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Category: particle physics – Page 220

One thing all quantum computers have in common is the fact that they manipulate information encoded in quantum states. But that’s where the similarities end, because those quantum states can be induced in everything from superconducting circuits to trapped ions, ultra-cooled atoms, photons, and even silicon chips.

While some of these approaches have attracted more investment than others, we’re still a long way from the industry settling on a common platform. And in the world of academic research, experimentation still abounds.

Now, a team from the University of Chicago has taken crucial first steps towards building a quantum computer that can encode information in phonons, the fundamental quantum units that make up sound waves in much the same way that photons make up light beams.

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Scientists have demonstrated entanglement and two-particle interference with phonon using an acoustic beam splitter.

Phonons are to sound what photons are to light. Photons are tiny packets of energy for light or electromagnetic waves. Similarly, phonons are packets of energy for sound waves. Each phonon represents the vibration of millions of atoms within a material.

Both photons and phonons are of central interest to quantum computing research, which exploits the properties of these quantum particles. However, phonons have proven challenging to study due to their susceptibility to noise and issues with scalability and detection.

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Quantum information (QI) processing may be the next game changer in the evolution of technology, by providing unprecedented computational capabilities, security and detection sensitivities. Qubits, the basic hardware element for quantum information, are the building block for quantum computers and quantum information processing, but there is still much debate on which types of qubits are actually the best.

Research and development in this field is growing at astonishing paces to see which system or platform outruns the other. To mention a few, platforms as diverse as superconducting Josephson junctions, trapped ions, topological qubits, ultra-cold neutral atoms, or even diamond vacancies constitute the zoo of possibilities to make qubits.

So far, only a handful of platforms have been demonstrated to have the potential for quantum computing, marking the checklist of high-fidelity controlled gates, easy qubit-qubit coupling, and good isolation from the environment, which means sufficiently long-lived coherence.

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Black holes, cosmic power stations, fuel the luminosity of quasars and active galactic nuclei (AGNs) through their intricate interaction of matter, gravity, and magnetic forces. Despite black holes themselves not possessing a magnetic field, the surrounding dense plasma in the accretion disc does. As this plasma orbits the black hole, its charged particles generate an electric current and consequently a magnetic field.

This magnetic field, assumed to be stable due to the unvarying plasma flow, caused scientists to scratch their heads when they found evidence of its directional change. Such a phenomenon, known as a magnetic reversal, is akin to an imaginary pole of a magnet switching from north to south or vice versa. While not uncommon in stars, and even witnessed in the Sun’s 11-year sunspot cycle or Earth’s infrequent magnetic shifts, such an event was thought improbable for supermassive black holes.

In 2018, a computer-aided sky survey detected a startling transformation in a galaxy 239 million light-years away named 1ES 1927+654, which had suddenly become a hundredfold brighter. Swift Observatory soon reported x-ray and ultraviolet light emissions from this region. Initial speculations suggested a tidal disruption event caused by a star venturing too close to the galaxy’s central supermassive black hole, disrupting gas flow into the accretion disc, as the reason for this unusual luminosity.

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Researchers discovered only relatively recently that black hole jets emit X-rays, and how the jets accelerate particles to this high-energy state is still a mystery. Surprising new findings in Nature Astronomy appear to rule out one leading theory, opening the door to reimagining how particle acceleration works in the jets—and possibly also elsewhere in the universe.

One leading model of how jets generate X-rays expects the jets’ X-ray emissions to remain stable over long time scales (millions of years). However, the new paper found that the X-ray emissions of a statistically significant number of jets varied over just a few years.

“One of the reasons we’re excited about the variability is that there are two main models for how X-rays are produced in these jets, and they’re completely different,” explains lead author Eileen Meyer, an astronomer at University of Maryland, Baltimore County. “One model invokes very low-energy electrons and one has very high-energy electrons. And one of those models is completely incompatible with any kind of variability.”

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The BEC phenomenon was first predicted by Satyendra Bose and Albert Einstein: when a given number of identical Bose particles approach each other sufficiently closely, and move sufficiently slowly, they will collectively convert to the lowest energy state: a BEC. This occurs when atoms are chilled to very low temperatures. The wavelike nature of atoms allows them to spread out and even overlap. If the density is high enough, and the temperature low enough (mere billionths of degrees above absolute zero), the atoms will behave like the photons in a laser: they will be in a coherent state and constitute a single “super atom.”

JILA’s Carl Wieman (University of Colorado, Boulder) and Eric Cornell (NIST) first started searching for a BEC around 1990 with a combination laser and magnetic cooling apparatus. Wieman pioneered the use of $200 diode lasers (the same type used in CD players) instead of the $150,000 lasers other groups were using. His approach was initially met with skepticism by his colleagues, but when he began to report real progress, several other groups joined the race to achieve the first BEC. Beginning with rubidium gas atoms at room temperature, the JILA team first slowed the rubidium and captured it in a trap created by laser light. This cooled the atoms to about 10 millionths of a degree above absolute zero—still far too hot to produce a BEC.

Once trapped, the lasers are turned off and the atoms are held in place by a magnetic field. The atoms are further cooled in the magnetic trap by selecting the hottest atoms and kicking them out of the trap. Then came the tricky part: trapping a sufficiently high density of atoms at temperatures that were cold enough to produce a BEC. To do this, Wieman and his colleagues had to devise a time-averaged orbiting potential trap (an improvement to the standard magnetic trap).

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