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The motion of a tiny number of charged particles may solve a longstanding mystery about thin gas disks rotating around young stars, according to a new study from Caltech.

These features, called accretion disks, last tens of millions of years and are an early phase of solar system evolution. They contain a small fraction of the mass of the star around which they swirl; imagine a Saturn-like ring as big as the solar system. They are called accretion disks because the gas in these disks spirals slowly inward toward the star.

Continue reading “Why does inside of solar system not spin faster? Old mystery has possible new solution” »

University of Chicago physicists have invented a “quantum flute” that, like the Pied Piper, can coerce particles of light to move together in a way that’s never been seen before.

Described in two studies published in Physical Review Letters and Nature Physics, the breakthrough could point the way towards realizing quantum memories or new forms of error correction in quantum computers, and observing quantum phenomena that cannot be seen in nature.

Assoc. Prof. David Schuster’s lab works on quantum bits —the quantum equivalent of a computer bit—which tap the strange properties of particles at the atomic and sub-atomic level to do things that are otherwise impossible. In this experiment, they were working with particles of light, known as photons, in the microwave spectrum.

But Cabello and others are interested in investigating a lesser-known but equally magical aspect of quantum mechanics: contextuality. Contextuality says that properties of particles, such as their position or polarization, exist only within the context of a measurement. Instead of thinking of particles’ properties as having fixed values, consider them more like words in language, whose meanings can change depending on the context: “Time flies like an arrow. Fruit flies like bananas.”

Although contextuality has lived in nonlocality’s shadow for over 50 years, quantum physicists now consider it more of a hallmark feature of quantum systems than nonlocality is. A single particle, for instance, is a quantum system “in which you cannot even think about nonlocality,” since the particle is only in one location, said Bárbara Amaral, a physicist at the University of São Paulo in Brazil. “So [contextuality] is more general in some sense, and I think this is important to really understand the power of quantum systems and to go deeper into why quantum theory is the way it is.”

Researchers have also found tantalizing links between contextuality and problems that quantum computers can efficiently solve that ordinary computers cannot; investigating these links could help guide researchers in developing new quantum computing approaches and algorithms.

A team led by Philipp Werner, professor of physics at the University of Fribourg and leader of NCCR MARVEL’s Phase 3 project Continued Support, Advanced Simulation Methods, has applied their advanced quantum simulation method to the investigation of the complex material 1T-TaS₂. The research, recently published in Physical Review Letters, helped resolve a conflict between earlier experimental and theoretical results, showing that the surface region of 1T-TaS₂ exhibits a nontrivial interplay between band insulating and Mott insulating behavior when the material is cooled to below 180 k.

1T-TaS₂ is a layered transition metal dichalcogenide that has been studied intensively for decades because of intriguing links between temperature dependent distortions in the lattice and phenomena linked to electronic correlations.

Upon cooling, the material undergoes a series of lattice rearrangements with a simultaneous redistribution of the electronic density, a phenomenon known as charge density wave (CDW) order. In the phase reached when the material is cooled to below 180 k, an in-plane periodic lattice distortion leads to the formation of star-of-David (SOD) clusters made of 13 tantalum atoms. Simultaneously, a strong increase in resistivity is observed. Additional interesting properties of the low temperature phase include a transition to a superconducting state under pressure as well as the possibility to switch this phase into long-lived metallic metastable phases by applying short pulses of laser or voltage, making the material potentially interesting for use in future memory devices.

Physicists have discovered that certain magnetic material freezes when the temperature rises to a certain point. We’ve typically only seen this behavior when we cool down magnetic materials, not when we heat them up. As such, it has left physicists scratching their heads and baffled by the development.

Physicists Alexander Khajetoorians of Radboud University in the Netherlands says that the freezing of the magnetic materials is the opposite of what we normally see. The result is “counterintuitive, like water that becomes an ice cube when it’s heated up,” according to Khajetoorians.

Normally, ferromagnetic materials like iron feature aligned spins. This means that the magnetic spins of the atoms are all spinning in the same direction. Essentially, the south and north magnetic poles are all aligned in the same direction. Some alloys made of both iron and copper, though, feature randomized spins. Physicists refer to this state as spin glass.

Though they are discrete particles, water molecules flow collectively as liquids, producing streams, waves, whirlpools, and other classic fluid phenomena.

