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An international team of researchers from the Max Born Institute in Berlin, University College London and ELI-ALPS in Szeged, Hungary, has demonstrated attosecond-pump attosecond-probe spectroscopy to study non-linear multi-photon ionization of atoms. The obtained results provide insights into one of the most fundamental processes in non-linear optics.

The detailed experimental and theoretical results have been published in Optica (“Attosecond investigation of extreme-ultraviolet multi-photon multi-electron ionization”).

Fig. 1: Two intense attosecond pulse trains (white) interact with an atom, resulting in the emission of three electrons (yellow). During this process four photons (blue) are absorbed. The probability of this process can be controlled by varying the temporal and the spatial overlap between the two attosecond pulses. (Image: Balázs Major)

A team of researchers affiliated with multiple institutions in the U.S., including Google Quantum AI, and a colleague in Australia, has developed a theory suggesting that quantum computers should be exponentially faster on some learning tasks than classical machines. In their paper published in the journal Science, the group describes their theory and results when tested on Google’s Sycamore quantum computer. Vedran Dunjko with Leiden University City has published a Perspective piece in the same journal issue outlining the idea behind combining quantum computing with machine learning to provide a new level of computer-based learning systems.

Machine learning is a system by which computers trained with datasets make informed guesses about new data. And quantum computing involves using sub-atomic particles to represent qubits as a means for conducting applications many times faster than is possible with classical computers. In this new effort, the researchers considered the idea of running machine-learning applications on quantum computers, possibly making them better at learning, and thus more useful.

To find out if the idea might be possible, and more importantly, if the results would be better than those achieved on classical computers, the researchers posed the problem in a novel way—they devised a machine learning task that would learn via experiments repeated many times over. They then developed theories describing how a quantum system could be used to conduct such experiments and to learn from them. They found that they were able to prove that a quantum computer could do it, and that it could do it much better than a classical system. In fact, they found a reduction in the required number of experiments needed to learn a concept to be four orders of magnitude lower than for classical systems. The researchers then built such a system and tested it on Google’s Sycamore quantum computer and confirmed their theory.

Nuclear fusion is a widely studied process through which atomic nuclei of a low atomic number fuse together to form a heavier nucleus, while releasing a large amount of energy. Nuclear fusion reactions can be produced using a method known as inertial confinement fusion, which entails the use of powerful lasers to implode a fuel capsule and produce plasma.

Researchers at Massachusetts Institute of Technology (MIT), University of Delaware, University of Rochester, the Lawrence Livermore National Laboratory, Imperial College London, and University of Rome La Sapienza have recently showed what happens to this implosion when one applies a strong magnetic field to the fuel capsule used for inertial confinement fusion. Their paper, published in Physical Review Letters, demonstrates that strong magnetic fields flatten the shape of inertial fusion implosions.

“In inertial confinement fusion, a millimeter-size spherical capsule is imploded using high-power lasers for nuclear fusion,” Arijit Bose, one of the researchers who carried out the study, told Phys.org. “Applying a magnetic field to the implosions can strap the charged plasma particles to the B-field and improve their chances of fusion. However, since magnetic field can restrict plasma particle motion only in the direction across the field lines and not in the direction along the applied field lines, this can introduce differences between the two directions that affect the implosion shape.”

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Noise in an electronic circuit is a nuisance that can scramble information or reduce a detector’s sensitivity. But noise also offers a way to learn about the microscopic quantum mechanisms at play in a material or device. By measuring a circuit’s “shot noise,” a form of white noise, researchers have previously shed light on conduction in quantum Hall and spintronic systems, for instance. Now, a collaboration led by Oren Tal at the Weizmann Institute of Science, Israel, and by Dvira Segal at the University of Toronto, Canada, has shown that an easier-to-measure form of noise, called “flicker noise,” can also be a powerful probe of quantum effects [1].

Continue reading “Pink Noise as a Probe of Quantum Transport” »

Researchers have cooled indium atoms to a temperature close to 1 mK, making indium the first group-III atom to be made ultracold.

At temperatures near to absolute zero, atoms move slower than a three-toed sloth, allowing physicists to gain unprecedented experimental control over these systems. New phases of matter can form when atoms become ultracold and quirky quantum properties can emerge, yet much of the periodic table remains unexplored in the ultracold regime. Now, Travis Nicholson of the National University of Singapore and colleagues have successfully cooled indium to close to 1 mK [1]. Indium is the first “main group-III” atom—a specific group of transition metals on the periodic table—to be cooled to such a low temperature. The demonstration opens the door to studying systems with properties previously unexplored by ultracold physicists.

For their experiments, Nicholson and colleagues used a magneto-optical trap—a standard tool for trapping and cooling atoms. But because this was the first attempt at making indium atoms ultracold, the team had to make their own version of the apparatus rather than using one designed to cool other atoms. “The systems used for this research are highly customized to specific atoms,” Nicholson says. So every part of the setup from designing the laser systems to picking the screws had to be “hashed out by us.” With their custom setup, the group loaded 500,000,000 indium atoms into the trap using a laser beam and then cooled them.

Imagining our everyday life without lasers is difficult. We use lasers in printers, CD players, pointers, measuring devices, etc. What makes lasers so special is that they use coherent waves of light: all the light inside a laser vibrates completely in sync.

Meanwhile, quantum mechanics tells us that particles like atoms should also be considered waves. As a result, we can build ‘atom lasers’ containing coherent waves of matter. But can we make these matter waves last so they may be used in applications? In research that was published in Nature, a team of Amsterdam physicists shows that the answer to this question is affirmative.

The particle-smashing machine has fired up again — sparking fresh hope it can find unusual results.

Circa 2022

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Physicists have found evidence of rare X particles in the quark-gluon plasma produced in the Large Hadron Collider (LHC) at CERN. The findings could redefine the kinds of particles that were abundant in the early universe.

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Differing values of the Hubble constant might be reconciled via the dark sector.