(air whooshes) (dramatic electronic music) (audience applauds) - Well, ladies and gentlemen, thank you for coming
to the lecture tonight. It's a great pleasure to talk to you on one of my favorite topics, the contribution of Einstein to the foundation of a new field of technology, namely quantum technology, and the preeminent example of
which is the quantum computer, which I hope will be widespread
in the mid-21st century. I'm here today in the United Kingdom. The Australian borders
were closed for two years and I managed to, as
soon as they came down, I was able to take up a fellowship that had been offered by The Royal Society a couple of years ago, a
Wolfson Visiting Fellow, which has supported my visit and my activities here in the
UK over the last few weeks. But tonight's lecture,
"Einstein's Revolution," this is a field of research that I've been engaged
with at a practical level for the last couple of decades, and my aim tonight is not
actually to present you with the blueprint of a 21st
century quantum computer, but to go through some of the
physics that sits behind it. And I should acknowledge that
the University of Melbourne, where I come from, where I work, is on the land of the Kulin Nation, the first discoverers and colonizers of the
continent of Australia more than 60,000 years ago. So this is indeed the
University of Melbourne. It's on a pleasant green campus on the edge of the city of Melbourne. You can see that blue
waters of Port Philip Bay in the distance, and the physics building
is there in the corner. And what's very important
about the physics building is not that it's surrounded
by numerous coffee shops where you can go to discuss
physics anytime you like, except when I'm giving lectures, but also in the basement is my laboratory. I have a large particle accelerator and a series of beam lines that we use for doing material
science and in particular, the material science directed towards our
quantum technology projects. We also have a cryogenic system for measuring the properties of materials at very low temperatures, particularly the behavior of spins, which I'll come onto later on. And over here, just down the
hall from the big accelerator is a small accelerator which we use for inserting
single atoms one at a time into crystals of silicon. More on that later. So here's the outline
of my lecture tonight. First of all, I wanna do
a quick retrospective of the dawn of the Computer Age and what I call the
First Quantum Revolution. Then I want to introduce you to the promise of quantum technology and the quantum atom's useful spin. And finally, I'll wrap up with a quick review of some
of the work we're doing on building a large scale device based on atom spins in silicon. So first, a quick retrospective. The First Quantum Revolution and the dawn of the Computer Age. So just recently I made a major milestone and I had occasion to reflect back over more than six decades on Planet Earth. So I just wanted to share with
you some of those reflections that brought me to where I am today. So in 1958, okay, I've
given the game away, the Americans launched their
first satellite into orbit. It was loaded with Geiger counters and it discovered the
Van Allen Radiation Belts in the magnetic field of the
Earth, charged particles, particularly protons and electrons, are trapped in the curving magnetic fields and they orbit backwards and forwards under the influence of magnetic forces. These radiation belts can be hazardous to humans
in orbit around the Earth and also to electronics,
as we'll see later on. But if we fast-forward to 1969. Wow, what a year that was
with the Apollo missions. And standing on the front
porch of my home in Melbourne, looking up at the Moon, and knowing there were a couple of people walking around on that Moon
was an extraordinary experience and I followed the space
program very avidly. Now, it was sometimes said that this was the dawn of the Space Age, but actually it wasn't
the dawn of the Space Age, it was the dawn of the Computer Age because for the first time,
humans had built machines which were too complicated
for a human being to control. And so the Lunar Module
and the Command Module and the Saturn V rocket were all controlled by
some advanced, for the day, computer technology. And indeed the computer
on the Lunar Lander here had a massive 2,800 silicon chips. Each chip was crammed with six transistors and there was a whopping 70
kilobytes of core memory. And this was responsible for getting the astronauts
down safely onto the Moon and safely back into orbit afterwards. And if we fast-forward to today, there are now robotic
explorers on the planet Mars. This is the Curiosity Rover. But the Martian atmosphere is very thin and radiation from space is
able to reach the surface, and that radiation consists
of energetic ions, protons, the nucleus of a hydrogen atom, which is able to make it down
through the thin atmosphere and pass through the
electronics on the Rover. And this inset here shows upsets in the memory of the computer every time a proton
goes zapping through it and maybe changes a bit
from a zero to a one or a one to a zero, or
causes other upsets. And the hardware and the software has to guard against those
random perturbations from outside so that the computer
continues to operate normally. Now, 1958 was also a
big year for Australia because for the first time, jet aircraft with a large capacity introduced mass travel. This is the Boeing 707, 1958. And of course, if we
fast-forward to today, we've got supersonic aircraft and you can go from Melbourne
to London in just a few hours. Well, unfortunately, we didn't go down that
particular timeline. What we got instead was that. (audience laughs) And I think we went
astray there somewhere. Okay, all right. So never mind. In 1958, if you wanted
to make a telephone call, you used a telephone. For the benefit of the young
people in the audience, this is a device that has
