2,069 research outputs found
Absolute Absorption and Dispersion in a Thermal Rb Vapour at High Densities and High Magnetic Fields.
Full text linkThis thesis presents a comparative study of the measured and calculated absolute absorption and dispersion properties of the Rb D lines through a dense thermal vapour in the absence and presence of an applied magnetic field. A detailed theoretical model valid in the weak-probe regime is calculated. The model uses a matrix representation of the atomic Hamiltonian including the magnetic field interaction for Rb in the completely uncoupled basis. Numerical diagonalisation allows the frequency detunings and transition strengths to be calculated. The lineshape of each transition is modelled as a Voigt profile, a convolution of the inhomogeneous and homogeneous profiles. The medium’s susceptibility is found by summing over all the electric-dipole-allowed transitions. For dense thermal vapours a modification to the homogeneous linewidth of each transition, which grows linearly with the number density of atoms, arises due to resonant dipole-dipole interactions between identical atoms in superpositions of the ground and excited terms. In the presence of an applied magnetic field we investigate the Stokes parameters of light propagating through a dense thermal vapour. For fields larger than 0.33 T we enter the hyperfine Paschen-Back regime on the Rb D lines. We present a compact optical isolator based on an atomic vapour, exploiting the spectral region of high transmission and large dispersion where we would normally expect absorption on the Rb D lines. Frequency up-conversion is shown in the fluorescence measurements over the visible and near infra-red regions for strong excitation. Low density transfer arises due to the energy-pooling effect between two identical atoms in their first excited terms. At
high densities resonant dipole-dipole interactions give rise to a threshold for the energy transfer. We characterise the threshold behaviour with increasing number density
Feshbach spectroscopy of an ultracold Rb-Cs mixture
Full text linkThis thesis reports the observation of interspecies Feshbach resonances in an ultracold mixture of Rb and Cs atoms. A versatile combined magnetic and optical potential has been designed and constructed which is capable of bringing both and to degeneracy, and reaching high phase-space density in . High phase-space density mixtures are the first step required in the production of ultracold polar molecules, the topic of much current research.
The apparatus capitalises on the efficient capture of atoms by a magnetic trap from a magneto-optical trap, and the efficient sympathetic cooling of Cs by Rb therein. Upon transfer to the crossed optical dipole trap condensates in excess of atoms and approximately atoms are produced after direct evaporation and gravito-magnetic tilting of the potential. The observation of six interspecies - Feshbach resonances are reported, three of which had only been predicted theoretically, allowing testing and development of the theoretical model. Furthermore, the extrapolation of this model has predicted numerous Feshbach resonances between and , none of which have been experimentally observed prior to this work. The versatile nature of this apparatus is discussed, including the application of the current system to cooling of . Initial experiments observed seven interspecies resonances, including a broad s-wave resonance at a magnetic field of G which is in excellent agreement with the theoretical prediction. Further work has revealed that fourteen Feshbach resonances exist in the 0-700 G magnetic field range between and atoms in the and states, respectively. Several of these resonances would be ideal for magneto-association of RbCs molecules, prior to transfer to the rovibrational ground-state
Realisation of a cold mixture of rubidium and caesium
Full text linkThis thesis describes a new apparatus designed to study cold, ultracold, and quantum degenerate mixtures of rubidium and caesium atoms. The Rb- Cs mixture is prepared using a double magneto-optical trap (MOT) system in which a two-species pyramid MOT acts as a source of cold atoms for a 'science' MOT. The first results of experiments on the magneto-optically trapped mixture are presented, including measurements of trap loss rates due to single-species and interspecies inelastic collisions. A technique for reducing interspecies loss by spatially separating the MOTs during loading is described. This technique allows 50-50 mixtures of Rb and Cs atoms to be loaded into a magnetic trap at close to their respective maximum single- species atom numbers. Alternatively, one species can be loaded with arbitrarily small amounts of the other. The displaced MOT technique is thus аn excellent starting point for investigations of interspecies Feshbach resonances and sympathetic cooling of Rb-Cs mixtures in magnetic and optical traps. In addition, a model of polarisation spectroscopy based on numerical integration of population rate equations is described. Theoretical polarisation spectra generated by the model are shown to agree with experimental spectra for the F = I + 1/2 → F' transitions in Rb and Cs. An investigation of the sub-Doppler dichroic atomic vapour laser locking (DAVLL) technique demonstrates how locking signals can be optimised for the Rb D2 transitions. The role of polarisation purity in generating the spectra is discussed, and impurities are modeled using a Jones matrix approach. Comparisons with polarisation spectroscopy and DAVLL are used to enhance understanding of atom-light interactions in spectroscopic systems, and indicate methods for optimising locking signals for use in cold atom experiments
A Quantum Degenerate Mixture of Rb and Cs
Full text linkThis thesis reports the formation of a dual-species Bose-Einstein condensate of Rb and Cs in the same trapping potential. Quantum degenerate mixtures exhibit rich physics inaccessible to single species experiments and provide an ideal starting point for the creation of ultracold dipolar molecules. These molecules offer a wealth of new research avenues including precision metrology, quantum simulation and computation.
