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Category: quantum physics – Page 521

Probability of a reaction occurring increases 100-fold and points to quantum control of chemistry.

A new step towards quantum control of chemistry has been achieved by researchers in the US, who found that tuning the magnetic field applied to colliding ultracold molecules could alter the probability of them reacting or undergoing inelastic scattering a 100-fold.1 The work could potentially prove useful for producing large ensembles of molecules in the same state and investigating their properties.

At room temperature, the random thermal motion of atoms and molecules blurs the quantum nature of chemistry. In an ultracold regime, however, this thermal motion is stilled, revealing chemical interactions as quantum interference processes between matter waves. Remarkable phenomena have been seen in ultracold atomic gases, such as the creation of Bose–Einstein condensates, in which atoms all enter the quantum ground state of a trap, allowing a macroscopic view of their quantum wavefunction. Wolfgang Ketterle at the Massachusetts Institute of Technology (MIT), whose group performed the new research, shared the 2001 physics Nobel prize for the creation of this condensate.

Cooling molecules to the ground state of a trap is much trickier than cooling atoms because they can contain thermal energy in so many internal degrees of freedom, and was only achieved by Jun Ye of JILA in the US and colleagues recently.2 In 2020, Ye’s group applied an electric field to potassium–rubidium molecules, which decay into diatomic potassium and rubidium molecules. The researchers showed that, at a specific field, the molecules were excited into states forbidden by quantum mechanics and could get close enough to react. This drastically slowed the decay rate. ‘For our system, we typically think that, if the two molecules get very close together, there is close to a 100% chance that they will undergo a chemical reaction,’ explains Kyle Matsuda, Ye’s PhD student and the 2020 paper’s lead author.

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A mathematical analysis helps illuminate the puzzle over how information escapes from a black hole.

A RIKEN physicist and two colleagues have found that a wormhole—a bridge connecting distant regions of the Universe—helps to shed light on the mystery of what happens to information about matter consumed by black holes.

Einstein’s theory of general relativity predicts that nothing that falls into a black hole can escape its clutches. But in the 1970s, Stephen Hawking calculated that black holes should emit radiation when quantum mechanics, the theory governing the microscopic realm, is considered. “This is called black hole evaporation because the black hole shrinks, just like an evaporating water droplet,” explains Kanato Goto of the RIKEN Interdisciplinary Theoretical and Mathematical Sciences.

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Identifying the shape of massive astronomical object is not a simple task. Even with recent observations of gravitational waves the mass and angular momentum of the object remain known with large uncertainty. Moreover, it exists exotic objects, as wormholes who can mimic the shape of black holes for example. The gravitational spectrum of wormholes has a wide range of interpretations. A current challenge addressed by researcher R. A. Konoplya consists of mathematically describing wormholes in order to be able to eventually identify them in the space.

According to current theory a wormhole is a theoretical passage through space-time that could create shortcuts in the universe. The original wormhole solution was discovered by Einstein and Rosen (ER) in 1935 and later John Wheeler has shown their importance in quantum gravity. It was then discovered that it was possible to construct “traversable” wormhole solutions since the ER=EPR proposal. It also appears the quantum fluctuations of the space-time are such that a tiny wormhole could connect Planckian pixel with the entanglement mechanism of quantum space-time itself.

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Time only moves forward—or does it?

Physicists refer to this idea as the “arrow of time,” and the idea of unidirectional time seems to hold true for life and objects on a human scale. But on a quantum scale, things seem to work differently, even strangely.

For physicists, the arrow of time is dictated by the second law of thermodynamics, which says that disorder (or entropy) increases over time. The transfer of heat is a perfect example of this. On a chilly day, you’d expect your coffee to get colder if the air around it is cooler. Heat scatters in the presence of lower temperatures; it doesn’t concentrate.

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Many people say that Einstein failed because he was simply ahead of his time. The knowledge and tools needed to complete a unified theory simply hadn’t been developed before Einstein died in 1955.

Today, many physicists are taking up his quest. The most promising approach appears to be string theory, which requires 10 or more dimensions and describes all elementary particles as vibrating strings, with different modes of vibration producing different particles.