only a single app on it. It's the telephone app. You can't put the Talk Tik
app on it for loading videos or anything, I think that's
what it's called, on it and you can't take it with you when you go because it's tethered
to the wall by a cable. Today, of course, if you
wanna make a telephone call, you almost certainly have
one of those, a mobile phone. In 1958, one of the first
single lens reflex cameras went on the market, the Minolta SR-7. I have one of these in my
vintage camera collection. And this device employs some of the best quantum nanotechnology you've probably never heard of but unfortunately, is now obsolete. But I don't have time
to say very much about the wonders of electrons in quantum wells inside silver halide crystals. But it's a wonderful
technology, now sadly obsolete. But fast-forward to today. Needless to say, if
you're gonna take a photo, you'll use one of these. In 1958, if you wanted
to do a calculation, you used a slide rule which exploited the
properties of logarithms to convert multiplication into summation. And if you fast-forward to today, you probably have a calculator
app on one of those. Now let's take a big step back. 60,000 years ago, this is one
of the first memory sticks that humans ever made, made with an early form of lithography. That is to say, the data was
scratched onto the memory stick with a sharp rock, a lithography process. Unfortunately, what algorithm is used to interpret the nine bits that have been stored
carefully on this memory stick has now been lost, so we don't know the
meaning of these nine bits but it's probably very
important in human development. If we fast forward to 1958, Jack Kilby discovered a way
of integrating transistors onto single chips of silicon. Before that, transistors
came in individual packages and had to be soldered together. But this idea of integrating
many transistors onto one chip eventually won him the Nobel
Prize in the year 2000. It took the Nobel Committee a little while to figure out that this invention conferred the greatest benefit
on humankind that should be. So yeah, the Swedish
Committee ponders very slowly. And today, of course, if you
want an updated memory stick, you don't have to scratch marks on bones, you can buy a two terabyte USB drive. That's an extraordinary amount of data that could be put onto
one of these sticks. Now what's interesting there is that the technology to produce that sort of density of
information is imperfect. And this memory stick has on board special error correction mechanisms to cope with the fact that not every memory element
works all the time. And the onboard algorithms detect when memory elements begin to fail or didn't work in the first place, and wall them off to prevent errors. So the key takeaway from
this technology is that it's possible to build large scale devices from tiny, tiny components
with imperfect techniques and still have them work, just like the Rover on Mars is imperfect because the radiation from
space is constantly causing upsets in the memory so you have onboard algorithms to detect and correct those errors. This is an important concept which I'll come back to later on. And today, of course, you can
buy personal computer chips with billions of transistors
integrated onto them and the cost per transistor
is about 10 nano dollars. That's an extraordinary
number of human artifacts available at a very low price. Or about three nano euros. A remarkable advance since 1958. So all of these bits
and pieces go together to make what I call the
First Quantum Revolution. The idea of quantum mechanics
is the foundation on which all these gadgets, computer
chips, optical fibers, mobile phones, super
computers, solar cells, implantable devices,
medical imaging systems, all of these things rest on the foundations of quantum mechanics. But most of these devices
operate via classical principles. The fundamental quantum phenomena are buried down inside the chips, inside the silicon crystals, which comprise the
fundamentals of these gadgets. And of course, this has led to a revolution in our society
in the 20th century, in the early 21st century, and here we see the modern
way of having a conversation in the cafe using apps on
the personal computers. I don't know if that's an advance or not, but this is the First Quantum Revolution. So now I wanna move on and talk about the seeds of a Second Quantum Revolution. And to do that, I want to illustrate
some of the basic physics that is leading to the
Second Quantum Revolution. And so it's a great thrill
to be speaking to you today in Thomas Young's Lecture Theater here at The Royal Institution, where he surely did this experiment to an interested audience such
as yourselves back in 1802. Now this experiment revealed that light was clearly a wave
passing through space. In 1802, it wasn't clear
what exactly was waving, but this was what Thomas Young did. Well, not exactly this but close to this. And this is what it looks
like in its modern form. First of all, you take a source of light. Of course, Thomas Young in 1802 didn't have an electric light bulb 'cause it hadn't been invented yet, so he used the light from a nearby star. The Sun obviously. Passed it through a narrow collimator whereupon it produced waves of light, which then it was incident
on a barrier with two slits and the waves that passed
through those two slits then created an interference
pattern on the screen. So I'd now like to
demonstrate this in real time in the lecture theater. So we've got our... We've updated it with using a laser, so it's a very bright source of light. - Got the lights on. - Yeah. So... And in front of the laser, there's this beautifully
handcrafted two slits. Is that right, Tom? Yep. And you can see the interference pattern created by the light waves
