Quantum Walk of Two Interacting Bosons

We study the effect of interactions on the bosonic two-particle quantum walk and its corresponding spatial correlations. The combined effect of interactions and Hanbury-Brown Twiss interference results in unique spatial correlations which depend on the strength of the interaction, but not on its sign. The results are explained in light of the two-particle spectrum and the physics of attractively and repulsively bound pairs. We experimentally measure the weak interaction limit of these effects in nonlinear photonic lattices. Finally, we discuss an experimental approach to observe the strong interaction limit using single atoms in optical lattices.Comment: 4 pages, 5 figures. Comments wellcom

Electromagnetically Induced Transparency and Light Storage in an Atomic Mott Insulator

We experimentally demonstrate electromagnetically induced transparency and light storage with ultracold 87Rb atoms in a Mott insulating state in a three dimensional optical lattice. We have observed light storage times of about 240 ms, to our knowledge the longest ever achieved in ultracold atomic samples. Using the differential light shift caused by a spatially inhomogeneous far detuned light field we imprint a "phase gradient" across the atomic sample, resulting in controlled angular redirection of the retrieved light pulse.Comment: 4 pages, 4 figure

Topological stability of stored optical vortices

We report an experiment in which an optical vortex is stored in a vapor of Rb atoms. Due to its 2\pi phase twist, this mode, also known as the Laguerre-Gauss mode, is topologically stable and cannot unwind even under conditions of strong diffusion. To supplement our finding, we stored a flat phase Gaussian beam with a dark center. Contrary to the optical vortex, which stays stable for over 100 microseconds, the dark center in the retrieved flat-phased image was filled with light at storage times as small as 10 microseconds. This experiment proves that higher electromagnetic modes can be converted into atomic coherences, and that modes with phase singularities are robust to decoherence effects such as diffusion. This opens the possibility to more elaborate schemes for two dimensional information storage in atomic vapors.Comment: 4 pages, 4 figures v2: minor grammatical corrections v3: problem with references fixed v4: minor clarifications added to the tex

Bose-Fermi mixtures in 1D optical superlattices

The zero temperature phase diagram of binary boson-fermion mixtures in two-colour superlattices is investigated. The eigenvalue problem associated with the Bose-Fermi-Hubbard Hamiltonian is solved using an exact numerical diagonalization technique, supplemented by an adaptive basis truncation scheme. The physically motivated basis truncation allows to access larger systems in a fully controlled and very flexible framework. Several experimentally relevant observables, such as the matter-wave interference pattern and the condensatefraction, are investigated in order to explore the rich phase diagram. At symmetric half filling a phase similar to the Mott-insulating phase in a commensurate purely bosonic system is identified and an analogy to recent experiments is pointed out. Furthermore a phase of complete localization of the bosonic species generated by the repulsive boson-fermion interaction is identified. These localized condensates are of a different nature than the genuine Bose-Einstein condensates in optical lattices.Comment: 18 pages, 9 figure

Numerical study of one-dimensional and interacting Bose-Einstein condensates in a random potential

We present a detailed numerical study of the effect of a disordered potential on a confined one-dimensional Bose-Einstein condensate, in the framework of a mean-field description. For repulsive interactions, we consider the Thomas-Fermi and Gaussian limits and for attractive interactions the behavior of soliton solutions. We find that the disorder average spatial extension of the stationary density profile decreases with an increasing strength of the disordered potential both for repulsive and attractive interactions among bosons. In the Thomas Fermi limit, the suppression of transport is accompanied by a strong localization of the bosons around the state k=0 in momentum space. The time dependent density profiles differ considerably in the cases we have considered. For attractive Bose-Einstein condensates, a bright soliton exists with an overall unchanged shape, but a disorder dependent width. For weak disorder, the soliton moves on and for a stronger disorder, it bounces back and forth between high potential barriers.Comment: 13 pages, 13 figures, few typos correcte

Analysis of Localization Phenomena in Weakly Interacting Disordered Lattice Gases

