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Category: particle physics – Page 450

Excitons are quasiparticles made from the excited state of electrons and—according to research being carried out EPFL—have the potential to boost the energy efficiency of our everyday devices.

It’s a whole new way of thinking about electronics. Excitons—or quasiparticles formed when electrons absorb light—stand to revolutionize the building blocks of circuits. Scientists at EPFL have been studying their extraordinary properties in order to design more energy-efficient electronic systems, and have now found a way to better control excitons moving in semiconductors. Their findings appear today in Nature Nanotechnology.

Quasiparticles are temporary phenomena resulting from the interaction between two particles within solid matter. Excitons are created when an electron absorbs a photon and moves into a higher energy state, leaving behind a hole in its previous energy state (called a “valence band” in band theory). The electron and electron hole are bound together through attractive forces, and the two together form what is called an exciton. Once the electron falls back into the hole, it emits a photon and the exciton ceases to exist.

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The characteristics of a new, iron-containing type of material that is thought to have future applications in nanotechnology and spintronics have been determined at Purdue University.

The native material, a topological , is an unusual type of three-dimensional (3D) system that has the interesting property of not significantly changing its when it changes electronic phases—unlike water, for example, which goes from ice to liquid to steam. More important, the material has an electrically conductive surface but a non-conducting (insulating) core.

However, once iron is introduced into the native material, during a process called doping, certain structural rearrangements and magnetic properties appear which have been found with high-performance computational methods.

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NASA launched the Juno mission to Jupiter on August 5, 2011. After a five-year flight, the spacecraft entered orbit on July 4, 2016.

Jupiter is the largest planet in the Solar System, with an equatorial diameter of 142,984 kilometers. It is so large that it could contain all of the other planets within its volume. Since Jupiter rotates in a mere 9.925 hours, its equatorial diameter is more than 9275 kilometers greater than the distance between its poles.

There are radiation belts around Jupiter, similar to the Van Allen radiation belts that surround Earth, except they are thousands of times more powerful. Juno’s electronics are, therefore, enclosed within a titanium shell, so that the energetic particles trapped around Jupiter will not interfere with its systems.

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Oxford University researchers have, for the first time, generated a massive 10 billion entangled bits in silicon, taking an important step towards a real world quantum computer.

The researchers cooled a piece of phosphorus-doped silicon to within one degree of absolute zero and applied a magnetic field. This process lined up the spins of one electron per phosphorus atom. Then the scientists used carefully timed radio pulses to nudge the nuclei and electrons into an entangled state. Across the silicon crystal, this produced billions of entangled pairs.

Stephanie Simmons, researcher and lead author on the paper Entanglement in a solid-state spin ensemble — published in Nature, says that quantum computers really start to give classical computers a run for their money at a few dozen qubits, but her team is working to skip that stage altogether by going directly from a two-qubit system to one with 10 billion.

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A team of researchers at the University of California, Berkeley, has found a new way to measure gravity—by noting differences in atoms in a supposition state, suspended in the air by lasers. In their paper published in the journal Science, the group describes their new technique and explain why they believe it will be more useful than traditional methods.

Currently, the standard way to conduct gravity experiments is to drop things down shielded tubes and measure them as they whiz by instruments. In addition to giving researchers a very brief glimpse of gravitational interactions, such methods often fall prey to inadvertent stray magnetic fields. In this new effort, the researchers have found a way to measure gravity that does not involve dropping objects at all.

The new approach involved releasing a cloud of cesium atoms into the air in a small chamber and then using to split several of them into a superposition state. Once split, lasers were used to keep all the atoms in fixed positions with one of each pair raised slightly higher than its mate. The team then measured each atom’s wave particle duality, which is impacted by gravity. By measuring the difference in duality between the paired atoms (because of the difference in their distances from Earth), the researchers were able to come up with a measurement for gravity.

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A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons of unprecedented intensity. This has made it possible to observe the interaction of multiple photons in a single such pulse with electrons in the inner orbital shell of an atom.

In order to observe the ultrafast electron motion in the inner shells of atoms with short light pulses, the pulses must not only be ultrashort, but very bright, and the photons delivered must have sufficiently high energy. This combination of properties has been sought in laboratories around the world for the past 15 years. Physicists at the Laboratory for Attosecond Physics (LAP), a joint venture between the Ludwig-Maximilians-Universität Munich (LMU) and the Max Planck Institute of Quantum Optics (MPQ), have now succeeded in meeting the conditions necessary to achieve this goal. In their latest experiments, they have been able to observe the non-linear interaction of an attosecond pulse with electrons in one of the inner orbital shells around the atomic nucleus. In this context, the term ‘non-linear’ indicates that the interaction involves more than one photon (in this particular case two are involved).

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Circa 2016

Laser physicists in Munich have measured a photoionization — in which an electron exits a helium atom after excitation by light — for the first time with zeptosecond precision. A zeptosecond is a trillionth of a billionth of a second (10^−21 seconds). This is the greatest accuracy of time determination ever achieved, as well as the first absolute determination of the timescale of photoionization.

If light hits the two electrons of a helium atom, one must be incredibly fast to observe what occurs. Besides the ultra-short periods in which changes take place, quantum mechanics also comes into play. Laser physicists at the Max Planck Institute of Quantum Optics (MPQ), the Technical University of Munich (TUM) and the Ludwig Maximilians University (LMU) Munich have now measured such an event for the first time with zeptosecond precision.

Either the entire energy of a light particle (photon) can be absorbed by one of the electrons or a division can take place, if a photon hits the two electrons of a helium atom. Regardless of the energy transfer, one electron leaves the atom. This process is called photoemission, or photoelectric effect, and was explained by Albert Einstein at the beginning of last century.

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