passing through the two slits. Where the peaks in one wave overlap with the peaks in the other wave, we get a bright line, and where the troughs of one wave overlap with the peaks of the other wave, we get a dark line,
destructive interference. So this is very different
to what you would get if light was classical particles. You could imagine throwing
very small tennis balls at the barrier with the two slits, and all you'd get on the screen here is the shadow of the two slits, not this beautiful extended
interference pattern that is a direct consequence of the wave-like nature of light. Thank you very much. And I should have mentioned that the diagram down here
on the lower right is in Thomas Young's own hand explaining why you get that interference
pattern of the bright and dark lines. Now this. And here's one we prepared
earlier in case it didn't work. But it did, of course it did. It's physics. It always works. (audience laughs) If we now fast-forward just
over 100 years to 1905, Einstein had his miraculous year where he published four
new ideas in physics, the consequences of which we are still unpacking
even in the 21st century. But the most radical idea
that he published in 1905 seemed to contradict Young's conclusion from
the Two Slit Experiments that light was a wave. Einstein wrote in the introduction to one of his 1905 papers, "According to the assumption
to be contemplated here," in his paper, "when a light ray is
spreading from a point, "the energy is not
distributed continuously "over ever increasing spaces, "but consists of a finite
number of energy quanta "that are localized in points in space, "move without dividing, "and can be absorbed or
generated only as a whole." And this sentence in Einstein's 1905 paper is widely attributed to be the most revolutionary
sentence written by a physicist in the 20th century. So it's a tricky thing to demonstrate in the lecture theater, but I wanna give you an
idea of how it works. First of all, I've
brought my woolen jumper all the way from Australia for
this demonstration for you. And those of you who were
admiring the painting out the front of this lecture theater, will recognize this bit of apparatus that appears in the painting. It's an electroscope. And what I'm gonna do is I'm gonna charge up the electroscope by rubbing a few electrons
off this plastic rod and bringing it into the electroscope, grounding it, and then moving it away. I've just charged the
electroscope by induction. For those of you who
are sitting up the back, it might be a bit hard to
see, but, oh there we go. So we can see the two
leaves of this electroscope have been deflected because
they've been charged up. Now this electroscope has got a sheet of zinc on the top of it and I'm now gonna shine a very
bright light onto the zinc and knock electrons out
of the surface of the zinc with this beautiful incandescent torch that's come out of the archives
of The Royal Institution for me to use in this
demonstration for you tonight. Is anything happening? Nothing's happening. Of course, nothing's happening because the photons in this torch are too feeble individually to knock an electron out of
the surface of the zinc plate. Now we tried every other bright light in the possession of The Royal
Institution this afternoon, including their very
dangerous ultraviolet light. But unfortunately, their ultraviolet light
is not dangerous enough and the photons are just
not energetic enough. So to show you this demonstration, I'll have to show you a demonstration recorded in my laboratory in Melbourne. But if you use photons that are individually
sufficiently energetic to knock electrons out of
the surface of the zinc, you discharge the electroscope. But this was Einstein's idea from 1905 to explain that phenomenon. The light coming out of that
torch or out of that laser or out of the very
dangerous ultraviolet lamp that I'll show you in a moment, consists of individual packets of energy that cannot be further subdivided. So in other words, you
can't have half a photon. You've gotta take the
whole photon or not at all. So this was a rather unusual idea in 1905, but it's been tested over and over again and found to be true. And this is the photoelectric effect that Einstein eventually
got the Nobel Prize for. So here's the basic idea. There's your piece of zinc, which has got a whole lot of electrons embedded in the surface. Here's some waves of light approaching the surface of the zinc. And here is the photon
associated with those waves. Now here's where the
strange idea comes in. Although that wave spreads itself out across the entire surface
of that piece of zinc, the photon can only be
absorbed in its entirety or not at all. So it's like the photon, each photon, somehow tastes all the electrons
on the surface of the zinc because it's a wave as it approaches it, and finds one electron
that it likes the taste of. I'm being metaphorical
here. Photons don't taste. And it knocks one electron
out of the surface. So it's as if the photon in
its wave-like manifestation is dispersed over a large area. It's in multiple places at the same time, but it's all absorbed finally in one place and gives all its energy to one photon. So this is what we can do in Melbourne with our very powerful light. So I'm just gonna fast-forward
this to two minutes. We don't need the sound on this 'cause I'll do the voiceover. So here my trustee assistant Steve has got this very dangerous
ultraviolet light. He's gonna turn on. Don't look at it Steve! No. Then he brings it over the electroscope, shines it on the zinc plate, and you could see the leaf
of the electroscope deflect as the charge leaks away
into the air in the room. So that's what happens if your photons are sufficiently energetic to interact with the electrons
and dislodge them one by one. And none of these other lights had an energetic enough photons. Another way of looking at this, which is easier perhaps to understand, is imagine you're surfing. I guess this doesn't
