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Physical Review A

Nuclear spin conversion in H2O revisited

P. L. Chapovsky, Alexander A. Mamrashev

Published Nov 29, 2021• 2 citations
Publisher

Abstract

Conversion of water nuclear-spin isomers by the quantum relaxation phenomenon is revisited and the high stability of water isomers is predicted. As an example, the isomer lifetime is found equal to 18 hours at room temperature and the water vapor pressure equal to $\ensuremath{\simeq}5$ torr. Our calculations correct the prediction of rather short lifetime of water spin isomers, $\ensuremath{\approx}1$ s, made by Cacciani et al. [Phys. Rev. A 85, 012521 (2012)].

DOI
10.1103/physreva.104.052816

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Conversion of water nuclear-spin isomers by the quantum relaxation phenomenon is revisited and the high stability of water isomers is predicted. As an example, the isomer lifetime is found equal to 18 hours at room temperature and the water vapor pressure equal to \ensuremath≃5\ensuremath{\simeq}5\ensuremath≃5 torr. Our calculations correct the prediction of rather short lifetime of water spin isomers, \ensuremath≈1\ensuremath{\approx}1\ensuremath≈1 s, made by Cacciani et al. [Phys. Rev. A 85, 012521 (2012)].
Determining the properties of molecules, such as bond angles and bond lengths, is an important part of materials science. Quantum simulators are expected to efficiently determine them by calculating their energy spectrum. Compared with the previous single-resonant quantum eigensolver adopted in simulating water molecule [Phys. Rev. Lett. 122, 090504 (2019)], we propose a multiresonant quantum eigensolver that can search for the energy spectrum of molecules in a parallel manner. Our approach can exponentially save the cost of finding the energy spectrum by a factor of 2r{2}^{r}2r, where rrr is the number of ancillary qubits. As an interesting demonstration, we have designed and implemented an experiment to determine the bond angle of water molecules on a four-qubit nuclear spin quantum processor. We experimentally estimate the ground and first excitation energies and their corresponding states for effective water Hamiltonians with different H-O bond angles. The experimental results clearly show that the molecule structure with $\ensuremath{\angle}\text{H-O}\ensuremath{\sim}{100}^{\ensuremath{\circ}}$ bond angle is most stable. We believe that our approach sheds light on further applications in solving quantum chemical problems.
We have calculated the magnetic dipolar spin-relaxation rates of magnetically trapped doubly-spin-polarized atomic deuterium gas. The results are expressed in a simple closed formula describing the dipolar-relaxation-limited stability in the Boltzmann ($T\ensuremath{\gg}{T}_{F}$), the degeneracy ($T\ensuremath{\ll}{T}_{F}$), and the crossover ($T\ensuremath{\simeq}{T}_{F}$) regimes. In the degeneracy regime we typically find lifetimes of some hours. We also discuss the dipolar decay of magnetically trapped spin-polarized fermionic alkali-metal atoms.