All language subtitles for NOVA.S51E14.Decoding.the.Universe.Quantum.1080p.WEB.h264-BAE_track3_[eng]

♪ ♪

ANNOUNCER:
The following "NOVA" program
contains scenes

of quantum physics,
which is known to cause

confusion, anxiety,
and even heartbreak.

Please see your physicist

if symptoms persist.

NARRATOR:
Quantum physics.

It's the science
of the very small,

but it punches
far above its weight.

Quantum physics has not just
been important,

it's been revolutionary.

NARRATOR:
It's the most successful
scientific theory

of the last 100 years.

Quantum mechanics already
permeates everything we do.

NARRATOR:
Everything from your computer
or cellphone

to how we keep time

depends on our understanding
of the quantum world.

DAVID KAISER:
We can say now that
we live in a quantum age.

NARRATOR:
And it's behind one of
the greatest discoveries

in the history of science:

gravitational waves,

tiny ripples in the fabric
of space-time itself.

SEAN CARROLL:
Gravitational waves
give us a whole new way

to look at the universe.

NARRATOR:
And yet, beyond the mathematics,

quantum physics
makes a shocking claim:

that at its deepest level,

reality plays like a game
of chance...

ELBA ALONSO-MONSALVE:
Probabilities are not

a measure of what we don't know.

They're just intrinsic
to the quantum theory.

NARRATOR:
...with mind-boggling behaviors
like superposition

and entanglement.

This is weird-- it's strange.

NARRATOR:
What quantum physics
really means

remains deeply mysterious.

But it's created
the world we live in today.

Quantum physics actually
governs everything around us.

TARA FORTIER:
It's not some weird outpost
of physics that's far away.

It's completely changed

the way we used to live
into the way we live now.

NARRATOR:
"Decoding the Universe:
Quantum."

Right now, on "NOVA."

♪ ♪

NARRATOR:
December 12, 1970.

NASA launches a Scout B rocket

from a former oil-drilling
platform off Kenya's coast.

♪ ♪

Its payload is a small satellite
named Uhuru,

a Swahili word
meaning "freedom."

Uhuru is the first space
telescope

dedicated to observing X-rays,

high-energy light waves
invisible to our eyes.

Powerful sources of X-rays
constantly bombard Earth,

but our atmosphere blocks them.

With this
groundbreaking telescope,

a new vista for exploration
opens.

But buried in the data collected
from Uhuru

is something ominous.

In 1971,

scientists reveal
that the constellation Cygnus,

the Swan,

contains what until then

was more of a
mythical mathematical beast.

A black hole.

ALONSO-MONSALVE:
Black holes are

the most mysterious objects
in the universe.

Also the most violent.

JANNA LEVIN:
Even Einstein didn't think
nature would allow

such a crazy object.

NARRATOR:
Black holes are
fearsome monsters,

capable of devouring
whole planets...

...whole stars...

...and even each other.

A black hole is created
when gravitational forces

bring together enough mass

to put a rip into the fabric
of space-time.

KAISER:
Some of them are genuinely
monstrous.

I mean, millions, billions,

maybe even ten billion times

the mass of our own sun.

ALONSO-MONSALVE:
We don't actually have

laws of physics to predict

what's going to happen to us
when we go in.

Hopefully, none of us will
experience it anytime soon.
(laughs)

NARRATOR:
In the decades
since the first sighting,

science has learned a lot about

these menacing and mysterious
objects of destruction.

They aren't that rare.

Supermassive black holes
sit at the center

of most large galaxies.

We have one in ours.

But it turns out
these cosmic behemoths

also may have an Achilles' heel.

First predicted by
Stephen Hawking in 1974,

scientists thought
of a black hole

as a one-way trip to oblivion.

That past its event horizon,
nothing could escape.

But Hawking disagreed.

He theorized something did
escape from these mighty giants:

radiation.

Ironically, the end result
of physics

at the tiniest of scales:
quantum physics.

♪ ♪

Clifford Johnson
is a nonfiction graphic author

and also a theoretical
physicist.

JOHNSON:
One of the key things

that was discovered in quantum
physics

is that empty space itself
is not empty.

It's seething with possibility.

Instead of having empty space
here,

a particle and its antiparticle
can appear,

dance around a little bit,

and then annihilate
back into empty space.

Now, imagine that happening
near a black hole horizon,

which we're told
is a one-way door.

What if one of those particles
falls in?

And now the partner doesn't have
anything to annihilate with.

