We theoretically develop and experimentally demonstrate a coherence population mapping (CPM) protocol to store atomic coherences in long-lived populations, enabling storage times far beyond the typically very short decoherence times of quantum systems. The amplitude and phase of an atomic coherence is written onto the populations of a three-state system by specifically designed sequences of radiation pulses from two coupling fields. As an important feature, the CPM sequences enable a retrieval efficiency, which is insensitive to the phase of the initial coherence. The information is preserved in every individual atom of the medium, enabling applications in purely homogeneously or inhomogeneously broadened ensembles even when stochastic phase jumps are the main source of decoherence. We experimentally confirm the theoretical predictions by applying CPM for storage of atomic coherences in a doped solid, reaching storage times in the regime of 1 min.

We report on the implementation of an all-solid-state optical parametric oscillator (OPO) laser system, pumped by a fiber laser, and extended by intra-cavity sum frequency generation (SFG) to provide tunable radiation with output powers well beyond 1 W in the visible regime between 605 and 616 nm. We use periodically poled sections for quasi phase-matched OPO and SFG processes, implemented on a single MgO:PPLN crystal. A Pound-Drever-Hall frequency stabilization reduces the laser linewidth to the range of 100 kHz (FWHM), determined by measurements of spectral hole burning in a rare-earth ion doped crystal as well as analysis of side-of-fringe transmission in a low finesse Fabry-Perot resonator.

We present experimental investigations of rephasing optically driven atomic coherences, prepared by electromagnetically induced transparency in a Pr3+:Y2SiO5 crystal. In particular, we systematically study rephasing based on rapid adiabatic passage and compare the performance of the latter with standard rephasing based on Hahn spin echoes. The data clearly demonstrate the superior performance of rapid adiabatic passage for any application of rephasing, which suffers from large inhomogeneous broadenings in the medium or inevitable fluctuations in the experimental parameters.

We present experimental investigations of rephasing optically driven atomic coherences, prepared by electromagnetically induced transparency in a Pr3+:Y2SiO5 crystal. In particular, we systematically study rephasing based on rapid adiabatic passage and compare the performance of the latter with standard rephasing based on Hahn spin echoes. The data clearly demonstrate the superior performance of rapid adiabatic passage for any application of rephasing, which suffers from large inhomogeneous broadenings in the medium or inevitable fluctuations in the experimental parameters.

We propose a simple and powerful protocol to map an arbitrary atomic coherence between two quantum states into a population distribution of three metastable states, and later to retrieve the atomic coherence from the population distribution. The protocol applies simple sequences of radiation pulses with arbitrary temporal profile, either as coincident or as consecutive pulses. Mapping of rather short-lived atomic coherences into very long-lived atomic populations permits the prolongation of storage times (e.g. of optical information encoded in atomic coherences) by many orders of magnitude — without the need for complicated techniques to reduce homogeneous broadenings.

We investigate light storage by electromagnetically induced transparency in a Pr3+:Y2SiO5 crystal. The retrieval efficiency versus storage time shows pronounced oscillations, which are due to beating of dark-state polaritons in multiple Zeeman-shifted Lambda systems. As a significant obstacle for applications, the beating leads to periodic collapses of the retrieved signal. We demonstrate how to systematically control the perturbing oscillations in the retrieval efficiency by external magnetic fields. This enables suppression of collapses and retrieval of stored data at any storage time, approaching the limit set by the coherence time in the medium.