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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complex topics, and as always
thank you so much for watching. I'll see
you next time
