Spatially strongly confined atomic excitation via a two dimensional stimulated Raman adiabatic passage.

We consider a method of sub-wavelength superlocalization and patterning of atomic matter waves via a two dimensional stimulated Raman adiabatic passage (2D STIRAP) process. An atom initially prepared in its ground level interacts with a doughnut-shaped optical vortex pump beam and a traveling wave Stokes laser beam with a constant (top-hat) intensity profile in space. The beams are sent in a counter-intuitive temporal sequence, in which the Stokes pulse precedes the pump pulse. The atoms interacting with both the traveling wave and the vortex beam are transferred to a final state through the 2D STIRAP, while those located at the core of the vortex beam remain in the initial state, creating a super-narrow nanometer scale atomic spot in the spatial distribution of ground state atoms. By numerical simulations we show that the 2D STIRAP approach outperforms the established method of coherent population trapping, yielding much stronger confinement of atomic excitation. Numerical simulations of the Gross-Pitaevskii equation show that using such a method one can create 2D bright and dark solitonic structures in trapped Bose-Einstein condensates (BECs). The method allows one to circumvent the restriction set by the diffraction limit inherent to conventional methods for formation of localized solitons, with a full control over the position and size of nanometer resolution defects.

Single-photon-level narrowband memory in a hollow-core photonic bandgap fiber.

An experimental platform operating at the level of individual quanta and providing strong light-matter coupling is a key requirement for quantum information processing. In our work, we show that hollow-core photonic bandgap fibers filled with laser-cooled atoms might serve as such a platform, despite their typical complicated birefringence properties. To this end, we present a detailed theoretical and experimental study to identify a fiber with suitable properties to achieve operation at the single-photon level. In the fiber, we demonstrate the storage and on-demand retrieval as well as the creation of stationary light pulses, based on electromagnetically induced transparency, for weak coherent light pulses down to the single-photon level with an unconditional noise floor of 0.017(4) photons per pulse. These results clearly demonstrate the prospects of such a fiber-based platform for applications in quantum information networks.

Arbitrarily Accurate Pulse Sequences for Robust Dynamical Decoupling.

We introduce universally robust sequences for dynamical decoupling, which simultaneously compensate pulse imperfections and the detrimental effect of a dephasing environment to an arbitrary order, work with any pulse shape, and improve performance for any initial condition. Moreover, the number of pulses in a sequence grows only linearly with the order of error compensation. Our sequences outperform the state-of-the-art robust sequences for dynamical decoupling. Beyond the theoretical proposal, we also present convincing experimental data for dynamical decoupling of atomic coherences in a solid-state optical memory.

Stopped Light at High Storage Efficiency in a Pr

We demonstrate efficient storage and retrieval of light pulses by electromagnetically induced transparency (EIT) in a Pr^{3+}:Y_{2}SiO_{5} crystal. Using a ring-type multipass configuration, we increase the optical depth (OD) of the medium up to a factor of 16 towards OD≈96. Combining the large optical depth with optimized conditions for EIT, we reach a light storage efficiency of (76.3±3.5)%. In addition, we perform extended systematic measurements of the storage efficiency versus optical depth, control Rabi frequency, and probe pulse duration. The data confirm the theoretically expected behavior of an EIT-driven solid-state memory.

Tunable, continuous-wave optical parametric oscillator with more than 1W output power in the orange visible spectrum.

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.

One-dimensional ultracold medium of extreme optical depth.

We report on the preparation of a one-dimensional ultracold medium in a hollow-core photonic crystal fiber, reaching an effective optical depth of 1000(150). We achieved this extreme optical depth by transferring atoms from a magneto-optical trap into a far-detuned optical dipole trap inside the hollow-core fiber, yielding up to 2.5(3)×10(5) atoms inside the core with a loading efficiency of 2.5(6)%. The preparation of an ultracold medium of such huge optical depth paves the way toward new applications in quantum optics and nonlinear optics.

Correction of arbitrary field errors in population inversion of quantum systems by universal composite pulses.

We introduce universal broadband composite pulse sequences for robust high-fidelity population inversion in two-state quantum systems, which compensate deviations in any parameter of the driving field (e.g., pulse amplitude, pulse duration, detuning from resonance, Stark shifts, unwanted frequency chirp, etc.) and are applicable with any pulse shape. We demonstrate the efficiency and universality of these composite pulses by experimental data on rephasing of atomic coherences in a Pr(3+):Y(2)SiO(5) crystal.

Stopped light and image storage by electromagnetically induced transparency up to the regime of one minute.

