Category Archive : La physique

La vie commence avec des vagues envoûtantes tourbillonnant sur des corps microscopiques, révèle une étude

 

Alors que la vie commence, le tourbillon fou commence. Ce n’est pas de la poésie ou de la philosophie. C’est de la science.

Une fois qu’un œuf est fécondé, des milliards de protéines ondulent sur sa surface, déclenchant une cascade vertigineuse de motifs tourbillonnants. Ces arcs en spirale ne sont pas pour le spectacle, cependant; le phénomène peut être joli, mais c’est aussi une partie fondamentale de la division cellulaire naissante.

 

“L’œuf est une énorme cellule, et ces protéines doivent travailler ensemble pour trouver son centre, afin que la cellule sache où se diviser et se replier, plusieurs fois, pour former un organisme,” dit le physicien Nikta Fakhri du MIT.

“Sans ces protéines faisant des vagues, il n’y aurait pas de division cellulaire.”

Dans une nouvelle étude, Fakhri et ses collègues chercheurs ont examiné de près à quoi ressemblent ces ondes tourbillonnantes, examinant leurs modes de propagation sur les membranes cellulaires des œufs d’étoiles de mer ( Patiria miniata ).

Au-delà de la compréhension de la biologie des ovocytes d’étoiles de mer, les chercheurs ont voulu voir comment ces modèles pourraient se comparer à des phénomènes de vagues similaires dans d’autres types de systèmes – des exemples de ce que les physiciens appellent défauts topologiques .

Comme l’expliquent les chercheurs dans un nouvel article , ces types de comportements de type turbulence peuvent être observés à la fois dans la matière physique et biologique, à des échelles qui varient entre le cosmologique et l’infinitésimal: de tourbillons tourbillonnants dans les atmosphères planétaires à la signalisation bioélectrique dans le cœur et le cerveau.

Pourtant, alors que les similitudes peuvent être abondantes, la nature de leur similitude reste mystérieuse, théoriquement parlant.

“Malgré des progrès aussi substantiels dans la compréhension des défauts topologiques et de leurs implications fonctionnelles, il n’est pas encore clair si les lois statistiques qui régissent ces structures topologiques dans les systèmes classiques et quantiques s’étendent à la matière vivante. , “ expliquent les auteurs .

Dans leurs expériences sur les étoiles de mer, l’équipe a introduit une hormone pour imiter le début de la fécondation dans les ovocytes, dans laquelle des ondes déclenchées d’une protéine de signalisation appelée Rho-GTP ondulent à travers la membrane pendant plusieurs années. minutes à la fois, les résultats étant imagés au microscope grâce à l’aide de colorants fluorescents qui se fixent à Rho-GTP.

En variant la concentration du déclencheur hormonal, les chercheurs ont pu observer une variété de spirales tourbillonnantes émanant à travers le milieu de surface de l’œuf.

“De cette façon, nous avons créé un kaléidoscope de différents modèles et examiné leur dynamique résultante”, Fakhri dit .

“On ne savait pas grand-chose sur la dynamique de ces ondes de surface dans les œufs, et après avoir commencé à analyser et modéliser ces ondes, nous avons constaté que ces mêmes schémas apparaissent dans tous ces autres systèmes. C’est une manifestation de cette très motif de vagues universel. ”

Après avoir filmé et analysé la vitesse de phase dans les modèles d’ondes, les chercheurs disent que les tout débuts de la vie, tels qu’ils sont observés dans ces œufs d’étoiles de mer, ressemblent à la dynamique observée dans la turbulence bactérienne , nématique active et les systèmes quantiques de condensats de Bose – Einstein .

Si c’est un peu lourd pour vous, en termes plus poétiques et philosophiques, c’est aussi – comme le chantent The Killers – un ouragan qui a commencé à tourner quand vous étiez jeune.

Les résultats sont rapportés dans Nature Physics .

Scientists Just Revealed The Electronic Structure of a Molecule That Exists in 126 Dimensions

Well, those crazy chemistry cats have done it. Nearly 200 years after the molecule was discovered by Michael Faraday, researchers have finally revealed the complex electronic structure of benzene.

 

This not only settles a debate that has been raging since the 1930s, this step has important implications for the future development of opto-electronic materials, many of which are built on benzenes.