So it will actually fly off,

and a distant observer
will see that particle

as radiation
coming from the black hole.

NARRATOR:
Without consuming more matter,
if it emits radiation,

it will gradually shrink
in size.

The black hole actually begins
to evaporate.

Now, this is a completely
stunning revelation.

its existence
is still only a theory.

But perhaps, given enough time--

and it is a very,
very, very long time...

For many black holes,

longer than the current age
of the universe.

NARRATOR:
...even a supermassive
black hole,

like the one at the heart
of the Milky Way,

may evaporate and disappear,

vanquished by the quantum world

and the physics
of the very small.

♪ ♪

The quantum world is often cast
as weird,

and it sure can look that way
in the movies.

JANET VAN DYNE:
You're sending a signal

down to the Quantum Realm.

(woman yelps)

Cassie!

♪ ♪

(whispers):
Where are we?

NARRATOR:
But what is quantum physics?

It arose as the solution
to a problem.

Science during the 19th century
had investigated

smaller and smaller amounts
of matter and energy.

But by the first two decades
of the 20th century,

the existing line
between the physics of particles

and the physics of waves

had grown murky,

especially
when trying to understand

the fundamental nature of light.

KAISER:
Sometimes it really is important
to describe light

as a wave, as an extended object
that sort of waves in space

and travels over time,

analogously to an ocean wave
in the water.

Other times, as people
like Albert Einstein and others

began to, to find, they really,
really had to describe

aspects of light as if
it was a collection of particles

that traveled almost
like miniature billiard balls.

NARRATOR:
Ultimately, the answer was
a new kind of physics,

quantum mechanics,

which included
an amalgam of ideas

about both particles and waves.

Its earliest formulation
dates back roughly 100 years.

This 1927 conference in Brussels

is where the world's leading
physicists met

to discuss
the newly formed theory.

(people talking in background)

NARRATOR:
And there was a lot to discuss.

Because quantum mechanics
represented a radical departure

from the previous paradigm
of physics--

what we call today
"classical physics."

CARROLL:
In classical physics,

handed down by Newton,
we had determinism.

We had the clockwork universe.

So if you throw a ball-- that's
a classical object--

with the same force,
the same speed,

the same angle,

it's always going to go
to the same place, right?

In principle,
if you knew exactly the state

of the whole world all at once,

and you knew the laws
of physics,

you could exactly predict
what everything was going to do

arbitrarily far in the future
and into the past.

NARRATOR:
In classical physics,

even events that we think of
as random aren't, really.

HAKEEM OLUSEYI:
There are things

that appear random in our
everyday lives,

like rolling dice.

It looks random, right?

But actually, it's a
deterministic

set of events which leads to

whatever outcome the dice shows.

If I told you exactly how
I was going to roll the dice...

OLUSEYI:
...you could predict,
based on that initial throw,

what the final outcome
is going to be.

It's a very hard
mathematical problem,

but it's not intractable.

Quantum mechanically,
that's not the case.

NARRATOR:
Quantum mechanics
tossed out the certainty

of the classical
clockwork universe

for one that only allowed
for probabilistic predictions

about potential observations.

Probability in quantum physics
is different.

Because even if we have

the most complete description

that the laws of physics will
allow us to have,

typically,
we're unable to predict

precisely what we'll see when
we observe a quantum system.

CARROLL:
Quantum mechanics says we can
know everything there is to know

about the setup right now.

And still, when we want to make
a measurement of it

in the future,
the best we can do is say,

"There's a 50% chance
of getting this outcome,

30% chance of that,
20% chance of that."

In the quantum theory,

probabilities are not
a measure of what we don't know.

They're just intrinsic
to the quantum theory.

We cannot get around them.

That is impossible.

NARRATOR:
Some physicists,
raised on determinism,

had trouble accepting
this new probabilistic view.

Albert Einstein famously said
that he didn't believe

God plays dice
with the universe.

But there is another related,
even stranger aspect

to quantum mechanics.

In classical physics,

external reality
is independent of the observer.

Looking at the moon
doesn't change the moon.

And if you look away,

the deterministic laws
of physics

continue to guide the moon
on its path.

But in quantum mechanics,
things are weirder.

CARROLL:
The basic idea
of quantum mechanics,

the thing that we really
struggle with

to get our heads around,
even as professional physicists,

is that unlike any other version
of physics,

quantum mechanics separates
what happens in a system

when we're not observing it

from what we see
when we measure it.

