Podcast: Quantum supremacy and ancient mammals

Host: Nick Howe

Welcome back to the Nature Podcast. This week, quantum supremacy…

Host: Shamini Bundell

And some new fossil mammals. I’m Shamini Bundell.

Host: Nick Howe

And I’m Nick Howe.

[Jingle]

Host: Shamini Bundell

First up on the show today, reporter Benjamin Thompson has been diving into the quantum world to find out about a significant milestone for computing.

Interviewer: Benjamin Thompson

Listeners, today I want to talk about quantum computers, which are rather different from the so-called ‘classical’ computers, like the laptop you might use at work. The fundamental building blocks that these classical computers use to run programmes are called binary digits or bits, and these can be set to 1 or 0. The equivalent unit in a quantum computer is called a quantum bit or qubit. These can be in a state of 0 or 1, but they can also be in states that capture aspects of both 0 and 1 simultaneously. It’s long been hoped that the qubits’ strange properties could be harnessed to allow quantum computers to perform certain kinds of tasks a lot quicker than classical computers. There’s also the thought that quantum computers have the potential to make calculations that are too complicated for classical computers to do at all. This idea is known as ‘quantum supremacy’, but despite the efforts of research teams around the world, actually demonstrating quantum supremacy has been really tricky for a number of reasons.

Interviewee: John Martinis

Quantum supremacy is difficult to achieve because you have to build quantum hardware, the quantum computer to run it on, that’s pretty capable.

Interviewer: Benjamin Thompson

This is John Martinis from Google and the University of California, Santa Barbara in the US.

Interviewee: John Martinis

And you need to have a certain size and number of quantum bits. That, right now, is hard. And you also have to build qubits where you can control them really well and they have very low error rates and the combination of those two things is kind of hard to do.

Interviewer: Benjamin Thompson

While demonstrating quantum supremacy may be hard to do, John and his colleagues claim to have done just that. You might have heard some rumblings about this a month-or-so back when a copy of their paper leaked online, but this week the team have published their findings in Nature, showing, for the first time, a quantum computer that’s able to accomplish a very specific task that the world’s most powerful super computer is unable to. So how did they do it? Well, they used some impressive hardware. At their quantum computer’s heart is a processor called Sycamore, which contains 53 individually controllable qubits that run operations called logic gates.

Interviewee: John Martinis

The computer is centred around a chip that we make in a cleanroom, like you would make for a standard electronics chip. The difference is that the computer is made out of superconducting materials. We connect this quantum computer chip which is operated at very low temperatures, about 1/100 of a kelvin, so this is about 1 part in 10,000 from room temperatures. We then connect wires to that to some room temperature control electronics which put out some various electrical signals and microwave pulses, which actually control the quantum computers to do the logic gates.

Interviewer: Benjamin Thompson

To see if this system could achieve quantum supremacy, the team set it a task that centres on a kind of quantum random number generator. The 53 qubits in the quantum chip were fed a series of random operations, and each qubit gave back either a 0 or a 1, giving a string of 53 0s and 1s in total. Now, there are a huge amount of different combinations of these strings – 2⁵³, in fact – but distribution of them is not random. Due to something called quantum interference, some combinations are more likely than others. You can think of it like this: imagine you have a six-sided die that is slightly weighted in favour of one number. If you roll the die once, you could get any number. However, if you roll it a million times you’ll be able to see the bias caused by the weighting and be able to figure out the probability of each number coming up. This is similar to what the computer did. By repeatedly sampling the results, it was able to give the probability distribution of each of the 53-long strings of 1s and 0s. Although this is very demanding computationally, the Sycamore-based quantum computer was able to take it in its stride, doing a million samples in 200 seconds to get an idea of the probability distribution. As Hartmut Neven, who’s also from Google, explains, this is quite a bit quicker than they estimated that the world’s top-rated supercomputer, known as Summit, would take to accomplish the same task.

Interviewee: Hartmut Neven

It was 200 seconds on the Sycamore chip versus 10,000 years on the Summit machine.

