, you can think about them spinning about their axis much like the Earth rotates on its axis, generating this tiny magnetic field. But this spin-like property is actually a quantum mechanical property of a particle and you need to create a type of electronic state in material like diamond that has this type of spin. Nitrogen is one of the few impurities you can add to the material that allows you to create electron whose spin can be controlled. So while there are many impurities and many colours of diamond, there's only a small subset that have these unusual properties.


SHANE HUNTINGTON

Now we're talking about individual atoms here, potentially arrays of them in a crystal.


DAVID AWSCHALOM

Correct.


SHANE HUNTINGTON

How do you go about determining whether or not they are actually there and finding them once you've done the work; we're talking about millions of atoms here around them.


DAVID AWSCHALOM

That's right. So when you make these types of impurities, one of the unique features of the impurity is that when you illuminate the impurity with light, say with a laser or certain types of just white light, they'll luminesce, they'll give off different colours. By looking at the surface of these diamonds and seeing where the light is emitted, you can identify where this defect is. They're extremely bright, so even though it's a single electron in a single defect, with a conventional microscope objective on a desktop, you can see it. So you can't see the electron, but you know it's coming from that region of space.


SHANE HUNTINGTON

David, once you've actually located one of these centers, how do you go about actually controlling it and using it as the equivalent of an addressable bit of data storage?


DAVID AWSCHALOM

So the challenge for us is how you control the spin of a single electron and there we can capitalise on existing technology of building miniature microwave circuits, because you manipulate the spin or this little magnetic particle with electromagnetic fields, with essentially very tiny coils that are built on the sample. We actually do that by making miniature wires of titanium and platinum and gold, so you can think about it as a type of exotic jewellery, titanium, platinum and gold on diamond, but these little antennas or little loops that are put around the individual spins manipulate them at gigahertz frequencies, very high frequencies. We use that to control these quantum states.


SHANE HUNTINGTON

Now we know in conventional computers, as we turn them off, some of the charges leak, they dissipate and so forth. When we're talking about spin on these individual centers or the electrons in these centers, is there dissipation in the same way? How long will this storage work?


DAVID AWSCHALOM

So the spin is always there and if we don't play with it or we don't irradiate it or we don't manipulate it, it's still there; it doesn't go away. So it's rather different than thinking about a charge technology, but it's a good question. We started this discussion by talking about heat generated by circuits as you move electrons through wires. You know, if you take a Pentium chip and you saw it in half and you look, over 80 per cent of it is just wires, not transistors, not devices, mostly wiring. That's what generates the heat.
In this case, the amount of energy it takes to just flip the spin of one particle, without moving the particle, so there is no motion, is a very, very, very tiny amount of energy, far smaller than conventional electronics. So there is some energy that's dissipated, but it's vanishingly small.


SHANE HUNTINGTON

When we look back at the history of computers, back into the early '50s and so forth, there were some very simple versions of circuitry that essentially were called computers. What's the criteria to be able to call what you're doing a quantum computer? If you have an array of these centers and they're interacting, at what point do we have something that can compute?


DAVID AWSCHALOM

Well this is a research area that's moving very rapidly. So if you asked me this question six or seven years ago, I would have thought it would be quite some time before we would have a rudimentary quantum computing machine. But in the last half dozen years or so, we've now come up with ways to create quantum bits, if you like, the quantum equivalent of zero and one. We can place them with tens of nanometres precision in systems, as you were just mentioning. So the next question is: how do you actually build a very small quantum machine and how many of these types of quantum bits does it take to build a computer at the quantum level?
So again, you might have to take a step back and realise that in today's technology you need many, many classical bits to form practical, useful quantum computers. With a quantum machine, you can start to think about doing things with a handful of quantum bits. You don't need millions or thousands. To do very complex quantum calculations, it's expected you do need thousands of quantum bits. But you can begin to think about doing things with just a handful.
The intriguing part about building a quantum machine with a handful of quantum bits is as you bring these particles together, as you were mentioning, they interact, but they interact in a very unusual way predicted by quantum mechanics which is called entanglement. That as they approach one another, they become indistinguishable, they form this very unusual state where they all interact at the same time and that's the basis or the heart of a quantum machine; it's this very unusual, very unphysical property called quantum entanglement.
To answer your question, how many of these different states do you need to entangle to do calculations, in the end it will depend on what the purpose of the machine is, whether it's five or whether it's 5000. That's an area that people are still discussing.


SHANE HUNTINGTON

I'm glad you mentioned entanglement, because this is something we have to touch on. Can you tell us what's going on? I mean this is this strange, weird effect at a distance that Einstein and others described almost 100 years ago now. It enables you to take two objects that are entangled, move them apart and presumably that interaction continues. How does this happen?


DAVID AWSCHALOM

So this is something that particularly when we teach quantum mechanics is very unnerving and frankly for some of us, remains unnerving. If you take a particle and, say, split it into two pieces, which you could imagine a particle composed of two different spin states and you pull them apart and I give you one and I have one and we go to different ends of the Earth, if I measure one, it will affect your instantaneously.
That's very unphysical because there's no obvious connection between the two, they are entangled, they act as one unit, even though they're physically distinct. So that is a fact of quantum physics. That has been measured in the laboratory, it's been measured over many, many kilometres, it does work. It's this unique property that allows you to perform calculations by mixing states, much like water waves interfere with each other or light going through a prism suddenly breaks into many components. These types of entangled states you can think about as a type of interference, which means you have an opportunity to perform vast numbers of calculations in one operation.
It's very different in today's computers where you do many, many things in a binary form. You need to do billions of operations on devices to do a calculation. Here you can think about calculations where, say, a clock speed of one hertz, one second, very, very slow in today's technology, would still do vast numbers of calculations.