The atomic structure of benzene is pretty well understood. It’s a ring consisting of six carbon atoms, and six hydrogen atoms, one attached to each of the carbon atoms.

Where it gets extremely tricky is when we consider the molecule’s 42 electrons.

“The mathematical function that describes benzene’s electrons is 126-dimensional,” chemist Timothy Schmidt of the ARC Centre of Excellence in Exciton Science and UNSW Sydney in Australia told ScienceAlert.

“That means it is a function of 126 coordinates, three for each of the 42 electrons. The electrons are not independent, so we cannot break this down into 42 independent three-dimensional functions.

The answer computed by a machine is not easy to interpret by a human, and we had to invent a way to get at the answer.”

So, that means mathematically describing the electronic structure of benzene needs to take 126 dimensions into account. As you can imagine, this is not exactly a simple thing to do. In fact, this complexity is why revealing the structure has remained a problem for so long, leading to debates about how benzene’s electrons even behave.

 

There are two schools of thought: that benzene follows valence bond theory, with localised electrons; or molecular orbital theory, with delocalised electrons. The problem is, neither really seems to quite fit.

“The interpretation of electronic structure in terms of orbitals ignores that the wavefunction is antisymmetric upon interchange of like-spins,” the researchers wrote in their paper. “Furthermore, molecular orbitals do not provide an intuitive description of electron correlation.”

voronoi benzeneVoronoi site showing electron spins (left), and cross sections of the site (right). (Liu et al. Nature Communications, 2020)

The team’s work was based on a technique they recently developed. It’s called dynamic Voronoi Metropolis sampling, and it uses an algorithmic approach to visualise the wavefunctions of a multiple-electron system.

This separates the electron dimensions into separate tiles in a Voronoi diagram, with each of the tiles corresponding to electron coordinates, allowing the team to map the wavefunction of all 126 dimensions.

And they found something strange.

“The electrons with what’s known as up-spin double-bonded, where those with down-spin single-bonded, and vice versa,” Schmidt said in statement. “That isn’t how chemists think about benzene.”

 

The effect of this is that the electrons avoid each other when it is advantageous to do so, reducing the energy of the molecule, and making it more stable.

“Essentially, this unites chemical thought, by showing how the two prevailing paradigms by which we describe benzene come together,” he told ScienceAlert.

“But we also show how to inspect what is called electron correlation – how the electrons avoid each other. This is almost always ignored qualitatively, and only invoked for calculations where only the energy is used, not the electronic behaviour.”

The research has been published in Nature Communications.

 

Australian Engineers Just Accidentally Solved a 58-Year-Old Quantum Mystery

Nearly 60 years ago, Nobel Prize-winning physicist Nicolaas Bloembergen predicted an exciting new phenomenon called nuclear electric resonance. But no one has been able to demonstrate it in action – until now.

 

Actual evidence of nuclear electric resonance has now been discovered by accident in a lab at the University of New South Wales (UNSW) in Australia, thanks to faulty equipment. The breakthrough gives scientists a new level of control over nuclei, and could seriously speed up the development of quantum computers.

Central to the phenomenon is the idea of controlling the spin of individual atoms using electrical rather than magnetic fields. That means more precise and more miniaturised management of nuclei, which could have profound impacts in a variety of fields.

“This discovery means that we now have a pathway to build quantum computers using single-atom spins without the need for any oscillating magnetic field for their operation,” says quantum physicist Andrea Morello, from UNSW.

“Moreover, we can use these nuclei as exquisitely precise sensors of electric and magnetic fields, or to answer fundamental questions in quantum science.”

In some situations, nuclear electric resonance has the potential to replace nuclear magnetic resonance, which is widely used today for a variety of purposes: for scanning human bodies, chemical elements, rock formations, and more.

 

The problem with the magnetic option is that it requires powerful currents, big coils, and a substantial amount of space – think about the size of an fMRI scanner at your local hospital, for example.

Not only that, in some ways it’s a bit of a blunt instrument too. If you want to control individual atomic nuclei – for quantum computing, perhaps, or very small sensors – then nuclear magnetic resonance isn’t a very good tool for the job.

“Performing magnetic resonance is like trying to move a particular ball on a billiard table by lifting and shaking the whole table,” says Morello. “We’ll move the intended ball, but we’ll also move all the others.”