The maximal storage duration is an important benchmark for memories. In quantized media, storage times are typically limited due to stochastic interactions with the environment. Also, optical memories based on electromagnetically induced transparency (EIT) suffer strongly from such decoherent effects. External magnetic control fields may reduce decoherence and increase EIT storage times considerably but also lead to complicated multilevel structures. These are hard to prepare perfectly in order to push storage times toward the theoretical limit, i.e., the population lifetime T(1). We present a self-learning evolutionary strategy to efficiently drive an EIT-based memory. By combination of the self-learning loop for optimized optical preparation and improved dynamical decoupling, we extend EIT storage times in a doped solid above 40 s. Moreover, we demonstrate storage of images by EIT for 1 min. These ultralong storage times set a new benchmark for EIT-based memories. The concepts are also applicable to other storage protocols.

Effects of laser polarization and interface orientation in harmonic generation microscopy.

We present systematic experimental investigations on the effects of laser polarization and interface orientation in second and third harmonic generation microscopy. We find that the laser polarization has no measurable effect on signal strength and resolution in third harmonic microscopy, while the second harmonic strongly depends upon the polarization direction of the driving laser. Moreover, we observe a strong effect of the interface orientation with respect to the laser beam direction-both in second and third harmonic generation. This affects the signal strength, as well as the obtained transversal and longitudinal resolution in microscopic imaging. As an (on the first glance) surprising feature, also surfaces parallel to the optical axis of the laser beam yield strong harmonic signal. This enables applications of harmonic microscopy in specific geometries. As an example we monitor the flow of immiscible microfluids in lateral cut by third harmonic microscopy.

Highly efficient broadband conversion of light polarization by composite retarders.

Driving on an analogy with the technique of composite pulses in quantum physics, we propose highly efficient broadband polarization converters composed of sequences of ordinary retarders rotated at specific angles with respect to their fast-polarization axes.

Variable ultrabroadband and narrowband composite polarization retarders.

We propose and experimentally demonstrate novel types of composite sequences of half-wave and quarter-wave polarization retarders, permitting operation at either ultrabroad spectral bandwidth or narrow bandwidth. The retarders are composed of stacked standard half-wave retarders and quarter-wave retarders of equal thickness. To our knowledge, these home-built devices outperform all commercially available compound retarders, made of several birefringent materials.

Efficient coherent population transfer among three states in NO molecules by Stark-Chirped rapid adiabatic passage.

We present the experimental demonstration of a novel, efficient, and selective technique to prepare population inversion. The technique is an extension of Stark-chirped rapid adiabatic passage (SCRAP), i.e., SCRAP among three states. In this process a Lambda-type quantum system is driven by two laser pulses, the pump and Stokes pulses, which are appropriately detuned from transition frequencies. A third laser pulse induces a dynamic Stark shift in the upper energy level, and the timing of all three pulses is controlled in order to prepare population inversion between the two lower states in the Lambda-type level scheme. Our data on population transfer in nitric oxide (NO) molecules clearly show that SCRAP among three states provides an advantageous alternative to such techniques as stimulated Raman adiabatic passage.

Robust population transfer by stimulated raman adiabatic passage in a Pr3+:Y2SiO5 crystal.

We report on the experimental implementation of stimulated Raman adiabatic passage (STIRAP) in a Pr3+:Y2SiO5 crystal. Our data provide clear and striking proof for nearly complete population inversion between hyperfine levels in the Pr3+ ions. The transfer efficiency was monitored by absorption spectroscopy. Time-resolved absorption measurements serve to monitor the adiabatic population dynamics during the STIRAP process. Efficient transfer is observed for negative pulse delays (STIRAP), as well as for positive delays. We identify the latter by an alternative adiabatic passage process.

Trace isotope detection enhanced by coherent elimination of power broadening.

The selectivity and spectral resolution of traditional laser-based trace isotope analysis, i.e., resonance ionization mass spectrometry (RIMS), is limited by power broadening of the radiative transition. We use the fact that power broadening does not occur in coherently driven quantum systems when the probing and excitation processes are temporally separated to demonstrate significant improvement of trace element detection, even under conditions of strong signals. Specifically, we apply a coherent variant of RIMS to the detection of traces of molecular nitric oxide (NO) isobars. For large laser intensities, the detected isotope signal can be increased by almost 1 order of magnitude without any loss in spectral resolution.

Experimental demonstration of selective coherent population transfer via a continuum.

We report the first experimental demonstration of coherent population transfer, induced by stimulated Raman adiabatic passage, via continuum states. Population is transferred from the metastable state 2s(1)S(0) to the excited state 4s(1)S(0) in helium atoms in a two-photon process mediated by coherent interaction with the ionization continuum. While incoherent techniques usually do not permit any population transfer in such a process, we show that stimulated Raman adiabatic passage allows significant population transfer to take place also via ultrafast decay channels.

High-order stimulated Raman scattering in a highly transient regime driven by a pair of ultrashort pulses.

We demonstrate efficient generation of high-order anti-Stokes Raman sidebands in a highly transient regime, using a pair of approximately 100-fs laser pulses tuned to Raman resonance with vibrational transitions in methane or hydrogen. The use of this technique looks promising for efficient subfemtosecond pulse generation.