gshc2020.com

Cette mise à jour améliorera l'expérience de plusieurs manières :

• Affichage de contenus plus pertinents localement, provenant de sites Web basés dans le pays de l'utilisateur
• Réduction des contenus sensationnalistes et des pièges à clics dans Discover
• Affichage de contenus plus approfondis, originaux et actuels provenant de sites Web ayant une expertise dans un domaine donné, en fonction de la compréhension du contenu d'un site par nos systèmes

Comme de nombreux sites font preuve d'une expertise approfondie dans un large éventail de domaines, nos systèmes sont conçus pour identifier l'expertise sur une base thématique. Ainsi, qu'un site démontre une expertise dans plusieurs domaines ou un seul, il a les mêmes chances d'apparaître dans Discover. Par exemple, un site d'actualités locales disposant d'une section dédiée au jardinage peut avoir établi une certaine expertise dans ce domaine, même s'il couvre d'autres sujets. En revanche, un site de critique de films qui n'a écrit qu'un seul article sur le jardinage ne sera sans doute pas considéré comme expert en jardinage.

Nous continuerons à afficher des contenus personnalisés en fonction des préférences des utilisateurs concernant les créateurs et les sources.

Comme pour toutes les mises à jour principales, ce changement peut entraîner des fluctuations du trafic Discover. Certains sites peuvent enregistrer une augmentation ou une diminution du trafic, tandis que pour beaucoup d'autres, il n'y aura aucun changement. Nous déployons d'abord cette mise à jour auprès des utilisateurs anglophones aux États-Unis, et la déploierons dans tous les pays et dans toutes les langues au cours des prochains mois.

Pour les propriétaires de sites qui recherchent des conseils, nos recommandations générales concernant les mises à jour principales s'appliquent, tout comme notre page d'aide "Apparaître sur Discover".

Si vous avez des questions, n'hésitez pas à nous contacter sur LinkedIn ou à rejoindre notre communauté d'aide Search Central pour échanger avec d'autres utilisateurs.

Sauf indication contraire, le contenu de cette page est régi par une licence Creative Commons Attribution 4.0, et les échantillons de code sont régis par une licence Apache 2.0. Pour en savoir plus, consultez les Règles du site Google Developers. Java est une marque déposée d'Oracle et/ou de ses sociétés affiliées.

Voulez-vous nous donner plus d'informations ? [[["Facile à comprendre","easyToUnderstand","thumb-up"],["J'ai pu résoudre mon problème","solvedMyProblem","thumb-up"],["Autre","otherUp","thumb-up"]],[["Il n'y a pas l'information dont j'ai besoin","missingTheInformationINeed","thumb-down"],["Trop compliqué/Trop d'étapes","tooComplicatedTooManySteps","thumb-down"],["Obsolète","outOfDate","thumb-down"],["Problème de traduction","translationIssue","thumb-down"],["Mauvais exemple/Erreur de code","samplesCodeIssue","thumb-down"],["Autre","otherDown","thumb-down"]],[],[],[]] %!s()

Quantum computers may eventually harness quantum phenomena to complete calculations that are intractable for the world’s best conventional computers. Similarly, a simulator harnessing quantum phenomena could help researchers to accurately model poorly understood materials or molecules.

This is especially true for materials such as superconductors, which conduct electricity with nearly perfect efficiency, because they derive this property from quantum effects that could be directly implemented on quantum simulators but would require more steps of mathematical translation on conventional devices.

Michelle Simmons at Silicon Quantum Computing in Australia and her colleagues have now created the biggest quantum simulator for quantum materials yet, called Quantum Twins. “The scale and controllability we have achieved with these simulators means we are now poised to tackle some very interesting problems,” she says. “We are designing new materials in previously unthought-of ways by literally building their analogues atom by atom.”

The researchers built several simulators by embedding atoms of phosphorus into silicon chips. Each atom became a quantum bit, or qubit, which is the basic building block of quantum computers and simulators, and the team could precisely arrange the qubits into different grids that emulated atoms’ arrangement in real materials. Each iteration of Quantum Twins was made up of a square grid of 15,000 qubits – more than any previous quantum simulator. Similar qubit arrays have previously been created from, for example, several thousands of extremely cold atoms.