work so well in the UK as it does in Australia. But imagine you're surfing and
you see this wave approaching and there's a whole bunch
of surfers lined up, ready to catch the wave. In Einstein's idea, only one
surfer can catch the wave. So it's like the other
two surfers left and right are left flat in the water and just the surfer guy in the middle catches the entire wave. And so in some ways the wave, the function that describes the wave, collapses just to one point
when it has to interact. This is a fundamental
mystery of quantum mechanics. The other day under the
terms of the Fellowship, I have to go around giving lectures at different universities and I went down to the
University of Surrey, caught the train down, on one of the non-strike
days, I emphasize. And I saw this sign at Gilford Station. As a physicist, this makes me very nervous because they're asking me to
spread out along the platform like a quantum particle, but I'm too big. I'm a classical particle so
I couldn't obey that sign. Or maybe just reading the sign caused me to decohere into this one
place so I could read the sign. I don't know. I think it's a very disturbing sign and there should be an asterisk,
"Do not take literally." (audience laughs) Let's fast-forward to 1911
when Ernest Rutherford reverse-engineered the atomic nucleus, discovered the nucleus, surrounded by its cloud of electrons. The nucleus is like the
size of a dust particle floating inside a cathedral representing the cloud of electrons. Something very tiny and very dense. And then his post-doc, Niels Bohr, just a few years later
discovered the quantum atom. He discovered how the electrons
that orbit that nucleus that his supervisor had
discovered how they orbit. And they orbit not by
classical trajectories like you have with
planets orbiting the Sun, but they orbit in quantum
mechanical standing waves. Now what's remarkable
about that idea is that quantum mechanics is
starting to be manifest in more and more places, not just with Einstein's
photoelectric effect. The other remarkable
thing about Bohr's paper, both Rutherford and Bohr were working at the
University of Manchester at the time of these two discoveries where I'm based at the moment, was that Bohr's paper was
read for the first time at a conference in my physics department at the University of Melbourne. I wasn't there in 1914 when it was read, but the British Association
for the Advancement of Science had its meeting in Australia in 1914. It rotated around the Commonwealth, mostly it was within the UK,
but once it went to Canada and this time it went to Australia. Rutherford was the President
of the British Association. His post-doc Niels Bohr wasn't
there, he was on holidays, so Rutherford read the paper. And it's remarkable that this original idea of the quantum atom should have been heard at a
conference for the first time in the old physics building at
the University of Melbourne. We have detailed records of the meeting and the chemists in the audience thought that physicists
should stick to physics and not meddle in atomic theory 'cause everyone knew atoms were square. But they reluctantly conceded that there seemed to be some grain
of truth in these ideas, even though they were quite radical. But we now know that we can describe the quantum
mechanical nature of matter using Schrodinger's Equation. Now just in case someone
stops you on the tube on the way home and asks you, "Did you go to that Einstein lecture "at The Royal Institution "and did you see Schrodinger's Equation?" You can say, "Yes, we did." But Schrodinger's Equation, there's nothing mysterious about it. It's simply what we're already familiar in the classical world that
the energy of a particle such as this cricket ball
propagating through space or this moon orbiting that planet is just given by the sum of
the energy due to motion, the kinetic energy, plus the
energy due to any interactions between the two objects such as gravity or electrostatic forces. But for quantum mechanics
we need to be able to describe things that are in
many places at the same time. A wave. And so, we just translate
these classical ideas, the kinetic energy and the
potential energy, into functions so that we can find the shape of the wave represented here by the Greek letter psi. But it's exactly the same concept, we're just replacing scalar quantities with function quantities. And that then even for a simple system like an electron orbiting a
proton in the hydrogen atom, leads to these beautiful
three-dimensional shapes that describe the nature of the electron, quantum mechanically speaking, in its orbit around its proton
nucleus in the hydrogen atom. And this can be applied to many other elements
in the periodic table, including phosphorus atoms
in the silicon crystal, which I'll come to later on. So the next step in our quantum
mechanical journey is the discovery of spin. Now it's worth spending just a few moments to talk about spin because this is actually
a rather strange concept. First of all, I have a child's
toy here, a very nice top. It's got a sharp point here which means... (top bangs)
Ah! (top bangs)
Ah! You just can't balance it, you know? (top bangs)
Just won't balance. But look what happens if
you give it a bit of spin. It does balance. It doesn't fall over
like what would happen if it wasn't spinning. But you can see in the
gravitational field of the Earth, gravity is trying to tip that over and for reasons to do
with the velocity vector constantly going around in
circles of the rim of the top, it processes around the
gravitational field direction which is vertical. And as it slows down due
to friction with the table, that procession or that wobble becomes more and more extreme. But this is up until finally
it succumbs to gravity as it always will. But this is a classical object. It turns out down inside the atom, the electrons that are
orbiting the nucleus also have spin like this. And so we represent them by