“The breakthrough of electric resonance is like being handed an actual billiards stick to hit the ball exactly where you want it.”

It was during a nuclear magnetic resonance experiment that the UNSW researchers cracked the puzzle set by Bloembergen in 1961, and it was all down to a broken antenna. After some head-scratching over unexpected results, the researchers realised their equipment was faulty – and demonstrating nuclear electric resonance.

With subsequent computer modelling, the team was able to show that the electrical fields could influence a nucleus at a fundamental level, distorting the atomic bonds around the nucleus and causing it to reorient itself.

Now that scientists know how nuclear electric resonance can work, they can research new ways to apply it. What’s more, we can add this to the growing list of significant scientific discoveries that have been made by accident.

“This landmark result will open up a treasure trove of discoveries and applications,” says Morello. “The system we created has enough complexity to study how the classical world we experience every day emerges from the quantum realm.”

“Moreover, we can use its quantum complexity to build sensors of electromagnetic fields with vastly improved sensitivity. And all this, in a simple electronic device made in silicon, controlled with small voltages applied to a metal electrode.”

The research has been published in Nature.

 

Selon les physiciens, seulement trois trous noirs en orbite peuvent briser la symétrie d'inversion du temps

 

La plupart des lois de la physique ne se soucient pas de la direction du temps. En avant, en arrière… de toute façon, les lois fonctionnent exactement de la même manière. Physique newtonienne, relativité générale – le temps n’est pas pertinent pour les mathématiques: c’est ce qu’on appelle la symétrie d’inversion du temps.

 

Dans le vrai univers, les choses deviennent un peu plus compliquées. Et maintenant, une équipe de scientifiques dirigée par l’astronome Tjarda Boekholt de l’Université d’Aveiro au Portugal a montré qu’il suffit de trois corps en interaction gravitationnelle pour briser la symétrie d’inversion du temps.

“Jusqu’à présent, une relation quantitative entre le chaos dans les systèmes dynamiques stellaires et le niveau d’irréversibilité restait indéterminée”, écrivaient-ils dans leur article .

“Dans ce travail, nous étudions les systèmes chaotiques à trois corps en chute libre en utilisant initialement le code à n corps précis et précis Brutus , qui va au-delà de l’arithmétique standard à double précision. Nous démontrons que la fraction des solutions irréversibles diminue en tant que loi de puissance avec une précision numérique. ”

Le problème des n-corps est un problème célèbre en astrophysique. Elle survient lorsque vous ajoutez plus de corps à un système en interaction gravitationnelle.

Les mouvements de deux corps de taille comparable en orbite autour d’un point central sont relativement simples à prédire mathématiquement, selon les lois de Newton du mouvement et la loi de Newton de la gravitation universelle.

Cependant, une fois que vous ajoutez un autre corps, les choses deviennent délicates. Les corps commencent à perturber gravitationnellement les orbites des autres, introduisant un élément de chaos dans l’interaction. Cela signifie que, bien qu’il existe des solutions pour des cas particuliers, il n’y a pas de formule unique – sous la physique newtonienne ou la relativité générale – qui décrit ces interactions avec une précision totale.

Même au sein du système solaire, que nous comprenons assez bien, nous ne pouvons prédire que quelques millions d’années dans le futur. Le chaos dans l’univers est une fonctionnalité, pas un bug. .

Ce qui n’est pas clair, c’est si cela est le résultat du chaos de ces systèmes, ou des problèmes avec les simulations, conduisant à une incertitude sur leur fiabilité.

Ainsi, Boekholt et ses collègues ont conçu un test pour comprendre cela. Lui et l’astrophysicien computationnel Simon Portegies Zwart de l’Université de Leiden aux Pays-Bas ont précédemment écrit un code de simulation à n corps appelé Brutus qui utilise la puissance de calcul par force brute pour réduire l’ampleur des erreurs numériques.

Maintenant, ils l’ont utilisé pour tester la réversibilité temporelle d’un système à trois corps.

“Puisque les équations de mouvement de Newton sont réversibles dans le temps, une intégration en avant suivie d’une intégration en arrière du même temps devrait récupérer la réalisation initiale du système (quoique avec une différence de signe dans les vitesses)”, [19459005 ] ils ont écrit dans leur journal .

“Le résultat d’un test de réversibilité est donc exactement connu.”

