Quasi‐classical fluctuation–dissipation description of dielectric loss in oxides with implications for quantum information processing

Abstract

ABSTRACT:One of the most important problems in developing devices for quantum computation is the coupling and dissipation of states by thermal noise. We present a study of a two-state electric dipole in a crystal coupling to noise from a reservoir. As a realization of such an energy-dissipating dipole, we report and analyze dielectric loss measurements in single crystal and polycrystalline Al 2 O 3 over the temperature range 70 -300 K. We are able to model the dielectric loss in terms of a quasi-classical model that uses the fluctuation-dissipation theorem. Two key parameters in this model are the crystal oscillator energy and reservoir-lattice coupling constant. In polycrystalline samples, it is assumed that the main effect of structural disorder is a modification of the spectrum of the thermal phonons, so that acoustical vibrations acquire some optical mode character. The temperature dependence of the linewidth of the high dielectric strength infrared (IR) mode at 438 cm Ϫ1 and the quasi-degenerate Raman mode of the k ϭ 0 (418 cm Ϫ1) transition are also investigated and are shown to be related simply to the dielectric loss. The model reproduces the unusual temperature dependence of the dielectric loss observed experimentally. The implications for the coupling of quantum mechanical objects to noise and quantum information processing are discussed.

Influence of point defects in KTaO3 on low-temperature dielectric relaxation

“…Moreover, when comparing the Raman response between ceramics and a single crystal, strict selection rules cannot be followed because of higher dampening of the phonon vibrations in ceramics and mixing of the modes, which in single crystals is not allowed. 10 In "pure" KTaO 3 ceramics a small shoulder at around 55 cm −1 is visible. The origin of the mode is not clear except that it may correspond to the above-mentioned evidence of structural disorders observed in ceramics.…”

“…Therefore, the dielectric loss, especially in low temperatures, is linked to mixing of the modes not observed in very high quality single crystals. 10 The information about the interaction between the low frequency modes can be obtained directly by Raman spectroscopy, far infrared spectroscopy and indirectly by dielectric measurements.…”

Synthesis, Sintering, and Microwave Dielectric Properties of KTaO3 Ceramics

“…The frequency‐dependent analysis of these peaks is beyond the scope of this paper and will be published elsewhere. The exact mechanism behind these anomalies can only be speculated here because mixing of phonon modes, driven by crystal‐lattice irregularities, is more pronounced in ceramics than single crystals 27,28 …”