Showing papers on "Atom interferometer published in 2003"

System and a method of measuring an optical path difference in a sensing interferometer

Abstract: An apparatus and a method of measuring an optical path difference in a sensing interferometer. Light from a source is directed in the sensing interferometer. The light reflected from the sensing interferometer is splitted into first and second beams respectively directed into two reference interferometers having optical path differences greater than the coherence length of the source and such that the optical signals are in quadrature. The intensities of the light transmitted by the reference interferometers and recombined light reflected from the reference interferometers are detected for measuring the optical path difference in the sensing interferometer. Additional light sources allow for correction of internal perturbations and absolute measurement of the optical path difference in the sensing interferometer.

Quantum theory of atomic clocks and gravito-inertial sensors: an update

Abstract: In the framework of the ABCDξ formulation of atom optics and with an adequate modelization of the beam splitters, we establish an exact analytical phase shift expression for atom interferometers. This result is valid for a time-dependent external Hamiltonian at most quadratic in position and momentum operators and is expressed in terms of coordinates and momenta of the wave packet centres at the interaction vertices only. As a specific application, the case of atom gyrometers and accelerometers is presented in detail.

Wide-band direct measurement of thermal fluctuations in an interferometer.

Abstract: We directly measured mechanical thermal fluctuations in mirrors over three decades of frequency range using a short-length Fabry-Perot interferometer. This is the first such measurement at wide off-resonant frequency band that is much lower than mechanical resonant frequencies. Theoretically, the mechanical fluctuation in mirrors had been thought to become the principal noise in precise interferometry, such as in gravitational wave detection. We identified the thermally induced noises in the interferometer, the so-called substrate Brownian noise, substrate thermoelastic noise, and coating Brownian noise.

Reaching the quantum noise limit in a high-sensitivity cold-atom inertial sensor

Abstract: In our high-precision atom interferometer, the measured atomic phase shift is sensitive to rotations and accelerations of the apparatus, and also to phase fluctuations of the Raman lasers. In this paper we study two principal noise sources affecting the atomic phase shift, induced by optical phase noise and vibrations of the setup. Phase noise is reduced by carrying out a phase lock of the Raman lasers after the amplification stages. We also present a new scheme to reduce noise due to accelerations by using a feed-forward on the phase of the Raman beams. With these methods, it should be possible to reach the range of the atomic quantum projection noise limit, which is about 1m rad rmsfor our experiment, i.e. 30 nrad s −1 Hz −1/2 for a rotation

Test mass materials for a new generation of gravitational wave detectors

Abstract: To obtain improved sensitivities in future generations of interferometric graviational wave detectors, beyond those proposed as upgrades of current detectors, will require different approaches in different portions of the gravitational wave frequency band. However the use of silicon as an interferometer test mass substrate, along with all-reflective interferometer topologies, could prove to be a design enabling sensitivity improvements at both high and low frequencies. In this paper the thermo-mechanical properties of silicon are discussed and the potenial benefits from using silicon as a mirror substrate material in future gravitational wave detectors are outlined.

MAGIA—using atom interferometry to determine the Newtonian gravitational constant

Abstract: We describe our experiment MAGIA (misura accurata di G mediante interferometria atomica), in which we will use atom interferometry to perform a high precision measurement of the Newtonian gravitational constant G. Free-falling laser-cooled atoms in a vertical atomic fountain will be accelerated due to the gravitational potential of nearby source masses (SMs). Detecting this acceleration with techniques of Raman atom interferometry will enable us to assign a value to G. To suppress systematic effects we will implement a double-differential measurement. This includes launching two atom clouds in a gradiometer configuration and moving the SMs to different vertical positions. We briefly summarize the general idea of the MAGIA experiment and put it in the context of other high precision G-measurements. We present the current status of the experiment and report on analyses of the expected measurement accuracy.

Diffraction phases in atom interferometers

Abstract: Diffraction of atoms by lasers is a very important tool for matter wave optics. Although the process is well understood, the phase shifts induced by this diffraction process are not well known. In this paper, we make analytical calculations of these phase shifts in some simple cases and use these results to model the contrast interferometer recently built by Pritchard and co-workers. We thus show that the values of the diffraction phases are large and that they probably contribute to the phase noise observed in this experiment.

A Preliminary Measurement of the Fine Structure Constant Based on Atom Interferometry

Abstract: Using an atom interferometer method, we measure the recoil velocity of a cesium atom due to the coherent scattering of a photon. This measurement is used to obtain a value of /MCs and the fine structure constant, α. The current fractional uncertainty is Δα/α = 7.4 × 10-9.

Dual-recycled cavity-enhanced Michelson interferometer for gravitational-wave detection.