Les trois corps du système sont des trous noirs , et ils ont été testés dans deux scénarios. Dans le premier, les trous noirs sont partis du repos, se rapprochant sur des orbites compliquées, avant que l’un des trous noirs ne soit expulsé du système.

Le deuxième scénario commence là où le premier se termine et est exécuté en arrière dans le temps, essayant de restaurer le système à son état initial.

Ils ont découvert que, 5% du temps, la simulation ne pouvait pas être inversée. Il a suffi de perturber le système de la taille d’un Longueur de Planck , qui, à 0,0000000000000000000000000000000000000016 mètre, est la plus petite longueur possible .

“Le mouvement des trois trous noirs peut être si énormément chaotique que quelque chose d’aussi petit que la longueur de Planck influencera les mouvements”, Boekholt a dit . “Les perturbations de la taille de la longueur de Planck ont ​​un effet exponentiel et brisent la symétrie temporelle.”

Cinq pour cent peuvent ne pas sembler beaucoup, mais comme vous ne pouvez jamais prédire laquelle de vos simulations tombera dans ces cinq pour cent, les chercheurs ont conclu que les systèmes à n corps sont donc “fondamentalement imprévisibles”.

Et ils ont montré que le problème n’est pas avec les simulations après tout.

“Ne pas pouvoir remonter le temps n’est plus seulement un argument statistique”, Portegies Zwart a déclaré . “Il est déjà caché dans les lois fondamentales de la nature. Pas un seul système de trois objets en mouvement, grands ou petits, planètes ou trous noirs, ne peut échapper à la direction du temps.”

La recherche a été publiée dans les avis mensuels de la Royal Astronomical Society .

In a Huge First, Physicists Have Captured Individual Atoms And Watched Them Merge

To understand how atoms unite to turn into molecules, we need to catch them in action. But to do that, physicists must force atoms to pause long enough for their exchanges to be recorded. That’s no easy task, and one physicists from the University of Otago have only just recently achieved.

 

Until now, the best physicists could do to understand the finer points of various atomic interactions was to calculate correlations based on averages among a crowd that’s been chilled down to the point that they all share an identity.

This crowd-sourced version of atomics provides plenty of useful insights, but can’t capture key details on the bump and grind of collisions between separate particles that sends some scattering and others merging.

Even if you do happen to capture a handful of atoms in one space, every collision risks sending atoms careening out of your experiment.

One way to analyse such encounters is to grab isolated atoms with the equivalent of a tiny pair of tweezers, hold them still, and record the changes as they meet.

Fortunately just such a pair of tweezers exists. Made from specially aligned polarised light, these laser-based forceps can act as optical traps for tiny objects.

Given short enough light waves, an experimenter has a good chance of trapping something as tiny as an individual atom in its pinch. Of course, first the atoms need to be cooled right down to make them easier to catch, and then separated into an empty space.

 

Describing it this way makes it sound easy. But it’s a process that requires the right technology and a lot of patience to achieve.

“Our method involves the individual trapping and cooling of three atoms to a temperature of about a millionth of a Kelvin using highly focused laser beams in a hyper-evacuated (vacuum) chamber, around the size of a toaster,” says physicist Mikkel F. Andersen.

“We slowly combine the traps containing the atoms to produce controlled interactions that we measure.”

The atoms in this case were all of the rubidium variety, which bond to form molecules of dirubidium, but just two atoms are not enough to achieve this. 

“Two atoms alone can’t form a molecule, it takes at least three to do chemistry,” says physicist Marvin Weyland.

Modelling how this takes place is a real challenge. It’s clear that two atoms have to come close enough in such a way that they can form a bond, while a third takes away a portion of that bonding energy to leave them connected.

Working out the mathematics of how just two atoms meet to build a molecule is hard enough. Taking into account the actions of any more can be a nightmare.

 

Three body recombination between atoms should, in theory, cause them to be forced out of their trap, usually adding yet one more problem for physicists trying to study interactions between multiple atoms.

Using a special camera to magnify the changes, the team captured the moment the rubidium particles came close together, revealing the rate of loss wasn’t anywhere near as common as expected.

In effect it also means the molecules weren’t coming together as quickly as existing models could explain.

Something about the confinement of the atoms and short-range quantum effects might help to explain this slowness, but the fact it’s unexpected means there’s plenty of physics to be explored using this process.

