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1:21

This is the Science Podcast for October 13th, 2023.

1:25

I'm Sarah Crespi. First up

1:27

on the show, after a dam is removed,

1:30

what do we do with the silty soil left

1:32

behind? Contributing correspondent

1:34

Warren Cornwall joins me to talk about

1:36

the world's largest dam removal

1:39

project and what ecologists

1:41

are going to do to revegetate

1:43

the 36 kilometers of newly revealed

1:46

River Edge. Next on the

1:48

show, we have freelance producer and former

1:50

guest,

1:51

Tanya Russe. She talks with

1:53

physicist Andrew Cleland about a science

1:55

paper from the summer on using the phonon

1:58

or a quantum of sound energy.

1:59

as the basis of quantum computing.

2:07

Now we have contributing correspondent Warren

2:09

Cornwall. He wrote a feature this week

2:11

on restoring land after dam

2:14

removal uncovers it. Hi Warren, welcome

2:16

back to the podcast. Hi

2:17

Sarah, great to be here. This is a really interesting

2:20

angle. You know, I feel like the science

2:22

behind dam removal, why it's a good idea,

2:24

has been discussed a lot. But

2:27

the technique, the science of what to

2:29

do with the newly revealed land

2:32

along

2:32

these reforming rivers,

2:34

I haven't heard much about that at all. And

2:36

your story is actually a bit forward

2:38

looking. It's focusing on the Klamath River dam

2:41

removal set for next year. Can

2:43

you set the scene for us there? What exactly is

2:45

going to happen in 2024 to these dams?

2:48

Yeah, so the Klamath River is a

2:50

long river, more

2:52

than 400 kilometers long. It

2:55

runs from sort of the high desert

2:58

of Oregon down through California

3:00

to the redwood forests of

3:03

the California coast. So it's this long

3:06

river was historically before

3:08

the dams went on it, the third most productive salmon

3:10

river on the west coast. A

3:13

number of dams were built along that river for

3:15

a number of reasons, some for irrigation, others

3:18

for hydropower.

3:19

There's six dams on

3:22

the main stem of the Klamath River. Almost

3:25

all of them are sort of pretty far upriver

3:28

in the drier, more arid area. And

3:31

four of those six are going

3:33

to be removed. One of them has already come

3:35

down, sort of the smallest one that didn't have a

3:37

reservoir. And then the

3:39

remaining three are going to come down in 2024. It

3:42

will be the world's largest dam removal

3:44

project to this point.

3:46

And how much land is it going to uncover

3:49

that's

3:49

been sitting underwater for, I don't know, 100 years?

3:52

Some of it's been 100 years, some of

3:54

it less, depending on when the dam got built. But

3:57

it's going to be more than 30 kilometers.

3:59

kilometers worth of river length.

4:02

So that's a lot.

4:03

Yeah. Now, when they do come

4:05

down, what we're going to see is just

4:08

kilometers and kilometers of land

4:11

next to a river just covered in snow. The

4:14

big question is, the focus of your story

4:16

anyway, is what will grow there and can the

4:18

deck be stacked

4:19

towards native plants?

4:21

Why is tending to riverside vegetation

4:24

so important? You know, is the big concern that

4:26

there will only be

4:28

invasive plants or there'll be a ton of erosion?

4:30

What do people want to happen and

4:31

what are they worried about? Well, you name some

4:34

of the key features. So think

4:36

about all the benefits that come from having

4:38

a healthy vegetation nearby,

4:41

particularly the long rivers. So riparian

4:44

habitat is critical. So that's

4:46

habitat that's right along the river. It's

4:48

critical for controlling erosion,

4:51

for improving water quality,

4:53

for providing shade that can pool rivers.

4:56

Not to mention providing habitat for all the creatures that

4:58

like to live in riparian settings.

5:01

So songbirds and other kinds of things like that.

5:04

Then you have, as you mentioned, the invasives

5:06

as a concern. And you know, invasives

5:09

can provide some of the functions that native

5:11

habitat can, but not always

5:13

and not in the same way.

5:15

And so there's a real incentive to

5:18

try to push the system

5:20

toward

5:21

robust native vegetation

5:24

and away from invasives. Who

5:26

is actually doing the restoration work

5:28

here along the river that's going

5:31

to be coming

5:32

about once the reservoirs

5:34

go down?