The experimental method exploits the efficient sympathetic cooling of Cs via elastic collisions with Rb, initially in a magnetic quadrupole trap and subsequently in a levitated optical trap. Evaporative cooling in the dipole trap must compete against a high interspecies three-body inelastic collision rate \mbox{~cms}. The two condensates each contain up to \mbox{} atoms and exhibit a striking phase separation, revealing the mixture to be immiscible due to strong repulsive interspecies interactions. Sacrificing all the Rb during the cooling leads to the creation of single-species Cs condensates of up to \mbox{} atoms. In addition this thesis reports the observation of an interspecies Feshbach resonance at 181.7(5)~G and the creation of a pure sample of Cs molecules via magneto-association on the 4(g)4 resonance at 19.8~G. These results represent important steps towards the creation of ultracold polar RbCs molecules
Optical frequency reference stabilized to Rb D2 transition controlled by FPGA lock-in module
No full textRevista con referatoFil: Luda, Marcelo Alejandro. Ministerio de Defensa. Instituto de Investigaciones Científicas y Técnicas para la Defensa; Argentina.Fil: Luda, Marcelo Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Codnia, Jorge. Ministerio de Defensa. Instituto de Investigaciones Científicas y Técnicas para la Defensa; Argentina.Fil: Codnia, Jorge. Universidad Nacional de General Sarmiento. Instituto de Ciencias; Argentina.La modulación y demodulación lock-in es utilizada con frecuencia para la estabilización de la longitud de onda de emisión de un láser sintonizable en laboratorios de metrología, espectroscopia, física atómica y óptica cuántica. En particular, la estabilización a una transición atómica particular es utilizada para generar patrones de frecuencia óptica de referencia. En este trabajo se presenta el desarrollo de un módulo de estabilización con tecnología de electrónica programable FPGA (del inglés, Field Programmable Gate Array) que permite realizar la modulación a frecuencia f y demodulación lock-in en frecuencias f y 3f. El módulo es económico, versátil y se puede controlar remotamente usando una plataforma de Software Libre. Se probó el desempeño del sistema estabilizando un láser sintonizable por cavidad externa (ECDL, del inglés External Cavity Diode Laser) a una de las transiciones hiperfinas del Rubidio (Rb), logrando una desviación estándar en la frecuencia óptica del orden de los 100 kHz, equivalentes a una estabilidad 2.6 10-10.Lock-in measurement is frequently used for tunable laser wavelength stabilization in metrology, spectroscopy atomic physics and quantum optics labs. In particular, wavelength stabilization to atomic transitions is used to build optical frequency references. In this work we present the development of a stabilization module build using FPGA (Field Programmable Gate Array) technology for modulating at f frequency and lock-in demodulating on f and 3f frequencies. The module is economic, versatile and can be remotely controlled using a Free Software platform. We tested the system performance stabilizing a tunable External Cavity Diode Laser (ECDL) to a Rubidium (Rb) hyperfine transition, achieving an optical frequency standard deviation of 100 kHz, equivalent to an stability of 2.6 10-10
Quantum Double Lock-in Amplifier
Full text linkQuantum lock-in amplifier aims to extract an alternating signal within strong
noise background by using quantum strategy. However, as the target signal
usually has an unknown initial phase, we can't obtain the complete information
of its amplitude, frequency and phase in a single lock-in measurement. Here, to
overcome this challenge, we give a general protocol for achieving a quantum
double lock-in amplifier and illustrate its realization. In analog to a
classical double lock-in amplifier, our protocol is accomplished via two
quantum mixers under orthogonal pulse sequences. The two orthogonal pulse
sequences act the roles of two orthogonal reference signals in a classical
double lock-in amplifier. Combining the output signals, the complete
characteristics of the target signal can be obtained. As an example, we
illustrate the realization of our quantum double lock-in amplifier via a
five-level double- coherent population trapping system with Rb
atoms, in which each structure acts as a quantum mixer and the two
applied dynamical decoupling sequences take the roles of two orthogonal
reference signals. Our numerical calculations show that the quantum double
lock-in amplifier is robust against experimental imperfections, such as finite
pulse length and stochastic noise. Our study opens an avenue for extracting
complete characteristics of an alternating signal within strong noise
background, which is beneficial for developing practical quantum sensing
technologies
Liquid structure of Rb-Hg alloys studied by neutron diffraction