Interviewer: Benjamin Thompson

10,000 years – for a supercomputer with over 9,000 CPUs and over 25,000 GPUs. Obviously, running a supercomputer for 10,000 years and waiting to see what the results are isn’t really feasible. The team actually came up with this value by getting classical computers to simulate simpler versions of the quantum random number generator and extrapolating the result out to work out how long the full version would take. There are suggestions though that this timeframe might not necessarily be accurate. In a very recent blog post, IBM claim that far from taking 10,000 years, with some adjustments, a classical computer could perform the same task in just 2.5 days. This of course needs to be tested, and it’s a debate that’s sure to continue. Whether or not Google’s quantum computer is capable of doing something that a super computer can’t, or just doing it much quicker, what does this result actually mean? The task that the research team chose doesn’t really have any practical use, and it was chosen specifically because it’s tough for classical computers to do. It will be a while before quantum computers are able to work on useful problems, but William Oliver, from the Massachusetts Institute of Technology in the US, who’s written a News and Views article on the work, thinks it’s an important step along the road.

Interviewee: William Oliver

I think that this is a very important milestone. It shows that a quantum computer can be controlled to a degree that it can outperform the best classical computers and it can do so using this universal set of gates, which in principal can be used to make arbitrarily complex and, in fact, interesting algorithms.

Interviewer: Benjamin Thompson

William likens the current work to the Wright brothers’ first demonstration of powered flight. That event didn’t change the world overnight, but it showed what was possible. He thinks there’s still a way to go until quantum computers are ready for prime time.

Interviewee: William Oliver

With quantum computers, this is just the beginning. The next steps are going to be to develop algorithms that are commercialisable, that solve real problems that we care about and then, in parallel, we have to develop and demonstrate quantum error-correcting codes that allow us to improve the robustness of these quantum processors just by adding redundancy into the system, and this is done with classical systems and we need to learn how to do it with quantum systems.

Host: Shamini Bundell

That was William Oliver from the Massachusetts Institute of Technology in the US. Head over to nature.com, where you can read his News and Views article. You’ll also find the paper by John Martinis and Hartmut Neven in the same place.

Host: Nick Howe

Later on, we’ll be finding out about a new gene-editing tool – that’s coming up in the News Chat. Now though, it’s time for some record-breaking Research Highlights with Anna Nagle.

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Anna Nagle

If you’ve ever run barefoot over hot sand, you can probably relate to Saharan silver ants, which have to traverse the over-60 ˚C desert to find food. To do this without succumbing to the heat, these ants have to be speedy, so speedy that researchers believe they are the world’s fastest ants. By using high-speed filming equipment and watching the ants in slow motion, scientists from Germany showed that the ants gallop, taking all their legs off the ground at once, and by doing so are able to achieve blistering speeds of 3 kilometres per hour. Pretty quick when you’re only about a centimetre in size. Speed over to that research in the Journal of Experimental Biology.

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Anna Nagle

To beat off competition for mates, many birds have some exaggerated traits, like the peacock’s tail feathers for example. But male white bellbirds impress their mates with sound, not looks. Have a listen.

[Bird Call]

This unpleasant noise, or rather ‘song’ of the bellbird, is the loudest ever documented bird call (when the volume isn’t turned down for podcast purposes). The researchers from Brazil, who captured the sounds, also found that there’s a trade-off for the bird’s loudness: the noisier they are, the shorter their songs become. What’s now baffling the researchers is why the females sit only four metres away while the males blast their songs directly at them, as it’s close enough to cause damage to their hearing. Listen out for that research over in Current Biology.

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Host: Shamini Bundell

Next up, Nick, I hear you’re taking us on a trip. I hope it’s somewhere nice, maybe Morocco or Madrid or the Maldives?

Interviewer: Nick Howe

Actually, I want to take you to the Mesozoic era, the time that dinosaurs ruled the Earth.

Host: Shamini Bundell

Ooh.

Interviewer: Nick Howe

This era started around 250 million years ago and ended with the dinosaur mass extinction 65 million years ago.

Host: Shamini Bundell

That’s great, I love dinosaurs. It will be like Jurassic Park.

Interviewer: Nick Howe

Actually, this trip isn’t about dinosaurs. It turns out there were plenty of other interesting creatures around at the time. Now, I always thought that the mammals that were living at the time of the dinosaurs were just small shrew-like creatures, and indeed that used to be the way palaeontologists viewed early mammals. But now, that view is changing. Here’s mammal palaeontologist Zhe-Xi Luo from the University of Chicago, to explain.

