Quantum Computers and Quantum Supremacy

hello

i’m john martinez and would like to talk

about our recent experiment on quantum

supremacy

computers are important for the modern

world in part because they continue to

become more and more powerful over time

as described by moore’s law however

physical

limits are slowing down such

advancements so that new computing ideas

are being researched

quantum computing is such a new

technology which promises to solve

certain problems

exponentially faster than current

computers

billions of dollars and decades of

research has been invested in quantum

computing

the aim of the quantum supremacy

experiment as google

was to explicitly demonstrate this speed

up

on at least one algorithm in particular

the quantum computer took data for 200

seconds

which then needed over a thousand years

to check on a supercomputer

thus showing the computational power of

quantum mechanics

now quantum panics was first developed

to describe how atoms work

for example take the hydrogen nucleus

which is a negatively charged electron

a electron circling a positive charge

proton nucleus

both particles attract each other and

classically you would expect them to

just stick together

this is not what happens since quantum

mechanics explains

the electron forms a small cloud around

the proton

whereas simultaneously at all parts

around the nucleus at the same time

physicists call this the superposition

principle

quantum explains why atoms have size an

important property of all the matter

around us the cloud is formed by a

precise physical theory

that can predict well the properties of

atoms

quantum computing abstracts the idea of

superposition to information

which is fundamentally described by bits

that are either

0 or 1. in a quantum computer each

quantum bit or qubit

can be both 0 and 1 at the same time in

a quantum superposition

if a qubit can be at 0 and one in the

same time

then is it possible to compute the

answer to zero

and the answer to one simultaneously

just like a parallel computer

this gives a factor of two speed up

which is interesting

but not necessarily useful it becomes

useful however

considering what happens to multiple

qubits

for example in two qubits it

simultaneously computes

the answer for 0 0 0 1 1

0 1 1 now a factor of 4 a parallelism

this increase in parallel computing is

doubled for each added qubit

and exponential increase versus size

thus at 50 cubits the parallelism is 2

to the 50th power

which then starts to compete with the

supercomputer

at 300 cubits 2 to the 300

is basically the number of atoms in the

universe

which is clearly a size that is gets to

be interesting

it’d never do classically we make our

quantum computer using artificial atoms

made out of superconducting electrical

circuits

here the macroscopic currents and

voltages in the circuit behave quantum

mechanically

it’s not obvious that nature allows

quantum mechanics to work this way

so that was my phd thesis in the

mid-1980s to prove it

the interesting idea here is that you

can build a complex quantum system

a quantum computer using integrated

circuit fabrication technology

just like that’s used for building a

computer chips

it has taken many people around the

world for about 30 years

to figure out exactly how to do this and

to get this

the circuits to work well for the

quantum supremacy experiment

we built at google a chip called

sycamore that had 53 qubits

where each qubit connected to each

neighbor in a square grid

the big step here was to precisely

control and calibrate

each qubit so we knew exactly what it

was doing

the quantum supremacy algorithm was

essentially building a quantum

random number generator which had a

quantum property similar to

laser speckle such that some num numbers

are more likely than other numbers

so we measured these random numbers from

a quantum computer

and then checked with a quantum

simulation on a supercomputer

that the numbers we measured were

actually the ones predicted

for 30 qubits one can check with your

laptop

at 40 you need a powerful workstation at

50

you need a super computer or a google

data center

at the 50 feet we eventually measure it

would take thousands of years to do the

check

now important science that was tested

here is that the quantum computer

worked just as predicted we found no new

physics that would prevent us from

making

even more powerful machines that’s

really good news

so now that we’ve shown a quantum

computer can be powerful the next step

is to show it can do

something useful for quantum algorithms

a big area of research is quantum

artificial intelligence

and quantum ominous optimization like

solving the traveling salesman problem

although this promises to have huge

commercial impact

useful algorithms have not yet been

invented and clearly in active area

research

i like the research into quantum

chemistry which is actually what richard

feynman first proposed in the 1980s

and now algorithms exist to solve such

problems

simplified versions are being run on

quantum computers now or giving sensible

results

it’s a good test of the theory what’s

going on

these algorithms can be thought of as

running let’s say a hundred to a

thousand

lines of code for for practical

applications we’re going to need larger

machines

maybe in the millions or billions of

lines of code

to do this we need to reduce qubit

errors by millions or billions

which requires quantum error correction

this is currently a frontier research

into making a quantum computer may take

maybe a decade to figure that all out

the field of quantum computing is

growing with billions of dollars of

research

funding now being planned although

building a quantum computer is

challenging

the quantum supremacy experiment has

shown that quantum computers can be

powerful as promised

and it’s the right time for investment

to now make them useful

okay thank you very much

you