[MUSIC]
With classical computing,
you reach some limitations, and
you run up against physical barriers.
And one of those is just related to
the ever decreasing size of the things
that are actually bits,
or doing the computation.
At these small length scales, you start
to affect atoms, individual atoms.
And you need to worry about this sort
of different regime of physics which is
typically related to the smaller systems,
which is quantum mechanics.
[MUSIC]
>> Okay,
let's get started as soon as possible.
My pleasure to have Eric today
defending his thesis and we are excited
to be able to ask some questions.
>> [LAUGH]
>> Thank you.
>> Good call.
>> I guess I'm into my sixth,
starting my seventh year at UCSB
in the physics PhD program.
So I'll be talking today about some of my
work in the group, and the title here,
computing prime factors using a Josephson
phase-qubit quantum processor.
So I thought I would start with just sort
of introducing the ideas of classical
computing, can look at where we are.
So if you think back to around the 50s
when we had this tabletop transistor,
which occupied a meter squared, all right?
And here we are today,
with Intel Sandy Bridge technology,
which fits a billion transistors in about
a chip this size, 100 millimeters squared.
As you continue to press these smaller and
smaller sizes, you no longer can do
the same things that you were able to do,
and you can either compete with that, or
you can decide to harness that power.
>> And
the copper powder filters are up here.
>> [MUSIC]
All right, there we go.
>> Wow,
I haven't seen this before.
>> Yeah, the copper can dude.
It's looking hot.
I'm going to pull off the bias tees with
the box and just leave the attenuators.
So I'm going to pull from the attenuators.
Does that make sense?
So pull from here.
>> Why?
>> So I wanna bring the bias to you in
the box.
>> Again in the box.
Okay, that's exactly what I was not doing.
>> It's not just that we're gonna try to
make it a better laptop or
a better new phone, or whatever.
It's actually a disruptive technology
in that it would be a different style
of computing.
It solves problems that on a classical
computer are retractable and
you just cannot do.
>> Let's first put on the safety can here.
>> [INAUDIBLE]
>> [MUSIC]
>> Let's come down.
>> I just want it flush up top.
[MUSIC]
>> Stop.
>> The o-ring is falling down.Yeah.
It's fine.
Perfect.
>> Yeah, we tore a little nylon.
Yeah, hey hey.
>> Yeah, and
definitely here.
>> Well,
that's a fixable problem.
>> Thanks guys, looks great.
>> As an experimentalist,
within the group that I work at, the
expectations are to be able to basically
propose an experiment and be able to
do every part of that experiment and
ideally, successfully
execute the experiment.
Not only in the sense of taking
the correct data analysis and all that but
also being able to write it
up in scientific journals.
That's kind of important for
your career and
what people, typically,
are gonna be interested in.
Of course, the exciting parts about
quantum computing is even the underlying
fact that we're using quantum
mechanics to do this computation now.
And rather than these really certain
position or momentum operators and
things we can actually say a particle is
actually located here, becomes this wash.
It's actually a probability distribution
where these things can be found.
And what we do in quantum computing is
it's actually a number of experiments
are run to come up with a probability.
The quantum bit, this qubit,
we measure it's gonna collapse in
one of this things, either 0 or 1.
But as you repeat the experiments you get
these probabilities of the system, right?
And it can be actually in a super position
of states, where it's both 0 and 1.
The question is whether this is
really something useful to have.
And then in practice,
can we actually build such a device?
So all right,
a practical use of a quantum computer
might be, say to compute prime factors.
Let me frame the picture.
Multiplying two large
numbers is challenging for
most humans, but relatively
straightforward for a classical computer.
Recall that computers used
to be used as calculators,
not just social networking devices.
Finding the prime factors
is the reverse problem.
The challenge here is,
say I gave you some composite number, N,
where N is composed of p times q.
And we seek these prime factors p and
q, okay?
Sounds easy enough.
Well, let's maybe try something
like the RSA number of 2048,
which is about a 617 decimal digit
composite number that looks like this.
So if you'd like, I can give you guys some
scratch paper and wait a few minutes here
for everyone to try to factor this.
>> [LAUGH]
>> And we'll start a clock.
And let's see how long it takes
to actually compute this.
So what is the time to compute?
Well, if I arm you with sort of
the best classical known algorithm,
which is the General Number Field Sieve,
and I'll take Peter Shor's algorithm,
the quantum algorithm, and
we'll press the go button, right?
We'll wait.
>> [MUSIC]
>> So it's gonna take about
the age of the universe for
you to solve it with the kinda
classical General Number Field Sieve,
whereas it will be on the order of
seconds here with Peter Shor's algorithm.
All right, it's this image that
really motivated me to actually do
this experiment.
So why is this relevant,
or why should anyone care?
Well, say you wanna send secure
information on the web, right?
And you give the credit card number,
bank account, whatever.
We encrypt that information between
you and the seller, the vendor,
whoever, with basically
this RSA encryption scheme,
which relies fundamentally on using these
large composite numbers that are composed
of two very big prime numbers multiplied
together to give you that number.
That's kind of the key with which we use
to pass this information back and forth.
However with Peter Shor's algorithm,
the quantum computer, one could crack this
very quickly, in order of seconds rather
than the edge of the universe right?
So then the question is well,
what security do we have left?
What's great is there's actually quantum
encryption, which one can actually find
out if someone is eavesdropping on their
transmission via quantum entanglement.
And it's a much stronger
test of your information,
of how well you secure your information.
So the experiment that I'm working
on is to actually map this idea
of using Peter Shor's algorithm
to factor a composite number.
One would need a lot more resources
to actually factor larger numbers.
So I've been working about 5 years
to factor 15 into its prime factors.
Got into the clean room,
I've made a device.
Have a quantum processor composed
of nine quantum elements.
Then we insert one of these devices
in a superconducting cavity,
wire bond it to make
electrical connections.
[MUSIC]
And mount it in a helium three,
helium four dilution refrigerator.
Thanks guys.
I think that's it, the rest,
I'm gonna take this can off and
finish wiring the boxes.
Appreciate it.
And in order to remove thermal noise, and
enter the regime dominated by quantum
mechanics, we evacuate the chamber and
cool the quantum processor
to just above absolute 0.
[MUSIC]
>> [INAUDIBLE]
[MUSIC]
>> And it is with this quantum
processor that I'm gonna again try and
find the factors of 15.
[MUSIC]
How's it going?
>> Okay, we should talk.
>> Okay.
>> We've been talking about this.
Is this folklore and
myth, or is this science?
So if we want to keep this as folklore and
myth, we don't do anything.
[MUSIC]
>> And we return that we get, indeed that
15 equals 3 times 5, 48% of the time.
>> [APPLAUSE]
>> Sir, 48% success rate that was what you
were supposed to get?
>> Ideally, you should get 50%, right?
>> That's the best that Shor's algorithm
will do.
>> Okay.
>> It's 50%
>> Okay.
>> Yeah.
>> So, this is clearly just
beautiful work.
But it does make me wonder, so what's
the number of qubits we're aiming for?
A thousand?
10 million?
>> 10 million would be great.
>> [LAUGH]
>> And that will be next year,
do you think?
>> Yeah, I think that will be next year.
Are you recording that?
>> [LAUGH]
[MUSIC]
