Quantum simulation of molecular response properties

Abstract

Accurate modeling of the response of molecular systems to an external electromagnetic field is challenging on classical computers, especially in the regime of strong electronic correlation. In this paper, we develop a quantum linear response (qLR) theory to calculate molecular response properties on near-term quantum computers. Inspired by the recently developed variants of the quantum counterpart of equation of motion (qEOM) theory, the qLR formalism employs "killer condition" satisfying excitation operator manifolds that offers a number of theoretical advantages along with reduced quantum resource requirements. We also used the qEOM framework in this work to calculate state-specific response properties. Further, through noise-less quantum simulations, we show that response properties calculated using the qLR approach are more accurate than the ones obtained from the classical coupled-cluster based linear response models due to the improved quality of the ground-state wavefunction obtained using the ADAPT-VQE algorithm.

Quantum Computation of Frequency-Domain Molecular Response Properties Using a Three-Qubit iToffoli Gate

“…Our work is also among the first to demonstrate the practical use of a native multi-qubit gate in quantum simulation. Although the particular problem in this work would require modification to scale efficiently to larger system sizes, other quantum algorithms for computing molecular spectra with potentially improved scalability have been developed [31][32][33][34][35][36] and could benefit from the use of multipartite gates. Further, LCU as a general algorithmic framework is not limited to determining transition amplitudes in frequency-domain response properties but has broader applications in areas such as solving linear systems [58], simulating non-Hermitian dynamics [59], and preparing quantum Gibbs states [60].…”

“…Although there are established methods to obtain ground-and excited-state energies on quantum computers [28][29][30], calculating transition amplitudes is less straightforward. Various schemes including variational quantum simulation [31][32][33], quantum subspace expansion [34] and quantum linear algebra [35] to determine frequency-domain response properties have been proposed. While variational quantum methods to compute frequency-domain response properties have been demonstrated [36], the accuracy of variational The circuits to calculate diagonal transition amplitudes, where a0 is the ancilla qubit and s0 and s1 are the system qubits.…”

Quantum computation of frequency-domain molecular response properties using a three-qubit iToffoli gate

“…Although there are established methods to obtain groundand excited-state energies on quantum computers [28][29][30] , calculating transition amplitudes is less straightforward. Various schemes including variational quantum simulation [31][32][33] , quantum subspace expansion 34 , and quantum linear algebra 35 to determine frequency-domain response properties have been proposed. While variational quantum methods to compute frequencydomain response properties have been demonstrated 36 , the accuracy of variational methods generally depends on the quality of the ansatz.…”