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Category: particle physics – Page 434

A new door to the quantum world has been opened: When an atom absorbs or releases energy via the quantum leap of an electron, it becomes heavier or lighter. This can be explained by Einstein’s theory of relativity (E = mc2). However, the effect is minuscule for a single atom. Nevertheless, the team of Klaus Blaum and Sergey Eliseev at the Max Planck Institute for Nuclear Physics has successfully measured this infinitesimal change in the mass of individual atoms for the first time. In order to achieve this, they used the ultra-precise Pentatrap atomic balance at the Institute in Heidelberg. The team discovered a previously unobserved quantum state in rhenium, which could be interesting for future atomic clocks. Above all, this extremely sensitive atomic balance enables a better understanding of the complex quantum world of heavy atoms.

Astonishing, but true: If you wind a mechanical watch, it becomes heavier. The same thing happens when you charge your smartphone. This can be explained by the equivalence of energy (E) and mass (m), which Einstein expressed in the most famous formula in physics: E = mc2 (c: speed of light in vacuum). However, this effect is so small that it completely eludes our everyday experience. A conventional balance would not be able to detect it.

But at the Max Planck Institute for Nuclear Physics in Heidelberg, there is a balance that can: Pentatrap. It can measure the minuscule change in mass of a single atom when an electron absorbs or releases energy via a quantum jump, thus opening a for precision physics. Such quantum jumps in the electron shells of atoms shape our world—whether in life-giving photosynthesis and general chemical reactions or in the creation of colour and our vision.

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Einstein bose condensate can make ultra powerful lasers. bigsmile

The general understanding of nature involves three, sometimes four states of matter. We all are well aware of solids, liquids and gases, plus – if we think about stars – plasmas. The state in which a specific “matter” is found depends on the relation between interaction energy and temperature. In 1924, a revolutionary article was published by Bose and Einstein theoretically describing that particles should undergo a phase transition at low temperatures even if there is no or negligible interaction between them. This phase transition would not rely on an interaction between the particles but occur only due to quantum statistical effects relying on the indistinguishable nature of particles with integer spin (called bosons). This was a striking prediction and it took 71 years until this phase transition could clearly be observed in dilute atomic gases by three research groups in 1995. Only 6 years later, the Nobel Prize in physics was awarded to E. A. Cornell, W. Ketterle and C. E. Wieman “for the achievement of Bose-Einstein condensation in dilute gases of alkali atoms, and for early fundamental studies of the properties of the condensates”. The headline was simpler: “New state of matter revealed: Bose-Einstein condensate”. This was just a beginning of a still exploding research field. Not only are Bose-Einstein condensate the coldest things in universe – temperatures below one nK (1 billionth of a K above absolute zero) have been observed, they also show unique properties, e.g. behave as one giant matter wave. Weakly interacting particles with half integer spin (Fermions) do not undergo a phase transition to a Bose-Einstein condensate (BEC). Still one can cool them so far that quantum statistical effects dominate. The system is called degenerate Fermi gas (DFG) and again strange behavior occurs. Both types of degenerate quantum gases, BEC and DFG, are investigated in optical lattices to study solid state physics. New methods for precise tuning of the atomic interaction were used to study effects of High-Tc super conductivity, to create molecular BECs or to investigate dipolar BECs.

Formation of Bose-Einstein condensates

Bose-Einstein condensates (BECs) are formed if the phase space density of the atom gas becomes greater than an integer number of order one. Above this point more and more atoms occupy the lowest energy state available leading to macroscopically occupied lowest energy quantum state. A more intuitive picture is based on the wave nature of the atoms. Atoms are not point like particles. They show wave-like behavior especially at low temperature. At the transition from a thermal gas to a Bose-Einstein condensate, the size of the atomic wave packet becomes comparable to the mean distance between atoms so all atoms start to feel their common identity. In order to increase the phase space density of a laser cooled atom cloud – that is making it colder and/or more dense — one transfers the atoms into a magnetic or optical dipole trap. Further cooling is achieved by evaporative cooling taking away high energy atoms and letting the remaining ones rethermalize, quite similar to the cooling of a hot cup of coffee or tea. Typically, Bose-Einstein condensation then occurs at temperatures on the order of 0.1 µK and is observed by a characteristic change in the shape of an atom cloud that was released from the trap, illuminated with a resonant laser beam and its shadow then observed with a CCD camera.

Continue reading “Degenerate Quantum Gases (BEC, DFG)” | >

Exotic atoms in which electrons are replaced by other subatomic particles of the same charge allow deep insights into the quantum world. After eight years of ongoing research, a group led by Masaki Hori, senior physicist at the Max Planck Institute of Quantum Optics in Garching, Germany, has now succeeded in a challenging experiment: In a helium atom, they replaced an electron with a pion in a specific quantum state and verified the existence of this long-lived “pionic helium” for the very first time. The usually short-lived pion could thereby exist 1000 times longer than it normally would in other varieties of matter. Pions belong to an important family of particles that determine the stability and decay of atomic nuclei. The pionic helium atom enables scientists to study pions in an extremely precise manner using laser spectroscopy. The research is published in this week’s edition of Nature.

For eight years, the group worked on this challenging experiment, which has the potential to establish a new field of research. The team experimentally demonstrated for the first time that long-lived pionic really exist. “It is a form of chemical reaction that happens automatically,” explains Hori. The exotic atom was first theoretically predicted in 1964 after experiments at that time pointed toward its existence. However, it was considered extremely difficult to verify this prediction experimentally. Usually, in an atom, the extremely short-lived decays quickly. However, in pionic helium, it can be conserved in a sense so it lives 1000 times longer than it normally does in other atoms.

