Hello. I'm Matin Durrani, and welcome to a
very special edition of the Physics World weekly
podcast,
where we're going to be revealing our top
10 breakthroughs in physics for 2024.
And we've been running the Physics World breakthrough
of the year since 2009, and there's been
some amazing successes during that time, including the
Higgs boson,
gravitational waves, and the shadow around a black
hole.
So taking you through our choices this year,
I'm joined by Margaret Harris, Tammy Freeman, Michael
Banks, and Hamish Johnson.
And before we start, a quick message from
our sponsors,
IOP Publishing's flagship journal reports on progress in
physics.
Do visit ioppublishing.org/ropp
to find out more.
So let's get cracking on the top 10
breakthroughs in physics for 2024,
and we always pick them based on the
following three criteria.
So in addition to having been reported in
Physics World in
2024, the selections have to represent a significant
advance in knowledge or understanding,
be important for scientific progress
and or development of real world applications,
and be of general interest to Physics World's
readers.
So Hamish, we're gonna start with some, quantum
physics because, it happens to be International Year
of Quantum Science and Technology next year, and
that this was some work we reported back
in July,
where physicists used entangled photons, which I think
are pretty weird in their own right, and
they used it for something really useful for
imaging purposes,
and particularly in biological samples. And have I
got this right? They imaged a bee.
That's right. Yeah. Actually, I I should point
out that that this,
particular entry is 2. It's a superposition
of 2, bits of research that were done
last year. So you're right. Yes. 1 had
to do with imaging bees, but the other
was sort of slightly weirder.
And, yeah, quantum mechanics. Wow. I mean, I
remember when I started studying it almost 40
years ago,
entanglement was sort of a curiosity that you
sort of looked at and shrugged your shoulders
and went on to, I don't know, calculate
the energy levels of a of a quantum
harmonic oscillator.
But today, entanglement
forms the basis of a growing number of
quantum technology.
And, this top ten entry, as I said,
involves 2 new imaging techniques that rely on
entanglement.
And the first was developed by
Chloe Vigner
and Hugo
Dauphine
at Sorbonne University in Paris.
And they've managed to use entangled photons
to encode an image into a beam of
light.
And the magical thing is that the image
is only revealed to an observer
who can detect
single photons. So you have to use a
special single photon detector.
And if you don't use that detector, you
can't see the image.
And, of course,
no guesses for what image they in they
encoded. It was a cat, of course. So
either the cat was there or not, depending
on what sort of detector
that you used.
And and these 2 researchers,
a little earlier this year,
joined forces with Patrick Cameron
at the universe, the UK's University of Glasgow
and others to create another entanglement based,
imaging system. And that's the one that you
referred to, where they looked at sort of
insect
insects and and and things like that.
And this uses entangled photons to enhance
adaptive
optics imaging.
And adaptive optics is something I think it
was initially,
developed by astronomers to deal with the turbulence
in the atmosphere. And the idea is that
you you sort of measure the turbulence,
between you and what you want to look
at. And then, you somehow try to correct
for it.
And,
it's been very successful in astronomy and other,
imaging techniques, particularly for, you know, biological materials
that are always sort of changing and and
becoming turbulent.
But here, they've used, entangled photons.
And the technique gets rid of something called
a guide star. You can see the, the
astronomy connection here. So it simplifies
the correction process
quite a bit.
And,
so, that's that technique.
And both of these techniques,
could have a range of uses in microscopy
and other imaging
applications as well as optical communications.
So
two clever uses
of entanglement.
That's our first entry.
Brilliant, Hamish. So that was, some work well,
2 pieces of work on entanglement.
So thanks, Hamish. Now Tammy, we can turn
to you. Still on a sort of biological
theme. I really like this next choice, which
we covered in September, and that involved researchers
using the optical properties of a common yellow
dye
to image a mouse. I mean, this sounds
really unbelievable. So, do you wanna talk us
through this one? So this is all about
imaging biological tissue.
Now one of the difficulties when you're using
optical imaging techniques is that tissue scatters light,
which makes it opaque so you can't see
through it.
And the problem arises because of different components
in tissue,
such as water and lipids, have different refractive
indices, and that's what causes the scattering.
So, the researchers from Stanford University in the
US
developed a way to make biological tissue transparent,
and they did this using the common food
dye, tartrazine,
which they applied to the skin of live
mice.
So this dye absorbs light in the near
UV and blue parts of the spectrum,
which alters the refractive index of the water
at red wavelengths such that it more closely
matches that of lipids in this part of
the spectrum.
Basically this reduces the refractive index contrast between
the water and the lipids and makes the
tissue appear more transparent.