5:34

Well, it's a mix. A lot of the people

5:37

who are out on the land doing the work

5:39

for re-regutation are members of tribes

5:41

who have lived along this river for

5:44

thousands of years. Many of

5:47

them are sort of young people in their

5:49

20s who I was talking to who were really out there

5:52

rolling up their sleeves and doing that work. But

5:55

you also had some folks from outside, people

5:57

who, you know, were ecologists and who were...

6:00

trained in this kind of restoration work. And

6:02

so it is a mix.

6:03

This is a bit of a modern problem, what

6:06

to do with land that's newly uncovered

6:08

by dam removal. So it hasn't

6:10

actually been that well studied how to

6:12

revegetate silty post

6:15

dam water or post dam land.

6:17

You talk a bit about the Elwha

6:19

River dam removal as an analog

6:21

or a precedent for what's happening here.

6:24

And there were restoration ecologists

6:26

on the scene there. How did that work out

6:29

and how might the Klamath project

6:31

be different?

6:32

The person who is leading the revegetation

6:35

effort and the Klamath River was the

6:37

person who led the revegetation effort on

6:40

the Elwha River. Okay. That

6:42

started in 2011 was really when

6:45

the water started to go down. They were

6:47

basically a dozen years ahead.

6:49

So the Elwha River is interesting

6:52

for a number of reasons. First of all, some of the people

6:54

who are involved in what's happening on the Klamath

6:57

sort of learned lessons directly because

6:59

they were there when the Elwha dams

7:01

came down. But also it's a bit of a

7:03

time machine. It's a different landscape.

7:06

The Elwha is on the Olympic

7:09

Peninsula in Washington state.

7:12

It's much wetter, it's shorter. Most

7:14

of it runs through a national park. So it's had

7:17

much less human impacts on it than

7:20

the Klamath River has. But nevertheless, they've

7:22

taken a number of lessons from

7:24

the time spent on the Elwha and

7:26

are trying to apply it to the Klamath.

7:29

What are some of the key steps that they're gonna take

7:31

because of what they learned from the Elwha? One

7:33

thing that they learned was that there

7:35

is this window of opportunity

7:38

right as the water is drawn down that

7:41

is sort of this prime chance for

7:44

plants to get a

7:46

root hold on the land there because

7:48

there's still significant amount of water in

7:51

the soil. One of the concerns

7:53

that they had on the Elwha was that the water was

7:55

gonna draw down and sort of nothing was gonna

7:57

be able to take root in this sort of sterile.

7:59

sediment that was left behind.

8:02

And what they found was that plants

8:05

that came in really early, either

8:07

because humans came in and planted

8:09

them in that first year, or

8:12

because the

8:13

sort of natural release

8:15

of seeds from surrounding trees happened

8:17

to coincide with the water decreasing,

8:20

those plants had a real advantage.

8:23

They're applying that to the Klamath, so

8:25

that's really driving a

8:27

lot of what they're doing in terms of the

8:29

urgency that they have to be really

8:32

ready to go when the water starts to come down.

8:34

What about the plants that did succeed? Were they

8:36

surprised by what took hold? Yeah,

8:38

they were. One of the common

8:41

trees that first moves into a disturbed

8:44

landscape in the Pacific Northwest is

8:46

Red Alder, so it might be a

8:48

place that's been taken out by a flood or

8:50

a landslide or something like that.

8:52

And before the dams

8:54

came down on the Elwha,

8:56

they had done experiments where they had tried

8:58

to grow Red Alder in silt that they dredged

9:01

up from the bottom of these reservoirs, thinking, well,

9:03

this will be an analog for what they have to grow

9:05

in later. And they all died.

9:07

The alders wouldn't grow. I think one.

9:09

One sapling survived. And so

9:12

some people were freaked out that this

9:14

important tree wasn't really going to

9:16

be able to take hold, and if it couldn't, what else

9:19

couldn't grow there? So fast forward.

9:21

So I went and visited the Elwha

9:23

last summer, and I walked through

9:26

an alder forest of 10-meter

9:29

tall alders, just dark green

9:31

full of birdsong. And these alders

9:34

that had sprung up on that sediment that they

9:36

were worried wasn't going to grow anything. Okay, so

9:38

not everything is going to be predictable from lab experiments

9:41

in this big setting.

9:42

You visited the Elwha, and you also visited

9:44

the clammyth, areas around the clammyth.