Interviewee: Zhe-Xi Luo

In the recent years, there are many spectacular discoveries all across the world but especially in China because the fossils are so complete, we get a much better understanding now about how do they move around, how did they live their life, and we generally know their anatomy a lot better.

Interviewer: Nick Howe

A lot of these Chinese fossils were formed due to volcanic eruptions covering the animals in ash, so they’re really well preserved. Some of them even have traces of fur and internal organs. These intact fossils are showing palaeontologists that Mesozoic mammals were far more diverse than previously thought. Take the Haramiyids, for instance.

Interviewee: Zhe-Xi Luo

These whole skeletal features show that many of the Haramiyids are actually living on the trees. They have these very modern tree-living mammal-like skeletons and some of them actually are preserved with skin membranes exactly like the modern gliders. So, we knew that these Haramiyids not only climbed up a tree, they actually took off from the tree and glided.

Interviewer: Nick Howe

And there weren’t just 160-million-year-old mammals that looked like flying squirrels, there have also been findings of mole-like burrowers and small platypus-like swimmers. From among this diversity of recently found fossils, Steve Brusatte, a vertebrate palaeontologist from the University of Edinburgh, told me about his favourite.

Interviewee: Steve Brusatte

There’s the mammal Repenommamus, which is one that was, as far as we know, one of the very, very largest mammals that lived with the dinosaurs, about the size of a badger or so, found with the bones of a little baby dinosaur in its stomach. So, this was a mammal that actually ate dinosaurs, which completely turns the table on that classic story of dinosaurs being the ones that were stepping all over the little mammals.

Interviewer: Nick Howe

This diversity is overturning a prevalent thought in palaeontology which suggested that while dinosaurs were present, mammals couldn’t diversify too much, as the dinosaurs were too dominant in the ecosystem, occupying nearly all of the ecological niches.

Interviewee: Steve Brusatte

The old stereotype was that mammals were there but they just were not very interesting, but now we know that not only were mammals there, but they were making a real statement. They were incredibly diverse. They were living in many different habitats. So, there was an enormous amount of diversity of behaviour, there was a big diversity of diets, and so mammals were playing key roles in ecosystems during the time of the dinosaurs, and that was a really unexpected thing.

Interviewer: Nick Howe

It also appears that mammals of this period were not only diverse, they were also bigger than we once thought, like the dino-eating Repenommamus you heard about earlier, which is thought to have weighed around 15 kilograms, like a medium sized dog – quite unlike my thought of the small shrew-type creatures. Some of these recently discovered fossils are also starting to reveal how the very first mammals evolved from reptiles. Here’s Luo again.

Interviewee: Zhe-Xi Luo

Mammals are very different from other vertebrates because we have very interesting biological adaptations. For example, we chew food. After we chew food, we can swallow the chewed down food in small quantities in a very polite way, instead of eating our prey whole chunks at a time like crocodiles. And this very interesting way of feeding allows us to diversify in a tremendously different way from other non-mammalian vertebrates. What we have discovered recently is we discovered the earliest modern mammals have hyoid bones little tiny bones in our throat around our Adam’s apple. In modern mammals, these hyoid bones are crucial for sustaining our way of swallowing and for sustaining our function to drink fluids. In babies, this hyoid structure made it possible for us to suckle mothers’ milk.

Interviewer: Nick Howe

These 165-million-year-old throat bones, from a vole like creature called Microdocodon gracilis, are not the only fossils revealing more about mammals’ emergence. Mammals also have tiny ear bones that have allowed them to develop a keen sense of hearing. These evolved from reptiles’ jaws and recently, a fossil has been found that shows an in between stage, not quite a jaw and not quite an ear, in a rat-like creature that lived 120 million years ago called Liaconodon. Our understanding of mammals has certainly expanded over the past few decades, but many questions still remain. Luo, for example, wants to know if these ancient mammals laid eggs like platypuses or whether the majority gave birth to live young, and Steve would like to know what happened after the dinosaurs’ extinction – to answer how mammals became some of the largest and most dominant animals on Earth today. In the end, there are a plethora of new mammal discoveries that are redefining the mammalian family tree, and Steve thinks in the next Jurassic Park film, maybe throwing some mammals in there wouldn’t be so bad.

