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We show that light-pulse atom interferometry with atomic point sources and spatially resolved detection enables multi-axis (two rotation, one acceleration) precision inertial sensing at long interrogation times. Using this method, we demonstrate a light-pulse atom interferometer for 87 Rb with 1.4 cm peak wavepacket separation and a duration of 2 T = 2.3 s. The inferred acceleration sensitivity of each shot is 6.7 × 10 −12 g, which improves on previous limits by more than two orders of magnitude. We also measure the Earth's rotation rate with a precision of 200 nrad/s.PACS numbers: 03.75. Dg, 37.25.+k, 06.30.Gv Light-pulse atom interferometry enables precision tests of gravity [1][2][3] and electrodynamics [4] as well as practical applications in inertial navigation, geodesy, and timekeeping. Phase shifts for light-pulse atom interferometers demonstrate sensitivity to the initial velocity distribution of the atom source, often resulting in inhomogeneous dephasing that washes out fringe contrast [5]. In this Letter, we show that use of spatially resolved imaging in combination with an initially spatially localized atomic source allows direct characterization of these phase shifts. We refer to this technique as point source interferometry (PSI).The contrast loss associated with such inhomogeneous dephasing is not fundamental, but is a consequence of atom detection protocols that average over velocitydependent phase shifts. With PSI we establish a correlation between velocity and position and use spatiallyresolved detection to form an image of the ensemble that reveals its velocity-dependent phase structure. A simple way to realize this correlation is through ballistic expansion of the ensemble. In the limit that the ensemble size at detection is much larger than its initial size, each atom's position is approximately proportional to its initial velocity. Consequently, any initial velocitydependent phase shift results in a spatial variation of the interferometer phase, yielding a position-dependent population difference between the two output ports of the interferometer.An important example of velocity sensitivity is due to rotation of the interferometer laser beams [3,6]. Rotation at a rate Ω leads to a phase shift (Table I, term 2) that depends on (v x , v y ), the initial transverse velocity of the atom. In a rotating frame, this effect may be interpreted as a Coriolis acceleration. PSI also allows observation of longitudinal velocity-dependent phase shifts in asymmetric atom interferometers [7] (e.g., Table I, term 3).To demonstrate PSI, we induce a velocity-dependent phase shift in a 87 Rb Raman light-pulse atom interferometer. We launch cold atoms from the bottom of a 10-meter tall vacuum enclosure (Fig. 1a) and apply a threepulse accelerometer sequence (π/2−π−π/2) [8]. The first pulse serves as an atom beamsplitter, coherently driving the atoms into a superposition of states |F = 1; p and |F = 2; p + k eff with momentum difference k eff = 2 k. Over the subsequent T = 1.15 s interrogation interval, the two...

We propose an atom interferometer gravitational wave detector in low Earth orbit (AGIS-LEO). Gravitational waves can be observed by comparing a pair of atom interferometers separated by a 30 km baseline. In the proposed configuration, one or three of these interferometer pairs are simultaneously operated through the use of two or three satellites in formation flight. The three satellite configuration allows for the increased suppression of multiple noise sources and for the detection of stochastic gravitational wave signals. The mission will offer a strain sensitivity of < 10 −18 / √ Hz in the 50 mHz-10 Hz frequency range, providing access to a rich scientific region with 123 1954 J. M. Hogan et al. substantial discovery potential. This band is not currently addressed with the LIGO, VIRGO, or LISA instruments. We analyze systematic backgrounds that are relevant to the mission and discuss how they can be mitigated at the required levels. Some of these effects do not appear to have been considered previously in the context of atom interferometry, and we therefore expect that our analysis will be broadly relevant to atom interferometric precision measurements. Finally, we present a brief conceptual overview of shorter-baseline ( 100 m) atom interferometer configurations that could be deployed as proof-of-principle instruments on the International Space Station (AGIS-ISS) or an independent satellite.

Laboratory optical atomic clocks achieve remarkable accuracy (now counted to 18 digits or more), opening possibilities to explore fundamental physics and enable new measurements. However, their size and use of bulk components prevent them from being more widely adopted in applications that require precision timing. By leveraging silicon-chip photonics for integration and to reduce component size and complexity, we demonstrate a compact optical-clock architecture. Here a semiconductor laser is stabilized to an optical transition in a microfabricated rubidium vapor cell, and a pair of interlocked Kerr-microresonator frequency combs provide fully coherent optical division of the clock laser to generate an electronic 22 GHz clock signal with a fractional frequency instability of one part in 10 13 . These results demonstrate key concepts of how to use silicon-chip devices in future portable and ultraprecise optical clocks. Main Text:Optical atomic clocks, which rely on high-frequency, narrow-linewidth optical transitions to stabilize a clock laser, outperform their microwave counterparts by several orders of magnitude due to their inherently large quality factors (1). Optical clocks based on laser-cooled and latticetrapped atoms have demonstrated fractional instabilities at the 10 -18 level (2), setting stringent new limits on tests of fundamental physics (3, 4) and may eventually replace microwave clocks in global timekeeping, navigation and the definition of the SI second (5). Despite their excellent performance, optical clocks are almost exclusively operated by metrological institutions and universities due to their large size and complexity.Although significant progress has been made in reducing the size of laser-cooled atomic clocks to fit inside a mobile trailer (6), applications of these clocks are still limited to metrological clock comparisons and precision geodesy (7). In contrast, optical oscillators referenced to thermal atomic or molecular vapors can be realized in small form factors and still reach instabilities below 10 -14 (8,9). A fully integrated optical clock would benefit many of the applications (10) that currently utilize compact or chip-scale (11) microwave atomic clocks but, until recently, techniques for on-chip laser stabilization to atoms (12) and optical frequency division (13) were not available. Here, we propose and demonstrate an architecture for an integrated optical clock, based on an atomic vapor cell implemented on a silicon chip and a