NARRATOR:
A few rare exceptions aside,

quantum mechanics says
that we can't know

the position of a particle
like an electron

when we're not observing it.

At best, it can only
be described mathematically

as a wave,

its exact position
given in probabilities.

But at the moment
that the particle is observed,

the probabilistic wave function
collapses

to one specific location.

To the observer, who never
sees this wave-like quality,

it is like the particle
was a particle all along.

That opens up a whole world
of questions, you know?

What happens to the
observational outcomes

that are not observed?

What picks out which outcome
is going to happen?

This is still what
we're thinking about today.

NARRATOR:
During that mysterious period,

when the particle is considered
neither here nor there,

it is said to be
in superposition--

in a sense, a combination
of all the possible outcomes.

But what does that really mean?

Is the electron everywhere
at the same time?

Is it nowhere at all?

Is it at one particular place
and we just don't know?

All of those questions
are actually outside

of what quantum theory itself
actually can answer.

It's not part of the theory
at all.

So if you ask me,
your guess is as good as mine.

(chuckles): Unfortunately,
that's the best I can do.

♪ ♪

NARRATOR:
For most people,
quantum mechanics remains

deeply unintuitive.

And yet it has proven itself
again and again

by making predictions
with uncanny accuracy.

In practical terms,

it is the most successful theory
science has ever produced,

and it has shaped
our modern life.

♪ ♪

OLUSEYI:
Quantum physics has not just

been important,
it's been revolutionary.

It's completely changed

the way we used to live
into the way we live now.

♪ ♪

NARRATOR:
Take our sense of time.

(tango music playing)

Perhaps there is no better
illustration

of our intimate relationship
with it

than music and dance.

♪ ♪

FORTIER:
The underlying movement of tango

is reliant on the beat, which is
reliant on timing,

which creates synchronization.

To create a truly smooth dance,

it's not enough to just be
synchronized on the beat.

It's also the synchronicity

between the beats
that's important.

That's the real beauty in it,

in finding that connection
through,

stretching out that second.

♪ ♪

NARRATOR:
Tara Fortier
is a tango professional

and a physicist deeply involved

in the science of time.

So, we have a number of systems
in this lab.

NARRATOR:
She works here...

These systems are used

to characterize atomic clocks,

and also compare
atomic clocks.

NARRATOR:
...at the Boulder, Colorado,
laboratories

of the National Institute
of Standards and Technology,

or NIST,

home to some
of the atomic clocks

that help set the official time
for the country.

Over the centuries,

we've tracked time
a variety of ways:

by the sun's movement,

the swing of pendulums,

the oscillations of springs,

and, in the 20th century,

the vibrations
of quartz crystals.

But since the 1960s,

time has been officially
determined

using atomic clocks

and the quantum characteristics
of atoms.

And the idea is that the laws
of physics are unchanging,

unlike something like
the rotation of the Earth.

The rotation of the Earth itself
can change

because of plate tectonics,

because the moon is moving away
from the Earth.

Its physics
is not truly fundamental.

JUN YE:
The reason why we love
atomic clock,

it's a universally defined time.

No matter who does
the experiment,

no matter
where you do the experiment,

you know, in principle, once
you've corrected

for all the systematic effects,

you should produce the same time
no matter where.

NARRATOR:
The consistency
of atomic clocks arises

from the very nature of atoms.

Atomic clocks depend crucially

on the quantum physics of atoms.

You have a nucleus,

around which there are electrons

in certain energy levels.

And these energy levels
are possible energy states

that the electron can have
inside the atom.

NARRATOR:
Since an electron can only be
at certain energy levels

and not in between,
to get to a higher level,

it needs to encounter
a very specific helping hand,

such as a particular photon.

If it were to absorb
an incoming photon,

it would have to be
of just the right energy

to jump from one level
to a higher level.

NARRATOR:
That special relationship

between the electrons
of a particular atom

and a photon
of a specific energy level

is a unique signature
for that atom.

It's called
a "resonant frequency."

JOHNSON:
So this characteristic signature
of this atom

gives us a very specific
frequency standard

that we can use to build
a time-keeping device.

NARRATOR:
Atomic clocks
work in different ways,

but they all use
a specific type of atom

or molecule
as a reference to lock in

the frequency
of an electromagnetic wave,

whose oscillations provide
the "ticking" of the clock.

Today, a second
is officially defined

by counting the oscillations

of the primary
resonant frequency

of a cesium-133 atom.

That's over nine billion
oscillations per second.