Abstract: The baseline design for an Advanced Laser Interferometer Gravitational-Wave Observatory (Advanced LIGO) is a dual-recycled Michelson interferometer with cavities in each of the Michelson interferometer arms. We describe one possible length-sensing and control scheme for such a dual-recycled, cavity-enhanced Michelson interferometer. We discuss the principles of this scheme and derive the first-order sensing signals. We also present a successful experimental verification of our length-sensing system using a prototype tabletop interferometer. Our results demonstrate the robustness of the scheme against deviations from the idealized design. We also identify potential weaknesses and discuss possible improvements. These results as well as other benchtop experiments that we present form the basis for a sensing and control scheme for Advanced LIGO.

Model of thermal wave-front distortion in interferometric gravitational- wave detectors. I. Thermal focusing

Abstract: We develop a steady-state analytical and numerical model of the optical response of power-recycled Fabry-Perot Michelson laser gravitational-wave detectors to nonlinear thermal focusing in optical substrates. We assume that the thermal distortions are small enough that we can represent all intracavity fields as linear combinations of basis functions derived from the eigenmodes of a Fabry-Perot arm cavity. We have included the effects of power absorption in optical substrates and coatings, mismatches between laser wave-front and mirror surface curvatures, and aperture diffraction. We demonstrate a detailed numerical example of this model using the MATLAB program Melody for the initial Laser Interferometer Gravitational Wave Observatory detector.

Stable Fabry-Perot interferometer

Abstract: A stable scanning or non-scanning Fabry-Perot interferometer and a method for stabilising the interferometer. The interferometer is composed of two plane mirrors arranged parallel to one another with a preselected optical distance between the optical surfaces of the mirrors. The interferometer radiates an output light signal in response to a light input signal applied parallel to the optical axis of the interferometer. The interferometer is stabilised by providing an arrangement for passing a plurality of reference light beams through the interferometer, the reference light beams being inclined at a preselected angle to the optical axis of the interferometer.

Stern Gerlach interferometry with metastable argon atoms: an immaterial mask modulating the profile of a supersonic beam

Abstract: A new Stern Gerlach interferometer operating with a nozzle beam of metastable argon atoms Ar* (3p5 4s, 3 P 2) is described. The selection of incoming (polarisation) and outgoing (analysis) Zeeman sublevels is achieved by use of laser induced transitions at two wavelengths, 811.5 nm (closed J = 2 → J = 3 transition) and 801.5 nm (open J = 2 → J = 2 transition). Linear superpositions of Zeeman sublevels, just beyond the polariser and just before the analyser, are prepared by means of two zones where Majorana transitions take place. In between, a controlled magnetic field configuration (the phase object) is produced within a triple μ-metal shielding. Standard interference patterns are obtained by scanning the field and detecting the atoms by secondary electron emission from a Faraday cup. When a static radial magnetic gradient is used, the beam profile is modulated by interference. The transverse pattern, which can be translated at will by adding a homogeneous field, is observed for the first time using a multi-channel electron multiplier followed by a phosphor screen and a CCD camera. The results satisfactorily agree with all theoretical predictions.

Mirror Thermal Noise in Interferometric Gravitational Wave Detectors

Abstract: The LIGO (Laser Interferometer Gravitational-wave Observatory) project has begun its search for gravitational waves, and efforts are being made to improve its ability to detect these. The LIGO observatories are long, Fabry-Perot-Michelson interferometers, where the interferometer mirrors are also the gravitational wave test masses. LIGO is designed to detect the ripples in spacetime caused by cataclysmic astrophysical events, with a target gravitational wave minimum strain sensitivity of 4 x 10^-22 around 100 Hz. The Advanced LIGO concept calls for an order of magnitude improvement in strain sensitivity, with a better signal to noise ratio to increase the rate of detection of events. Some of Advanced LIGO's major requirements are improvements over the LIGO design for thermal noise in the test mass substrates and reflective coatings. Thermal noise in the interferometer mirrors is a significant challenge in LIGO's development. This thesis reviews the theory of test mass thermal noise and reports on several experiments conducted to understand this theory. Experiments to measure the thermal expansion of mirror substrates and coatings use the photothermal effect in a cross-polarized Fabry-Perot interferometer, with displacement sensitivity of 10^-15 m/rHz. Data are presented from 10 Hz to 4kHz on solid aluminum, and on sapphire, BK7, and fused silica, with and without commercial TiO2/SiO2 dielectric mirror coatings. The substrate contribution to thermal expansion is compared to theories by Cerdonio et al. and Braginsky, Vyatchanin, and Gorodetsky. New theoretical models are presented for estimating the coating contribution to the thermal expansion. These results can also provide insight into how heat flows between coatings and substrates relevant to predicting coating thermoelastic noise. The Thermal Noise Interferometer (TNI) project is a interferometer built specifically to study thermal noise, and this thesis describes its construction and commissioning. Using LIGO-like designs, components, and processes, the TNI has a minimum length noise in each of two arm cavities of 5 x 10^-18 m/rHz around 1 kHz.