9:47

What were the researchers, the ecologists,

9:49

doing when you were there? What kind of work

9:51

did you see?

9:52

Well, mostly I saw a lot of really

9:54

hard, sweaty work. So

9:58

I did see some what was going on.

14:00

And so Chaya could very well come out

14:02

with insights about what

14:05

forces are really reshaping that

14:07

landscape and how what

14:09

the people are trying to do interacts

14:12

with these sort of natural forces.

14:15

How they can lean into what works

14:17

for their plantings. That's great. Yeah.

14:20

I mean, I think, you know, I mean, there is also a key underlying message, which

14:22

is, you know, it's easier to break things than to fix

14:24

them. Absolutely. This seems like kind

14:26

of a massive undertaking now that we've

14:28

talked through all the steps. One of the things

14:30

that I was really struck by when I

14:32

was down

14:34

talking with the people who

14:36

were doing the real hard work, really

14:38

on the front lines of this, almost

14:41

all the people that I talked to were members of tribes

14:44

who have been on this land

14:46

thousands of years. And they

14:50

were doing some of the sort of hardest,

14:53

most grueling work, but they

14:55

really seem to be motivated by a genuine

14:57

sense of purpose. You

15:00

know, I spoke with one person,

15:02

Richard Green, who is a tribal

15:05

forestry student at university

15:08

nearby, and he

15:10

was out there pulling up by

15:12

hand these yellow star

15:15

thistles that I mentioned that are just these spiky,

15:17

gnarly weeds. And he talked

15:20

about how his grandmother, Bonnie Green,

15:22

was a political

15:24

leader for the Yurok tribe. And he remembers as

15:26

a child seeing her traveling

15:29

to Sacramento and Washington, D.C.,

15:31

and really dedicating her life to

15:34

seeing the Klamath River freed

15:36

up. And he felt like what he was

15:38

doing was really carrying that mantle

15:41

forward.

15:42

And so I was really struck

15:43

for these folks. It's not just a scientific experiment

15:46

and it's not just a job that they're really there with

15:48

with a mission. Wonderful. Thank you so

15:51

much, Warren. No, thank you, Sarah. Warren

15:53

Cornwall is a contributing correspondent based

15:55

in Bellingham, Washington. You can find a link

15:57

to the story we discussed at Science.

18:00

in what's called measurement based quantum

18:22

Yeah, so one reason is

18:24

that sound waves travel

18:27

very very slowly. They're about

18:29

a hundred thousand times slower than

18:31

light waves and that means

18:34

that you have a lot more time to interact

18:36

with them so that you can better

18:38

control exactly what they're doing

18:41

and exactly where they're going.

18:43

That's so interesting. How do you

18:45

guys make these phonons or sound waves?

18:47

Most of our experiments are based

18:49

on a kind of conventional

18:52

qubit called a superconducting qubit and

18:54

superconducting qubits are basically electrical

18:57

circuits and we need

18:59

to take the energy in one

19:01

of these electrical circuits and convert

19:04

it into a sound wave

19:06

and the way we do that is that we use a material

19:09

that's known as a piezoelectric material

19:11

which when you apply

19:14

electrical energy to it it will deform

19:17

mechanically so if you apply

19:20

like an oscillating electrical

19:22

signal to it it will oscillate

19:24

and generate a sound wave on

19:26

the surface of that material.

19:28

That's so cool. So the output of the qubit

19:30

is a sound wave in this case. Essentially

19:33

that's right. Yeah. Okay

19:34

and so you make these tiny waves

19:37

or phonons and then what do you do with them

19:39

once

19:39

you make one? So first what we had to learn

19:41

was how to take a qubit and generate

19:43

one phonon and what's nice is

19:46

that they're turns out they're at the same

19:48

frequency so when

19:50

you excite a qubit

19:52

and then you release the energy as a sound

19:55

wave you get automatically one quantum

19:57

of energy in other words one phonon. of

20:00

it but first we had to learn how to do that.

20:03

The next thing we had to learn was how to catch

20:06

that phone on when it traveled through

20:08

the material and reached

20:10

another qubit. So we figured out how to do

20:12

that and so far what

20:14

we've done other than what we call

20:17

pitch and catch these phone-ons is

20:19

we've put a beam splitter to see

20:21

what happens when we essentially

20:23

have the sound wave hit.

