Quantum computation solves a half-century-old enigma: Elusive vibrational states of magnesium dimer found

Abstract

The high-lying vibrational states of the magnesium dimer (Mg2), which has been recognized as an important system in studies of ultracold and collisional phenomena, have eluded experimental characterization for half a century. Until now, only the first 14 vibrational states of Mg2 have been experimentally resolved, although it has been suggested that the ground-state potential may support five additional levels. Here, we present highly accurate ab initio potential energy curves based on state-of-the-art coupled-cluster and full configuration interaction computations for the ground and excited electronic states involved in the experimental investigations of Mg2. Our ground-state potential unambiguously confirms the existence of 19 vibrational levels, with ~1 cm−1 root mean square deviation between the calculated rovibrational term values and the available experimental and experimentally derived data. Our computations reproduce the latest laser-induced fluorescence spectrum and provide guidance for the experimental detection of the previously unresolved vibrational levels.

Mapping renormalized coupled cluster methods to quantum computers through a compact unitary representation of non-unitary operators

“…These formulations played an immense role in understanding fundamental problems in many-body physics [11][12][13][14][15][16][17][18][19][20][21] (for an excellent review of these developments see Ref. 22), quantum field theory, [23][24][25][26][27] quantum hydrodynamics, 28,29 nuclear structure theory, [30][31][32][33] quantum chemistry, [34][35][36][37][38][39][40][41][42] and condensed phase systems. [43][44][45][46][47][48][49][50][51][52][53][54] For a single-reference (SR) CC formulations, where one can approximate the exact wave function |Ψ by a single determinant |Φ , the CC a) Electronic mail: peng398@pnnl.gov b) Electronic mail: karol.kowalski@pnnl.gov Ansatz given by the expansion…”

Coupled Cluster Downfolding Theory: towards efficient many-body algorithms for dimensionality reduction of composite quantum systems

“…The coupled cluster (CC) methodology [1][2][3][4][5][6][7][8][9] is a driving engine of high-precision simulations in physics, chemistry, and material sciences. Several properties of CC made it especially efficient in capturing correlation effects in many-body quantum systems ranging from quantum field theory, [10][11][12][13][14] quantum hydrodynamics, 15,16 and nuclear structure theory [17][18][19] to quantum chemistry [20][21][22][23][24][25][26][27] and material sciences. [28][29][30][31][32][33][34][35] In this article, we will mainly focus our attention on the application to quantum chemistry.…”

Dimensionality reduction of many-body problem using coupled-cluster sub-system flow equations: classical and quantum computing perspective

“…Over the last few decades, the coupled-cluster (CC) theory [1][2][3][4][5][6][7][8][9] has evolved into one of the most accurate and dominant theory to describe various quantum systems across spatial scales hence addressing fundamental problems in nuclear structure theory, [10][11][12] quantum chemistry, [13][14][15][16][17][18][19][20] and material sciences. [21][22][23][24][25][26][27][28] Many strengths of the single-reference CC formalism (SR-CC) originates in the exponential parametrization of the ground-state wave function…”

“…[31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] More recently, CC methodologies have been integrated with stochastic Monte Carlo methods probing configurational space and leading to near full-configuration-interaction accuracy of calculated energies. 20,47,48 However, the applicability of canonical formulations of these theories (especially to large molecular systems) may be limited by their steep (polynomial) numerical scaling. Unfortunately, even with rapid progress in computational technologies, problems with data locality, data movement, and polynomial scaling of high-rank canonical CC methods lead to insurmountable numerical problems in modeling large systems.…”