Magnetic-field-driven localization of light in a cold-atom gas

Laser frequency stabilization by modulation transfer spectroscopy and balanced detection of molecular iodine for laser cooling of 174Yb

We report laser frequency stabilization by the combination of modulation transfer spectroscopy and balanced detection of a relatively weak hyperfine transition of the R(158)25-0 line of molecular iodine (127I2), which is used as a new frequency reference for laser trapping and cooling of 174Yb on the 1S0 - 3P1 transition. The atomic cloud is characterized by time-of-flight measurements, and an on-resonance optical depth of up to 47 is obtained. We show laser noise reduction and characterize the short-term laser frequency instability by the Allan deviation of the laser fractional frequency. The minimum measured value is 3.9 ×10-13 at 0.17 s of averaging time.

Loading of a large Yb MOT on the 1S0 → 1P1 transition

We present an experimental setup to laser cool and trap a large number of ytterbium atoms. Our design uses an oven with an array of micro-tubes for efficient collimation of the atomic beam, and we implement a magneto-optical trap of 174Yb on the 1S0 → 1P1 transition at 399 nm. Despite the absence of a Zeeman slower, we obtain a loading of 4 × 109 at./s. We trap up to N = 109 at., where light-assisted collisions become the dominant loss mechanism. We precisely characterize our atomic beam, the loading rate of the magneto-optical trap, and several loss mechanisms relevant for trapping a large number of atoms.

Intensity of Waves Inside a Strongly Disordered Medium

Anderson localization does not lead to an exponential decay of intensity of an incident wave with the depth inside a strongly disordered three-dimensional medium. Instead, the average intensity is roughly constant in the first half of a disordered slab, sharply drops in a narrow region in the middle of the sample, and then remains low in the second half of the sample. A universal, scale-free spatial distribution of average intensity is found at mobility edges where the intensity exhibits strong sample-to-sample fluctuations. Our numerical simulations allow us to discriminate between two competing local diffusion theories of Anderson localization and to pinpoint a deficiency of the self-consistent theory.

Aperiodic Photonics of Elliptic Curves

In this paper we propose a novel approach to aperiodic order in optical science and technology that leverages the intrinsic structural complexity of certain non-polynomial (hard) problems in number theory and cryptography for the engineering of optical media with novel transport and wave localization properties. In particular, we address structure-property relationships in a large number (900) of light scattering systems that physically manifest the distinctive aperiodic order of elliptic curves and the associated discrete logarithm problem over finite fields. Besides defining an extremely rich subject with profound connections to diverse mathematical areas, elliptic curves offer unprecedented opportunities to engineer light scattering phenomena in aperiodic environments beyond the limitations of traditional random media. Our theoretical analysis combines the interdisciplinary methods of point patterns spatial statistics with the rigorous Green’s matrix solution of the multiple wave scattering problem for electric and magnetic dipoles and provides access to the spectral and light scattering properties of novel deterministic aperiodic structures with enhanced light-matter coupling for nanophotonics and metamaterials applications to imaging and spectroscopy.

Microscopic and Macroscopic Signatures of 3D Anderson Localization of Light

Apart from the difficulty of producing highly scattering samples, a major challenge in the observation of Anderson localization of 3D light is identifying an unambiguous signature of the phase transition in experimentally feasible situations. In this Letter, we establish a clear correspondence between the collapse of the conductance, the increase in intensity fluctuations at the localization transition and the scaling analysis results based on the Thouless number, thus connecting the macroscopic and microscopic approaches of localization. Furthermore, the transition thus inferred is fully compatible both with the results based on the eigenvalue analysis of the microscopic description and with the effective-medium Ioffe-Regel criterion.

Localization Transition for Light Scattering by Cold Atoms in an External Magnetic Field

We establish a localization phase diagram for light in a random three-dimensional (3D) ensemble of motionless two-level atoms with a threefold degenerate upper level, in a strong static magnetic field. Localized modes appear in a narrow spectral band when the number density of atoms ρ exceeds a critical value ρ_{c}≃0.1k_{0}^{3}, where k_{0} is the wave number of light in the free space. A critical exponent of the localization transition taking place upon varying the frequency of light at a constant ρ>ρ_{c} is estimated to be ν=1.57±0.07. This classifies the transition as an Anderson localization transition of 3D orthogonal universality class.

Probing scattering resonances of Vogel's spirals with the Green's matrix spectral method

Using the rigorous Green's function spectral method, we systematically investigate the scattering resonances of different types of Vogel spiral arrays of point-like scatterers. By computing the distributions of eigenvalues of the Green's matrix and the corresponding eigenvectors, we obtain important physical information on the spatial nature of the optical modes, their lifetimes and spatial patterns, at small computational cost and for large-scale systems. Finally, we show that this method can be extended to the study of three-dimensional Vogel aperiodic metamaterials and aperiodic photonic structures that may exhibit a richer spectrum of localized resonances of direct relevance to the engineering of novel optical light sources and sensing devices.

Subradiance in a Large Cloud of Cold Atoms

Since Dicke's seminal paper on coherence in spontaneous radiation by atomic ensembles, superradiance has been extensively studied. Subradiance, on the contrary, has remained elusive, mainly because subradiant states are weakly coupled to the environment and are very sensitive to nonradiative decoherence processes. Here, we report the experimental observation of subradiance in an extended and dilute cold-atom sample containing a large number of particles. We use a far detuned laser to avoid multiple scattering and observe the temporal decay after a sudden switch-off of the laser beam. After the fast decay of most of the fluorescence, we detect a very slow decay, with time constants as long as 100 times the natural lifetime of the excited state of individual atoms. This subradiant time constant scales linearly with the cooperativity parameter, corresponding to the on-resonance optical depth of the sample, and is independent of the laser detuning, as expected from a coupled-dipole model.