Plasma made from matter and antimatter

Pulsar has atmosphere of matter and anti matter.

Pulsar has atmosphere of matter and anti matter.

One of the all-time great mysteries in physics is why our Universe contains more matter than antimatter, which is the equivalent of matter but with the opposite charge. To tackle this question, our international team of researchers have managed to create a plasma of equal amounts of matter and antimatter – a condition we think made up the early Universe.

Matter as we know it appears in four different states: solid, liquid, gas, and plasma, which is a really hot gas where the atoms have been stripped of their electrons. However, there is also a fifth, exotic state: a matter-antimatter plasma, in which there is complete symmetry between negative particles (electrons) and positive particles (positrons).

This peculiar state of matter is believed to be present in the atmosphere of extreme astrophysical objects, such as black holes and pulsars. It is also thought to have been the fundamental constituent of the Universe in its infancy, in particular during the Leptonic era, starting approximately one second after the Big Bang.

One of the problems with creating matter and antimatter particles together is that they strongly dislike each other – disappearing in a burst of light whenever they meet. However, this doesn’t happen straight away, and it is possible to study the behaviour of the plasma for the fraction of a second in which it is alive.

Understanding how matter behaves in this exotic state is crucial if we want to understand how our Universe has evolved and, in particular, why the Universe as we know it is made up mainly of matter. This is a puzzling feature, as the theory of relativistic quantum mechanics suggests we should have equal amounts of the two. In fact, no current model of physics can explain the discrepancy.

Despite its fundamental importance for our understanding of the Universe, an electron-positron plasma had never been produced before in the laboratory, not even in huge particle accelerators such as CERN. Our international team, involving physicists from the UK, Germany, Portugal, and Italy, finally managed to crack the nut by completely changing the way we look at these objects.

Instead of focusing our attention on immense particle accelerators, we turned to the ultra-intense lasers available at the Central Laser Facility at the Rutherford Appleton Laboratory in Oxfordshire, UK. We used an ultra-high vacuum chamber with an air pressure corresponding to a hundredth of a millionth of our atmosphere to shoot an ultra-short and intense laser pulse (hundred billions of billions more intense that sunlight on the Earth surface) onto a nitrogen gas. This stripped off the gas’ electrons and accelerated them to a speed extremely close to that of light.

The beam then collided with a block of lead, which slowed them down again. As they slowed down they emitted particles of light, photons, which created pairs of electrons and their anti-particle, the positron, when they collided with nuclei of the lead sample. A chain-reaction of this process gave rise to the plasma.

However, this experimental achievement was not without effort. The laser beam had to be guided and controlled with micrometer precision, and the detectors had to be finely calibrated and shielded – resulting in frequent long nights in the laboratory.

But it was well worth it as the development means an exciting branch of physics is opening up. Apart from investigating the important matter-antimatter asymmetry, by looking at how these plasmas interact with ultra powerful laser beams, we can also study how this plasma propagates in vacuum and in a low-density medium. This would be effectively recreating conditions similar to the generation of gamma-ray bursts, some of the most luminous events ever recorded in our Universe.

 

Source:  sciencealert.com

MIT discovers a new kind of magnetism

MIT discovers a new state of matter, a new kind of magnetism:

MIT discovers a new state of matter, a new kind of magnetism

MIT discovers a new state of matter, a new kind of magnetism

Researchers at MIT have discovered a new state of matter with a new kind of magnetism. This new state, called a quantum spin liquid (QSL), could lead to significant advances in data storage. QSLs also exhibit a quantum phenomenon called long-range entanglement, which could lead to new types of communications systems, and more. Generally, when we talk about magnetism’s role in the realm of technology, there are just two types: Ferromagnetism and antiferromagnetism. Ferromagnetism has been known about for centuries, and is the underlying force behind your compass’s spinning needle or the permanent bar magnets you played with at school. In ferromagnets, the spin (i.e. charge) of every electron is aligned in the same direction, causing two distinct poles. In antiferromagnets, neighboring electrons point in the opposite direction, causing the object to have zero net magnetism (pictured below). In combination with ferromagnets, antiferromagnets are used to create spin valves: the magnetic sensors used in hard drive heads.

Antiferromagnetic ordering

In the case of quantum spin liquids, the material is a solid crystal — but the internal magnetic state is constantly in flux. The magnetic orientations of the electrons (their magnetic moment) fluctuate as they interact with other nearby electrons. “But there is a strong interaction between them, and due to quantum effects, they don’t lock in place,” says Young Lee, senior author of the research. It is these strong interactions that apparently allow for long-range quantum entanglement. The existence of QSLs has been theorized since 1987, but until now no one has succeeded in actually finding one. In MIT’s case, the researchers spent 10 months growing a tiny sliver of herbertsmithite (pictured above) — a material that was suspected to be a QSL, but which had never been properly investigated. (Bonus points if you can guess who herbertsmithite is named after.) Using neutron scattering — firing a beam of neutrons at a material to analyze its structure — the researchers found that the herbertsmithite was indeed a QSL. Moving forward, Lee says that the discovery of QSLs could lead to advances in data storage (new forms of magnetic storage) and communications (long-range entanglement). Lee also seems to think that QSLs could lead us towards higher-temperature superconductors — i.e. materials that superconduct under relatively normal conditions, rather than -200C. Really, though, the most exciting thing about quantum spin liquids is that they’re completely new, and thus we ultimately have no idea how they might eventually affect our world. “We have to get a more comprehensive understanding of the big picture,” Lee says. “There is no theory that describes everything that we’re seeing.”