“Our work is the first time this basic process has been studied in isolation, and it turns out that it gave several surprising results that were not expected from previous measurement in large clouds of atoms,” says Weyland.

“With development, this technique could provide a way to build and control single molecules of particular chemicals.”

Further experiments will help to refine those models to better explain how groups of atoms operate together to meet and bond under various conditions.

In a world of ever-shrinking tech, it’s not hard to imagine a need for processes where microscopic circuits and advanced medications are built atom-by-atom, one union at a time.

“Our research tries to pave the way for being able to build at the very smallest scale possible, namely the atomic scale, and I am thrilled to see how our discoveries will influence technological advancements in the future,” says Andersen.

This research was published in Physical Review Letters.

 

Scientists Have Discovered a Brand New Electronic State of Matter

Scientists have observed a new state of electronic matter on the quantum scale, one that forms when electrons clump together in transit, and it could advance our understanding and application of quantum physics.

 

Movement is key to this new quantum state. When electric current is applied to semiconductors or metals, the electrons inside usually travel slowly and somewhat haphazardly in one direction.

Not so in a special type of medium known as a ballistic conductor, where the movement is faster and more uniform.

The new study shows how in very thin ballistic conducting wires, electrons can gang up – creating a whole new quantum state of matter made solely from speeding electrons.

“Normally, electrons in semiconductors or metals move and scatter, and eventually drift in one direction if you apply a voltage,” says physicist Jeremy Levy, from the University of Pittsburgh. “But in ballistic conductors the electrons move more like cars on a highway.”

“The discovery we made shows that when electrons can be made to attract one another, they can form bunches of two, three, four and five electrons that literally behave like new types of particles, new forms of electronic matter.”

Ballistic conductors can be used for stretching the boundaries of what’s possible in electronics and classical physics, and the one used in this particular experiment was made from lanthanum aluminate and strontium titanate.

 

Interestingly, when the researchers measured the levels of conductance they found they followed one of the most well-known patterns in mathematics – Pascal’s triangle. As conductance increased, it stepped up in a pattern that matches one of the rows of Pascal’s triangle, following the order 1, 3, 6, 10 and so on.

 

“The discovery took us some time to understand but it was because we initially did not realise we were looking at particles made up of one electron, two electrons, three electrons and so forth,” says Levy.

This clumping of electrons is similar to the way that quarks bind together to form neutrons and protons, according to the researchers. Electrons in superconductors can team up like this too, joining together in pairs to coordinate movement.

The findings may have something to teach us about quantum entanglement, which in turn is key to making progress with quantum computing and a super-secure, super-fast quantum internet.

According to Levy, it’s another example of how we’re reverse engineering the world based on what we’ve found from the discovery of the fundamentals of quantum physics – building on important work done in the last few decades.

“Now in the 21st century, we’re looking at all the strange predictions of quantum physics and turning them around and using them,” says Levy.

“When you talk about applications, we’re thinking about quantum computing, quantum teleportation, quantum communications, quantum sensing – ideas that use the properties of the quantum nature of matter that were ignored before.”

The research has been published in Science.

 

Amazing Video Footage Reveals The Moment Two Separate Droplets Coalesce Into One

Scientists have used super high-speed cameras to capture the moment liquid droplets combine together, providing a unique, preternatural glimpse of fluid dynamics the human eye can’t observe on its own.

 

Using an experimental setup involving two synchronised high-speed cameras – one shooting from the side, and the other looking upwards (courtesy of a mirror angled under a glass slide) – the researchers were able to study the interaction of two separate droplets, as a dyed blue impactor connected with a clear droplet resting still on the glass surface.

010 droplet 700(University of Leeds)

“In the past, there have been instances when two droplets impact and you were left wondering whether they have mixed or has one droplet just passed over the other,” says fluid mechanics researcher Alfonso Castrejón-Pita from the University of Oxford.

“Having two cameras record the droplet interaction from different viewpoints answers that question.”

010 droplet apparatus diagram(Sykes et al., Physical Review Fluids, 2020)

In the footage captured, you can see the blue droplet – dripped from a pump suspended above the slide – pass over the top of the clear droplet like a blanket, creating a surface jet that forms in less than 15 milliseconds (15 thousandths of a second) after the pair coalesce.

