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An international team of researchers have found evidence of a mysterious new state of matter, first predicted 40 years ago, in a real material. This state, known as a quantum spin liquid, causes electrons — thought to be indivisible building blocks of nature — to break into pieces.

The researchers, including physicists from the University of Cambridge, measured the first signatures of these fractional particles, known as Majorana fermions, in a two-dimensional material with a structure similar to graphene. Their experimental results successfully matched with one of the main theoretical models for a quantum spin liquid, known as a Kitaev model. The results are reported in the journal Nature Materials.

Quantum spin liquids are mysterious states of matter which are thought to be hiding in certain magnetic materials, but had not been conclusively sighted in nature.

One of the main principles of quantum physics is the superposition of states. Systems are simultaneously in different states, i.e. “alive and dead” at the same time such as Schrödinger’s cat, until someone measures them and the system opts for one of the possibilities. As long as the superposition lasts the system is said to be in a coherent state. In real systems, sets of diverse elemental particles or atoms existing in a state of superposition, for example, in different positions simultaneously, with different levels of energy, or with two opposite spin orientations, have weak coherence: the superposition is broken easily by the vibrations associated with temperature and the interactions with the environment.

In the scientific article, researchers from the Universitat Autònoma de Barcelona Department of Physics Andreas Winter and Dong Yang propose a groundbreaking method with which to measure the degree of coherence in any given quantum state. The researchers created simple formulas to calculate how much “pure coherence” is contained in a given quantum state, by answering two fundamental questions: How efficiently can one transform the state into “pure coherence”? And how efficient is the reverse process?

“At first the quantum state must be distilled. We must see how much coherence can be extracted from it,” explains Andreas Winter, to later “once again form a noisy state in which the coherence is diluted.” The distillation and dilution process allows measuring the strength of coherence of the initial state of superposition with experiments which can be tailored to each particular case. This is an outstanding contribution to the study of quantum physics given that “traditionally, to measure the degree of coherence of a superposition it was necessary to be able to measure the visibility of interference fringes, linked to standardised experiments,” Winter highlights. “With our approach, in contrast, the experiment can be adapted to every state in order to make the quantum coherence manifest itself better.”

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Researchers of CWI, University of Gdansk, Gdansk University of Technology, Adam Mickiewicz University and the University of Cambridge have proven that quantum communication is based on nonlocality. They show that whenever quantum communication is more efficient than classical communication, it must be possible find a nonlocal correlation somewhere. Their paper ‘Quantum communication complexity advantage implies violation of a Bell inequality’, appeared in this month’s issue of the influential journal PNAS.

It has long been known that quantum mechanics predicts counterintuitive effects such as instantaneous interaction at a distance between entangled particles. This teleportation effect, which Albert Einstein famously called ‘spooky action at a distance,’ was long thought to show that the theory of quantum mechanics was incomplete. However, in 1964, physicist J.S. Bell proved that no theory involving the principle of locality can ever reproduce all predictions of quantum mechanics. In other words, it is impossible to find classical explanations for quantum correlations. This evidence for the existence of nonlocality became known as Bell’s inequality.

For a long time, the existence of quantum correlations was merely of interest to philosophically minded physicists, and was considered an exotic peculiarity rather than a useful resource for practical problems in physics or computer science. This has changed dramatically in recent years. Quantum correlation proved to be very useful in information processing. In several communication tasks, using quantum effects substantially reduced the communication complexity: the minimum number of steps necessary to complete a certain task between two parties. In such cases, there is a so-called quantum advantage in communication complexity.

A University of Oklahoma-led team of physicists believes chip-based atomic physics holds promise to make the second quantum revolution—the engineering of quantum matter with arbitrary precision—a reality. With recent technological advances in fabrication and trapping, hybrid quantum systems are emerging as ideal platforms for a diverse range of studies in quantum control, quantum simulation and computing.

James P. Shaffer, professor in the Homer L. Dodge Department of Physics and Astronomy, OU College of Arts and Sciences; Jon Sedlacek, OU graduate student; and a team from the University of Nevada, Western Washington University, The United States Naval Academy, Sandia National Laboratories and Harvard-Smithsonian Center for Astrophysics, have published research important for integrating Rydberg atoms into hybrid quantum systems and the fundamental study of atom–surface interactions, as well as applications for electrons bound to a 2D surface.

“A convenient surface for application in hybrid quantum systems is quartz because of its extensive use in the semiconductor and optics industries,” Sedlacek said. “The surface has been the subject of recent interest as a result of it stability and low surface energy. Mitigating electric fields near ‘trapping’ surfaces is the holy grail for realizing hybrid quantum systems,” added Hossein Sadeghpour, director of the Institute for Theoretical Atomic Molecular and Optical Physics, Harvard-Smithsonian Center for Astrophysics.

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Dark matter is one of the greatest revelations in modern physics. Even though it hasn’t been directly detected yet, we know that it makes up around five-sixths of the total matter in the universe, binding much of it together in dramatic ways. It is this matter that stops galaxies from being torn apart as they spin.

As a new study published in the journal Physics of the Dark Universe notes, dark matter can also be destroyed. A signature of dark matter’s annihilation could potentially reveal what it was composed of in the first place, and this team of researchers from Harvard University think they’ve found one right in the heart of our own Milky Way.

Scientists are still debating what dark matter may actually be composed of, and one recent suggestion implies the particles are so dense that they are on the verge of becoming miniature black holes. Whatever they turn out to be, many astrophysicists think that these particles share a property with “ordinary” matter: they come in two flavors, matter and antimatter. When matter encounters antimatter, both are destroyed in a powerful blast that emits high-energy radiation.

Continue reading “There’s A Powerful And Mysterious Signal Coming From The Core Of The Milky Way” »

By studying the spatial distribution of gamma-ray emission in the Milky Way, astronomers believe they have identified a signature of dark matter annihilation.

We live in a dramatic epoch of astrophysics. Breakthrough discoveries like exoplanets, gravity waves from merging black holes, or cosmic acceleration seem to arrive every decade, or even more often. But perhaps no discovery was more unexpected, mysterious, and challenging to our grasp of the “known universe” than the recognition that the vast majority of matter in the universe cannot be directly seen. This matter is dubbed “dark matter,” and its nature is unknown. According to the latest results from the Planck satellite, a mere 4.9% of the universe is made of ordinary matter (that is, matter composed of atoms or their constituents). The rest is dark matter, and it has been firmly detected via its gravitational influence on stars and other normal matter. Dark energy is a separate constituent.

Understanding this ubiquitous yet mysterious substance is a prime goal of modern astrophysics. Some astronomers have speculated that dark matter might have another property besides gravity in common with ordinary matter: It might come in two flavors, matter and anti-matter, that annihilate and emit high energy radiation when coming into contact. The leading class of particles in this category are called weakly interacting massive particles (WIMPS). If dark matter annihilation does occur, the range of options for the theoretical nature of dark matter would be considerably narrowed.

Continue reading “Astronomers Identify a Signature of Dark Matter Annihilation” »

The classic quantum mechanics problem is a particle in a 1-D box. Here is a numerical solution to that problem.

Atoms in spin liquids take the form of a kagome lattice structure, named after a Japanese basket weaving technique.