So to test this idea,
the researchers rubbed the dye on the abdomen,
scalp, and hind limbs of the live mice
and they saw that their skin became transparent
in just a few minutes.
They could then see the animal's internal organs,
such as their liver, small intestine, and bladder
through the skin.
They could also observe fluorescent protein labeled nerve
cells in the abdomen,
visualize blood flow in their brains, and see
the fine structure of muscle fibers in their
legs.
And then when you don't need transparent mice
anymore the effect can be reversed by simply
rinsing off the dye.
So so far this has only been used
with animals, but the researchers say that if
it was extended to humans there could be
a lot of benefits. So for example,
doctors might be able to diagnose deep tumors
simply by imaging a person's tissue and that
would remove the need for an invasive biopsy.
It could also make blood draws less painful
by helping to locate veins under the skin.
And the team is now working to find
other dye molecules with greater efficiency in achieving
this tissue transparency. So there's there's lots of
potential ahead with this.
So something amazing to think about next time
you're doing some cooking with, food dye, that
type. But,
Tammy, we always keep a cut a close
eye on medical physics here at Physics World.
And, the 3rd top ten breakthrough of the
year was for some research that involved
modeling cells in the lung
in a way that could help us personalize
radiotherapy treatments. And now that sounds really potentially
good news for patients. Yeah. Indeed. So over
half of all patients with lung cancer are
treated using radiotherapy.
And while this is an effective treatment, it
leaves up to a third of recipients with
radiation induced injuries.
And and this potential to damage healthy tissue
also limits the dose that can be delivered
to the tumor.
So, to minimize the risk of radiation damage,
researchers from the University of Surrey in the
UK,
GSI Helmholtz Centre For Heavy Iron Research in
Germany,
and Massachusetts General Hospital Harvard Medical School in
the US
have created a computational model that could improve
radiotherapy outcomes for patients with lung cancer.
So, what they did is they developed an
agent based model, which consists of separate interacting
units or agents that mimic lung cells coupled
with Monte Carlo simulations.
And, the model simulates irradiation of lung tissue,
in this case 18 alveoli,
which are the tiny air
tiny air sacs within the lungs,
and it simulates these at microscopic and nanoscopic
scales.
Then based on the radiation dose that it
predicts will be delivered to each cell and
its distribution,
the model predicts whether each cell will live
or die.
It can also determine the severity of radiation
damage, hours, days, months, or even years after
treatment.
So this is all really useful information.
Now, importantly, the researchers found that their model
produced results that matched experimental observations from various
labs and hospitals,
and this suggests that it could, in principle,
be used within clinical setting.
So, currently, radiotherapy fractionation,
which is the scheme of small doses or
fractions used to deliver the entire radiation course
over time, so that this scheme isn't optimized
for individual patients,
but the researchers hope that one day their
model could be used to create personalized treatment
schemes for each patient.
So basically, they'd use information from an individual's
scans, biopsies, and other tests
from feed this into the model.
And then it would output a tailored treatment
plan that would improve the patient's chances of
survival.
So as you say, really potentially great news
for patients.
Thanks, Tammy. Now, Michael, we always love a
bit of, astronomy and space science here at
Physics World. And, one of the highlights for
us this year was China's Changi 6 mission,
which has returned samples from the dark side
of the moon, for the first time, or
should I say the far side of the
moon. And, that's made it onto our top
10 breakthroughs.
Yeah. That's right. So while the moon's so
called near side, so that's the side of
the moon that always faces Earth, has been
relatively well studied through,
robotic missions,
as well as crude ones. The so called
far side, that's the side that doesn't face
earth,
hasn't.
And that's partly because,
due to its tricky terrain,
it's got a lot not much flat surfaces
and a lot of, giant craters and so
so forth. Yet scientists, of course, are interested
in the relatively unexplored far side and why
it happens to look so different from the
near side.
So in 2019,
China launched the Changi 4 mission,
which was the first to perform a soft
landing
on the moon's far side.
It consisted of a lander and a rover,
and together they made various measurements of the
chemical composition of nearby rocks.
But, of course, to carry out more thorough
measurements,
scientists ideally need to bring samples back to
Earth.
And that happened actually for the first time
this year, thanks to the Changi 6 mission,
which launched on the 3rd May.
It touched down in the Apollo basin and
in June managed to bring back to Earth,
around 2 kilograms of material.
