Electromagnetically induced transparency (EIT) due to Zeeman coherences in the Rb buffer gas cell is studied for different laser beam profiles, laser beam radii and intensities from 0.1 to 10 mW cm −2 . EIT line shapes can be approximated by the Lorentzian for wide Gaussian laser beam (6.5 mm in diameter) if laser intensity is weak and for a laser beam profile of the same diameter. Line shapes of EIT become non-Lorentzian for the Gaussian laser beam if it is narrow (1.3 mm in diameter) or if it has a higher intensity. EIT amplitudes and linewidths, for both laser beam profiles of the same diameter, have very similar behaviour regarding laser intensity and Rb cell temperature. EIT amplitudes are maximal at a certain laser beam intensity and this intensity is higher for narrower laser beams. The EIT linewidth estimated at zero laser intensity is about 50 nT or 0.7 kHz, which refers to 1.5 ms relaxation times of Zeeman coherences in 87 Rb atoms in our buffer gas cell. Blocking of the centre of the wide Gaussian laser beam in front of the photo detector yields Lorentzian profiles with a much better contrast to the linewidth ratio for EIT at higher intensities, above ∼2 mW cm −2 .

Rare-earth doped crystals have numerous applications ranging from frequency metrology to quantum information processing. To fully benefit from their exceptional coherence properties, the effect of mechanical strain on the energy levels of the dopants -whether it is a resource or perturbation -needs to be considered. We demonstrate that by applying uniaxial stress to a rare-earth doped crystal containing a spectral hole, we can shift the hole by a controlled amount that is larger than the width of the hole. We deduce the sensitivity of Eu 3+ ions in an Y2SiO5 matrix as a function of crystal site and the crystalline axis along which the stress is applied. PACS numbers: 42.50.Wk,42.50.Ct.,76.30.Kg Rare-earth ions embedded in a crystalline matrix, at cryogenic temperatures, exhibit optical transitions with excellent coherence properties [1] combined with the ease of use of solid state materials. Such properties can be used for example in classical [2] and quantum [3-6] information processing schemes, quantum optical memories [7,8], quantum probes of photonic effects [9], and in ultra-high-precision laser stabilisation and spectroscopy [10][11][12]. In these materials, randomly distributed perturbations from the local matrix result in a broad inhomogeneous profile of the ion absorption spectrum, but spectral hole burning techniques can be used to realize narrow spectral features with a resolution only limited by the individual doping ions. Moreover, as the spectral properties of the individual ions are sensitive to the surrounding crystalline matrix, external stress applied to the crystal in the plastic regime will frequency displace a previously imprinted spectral hole, providing an interesting resource for tuning spectral holes reversibly, in addition to probing stress fields in a spatially resolved manner. Other applications of stress sensitivity can be found in the field of quantum optomechanics [13], where the vibrations of a mechanical resonator modulate the energy levels of quantum two-level system emitters embedded in the resonator material itself, as observed experimentally in resonators containing quantum dots [14] or Nitrogen-Vacancy centers [15][16][17], and proposed theoretically for rare-earth ions doped resonators [18,19].In this work, we concentrate on Eu 3+ ions in a Y 2 SiO 5 host matrix (Eu:YSO) at a temperature of 3.15 K, as this material exhibits one of the narrowest optical transitions among solid-state emitters. We exploit the 580 nm optical transition 7 F 0 → 5 D 0 which possesses near lifetime limited coherence times in the ms range [20,21]. The YSO crystal has two non-equivalent locations within the unit cell where Eu 3+ can substitute for Y 3+ , referred to as site 1 and 2 (vacuum wavelengths of 580.04 nm and 580.21 nm, respectively). We use the technique of spectral hole burning to benefit from the narrow homogeneous linewidth and at the same time the large signal to noise ratio coming from working with an ensemble of ions. Spectral holes are formed by resonant optical excitation and dec...

As light localization becomes increasingly pronounced in photonic systems with less order, we investigate optically induced two-dimensional Fibonacci structures which are supposed to be amongst the most ordered realizations of deterministic aperiodic patterns. For the generation of corresponding refractive index structures, we implement a recently developed incremental induction method using nondiffracting Bessel beams as waveguide formation entities. Even though Fibonacci structures present slightly reduced order, we show that transverse light transport is significantly hampered here in comparison with periodic lattices that account for discrete diffraction. Our experimental findings are supported by numerical simulations that additionally illustrate a development of transverse light localization for increasing propagation distance.