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 $\pi$ , 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.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 $\pi$, 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.

Jul 23, 20203 citations

Quantum Fields and Particles

Springer eBooksDec 12, 20050 citations

Quantum Computation of Conical Intersections on a Programmable Superconducting Quantum Processor

Shoukuan Zhao, Diandong Tang, Xiaoxiao Xiao +7 more

Conical intersections (CIs) are pivotal in many photochemical processes. Traditional quantum chemistry methods, such as the state-average multiconfigurational methods, face computational hurdles in solving the electronic Schrödinger equation within the active space on classical computers. While quantum computing offers a potential solution, its feasibility in studying CIs, particularly on real quantum hardware, remains largely unexplored. Here, we present the first successful realization of a hybrid quantum-classical state-average complete active space self-consistent field method based on the variational quantum eigensolver (VQE-SA-CASSCF) on a superconducting quantum processor. This approach is applied to investigate CIs in two prototypical systems─ethylene (C 2 H 4 ) and triatomic hydrogen (H 3 ). We illustrate that VQE-SA-CASSCF, coupled with ongoing hardware and algorithmic enhancements, can lead to a correct description of CIs on existing quantum devices. These results lay the groundwork for exploring the potential of quantum computing to study CIs in more complex systems in the future.Conical intersections (CIs) are pivotal in many photochemical processes. Traditional quantum chemistry methods, such as the state-average multiconfigurational methods, face computational hurdles in solving the electronic Schrödinger equation within the active space on classical computers. While quantum computing offers a potential solution, its feasibility in studying CIs, particularly on real quantum hardware, remains largely unexplored. Here, we present the first successful realization of a hybrid quantum-classical state-average complete active space self-consistent field method based on the variational quantum eigensolver (VQE-SA-CASSCF) on a superconducting quantum processor. This approach is applied to investigate CIs in two prototypical systems─ethylene (C 2 H 4 ) and triatomic hydrogen (H 3 ). We illustrate that VQE-SA-CASSCF, coupled with ongoing hardware and algorithmic enhancements, can lead to a correct description of CIs on existing quantum devices. These results lay the groundwork for exploring the potential of quantum computing to study CIs in more complex systems in the future.

arXiv:2402.12708The Journal of Physical Chemistry LettersJul 8, 20248 citations

Optically induced conical intersections in traps for ultracold atoms and molecules

Alisdair O. G. Wallis, Jeremy M. Hutson

We show that conical intersections can be created in laboratory coordinates by dressing a parabolic trap for ultracold atoms or molecules with a combination of optical and static magnetic fields. The resulting ring trap can support single-particle states with half-integer rotational quantization and many-particle states with persistent flow. Two well-separated atomic or molecular states are brought into near resonance by an optical field and tuned across each other with an inhomogeneous magnetic field. Conical intersections occur at the nodes in the optical field.We show that conical intersections can be created in laboratory coordinates by dressing a parabolic trap for ultracold atoms or molecules with a combination of optical and static magnetic fields. The resulting ring trap can support single-particle states with half-integer rotational quantization and many-particle states with persistent flow. Two well-separated atomic or molecular states are brought into near resonance by an optical field and tuned across each other with an inhomogeneous magnetic field. Conical intersections occur at the nodes in the optical field.

arXiv:1109.1139Physical Review ANov 18, 20115 citations

Quantum Fields in Action

Eduardo C. Marino

Cambridge University Press eBooksOct 25, 20170 citations

\pi

, 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.