And you interact
with that time reference

more than you might think.

For example, through
the Global Positioning System:

GPS.

♪ ♪

GPS:
Turn left.

FORTIER:
I think that GPS

is actually kind of crazy,
when you think about it.

How did we do anything
before GPS?

NARRATOR:
The U.S.-based GPS system

uses over 30 dedicated
orbiting satellites,

each with
multiple atomic clocks.

When you use the GPS
on your cell phone,

its receiver checks the signals

from four or more satellites.

The signal contains information

about the satellite's position
and the time it sent the signal.

That time stamp is critical.

Your phone uses it to calculate
how long it took

to receive the signal,
and from that,

knows the distance
to the satellite.

With that information
from multiple satellites,

it is possible to triangulate
the phone's position

within a few yards.

But the whole system depends
on knowing the time.

FORTIER:
In the end, I find it amazing,

how strongly we're committed
and tied to atomic clocks

and how much we take it
for granted.

Even though I build
atomic clocks,

but when I'm driving,

being guided
by this GPS service,

you don't really become aware

of how much atomic clock
technology has permeated

everywhere in modern life.

♪ ♪

Have you had a chance to look

at more systematically
varying the V-Z?

NARRATOR:
Jun Ye is a physicist
with joint appointments:

with NIST,

the University of Colorado-
Boulder,

and their joint institute, JILA.

What if you locked exactly
on top of each other

and see whether
that peak disappears completely?

NARRATOR:
He works on the new generation
of atomic clocks,

known as optical atomic clocks.

While cesium clocks

use microwaves,

optical clocks use lasers,

which run at higher frequencies.

That also means
using a different atom.

Instead of cesium, Jun's work
mostly uses strontium atoms,

along with a laser
carefully tuned

to one of strontium's
resonant frequencies.

It puts one of the strontium
electrons into superposition,

so it is both excited
and unexcited at the same time,

creating what Jun calls
a quantum pendulum.

This pendulum
is swinging at a speed

of nearly one million
billion cycles per second.

It's going back and forth,
back and forth.

And this superposition
creates this quantum pendulum.

NARRATOR:
And when it comes
to accuracy,

more swings or higher frequency

equals more precision.

If you think of swings
as marks on a ruler,

the more marks you have, the
more exactly you can measure.

So, compared to a cesium clock,
Jun's strontium clock

is around 100,000 times
more precise.

And that much sensitivity makes
all the more apparent

some of the stranger aspects
of time,

including one first predicted
by Einstein:

gravitational time dilation.

In the movie "Interstellar,"

part of the crew of a spaceship

descends in a shuttle
to a planet

orbiting
a supermassive black hole.

When the shuttle returns,

those on the mission feel

they've only been gone for three
hours,

but not the crew member who
remained in orbit.

Hello, Rom.

I've waited years.

CASE: 23 years, four months,
eight days.

NARRATOR: The difference in time
is another effect

The warping not only means
gravity gets stronger

closer to the black hole,
but time gets slower, too.

And you don't need a black hole
to be able to measure it.

Even on Earth, gravity varies,

and so does time,
based on the distance

from the planet's center.

So a person at the top
of the Empire State Building

experiences weaker gravity

and time going faster

than a person at street level,

where gravity is stronger.

But all that happens
imperceptibly.

Our wristwatches
just aren't accurate enough

to show the difference.

But Jun's optical clocks
are so accurate

that even a small difference
in elevation between two clocks

will reveal a discrepancy
in the passage of time.

When the clock changes elevation
by a few hundred microns,

basically size of a human hair,

you will start to be able to see

that time is actually running
differently.

♪ ♪

NARRATOR:
With that much accuracy,
a clock transforms

into something more
than a timepiece.

It becomes a new window
into the nature of the universe.

♪ ♪

YE:
Making a clock is much more
than just a piece to keep time.

It is a sensor to explore
fundamental physics,

to expand our curiosity,

to build new technologies
that can connect

to quantum computing,
quantum information processing,

and communication.

♪ ♪

NARRATOR:
Central to making Jun's
precision atomic clocks work

are ultra-stable lasers,

which themselves are also
a quantum technology.

They date back to the 1960s.

GOLDFINGER:
You are looking
at an industrial laser,

which emits
an extraordinary light

not to be found in nature.

I will show you.

(laser cracks)

NARRATOR:
This scene from 1964's
"Goldfinger"

is said to be one of the first
popular depictions

of this new, cutting-edge tech.

I think you've made your point,
Goldfinger.