So scientists are now feverishly
analyzing these samples, and some first results were
published in November
in which they found that the lunar far
side was volcanically active at least 2,800,000,000
years ago. So thanks to this monumental achievement,
we can now expect many more discoveries from
those 2 kilograms of soil and rock fragments,
over the coming months years ahead. So thanks,
Michael. That's, 4 of the top 10 breakthroughs
of the year done. So back to you,
Tammy. It wouldn't be a Physics World top
10 without something going on at that hotbed
of physics, CERN.
But, our next choice isn't particle physics, but
something else going on at what is probably
the world's biggest physics lab, and it involves
cooling atoms.
Okay. So, well, the atom in question is
actually positronium,
which is an atom like system made of
an electron and a positron.
Now positronium
is currently created in warmish clouds,
in which the atoms have a large distribution
of velocities,
so this makes it difficult to do precision
spectroscopy
because the motion of all the atoms will
broaden the measured spectral lines.
So if you could cool the positronium
to low temperatures
you could open up new more accurate ways
to study the properties of antimatter.
Now, this breakthrough nomination is given to 2
teams:
the AEGIS collaboration at CERN,
and a research team at the University of
Tokyo,
who simultaneously
demonstrated laser cooling of clouds of positronium.
Now, this laser cooling of positronium is actually
really difficult to achieve, as positronium is really
unstable and annihilates itself after 140 nanoseconds.
So this means that the laser pulses must
interact with the positronium cloud faster than it
decays.
So to do this, the CERN team start
the cooling process by containing a cloud of
positrons in a penning trap and then shooting
the positrons through a nano channel silicon converter,
where they bind to electrons on its surface
and create the positronium.
So, this stage acts as a pre cooling
step.
Next, the positronium atoms are collected in a
vacuum chamber where their laser cooled, and this
involves the atoms absorbing and re emitting photons
from a laser and losing kinetic energy in
the process.
And using this method the CERN team was
able to reduce the temperature of the positronium
cloud from 380 to 170 ks.
But but why is this important? So,
for 1,
reducing the velocity of positronium
enables researchers to produce 1 to 2 orders
of magnitude more anti hydrogen, and this is
an anti atom comprising a positron and an
antiproton,
and this is of really great interest to
physicists for their experiments.
Also, this research paves the way to using
positronium
to test aspects of the standard model, such
as quantum electrodynamics,
for example, or to probe the effects of
gravity on antimatter.
So
there's lots of really exciting studies ahead here.
So thanks, Tammy. So that was all about
cooling a gas of positronium,
but going down to an even smaller scale
to the nuclear physics level,
we've got a cool bit of research,
that involves measuring the decay of helium nuclei.
But was it done in a rather unusual
way? Marg Margaret, what's what's this one about?
Yeah, Matine. So this works actually on a
bigger scale than positronium because it involves helium
nuclei, so 2 protons and 2 neutrons.
Helium nuclei sometimes called alpha particles. And you
may remember stories about them from your history
of physics classes,
about people studying radioactivity
by watching radioactive atoms spit out these alpha
particles as they decay.
And that's kind of what the physicists in
this next piece of research did, except they
actually measured the recoil due to this ejection
of the alpha particle.
And they did this by embedding a big,
fluffy, unstable radioactive atom, lead 212,
in a microscopic sphere made of silica. And
then levitating this microscopic sphere using optical tweezers,
which is basically a focus laser beam with
a microsphere trapped at the focus. And once
they had this microsphere suspended in
space, they used the principle
of conservation of momentum to determine when the
radioactive atom in the microsphere decayed and kicked
out a helium nucleus.
This is really cool because, like, one of
the researchers involved, Zhangxing Wang at Yale University,
compared to to a person throwing a ball
while they're standing on a
skateboard. As soon as the ball gets thrown,
the skateboard rolls backwards.
It's really pretty cool to be able to
measure that back reaction. It involves physics everyone's
heard about, and it might have applications for
detecting neutrinos in the future. So that's why
it's in our top ten.
So thanks, Margaret. And, still on the nuclear
physics theme, Hamish, we've picked a piece of
research that we reported back in October.
And I know you're always passionate about making
sure we, don't ignore theoretical physics. And this
one combines those two areas, theory and nuclear
physics.
So this one's quite subtle. So, I'm waiting
for you to explain it to us.
Well, I'll do my best. So,
we have a category on the Physics World
website called particle particles and nuclei, or nuclear
and particle. And that sort of makes the
suggestion that nuclear physics and particle physics are
somehow different.
But, you know, the reality is that, a
nucleus is just a big particle.
And but traditionally, there have been 2 different
ways of looking at nuclei.
The particle physics view is that nuclei are
a bunch of quarks, lots of quarks, in
the case of a lead nucleus, for example,
that are all held together by gluons, which
mediate the strong force.
