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 16MHz. 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 ∼10mT. However, at conventional experimental temperatures T>1.5K, 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.
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 ...
While conventional lasers are based on gain media with three or four real levels, unconventional lasers including virtual levels and two-photon processes offer new opportunities. We study lasing that involves a two-photon process through a virtual lower level, which we realize in a cloud of cold ytterbium atoms that are magneto-optically trapped inside a cavity. We pump the atoms on the narrow 1 S0 → 3 P1 line and generate laser emission on the same transition. Lasing is verified by a threshold behavior of output power vs. pump power and atom number, a flat g (2) correlation function above threshold, and the polarization properties of the output. In the proposed lasing mechanism the MOT beams create the virtual lower level of the lasing transition. The laser process runs continuously, needs no further repumping, and might be adapted to other atoms or transitions such as the ultra narrow 1 S0 → 3 P0 clock transition in ytterbium.
Electromagnetically induced transparency allows for the controllable change of absorption properties, which can be exploited in a number of applications including optical quantum memory. In this paper, we present a study of the electromagnetically induced transparency in a 167Er:7LiYF4 crystal at low magnetic fields and ultra-low temperatures. The experimental measurement scheme employs an optical vector network analysis that provides high precision measurement of amplitude, phase and group delay and paves the way towards full on-chip integration of optical quantum memory setups. We found that sub-Kelvin temperatures are the necessary requirement for observing electromagnetically induced transparency in this crystal at low fields. A good agreement between theory and experiment is achieved by taking into account the phonon bottleneck effect.
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