Kind: captions
Language: en
[Applause]
a classical computer performs operations
using classical bits which can be either
zero or one now in contrast a quantum
computer uses Quantum bits or Q bits and
they can be both zero and one at the
same time and it is this that gives a
quantum computer its Superior computing
power there are a number of physical
objects that can be used as a cubit a
single Photon a nucleus or an electron I
met up with researchers who are used
using the outermost electron in
phosphorus as a cubit but how does that
work well all electrons have magnetic
fields so they're basically like tiny
bar magnets and this property is called
spin if you place them in a magnetic
field they will align with that field
just like a compass needle lines up with
the magnetic field of the earth now this
is the lowest energy state so you could
call it the zero state or we call it for
the electron spin down now you can put
it in a one state or spin up but that
takes some energy if you took out the
glass from your compass you could turn
the needle the other way but you would
have to apply some Force to it you have
to push it to flip to the other side and
that is the highest energy state in
principle if you were so delicate to
really put it exactly against the
magnetic field it would stay there now
so far this is basically just like a
classical bit it's got two states spin
up and spin down which are like the
classical one and zero
but the funny thing about Quantum
objects is that they can be in both
States at once now when you measure the
spin it will be either up or down but
before you measure it the electron can
exist in what's called a Quantum
superposition where these coefficients
indicate the relative probability of
finding the electron in one State or the
other now it's hard to imagine how this
enables the incredible computing power
of quantum computers without considering
two interacting Quantum bits hello hi
now there are four possible states of
these two electrons you could think that
well that's just like two bits of a
classical computer right if you have two
bits you can write 0 0 0 1 1 0 1 1 right
there four
numbers but these are still just two
bits of information right all I need to
say to determine which one of the four
numbers you have in your computer code
is the value of the first bit and the
value of the second bit
right here
instead quantum mechanics allows me to
make
superposition of each one of these four
states so I can write a quantum
mechanical state which is perfectly
legitimate that is some coefficient
times this plus some coefficient times
that plus some coefficient times that
plus some
coefficient so to determine the state of
this two spin system I need to give you
four numbers four coefficients whereas
in the classical example of the two bits
I only need to give you two
bits so this is how you understand why
two cubits actually contain four bits of
information I need to give you four
numbers to tell you the state of this
system whereas here I only need two now
if we made three spins we would have
eight different states and need to give
you eight different numbers to define
the state of those three spins whereas
class is just three bits if you keep
going what you'll find is that the
amount of equivalent classical
information contained by n cubits is 2
to the power n classical
bits and of course the power of
exponentials tells you that once you
have let's say 300 of those
cubits in what we call the fully
entangled state so you must be able able
to create these really crazy states
where there is a superposition of all
three unds being one way and another way
and another way and so on then you have
like two to the 300 classical bits which
is as many particles as there are in the
universe but there's a catch although
the cubits can exist in any combination
of States when they are measured they
must fall into one of the basis States
and all the other information about the
state before the measurement is lost so
you don't want generally to have as the
final result of your Quantum
computation something that is a very
complicated superposition of States
because you cannot measure a
superposition you can only measure one
of these basis States right like down
down up yeah so what you want is
to um design the logic operations that
you need to get to the final
computational result in such a way that
the final result is something you're
able to measure it's just a unique State
essenti that's not true that's not
trivial and it's essentially I'm kind of
stretching things here but I guess it's
to some degree the reason why quantum
computers are not a replacement for
classical computers they're not no
they're not they're not universally
faster they're only faster for special
types of calculations where you can use
the fact that you have all these Quantum
superpositions available to you at the
same time to do some kind of
computational
parallelism if you just want to watch a
video in high in high definition or
browse the internet or or write some
document in Word they're not going to
give you any particular um Improvement
if you need to use a classical algorithm
to get to the result so you should not
think of a quantum computer as something
where where every operation is faster in
fact every operation is probably going
to be slower than in the computer you
have on the desk but it's an a computer
where the number of operations required
to arrive at the result is exponentially
small so the Improvement is not in the
speed of the individual operation is in
the total number of operations you need
to arrive at the result but that is only
the case in particular types of
calculations in particular algorithms is
universally which is why it's not a
replacement of a classical
comp very positive voltage on here so
let's say you have a battery of about
let's say two
volts what this will do you see the