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Researchers at the Department of Energy’s (DOE’s) Oak Ridge National Laboratory (ORNL) have finished the preliminary commissioning of a new 14-tesla magnet at the Spallation Neutron Source (SNS). This new sample environment allows researchers to explore the fundamental physics behind complex behavior of quantum matter.

The magnet, which also features an optional dilution refrigerator insert, is the latest low-temperature sample to be commissioned at SNS. Weighing 2,670 pounds and standing nearly 7 feet tall, this massive device is an excellent tool for researchers wanting to learn more about materials that exhibit quantum phenomena. Its powerful magnetic field forces quantum particles to behave in an orderly way, giving scientists the opportunity to locate patterns in otherwise disordered . And with its refrigerator—which can chill samples to −459.65° F—scientists can essentially “freeze” molecular vibrations in materials that might appear as background noise in neutron scattering studies. This allows for more accurate measurements of the excitations associated with quantum magnets.

“Quantum systems often lack discernible order. This makes it difficult to understand their fundamental characteristics. This new sample environment lets us bring order to these systems we’re interested in studying,” said Matt Stone, a lead instrument scientist at ORNL.

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The U.S. Department of Defense wants to test a directed energy weapon in space, one that it hopes will someday destroy ballistic missiles moments after launch. The weapon, a so-called neutral particle beam, would be boosted into space and tested from orbit in 2023.

Neutral particle beams don’t get as much attention as lasers but are attractive in their own right. The weapons work by accelerating particles without an electric charge—particularly neutrons—to speeds close to the speed of light and directing them against a target. The neutrons knock protons out of the nuclei of other particles they encounter, generating heat on the target object.

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Two decades ago, an experiment at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory pinpointed a mysterious mismatch between established particle physics theory and actual lab measurements. When researchers gauged the behavior of a subatomic particle called the muon, the results did not agree with theoretical calculations, posing a potential challenge to the Standard Model—our current understanding of how the universe works.

Ever since then, scientists around the world have been trying to verify this discrepancy and determine its significance. The answer could either uphold the Standard Model, which defines all of the known subatomic particles and how they interact, or introduce the possibility of an entirely undiscovered physics. A multi-institutional research team (including Brookhaven, Columbia University, and the universities of Connecticut, Nagoya and Regensburg, RIKEN) have used Argonne National Laboratory’s Mira supercomputer to help narrow down the possible explanations for the discrepancy, delivering a newly precise theoretical calculation that refines one piece of this very complex puzzle. The work, funded in part by the DOE’s Office of Science through its Office of High Energy Physics and Advanced Scientific Computing Research programs, has been published in the journal Physical Review Letters.

A muon is a heavier version of the electron and has the same electric charge. The measurement in question is of the muon’s magnetic moment, which defines how the particle wobbles when it interacts with an external magnetic field. The earlier Brookhaven experiment, known as Muon g-2, examined muons as they interacted with an electromagnet storage ring 50 feet in diameter. The experimental results diverged from the value predicted by theory by an extremely small amount measured in parts per million, but in the realm of the Standard Model, such a difference is big enough to be notable.

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Circa 2018

After 10 years, Prof. Raimar Wulkenhaar from the University of Münster’s Mathematical Institute and his colleague Dr. Erik Panzer from the University of Oxford have solved a mathematical equation which was considered to be unsolvable. The equation is to be used to find answers to questions posed by elementary particle physics. In this interview with Christina Heimken, Wulkenhaar looks back on the challenges encountered in looking for the formula for a solution and he explains why the work is not yet finished.

You worked on the solution to the equation for 10 years. What made this equation so difficult to solve?

It’s a non-linear integral equation with two variables. Such an equation is so complex that you do actually think there can’t possibly be any formula for a solution. Two variables alone are a challenge in themselves, and there are no established approaches for finding a solution for non-linear integral equations. Nevertheless, again and again during those 10 years there were glimmers of hope and as a result, and despite all the difficulties, I thought finding an explicit formula for a solution – expressed through known functions – was actually possible.

Continue reading “Mathematician discusses solving a seemingly unsolvable equation” | >

Here’s a new chapter in the story of the miniaturisation of machines: researchers in a laboratory in Singapore have shown that a single atom can function as either an engine or a fridge. Such a device could be engineered into future computers and fuel cells to control energy flows.

“Think about how your computer or laptop has a lot of things inside it that heat up. Today you cool that with a fan that blows air. In nanomachines or quantum computers, small devices that do cooling could be something useful,” says Dario Poletti from the Singapore University of Technology and Design (SUTD).

This work gives new insight into the mechanics of such devices. The work is a collaboration involving researchers at the Centre for Quantum Technologies (CQT) and Department of Physics at the National University of Singapore (NUS), SUTD and at the University of Augsburg in Germany. The results were published in the peer-reviewed journal npj Quantum Information on 1 May.

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Non-thermal (or cold) plasma has been around for years. A version of this technology is incorporated into power plants to stop particles being released into the atmosphere. It can also be used to decontaminate food.

Now, researchers have developed an exciting new use for the stuff – the eradication of potentially dangerous viruses floating in the air.

Indeed, cold plasma is so good at its job, it can kill 99.9 percent of airborne viruses, researchers at the University of Michigan found. Their research is published in the Journal of Physics D: Applied Physics.

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