objects that look like this. And this is just one I made myself from the stuff I got
from the local craft shop and a very nice tube of
self-adhesive glitter. So you can think of this as an
electron or an atomic nucleus and it's spinning about its axis and we represent the direction of the spin using the right-hand rule where my thumb points in
the direction of the vector representing the direction of the spin. Now what was discovered in 1921 was that in a silver atom, which was known to have no spin except for the last electron added to make up the whole atom, which was all by itself
in the outer shell. So the whole spin of the silver atom was basically carried
by that last electron. And when you boil silver atoms
in a vacuum out of a furnace and pass them through a
very strong magnetic field, you find that the beam of
silver atoms splits in two when it passes through the magnetic field. In the same way we saw
the wobbles of this top due to the presence of
the gravitational field. But now we're talking about
a quantum mechanical spin in a magnetic field. But the physical principles
are very similar. And when this experiment
was done, first of all, this is the result of
a beam of silicon atoms hitting this postcard. Without the magnetic field, you just see a line of silver
atoms piling into the card. Then when you turn on the magnetic field, you find the line splits in two. They're not two parallel lines because you need to use a very
strong inhomogeneous field. But this discovery was immediately
reported to Niels Bohr, who by then had left Manchester
and come back to Copenhagen to head up a new research institute because it was so exciting, so unexpected, that down inside the atom there were objects we now
know are the electrons that were spinning and they
process in a magnetic field in the same way this top processes
in a gravitational field. And what was mysterious was that the spin could only have
two possible orientations reflected by the fact that
there are only two lines here. So it was concluded that the quantum mechanical
attribute of an electron was such that it could either be spin up or spin down, but nothing in between. Space was found to be quantized. It was like this top could
only wobble like that or like that. Nothing in between, which of course, is not
the case for the real top because it's a huge macroscopic object and quantum mechanics is hidden. So this was a further
quantum attribute of matter that was discovered in 1922. Now you can see the same effect
by taking light from the Sun and passing it through a
slit and into a spectrometer, like dispersing the light through all the colors of the rainbow. And here is this black line represents the slit of a spectrometer and it passes across a Sun spot where the magnetic field is very strong. And sure enough when you look at the colors of the light coming
from the surface of the Sun, you find that away from the
Sun spot, it's a single color. And then as the light
comes from the Sun spot, in this case it splits into three. Not two, three. And this was later found
to be due to the fact that the spin had a different quantum number, an integer rather than for an electron the spin is always one half. So this uncovered a lot about the internal machinery of how electrons orbited the atomic nucleus. So all of this stuff was boiled down into the first iteration
of quantum mechanics, of which Paul Dirac, here in the UK, was one of the leading exponents. But in 1928 he made the
somewhat depressing observation, "The underlying physical laws "necessary for the mathematical theory," Schrodinger's Equation,
"of a large part of physics "and the whole of chemistry
are thus completely known." I don't know if the
chemists would've agreed, but that's the physicist's view. "And the difficulty is only that "the exact application of these laws "leads to equations much too
complicated to be soluble." So let's go back to the caffeine molecule. What a wonderful molecule. It docks with all the physics
receptors in the brain and makes them go round
faster and you get new ideas and it's great to talk about
quantum mechanics and spin and Dirac's depressing observation. But the caffeine molecule has
got 100 of spinning electrons orbiting the carbon, the hydrogen, and the oxygen that make up the molecule. That's a little electron I made as well, which can only have two
orientations in space. And the number of
electron-electron interactions across those 100 outer shell
electrons in the molecule are governed by Schrodinger's Equation. But there are so many interactions that even the world's best
super computer is powerless to calculate the structure
of the caffeine molecule. It's just to complicated for
a classical computer to solve. Even the most powerful
supercomputers today can only do about 30 electrons. And every time you add another electron, you get more and more
electron-electron interactions and the problem becomes
exponentially difficult. So there it sat for 70 or 80 years. But in 1959, Feynman gave
this remarkable lecture, "There's Plenty of Room at the Bottom," where he put forward this idea for a new type of calculation. Not just using classical circuits but a system involving
the quantized energy level or the interaction of quantized spins. In other words, to build a computer that employs
quantum spins as its bits instead of classical bits that would allow you
to use a quantum system to model another quantum system. But there was no technology in 1959 to do anything with that idea. But we are trying to do
something with that idea, and this is a phosphorus atom that goes into a silicon
crystal beautifully and we can see it's got a nuclear spin inside the phosphorus nucleus and there's a single
electron orbiting around it which also has a spin which can be harnessed for
technological applications. So let me explain the