Interviewee: Steve Brusatte

I would love to see a Hollywood film about the pre-historic past that has some of these funky new Mesozoic mammals in it. I think they would be endearing little characters. I think everybody would be cheering them along because they would be cheering along us. We would be cheering along us. These are our ancestors, our close cousins.

Host: Nick Howe

That was Steve Brusatte from the University of Edinburgh here in the UK. You also heard from Zhe-Xi Luo from the University of Chicago in the US. If you want to find out more about early mammals, then you can head over to nature.com/news to find a feature all about them.

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Interviewer: Nick Howe

Finally, on the show this week, it’s time for the News Chat and joining us once again is Heidi Ledford, senior reporter here at Nature. Heidi, thanks for joining me.

Interviewee: Heidi Ledford

Hi, thanks.

Interviewer: Nick Howe

In addition to being our senior reporter here, you’re also our go-to CRISPR person, and in the News Chat this week we’ve got a couple of CRISPR-related stories. For our first one, listeners may remember that back in June, a Russian scientist declared that he was intending to create gene-edited babies using CRISPR, and now there seems to be a new development in this.

Interviewee: Heidi Ledford

Yeah, well, so that scientist, Denis Rebrikov has said that he is pursuing his project. Now, that doesn’t mean that he’s necessarily creating gene-edited babies just yet, but he is working with human embryos in the lab to try to learn more about the particular target that he’s chosen, which is a gene involved in deafness.

Interviewer: Nick Howe

And what specifically is he doing in relation to deafness?

Interviewee: Heidi Ledford

So, he plans to edit mutations that sometimes occur in a gene called GJB2. People who have two copies of a mutated GJB2 often have difficulty with hearing. Sometimes it can be helped with a hearing aid or a cochlear implant, but it is a mutation associated with deafness.

Interviewer: Nick Howe

So, he’s looking to modify these genes in humans, but he’s a bit different from He Jiankui, who CRISPR-edited humans before, as he’s waiting for permission.

Interviewee: Heidi Ledford

Yeah, that’s right. So, he has said he’s not going to go forward with the plans and actually implant an edited embryo until he gets permission from the Ministry of Health of the Russian Federation, and a little while ago the Ministry of Health said they are not ready to give that permission yet, so we would hope and expect that it’s not going to happen anytime soon, but he is clearly sort of laying plans to be ready if that permission does come through.

Interviewer: Nick Howe

And what’s been the response from scientists and ethicists about him pushing this forward?

Interviewee: Heidi Ledford

I think a fair amount of shock and horror. I think the instance in China last year – He Jiankui and his experiments with embryos – was pretty widely condemned, I would say, by the scientific community and most scientists would agree that the technology is not ready yet, never mind the social and ethical discussions that need to be held around this kind of use of gene editing. The technology itself is even not ready.

Interviewer: Nick Howe

Well, Nature actually had the opportunity to talk to Rebrikov – what sorts of things did he say?

Interviewee: Heidi Ledford

Well, our reporter asked him about some of the technical concerns that scientists have, such as the possibility of generating off-target mutations at sites that he didn’t necessarily mean to edit and I think he acknowledged that that may be a concern but he feels that his technique is much safer than the one that was used by He Jiankui. He did also sort of explain that he is open to communication about his plans, which was something I think with He Jiankui, part of the shock of that was just that it sort of seemed to come out of nowhere all of a sudden – one day you find out that this has already happened and these children have already been born. I at least have some hope that we’ll know a bit more about what Rebrikov is doing ahead of time. But it is also clear, I guess, form his answers, that he feels this is going to happen and it is going to go forward at some point and it’s just sort of inevitable and he’s going to be ready to go.

Interviewer: Nick Howe

Well, sticking with gene editing for the time being, there’s also another story about a new type of gene-editing technology, this prime editing. Heidi, what can you tell me about this?

Interviewee: Heidi Ledford

It’s a really neat system that was developed in David Liu’s lab at the Broad Institute in Massachusetts and it’s a modified version of CRISPR really. So, it’s got some of the components that we may be familiar with by now, but basically what it does is it allows researchers to edit genes in a much more reliable way.

