We explore optical coherence and spin dynamics of an isotopically purified 166 Er: 7 LiYF 4 crystal below 1 K and at weak magnetic fields < 0.3T. Crystals were grown in our lab and demonstrate narrow inhomogeneous optical broadening down to 16MHz. Solid-state atomic ensembles with such narrow linewidths are very attractive for implementing of off-resonant Raman quantum memory and for the interfacing of superconducting quantum circuits and telecom C-band optical photons. Both applications require a low magnetic field of ∼10mT. However, at conventional experimental temperatures T>1.5K, optical coherence of Er:LYF crystal attains m 10 s time scale only at strong magnetic fields above 1.5 T. In the present work, we demonstrate that the deep freezing of Er:LYF crystal below 1 K results in the increase of optical coherence time to m 100 s at weak fields.

The main goal of this study was creating multifunctional nanoparticles based on rare-earth doped LaF 3 nanocrystals, which can be used as fluorescence thermal sensors operating over the 80-320 K temperature range including physiological temperature range (10-50 ∘ C). The Pr 3+ :LaF 3 ( Pr = 1%) microcrystalline powder and the Pr 3+ :LaF 3 ( Pr = 12%, 20%) nanoparticles were studied. It was proved that all the samples were capable of thermal sensing into the temperature range from 80 to 320 K. It was revealed that the mechanisms of temperature sensitivity for the microcrystalline powder and the nanoparticles are different. In the powder, the 3 P 1 and 3 P 0 states of Pr 3+ ion share their electronic populations according to the Boltzmann and thermalization of the 3 P 1 state takes place. In the nanoparticles, two temperature dependent mechanisms were suggested: energy migration within 3 P 0 state in the temperature range from 80 K to 200 K followed by quenching of 3 P 0 state by OH groups at higher temperatures. The values of the relative sensitivities for the Pr 3+ :LaF 3 ( Pr = 1%) microcrystalline powder and the Pr 3+ :LaF 3 ( Pr = 12%, 20%) nanoparticles into the physiological temperature range (at 45 ∘ C) were 1, 0.5, and 0.3% ∘ C −1 , respectively.

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The Pr3+:LaF3 (CPr = 3, 7, 12, 20, 30%) nanoparticles were characterized by means of high-resolution transmission electron microscopy, X-ray diffraction, optical spectroscopy, energy dispersive X-ray spectroscopy, dynamic light scattering, and MTT assay. It was revealed that the average diameter of all the NPs is around 14–18 nm. The hydrodynamic radius of the Pr3+:LaF3 (CPr = 7%) nanoparticles strongly depends on the medium. It was revealed that hydrodynamic radii of the Pr3+:LaF3 (CPr = 7%) nanoparticles in water, DMEM, and RPMI-1640 biological mediums were 18 ± 5, 41 ± 6, and 186 ± 8 nm, respectively. The Pr3+:LaF3 (CPr = 7%) nanoparticles were nontoxic at micromolar concentrations toward COLO-320 cell line. The lifetime curves were fitted biexponentially, and for the Pr3+:LaF3 (CPr = 7%) NPs, the luminescence lifetimes of Pr3+ ions were 480 ± 2 and 53 ± 5 nanosec.

We present optical vector network analysis (OVNA) of an isotopically purified 166 Er 3+ : 7 LiYF4 crystal. The OVNA method is based on generation and detection of modulated optical sideband by using a radio-frequency vector network analyzer. This technique is widely used in the field of microwave photonics for the characterization of optical responses of optical devices such as filters and high-Q resonators. However, dense solid-state atomic ensembles induce a large phase shift on one of the optical sidebands which results in the appearance of extra features on the measured transmission response. We present a simple theoretical model which accurately describes the observed spectra and helps to reconstruct the absorption profile of a solid-state atomic ensemble as well as corresponding change of the refractive index in the vicinity of atomic resonances.Amplitude modulation (AM) spectroscopy represents one of the widely exploited modulation techniques in the rapidly advancing field of microwave photonics, which merges the worlds of radio-frequency and optoelectronics [1]. Modulation methods are used to convert radio-frequency (RF) signals into the optical domain and vica versa in order to characterize optical components such as high-Q optical filters [2,3], to perform signal processing and to filter-out undesired sidebands [4]. The basic idea of the implemented technique is to use a RF vector network analyzer to modulate the optical signal with its own RF signal and detect its magnitude and phase delay by performing transmission measurement in a closed opto-electronic loop. In this context, generation of optical sidebands by precisely controlled RF/microwave signals opens up new possibility for quantum information processing with rare-earth (RE) doped solids. Particularly one can implement high-resolution spectroscopy, optical hole burning [5], electromagnetically induced transparency, state manipulation and Raman echoes by using very powerful methods of RF vector network analysis in a continuous as well as in a pulsed regime, such as those which have been developed for superconducting quantum circuits [6,7].In the present work we perform crucial step towards the realization of quantum control on solid-state atomic ensembles in a closed opto-electronic loop. We demonstrate optical vector network analysis (OVNA) by using normal AM spectroscopy of ultra-narrow 4 I 15/2 ↔ 4 I 13/2 optical transition of isotopically purified 166 Er 3+ : 7 LiYF 4 (Er:LYF) crystal. We also present a theory which accurately describes the observed modulation response, enabling the extraction of the absorption coefficient and change of refractive index in the vicinity of an atomic resonance.Isotopically purified, low-strain crystals doped with specific isotopes of rare-earth (RE) ions represent rather interesting materials for the implementation of optical quantum memory. Due to the ordered crystal structure, the inhomogeneous broadening of optical transitions of RE ions is mainly limited by nuclear spin fields of a host matrix [8,9]. For ...