High-precision inertial sensing demonstrations with light pulse atom interferometry have typically used Raman pulses having durations orders of magnitude shorter than the dwell time between interferometer pulses. Environmentally robust sensors operating at high-bandwidth will be required to operate at short (millisecond scale) dwell times between Raman pulses. In such an operational mode, the Raman pulse duration becomes an appreciable fraction of the dwell time between pulses. In addition, high-precision inertial sensing applications have typically been demonstrated in mildly dynamic or nondynamic environments having low rate of change of inertial input, ensuring that applied Raman pulses satisfy the Raman resonance condition. Application of nonresonant pulses will be inevitable in sensors registering time-varying inertial input. We present a diagrammatic technique for calculation of atomic output state populations for multipulse atom optics manipulations that explicitly account for the effects of finite pulse duration and finite Raman detuning effects on the laser-induced atomic phase. We analyze several atom interferometer sequences. We report accelerometer and gyroscope phase evolution for fixed Raman laser frequency difference incorporating corrections in powers of the ratio of pulse duration to time interval between interferometer pulses. Our accelerometer result agrees with other published results.
Light pulse atom interferometers have demonstrated remarkable sensitivity and stability for acceleration and rotation rate measurement. However, typical manifestations are designed for laboratory environments and thus rely on a fixed magnitude and direction of gravity, and limited ambient rotation rate. We have enhanced the application space of atom interferometers towards more dynamic environments, with special attention for inertial navigation. I present our work in the domain of short time-of-flight atom interferometry, whereby the magnitude of ensemble excursion is constrained. The limited interrogation time results in a significant loss of sensitivity. We recover a fraction of the lost sensitivity by operating with an enhanced duty-cycle and data-rate. To demonstrate this concept, we construct an atom interferometer accelerometer capable of operating at data-rates as high as 300 Hz with sensitivities at μg/rtHz levels, which represents a competitive figure for inertial navigation application. For the bulk of this work, we demonstrate a dual-axis sensor capable of simultaneous acceleration and rotation-rate measurements. The sensor relies on a technique we refer to as "ensemble exchange" which provides a high flux source of ultracold atoms by swapping atomic ensembles between two MOTs. We achieve a steady-state atom number of 7e6 atoms/shot using a minimal loading time of a few milliseconds each shot. Furthermore, we find this technique to be robust under dynamic conditions as large as 10 g of acceleration and 20 rad/s of rotation rate, representing a significant enhancement in ultra-cold atom sample preparation. The sensor achieves μg/rtHz and μrad/s/rtHz sensitivities, making this technique a compelling prospect for inertial navigation applications. Through the use of auxiliary cosensors and a real-time combinatorial loop with feedforward and feedback mechanisms, we demonstrate an unprecedented enhancement of the sensor dynamic range up to 20 mg. Finally, I will discuss a novel manifestation of short time-of-flight atom interferometry in a warm atomic vapor, which avoids the complication of cold sample preparation and has the potential for significantly simplified laser systems.
We demonstrate a light-pulse atom interferometer based on the diffraction of free-falling atoms by a picosecond frequency-comb laser. More specifically, we coherently split and recombine wave packets of cold ^{87}Rb atoms by driving stimulated Raman transitions between the |5s ^{2}S_{1/2},F=1⟩ and |5s ^{2}S_{1/2},F=2⟩ hyperfine states, using two trains of picosecond pulses in a counterpropagating geometry. We study the impact of the pulses' length as well as the interrogation time onto the contrast of the atom interferometer. Our experimental data are well reproduced by a numerical simulation based on an effective coupling that depends on the overlap between the pulses and the atomic cloud. These results pave the way for extending light-pulse interferometry to transitions in other spectral regions and therefore to other species, for new possibilities in metrology, sensing of gravito-inertial effects, and tests of fundamental physics.
We demonstrate a closed-loop light-pulse atom-interferometer inertial sensor that can realize continuous decoupled measurements of acceleration and rotation rate. The sensor operates with double-loop atom interferometers, which share the same Raman light pulses in a spatially separated Mach-Zehnder configuration and use continuous cold atomic beams propagating in opposite directions from two
2D+ magneto-optical trappings. Acceleration and the rotation rate are decoupled and simultaneously measured by the sum and difference of dual-atom-interferometer signals, respectively. The sensitivities of inertial measurements are also increased to be approximately 1.86 times higher than that of a single atom interferometer. The acceleration phase shift is compensated in real time by phase locking these interferometers via the Raman laser phases from the sum-interferometer signal, and the gyroscope performance is improved. We achieve long-term stabilities of $6.1\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\text{g}$ and 840 nrad/s for the acceleration and the rotation rate, respectively, using a short interrogation time of 0.87 ms (interference area
A=0.097mm2). This work provides a building block for an atomic interferometer-based inertial measurement unit for use in field applications that require a high data rate and high stability.
