A variety of experimental techniques and equipment for the measurement of inertial effects are herein presented. The bulk of the work relates to improvements to an existing local gravitational acceleration "little-g'' measurement apparatus. These improvements are predicted to push the statistical uncertainty in the measurement of g to less than 1 part-per-billion (ppb). To accomplish this goal, several other projects were undertaken. These include a finite-element model of the magnetic field coil setup used in the experimental apparatus, as well as the design and construction of a hermetically-sealed diode laser system with excellent long-term frequency stability. Additionally, a direct digital synthesis-based frequency generator was designed and built for a proposed frequency-domain atom interferometer experiment. Finally, a side-project involving the evaluation of the magnetic field uniformity/stability of a commercial optical isolator was performed, and its results are presented as an appendix.
A variety of experimental techniques and equipment for the measurement of inertial effects are herein presented. The bulk of the work relates to improvements to an existing local gravitational acceleration "little-g'' measurement apparatus. These improvements are predicted to push the statistical uncertainty in the measurement of g to less than 1 part-per-billion (ppb). To accomplish this goal, several other projects were undertaken. These include a finite-element model of the magnetic field coil setup used in the experimental apparatus, as well as the design and construction of a hermetically-sealed diode laser system with excellent long-term frequency stability. Additionally, a direct digital synthesis-based frequency generator was designed and built for a proposed frequency-domain atom interferometer experiment. Finally, a side-project involving the evaluation of the magnetic field uniformity/stability of a commercial optical isolator was performed, and its results are presented as an appendix.
Inertial sensors based on cold atom interferometry exhibit many interesting features for applications related to inertial navigation, particularly in terms of sensitivity and long-term stability. However, at present the typical atom interferometer is still very much an experiment—consisting of a bulky, static apparatus with a limited dynamic range and high sensitivity to environmental effects. To be compliant with mobile applications further development is needed. In this work, we present a compact and mobile experiment, which we recently used to achieve the first inertial measurements with an atomic accelerometer onboard an aircraft. By integrating classical inertial sensors into our apparatus, we are able to operate the atomic sensor well beyond its standard operating range, corresponding to half of an interference fringe. We report atom-based acceleration measurements along both the horizontal and vertical axes of the aircraft with one-shot sensitivities of 2.3 × 10−4 g over a range of ∼ 0.1 g. The same technology can be used to develop cold-atom gyroscopes, which could surpass the best optical gyroscopes in terms of long-term sensitivity. Our apparatus was also designed to study multi-axis atom interferometry with the goal of realizing a full inertial measurement unit comprised of the three axes of acceleration and rotation. Finally, we present a compact and tunable laser system, which constitutes an essential part of any cold-atom-based sensor. The architecture of the laser is based on phase modulating a single fiber-optic laser diode, and can be tuned over a range of 1 GHz in less than 200 μs.
We investigate the limits of our cold atoms interferometer to rotation and acceleration measurements. In contrast with previous atomic setups, emphasis was placed on the long term stability and compactness of the device through the use of laser cooled atoms, as previously shown with the field of atomic clock. It has been designed to give access to all six axes of inertia (three accelerations and three rotations). The expected improvement in stability will enable to consider applications in inertial navigation, geophysics and tests of general relativity as the equivalence principle or Lense-Thirring effect.
Atom interferometry has hugely benefitted from advances made in cold atom physics over the past twenty years, and ultra-precise quantum sensors are now available for a wide range of applications [1]. In particular, cold atom interferometers have shown excellent performances in the field of acceleration and rotation measurements [2,3], and are foreseen as promising candidates for navigation, geophysics, geo-prospecting and tests of fundamental physics such as the Universality of Free Fall (UFF). In order to carry out a test of the UFF with atoms as test masses, one needs to compare precisely the accelerations of two atoms with different masses as they fall in the Earth’s gravitational field. The sensitivity of atom interferometers scales like the square of the time during which the atoms are in free fall, and on ground this interrogation time is limited by the size of the experimental setup to a fraction of a second. Sending an atom interferometer in space would allow for several seconds of excellent free-fall conditions, and tests of the UFF could be carried out with precisions as low as 10-15 [4]. However, cold atoms experiments rely on complex laser systems, which are needed to cool down and manipulate the atoms, and these systems are usually very sensitive to temperature fluctuations and vibrations. In addition, when operating an inertial sensor, vibrations are a major issue, as they deteriorate the performances of the instrument. This is why cold atom interferometers are usually used in ground based facilities, which provide stable enough environments. In order to carry out airborne or space-borne measurements, one has to design an instrument which is both compact and stable, and such that vibrations induced by the platform will not deteriorate the sensitivity of the sensor. We report on the operation of an atom interferometer on board a plane carrying out parabolic flights (Airbus A300 Zero-G, operated by Novespace). We have constructed a compact and stable laser setup, which is well suited for onboard applications. Our goal is to implement a dual-species Rb-K atom interferometer in order to carry out a test of the UFF in the plane. In this perspective, we are designing a dual-wavelength laser source, which will enable us to cool down and coherently manipulate the quantum states of both atoms. We have successfully tested a preliminary version of the source and obtained a double species magneto-optical trap (MOT).