And then, there's the nuclear physics point of
view. And that sort of assumes that nuclei
comp comprise protons and neutrons,
so individual particles, distinct particles,
that again, interact with each other via gluons,
and the strong force. But, of course, the
real picture is somewhere in between.
And it's very complicated,
which is, of course, the reason why we
tend to have the two views
of the nucleus.
But now,
2 physicists, Andrew Denniston
at MIT
and Thomas
Gesso
at the University of
nucleus.
And
that's
when
the
distinction
is
to each other in a nucleus. And that's
when the distinction
is blurred. You know, are they individual protons
or neutrons,
or is it just a bunch of quarks,
getting very close together? So they've tested and
refined their model with experimental data,
that
from nuclei that range from tiny helium,
all the way up to hefty lead.
And they've found very good agreement.
So
we see this as an important step forward
in understanding
nuclear structure and also the strong force itself.
So very fundamental. And that's why it's, it's
in our top ten this year.
Sounds a worthy contender. And, Hamish, back down
to earth and the real world, if you
like. And now back in July, we reported
on researchers who've made a new kind of
titanium sapphire laser.
Now those aren't lasers aren't new, but this
one seems to be a lot cheaper and
smaller and kind of better in lots of
different ways.
Yeah. The titanium
sapphire laser is is a very, very useful
device,
in science and technology.
They produce powerful beams of both
narrow band continuous light,
and they can also be used to create
broadband
pulses
of light.
And the latter have been crucial in the
development
of frequency cones.
And and these are lasers that have played
important well, they play important roles in metrology
and spectroscopy,
including
atomic clocks. So this is a central
laser technology.
But the problem so far is that they
tend to be very big
and very expensive.
So their use is is fairly limited.
But now, Yelena Vukovich
and colleagues at Stanford University in the US
have created a titanium sapphire laser
that is a 1000 times smaller, and possibly
even more important, a 1000 times cheaper
than existing systems.
So, I I think in the in the
news story, that we wrote about this, we
described it as a potential
democratization
of the laser, in that there's gonna be
a lot more,
scientific and and also technological applications of of
this device.
Of this device. You know, for for example,
these lasers can be used,
in spectroscopy,
but, you know, you can't really take it
out of the lab, or if you try
to take it out of the lab, it's
it's
can't really take it out of the lab,
or if you try to take it out
of the lab, it's going to be very
difficult. But if you've got this tiny sort
of titanium sapphire laser on a chip, you
can imagine lots of, you know,
for example, environmental monitoring applications
that you could use, and industrial applications as
well. So who knows? Maybe there'll be one
coming
to your mobile phone soon, you know, allow
you to do spectroscopy
on,
on on, I don't know, the
food you buy in the shop to make
sure it's still fresh. I'm not sure I
wanna tie Saflids in my pocket. I'm not
sure in the shop to make sure it's
still fresh. I'm not sure I wanna tie
saffles in my pocket. There's
powerful stuff there.
Well, we'll see. Yeah. So yeah. That I
mean, we thought that that was a huge,
scientific and technological breakthrough. So, yep, that's why
it's on our list this year. So thanks,
Hamish. So we're down to the final 2
top 10 breakthroughs of the year for 2024.
And, well, 20 years on from the creation
of Graphene for the first time, Margaret, we'll
be recognizing some work in that area. So
what's this,
pick all about?
Yeah. So just to remind our listeners, Graphene
is this two dimensional sheet of carbon atoms
arranged in a hexagonal lattice like honeycomb. So
back to the bees again.
And when it was first isolated 20 years
ago, there was a lot of excitement about
its properties. It's a great conductor of electricity,
for example. It's better than a metal in
that respect. And there was almost an expectation
that it would revolutionize
electronics.
That revolution hasn't quite happened yet for a
variety of reasons.
It took time to work out how to
make graphene well and reliably and in the
right quantities with the right parameters and so
on. But this year has seen some exciting
developments. We've made 2 of them a joint
entry in our top ten because they both
involve electronic switching.
The first piece of research we're covering here
was led by Marcelo Lozada Hidalgo
of the University of Manchester.
And his team used the fact that graphene
is good at conducting electrons and protons
to create a switch that can perform both
logic and memory operations in a single device.
So roughly speaking, there are some more complicated
details, of course, they use the proton current
in graphene to do the logic operation
and the electron current from memory storage. And
they were able to control those two things
independently.
Now putting those two functions together is important
because today's computers definitely don't do that. If
you look inside a standard silicon based computer
chip, you'll find that the circuit elements that
do that do the logic operations
are physically separated from the ones that do
the memory operations.
