I don't know about you, but I'm at a loss. See, I keep reading headlines about
quantum computing and how it's gonna change the world but every time I try to
dig into what it actually is I feel like my brain glitches out a little bit. But
I'm not giving up, and today I am on a quest to make quantum computing—and what
it means for our world—understandable once and for all.
*rock music intro*
Basically it's using quantum mechanics to compute things. But essentially, the idea is that unlike
classical systems in a quantum computer or a quantum device you can have the
system, it can be in two states at the same time and that gives you a kind of
parallelism that allows you to do two things at once, in a way that that for
certain kinds of problems allows you to solve them potentially exponentially
faster than you could ever do classically. What?! OK, hold on, we gotta
back it up a little bit. What does quantum mean?
No, no not like that I mean, in a physics way?
So, here's me. I'm made up of a bunch of different living tissues, which are made
up of molecules which are made up of atoms of all of the different elements
we're made of. And our atoms are made of subatomic particles: protons, neutrons and
electrons. And then if you can believe it we can go even further down than that
because protons and neutrons are made up of even smaller particles called
elementary particles like quarks leptons and bosons. And this world of subatomic
and elementary particles is what's called the quantum realm and this is where the physics
things follow the rules of quantum of mechanics which basically means that at
this level, things this small behave really strangely—like, different than how
the world behaves at the larger level of say you and me
So classical computers work with digital logic, most of them, which means that you
express everything in terms of bits that are zeros and ones and you manipulate
those with what are called logic operations and that's the basis of a
program so you have some input bits, you manipulate them, you get some output bits
in that your answer. And then the magic of a quantum system is that you
can have an analogous thing but instead of a bit you have what's called a
quantum bit, a qubit. Sounds cute.
Just to recap, this is how all of our computing that we're used to—which is called classical computing—works:
we use electrons to send signals from one piece of machinery inside the computer to
another. These signals are either on or off, there is either a flow of electrons
at a discrete voltage or at another specific, measurable voltage and that's
your signal. This on or off binary signal is encoded by us digitally in
ones and zeros, that's how we tell the computer what we want it to do and then
how we read the signals that come out on the other end. This also means we're
limited by a bunch of things, including the constraints of electricity like the
loss of energy through resistance and the generation of heat. It's also getting
harder and harder to cram more and more transistors into smaller and smaller
spaces, like throughout computing history we've seen steady progress in
improvement of computing power but we're reaching the end of that trend, we're
reaching the limit of what's called Moore's Law. B: There's never been anything
like it in human history. It's really remarkable. We're now getting
to the point where transistors are just a few tens of atoms across, so they just
can't keep getting much smaller and the cost of building the fabrication
facilities is just phenomenal, and so it's very difficult to to
continue progress. So all projections are that in the early
2020s this will run its limit, so what will happen then? M: This is where all kinds of
computing innovation comes in, including quantum computing! So back to how quantum
computers do what they do. With one classical computing bit that unit can
give two answers: one or zero, yes or no, on or
off, you get the picture. But in quantum computing, instead of being just zero or
one it could be any sort of combination of zero and one. And then if you put two
together those can be in any combination of zero and one both, and so the size of
the space that is effectively possible grows really quickly with the
number of qubits you have, right, and it's because they can be in f all
all the different states at the same time. You could imagine something that
had every possible value between zero and one, sure, and that would be
pretty cool, but the quantum system actually does more than that. Not only
can you have any number between 0 and 1 you can have what's called a phase. You
can have a relative phase between 0 and 1 so that adds an extra axis, and
instead of this just being a line they live on the surface of a sphere. M: ok,
ok, so if a bit is two points on a line, a qubit is a 3d sphere where any
of your quantum states are any point on the surface of that sphere? That's right.
Exactly. Ok, so qubits can give us way more possible computing power
because they can ask many questions at the same time. Plus when you're adding a
computing unit, a qubit, you're getting way more bang for your buck than if
you're adding another bit to a classical system. And that all sounds great! But
those benefits are only true if you can ask your quantum system your questions
in a way that makes sense and then also read the answer that it's giving you in
a way that means something to you. J: if you measure it from from classical world, it
doesn't give you the answer of what that any possibility is, it gives
you that classical response back, so it gives you either 0 or 1.
