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.

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.

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.