Quantum simulator helps to unlock a major science mystery

"That constraint, called a geometric phase, isn't impossible to measure, but nobody has been able to do it." Until now. 

To navigate this intricate quantum terrain, the researchers employed a quantum simulator—a tool inspired by the realm of quantum computing. 

This innovative approach addresses a longstanding question in chemistry, a fundamental inquiry with applications from the natural processes of photosynthesis to the mysteries of vision and photocatalysis. 

The study exemplifies how the strides made in quantum computing are now being harnessed to unlock the secrets of fundamental science.

What is a conical intersection?

Conical intersection may sound complicated but Phys.org provides a digestable explanation. That is, conical intersection is like two peaks of a mountain touching at their tips. 

The bottom half symbolizes the energy states and locations of an unexcited molecule. The top half represents the same molecule with electrons excited due to energy absorption from incoming light particles. 

The molecule's atoms then rearrange themselves to revert to a lower energy state, either successfully transitioning or releasing excess energy.

Here, the quantum realm comes into play. The molecule, electrons, and atoms exhibit quantum effects—occupying multiple states simultaneously.

This phenomenon can be likened to a blanket draped over various parts of a mountain landscape. However, specific transformations become forbidden due to a mathematical peculiarity known as the geometric phase; the metaphorical blanket can't fully wrap around the entire mountain.

"It's an effect that's hard to gain intuition for, because geometric phase is weird even from a quantum mechanical standpoint," explained Jacob Whitlow, a doctoral student working in Brown's laboratory.

Remarkably, the researchers achieved these insights using trapped ions, a controlled environment that simplified the experimental setup. 

The ions, with their quantum dynamics occurring at a slower pace, enabled direct measurements of the geometric phase—a phenomenon that appears as a crescent moon-shaped graph.

The beauty of trapped ions is that they get rid of the complicated environment and make the system clean enough to make these measurements," Brown emphasized.

Intriguingly, an independent study at the University of Sydney, Australia, confirmed Duke's findings, providing consistent observations using an ion trap quantum simulator. While technical details varied, the overarching conclusions aligned, showcasing the power of quantum simulators.

As the boundaries of quantum understanding continue to expand, this research paves the way for a deeper comprehension of the intricacies governing fundamental chemical processes.  Quantum simulators emerge as the guiding light, illuminating the path towards unlocking nature's most enigmatic phenomena.

The full study was published in Nature Chemistry on August 28 and can be found here.

Study abstract:

Conical intersections often control the reaction products of photochemical processes and occur when two electronic potential energy surfaces intersect. Theory predicts that the conical intersection will result in a geometric phase for a wavepacket on the ground potential energy surface, and although conical intersections have been observed experimentally, the geometric phase has not been directly observed in a molecular system. Here we use a trapped atomic ion system to perform a quantum simulation of a conical intersection. The ion’s internal state serves as the electronic state, and the motion of the atomic nuclei is encoded into the motion of the ions. The simulated electronic potential is constructed by applying state-dependent optical forces to the ion. We experimentally observe a clear manifestation of the geometric phase using adiabatic state preparation followed by motional state measurement. Our experiment shows the advantage of combining spin and motion degrees for quantum simulation of chemical reactions.