Thank you for the demonstration.

♪ ♪

NARRATOR:
Today, lasers are everywhere.

There are medical lasers
to correct vision,

lasers at the checkout counter,

lasers for cutting,

communicating,

entertaining cats,

and, of course, for light shows.

(crowd cheering)

NARRATOR:
Which encourage us all
to trip the light fantastic.

(band playing)

(cheering)

(plays note)

(note stops)

NARRATOR:
Which may be why...

♪ ♪

...experimental physicist
Rana Adhikari

is laser-focused on lasers.

When I talk about how,

how beautiful a laser
is as a instrument,

I don't want to gush about
it too much.

Like, I'm in love with lasers,
I don't know.

I feel like a weirdo fanatic

or something like that, but...

They're just,
there's something about them.

NARRATOR:
To understand what makes
laser light so special,

it makes sense to look
at an ordinary light bulb--

the old-fashioned kind,
with a tungsten filament.

It produces light through
thermal radiation--

an electric current
passing through the filament

heats it up.

Its tungsten atoms
become excited

and vibrate at different speeds,

which causes them
to emit photons

in all directions,
across a variety of wavelengths.

Compared to a laser,
this is chaos.

ADHIKARI:
The way you should think
about a light bulb

is something like,

they're just a mob of people,

all singing at different pitch,

so it's like
a rock concert audience.

CROWD (singing):
♪ We will, we will rock you ♪

But a laser,
a laser is more like

if you go to Juilliard
or Berklee School of Music

and you go to a concert.

(singing on one pitch)

ADHIKARI:
It's like a choir of people

who have got perfect pitch,

but it's a choir
of something like

a million trillion people

singing at the same time,
the same tone.

NARRATOR: That's because

laser light is generated

in an entirely different way,

a fact hidden in its name:

stimulated emission.

Let's say we have,
inside an atom,

an electron that's
at some excited state,

some higher energy level,

and now a photon of
just the right frequency

passes by the atom.

It triggers the atom
to do something interesting.

The electron loses energy
and goes to a lower energy,

and emits a photon of
precisely the same frequency

as the one that came in.

It's going in the same direction
and it has the same phase.

So what we have there is

a quantum mechanical
amplification process.

NARRATOR:
If we place a group of
those same excited atoms

inside a chamber
with mirrors at both ends,

the emitted photons
will bounce back and forth,

continuing to stimulate
the emission of more photons,

which in turn stimulate
even more photons.

One of the mirrors is only
partially reflective.

It allows some of the light
to escape.

Now, that light's very special.

It's composed of photons

that are all
the same frequency--

so, the same color--
and they're all the same phase,

and all going in
the same direction.

So you have this intense
pure beam of light,

and that's the laser.

♪ ♪

NARRATOR:
Lasers have proven to be
an extremely versatile tool,

including for
measuring distance.

Rana's work with
stable high-frequency lasers

takes that to an extreme.

When you use them,

you're in a whole different
realm of measurement

than anything else
that has to do with rulers

and any of that other stuff.

Anybody who is, like, a real pro

knows that the only thing
that you ever measure

is frequency.

If you're measuring
anything else,

you're kind of an amateur.

NARRATOR:
Thanks to the fixed speed
of light,

the beam
of a high-frequency laser

has an incredibly short
wavelength,

perfect for measuring extremely
small changes in distance.

Since 1996, Rana has been part
of a project

that uses laser light

to measure something incredibly,
unimaginably small--

and weird:

tiny fluctuations

in the fabric of space and time
itself.

Space and time ripple.

They're not fixed things,
and so,

the distance
between my two hands

is not always going to be this
if I hold them steady.

NARRATOR:
The idea, like so many,

goes back to Einstein.

In the early 20th century,
his work led

to the merging of space and time
into one concept:

space-time.

And he theorized that gravity

was the warping
of that space-time fabric

by the mass of objects.

But that carried
a startling implication,

that the acceleration
of objects with mass

would create ripples
in space-time

that spread
at the speed of light:

gravitational waves.

TIFFANY NICHOLS:
Gravitational waves

were first predicted
by Einstein,

and he didn't believe it
at first.

So he went back and forth

through, I believe,
the mid-'30s.

But his first prediction was

they were too minute
to ever be detected.

♪ ♪

NARRATOR:
By the 1980s, that
sentiment had changed,

and LIGO--
the Laser Interferometer

Gravitational Wave
Observatory--

was founded as a joint
Caltech and M.I.T. project.