20:26

What's like a mirror but it's actually a bad

20:28

mirror so it lets half

20:30

the sound through and reflects the

20:32

other half of the sound back towards

20:35

where it came from.

20:36

Why would you want to do that?

20:37

What that is, that's a beam splitter and

20:40

a beam splitter is a very useful

20:42

and fundamental tool when you work

20:44

with light because when you send a light

20:47

wave into an optical beam splitter

20:49

half of it gets reflected half of it gets

20:51

transmitted and when you do that with

20:54

light at the quantum level so single

20:56

photons what happens when a

20:58

photon which is an indivisible object

21:01

when that hits a beam splitter it

21:03

can't split in half and go

21:05

half back and half forwards instead

21:08

it goes into what's called a quantum superposition

21:11

state where

21:12

the photon both gets reflected

21:14

and gets transmitted and so

21:16

what you're generating is something called quantum

21:19

entanglement just by sending it

21:21

through what is a optical bad

21:23

mirror and we wanted to check and see

21:26

does the same thing happen with a

21:28

phonon as opposed to a photon

21:31

and just to make it sound kind of

21:33

more

21:34

exotic photons are kind

21:36

of abstract objects they're combinations

21:39

of electric and magnetic fields that are oscillating

21:42

and the fact that you can make a photon

21:44

it's not divisible doesn't seem

21:47

quite so outrageous but what's outrageous

21:50

about the phonons that we use they

21:53

make up the collective motion

21:55

of a lot of atoms and solvents

21:58

huge numbers so trillions and trillions of atoms in a photon. trillions

22:00

of atoms make up one of these phonons.

22:02

When you send one of these phonons into a beam

22:05

splitter and you get this superposition

22:08

in an entangled state at the output,

22:11

you have trillions of atoms

22:14

on one side of the beam splitter doing

22:16

something and trillions of atoms on

22:18

the other side of the beam splitter doing something, this

22:21

enormous astronomical number of atoms

22:24

is in this entangled state. And

22:26

so it's kind of shocking that

22:28

this actually

22:29

works out.

22:30

Can you just explain to our listeners what entanglement

22:33

is?

22:33

So entanglement is... So

22:35

when we send this phonon,

22:38

just think of it as a marble, to the beam

22:40

splitter. And what happens is the

22:43

marble goes into a state where

22:45

it's both been reflected from the mirror and

22:48

transmitted through the mirror. There's just

22:50

one marble and it's in

22:52

this state where it's both

22:55

been reflected and transmitted at the same

22:57

time. So if you were to physically

22:59

look at it, which means measure it, you

23:01

would force it to be on one side

23:04

of the other of the beam splitter. But as

23:06

long as you don't look at it, it's actually

23:09

in both states at the same

23:11

time. And these two states are

23:14

entangled in a way that if you see

23:16

it on one side, the other side immediately disappears

23:19

and vice versa.

23:20

Once you have them in the entangled state, you can

23:22

do things like interfere them with itself,

23:25

right?

23:25

That's correct. So we've done

23:27

experiments where we can catch

23:30

this phonon in entangled

23:33

state where it's on

23:35

one side and on the other side at the same

23:37

time, but it's only one of the other at

23:40

the same time. You can catch them

23:42

with the qubits and then reinvent them and

23:44

have them interfere with each other in

23:47

a way that you can kind of decide what's

23:49

going to happen by controlling the

23:51

details of that interference.

23:54

Why would you want to make the wave

23:56

interfere with itself? Is that useful for

23:58

quantum computing?

23:59

Yeah, basically, if we can use

24:02

this many times

24:04

over, make a system that has a lot

24:06

of these beam splitters and generate

24:09

a lot of interference between a lot of phonons

24:11

all at the same time, it's a version

24:14

of a quantum computer. We're nowhere

24:16

close to doing that yet. We've just shown

24:18

that we can do basic steps towards that,

24:20

but that's the goal of pursuing

24:23

this direction and research.

24:25

So another thing that your group demonstrated

24:28

was the Hong-U mandal effect,

24:30

which is a way of showing two phonons

24:33

interacting with each other. Can you describe

24:35

why you would want to do that? One

24:37

of the problems with photons

24:39

at the quantum of light and phonons,

24:42

the quantum of sound that we're working with, is

24:44

that they don't interact with

24:47

each other. They will pass right through each other

24:49

without any sign that they

24:51

saw the other phonon

24:53

or photon. So there's just no

24:55

interactions. But it turns

24:58

out that the Hong-U mandal effect is

25:00

a way to effectively make

25:03

photons or phonons interact

25:05

with each other.

