Where are Protons and Deuterons in KH_pD_{1-p}CO_3? A Neutron Diffraction Study

The crystals of potassium hydrogen carbonate (KHCO3) and the KDCO3 analogue are isomorphous. They are composed of hydrogen or deuterium bonded centrosymmetric dimers (HCO3-)(2) or (DCO3-)(2). The space group symmetry of KHpD1-pCO3 (p approximate to 0.75) determined with neutron diffraction is identical to those of KHCO3 and KDCO3. This is at variance with a random distribution of H and D nuclei. These crystals are macroscopic quantum systems in which protons or/and deuterons merge into macroscopic states

Nonlocal protons and deuterons opposed to disorder: a single-crystal neutron diffraction study of KH0.76D0.24CO3 and a theoretical framewok

We show with neutron diffraction that a single-crystal of potassium hydrogen deuterium carbonate at room temperature, namely KH$_{0.76}$D$_{0.24}$CO$_3$, is isomorphous with the KHCO$_3$ and KDCO$_3$ derivatives. Protons and deuterons are not disordered particles located at definite sites and Bragg peaks are best fitted with separate H and D sublattices. We propose a theoretical framework for nonlocal observables and macroscopic states compatible with the crystal field

Evidence of macroscopically entangled protons in a mixed isotope crystal of KHp_{p}D1−p_{1-p}CO3_3

International audienceWe examine whether protons and deuterons in the crystal of KH$_{0.76}$D$_{0.24}$CO$_3$ at 300 K are particles or matter waves. The neutron scattering function measured over a broad range of reciprocal space reveals the enhanced diffraction pattern anticipated for antisymmetrized macroscopic states for protons (fermions). These features exclude a statistical distribution of protons and deuterons. Raman spectra are consistent with a mixture of KHCO$_3$ and KDCO$_3$ sublattices whose isomorphous structures are independent of the isotope content. We propose a theoretical framework for decoherence-free proton and deuteron states

A neutron diffraction study of macroscopically entangled proton states in the high temperature phase of the KHCO3 crystal at 340 K

International audienceWe utilize single-crystal neutron diffraction to study the $C2/m$ structure of potassium hydrogen carbonate (KHCO$_3$) and macroscopic quantum entanglement above the phase transition at $T_c = 318$ K. Whereas split atom sites could be due to disorder, the diffraction pattern at 340 K evidences macroscopic proton states identical to those previously observed below $T_c$ by F. Fillaux et al., (2006 \textit{J. Phys.: Condens. Matter} \textbf{18} 3229). We propose a theoretical framework for decoherence-free proton states and the calculated differential cross-section accords with observations. The structural transition occurs from one ordered $P2_1/a$ structure ($T < T_c$) to another ordered $C2/m$ structure. There is no breakdown of the quantum regime. It is suggested that the crystal is a macroscopic quantum object which can be represented by a state vector. Raman spectroscopy and quasi-elastic neutron scattering suggest that the $|C2/m\rangle$ state vector is a superposition of the state vectors for two $P2_1/a$-like structures symmetric with respect to $(a,c)$ planes

Crystal structures and proton dynamics in potassium and cesium hydrogen bistrifluoroacetate salts with strong symmetric hydrogen bonds

The crystal structures of potassium and cesium bistrifluoroacetates were determined at room temperature and at 20 K and 14 K, respectively, with the single crystal neutron diffraction technique. The crystals belong to the I2/a and A2/a monoclinic space groups, respectively, and there is no visible phase transition. For both crystals, the trifluoroacetate entities form dimers linked by very short hydrogen bonds lying across a centre of inversion. Any proton disorder or double minimum potential can be rejected. The inelastic neutron scattering spectral profiles in the OH stretching region between 500 and 1000 cm^{-1} previously published [Fillaux and Tomkinson, Chem. Phys. 158 (1991) 113] are reanalyzed. The best fitting potential has the major characteristics already reported for potassium hydrogen maleate [Fillaux et al. Chem. Phys. 244 (1999) 387]. It is composed of a narrow well containing the ground state and a shallow upper part corresponding to dissociation of the hydrogen bond.Comment: 31 pages, 7 figure

The quantum phase-transitions of water

It is shown that hexagonal ices and steam are macroscopically quantum condensates, with continuous spacetime-translation symmetry, whereas liquid water is a quantum fluid with broken time-translation symmetry. Fusion and vaporization are quantum phase-transitions. The heat capacities, the latent heats, the phase-transition temperatures, the critical temperature, the molar volume expansion of ice relative to water, as well as neutron scattering data and dielectric measurements are explained. The phase-transition mechanisms along with the key role of quantum interferences and that of Hartley-Shannon's entropy are enlightened. The notions of chemical bond and force-field are questioned

A neutron diffraction study of the crystal of benzoic acid from 6 to 293K and a macroscopic-scale quantum theory of the lattice of hydrogen-bonded dimers

International audienceThe crystal of benzoic acid is comprised of tautomeric centrosymmetric dimers linked through bistable hydrogen bonds. Statistical disorder of the bonding protons is excluded by neutron diffraction from 6 K to 293 K. In addition to diffraction data, vibrational spectra and relaxation rates measured with solid-state-NMR and quasi-elastic neutron scattering are consistent with wave-like, rather than particle-like protons. We present a macroscopic-scale quantum theory for the bonding protons represented by a periodic lattice of fermions. The adiabatic separation, the exclusion principle, and the antisymmetry postulate yield a static lattice-state immune to decoherence. According to the theory of quantum measurements, vibrational spectroscopy and relaxometry involve realizations of decoherence-free Bloch states for nonlocal symmetry species that did not exist before the measurement. The eigen states are fully determined by three temperature-independent parameters which are effectively measured: the energy difference between tautomer sublattices; the double-well asymmetry for proton oscillators; the delocalization degree of the wavefunctions. The spontaneous decay of Bloch states accounts for relaxometry data. On the other hand, static states realized by elastic scattering account for diffraction data. We conclude that both quantum and classical physics hold at every temperature