power of a quantum bit instead of a classical bit. First of all, let's take this abacus. Used for thousands of years and the same principles behind that abacus is also at the heart of
the classical processing that's going on in my mobile phone here. Now the way an abacus works, for those of you who
need a quick refresher, is that the value of the bit is determined by its position on the wire
in the frame of the abacus. So that bit on the top right
there is in the down position, that's called zero. But if you flip the bit and
put it to the up position, that represents a one. So effectively what you've done is you've replaced the bit with an arrow, which we can call a vector, and by flipping the vector
through 180 degrees, you change the value of the classical bit. But they're the only two possible values that classical bit can have. It's either down, zero or up, one. Now imagine grabbing the wire
out of the frame of the abacus and allowing it to occupy
any orientation in space. This is what a quantum bit is. A quantum bit exists as a super position of being in
two places at the same time, like Einstein's photon being a wave, and it can be in the sum of the zero state and the one state, which determines its orientation in space. There's only one catch. You can exploit this remarkable large versatility providing
you don't observe the qubit because as soon as you observe it, it'll instantly decohere, just like the photon changes
from a wave to a particle when it interacts with just one electron into its classical values of zero or one. So you can do massive computations to exploit this enormous phase space, as we say in technical speak, providing the quantum computer
exploiting this technology doesn't interact with the outside world until it finishes the calculation. That's a challenging thing to do. Nevertheless, in 1998, young post-doc at the
University of New South Wales, Bruce Kane, published this
single author paper in "Nature," the journal, a silicon based
nuclear spin quantum computer based on phosphorus atoms embedded in a silicon crystal lattice. This paper has been
cited thousands of times and triggered a reappraisal
of the idea of qubits in an engineered device. Today with my colleagues in the Center for Quantum Computation and Communication Technology in Australia, we have refined Bruce Kane's architecture into something we believe we can build based on single phosphorus
atoms embedded in silicon, each of which is individually controlled by electrodes integrated
into the surface of the chip in the same way there
are myriads of electrodes integrated into the classical
devices inside this phone. So basically, we're using the standard tools of the
semiconductor industry, perfected now over 60 or 70 years, to enter the quantum domain. So this is now the Second
Quantum Revolution just emerging. And why do we wanna do this? Well, getting back to
Feynman's idea of using a quantum system to model
another quantum system, one day, the next pandemic may be fought not with test tubes and Petri
dishes in the traditional way, but by reverse-engineering
the spike protein in the next virus and then
engineering in silicon the shape of a molecule
needed to gum up the works and act as a vaccine. This is a dream which would
have enormous benefit. And today, quantum computers
are already being built with tens or even hundreds of qubits where the first tentative
steps in that direction are being taken. But if you are gonna devise a vaccine, you're gonna have to do
massive calculations. You'll need millions or
even billions of qubits. And what's the cheapest qubit? It's possible to make a
qubit based on a single atom. Atoms are really cheap. There are other quantum
attributes including entanglement, barrier tunneling, coherence, decoherence, Schrodinger's Cat, and teleportation that
could also be incorporated into new quantum technologies, but I don't have enough time
to say very much about them. So in the last part of my talk, I wanna describe some
of the work we're doing in building a large scale device
by using iron implantation to insert single phosphorus atom qubits into silicon crystals. And this cartoon shows
the way it might work. We see a whole array of phosphorus atoms just below the surface
of a silicon crystal and each atom is
controlled by an electrode integrated on the surface. And by changing the bias
voltages on the electrodes, we can cause the qubits to interact without doing any measurement
so that they retain their delicate quantum
states of being in two places at the same time. So this brings me to the
classical quantum divide. After Young's Two Slit
Interference Experiment, the question was asked, "Okay, it works beautifully with photons. "Does it work with matter?" Can a particle of
matter, like an electron, be in two places at the same time? And this is a diagram taken from Feynman's famous lectures in physics. I'm putting this up because
I once sat next to Feynman at a colloquium when I was
a post-doc at Cal Tech. And I'll tell you the charisma. Wow! It was amazing. What a remarkable guy. A little dangerous perhaps,
but a brilliant physicist. But in his famous textbook, he described the way matter behaves using Young's Two Slit
Interference Experiment. He said, "You can take an electron gun "emitting particles of matter, electrons, "you can direct them to a
wall that contains two slits. "And over here on the back
stop, there's a detector "for measuring the position
of all the electrons "that pass from the electron
gun through the barrier "to the detector." "And when you do this," he said, "you'll end up with a Young's
Two Slit Interference pattern, "not the classical shadow
of these two slits." But he comments, "This experiment has never
been done in this way." Because when these lectures
were published in the early 60s, there was no technology for detecting single electrons at a time. But folks, let's look at the
shocking truth of the way this experiment works. An electron, a particle of matter, emerges from the electron gun
