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Quantum 2.0 Conference and Exhibition

Direct observation of geometric phase in dynamics around a conical intersection with a trapped ion analog quantum simulator

Christophe H. Valahu, V. C. Olaya-Agudelo, Ryan J. MacDonell, Tomas Navickas, Arjun D. Rao, Maverick J. Millican, Michael J. Biercuk, Ting Rei Tan, Ivan Kassal

Published Jan 1, 2023• 0 citations
Publisher

Abstract

We review our recent results in which we use trapped ions to observe geometric phase interference around a conical intersection [arXiv:2211.07320, 2022]. This is a key demonstration towards using mixed-qubit boson simulators to solve difficult chemical dynamics problems.
DOI
10.1364/quantum.2023.qm3a.3

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•Jul 23, 2020•3 citations
Conical intersections are common in molecular physics and photochemistry, and are often invoked to explain observed reaction products. A conical intersection can occur when an excited electronic potential energy surface intersects with the ground electronic potential energy surface in the coordinate space of the nuclear positions. Theory predicts that the conical intersection will result in a geometric phase for a wavepacket on the ground potential energy surface. Although conical intersections have been observed experimentally, the geometric phase has not been observed in a molecular system. Here we use a trapped atomic ion system to perform a quantum simulation of a conical intersection. The internal state of a trapped atomic ion serves as the electronic state and the motion of the atomic nuclei are encoded into the normal modes of motion of the ions. The simulated electronic potential is constructed by applying state-dependent forces to the ion with a near-resonant laser. We experimentally observe the geometric phase on the ground-state surface using adiabatic state preparation followed by motional state measurement. Our experiment shows the advantage of combining spin and motion degrees of freedom in a quantum simulator.
Analog quantum simulators, which efficiently represent model systems, have the potential to provide new insight toward naturally occurring phenomena beyond the capabilities of classical computers.Incorporating dissipation as a resource unlocks a wider range of out-of-equilibrium processes such as chemical reactions.Here, we operate a hybrid qubit-oscillator circuit quantum electrodynamics simulator and model nonadiabatic molecular dynamics through a conical intersection.We identify dephasing of the electronic qubit as the mechanism that drives wave-packet branching when the corresponding oscillator undergoes large amplitude motion.Furthermore, we directly observe enhanced branching when the wave-packet passes through the conical intersection.Thus, the forces that influence a chemical reaction can be viewed from the perspective of measurement backaction in quantum mechanics-there is an effective measurement-induced dephasing rate that depends on the position of the wave packet relative to the conical intersection.Our results set the groundwork for more complex simulations of chemical dynamics using quantum simulators, offering deeper insight into the role of dissipation in determining macroscopic quantities of interest such as the quantum yield of a chemical reaction.
Conical intersections (CIs) between energy surfaces arise in various physical contexts. A rich example, involving the interaction of a qubit with a bosonic field, is the energy landscape of the asymmetric quantum Rabi model (AQRM). Conventional approximations for this model, including the slow-qubit approximation, fail to capture the correct location of the CIs. To go beyond this limitation, we introduce a relatively simple solvable light-matter interaction model, which by construction, shares the same CIs as the AQRM. As a demonstration of the use of this simplified model we calculate the geometric phases around CIs in the energy landscape. We find that the geometric phases acquired by closed loops in parameter space around CIs are multiples of π\piπ, depending on the CIs encircled by the trajectories considered. These results are seen to be in agreement with numerical results for the corresponding geometric phases of the AQRM.