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Category: quantum physics – Page 620

Circa 2019

Google claims it has designed a machine that needs only 200 seconds to solve a problem that would take the world’s fastest supercomputer 10,000 years to figure out.

The speed achieved by the computer represents a breakthrough called “quantum supremacy,” according to a blog post from the company and an accompanying article in the scientific journal Nature.

The results announced Wednesday herald the rise of quantum computers, which can store and process much more information than their classical cousins by tapping into the powerful forces contained in the field of physics known as quantum mechanics.

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“The best-kept secret in quantum computing.” That’s what Cambridge Quantum Computing (CQC) CEO Ilyas Khan called Honeywell’s efforts in building the world’s most powerful quantum computer. In a race where most of the major players are vying for attention, Honeywell has quietly worked on its efforts for the last few years (and under strict NDA’s, it seems). But today, the company announced a major breakthrough that it claims will allow it to launch the world’s most powerful quantum computer within the next three months.

In addition, Honeywell also today announced that it has made strategic investments in CQC and Zapata Computing, both of which focus on the software side of quantum computing. The company has also partnered with JPMorgan Chase to develop quantum algorithms using Honeywell’s quantum computer. The company also recently announced a partnership with Microsoft.

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In 1966, Japanese physicist Yosuke Nagaoka predicted the existence of a rather striking phenomenon: Nagaoka’s ferromagnetism. His rigorous theory explains how materials can become magnetic, with one caveat: the specific conditions he described do not arise naturally in any material. Researchers from QuTech, a collaboration between TU Delft and TNO, have now observed experimental signatures of Nagaoka ferromagnetism using an engineered quantum system. The results were published today in Nature.

Familiar magnets such as the ones on your refrigerator are an everyday example of a phenomenon called . Each electron has a property called ‘spin’, which causes it to behave like a miniscule magnet itself. In a ferromagnet, the spins of many electrons align, combining into one large magnetic field. This seems like a simple concept, but Nagaoka predicted a novel and surprising mechanism by which ferromagnetism could occur—one that had not been observed in any system before.

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If it works, they would be able to input quantum information into one “black hole” circuit, which would scramble, then consume it. After a little while, that information would pop out of the second circuit, already unscrambled and decrypted. That sets it apart from existing quantum teleportation techniques, Quanta reports, as transmitted information emerges still fully scrambled and then needs to be decrypted, making the process take longer and be less accurate as an error-prone quantum computer tries to recreate the original message.

While the idea of entangled black holes and wormholes conjures sci-fi notions of intrepid explorers warping throughout the cosmos, that’s not quite what’s happening here.

Rather, it’s an evocative way to improve quantum computing technology. Recreating and entangling the bizarre properties of black holes, University of California, Berkely researcher Norman Yao told Quanta, would “allow teleportation on the fastest possible timescale.”

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A group of scientists from the RIKEN Center for Emergent Matter Science in Japan has succeeded in taking repeated measurements of the spin of an electron in a silicon quantum dot (QD) without changing its spin in the process. This type of “non-demolition” measurement is important for creating quantum computers that are fault-tolerant. Quantum computers would make it easier to perform certain classes of calculations such as many-body problems, which are extremely difficult and time-consuming for conventional computers. Essentially, the involve measuring a quantum value that is never in a single state like a conventional transistor, but instead exists as a “superimposed state”—in the same way that Schrodinger’s famous cat cannot be said to be alive or dead until it is observed. Using such systems, it is possible to conduct calculations with a qubit that is a superimposition of two values, and then determine statistically what the correct result is. Quantum computers that use single electron spins in silicon QDs are seen as attractive due to their potential scalability and because silicon is already widely used in electronics technology.

The key difficulty with developing quantum computers, however, is that they are very sensitive to external noise, making error correction critical. So far, researchers have succeeded in developing single electron spins in silicon QDs with a long information retention time and high-precision quantum operation, but quantum non-demolition measurement—a key to effective error correction—has proven elusive. The conventional method for reading out single electron spins in silicon is to convert the spins into charges that can be rapidly detected, but unfortunately, the electron spin is affected by the detection process.

Now, in research published in Nature Communications, the RIKEN team has achieved such non-demolition measurement. The key insight that allowed the group to make the advance was to use the Ising type interaction model—a model of ferromagnetism that looks at how the electron spins of neighboring atoms become aligned, leading to the formation of ferromagnetism in the entire lattice. Essentially, they were able to transfer the spin information—up or down—of an electron in a QD to another electron in the neighboring QD using the Ising type interaction in a magnetic field, and then could measure the spin of the neighbor using the conventional method, so that they could leave the original spin unaffected, and could carry out repeated and rapid measurements of the neighbor.

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Materials that exhibit topological phases can be classified by their dimensionality, symmetries and topological invariants to form conductive-edge states with peculiar transport and spin properties. For example, the quantum Hall effect can arise in two-dimensional (2-D) electron systems subjected to a perpendicular magnetic field. When distinct characteristics of quantum Hall systems are compared with time-reversal symmetric (entropy conserved) topological insulators (TIs), they appear to rely on Coulomb interactions between electrons to induce a wealth of strongly correlated, topologically or symmetry-projected phases in a variety of experimental systems.

In a new report now on Science, Louis Veyrat and a research team in materials science, and optoelectronics in France, China and Japan tuned the ground state of the graphene zeroth Landau level i.e. orbitals occupied by charged particles with discrete energy values. Using suitable screening of the Coulomb interaction with the high dielectric constant of a strontium titanate (SrTiO3) substrate, they observed robust helical edge transport at magnetic fields as low as 1 Tesla, withstanding temperatures of up to 110 kelvin across micron-long distances. These versatile graphene platforms will have applications in spintronics and topological quantum computation.

Topological insulators (TIs), i.e., a material that behaves as an insulator in its interior but retains a conducting surface state, with zero Chern number have emerged as quantum Hall (QHTIs) arising from many-body interacting Landau levels. They can be pictured as two independent copies of quantum Hall systems with opposite chirality, but the experimental system is at odds with the described scenario, where a strong insulating state is observed on increasing the perpendicular in charge-neutral, high-mobility graphene devices.

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At a quantum level, the vanishingly tiny particles that make up the building blocks of everything don’t even have a set location, just a smear of possible positions dictated by complex rules of probability.

And theoretical physicist Sean Carroll is entirely happy with that. He says that the fact that tiny particles like electrons and photons don’t have one set place in the universe is evidence that there are many parallel universes.

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