SHANE HUNTINGTON

I'm Shane Huntington and my guest today is physicist Professor David Awschalom. We're talking about the use of diamond in quantum computers here on Up Close, coming to you from the University of Melbourne, Australia.
David, if we think of a normal switch in a computer being on or off, having two states, a zero or a one, what's the equivalent for a quantum element?


DAVID AWSCHALOM

So one of the attractions about a quantum element is that in contrast to being a zero or a one, they're not like a transistor we discussed earlier or in your magnetic hard drive or your magnetised in one direction or another, one electron spin can point in an almost infinite number of directions. So if you think about this as a little arrow where you pin the tail down and the head of the arrow can move in any direction, if you let it run for a while, it would trace out the surface of a sphere. Every point on that sphere is a data point, so in contrast to say a classical memory, that's a one or a zero, one electron spin could hold an almost infinite number of memory states. So that alone would have a very big impact in technology; quantum memories that could hold astronomical amounts of information in micron scale volumes would change the way we think about information per se.


SHANE HUNTINGTON

David, coming back to diamond, how does the feature of entanglement that we talk about in quantum mechanics applicable to making a device in diamond?


DAVID AWSCHALOM

So to capitalise on the quantum property of entanglement in the material like diamond, there are a few different ways one can think about approaching this, or engineering entanglement. The simplest might be to think about placing these electron spins that we've been discussing close enough to one another that they sense each other's magnetic fields. Through these magnetic fields they can become entangled, a little bit like putting a bunch of magnets near each other on a table. If you flip one of them, another one will flip nearby. In this sense, the tiny electromagnetic fields that come from the individual spins will mix with one another and generate an entangled state.
Another way to think about creating entanglement in an array of electron spin states is to take advantage of the fact, stepping back, that diamond is a semi conductor. One of the properties of semi conductors is that electrons can generate light quite easily in the way that LEDs work, right, or the way that display technologies work. So one can use beams of light to connect these types of electron spins, wiring them together with photons instead of electrical circuits and by using on-chip photonics today, making miniature optical cavities and miniature lasers, in materials like diamond it's possible to conceive of architectures where photons would wire these spin states together and entangle them.


SHANE HUNTINGTON

Now David, in terms of where we're at right now in terms of progress and not just your own group but also around the world, has anyone actually put out the announcement that they have built a quantum computer at this point?


DAVID AWSCHALOM

Well there are lots of techniques being used to generate entanglement. People have entangled quantum bits, numbers of them now and shown that this is possible. Lots of different technologies are being used from super conductors to trap atoms, to ions, to electrons and semi conductors. Many, many of these systems have advantages and challenges. So people have now demonstrated simple quantum algorithms with entangled states of matter with vary small numbers of quantum bits. So I think we'll see this - you asked me earlier on about predictions. It's very difficult to make them, but my personal view is within the next few years we will see small quantum machines appearing. So far, things are going so well and so quickly, it seems inevitable to me that this will be the case.


SHANE HUNTINGTON

Now David, we've seen an explosion of different areas in the workforce as a result of traditional computers coming about over the last three to four decades. In terms of the quantum applications we're talking about, are we ready for this in terms of the workforce that we've trained and if not, what would be required to get us up to speed?


DAVID AWSCHALOM

So this is a very important issue and very important in the sense that it's an extraordinary opportunity for students that have interests in science and technology. So we need to generate a new type of quantum engineer which is sort of a mixture of scientist, engineer, technologist, computer scientist, mathematician, all rolled into one. So it means that we have to train students differently and think a little bit like people do in medicine, that you work together in teams to solve very complicated problems that one person may not be able to solve. It does mean we have to change the education system and we need to think about how to train students differently.
One of the wonderful things about this field of quantum information science in general is that it's truly a magnet for bringing in extraordinary students with these broad range of interests, in a sense that they're looking for the killer app of quantum physics. In a way, quantum information is serving that need. It's a new area that is certainly going to have an impact in society and technology. It's not obvious what that is yet, but the field is moving so rapidly and so well that students will have a huge role in this and we do need to train them.


SHANE HUNTINGTON

Professor David Awschalom is the Peter J Clarke Professor of Physics, Electrical and Computer Engineering and the University of California, Santa Barbara and director of the California NanoSystems Institute and the Center for Spintronics and Quantum Computation. David thank you very much for being our guest on Up Close today and giving us an understanding of the latest work in diamond based quantum computing.


DAVID AWSCHALOM

Well thank you very much for having me here.


SHANE HUNTINGTON

Relevant links, a full transcript and more info on this episode can be found at our website at upclose.unimelb.edu.au. Up Close is a production of the University of Melbourne, Australia. This episode was recorded on 19 January 2012. Our producers for this episode were Kelvin Param and Eric van Bemmel, audio engineering by Gavin Nebauer, background research by Dyani Lewis. Up Close is created by Eric van Bemmel and Kelvin Param. I'm Shane Huntington, until next time, good bye.


VOICEOVER

You've been listening to Up Close. We're also on Twitter and Facebook. For more info visit upclose.unimelb.edu.au, copyright 2012, The University of Melbourne.


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