M: Because you're asking it from a classical system? J: Kind of, yeah. There
there is a sort of paradox in the sense you want this thing which is purely
quantum mechanical, which can live in multiple states, but as soon as
you interact with it from the classical world, which is where we're living and
where we're going to construct all the problems we're asking, it interferes with
that system and essentially imposes classicalness on it, so even the
materials that you build the system out of they effectively can measure the
states of the quantum computer and you don't know what question was asked so
that's what ends up making it like it randomly projects into one of those
those state. So that's a big source of error. M: Well, it has to freeze at the
moment it is in that time and give you where it is at that one moment, it's not
gonna give you all the possibilities but that exist. J: Sure, that's right. M: Plus
there's this whole issue of noise. Because stuff on the quantum level is so
freakin tiny it can be disturbed by super tiny things like the movement of
molecules...and another way to put the movement of molecules is: temperature
The other aspect about quantum computing is, unlike a phone that you carry around
with you and it lives you know in warm and cold environments, a quantum computer,
to keep those qubits pristine and keep them from getting perturbed by the
environment, they have to be kept at extraordinarily cool temperatures. M: And I've
seen the tank, it's like a big tank that like you need to keep at cryo
temperature, like as close to absolute zero as you can get. B: Exactly
right, and so those aren't things you can carry around with you, they're always
going to be housed in some specialized facility. M: So we've got the problem of the
classical and quantum worlds interacting, you've got the noise issue, and then
there's also the problem of scaling up. B: We'll need them to get better in several
dimensions: we'll need to have more qubits, we'll need to have better control
over those qubits, we'll need to be able to sustain those qubits from getting
perturbed by the environment for long periods of time. And all those are
extremely challenging problems in manufacturing, in physics, in material
science. Maren: A hypothetical ideal quantum computer that we could reliably use to
give us accurate answers to the questions that we ask it is sometimes
called a universal quantum computer. But even if we can get there,
what would this help us do? Like what would this huge possible leap in
computing actually mean for us? J: I guess one of the best-known things is this
so-called Shor's factoring algorithm. One aspect of modern
cryptography involves factoring prime numbers, and I won't get into the details,
but it's useful cryptographically because it's something you can represent with a
short string and it's very hard to figure out how to break that apart, how
to find out what the sort of secret key is. M: Like even for a super powerful computer, it's really difficult for them
to run through all of the possibilities so it's hard to break into something if
you use that algorithm to protect information. J: Yeah absolutely.
In fact it's considered to be exponentially hard, so that means if I
have a 100 bits then it's like two to the hundredth power is the sort of the
proportional amount of time, naively, required to figure that out. M: OK, but if
we had this hypothetical universal quantum computer we just might be able
to solve Shor's algorithm. Like, in a reasonable amount of time. That
would change computer security really drastically. But we've got a pretty long
way to go before we can do something like that, like we're really not there
yet. B: We still need a few miracles before we're really in an age where quantum
computing goes mainstream. M: So even though we may not be at fully functioning
quantum computing yet, the prototypes that are being built all over the world,
including here at LLNL, are still very useful and necessary and can tell
us a lot of important stuff. J: I think in 10 years we may see basic demonstrations
of building blocks of this universal thing, but in this next 10 years it's
really going to be about how do we make the most use out of these systems? And
then I think there will be huge impacts again, on sort of basic science because
we're able to build systems that normally we would we'd only get
given to us from from nature, we can build them in a way so to ask specific
questions about basically how quantum mechanics works when you have lots of
components, right? M: It's like, who knew building a quantum computer is gonna
tell you a lot about the quantum world? It's like a very happy sort of
almost byproduct of trying build a quantum computer. J: Absolutely. We
also are in a position to help the field. I mean, that's also part of our role is
where we have this huge breadth of capabilities, you know people and applied
math, computer science, physics, biology— and we can all come together to look at
different aspects of these problems: one on the side of trying to figure out well
what is the useful thing you could do with this, now the other is how can we
solve these technical problems in terms of the materials, the control electronics,
and all that kind of stuff. M: Exactly, like I think the interdisciplinary nature of
the Lab is really key to our experimentation in every field, including
quantum computing. M: And where does quantum computing fit in with classical
computing? While quantum computing may be able to do some things better than
classical systems, we're still gonna need classical computing...and a lot of it. Like,
we're still going to need our upcoming exascale capabilities, aka the fastest
and most powerful classical supercomputers in the world, in addition
to quantum computing systems. And maybe we'll even need to use them together.
B: Our ability to continue to eke more out of our machines through architectural
innovations, that'll last 5, 10, maybe 15 years, you know, and that will
give quantum computing more time to mature. At some point as we're thinking
about these very specialized computers, they won't look that different from a
specialized computer made in a very different way, maybe from
different kinds of kind of physics, and so there might be a role then in the
same way we're using a host of specialized processors to do our
computations, we could plug a quantum a coprocessor into that mix to solve
certain problems that quantum devices are very good at solving. M: So you can see
this sort of Lego house of a computer that has a classical computing
component, a quantum component, and maybe the classical component that's been
architected to do a very specific thing, maybe a conglomerate machine that would
be really good at a lot of different things. B: Exactly. There's this
tremendous uncertainty about what computing will look like ten or fifteen
y years from now, and that can be scary but it's also incredibly
energizing and exciting. So so we've been on this trajectory with Moore's law
for 50 years that's taken us to phenomenal places and now as that
reaches its end, we need fresh ideas. We need new ways of thinking about
computing, we need new interdisciplinary collaborations, and those are things the
Labs are really good at. And so it's gonna be a very exciting time.
M: OK, that was a lot. But hopefully it gave you guys some more insight into quantum computing
and its place in our wider computing world. If you guys have questions about
this, or quantum mechanics, or anything related then leave them down
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our videos, including ones like this that take you on a deep dive into super
complex topics, and as always thank you so much for watching. I'll see
you next time