010 droplet 700(University of Leeds)

The image recorded from the camera at the side shows that the blue droplet is sitting on top of the clear droplet, with surface tension preventing mixing from happening.

“Given sufficient lateral separation between droplets of identical surface tension, a robust surface jet is identified on top of the coalesced droplet,” the research team, led by first author Thomas C. Sykes from the University of Leeds, explains in their study.

 

“Image processing shows this jet is the result of a surface flow caused by the impact inertia and an immobile contact line.”

But two droplets don’t always become one droplet the exact same way. The surface jet created in this kind of event can be enhanced or even suppressed, depending on manipulations of surface tension. This is an example of a phenomenon called the Marangoni effect, which affects mass transfer along an interface between two fluids.

010 droplet 700The side view, showing that the droplets are not mixing while the surface tension persists. (University of Leeds)

Aside from being pretty to watch, understanding the fluid dynamics at work here could lead to new advancements in the field of 3D printing, helping us learn how globular chemicals will react when they are dropped by the printer beside one another.

Of course, you need some pretty high-end imaging to capture this minute coalescing as it happens – a feat made possible here by cameras operating at up to 25,000 frames per second.

“The imaging techniques developed have opened-up a new window on droplet technology,” explains mechanical engineer Mark Wilson from the University of Leeds.

“We were able to expose the internal flows, whilst imaging at a sufficient speed to capture the fast dynamics.”

The findings are reported in Physical Review Fluids.

 

Physicists Have Filmed The Moment an Atom Undergoes a Quantum Measurement

Before it’s observed, an electron is a hot mess of possibility. Just like the metaphorical Schrödinger’s cat, it’s only once we lift the lid from its metaphorical box and take a good, close look that an electron settles on a clear position around an atom.

 

We’ve now had a closer look at exactly how this settling happens. By taking a series of snapshots of a strontium ion held in an electric field, a team of physicists from Sweden, Germany and Spain have found an electron’s transition from ‘maybe’ to ‘reality’ isn’t quite an all or nothing affair.

For the better part of a century it’s been fairly clear that the Universe we experience in our daily lives isn’t quite like the one we see when we try to look at it up close.

One extraordinary consequence of the strangeness at the heart of physics is objects can only be described using sets of probabilities called superpositions – up until we poke them with probes and bombard them with light to determine for certain their size and nature. 

In our classical world of absolutes, this is hard to picture. Even the famous physicist Erwin Schrödinger mocked the idea when he first heard it, posing a thought experiment involving an imagined cat that was at once alive and dead until we looked.

 

Only by opening the box and observing is the cat’s potential life either sustained or extinguished, at least in the eyes of the observer.

Schrödinger found it silly, as did Einstein, but since then it’s been shown time and time again that this metaphorical cat is indeed an accurate description of the way physics works.

One question that remains is whether there’s such a thing as an ideal quantum measurement, one that can measure aspects of a system without causing its entire superposition to collapse into a final answer.

In the 1940s, the American-Hungarian mathematician John von Neumann figured that measuring one part of a quantum system – such as the position of an electron in an orbit – would create sufficient quantum noise to it all to give up its probabilistic nature.

Years later, a German theoretical physicist named Gerhart Lüders contested von Neumann’s assumptions, pointing out that some undecided qualities of a particle’s possibilities could stick around even while others become clear.

While physicists have agreed with Lüders in theory, it’s not the easiest thing to demonstrate experimentally, relying on measuring certain actions that occur naturally in a way that they don’t interfere with one another.

 

The researchers settled on an atom of strontium with missing electrons, trapping the ion in a way that makes it unclear which of two orbits the remaining electrons are in, leaving them in a smear of both.

It’s more or less the same set-up used in many quantum computers. A laser then forces the superposition of electrons in the ion to move, with the potential shift in orbit confirmed by detecting the light that’s emitted as the electron falls back into place.

Only on detection of the light can we consider the absolute position of the electron as locked in place.

“Every time when we measure the orbit of the electron, the answer of the measurement will be that the electron was either in a lower or higher orbit, never something in between,” says Stockholm University physicist Fabian Pokorny.

“The measurement in a sense forces the electron to decide in which of the two states it is.”

Capturing numerous photons as the strontium ion is rotated into different states with separate laser provided the team with a picture of the process’s evolution as it took place over a span of a millionth of a second.