Interviewer: Nick Howe

So, how does it compare to the existing CRISPR technologies? How is it more reliable?

Interviewee: Heidi Ledford

I think many researchers will know this but I think a lot of people who hear about CRISPR in the media may not be aware of the fact that it is pretty darn unreliable. So, if you want to make a specific change in a gene, often times you’re not going to get that specific change every single time in every single cell that you try to edit. So, regular CRISPR, as a biological technique, really doesn’t edit the genes. All it does is it uses an enzyme that makes a cut in both strands of the DNA at a specific site, and you can tell it where to cut. So, that’s really nifty. At that point, you’re just relying on the cell’s DNA repair to fix that break and because that DNA repair tends to make mistakes, you might get a few extra DNA letters thrown in or a few extra taken out. You might, if you’re lucky, be able to actually provide a template and insert a new sequence at that site, but often the efficiency of that is really low. So, even though we talk about CRISPR as being this amazing tool that allows researchers to make changes at will, in fact it can be pretty frustrating sometimes to work with, and when you’re thinking about clinical applications that becomes really important.

Interviewer: Nick Howe

And this new technology sort of gets over some of these problems. How does it work?

Interviewee: Heidi Ledford

Yeah, so this new technology doesn’t rely on the DNA repair systems inside the cell to make the edits. So instead what it does, it still uses this Cas9 enzyme to target a specific location in the genome, but then once it gets there, it just breaks one strand and it allows another enzyme that’s been tacked on to it called reverse transcriptase to then write in a new sequence at that site, and then there’s some other things that happen at that point. But what this means is that now you can control much better than you could before what happens at that site that you want to edit and you can insert something, a few letters, you can delete a few letters, you can put in a totally new set of letters, you can change just one letter, and so on. So, it’s a very versatile tool but I think really what researchers are really going to love is that you can predict finally what you’re going to get when you do your edit.

Interviewer: Nick Howe

And with this ability to predict what you’re going to get, what are the potential applications for it?

Interviewee: Heidi Ledford

I think the first thing that comes to my mind, I guess, is really the human therapy applications because it’s long been a concern about how can you assess the safety of a therapy if you get this mix of different edits. Regulators are going to want to know what the effect of each edit is and so there’s a certain amount of uncertainty that would just be wrapped into that whole process. So, if you can instead say, ‘When I use this therapy, we will get this change at this site,’ that becomes a more straightforward therapy to evaluate in terms of safety and efficacy.

Interviewer: Nick Howe

Presumably, researchers are quite excited about this technology?

Interviewee: Heidi Ledford

It sounds like they are. I mean everyone I talked to said it was elegant, it was fascinating, it was exciting. I spoke to someone who was at a meeting recently where she first heard about this in a talk and she said she ran afterwards to go and see the poster and the poster section was two hours long. The poster was just completely packed. She just couldn’t get to the front and in the two hours she had to stick around until afterwards and so on. So, yeah, it does seem as though there’s a lot of excitement.

Interviewer: Nick Howe

So, thinking back to our first story, with a technology like this where there are less chances of off-target mutations and things occurring, do you think it will encourage people like Rebrikov to perform more germline gene editing?

Interviewee: Heidi Ledford

I hope not because it’s still not ready and definitely this is just the first report of this particular technology so we still don’t know fully how well it works. It does look like it’s more reliable and it does look like it has fewer off-target mutations as well. That doesn’t solve the problem of mosaicism, where you may have edits in some cells and not in others. It certainly doesn’t go anywhere near the social and ethical questions that are raised by the thought of heritable gene editing, so I would hope it doesn’t necessarily encourage people to go forward until they’ve had those discussions, but we don’t really know.

Interviewer: Nick Howe

Thanks, Heidi. Listeners, for more on those stories head over to nature.com/news.

Host: Shamini Bundell

That’s all for this week but if you want some science for your eyes as well as your ears, you can visit youtube.com/naturevideochannel to find out why neuroscientists are putting tiny 3D glasses on praying mantises, and hear from reporter Lizzie Gibney on that quantum supremacy story. I’m Shamini Bundell.

Host: Nick Howe

And I’m Nick Howe. See you next time.