Enhanced Atom Interferometer Readout through the Application of Phase Shear

Abstract

We present a method for determining the phase and contrast of a single shot of an atom interferometer. The application of a phase shear across the atom ensemble yields a spatially varying fringe pattern at each output port, which can be imaged directly. This method is broadly relevant to atom interferometric precision measurement, as we demonstrate in a 10 m 87 Rb atomic fountain by implementing an atom interferometric gyrocompass with 10 millidegree precision.PACS numbers: 03.75. Dg, 37.25.+k, 06.30.Gv Light-pulse atom interferometers use short optical pulses to split, redirect, and interfere freely-falling atoms [1]. They have proven widely useful for precision metrology. Atom interferometers have been employed in measurements of the gravitational [2, 3] and fine-structure [4] constants, in on-going laboratory tests of the equivalence principal [5] and general relativity [6,7], and have been proposed for use in gravitational wave detection [8,9]. They have also enabled the realization of high performance gyroscopes [10], accelerometers [11], gravimeters [12], and gravity gradiometers [13].Current-generation light-pulse atom interferometers determine phase shifts by recording atomic transition probabilities [1]. These are inferred from the populations of the two atomic states that comprise the interferometer output ports. Due to experimental imperfections, interference contrast is not perfect -even at the extremes, the dark port does not have perfect extinction. This results in the need to independently characterize contrast prior to inferring phase. Typically, this is done with a sequence of multiple shots with different phases, such that the population ratio is scanned through the contrast envelope [14]. Such an experimental protocol relies on the stability of the contrast envelope. In many cases, the contrast varies from shot to shot, introducing additional noise and bias in the phase extraction process.We present a broadly applicable technique that is capable of resolving interference phase on a single experimental shot. This is accomplished through the introduction of a phase shear across the spatial extent of the detected atom ensemble. The shear is manifest in a spatial variation of the atomic transition probability, which, under appropriate conditions, can be directly observed in an image of the cloud [ Fig. 1(b)]. Using this phase shear readout (PSR), it is no longer necessary to vary the phase over many shots to determine the contrast envelope. Instead, the contrast of each shot can be inferred from the depth of modulation of the spatial fringe pattern on the atom ensemble. The interferometer phase is directly determined from the phase of the spatial fringe.The analysis of PSR fringes reveals rich details about atom interferometer phase shifts and systematic effects, much as the analysis of a spatially varying optical in- Once they fall back to the bottom, the wavepackets are overlapped and an interference pattern (blue fringes) is imaged by two perpendicular cameras (CCD1,2). An additional optical...

High-Resolution Atom Interferometers with Suppressed Diffraction Phases

“…We decrease the influence of diffraction phases by an amount that is considerably larger than the increase in sensitivity and are in fact able to null them by feedback to the laser pulse intensity. With this increase in signal and suppression of diffraction phase systematics, we expect to see improvements in many applications of atom interferometry, such as measuring gravity and inertial effects [10][11][12][13] …”

“…We decrease the influence of diffraction phases by an amount that is considerably larger than the increase in sensitivity and are in fact able to null them by feedback to the laser pulse intensity. With this increase in signal and suppression of diffraction phase systematics, we expect to see improvements in many applications of atom interferometry, such as measuring gravity and inertial effects [10][11][12][13], measuring Newton's gravitational constant G [14,15], testing the equivalence principle [16][17][18][19][20][21][22], CPT and Lorentz symmetry [23] and perhaps even antimatter physics [24] and detecting gravitational waves [25]. Diffraction phases occur between the waves reflected and transmitted by a beam splitter and cause an unwanted (usually) shift of the interference pattern in an interferometer.…”

Inertial quantum sensors using light and matter

“…Nevertheless, our quest for improving the sensitivity of ground-based atom interferometers will soon reach a limit imposed by gravity and by the requirements of ultra-high vacuum and a very well controlled environment. Current state-of-the-art experimental apparatuses allow for seconds of interrogation with 10 to 120 meters of free-fall [69,70,71,72,67]. Space-based applications ‡, currently under study, will enable physicists to increase even further the interrogation time, thereby increasing dramatically the sensitivity and accuracy of atom interferometers.…”

“…For a cloud of bosonic (integer spin) atoms, all the atoms accumulate in the same quantum state (the atomoptical analog of the laser effect in optics). Access to BECs and atom laser sources have brought major conceptual advances in atom interferometry [68,69,70,71,72], in a similar fashion to what lasers did for the field of optical interferometry. Nevertheless, the relative complexity of BEC production has pushed scientists to explore new techniques by using, for instance, optical traps [73], atom chips [74], or avoiding evaporation and relying solely on laser cooling [75].…”

Effective velocity distribution in an atom gravimeter: Effect of the convolution with the response of the detection

“…In the latter case, a careful control of the mirror motion is necessary to avoid any residual synchronous vertical acceleration, that would bias the gravity measurement. Remarkably, the use of large free fall times and ultracold samples offers the possibility to map transverse effects by measuring the populations in the two output ports of the interferometer with a spatially resolved CCD imaging, as demonstrated in [12]. In this case, one measures not only the average value, but also the dispersion of the phase shifts due to Earth rotation and wavefront aberrations, which in principle could also help to reconstruct the wavefront of the lasers, and make a precise determination of its influence in the measurement.…”