Disorder plays a crucial role in many systems particularly in solid state physics. However, the disorder in a particular system can usually not be chosen or controlled. We show that the unique control available for ultracold atomic gases may be used for the production and observation of disordered quantum degenerate gases. A detailed analysis of localization effects for two possible realizations of a disordered potential is presented. In a theoretical analysis clear localization effects are observed when a superlattice is used to provide a quasiperiodic disorder. The effects of localization are analyzed by investigating the superfluid fraction and the localization length within the system. The theoretical analysis in this paper paves a clear path for the future observation of Anderson-like localization in disordered quantum gases.Comment: 9 pages, 13 figure

Metal micro-detectors: development of “transparent” position sensitive detector for beam diagnostics

Metal Micro-strip Detector (MMD) represents a novel position sensitive detector for wide range of applications. The main advantages of MMD are low thickness, high radiation resistance and high spatial resolution. MMD production technology includes some stages: micro-strip layout made by photo-lithography on silicon wafer, plasma-chemistry etching of the silicon wafer in the operating window, micro-cabling connection to the readout electronics and DAQ. Commercially available read-out systems (VA_SCM3 microchip preamplifier, Time Pix readout chip, Gotthard, X-DAS) have been studied for use with MMD. Characterization studies of the MMD are presented in details.Металлический микростриповый детектор (ММД) представляет собой новый позиционно- чувствительный детектор для широкого спектра применений. Основные преимущества ММД: малая толщина, высокая радиационная стойкость, высокое пространственное разрешение. Технология производства ММД включает в себя несколько этапов: микростриповая структура создается при помощи фотолитографии на кремниевой пластине, плазмо-химическое травление кремниевой пластины в рабочем окне, подключение микро-кабелем к считывающей электронике. Коммерчески доступные системы считывания и обработки данных (VA_SCM3, TimePix, Gotthard, X-DAS) были изучены для использования с ММД. Представлены результаты исследований MMD на пучках разных частиц.Металевий мікростріповий детектор (ММД) являє собою новий позиційно-чутливий детектор для широкого спектру застосувань. Основні переваги ММД: мала товщина, висока радіаційна стійкість, висока просторова роздільна здатність. Технологія виробництва ММД включає в себе кілька етапів: мікростріпова структура створюється за допомогою фотолітографії на кремнієвій пластині, плазмо-хімічне травлення кремнієвої пластини в робочому вікні, підключення мікро-кабелем до зчитуючої електроніки. Комерційно доступні системи зчитування й обробки даних (VA_SCM3, TimePix, Gotthard, X-DAS) були вивчені для використання з ММД. Представлено результати дослідження MMD на пучках різних частинок

Theory of Thermal Motion in Electromagnetically Induced Transparency: Diffusion, Doppler, Dicke and Ramsey

We present a theoretical model for electromagnetically induced transparency (EIT) in vapor, that incorporates atomic motion and velocity-changing collisions into the dynamics of the density-matrix distribution. Within a unified formalism we demonstrate various motional effects, known for EIT in vapor: Doppler-broadening of the absorption spectrum; Dicke-narrowing and time-of-flight broadening of the transmission window for a finite-sized probe; Diffusion of atomic coherence during storage of light and diffusion of the light-matter excitation during slow-light propagation; and Ramsey-narrowing of the spectrum for a probe and pump beams of finite-size.Comment: Reference added, typos correcte

Mean-field phase diagram of disordered bosons in a lattice at non-zero temperature

Bosons in a periodic lattice with on-site disorder at low but non-zero temperature are considered within a mean-field theory. The criteria used for the definition of the superfluid, Mott insulator and Bose glass are analysed. Since the compressibility does never vanish at non-zero temperature, it can not be used as a general criterium. We show that the phases are unambiguously distinguished by the superfluid density and the density of states of the low-energy exitations. The phase diagram of the system is calculated. It is shown that even a tiny temperature leads to a significant shift of the boundary between the Bose glass and superfluid