25:06

And this is an important ingredient

25:08

for quantum computing using this

25:10

kind of pattern. Right.

25:13

With that first element in hand, we can then

25:15

try to actually do something called

25:17

a gate

25:18

between the two phonons.

25:19

Can you tell us what a gate is?

25:22

Logic gates in classical

25:24

computers are the way you perform

25:26

operations between classical bits,

25:28

things like AND gates or gates, not

25:31

gates. Basically that kind of

25:33

movie in logic is how you build

25:35

a classical computer. And

25:37

quantum computers also have gates that

25:40

are different from classical computer

25:42

gates.

25:43

And if you can perform enough of the gates

25:46

in a quantum computer, then you can actually build

25:48

a quantum computer. And a lot of the

25:51

hard work that's being put into trying to make

25:53

quantum computers is to make

25:55

these quantum gates work and

25:57

work well enough that you don't make

26:00

more errors than you do proper

26:02

calculations. And so what we're

26:04

trying to do is to basically see if we can

26:06

make these gates with phonons.

26:09

Quantum computing is a young field.

26:12

It's kind of growing quickly right

26:14

now and there's a lot of different proposals for

26:16

how we will even build one. How

26:18

do you feel being really on the cutting

26:21

edge of exploring like brand

26:23

new modalities for quantum computing?

26:26

Well it's really exciting. There are, you're

26:28

right, a lot of different flavors

26:30

proposed for qubits and a lot

26:33

of that is because it's not clear which

26:35

qubit is going to be the one that

26:37

gets us there. But the promise

26:39

of quantum computing, the promise that you can

26:41

get this exponentially more powerful

26:44

computer using quantum mechanics,

26:47

is sufficient excitement for me that

26:49

I'm willing to try new things.

26:50

Yeah, fair enough.

26:52

If you had a quantum computer tomorrow, what would

26:55

be the first thing you computed with it?

26:57

Well the problem is that

26:59

quantum computers are useful

27:01

for a lot of bad things. Probably

27:04

the good thing that they're capable of doing

27:06

is quantum simulation. So you

27:09

can do things in principle if you have

27:11

a quantum computer, you can simulate

27:14

other quantum systems. For instance, one

27:16

of the goals is to build a quantum computer

27:19

that can simulate molecules and that

27:21

might help in molecular design, enzymes,

27:24

or in pharmaceuticals, or things like that. And

27:27

that's I think one of the most sort of positive looking

27:30

applications for a quantum

27:32

computer. Superconductivity

27:33

is in the news.

27:35

Could you simulate a superconducting

27:37

system to help design better superconductors?

27:40

Yeah, I mean a quantum computer,

27:42

if one is built, is supposed to be what's called a

27:44

universal computer. So it should be

27:46

able to do if anything that a classical

27:49

computer can do and do certain

27:52

quantum algorithms far

27:54

far more efficiently and

27:56

more quickly than a classical computer.

27:59

So yeah, principle, it could simulate

28:01

a superconductor. It might help us

28:03

discover a real room temperature

28:06

superconductor. Yes,

28:09

perhaps one day. Well,

28:10

that's so fascinating. Thank you, Dr.

28:12

Cleland, for chatting with us. I hope

28:15

to see more from your group in the coming months.

28:17

Yeah, it's been fun. Thank you very much for

28:19

the opportunity.

28:20

Thank you.

28:22

And that concludes this edition of the Science

28:24

Podcast. If you have any comments

28:27

or suggestions, write to us at

28:29

sciencepodcasts.aas.org. If

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you're particularly happy with this week's show, go

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write us a review on your podcast app of

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choice. To find us on those apps,

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search for Science Magazine. Of course,

28:42

you can listen to the show on our website, science.org.

28:44

This show was edited

28:47

by me, Sarah Cresty, and Kevin McLean,

28:49

with production help from Podigy. Special

28:52

thanks to Tanya Ruthie for her segment on

28:54

phonons. Jeffrey Cook composed

28:56

the music. On behalf of Science and its

28:58

publisher, Triple S, thanks for joining

29:01

us.