Part of Rana's work at Caltech
has been

to continuously improve
the essential art of LIGO:

laser interferometry.

This is the,
where it all begins.

I'm going to show you

the whole laser interferometer
in here

that's a prototype
of the LIGO system.

NARRATOR:
The basic design
is easy to understand.

The LIGO interferometer
has two arms

at right angles
to each other.

A very stable infrared laser

feeds into a beam splitter,

which directs half the beam
down each arm.

ADHIKARI:
Half of the light goes one way
and half goes the other way.

And then you have mirrors
at the ends,

and they reflect the light back.

NARRATOR:
The phase of one arm
of the laser

is the reverse of the other.

If all is normal,

when recombined,
they will cancel each other out,

resulting in no signal.

But if a gravitational wave
passes through,

distorting space-time,

the length of each arm
will change,

shifting the phase
of the two beams.

For a brief moment,

the equipment will register
a signal.

Instead of having exact
cancellation

and destructive interference,

you have a little bit of light
leaking out.

And that little bit of light

that leaks out
is what we detect.

NARRATOR:
But there is a key difference

between Rana's working testbed

and the real deal:

size.

This is one of
two LIGO installations

in the United States.

While the arms of
the Caltech instrument

are about 44 yards long,

the ones here cover about
two-and-a-half miles each.

Costing hundreds
of millions of dollars,

LIGO was a huge gamble
on an unproven idea...

...that paid off.

♪ ♪

In 2015, a signal was detected.

And it was a doozy.

LEVIN:
The first event
that LIGO detected

was the most powerful event
human beings had recorded

since the Big Bang itself.

More power came out

of that collision
of those two black holes

than was emanated by

all the stars in the universe
combined.

All of that power came out

in the ringing of the drum
of space time.

NARRATOR:
Since the original event,

LIGO has confirmed the detection

of more than 80 others.

It is hard to overstate

the significance
of the discovery.

♪ ♪

LIGO is massive.

Albert Einstein predicted

that gravitational waves
should exist,

and now we measure them.

This is the most
direct observation

of black holes
that we've ever had.

This is a complete revolution
in science.

NARRATOR:
And it's all possible

because of that
quantum technology

that has become completely
embedded in our lives:

the laser.

The more stable your laser is,

the more things in the universe
you can measure.

And there's no limit to it.

So every year, when we get
lasers

better and better, we'll be able
to see

further out into the universe

and see tinier things

in the microscopic nature
of reality, matter,

space and time--
anything like that.

You just have to keep working
on this one tool

and make it better and better.

♪ ♪

NARRATOR:
Arguably, the most important
change in quantum physics

in recent decades
is a deeper understanding

of a special kind
of shared state

called quantum entanglement.

Imagine a machine that spits out
pairs of coins,

which, on the surface,
look like ordinary coins.

If you flip one,
it comes up heads or tails

about 50% of the time.

Nothing strange there.

But using a pair of coins
fresh out of the machine,

you flip one, it comes up heads.

And then the other,

it also comes up heads.

That could just be luck.

(machine chirping,
crowd cheering)

NARRATOR:
So then you do the same thing
with another fresh pair.

This time,
the first coin is tails,

and so is the second--

agreement again.

So you flip another pair,

and then another,

and another,

and another.

the two coins always agree
on the first flip.

What's going on?

Maybe the first flipped coin,

once it comes up heads or tails,

is somehow telling
the other coin how to behave.

To make sure that can't happen,

you separate the coins
by flying one to the moon

and flip them at the same time,

so no message could possibly
travel between them.

Still, they come up
in agreement.

♪ ♪

It all sounds too strange
to be true,

but particles really can behave
like those coins.

In quantum physics,
it's called "entanglement."

KAISER:
Entanglement is really just
a stubborn, stubborn,

exciting and/or frustrating
fact

that takes a long time

to try to get our heads around.

Entanglement is certainly

the most interesting and the
most confusing

aspect of quantum.

It's one of these things
we don't see,

you know, naively
in the world around us,

but it is taking place deep
in the materials

that exist around us
every day.

NARRATOR:
And while you probably
won't come across

a coin entangler anytime soon,

in the lab, scientists
routinely generate

pairs of entangled particles

that share a quantum state
so fully,

they can be thought of
as one quantum object.

You simply can't differentiate
between them.

It's just one pure state.

It's as though
you have a single entity

that's spatially separated
without a physical connection.

