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arXiv:0909.4169

Spin states of para-water and ortho-water molecule in gas and liquid phases

Vadim K Konyukhov

Published Sep 23, 2009• 2 citations
arXivHTMLPDF

Abstract

Spin degrees of freedom of water molecule in gas and liquid state were investigated in order to provide a reasonable answer about the unsolved problem of a long-term behavior of water spin isomers. The approach used involves an assumption that molecules change their spin state from a pure state to a mixed one when they interact with some sorts of adsorbent surface. Some models and conceptions of the quantum information processing were used.

DOI
10.48550/arxiv.0909.4169

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Spin degrees of freedom of water molecule in gas and liquid state were investigated in order to provide a reasonable answer about the unsolved problem of a long-term behavior of water spin isomers. The approach used involves an assumption that molecules change their spin state from a pure state to a mixed one when they interact with some sorts of adsorbent surface. Some models and conceptions of the quantum information processing were used.
Introduction. In modern information theory, the idea of a fundamental connection between information, quantum mechanics and thermodynamics is becoming increasingly important. After the works of R. Landauer, the principle was formulated, which became the basis of a new field — information thermodynamics. On the other hand, the search for new ways of physical realization of qubits remains an urgent scientific problem. One of the potential quantum systems that has a natural two-state structure is the ortho- and para-states of the hydrogen molecule. The purpose. Hypothetical identification of the physical essence of the quantum-mechanical nature of information in the ortho/pair conversion of a hydrogen molecule, from the point of view of statistical mechanics and Landauer's thermodynamic principle as a fundamental energy limit for the legalization of information qubits. Results. From the point of view of quantum informatics, ortho/pair hydrogen molecules as quantum spin isomers can behave as different quantum components, because they have different statistical entropy. Therefore, they can be interpreted as two information configurations of one quantum system. Such a system is informationally and thermodynamically ordered in accordance with the Landauer principle and mathematically corresponding to the structure of a qubit or a logical two-level subsystem, isolated from the full four-dimensional Hilbert space of the two spins. The mathematical structure of this system corresponds to a two-level information space, which allows it to be interpreted as a potential model of an elementary quantum information carrier. Due to its antisymmetric structure, it shows increased adaptation in accordance with certain types of magnetic fluctuations, ions, chemical interactions and collective perturbations. The effective use of spin isomers as information carriers requires controlled quantum media, the creation of cryogenic and magnetic influences or isolated systems, and the synchronization of information operations with characteristic coherence times. Conclusions. The proposed conceptual and quantum-information analysis allows us to formulate a consistently consistent system of assumptions regarding a possible hypothesis about the interpretation of spin isomers of hydrogen as potential natural carriers of artificial quantum information. The practical implementation of this concept on the example of hydrogen requires further theoretical and experimental research aimed at studying the mechanisms of coordinated coherence, control of ortho/para-conversion and the possibilities of controlling the spin states of molecular systems. Keywords: quantum information, hydrogen isomer, qubit, entropy, spin conversion, ortho/pair transitions, quantum computer, Landauer's principle.
Spin dynamics and ortho-para conversion in H2_{2}2​O during the phase transition from gas to solid in external magnetic fields
The spin dynamics of water ice in the presence of external magnetic fields are investigated. The employed model is based on the approach introduced by Buntkowsky et al. [Z. Phys. Chem. 222, 1049 (2008)], which considers two nearest-neighbor water molecules and yields a four-spin system, as the abundant oxygen isotope has zero nuclear spin. The model is extended to include coupling to external magnetic fields, allowing us to analyze the interplay between magnetic dipole-dipole interactions and magnetic field coupling. Two types of configurations are examined: (i) static, homogeneous fields, corresponding to a time-independent interaction, and (ii) spatially varying sinusoidal fields in relative motion with the molecules, leading to a time-dependent interaction. All computations are performed within the density operator formalism. The ortho/para populations and the total spin projections are evaluated during the first tens of milliseconds following the gas-to-solid phase transition. For static homogeneous fields, we show that increasing field strength suppresses dipolar-induced depolarization. Assuming that all molecules are initially in the para state, we show that static homogeneous fields can drive the ortho population up to approximately 50%50\%50%, whereas suitably chosen sinusoidal-field configurations can increase it beyond 90%90\%90%. These results are relevant for schemes aiming to preserve or manipulate nuclear-spin polarization during deposition.