And that separation
increases data transfer times and raises power consumption.
So a device that can avoid those two
things, those two problems,
is pretty cool, actually.
The other piece of research that we've squeezed
into this entry for our top ten comes
from Walter Daher and Lei Ma at the
Georgia Institute of Technology in the US and
Tianjin University in China.
And they kind of did the opposite. They
worked out how to make a form of
graphene that doesn't conduct electricity quite so well.
This new form of graphene is called epigraphene,
and it's a semiconductor,
like silicon.
And that means it has a band gap
that electrons have to overcome if the current
is going to flow.
That might sound like a disadvantage, but it's
that band gap that means you can make
transistors, which are really just a fancy kind
of switch,
out of silicon.
Except in Graphene, the electron mobility is 10
times higher than in silicon.
DeHir had a nice analogy. He compared electron
mobility in silicon to driving on a gravel
road. Whereas in epigraphene,
you're cruising on electron freeway.
It's more efficient. It doesn't heat up as
much, and allows for higher speeds so that
electrons can move faster. And again, you have
the potential to create much more efficient electronic
devices.
And that's why it's in our top ten.
Excellent, Margaret. So that was, graphene. And finally,
we've got some work. Well, again, it's 2
pieces of work that we've, squeezed in. And
one was quite late breaking, and this has
to do with quantum computing.
I mean, there's so much going on in
that area, Margaret. But, these two bits of
work really stood out, didn't they?
Yes. As you say, this is another 2
for 1 entry. And it's kind of nice
because one of the results, as you say,
came out just a couple days ago, actually.
And the other came out, funnily enough, just
after we announced our list of last year's
top 10 breakthroughs.
So the works in this breakthrough kind of
bookend the year and they're both about error
correction in quantum computing. The first of them
chronologically comes from Misha Lukin and colleagues at
Harvard, MIT, Queer Computing,
and the NIST University of Maryland Joint Center
For Quantum Information and Computer Science,
all in the US.
At the very tail end of last year,
they surprised the quantum community really by announcing
that they created a quantum processor with 48
logical cubits.
Now, if you follow quantum computing a little
bit but not super closely,
that might not sound like a big deal.
There are other devices out there that have
more than a 1000 cubits. So what's the
big deal about 48?
Well, you may have noticed, if you're listening
carefully, that I said that they were logical
cubits. And what that means is that there
are additional physical cubits in the system that
are keeping these logical cubits in line and
correcting their errors.
That's really important because errors are the Achilles
heel of quantum computers.
That's because the quantum superposition states they run
on are really fragile and very prone to
lose their quantum nature due to noise from
their environment.
So
being able to correct those errors while manipulating
multiple cubits at once is huge.
And interestingly, Lukin and colleagues did it with
a device that uses neutral atoms as cubits.
This is a cubit platform, as they call
it, that until very recently had kinda lagged
behind superconducting circuits and trapped ions in terms
of its
Like I said, this result was surprising. The
second more recent work, really hot off the
presses, comes from a team at Google Quantum
AI. Their result was maybe less surprising since
it happened not only after Lukin's
work, but
also after a previous Google Quantum AI result
that fell just
short of the goal.
But what this team did is just as
impressive because they demonstrated a quantum processor with
an error rate that goes down as you
add more physical cubits to it.
In technical terms, they showed that it's possible
to do error correction below what's called the
surface code threshold,
which is the point where an error correction
code called the surface code, lets you start
to, in effect, win the game against noise
in your machine.
And the implications of that are huge.
It opens the door to making quantum computers
that are much more powerful and capable of
running much more complex algorithms
than anything we've seen so far.
Now there's still a long way to go
before we get a quantum computer that's gonna
solve important real world problems.
But this result gives us more confidence that
that's going to be possible eventually. And that's
why it's in our list of this year's
top 10 breakthroughs.
That sounds incredible, Margaret. So that was, the
final entry in the physics world top 10
breakthroughs for the year. So as you've heard,
there's been quantum physics, nuclear physics, biological,
medical, atomic, space science, condensed matter, and lasers.
But to find out which one of those
bagged the overall top prize for the physics
world breakthrough of the year, We'll be announcing
on Thursday, 19th December, in a news story
and in the next episode of the Physics
World weekly podcast. So do stay tuned for
that.
So finally, big thanks to Tammy, Margaret, Hamish,
and Michael for joining me. Thanks to our
sponsors, Reports on Probes in Physics,
and to our producer, Fred Iles. And thanks
for listening, and do join us again next
week for the big reveal.