NARRATOR:
Entangled particles
remain connected

even when they're separated
by hundreds of miles--

and likely far more.

KAISER:
So does that mean it can
go between here and Andromeda?

Probably-- the equations give us
no reason to think it wouldn't.

NARRATOR:
Entanglement sounds bizarre.

Einstein derided the idea

as "spooky action
at a distance."

But since the 1970s,

experiment after experiment
has confirmed

entanglement is a real
quantum phenomenon.

Now, of course, many,
many decades later,

we know that entanglement is
undeniably a part of the world.

It's how the world works at
the quantum mechanical level.

We better get used to that,

and now see,
what can we do with it?

Because it's powerful,
let's try to use it.

It's become this new tool.

Being able to
create and control it

might be arguably thought of
as one of the biggest

scientific and engineering
developments

of the 21st century.

NARRATOR:
And that's happening
on several fronts.

Entanglement
has been put to work

in quantum cryptography

and quantum communication,

in atomic clocks,

and in continuing improvements
to LIGO,

but perhaps with
the greatest fanfare

in quantum computing.

And that starts with this:

the qubit.

The qubit gets its name
from its cousin

in classical computing,
the binary bit.

♪ ♪

Like its name suggests,

a binary bit can only be set
to zero or one.

But from such humble beginnings,
much has flowed--

more or less all the computing
that makes up the modern world.

All the calculations,
all emails.

Whether you're talking
to your friend

or whether you
are a NASA scientist

doing some rocket calculation,

all of that can boil down
to just zeros and ones

switching inside your computer,

which is kind of amazing,
that it's that universal.

NARRATOR:
Despite its many successes,

the binary bit
is the equivalent

of a light switch--

on or off.

The qubit is far more subtle.

ALONSO-MONSALVE:
The special thing about a qubit

is that it operates by the laws
of quantum mechanics.

It doesn't have to be
just in the zero state

or just in the one state.

It can be in a superposition
of both.

NARRATOR:
That superposition creates

a mathematical space

often represented by a sphere.

SOPHIE HERMANS:
Where a classical bit

can only sit at the South Pole
or the North Pole,

a quantum bit can be anywhere

on the surface of the sphere.

It opens up a whole new array

of possibilities
of mathematical operations.

NARRATOR:
But a single qubit will only
take you so far in computing.

LANES:
One qubit by itself
is not a computer,

or it would be the world's
smallest, most useless computer.

But when you combine them,

it can provide enough
computation and calculations

that you can get something
on the other end.

NARRATOR:
Using several qubits together

opens up the power
of entanglement

and unleashes mind-boggling
levels of complexity.

PRESKILL:
If I wanted to give
a complete description

of what's happening
with just a few hundred qubits,

very highly entangled
with one another,

I would have to write down
more bits

than the number of atoms in the
visible universe.

that we wish to exploit
in a quantum computer.

NARRATOR:
Beyond the work being done
at universities,

there are
about 100 companies

developing qubits

and quantum
computing hardware.

Major players
include Google,

Microsoft,

Amazon,

and IBM.

Its hardware development effort
is centered here,

at the Thomas J. Watson
Research Center

in Yorktown Heights
outside New York City.

Okay, let me introduce you

to our IBM Quantum System Two.

Actually, inside here
is three quantum processors,

and the team is working on how
you investigate algorithms

that use multiple
different processors.

NARRATOR:
IBM's qubits employ small loops
of superconducting metal.

Since superconductors

require cold temperatures
to operate,

the center section
of the computer

is a refrigeration unit.

In fact,

the cooling unit
of a quantum computer

can look so cool,

it's often confused
for the star of the show.

♪ ♪

LANES:
So this is a dilution
refrigerator.

A lot of people think this
entire cool shiny machine here

is a quantum computer,

but that's actually
not the case.

This is not a quantum computer.

This is a quantum computer,

this tiny little chip down here.

(laughing):
This is a freezer, basically.

But you can't deny
that it is amazing-looking.

All of these fancy shiny parts

are just plumbing parts
and cables

designed to keep the quantum
computer insanely cold.

I mean, it's, like,

minus-400-something degrees
Fahrenheit.

Like, there's absolute zero.

We are .015 above that.

It has to be so insanely cold

because we use superconductors
to make our qubits.

And then furthermore,

we want to remove
any type of noise

or thermal excitations,
which can disturb the qubits

and make them behave
in ways that we don't like.

♪ ♪

NARRATOR:
Since 2016, IBM has made
its quantum computers

accessible to the public
over the internet.

