Jeremy M. Smith | Searcharxiv

arXiv2023

Quantum Computation of Hydrogen Bond Dynamics and Vibrational Spectra

Calculating the observable properties of chemical systems is often classically intractable and is widely viewed as a promising application of quantum information processing. Yet one of the most common and important chemical systems in nature - the hydrogen bond - has remained a challenge to study using quantum hardware on account of its anharmonic potential energy landscape. Here, we introduce a framework for solving hydrogen-bond systems and more generic chemical dynamics problems using quantum logic. We experimentally demonstrate a proof-of-principle instance of our method using the QSCOUT ion-trap quantum computer, in which we experimentally drive the ion-trap system to emulate the quantum wavepacket of the shared-proton within a hydrogen bond. Following the experimental creation of the shared-proton wavepacket, we then extract measurement observables such as its time-dependent spatial projection and its characteristic vibrational frequencies to spectroscopic accuracy (3.3 cm$^{-1}$ wavenumbers, corresponding to > 99.9% fidelity). Our approach introduces a new paradigm for studying the quantum chemical dynamics and vibrational spectra of molecules, and when combined with existing algorithms for electronic structure, opens the possibility to describe the complete behavior of complex molecular systems with unprecedented accuracy.

quant-ph↗

arXiv2021

Mapping quantum chemical dynamics problems onto spin-lattice simulators

The accurate computational determination of chemical, materials, biological, and atmospheric properties has critical impact on a wide range of health and environmental problems, but is deeply limited by the computational scaling of quantum-mechanical methods. The complexity of quantum-chemical studies arises from the steep algebraic scaling of electron correlation methods, and the exponential scaling in studying nuclear dynamics and molecular flexibility. To date, efforts to apply quantum hardware to such quantum chemistry problems have focused primarily on electron correlation. Here, we provide a framework which allows for the solution of quantum chemical nuclear dynamics by mapping these to quantum spin-lattice simulators. Using the example case of a short-strong hydrogen bonded system, we construct the Hamiltonian for the nuclear degrees of freedom on a single Born-Oppenheimer surface and show how it can be transformed to a generalized Ising model Hamiltonian. We then demonstrate a method to determine the local fields and spin-spin couplings needed to identically match the molecular and spin-lattice Hamiltonians. We describe a protocol to determine the on-site and inter-site coupling parameters of this Ising Hamiltonian from the Born-Oppenheimer potential and nuclear kinetic energy operator. Our approach represents a paradigm shift in the methods used to study quantum nuclear dynamics, opening the possibility to solve both electronic structure and nuclear dynamics problems using quantum computing systems.

physics.chem-ph↗