We demonstrate coherent electron and electron-nuclear spin manipulations using the impurity trivalent gadolinium ion and the nearby Li-7 and F-19 nuclei incorporated in the LiYF(4 )host crystal. In particular, we present the electronic Rabi oscillations corresponding to -1/2 <-> 1/2 and 5/2 <-> 7/2 transitions between the projections of the Gd3+ spin S = 7/2 of the lowest manifold S-8(7/2), together with the spin-lattice and spin-spin coherence times of these transitions. High-resolution pulsed electron-nuclear double resonance spectra involving -1/2 <-> 1/2 or 5/2 <-> 7/2 gadolinium transitions and either Li-7 (nuclear spin I = 3/2) or F-19 (I = 1/2) nuclear spin transition are obtained. The results suggest that the particular system can be potentially used for the implementation of hybrid quantum calculations utilizing both the electronic high-spin gadolinium states and the nuclear spin states of the adjacent ions.

Optically active point defects in semiconductors have received great attention in the field of solid-state quantum technologies. Hexagonal boron nitride, with an ultra-wide band gap E_g = 6 eV, containing a negatively charged boron vacancy (V_B^-) with unique spin, optical, and coherent properties presents a new two-dimensional platform for the implementation of quantum technologies. This work establishes the value of V_B^ - spin polarization under optical pumping with {\lambda}ext = 532 nm laser using high-frequency ({\nu}mw = 94 GHz) electron paramagnetic resonance (EPR) spectroscopy. In optimal conditions polarization was found to be P = 38.4 %. Our study reveals that Rabi oscillations induced on polarized spin states persist for up to 30-40 microseconds, which is nearly two orders of magnitude longer than what was previously reported. Analysis of the coherent electron-nuclear interaction through the observed electron spin echo envelope modulation (ESEEM) made it possible to detect signals from remote nitrogen and boron nuclei, and to establish a corresponding quadrupole coupling constant Cq = 180 kHz related to nuclear quadrupole moment of 14N. These results have fundamental importance for understanding spin properties of boron vacancy.

To measure magnetostriction in LiTmF4 and LiDyF4 single crystals, the acoustic resonance method was used. It is shown that the combination of capacitive dilatometry and the acoustic resonance method makes it possible to measure not only the field dependence of the crystal dimensions but also the field dependence of the sound speed.

We present the optical and magneto-optical spectroscopy and electron paramagnetic resonance (EPR) investigations of CaMoO4 single crystals doped with the erbium ions. Telecom-wavelength resonance transition inhomogeneous line width of Er3+ is relatively narrow for oxide crystals which makes this material promising for quantum technologies applications. The hyperfine structure in optical spectra of 167Er3+ isotope is well resolved. Energies and symmetries of wavefunctions of 39 energy levels of Er3+ ions in the crystal-field (CF) of S4 symmetry and g-factors of some CF Kramers doublets were measured and successfully simulated on the basis of CF calculations. The obtained set of CF parameters was used for modeling the hyperfine structure profiles observed in the optical absorption spectra.

We report on the first observation of diffusion anisotropy of gaseous helium-3 entrapped in ordered aerogels at 4.2 K. The origins of 3He diffusion anisotropy in aerogels of different porosity are discussed. The correlations between gas diffusion coefficient and basic parameters of aerogels, such as porosity, fiber diameter, and fiber's degree of alignment, are inspected using simple diffusion simulations within the framework of classical diffusion model in both oriented and chaotic aerogels under conditions of diffuse (Knudsen diffusion) and specular reflections of atoms from the walls. The failure of the two-phase and Knudsen diffusion models at low temperature in isotropic and anisotropic aerogels is observed. The effect of a wall attractive potential on the gas dynamics is suspected to play a crucial role in the gas diffusion and its anisotropy. The rough theoretical estimates of that effect at low temperatures in aerogel space confirm this assumption. The observed peculiar diffusion is universal and is expected to occur with other probe gases at higher temperatures.

The results of investigations of Er3+ ions at an optical transition with a telecommunication wavelength (λ~1530 nm) in a YPO4 crystal by using photon echo and high-resolution laser spectroscopy in magnetic fields up to 4 T are presented. The maximum coherence time (T2) was 113 μs in a magnetic field of 4 T when it is oriented along the optical axis c of the crystal. The main sources of decoherence are discussed.

We present the results of the quantum calculation of the ground state energies and magnetic g-factors of two rare earth (RE) ions: Yb3+ in Y2Ti2O7 crystal and Er3+ in YPO4 crystal. The Variational Quantum Eigensolver (VQE) algorithm has been performed on 5-qubit IBM super-conducting quantum computers via IBM Quantum Experience cloud access. The Hamiltonian of the lowest spectroscopic multiplet of each RE ion, containing crystal field and Zeeman inter-action, has been projected onto the collective states of three (Yb3+) and four (Er3+) coupled transmon qubits. The lowest-energy states of RE ions have been found by minimizing the mean energy in similar to 250 - 350 iterations of the algorithm: the first part was performed on a quantum simulator, and the last 25 iterations were conducted on the real quantum computing hardware. All the calculated ground-state energies and magnetic g-factors agree well with their exact val-ues, while the estimated error of 2 divided by 15% is mostly attributed to the decoherence associated with the two-qubit operations.