Through this patterning process and by adding electronic components to each chip, the researchers also controlled properties of electrons in the chip. This mimicked controlling electrons in simulated materials, which is crucial for understanding, for instance, the flow of electricity within them. For example, the researchers could tune how difficult it would be to add an electron to any point in the grid or how difficult it would be for an electron to “hop” between two points.

Simmons says conventional computers struggle with simulating large two-dimensional systems, as well as certain combinations of electrons’ properties, but Quantum Twins simulators have shown promise for those cases. She and her team tested their chips by simulating a transition between metallic (or conducting) and insulating behaviour of a famous mathematical model for how “dirt” in a material can affect its ability to support electric currents. They also measured the system’s “Hall coefficient” as a function of temperature, which captures how the simulated material behaves when exposed to magnetic fields.

The size of the devices used in the experiment and the team’s ability to control variables mean Quantum Twins simulators could go on to tackle unconventional superconductors next, says Simmons. How conventional superconductors work at the level of their electrons is relatively well understood, but they must be made extremely cold or put under tremendous pressure to superconduct, which is impractical. Some superconductors can work in milder conditions, but to engineer them to function at room temperature and pressure, researchers need to understand them more microscopically – the kind of understanding that quantum simulators could offer in the future.

Additionally, Quantum Twins could be used to study interfaces between different metals and molecules similar to polyacetylene that could be useful for drug development or artificial photosynthesis devices, says Simmons. %!s()

One of the more absurd things about science is that you can spend years studying and reading about the universe’s deepest mysteries – dark matter, quantum gravity, the nature of time – and still get tripped up by something deceptively simple. Nobel-prizewinning theoretical physicist Richard Feynman famously confessed that as a student he didn’t really understand why mirrors flip images left to right rather than up and down. I’m no Feynman; I know how mirrors work. But I’ve had my own humbling reckoning with the obvious: temperature.

We’ve known that things can be hot or cold since the first cave-child stuck their hand in a fire and got yelled at by a concerned parent. But what we mean by temperature has changed a lot over the centuries, and continues to evolve today, as physicists push it into weirder, quantum corners.

My own brush with this came by way of my partner, who once asked: “My beautiful and stunningly intelligent wife, didn’t you study physics? Then tell me, can a single particle have a temperature?” I may be paraphrasing here slightly, but that was basically his question.

Now, his initial hunch was right: no, it can’t, not really. Most science enthusiasts know that temperature isn’t something you can assign to just one particle. The business of hot and cold only makes sense as a property of systems with many, many particles – things like gas-filled pistons, pots of coffee or stars. That’s because temperature, as we normally define it, is a kind of shorthand. It captures the average energy of a system’s microscopic components once they’ve bounced around and spread their energy out evenly, reaching a state known as equilibrium.

Imagine it like a ladder, with each rung representing a different energy level. The higher the rung, the more energy a particle has. When there are lots of particles, we expect them to be spread out across the rungs predictably. Most particles settle near the bottom, a few have enough energy to climb one rung higher, and fewer higher than that. The result is a smooth, declining number of particles as you go up the ladder.

But why do we define temperature this way? Sure, it’s an average, but there’s nothing in mathematics that forbids us from taking the mean of a dataset with a single point. If there’s one tall person in a room, we don’t blink at calling the average height of people in that room 6 feet. Why not do the same here?

It’s because temperature isn’t just descriptive, it’s predictive. For the scientists trying to harness the power of fuel, fire and steam in the 17th and 18th centuries, it was most useful for a temperature to tell them what would happen when two systems interacted.

That’s what gave rise to the zeroth law of thermodynamics, the last of these laws to be established but the most fundamental. It goes like this: if a thermometer reaches 80°C in a cup of warm water, and also reaches 80°C in a cup of warm milk, then if we mix the two liquids, there should be no net exchange of heat between them. This might sound obvious – banal, even – but it’s the bedrock of classical thermometry.

And it only holds because large systems behave in statistically stable ways. Tiny fluctuations in energy between specific particles get washed out and the law of large numbers allows us to write generalisable outcomes.