Not so with electricity. While an electric current is also a construct of distinct particles—in this case, electrons —the particles are so small that any collective behavior among them is drowned out by larger influences as electrons pass through ordinary metals. But, in certain materials and under specific conditions, such effects fade away, and electrons can directly influence each other. In these instances, electrons can flow collectively like a fluid.

Now, physicists at MIT and the Weizmann Institute of Science have observed electrons flowing in vortices, or whirlpools—a hallmark of fluid flow that theorists predicted electrons should exhibit, but that has never been seen until now.

A team of physicists at the University of Edinburgh’s School of Physics and Astronomy has used mathematical calculations to show that quantum communications across interstellar space should be possible. In their paper published in the journal Physical Review D, the group describes their calculations and also the possibility of extraterrestrial beings attempting to communicate with us using such signaling.

Over the past several years, scientists have been investigating the possibility of using quantum communications as a highly secure form of message transmission. Prior research has shown that it would be nearly impossible to intercept such messages without detection. In this new effort, the researchers wondered if similar types of communications might be possible across interstellar space. To find out, they used math that describes that movement of X-rays across a medium, such as those that travel between the stars. More specifically, they looked to see if their calculations could show the degree of decoherence that might occur during such a journey.

With quantum communications, engineers are faced with quantum particles that lose some or all of their unique characteristics as they interact with obstructions in their path—they have been found to be quite delicate, in fact. Such events are known as decoherence, and engineers working to build quantum networks have been devising ways to overcome the problem. Prior research has shown that the space between the stars is pretty clean. But is it clean enough for quantum communications? The math shows that it is. Space is so clean, in fact, that X-ray photons could travel hundreds of thousands of light years without becoming subject to decoherence—and that includes gravitational interference from astrophysical bodies. They noted in their work that optical and microwave bands would work equally well.

A team of researchers at the European Council for Nuclear Research (CERN) has discovered three new composite particles from observations made through the Large Hadron Collider – the world’s most powerful particle accelerator located in Switzerland and France. The discovery included a pair of tetraquarks and a pentaquark – thereby showcasing an even wider range of ways in which fundamental particles of the universe can interact with each other.

A quark is a fundamental particle, which means that it has no further known subdivisions in particle physics, as of now. Quarks, along with electrons, form the building blocks of all matter in the universe. A combination of multiple quarks is known as a hadron, which include two type – the positively charged proton and the neutral neutron.

While quarks have commonly been observed to come in combinations of twos and threes, the newly discovered hadrons are being referred to as “exotic” by the scientists because they feature four and five quarks in them. These particles are called ‘composite particles’, since they are composed of smaller fundamental building blocks – the quarks themselves.

The two tetraquarks, T^a_cs0 (2900)⁺⁺ and T^a_cs0 (2900)⁰, are observed in joint analysis of the B⁰→ D⁰D_s⁺π^– and B⁺→D^– D_s⁺ π⁺ decays. The new tetraquarks are observed with masses around 2.9 GeV in both the D_s⁺π⁺ and D_s⁺π^– mass spectra. The former corresponds to the first observation of a doubly charged open-charm tetraquark with minimal quark content csud and the latter is a neutral tetraquark composed of csud quarks. The D_s⁺π⁺ and D_s⁺π^– mass spectra in the top images above indicate that the sum of contributions from conventional resonances (particles) cannot explain experimental distribution around the mass of 2.9 GeV. On the other hand, the experimental distributions are well understood when the contributions of the two new teraquarks are included in the analysis as shown in the two bottom images above. The mass and the width are determined to be 2.908±0.011±0.02 GeV and 0.136±0.023±0.011 GeV, respectively. The quantum numbers are determined to be J^P=0⁺. In the language of particle physics the two tetraquarks are isospin partners.

In the conventional quark model, strongly interacting particles known as hadrons are formed either from quark-antiquark pairs (mesons) or three quarks (baryons). Particles which cannot be classified within this scheme are referred to as exotic hadrons. In their fundamental 1964 papers [1] and [2], in which they proposed the quark model, Murray Gell-Mann and George Zweig mentioned the possibility of adding a quark-antiquark pair to a minimal meson or baryon quark configuration. It took 50 years, however, for physicists to obtain unambiguous experimental evidence of the existence of these exotic hadrons. In April 2014 the LHCb collaboration published measurements that demonstrated that the Z(4430)^– particle, first observed by the Belle collaboration, is composed of four quarks (ccdu).