Atom interferometer-based gravity gradiometer measurements

Abstract: Atom Interferometer-Based Gravity Gradiometer Measurements Jeffrey B. Fixler 2003 A cold source, Cesium atomic fountain instrument was constructed to measure gravitational gradients based on atomic interference techniques. Our instrument is one of the first gradiometers that is absolute. The defining ruler in our apparatus is the wavelength of the cesium ground-state hyperfine splitting, which has an accuracy of ≤ 1 part per thousand determined by the oscillators used in our clocks. The gradiometer is based on the light pulse atom interferometer technique employing a π/2− π − π/2 pulse sequence on two identical ensembles of cesium atoms. We have achieved a differential acceleration sensitivity of 4×10−9g/√Hz with an accuracy of ≤ 1× 10−9g in a vertical gravity gradiometer configuration. A detection system was implemented to suppress sensitivity to laser amplitude and frequency noise. Immunity to vibration-induced acceleration noise was implemented with a data analysis technique not requiring the use of an active vibration isolation system. The gravity gradiometer was characterized against systematic environmental effects including reference platform tilt and vibration. The accuracy of the gradiometer was characterized through a measurement of the Newtonian gravitational constant, G. The change in the gravitational field along one dimension was measured when a well-characterized lead, Pb, mass is displaced. A value of G = (6.693 ± 0.027 ± 0.021)×10−11 m/(kg ·s2) is reported with the two errors representing statistics and systematics, respectively. The experiment introduces a new class of precision measurement experiments to determine G through the

Noise limits in matter-wave interferometry using degenerate quantum gases

Abstract: We analyze the phase resolution limit of a Mach-Zehnder atom interferometer whose input consists of degenerate quantum gases of either bosons or fermions. For degenerate gases, the number of atoms within one de Broglie wavelength is larger than unity, so that atom-atom interactions and quantum statistics are no longer negligible. We show that for equal atom numbers, the phase resolution achievable with fermions is noticeably better than for interacting bosons.

Grid-based simulation program for gravitational wave interferometers with realistically imperfect optics

Abstract: We describe an optical simulation program that models a complete, coupled-cavity interferometer such as those used by the Laser Interferometer Gravitational-Wave Observatory (LIGO) Project. A wide variety of interferometer deformations can be modeled, including general surface roughness and substrate inhomogeneities, with no a priori symmetry assumptions about the nature of interferometer imperfections. Several important interferometer parameters are optimized automatically to achieve the best possible sensitivity for each new set of perturbed mirrors. The simulation output dataset includes the circulating powers and electric fields at various points in the interferometer, both for the main carrier beam and for its signal-sideband auxiliary beams, allowing an explicit calculation of the shot-noise-limited gravitational-wave sensitivity of the interferometric detector to be performed. Here we present an overview of the physics simulated by the program, and demonstrate its use with a series of runs showing the degradation of LIGO performance caused by realistically deformed mirror profiles. We then estimate the effect of this performance degradation upon the detectability of astrophysical sources of gravitational waves. We conclude by describing applications of the simulation program to LIGO research and development efforts.

Experiments with Degenerate Bose and Fermi Gases

Abstract: Two sets of studies are described in this thesis. In the first set, an atom interferometry technique was developed for the measurement of the fine structure constant using a BoseEinstein Condensate. In the second set, degenerate Fermi gases were prepared and their properties explored in a regime of strong interactions. We have developed an atom interferometer which is capable of measuring with high precision the “photon recoil frequency” (ωrec). ωrec corresponds to the kinetic energy of an atom recoiling due to absorption of a photon. ωrec can be used to determine the quantity h/matom and the fine structure constant, α. A preliminary measurement using a 23Na BoseEinstein Condensate yielded ωrec with a precision of 7 × 10−6 which deviated by 2 × 10−4 from the currently accepted value. Plausible upgrades to the apparatus should produce a precision of 10−9 which would bring within reach a measurement of h/matom and α in the 10−9 range. Such accuracy would be of considerable scientific and metrological import. A quantum degenerate gas of 6Li fermions was produced by sympathetic cooling with 23Na bosons in a two-species atom trapping apparatus. The cooling strategy was optimized to enable production of fermions with atom numbers up to 7 × 107 at half the Fermi temperature (TF ), or temperatures down to 0.05TF ∼ 100 nK with 3× 107 atoms. We can also produce degenerate Bose-Fermi mixtures with several million atoms in each species. We studied the behavior of mixtures of fermi gases in regimes of strong interactions near “Feshbach” resonances. A study of system stability enabled the experimental observation of two such Feshbach resonances. We carried out a theoretical study to interpret the observation (by many experimental groups) of hydrodynamic behavior of fermi gases during expansion out of an atom trap in a strongly-interacting regime. The study concluded that this behavior was not a qualitative signature of fermionic superfluidity and could arise from classical collisions. Finally, radio-frequency (RF) spectroscopy was used to probe interaction in 6Li. We demonstrated the absence of mean field “clock” shifts of RF transitions in a two-(spin)state fermion system. Using a three-state system, we measured the interaction strength between different spin states. The measurements near Feshbach resonances indicate a saturation of the interaction strength at a large negative value. This result is of relevance in the continuing quest for fermionic superfluidity in atomic gases. Thesis Supervisor: David E. Pritchard Title: Cecil and Ida Green Professor of Physics Thesis Supervisor: Wolfgang Ketterle Title: John D. MacArthur Professor of Physics