Thermodynamics is strange in that way. Unlike, say, Isaac Newton’s laws of motion, which work just fine for one falling apple or a thousand, thermodynamic laws only emerge at scale. They rely on averages, ensembles and the mathematical magic that happens when your particle count climbs into the billions.

So: single particles don’t have temperatures. Case closed.

Or so I thought. But just when I felt ready to move on, physics threw me a curveball. The first dead giveaway that things are about to get really weird is that many quantum systems are composed of very few particles that never have stable properties.

Tiny systems – like individual atoms or singular spins – can be trapped states that never really settle. Some are even deliberately engineered to resist the peaceful state of equilibrium entirely. So, if temperature is supposed to describe what happens after things calm down, then doesn’t our definition of temperature fall apart?

Physicists have been working hard to retool temperature from the foundations up, considering what it even means to have temperature in the quantum realm.

In the same spirit as the pioneers of thermodynamics, researchers are now asking not what temperature is but what it does. If we take a quantum system and connect it to something else, which way does the heat move? Can the system warm up its neighbour? Can it cool it down?

In the quantum world, the answer can be both! Let’s go back to the temperature ladder that particles can climb. In the classical world, the rules of temperature here are simple. When two ladders (two systems) interact, energy always flows from the system with more particles on higher rungs to the one with fewer.

But a quantum system doesn’t obey the same rules. Quantum systems could have no particles on the bottom rung, and instead have them all crowded on rungs higher up. They could have patchy distributions of particles equally spread out on all rungs. Superposition also makes it possible for particles to exist between rungs. When quantum mechanics comes into play, our ladder is no longer what physicists call “thermally ordered”.

This makes it hard to predict how heat might flow if one ladder were to interact with something. To deal with that, physicists have developed a curious solution: let quantum systems have two temperatures. Imagine a sort of reference ladder that represents a simple thermal system. One temperature tells you the hottest such ladder your system can still pull heat down from. The other tells you the coldest ladder that your system can push heat up to. Outside this bracket, heat flows in a predictable direction, but inside it, the outcome depends on the exact nature of the quantum system. It’s the new zeroth law of thermodynamics, something that can help us restore logic to how heat flows in the quantum world.

These two bounds reflect the system’s potential to give or take energy, regardless of whether it’s in a state of equilibrium. Crucially, these temperatures depend not just on energy, but on how that energy is structured: how quantum particles or states are distributed across energy levels, and what kind of transitions the whole system supports.

And like their thermodynamical predecessors, quantum physicists are interested in making their systems do work. Imagine two atoms that are entangled – their properties are so closely correlated that measuring one affects the other. Now expose one atom to the environment. When that atom gains or loses energy, it tugs on the invisible quantum link connecting the pair. Breaking or degrading that link has a cost, like snapping a stretched rubber band. This creates a flow of heat that wouldn’t happen without the quantum link, which can then be harnessed – by coupling the atom to a tiny quantum “piston” – to perform work, until the entanglement is used up. By assigning hot and cold effective temperatures to any quantum state, researchers can determine when a system can reliably transfer heat, extract work or drive tasks such as refrigeration and computation.

If you’ve made it this far, here’s my confession: I argued with my partner that a single particle could have temperature, despite his intuition being correct. Being a sore loser sent me spiralling down a major rabbit hole – and at the bottom, I’ve found that we’re both right, sort of. A single particle can’t have a temperature, but it can have two. %!s()

• F1: Back at Base is an IMG Production for the BBC, hosted by Rosamund Pike
• Co-hosts & Executive Producers are Sarah Holt and Holly Samos
• The Producers are Alasdair Cresswell, Joe Aldridge, Jack Winstanley and Mitchell Marshall
• Production Management from Abbie Collingwood, Katie Killeen and Giulia Duggan
• The Senior Producer is Ollie Kneen
• The Executive Producer for IMG is Steve Tebb
• The Story Editor and Scriptwriter is Sarah Holt
• The Showrunner is Holly Samos
• And the Commissioning Editor at the BBC is Stevie Middleton
  Programme WebsiteMore episodes