Full text linkThe structures of liquid Rb–Hg alloys were studied as a function of composition by neutron diffraction. In the intermediate Rb concentration range, the obtained structure factors show a small prepeak, which may be an evidence of the formation of Hg polyanion units in liquids. The Reverse Monte Carlo (RMC) analysis was applied to separate the total radial distribution function into the corresponding partial radial distribution functions. Up to 10 at.% Rb, no obvious changes are found for the first peak position of the partial radial distribution functions of the Hg–Hg pair and that of the Hg–Rb pair. The first peak position between the Hg–Rb pairs increases above 20 at.% Rb. In addition to the first peak, a subpeak between Hg–Hg pairs can be seen in the large distance. At 60 at.% Rb, the nearest neighbor distance between Hg atoms shows the closest value in the concentration range studied. These results indicate that with the progress of charge transfer the solvation structure in the dilute Rb concentration range changes into the structure containing polyanions composed of Hg species
Applications of Electrodeless Discharge Rb Vapor Lamp for frequency stabilization of 1529 nm laser
No full textOptical-optical double-resonance (OODR) Spectra for the 5(2)P(1/2) -6(2)S(1/2) and the 5(2)P(3/2) -4(2)D(3/2,5/2) transition of (87)Rb have been used for frequency stabilization in near-infrared region for many years. Though the method works well, it calls for locked 780nm lasers to pump Rb atoms into 5(2)P(3/2). We are trying to use an electrodeless discharge Rb vapor lamp to replace the complex locked pumping laser. The lamp's spectra show us that there are two spectral signals, 780nm and 795nm, are much larger than others. We are trying to make 5(2)P(3/2) level populated by shining the lamp light into a Rb vapor cell. Meantime, the lamp could absorb 1529 nm laser most seriously when operating in red mode. The absorption signal with high SNR but with several hundred megahertz line-width is hopefully to be used to lock the 1529 nm laser directly without 780 nm laser. The advantage of the lamp used in the frequency stabilized system is to reduce the size and cost of 1.5 mu m wavelength standard for optical communication application.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000295261600160&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Engineering, Electrical & ElectronicPhysics, AppliedTelecommunicationsEICPCI-S(ISTP)
Fractional Edge Cover Number of Model RB
No full textModel RB is a random constraint satisfaction problem with a growing domain size, which exhibits exact phase transition phenomena. Many hard instances with planted solutions can be generated via Model RB, to be used as benchmarks for algorithmic competitions and researches. In the past, some structural parameters of constraint hypergraphs are analyzed to show hardness of Model RB, such as hinge width, decycling number, treewidth, and hypertree width. In this paper, one more structural parameter of constraint hypergraphs of Model RB, namely the fractional edge cover number, is analyzed. We show upper and lower bounds on the fractional edge cover number of Model RB. In particular, the fractional edge cover number of Model RB is shown to be asymptotically linear in the number of variables, like hinge width, decycling number, treewidth and hypertree width. These results together provide further evidences on the hardness of Model RB.EICPCI-S(ISTP)[email protected]
Incommensurately modulated Rb<sub>2</sub>ZnCl<sub>4</sub>
No full textRubidium zinc chloride (RbZnCl) is isostructural to β-KSO and shows ferroelectric behaviour below 192K [1]. It belongs to ABX crystal family and exhibits successive phase transitions which are characteristic of this family. At high temperature it has an orthorhombic structure with Pmcn as its space group with some disorder associated with ZnCltetrahedra, then an incommensurate modulation develops along c-axis at 303K with the wavevector q = (1/3 – δ) c*, where ‘δ’ is the parameter which shows the incommensurability and it decreases with decreasing temperature. At around Tc = 192K, ‘δ’ becomes zero and thus RbZnCl goes from an incommensurately modulated structure to a commensurately modulated structure [2]. Finally, RbZnCl undergoes an additional phase transition around 75K [3] with a probable monoclinic distortion and additional satellites in a*b* plane. In the incommensurate phase the modulation wave function goes from a harmonic sinusoidal function to a highly anharmonic function as it approaches lock-in phase transition at Tc. The modulation function in the incommensurate phase of RbZnCl is not only given by displacive modulation but also by the modulations of atomic displacement parameters (ADPs) and anharmonic ADPs [4-5]. In the low temperature phase (T<75K), the additional modulation arises in the ab plane with the wavevector q = 0.5a*+0.5b*. The detailed structural analysis in each phase, especially near the lock-in transition along with the lattice dynamics studies help us to understand the relation between aperiodic order and physical properties
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