Precision measurements of gravitational acceleration g have far reaching applications in navigation and sensing as well as for tests of general relativity. Grating-echo atom interferometers (AIs) utilize simple setups and distinctive excitation schemes that involve a single excitation laser, and do not require velocity selection. They have demonstrated measurements of gravity precise to 75 parts per billion (ppb) by dropping laser-cooled atomic samples through ~ 1 cm. Here we describe progress toward realizing a cold atom gravimeter using an echo AI designed for drop heights of ~30 cm. The experimental technique involves illuminating the falling sample of laser-cooled rubidium atoms with two standing wave (sw) pulses separated by time t = T. The sw pulses are composed of two traveling-wave components, each having a wave vector of magnitude k = 2π/λ. Momentum state interference produces one-dimensional density gratings with a period λ/2 immediately after each excitation pulse. These gratings dephase due to the velocity distribution of the sample along the sw axis. The AI uses an echo technique to cancel the effect of velocity dephasing and observe a rephased density grating in the vicinity of the echo time τ = 2Τ. The grating contrast and phase are measured by coherently backscattering a traveling wave readout pulse from the sample. The grating phase, measured with respect to a vibrationally stabilized inertial reference frame, scales as 2kgΤ2. A drawback of echo AIs is the signal-to-noise ratio, which is limited by the contrast of the grating and systematic effects due the refractive index of the sample. Here, we review improvements to the experimental design and investigate methods of improving the signal-to-noise ratio by optimizing the atom-field coupling. We describe progress toward realizing our goals of increasing the grating contrast and the backscattered signal. The improved contrast is expected to allow the experiment to be carried out at a lower density to reduce corrections due to the refractive index. We discuss a variety of excitation schemes for achieving a target precision of a few ppb.
This dissertation describes the development of a suite of interlinked techniques for precision metrology with matter wave lattices realized in a ceiling-to-floor non-magnetic atom trapping apparatus. This work involves the development of a single-state atom interferometer that relies on the observation of density gratings formed in the atomic ground state of a laser-cooled sample. These gratings, the result of Kapitza-Dirac diffraction of momentum states following a standing wave optical excitation pulse, typically dephase according to their velocity distribution, and motional properties of the sample, including the local value of gravitational acceleration g, are imprinted on the grating contrast and phase. These features can be extracted by coherently backscattering a travelling wave readout field applied within the thermal coherence time of the sample and measuring the grating free-induction decay. Alternatively, a grating echo, resulting from the application of two standing wave pulses separated by t=T_{21}, can be detected using the same backscattering method in the vicinity of the echo time t=2T_{21} on time scales defined by the transit of cold atoms out of the standing wave beam volume. This dissertation presents five main experimental results that impact a new generation of cold atom quantum sensors. Firstly, we investigate a technique for measuring the magnetic moments and sublevel distributions of laser-cooled gases. Secondly, we study optical channell-ing which can be used to increase the scattering efficiency of optical lattices and the sensitivity of grating-echo interferometers. Thirdly, we describe Bragg scattering of a readout pulse from optical lattices and develop a technique to optimize this process in dilute gas lattices, leading to increased signal strengths in echo interferometers. Fourthly, we demonstrate a novel "Ramsey" velocimeter which can measure sample center-of-mass velocity with a precision of 600 µm/s. Finally, we present a measurement of g which represents the first realization of a frequency domain echo-type gravimeter, with a sensitivity to g of 2 parts per million. We outline the basis for improving the precision of these sensors to realize devices capable of measuring g with a sensitivity of 10 parts per billion and probing velocities more precisely than all other atomic velocimeters.
The research on cold-atom interferometers gathers a large community of about 50 groups worldwide both in the academic and now in the industrial sectors. The interest in this sub-field of quantum sensing and metrology lies in the large panel of possible applications of cold-atom sensors for measuring inertial and gravitational signals with a high level of stability and accuracy. This review presents the evolution of the field over the last 30 years and focuses on the acceleration of the research effort in the last 10 years. The article describes the physics principle of cold-atom gravito-inertial sensors as well as the main parts of hardware and the expertise required when starting the design of such sensors. The author then reviews the progress in the development of instruments measuring gravitational and inertial signals, with a highlight on the limitations to the performances of the sensors, on their applications and on the latest directions of research.