Adaptive optics approach for prefiltering of geometrical fluctuations of the input laser beam of an interferometric gravitational waves detector

Abstract: In this article we present a preliminary study and experimental results on the use of an adaptive optics (AO) system for the reduction of geometrical fluctuations in a laser beam. The AO system is based on a Shack–Hartmann wave front sensor and a micromachined deformable mirror as a corrective element. The aim of this work is to investigate the applicability of such technologies to improving wave front clean-up conditions in long baseline interferometric gravitational wave detection.

Gravity field measurements using cold atoms with direct optical readout

Abstract: We show theoretically that measuring an optimum observable of an electromagnetic wave propagating in an atomic medium moving freely in a gravitational field results in a sensitive detection of the acceleration of gravity and its gradient. The best achievable sensitivity of such a measurement is comparable with that of light-pulse atom interferometers based on measuring the atomic internal state. This optical technique is useful for nondestructive detection of ultracold atoms in atomic interferometers.

HYPER and gravitational decoherence

Abstract: We study the decoherence process associated with the scattering of stochastic backgrounds of gravitational waves. We show that it has a negligible influence on HYPER-like atomic interferometers although it may dominate decoherence of macroscopic motions, such as the planetary motion of the Moon around the Earth.

Interferometry with entangled atoms

Abstract: A quantum gravity-gradiometer consists of two spatially separated ensembles of atoms interrogated by pulses of a common laser beam. The laser pulses cause the probability amplitudes of atomic ground-state hyperfine levels to interfere, producing two, motion-sensitive, phase shifts, which allow the measurement of the average acceleration of each ensemble, and, via simple differencing, of the acceleration gradient. Here we propose entangling the quantum states of atoms from the two ensembles prior to the pulse sequence, and show that entanglement encodes their relative acceleration in a single interference phase which can be measured directly, with no need for differencing.

Quantum noise in gravitational wave interferometers: an overview and recent developments

Abstract: We present an overview of quantum noise in gravitational wave interferometers. Gravitational wave detectors are extensively modified variants of a Michelson interferometer and the quantum noise couplings are strongly influenced by the interferometer configuration. We describe recent developments in the treatment of quantum noise in the complex interferometer configurations of present-day and future gravitational-wave detectors. In addition, we explore prospects for the use of squeezed light in future interferometers, including consideration of the effects of losses, and the choice of optimal readout schemes.

Mapping a cloud of ultracold atoms onto a miniature storage ring

Abstract: We describe how to realize magnetic and magneto-optical confinement of ultracold atoms in a torus with adjustable diameter and how an elliptical cloud of ultracold atoms can be adiabatically transformed to have a toroidal shape. An experiment with cold 87Rb atoms demonstrates the feasibility of shape transformations. These techniques can be used for atom interferometry and quantum computation.

Low-coherence tandem interferometer for remote calibration of gauge blocks

Abstract: A low-coherence tandem interferometer with a single-mode optical fiber is developed for remote-measurement of length. The optical path difference provided in the first low-coherence interferometer is transmitted through the optical fiber to the second low-coherence interferometer. Low-coherence interference fringes are generated when the optical path difference in the second interferometer, which correspond to the length being measured, compensates that of the first interferometer. A gauge block of 50 mm long has been calibrated remotely through the single-mode optical fiber of 3 km length with a stnadard deviation of 0.12 μm.

A Crystal-based Matter-wave Interferometric Gravitational-wave Observatory

Abstract: It is shown that atom interferometry allows for the construction of MIGO, the Matter-wave Interferometric Gravitational-wave Observatory. MIGOs of the same sensitivity as LIGO or LISA are expected to be orders of magnitude smaller than either one. A design for MIGO using crystalline diffraction gratings is introduced, and its sensitivity is calculated.