The spin-noise spectroscopy (SNS) method implies high efficiency of conversion of the spin-system magnetization to the Faraday rotation angle. Generally, this efficiency cannot be estimated using the characteristics of the regular magneto-optical activity of a paramagnet. However, it may be drastically enhanced in systems with strong inhomogeneous broadening of the optical transitions. This enhancement leads to the giant spin-noise gain effect and previously allowed one to apply the SNS to rare-earth-activated crystals. We show that the nonlinear resonant Faraday effect can be used to measure the homogeneous width of the inhomogeneously broadened transition and, thus, to estimate the applicability of the SNS to this type of paramagnet. We present the theoretical description of the effect and perform measurements on intraconfigurational (4f-4f) transitions of the trivalent rare-earth ions of neodymium and ytterbium in fluorite-based crystals. The proposed experimental approach establishes new links between the effects of nonlinear optics and spin-noise characteristics of crystals with paramagnetic impurities and offers new ways of research in the physics of impurity crystals.

The procedure of calculation of the spectral line shape in optical spectra of rare-earth ions in crystals with the inclusion of random deformations of an elastically anisotropic crystal lattice caused by point defects is developed. The distribution function of components of the random strain tensor in the case of a low defect concentration is obtained as the generalized six-dimensional Lorentz distribution. The distribution function parameters are represented by the integral functional of the strain tensor components on a sphere of unit radius containing an isotropic point defect in its center. The numerical calculations of the strain tensors induced by point defects and the parameters of the distribution functions of random strains in LiLuF4 and LaAlO3 crystals have been performed. The calculated envelope with the doublet structure corresponding to the Γ2(3H4) → Γ34(3H5) singlet–doublet transition in the absorption spectrum of Pr3+ ions in the LiLuF4 crystal agrees well with the data of the measurements.

We show that strong coupling with the nuclear spin ensemble leaves an imprint on the nutation dynamics of the electron spin in the form of forced oscillations. The frequency of these oscillations equals Larmor precession frequency of the nuclear spins. This effect is evidenced by our experimental data on Rabi oscillations of paramagnetic nitroxyl radical TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl) dispersed in glassy and crystalline ethanol. The data are interpreted in terms of a simple model that represents an impact of the proton spin bath as random local field with certain probability distribution. The electron spin coherence times of TEMPO in ethanol obtained by means of Hahn spin echo and Carr-Purcell-Meiboom-Gill sequences are compared with the calculations based on a spin diffusion model.

We report on a high-resolution optical and magneto-optical spectroscopy, luminescence, and electron paramagnetic resonance (EPR) studies of yttrium orthophosphate single crystals doped with erbium, which are promising telecom-wavelength materials for applications in quantum electronics and quantum information processing. An observation of the hyperfine structure in optical spectra of Er-167 isotope in Er : YPO4 is presented. Energies and symmetries of 40 crystal-field levels of Er3+ in Er : YPO4 and g factors of some of them were determined and successfully modeled on the basis of crystal-field calculations. The obtained set of crystal-field parameters was used in modeling the hyperfine structure observed in the optical and EPR spectra of Er : YPO4 single crystals.

AbstractThe procedure of calculation of the spectral line shape in optical spectra of rare-earth ions in crystals with the inclusion of random deformations of an elastically anisotropic crystal lattice caused by point defects is developed. The distribution function of components of the random strain tensor in the case of a low defect concentration is obtained as the generalized six-dimensional Lorentz distribution. The distribution function parameters are represented by the integral functional of the strain tensor components on a sphere of unit radius containing an isotropic point defect in its center. The numerical calculations of the strain tensors induced by point defects and the parameters of the distribution functions of random strains in LiLuF_4 and LaAlO_3 crystals have been performed. The calculated envelope with the doublet structure corresponding to the Γ_2(^3 H _4) → Γ_34(^3 H _5) singlet–doublet transition in the absorption spectrum of Pr^3+ ions in the LiLuF_4 crystal agrees well with the data of the measurements.

Abstract We report the observation of the conventional and pulsed electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR) spectra from 19F and 7Li nuclei on impurity Nd3+ ions in LiYF4 crystal doped with Nd3+ ions in parallel orientation at microwave frequency of ν ≈ 95 GHz (W-band). The resolved structure from the nearby and remote nuclei in spectra is observed. The outcome shows that LiYF4:Nd3+ system can be exploited as a convenient matrix for performing spin manipulations and adjusting quantum computation protocols while ENDOR technique is usable for the investigation of electron-nuclear interaction with the nuclei of the system.

We study the coherence times and perform manipulations on the lowest-energy states of trivalent cerium ion in calcium tungstate crystal. We find the phase memory time reaching 14.2 mu s and the time of coherent manipulations reaching 0.3 mu s in the low-temperature limit, the latter can potentially be elongated by using the rotation angle and off-resonance error correction schemes.

We have demonstrated electron-electron and electron-nuclear spin manipulations of Gd3+ ion in CaWO4 crystal. The results suggest that the studied system is perspective for multiqubit implementation in quantum computing.

The longitudinal and transverse relaxation times for a transition between hyperfine sublevels of the lower electronic states of the 4I15/2 and 4I9/2 multiplets of 167Er3+ ions in 7LiYF4 crystals have been determined for the first time using two-pulse and stimulated photon echo measurements in zero magnetic field at a temperature of 4 K. The decay of the photon echo signal has been shown to be modulated, which is tentatively attributed to the superhyperfine interaction of the 167Er3+ ions with their 19F− nearest neighbours. The contributions of various types of interaction to the ultranarrow linewidth (~24 MHz) of the transition in question are discussed. Our results demonstrate that this optical transition of the 167Er3+ ion in 7LiYF4 crystals is potentially attractive for use in Raman quantum memory schemes.