Cold-atom inertial sensors target several applications in navigation, geoscience and tests of fundamental physics. Reaching high sampling rates and high inertial sensitivities, obtained with long interrogation times, represents a challenge for these applications. We report on the interleaved operation of a cold-atom gyroscope, where 3 atomic clouds are interrogated simultaneously in an atom interferometer featuring a 3.75 Hz sampling rate and an interrogation time of 801 ms. Interleaving improves the inertial sensitivity by efficiently averaging vibration noise, and allows us to perform dynamic rotation measurements in a so-far unexplored range. We demonstrate a stability of
3×10−10 rad.s
−1, which competes with the best stability levels obtained with fiber-optics gyroscopes. Our work validates interleaving as a key concept for future atom-interferometry sensors probing time-varying signals, as in on-board navigation and gravity-gradiometry, searches for dark matter, or gravitational wave detection.
Ushered forth by advances in time and frequency metrology, atom interferometry remains an indispensable measurement tool in atomic physics due to its precision and versatility. A sequence of four
pi/2 beam splitter pulses can create either an interferometer sensitive to the atom's recoil frequency when the momentum imparted by the light reverses direction between pulse pairs or, when constructed from pulses without such reversal, sensitive to the perturbing potential from an external optical field. Here, we demonstrate the first atom interferometer with laser-cooled lithium, advantageous for its low mass and simple atomic structure. We study both a recoil-sensitive Ramsey-Bord\\'e interferometer and interferometry sensitive to the dynamic polarizability of the ground state of lithium. Recoil-sensitive Ramsey-Bord\\'e interferometry benefits from lithium's high recoil frequency, a consequence of its low mass. At an interrogation time of 10 ms, a Ramsey-Bord\\'e lithium interferometer could achieve sensitivities comparable to those realized at much longer times with heavier alkali atoms. However, in contrast with other atoms that are used for atom interferometry, lithium's unresolved excited-state hyperfine structure precludes the the cycling transition necessary for efficient cooling. Without sub-Doppler cooling techniques. As as result, a lithium atomic gas is typically laser cooled to temperatures around 300
muK, above the Doppler limit, and well above the recoil temperature of 6
muK. This higher temperature gas expands rapidly during the operation of an atom interferometer, limiting the experimental interrogation time and preventing spatially resolved detection. In this work, a light-pulse lithium matter-wave interferometer is demonstrated in spite of these limitation. Two-photon Raman interferometer pulses coherently couple the atom's spin and momentum and are thus able to spectrally resolve the outputs. These fast pulses drive conjugate interferometers simultaneously which beat with a fast frequency component proportional to the atomic recoil frequency and an envelope modulated by the two-photon detuning of the Raman transition. We detect the summed signal at short experimental times, preventing perturbation of the signal from vibration noise. This demonstration of a sub-recoil measurement with a super-recoil sample opens the door to similar scheme with other particles that are difficult to trap and cool well, like electrons. An interferometer instead composed of
pi/2-pulses with a single direction of momentum transfer, can be sensitive to the dynamic polarizability of the atomic ground state. By scanning the frequency of an external driving field, such a measurement can be used to determine the atom's tune-out wavelength. This is the wavelength at which the frequency-dependent polarizability vanishes due to compensating ac-Stark shifts from other atomic states. Lithium's simple atomic structure allows for a precise computation of properties with only {\\em ab initio} wave functions and spectroscopic data. A direct interferometric measurement of lithium's red tune-out wavelength at 670.971626(1) nm, is a precise comparison to existing `all-order' atomic theory computations. It also provides another way to experimentally determine the
S− to
P− transitions matrix elements, for which large correlations and small values complicate computations. Finally, a future measurement of lithium's ultraviolet tune-out wavelength of at 324.192(2) nm would be sensitive to relativistic approximations in the atomic structure description.Atom interferometry simultaneously verifies existing atomic theory with measurements of atomic properties and searches for exotic physics lurking in plain sight. The techniques developed here broaden the applicability of interferometry and increase measurement sensitivity by simplifying cooling, increasing atom number and reducing the cycle time. Overcoming the current experimental limitations on interrogation time would allow for ultra-precise measurements of both the tune-out wavelength and the fine structure constant.