Thank you very much everyone for being
here. My name is Carlos Perez Delgado and
I'm going to talk about what is a
quantum computer. So, before I introduce
myself, why do we even care what a
quantum computer is? Here's a few news pieces
that I've taken off the web in
the past three months. This is the
beginning of 2018, and it refers to large
important companies that we all know
about: Google, IBM, Intel, NEC, they're
all jumping into this area of quantum
computing. They're pouring millions of
dollars, millions of euros and millions
of pounds and they're getting there and
they're achieving very important stuff.
Now, who am I? I'm a lecturer here at the
University of Kent in computer science,
have 10 years of experience working on
quantum computing and quantum computing
research, I have a PhD from the Institute
of Quantum Computing at the University
of Waterloo in Canada. I worked for a
while at the Center for Quantum
Technologies at the National University
of Singapore in Singapore. Now the
reason I say all this is to make it
clear to all of you here in the audience
and at home that I'm not going to lie to
you, everything that I say here is going
to be perfectly accurate. Now I will
simplify stuff, I will simplify some...
you won't see any mathematics up there
and this is a very technical subject but
what I promise is that I will simplify
as much as I can but no more than that.
So, let's get started. What is a
quantum computer? To understand what a
quantum computer is first we need to
understand what quantum theory is. In the
words of Richard Feynman, one of the most
famous physicists of our time, quantum
theory is the most successful theory of
all time. It is so successful in fact
that it's similar in its predictive powers
to measuring the distance between Los
Angeles and New York down to the breath
of a human hair. Now all this accuracy
has a cost and the cost has been the
erosion of our human intuition. Quantum
theory is simply not intuitive. Now we
can summarise the basic tenets of
quantum theory into three basic tenets:
the first one is that both matter
and energy behave like particles and
waves; the second is that quantum systems
can be in, what we call super positions,
these are complicated states and the
best example of this is something that
I'm sure all of you have heard of which
is Schrodinger's cat. It's a cat that's
in a box and as long as I don't look at
it that cat can be both dead and alive
at the same time. It's not that it's
either dead or alive, it's both or
neither and I'll explain more of that in
a second; a third tenet of quantum theory
is that when I measure a quantum system
I invariably alter its state. I cannot
measure a quantum system without
disturbing it. Now let's focus on the
second tenet because we can use that for
quantum computation. Much like
Schrodinger's cat can be both dead and
alive, a quantum bit can be both in the
state 0 and 1 at the same time. To remind
you all a classical bit is the essential
building block, the fundamental building
block of computers. A bit can be either 0 or 1. A quantum bit can be in
both and that means that if I have two
quantum bits I can have the state 0 1 2
& 3 simultaneously. Let's try to explain
this with with a little bit of help from
from some pictures. Think of the
Cartesian co-ordinates your XY plane
north-south-east-west.
Now, a classical bit will always be on
one of these axis, so we can represent a
bit being in the state 0 by being on the
x axis and in the a bit in the
state 1 by being on the y axis and
that's a classical bit you can only
either be on one those one of those two
lines, one of those two blue lines. A
quantum bit, however, can be an on a
diagonal and it can be in any direction
whatsoever. Important to remember is that
if I measure that quantum bit I'll only
ever measure a 0 or a 1, which one will I
measure.
Well, if we were to cast a torch from the
very top that line that blue line will
cast a shadow onto the X axis and that
shadow that you see there is
proportional to the probability of me
measuring a zero. Similarly, if I shine
the torch from the far right the shadow
that it casts onto the y-axis is
proportional to the probability of
measuring a 1. So if I measure a quantum
bit
I only measure 0 or a 1 but as long as I
don't measure it, it can be in this
strange diagonal state which is neither
0 or 1. We can use this
quantum computing power to
speed up some computations. The punchline
is that you can't solve all problems
faster on a quantum computer but you can
solve some problems somewhat faster and
you can solve a fewer problems a lot
faster. What are quantum computers
specifically good for? Well they're very
good at simulation, they're very good at
solving some hard optimisation problems,
some hard mathematics problems, they're
also good at machine learning and
they're also very good at one other
thing that I won't mention quite yet.
Before I get there let's talk about the
internet. We all use the internet here,
we'll go online, shop online, go on
Facebook, post pictures of ourselves, we
all care about our privacy in the
security of our information and all that
in all that information is safeguarded
by what we call cryptography. There's a
particular type of cryptography which we
call public key cryptography, which is
what we use to authenticate people on
the internet and to create private
communication. By authentication I mean
that you can prove that you are who you
say you are, or for example when you go
to your bank's webpage you know that
that webpage actually belongs to your
bank and you're not being scammed out of
your money. Together public key
cryptography is used in all sorts of
applications, from online banking to your
private communication, your email, your
RSA two-factor key,s etc etc. Without
public key cryptography literally the
internet would stop working tomorrow. Now
public key cryptography
as we know it is all based on certain
types of problems that are very easy to
perform but very difficult to undo and a
good example of that is multiplication
versus factoring. If I give you two
numbers, for example 23 and 11, and ask
you to multiply them,
that's generally easy for you if you're
thinking 253 that's the right answer. But
if I give you a large number and ask you
what two numbers multiply to that number
that's harder, if I give you the number
221 and ask you what two numbers
multiplied together give you 221, that's
harder. The answer, by the way, is 13 and
17. It's important to know though that
this isn't just harder for you and me as
people, it's also harder for computers in
fact the difficulty of factoring the
difficulty of finding the factors is an
intrinsic part of the security of public
key cryptography. The
most used out there public key crypto
graphic tool is RSA 2048, it is the gold
standard and it's based on factoring. Now
that introduces a problem because
quantum computers are really good, really
good at factoring. How good are they? Well
let's put up an example. If I gave you
the most powerful classical computers
today, take your pick,
it would take them around several times
the age of the universe to break RSA
2048, again RSA 2048 it's the gold
standard of security today and the
reason is because your classical
computers would take millions and
millions of years to break it. What a
quantum computer, a modest quantum
computer bigger than any quantum computer
we have today but not nowhere near as
powerful as the classical computers that
we have today that quantum computer
would only take 14 minutes to break RSA
2048. So you can see the problem here.
Now, fortunately as I said quantum
computers today are simply not large
enough to break RSA 2048
but some of us predict some of my
colleagues and myself have predicted
that there's a good probability that by
the year 2030 there will be quantum
computers large enough to break RSA 2048.
Fortunately there's a plan, in fact
there's two plans, there's a two-tiered
approach, the first one consisting of
what we call post quantum cryptography.
Post quantum cryptography simply refers
to cryptographic systems that are not
known to be breakable by quantum
computers, so there's there's no attack
there's no quantum computing attack for
post quantum crypto. But another idea is
to use the power of quantum theory
itself to create security. If you
remember towards the beginning of my
talk I mentioned how when you measure a
quantum system you invariably alter its
state so I can prepare quantum systems
in particular states and if someone else
comes in and observes them, just looks at
them I'll know because they'll alter its
state. It's like nature is providing its
very own intrusion detection system and
we can use this, we can use this to build
cryptographic tools to regain the
security that we'll be losing and create
even better security tools unlike
you've ever seen before, Now if you want
to learn more about that you'll have to
stay tuned on this channel. For today
that's all for me. Thank you all very
much for your attention.
