51x17 - Decoding the Universe: Quantum

[bunniefuu]

♪ ♪

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.

NARRATOR: Known
as Hawking Radiation,

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 ba*ls.

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,




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

of the black hole's warping
of the fabric of space-time.

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.

Pair after pair,

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.

And it's that extravagance
of the quantum language

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,"



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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