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Over eighty years ago, Rabi oscillations were proposed to describe the strong coupling and population transfer in a two-level quantum system exposed to an oscillatory driving field. As compared to atoms, molecules have an extra degree of vibration, which adds an additional knob to the Rabi oscillations in light-molecule interactions. However, how such a laser-driven Rabi oscillation during the stretching of molecular bonds determines the kinetic energy release (KER) spectrum of dissociative fragments is still an open question.

In a new article published in Light: Science & Applications, a joint team of scientists, led by Professor Feng He from Shanghai Jiao Tong University and Professor Jian Wu from East China Normal University has investigated Rabi oscillations in a stretching molecule and discovered the strong-field-induced dissociation dynamics beyond the well-accepted resonant one-photon dissociation scenario. During the dissociation of the simplest molecular ion of H₂⁺, coupled with the laser field, the electron hops between the 1sσ_g and 2pσ_u states, forming the Rabi oscillations.

The ionization-created nuclear wave packet (NWP) may propagate alternatively along the two potential energy curves towards a larger internuclear distance monotonically, termed as the rolling process, or may propagate outwards along the 2pσ_u curve followed by the inward propagation in the 1sσ_g curve and then be relaunched to 2pσ_u state again followed by subsequent dissociation, termed as the looping process. The rolling and looping dissociation pathways lead to different KERs of the ejected dissociative fragments, which have been verified by comparing experimental measurements with quantum simulation results.

Experts assembling sPHENIX, a state-of-the-art particle detector at the U.S. Department of Energy’s Brookhaven National Laboratory, successfully installed a major tracking component on Jan. 19. The Time Projection Chamber, or TPC, is one of the final pieces to move into place before sPHENIX begins tracking particle smash-ups at the Relativistic Heavy Ion Collider (RHIC) this spring.

The TPC is a gas-filled detector that, combined with the detector’s strong magnetic field, allows nuclear physicists to measure the momentum of charged particles streaming from RHIC collisions. It is one of many detector components that nuclear physicists will use to glean more information about the quark-gluon plasma (QGP)—a primordial soup made up of matter’s fundamental building blocks, quarks and gluons.

“QGP existed at the dawn of the universe some 14 billion years ago, about a millionth of a second after the Big Bang,” said Thomas Hemmick, a physicist at Stony Brook University (SBU) and a collaborator on RHIC research “RHIC’s collisions and sPHENIX’s ability to capture snapshots of particles traversing the QGP will help scientists understand how quarks and gluons cooled and coalesced to form the protons and neutrons that make up the atomic nuclei of all visible matter in the universe today.”

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What is time? Does the past still exist? How did the universe begin and how will it end? Do particles think? Was the universe made for us? Why doesn’t anyone ever get younger? Has physics ruled out free will? Will we ever have a theory of everything? According to Sabine Hossenfelder, it is not a coincidence that quantum entanglement and vacuum energy have become the go-to explanations of alternative healers, or that people believe their deceased grandmother is still alive because of quantum mechanics. Science and religion have the same roots, and they still tackle some of the same questions: Where do we come from? Where do we go to? How much can we know? The area of science that is closest to answering these questions is physics. Over the last century, physicists have learned a lot about which spiritual ideas are still compatible with the laws of nature. Not always, though, have they stayed on the scientific side of the debate.

Continue reading “Free Will and Determinism from a Physicist’s Perspective (Sabine Hossenfelder)” »

It is “designed to use an inherently safe and extremely robust fuel form.”

The future of deep space exploration is near. Rolls-Royce revealed a new image of a micro-reactor for space that it says is “designed to use an inherently safe and extremely robust fuel form.”

The iconic engineering firm recently tweeted the image alongside a caption. It is designing the nuclear fission system as part of an agreement it penned with the UK Space Agency in 2021.

Continue reading “Rolls-Royce’s new micro-reactor design could send humans to Mars” »

The performance of some quantum technologies could be boosted by exploiting interactions between nitrogen-vacancy (NV) centres and defects on the surface of diamond – according to research done by two independent teams of scientists in the US.

NV centres in diamond have emerged as a promising solid-state platform for quantum sensing and information processing. They are defects in the diamond lattice in which two carbon atoms are replaced with a single nitrogen atom, leaving one lattice site vacant. NV centres are a two-level spin system into which quantum information can be written and read out using laser light and microwaves. An important property of NV centres is that once they have been put into a specific quantum state, they can remain in that state for a relatively long “coherence” time – which makes them technologically useful.

Professors Miguel Ángel Herrada of the University of Seville and Jens G. Eggers of the University of Bristol have uncovered a mechanism that explains the erratic movement of bubbles rising in water. The findings, published in the prestigious journal Proceedings of the National Academy of Sciences, could provide insights into the behavior of particles that fall between solid and gas states.

Leonardo da Vinci observed five centuries ago that air bubbles, if big enough, periodically deviate in a zigzag or spiral from a straight-line movement. However, no quantitative description of the phenomenon or physical mechanism to explain this periodic motion had ever been found.

Physicists are increasingly using ultracold molecules to study quantum states of matter. Many researchers contend that molecules have advantages over other alternatives, such as trapped ions, atoms or photons. These advantages suggest that molecular systems will play important roles in emerging quantum technologies. But, for a while now, research into molecular systems has advanced only so far because of long-standing challenges in preparing, controlling and observing molecules in a quantum regime.

Now, as chronicled in a study published in Nature (“Probing site-resolved correlations in a spin system of ultracold molecules”), Princeton researchers have achieved a major breakthrough by microscopically studying molecular gases at a level never before achieved by previous research. The Princeton team, led by Waseem Bakr, associate professor of physics, was able to cool molecules down to ultracold temperatures, load them into an artificial crystal of light known as an optical lattice, and study their collective quantum behavior with high spatial resolution such that each individual molecule could be observed.

“We prepared the molecules in the gas in a well-defined internal and motional quantum state. The strong interactions between the molecules gave rise to subtle quantum correlations which we were able to detect for the first time,” said Bakr.

Spintronics is a technology that utilizes the spin of electrons — in addition to their charge — in order to store and process information. Unlike traditional electronics, which rely on the movement of electrons to perform their functions, spintronics uses the intrinsic angular momentum of electrons to achieve the same results. Spintronics offers the potential to address some limitations of traditional, charge-based computing and it has the potential for developing new types of devices such as spin-based transistors and logic gates.

Accidental discovery shows that N-heterocyclic carbenes can act as sources of atomic carbon.