Anyone can come up
with a quantum algorithm,

akin to a classical
computer program,

and submit it to be run.

GAMBETTA:
Since we first put it
on the cloud,

people have run
over three trillion jobs

on the quantum computers.

NARRATOR:
Running an algorithm
on a quantum computer

involves setting the initial
state of the qubits,

and then manipulating them
in a series of steps.

To do that, on its systems,
IBM uses microwave pulses.

GAMBETTA:
These microwave pulses

essentially either
flip the qubit,

create it in a superposition,

or measure it.

NARRATOR:
After all the manipulation,
the qubits are read,

collapsing their quantum state
into either a zero or one.

But there's a catch.

LANES:
On a quantum computer,
the chip can

spontaneously decay
from the excited state,

or the one state,
into the zero state

when we don't want it to.

And this can occur, you know,

about every millisecond or so.

These errors
are basically inherent

to the quantum nature
of the device.

NARRATOR:
Correcting these errors

is one of the
built-in challenges

of quantum computing.

The current generation
of quantum computers

are not yet able
to do it themselves.

So there's one final step.

GAMBETTA:
The information
then comes back out.

Then it gets sent over
to a computer

where we do things
like error mitigation,

post-process the results,
correct for any extra noise,

and then we send it back
through the cloud.

♪ ♪

NARRATOR:
It is easy to imagine
that quantum computing

is the next phase
of classical computing.

That soon, you'll see
a box that says

"New Qubitium chip inside!"

The most common question

people always ask me,
which is, like,

"When will I be able
to play 'Minecraft,'

when will I be able to play
'Doom' on my quantum computer?"

Quantum computers
are not good for everything.

In the future, there won't
be quantum PowerPoint,

there won't be quantum Word.

We don't need to do that,

because we have
classical computers

and Xboxes that are
perfectly suitable

for those types of applications.

NARRATOR:
Quantum computers
function very differently

and are aimed
at very different tasks.

Experts see a role
for quantum computers in areas

like simulation
of quantum behaviors

in chemistry and materials,

or optimization
of complex systems

ranging from energy distribution

to database searches.

In any case, the future
of quantum computing

is far from written.

GHOSE:
So because things are really
speeding up all over the world,

I think we're going to
very quickly see

a demonstration of a task

that's been done with
a quantum computer

that just is well,
well outside the capability

of current computers.

And that'll probably
happen within the next

five to ten years,
I would say.

The future of computing

is going to have
classical accelerators,

it's going to have
A.I. accelerators,

and it's going to have
quantum computing accelerators

all working together.

And for me, that's one
of the most exciting things,

is, how do we actually
take advantage

of all these different
accelerators?

CARROLL:
I think that a well-functioning
quantum computer

will be able to do certain
things much, much faster.

But number one, we don't know
for sure.

And number two, it might
turn out,

the pessimistic view of this,

that those problems
are kind of limited,

that they're very, very
specialized.

But that's all exciting,
fun work in progress.

That's what makes it
interesting.

♪ ♪

NARRATOR:
The roots of quantum physics
go back 100 years.

But only in recent decades

have we started to gain control
over the quantum realm.

And that has already
transformed the way we live.

There has been
astonishing change

in the kinds of quantum systems

we can build and manipulate.

Quantum mechanics itself

already permeates
everything we do.

They're part of how
we manipulate the world.

They're part of every transistor
and every computer.

LANES:
It's about how things interact
on a fundamental level,

but it turns out we need
to know how things interact

on a fundamental level
to do big things, as well.

KAISER:
There are still deep mysteries
to puzzle with.

That part hasn't gone away.

What's increased, in a way
that I still find remarkable,

is that these same curious,

mind-boggling quantum features

are now built into how people

navigate the world
every single day.

NARRATOR:
But what about the future?

What will quantum technology
offer

in the coming decades?

Just like we can tell
our kids, "Oh, yeah,"

you know, "I was born
before the internet,

I was born before
smartphones,"

50 years from now,

people are going to be
telling stories

about technologies
that are normal

that today we can't even fathom.

I believe 50 years from now,

people growing up
won't think twice

about entanglement,
superposition...

I think that will be
commonplace.

One of the things I love
about quantum mechanics

is that it seems non-intuitive
to us.

It tells us
that there's something

beyond just what we think
we understand.

We can't always rely
on our intuition.

We have to rely
on our understanding

to make progress.

And quantum mechanics
just shows us that so clearly.

♪ ♪

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