and passes through both slits. The electron, a particle of matter, is in two places at the same time 'cause somehow it turns from a particle when it emerges from the
electron gun into a wave, passes through both slits and then converts itself
back into a particle to make the detector go ping. And it all goes to one place, just like Einstein's photon
in the photoelectric effect. Humanity finds this rather shocking, the idea that a particle can be in two places at the same time. So when we teach this in
undergraduate physics, we bury it under a thick
layer of mathematics to conceal from the students the shocking truth of what's
actually happening here. And if they ask questions about what's actually happening here, we just say, "Shut up and calculate." I've been doing it for 20 years. But I reveal the shocking truth. So here we have the electron
behaving like a quantum wave as it passes through both
slits at the same time. And then here we have the
electron behaving like a particle when it all converges on the detector and makes the detector go ping. So when you move the detector up and down along the backstop, you record the intensity of the electrons forming the interference pattern, which you saw in the lecture
theater at the beginning. And so today this is the
quantum classical divide. We need a classical readout device for our quantum mechanical operations that we've engineered into our device. And I was very taken with
this paper published in 2013 where the authors are very cheeky. They copy Feynman's diagram
from his book and say, "Actually we have done that experiment." They did take an electron gun, they did pass the electrons
through the two slits, and they did have a detector, and they recorded the interference pattern as the electrons interfere because of their quantum attributes. Furthermore, a group in Austria
has done the same experiment with a Buckyball. 60 carbon atoms in this giant
molecule fired at a grating, and the molecule can be
in two or three places at the same time and make a Young's Two
Slit Interference pattern. I find that very spooky, but a wonderful aspect of the real world. And today, this classical quantum divide seen here where we have quantum attributes, is engineered into quantum
computer devices, the prototypes. These are superconducting qubits consisting of little magnetic circuits where the magnetic field can be up or down or in a superposition of up and down. And each of these devices now
has a classical readout device to report the results
to the outside world. Our architecture consists
of a single phosphorus atom in a block of silicon
with control circuitry. The spin of the phosphorus
atom is our quantum particle. It can be spinning in both
orientations at the same time, represented by the double arrow here. And then there's a single
electron transistor formed by these electrodes, which is connected to an oscilloscope, and all these guys are
looking at the oscilliscope to decohere the nucleus
into either the spin up or the spin down orientation. The observer has to be
in the loop it seems. And the first time we got this to work, I was in my office in Melbourne. I got the call from Sydney
where the measurement is done after we implanted the phosphorus atoms and they said, "It's working!" After all these years of work,
finally we've got a device that is displaying the quantum attributes we've been eagerly seeking. So I said, "Don't touch
anything! Don't touch anything! "I'm coming right now!" I went to the airport, I got
on the next available flight. You know much Qantas charges
if you go to the airport and say, "Put me on the
next flight to Sydney?" It was extortion. But I was in the lab a
couple of hours later and I saw with my own eyes something I'd been
teaching for two decades actually happening in the laboratory. We could see the electron
spin orientation, we could see the nuclear spin orientation, we could see that nature was digital at the fundamental level. So this is the heart of our device, a silicon crystal lattice
consisting of silicon atoms and one of which we replace
with a phosphorus atom using iron implantation. Now silicon is not perfect. There is a rare isotope
naturally occurring called silicon-29, about
5% of natural silicon. And it has a nucleus,
which is a bit peculiar. It's got an extra neutron and that extra neutron
confers spin on the nucleus. Whereas all the other silicon isotopes have no spin in the nucleus 'cause all the nucleons are
beautifully paired up together. So that's like having a little
bar magnet inside our chip, which is interacting
with our phosphorus atoms and destroying the quantum coherence. So step one is to remove the silicon-29s and replace them with silicon-28,
the zero spin isotope. And this is like a vacuum
with nothing going on except what we've engineered into it with our phosphorus atom. It's the next best thing to a real vacuum for doing quantum mechanics. We then use radio frequency pulses to flip the spin orientations from the zero state to the one state, or indeed to put them in the quantum superposition of being spin up and spin down at the same time. This is what the device looks like. This is about, I guess about, a million times actual size on the screen in the lecture theater. Right in the middle is a small area where we implant a number
of phosphorus atoms and then we use these control gates to tune in on just one of them, and that's where we do
our quantum experiments. And this is what it
looks like in a cartoon. A single electron is brought across onto the phosphorus atom. Then we do a radio frequency pulse to put it in the quantum superposition. This is all at 100 millikelvin. It has to be very cold. And then by controlling the
position of the electron, we move it back into this
single electron transistor. There's a flow of current and that's connected to an oscilloscope and we can see the quantum