They found that the transition of the quantum system from maybe to actually isn’t an absolute affair. Aspects of it can be measured, such as the final resting place of the electron, while leaving some features of its superposition untouched and undecided. Just as Lüders had argued.

“These findings shed new light onto the inner workings of nature and are consistent with the predictions of modern quantum physics”, says lead researcher Markus Hennrich, also a physicist from Stockholm University.

What’s more, this shift isn’t instantaneous. By taking snapshots of the atom as one of its electrons adopts a clear orbit, the team showed the change is an unfolding one, as if the transition from complete uncertainty into a specific orbit is a matter of increasing probability, rather than a sudden decision.

This isn’t the first experiment to show how quantum jumps in an electron’s possibility is an unfolding process like “the eruption of a volcano“, rather than a switch. But it does add some interesting details to the way this change occurs that allows for such ideal measurements.

Sadly none of this tells us what a transition of quantum possibilities into a clear measurement means in the grand scheme of things, let alone how to think of Schrödinger’s poor cat as it waits patiently in the darkness.

All we know is lifting the lid on the poor animal doesn’t rob it completely of its mystery. Even if it risks a slower death than von Neumann might have imagined.

This research was published in Physical Review Letters.

 

Physicists Detect Signs of Elusive Form of Magnetism Predicted to Exist 50 Years Ago

Back in 1966, Japanese physicist Yosuke Nagaoka came up with the idea of an unusual new mechanism that could cause ferromagnetism – the phenomeon that powers magnets as we know them.

 

His idea made sense theoretically, but it’s never been observed in natural materials. Now, we have our first signs of it happening in the lab.

Once again we’re indebted to quantum physics for the discovery. Scientists were able to generate what they call “experimental signatures” of Nagaoka ferromagnetism (as it came to be named) in a tightly controlled, custom-made quantum electrical system.

While it’s too early to use this new magnetism setup practically, what makes the finding exciting is the indication that Nagaoka’s 54-year-old prediction is right; and that could have a major impact on how quantum systems of the future get developed.

“The results were crystal clear: we demonstrated Nagaoka ferromagnetism,” says quantum physicist Lieven Vandersypen, from Delft University of Technology in the Netherlands.

“When we started working on this project, I wasn’t sure whether the experiment would be possible, because the physics is so different from anything else that we have ever studied in our lab.”

The simplest way to think about Nagaoka ferromagnetism is as a child’s puzzle game, the one with sliding blocks you have to put into a picture or pattern. In this analogy, each block is an electron with its own spin or alignment.

 

When the electrons align in one direction, a magnetic field is created. Nagaoka described a sort of ideal version of itinerant ferromagnetism, which is where electrons are free to move but the material stays magnetic.

In Nagaoka’s version of the puzzle game, all the electrons are aligned in the same direction – that means however the puzzle blocks are shuffled around, the magnetism of the system as a whole stays constant.

Because shuffling the electrons (or puzzle tiles) around makes no difference to the overall configuration, less energy is required by the system.

ferro 2Nagaoka ferromagnetism in puzzle form, with all the spins aligned on the right. (Scixel de Groot for QuTech)

To show Nagaoka ferromagnetism in action, the scientists actually built a 2D, two-by-two lattice made up of quantum dots, tiny semiconductor particles that have the potential to form the next generation of quantum computers.

The whole system was cooled down to close to absolute zero (-272.99°C or -459.382°F), then three electrons were trapped inside it (leaving one ‘puzzle block’ empty). The next step was demonstrating that the lattice behaved like a magnet as Nagaoka suggested it might.

 

“We used a very sensitive electric sensor which could decipher the spin orientation of the electrons and convert it into an electrical signal that we could measure in the lab,” says quantum physicist Uditendu Mukhopadhyay, from Delft University of Technology.

The sensor showed that the super-small, super-delicate quantum dot system did indeed align the electron spins as expected, naturally preferring the lowest energy state.

Having previously been described as one of the hardest problems in physics, it’s a significant step forward in our understanding of both magnetism and quantum mechanics, showing that a long-standing idea about how ferromagnetism works at the nanoscale is actually correct.

Further down the line the discovery should help in the development of our own quantum computers, devices able to take on calculations beyond the scope of our current technology.

“Such systems permit the study of problems that are too complex to solve with today’s most advanced supercomputer, for example complex chemical processes,” says Vandersypen.