String theory has not yet made any testable predictions, and some scientists worry that string theorists have, like Einstein in his later years, strayed too far from physical reality in their obsession with beautiful mathematics. But many others believe string theory does indeed hold the key to completing Einstein’s quest, and researchers are hoping to find ways to test some of the predictions of string theory.

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To classify as a DTC, a system also needs to be truly many-body, and its coherence times (that is, the time over which fragile quantum states persist without being destroyed by interactions with their environment) must be long enough that its periodic variations are not mistaken for a short-term system change. Finally, one must be able to prepare the system in arbitrary initial states and show that all of them result in similar DTC behaviour.

A major milestone

The Melbourne team’s work, which is described in Science Advances, builds on earlier reports of DTCs that used quantum processors based on nine nuclear spins in diamond and 20 superconducting qubits. As in these previous experiments, the team turned a quantum computer into an experimental platform — a quantum simulator – in which all the requirements of DTCs could be met.

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Researchers have proposed a novel principle for a unique kind of computer that would use analog technology in place of digital or quantum components.

The unique device would be able to carry out complex computations extremely quickly—possibly, even faster than today’s supercomputers and at vastly less cost than any existing quantum computers.

The principle uses to overcome the barriers in optimization problems (choosing the best option from a large number of possibilities), such as Google searches—which aim to find the optimal results matching the search request.

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The development of functional nanomaterials has been a major landmark in the history of materials science. Nanoparticles with diameters ranging from 5 to 500 nm have unprecedented properties, such as high catalytic activity, compared to their bulk material counterparts. Moreover, as particles become smaller, exotic quantum phenomena become more prominent. This has enabled scientists to produce materials and devices with characteristics that had been only dreamed of, especially in the fields of electronics, catalysis, and optics.

But what if we go smaller? Sub-nanoparticles (SNPs) with particle sizes of around 1 nm are now considered a new class of materials with distinct properties due to the predominance of quantum effects. The untapped potential of SNPs caught the attention of scientists from Tokyo Tech, who are currently undertaking the challenges arising in this mostly unexplored field. In a recent study published in the Journal of the American Chemical Society, a team of scientists from the Laboratory of Chemistry and Life Sciences, led by Dr. Takamasa Tsukamoto, demonstrated a novel molecular screening approach to find promising SNPs.

As one would expect, the synthesis of SNPs is plagued by technical difficulties, even more so for those containing multiple elements. Dr. Tsukamoto explains: “Even SNPs containing just two different elements have barely been investigated because producing a system of subnanometer scale requires fine control of the composition ratio and particle size with atomic precision.” However, this team of scientists had already developed a novel method by which SNPs could be made from different metal salts with extreme control over the total number of atoms and the proportion of each element.

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What happens to information after it has passed beyond the event horizon of a black hole? There have been suggestions that the geometry of wormholes might help us solve this vexing problem – but the math has been tricky, to say the least.

In a new paper, an international team of physicists has found a workaround for better understanding how a collapsing black hole can avoid breaking the fundamental laws of quantum physics (more on that in a bit).

Although highly theoretical, the work suggests there are likely things we are missing in the quest to resolve general relativity with quantum mechanics.

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Superconductors—metals in which electricity flows without resistance—hold promise as the defining material of the near future, according to physicist Brad Ramshaw, and are already used in medical imaging machines, drug discovery research and quantum computers being built by Google and IBM.

However, the super-low temperatures need to function—a few degrees above absolute zero—make them too expensive for wide use.

In their quest to find more useful superconductors, Ramshaw, the Dick & Dale Reis Johnson Assistant Professor of physics in the College of Arts and Sciences (A&S), and colleagues have discovered that magnetism is key to understanding the behavior of electrons in “high-temperature” superconductors. With this finding, they’ve solved a 30-year-old mystery surrounding this class of superconductors, which function at much higher temperatures, greater than 100 degrees above absolute zero. Their paper, “Fermi Surface Transformation at the Pseudogap Critical Point of a Cuprate Superconductor,” published in Nature Physics March 10.

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