state of our electron and then we re-initialize the device and it starts all over again. So here's the spooky
quantum bit in our device. Einstein in 1916 said, "Imagine you've got a quantum object "which can be in two energy states, "a low energy state and
a high energy state." And that is indeed what happens when you put a spin in a magnetic field. It's like putting two
bar magnets together. When the north and south
poles are together, they stick together beautifully. But if you try and push
two north poles together, it doesn't work. It's in a higher energy state,
will spontaneously flip. Now in a spin which can be
up, the low energy state, or down, the high energy state, you can flip the spin by
hitting it with a photon. There's a lot of photons going on here, but this is a microwave photon. Now Einstein said, "If you
are in the high energy state, "after the low energy
state absorbs a photon "and goes to the high energy state, "another photon of the same energy "will cause it to decay
back to the ground state." So while the photons are on, they are both lifting the spin
into the high energy state and inducing it to decay
back into the ground state. So when you turn the photons off, the spin is in this quantum
superposition of being up plus down. And because I've been
lecturing to undergraduates, I have to put, "This is the spooky
quantum bit of the device." So sorry about that. And then when you read
it out, you decohere it, the detector goes ping
either in the spin downstate, high energy or spin upstate, low energy. And you repeat that over and over again with increasing time intervals after you turn the photons off. And if this was a classical particle, 50% of the time when
you do the measurements, you'd find it's in the high energy state and 50% of the time it would
be in the low energy state. It would just be random. And indeed Galileo and
Newton would predict this is the result you would
get for this experiment. But when we do the experiment, because this spin is a quantum entity, we find it's not a probability
of 50% up and 50% down, it actually oscillates between the up and down configurations because of its quantum nature, the wave-like nature of the spin. And the longer those oscillations go on, the more quantum calculations you can do when it's in that superposition
of quantum states. And we found that the atomic nucleus can last for more than 30 seconds in this superposition of up and down because of the duration
of these oscillations. And 30 seconds is an
eternity for a quantum state, and so we were very pleased to get this expected quantum state. So this is our device. We remove the silicon-29s, we implant a few phosphorus atoms, we tune in on just one, and we do all these experiments. But this is not good enough
for a large scale device. So just to conclude, let me explain how we're gonna take the
results we've obtained just on our single phosphorus atoms and take it to the tens or even hundreds. This is a silicon lattice. We implant phosphorus atoms into it using the standard techniques
of the semiconductor industry. There's probably 15 or 20
different iron implantation steps that have gone to make
the silicon chip in here. Then we heat up the crystal and we push the implanted phosphorus atoms onto the crystal lattice site. But the way that's done in industry, it's like raindrops on a window. The raindrops fall at
random points on the window. This is not good enough for
making a large scale device. We have to have order. And so what we wanna do is make this deterministic non-stochastic. We wanna put the atoms in an orderly array so they can be coupled to the
surface control electrodes and we can do large scale
quantum computations that better not take too long. So we have re-engineered
an atomic force microscope that has the precision
to localize the implants using this tiny nano aperture. So the iron beam rains
down on the cantilever, there's the little tip of
the atomic force microscope. And every time a single phosphorus atom passes through the nano
aperture and implants, we hear a click. And so here, folks, is the
sound of single phosphorus atoms being implanted into a silicon chip. Let me just get the sound going here. (atoms ping) Bit uncertain that one. (atom pings) Another one, another one. You can hear it's like rain on a tin roof. And every time we hear one of those pings, we move the cantilever to a new location and wait for another one to come down. (atoms ping) This soundtrack was featured on the Australian Broadcasting
Commission's Sounds of Science. So if you Google it up, you could download it and use it as your ring tone if you wish. (audience laughs) So we are now in the process of building a large scale device
using this technology. We have already built a three
cubic device just by luck. We found two phosphorus atoms, which were close enough together
that we could couple them. And this is the artist's impression of
those two phosphorus atoms with a single electron in
orbit around both of them. This is an artist's impression, but you've gotta have
fancy artist's impression if you wanna get on the cover of "Nature," as we did back in January
with this discovery. And this device worked beautifully. We were able to maintain
the spooky quantum state for a very long time and we made a very high fidelity gate set, something that is the building block of
a large scale machine. And this was very satisfying, even though we made it only one device out of
many we made work like this because we were just
implanting the atoms at random. But now we're gonna
impose order on our device and build large scale devices
of single phosphorus atoms in our ultrapure silicon. And so I hope you'll stay tuned for more developments in this
area in the years to come. Thank you very much for your attention. (audience applauds)
It's my favorite century for quantum computing, how did they know??
Cold water for the hype train. https://youtu.be/CBLVtCYHVO8