Optical response from terahertz to visible light of electronuclear transitions inLiYF4:Ho3+

Abstract

Because of its role as a model system with tunable quantum fluctuations and quenched disorder, and the desire for optical control and readout of its states, we have used high resolution optical absorption spectroscopy to measure the crystal field excitations for Ho 3+ ions in LiHoxY1−xF4 from the THz to visible regimes. We show that many of the excitations yield very narrow lines visibly split even by the nuclear hyperfine interaction, making Ho 3+ in LiHoxY1−xF4 a candidate host for optically addressable electro-nuclear qubits with quality factors as high as Q=4.7 × 10 5 , where the higher lying levels are electronic singlets. Optical transitions in the easily accessible near and midinfrared are narrow enough to allow readout of the ground state electronuclear qubits responsible for the interesting magnetism of LiHoxY1−xF4. While many of the higher-lying states have been observed previously, we also report here detailed THz domain excitations. The strengths of the electric-and magnetic dipole crystal field transition lines of five of the lowest excited spin-orbit manifolds of dilute LiYF4:Ho 3+ were calculated and compared with measurement. The magnitude of the nuclear hyperfine coupling was used to assign the correct upper and lower states to transition lines.

Tuning high-Q nonlinear dynamics in a disordered quantum magnet

“…On the other hand, the non-equilibrium dynamics are dominated by small multilevel systems describable in terms of some generalized Bloch equation, exactly as is the case, e.g., for NMR performed even at room temperature, and are therefore quantum mechanical. The linewidth increases exponentially with T , consistent with a thermally activated process with a gap Δ = 740 mK, which is an energy well below the 9.4 K first excited crystal-field state energy but of the same order as nearest-neighbor spin couplings as well as the energy difference 34,41,56 (~750 mK) between electronuclear states with nuclear moments of 7/2 and 1/2. This suggests that hole burning is favored when Ho nuclear spins are not relaxing relative to electron spins, but does not exclude composite electronuclear wavefunctions involving several Ho ions.…”

“…The non-magnetic Y 3+ ions randomly occupy the same sites as the magnetic Ho 3+ ions with probability 1− x . The hierarchy of quantum levels accounting for the charge-neutral excitations of individual Ho 3+ ions (in the dilute limit where x ≪ 1) of this wide-gap insulator has been summarized recently by Matmon et al 34 . Most relevant for the current low-temperature study are the ground-state doublet for the Ising spins with a crystal-field-derived 9.4 K gap to the first excited state and the hyperfine interaction between the electronic ( J = 8) and nuclear ( I = 7/2) spins of the Ho 3+ ions 32 , which yields a nuclear Zeeman ladder consisting of eight states with spacing 0.2 K between consecutive levels.…”

Taking advantage of multiplet structure for lineshape analysis in Fourier space

“…This leads to an overestimation of the width and deviation from actual profile shape. We note that a second order hyperfine interaction in the example spectrum (for details see [18]) results in a 2.7 % deviation from equidistancy of the eight hyperfine lines. Nevertheless we obtain equivalent results for line width and shape, showing the robustness of the method against small (on the scale of ∆x/N) relaxation in finite-periodicity of 3%.…”

“…Thanks to the ultra-high resolution FTIR in combination with the highly collimated, high-brillance infrared beam we achieved 0.001 cm −1 (30 MHz) resolution, corresponding to 4779 measurement points in total and ∼ 16 points per individual peak width. We refer to Matmon et al [18] for details on the general experimental setup and FTIR technique as well as for more extensive, spectroscopic work on LiY 1−x Ho x F 4 . The FLA method is ideal for analysis of multiple spectra as a function, e.g., of temperature as in the latter case, thanks to its efficiency.…”

“…Approaches to lineshape determination (see [13] for an overview) deal with efficient numeric approximations [14,15] or tackle the deconvolution of single peaks in Fourier space [13,16,17], avoiding direct and computationally intensive Voigt profile fitting while allowing for correction of spurious frequencies. However, none of these numeric methods were applied in the context of multiplets, in spite of the numerous cases of finite-periodic signals, e.g., for electronic multiplets of ions in solids [18], rotational spectra of molecules [19][20][21], neutron-scattering-resolved hyperfine interaction [22], X-ray diffraction of superlattices [23], and frequency combs [24,25]. Directly fitting a sum of profiles apparently exacerbates the problems of a direct single profile fit and would sacrifice the benefits (e.g., computational speed-up) of Fourier space analysis.…”