“Proof-of-principle experiments, such as the realisation of Nagaoka ferromagnetism, provide important guidance towards developing quantum computers and simulators of the future.”

The research has been published in Nature.

 

Dans une première énorme, les physiciens ont capturé des atomes individuels et les ont vus fusionner

 

Pour comprendre comment les atomes s’unissent pour se transformer en molécules, nous devons les attraper en action. Mais pour ce faire, les physiciens doivent obliger les atomes à s’arrêter suffisamment longtemps pour que leurs échanges soient enregistrés. Ce n’est pas une tâche facile, et un physicien de l’Université d’Otago vient tout juste de terminer.

 . .

Même s’il vous arrive de capturer une poignée d’atomes dans un espace, chaque collision risque d’envoyer des atomes se décoller de votre expérience.

Une façon d’analyser de telles rencontres est de saisir des atomes isolés avec l’équivalent d’une minuscule paire de pinces, de les maintenir immobiles et d’enregistrer les changements à mesure qu’ils se rencontrent.

Heureusement, une telle paire de pinces existe. Fabriqués à partir de lumière polarisée spécialement alignée, ces pinces à laser peuvent servir de pièges optiques pour de minuscules objets.

Compte tenu des ondes lumineuses suffisamment courtes, un expérimentateur a de bonnes chances de piéger quelque chose d’aussi petit qu’un atome individuel dans son pincement. Bien sûr, les atomes doivent d’abord être refroidis pour les rendre plus faciles à attraper, puis séparés dans un espace vide.

Le décrire de cette façon le rend plus facile. Mais c’est un processus qui nécessite la bonne technologie et beaucoup de patience pour y parvenir. . “ dit le physicien Mikkel F. Andersen .

“Nous combinons lentement les pièges contenant les atomes pour produire des interactions contrôlées que nous mesurons.”

Les atomes dans ce cas étaient tous de la variété rubidium, qui se lient pour former des molécules de dirubidium , mais seulement deux atomes ne suffisent pas pour y parvenir.

“Deux atomes seuls ne peuvent pas former une molécule, il en faut au moins trois pour faire de la chimie”, dit le physicien Marvin Weyland .

Modéliser comment cela se passe est un véritable défi. Il est clair que deux atomes doivent se rapprocher suffisamment pour pouvoir former une liaison, tandis qu’un troisième enlève une partie de cette énergie de liaison pour les laisser connectés.

Il est déjà assez difficile de calculer comment deux atomes se rencontrent pour construire une molécule. Prendre en compte les actions de tout autre peut être un cauchemar. . entre plusieurs atomes.

À l’aide d’une caméra spéciale pour agrandir les changements, l’équipe a capturé le moment où les particules de rubidium se sont rapprochées, révélant que le taux de perte n’était pas aussi proche que prévu.

En fait, cela signifie également que les molécules ne se rassemblent pas aussi rapidement que les modèles existants pourraient l’expliquer.

Quelque chose au sujet du confinement des atomes et des effets quantiques à courte portée pourrait aider à expliquer cette lenteur, mais le fait qu’il soit inattendu signifie qu’il y a beaucoup de physique à explorer en utilisant ce processus.

“Notre travail est la première fois que ce processus de base est étudié isolément, et il s’avère qu’il a donné plusieurs résultats surprenants qui n’étaient pas attendus des mesures précédentes dans de grands nuages ​​d’atomes”, dit Weyland .

“Avec le développement, cette technique pourrait fournir un moyen de construire et de contrôler des molécules uniques de produits chimiques particuliers.”

D’autres expériences aideront à affiner ces modèles pour mieux expliquer comment les groupes d’atomes fonctionnent ensemble pour se rencontrer et se lier dans diverses conditions.

Dans un monde de technologie en constante diminution, il n’est pas difficile d’imaginer un besoin de processus où les circuits microscopiques et les médicaments avancés sont construits atome par atome, une union à la fois.

“Nos recherches tentent d’ouvrir la voie pour pouvoir construire à l’échelle la plus petite possible, à savoir l’échelle atomique, et je suis ravi de voir comment nos découvertes influenceront les progrès technologiques à l’avenir,” [ 19459007] dit Andersen .

Cette recherche a été publiée dans Physical Review Letters .