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...

Object. Emerging evidence supports the hypothesis that modulation of specific central neuronal systems contributes to the clinical efficacy of deep brain stimulation (DBS) and motor cortex stimulation (MCS). Real-time monitoring of the neurochemical output of targeted regions may therefore advance functional neurosurgery by, among other goals, providing a strategy for investigation of mechanisms, identification of new candidate neurotransmitters, and chemically guided placement of the stimulating electrode. The authors report the development of a device called the Wireless Instantaneous Neurotransmitter Concentration System (WINCS) for intraoperative neurochemical monitoring during functional neurosurgery. This device supports fast-scan cyclic voltammetry (FSCV) at a carbon-fiber microelectrode (CFM) for real-time, spatially and chemically resolved neurotransmitter measurements in the brain.Methods. The FSCV study consisted of a triangle wave scanned between −0.4 and 1 V at a rate of 300 V/second and applied at 10 Hz. All voltages were compared with an Ag/AgCl reference electrode. The CFM was constructed by aspirating a single carbon fiber (r = 2.5 μm) into a glass capillary and pulling the capillary to a microscopic tip by using a pipette puller. The exposed carbon fiber (that is, the sensing region) extended beyond the glass insulation by ~ 100 μm. The neurotransmitter dopamine was selected as the analyte for most trials. Proof-of-principle tests included in vitro flow injection and noise analysis, and in vivo measurements in urethane-anesthetized rats by monitoring dopamine release in the striatum following high-frequency electrical stimulation of the medial forebrain bundle. Direct comparisons were made to a conventional hardwired system.Results. The WINCS, designed in compliance with FDA-recognized consensus standards for medical electrical device safety, consisted of 4 modules: 1) front-end analog circuit for FSCV (that is, current-to-voltage transducer); 2) Bluetooth transceiver; 3) microprocessor; and 4) direct-current battery. A Windows-XP laptop computer running custom software and equipped with a Universal Serial Bus-connected Bluetooth transceiver served as the base station. Computer software directed wireless data acquisition at 100 kilosamples/second and remote control of FSCV operation and adjustable waveform parameters. The WINCS provided reliable, high-fidelity measurements of dopamine and other neurochemicals such as serotonin, norepinephrine, and ascorbic acid by using FSCV at CFM and by flow injection analysis. In rats, the WINCS detected subsecond striatal dopamine release at the implanted sensor during high-frequency stimulation of ascending dopaminergic fibers. Overall, in vitro and in vivo testing demonstrated comparable signals to a conventional hardwired electrochemical system for FSCV. Importantly, the WINCS reduced susceptibility to electromagnetic noise typically found in an operating room setting.Conclusions. Taken together, these results demonstrate that the WINCS is well suited fo...

A multi-analyte sensor array platform has been developed which consists of analyte specific features that are indexed by shape. The array features are batch-fabricated lithographically from poly(ethylene glycol) diacrylate hydrogel pre-polymer and can accommodate a wide variety of different sensing chemistries. Depending on the physical scale of the sensing moiety, it is either copolymerized to the hydrogel matrix (e.g., oligonucleotides, aptamers), or it is merely physically encapsulated, an important strategy for preserving the biological activity of the larger and more complex sensing elements (e.g., antibodies, proteins, cells). This three-dimensional hydrogel sensor platform has an advantage over two-dimensional platforms in that it offers an increased signal density, and because the array is constructed of poly(ethylene glycol), it has virtually no background noise due to nonspecific adsorption of labeled analytes. To highlight the capabilities of this platform to make high signal-tonoise measurements using diverse sensing chemistries, two demonstrations are described herein that illustrate the platform's efficacy in oligonucleotide sensing and cell-based sensing.

Recent robotic manipulation competitions have highlighted that sophisticated robots still struggle to achieve fast and reliable perception of task-relevant objects in complex, realistic scenarios. To improve these systems' perceptive speed and robustness, we present SegICP, a novel integrated solution to object recognition and pose estimation. SegICP couples convolutional neural networks and multi-hypothesis point cloud registration to achieve both robust pixel-wise semantic segmentation as well as accurate and real-time 6-DOF pose estimation for relevant objects.Our architecture achieves 1 cm position error and < 5 • angle error in real time without an initial seed. We evaluate and benchmark SegICP against an annotated dataset generated by motion capture.