Noise Electrometry of Polar and Dielectric Materials

Abstract

A qubit sensor with an electric dipole moment acquires an additional contribution to its depolarization rate when it is placed in the vicinity of a polar or dielectric material as a consequence of electrical noise arising from polarization fluctuations in the latter. Here, we characterize this relaxation rate as a function of experimentally tunable parameters such as sample-probe distance, probe-frequency, and temperature, and demonstrate that it offers a window into dielectric properties of insulating materials over a wide range of frequencies and length scales. We discuss the experimental feasibility of our proposal and illustrate its ability to probe a variety of phenomena, ranging from collective polar excitations to phase transitions and disorder-dominated physics in relaxor ferroelectrics. Our proposal paves the way for a novel table-top probe of polar and dielectric materials in a parameter regime complementary to existing tools and techniques.

Figures (2)

• Figure 1: Overview of Qubit Noise Electrometry. (a) We propose a qubit sensing experiment where a probe qubit (top right), with splitting $\omega_q$, is a distance $d$ away from a material. Fluctuations in the material's dipoles source electrical noise at the qubit causing it to relax from $\ket{1}$ to $\ket{0}$ at a rate $1/T_1$. The qubit is sensitive to fluctuations at frequency $\omega_q$ and wavevectors near $1/d$ (see filter on top left). In panel (b), we show the regimes of applicability of qubit sensors and other probes including microscopy techniques [atomic-force, piezoresponse-force, and transmission electron microscopy (AFM, PFM, and TEM)], spectroscopy techniques [x-ray photon correlation, second harmonic generation, x-ray linear dichroism spectroscopy with and without photoemission electron microscopy (XPCS, SHG, XRLD, PEEM)] and electrical transport techniques SHGReview_McCullian2020XRLD_Polisetty_2012PFM_Review_Gruverman2019XPCS_Grbel2008TEM_Winkler2012DielectricSpectroscopy_Grigas2019Parsonnet2020pump_probe_ft. Techniques often requiring high intensity light sources are marked with a $*$.
• Figure 2: Applications and Feasibility of Qubit Relaxometry. We explore different applications of qubit relaxometry and assess the feasibility of exploring them in contemporary experiments. For example, such sensors can characterize transitions between different polar phases, e.g. between paraelectrics (a) and ferroelectrics (b). These transitions are probed by coupling to "spectating modes" that appear near transitions, shown schematically for isotropic/XY anisotropic (c, top) and Ising anisotropic (c, bottom) materials. (d) Moreover, the physics of disordered "relaxor" ferroelectrics---often characterized by the formation of randomly-oriented polar domains---can also be probed; the characteristic size $\xi$ and dynamics of these domains are ascertained by the distance and frequency dependence of $1/T_1$. (e) To assess experimental feasibility, we make predictions for the relaxation rate arising from phase transitions in Ising and XY anisotropic/isotropic materials. Estimates are shown for values of $t \Omega_0^2$ (defined in the main text) ranging from $10^{-2}$ -- $10^{-4}$$\mathring{\text{A}}$ eV$^2$ (light to dark) and material parameters defined near Eq. \ref{['eq:t1xy']}.