Quantum atom interfermoter gravity gradiometer in space
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atom-wave interferometer gravity gradiometer↗
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Ultra-sensitive inertial sensors via neutral-atom interferometry
Upon looking at the various colossal interferometers, etc., discussed at this conference to test gravitational theory, one cannot avoid feeling that easier approaches exist. The use of low velocity, neutral atom matter waves in place of electromagnetic waves in sensitive inertial interferometer configurations is proposed. For applications, spacecraft experiments to sense a drag-free condition, to measure the Lense-Thirring precession, to measure the gravitomagnetic effect and/or the earth's geopotential (depending on altitude), and to detect long period gravitational waves are considered. Also, a terrestrial precision test of the equivalence principle on spin polarized atoms, capable of detecting effects of the 5th force is considered. While the ideas described herein are preliminary, the orders of magnitude are sufficiently tantalizing to warrant further study. Although existing proposed designs may be adequate for some of these experiments, the use of matter-wave interferometry offers reduced complexity and cost, and an absence of cryogenics.
Clauser, John F.↗
Quantum Interferometry
Recently, several researchers, including yours truly, have been able to demonstrate theoretically that quantum photon entanglement has the potential to also revolutionize the entire field of optical interferometry, by providing many orders of magnitude improvement in interferometer sensitivity. The quantum entangled photon interferometer approach is very general and applies to many types of interferometers. In particular, without nonlocal entanglement, a generic classical interferometer has a statistical-sampling shot-noise limited sensitivity that scales like 1/Sqrt[N], where N is the number of particles (photons, electrons, atoms, neutrons) passing through the interferometer per unit time. However, if carefully prepared quantum correlations are engineered between the particles, then the interferometer sensitivity improves by a factor of Sqrt[N] (square root of N) to scale like 1/N, which is the limit imposed by the Heisenberg Uncertainty Principle. For optical (laser) interferometers operating at milliwatts of optical power, this quantum sensitivity boost corresponds to an eight-order-of-magnitude improvement of signal to noise. Applications are to tests of General Relativity such as ground and orbiting optical interferometers for gravity wave detection, Laser Interferometer Gravity Observatory (LIGO) and the European Laser Interferometer Space Antenna (LISA), respectively.
Dowling, Jonathan P.↗
Longitudinal structure in atomic oxygen concentrations observed with WINDII on UARS
WINDII, the Wind Imaging Interferometer on the Upper Atmosphere Research Satellite, began atmospheric observations on September 28, 1991 and since then has been collecting data on winds, temperatures and emissions rates from atomic, molecular and ionized oxygen species, as well as hydroxyl. The validation of winds and temperatures is not yet complete, and scientific interpretation has barely begun, but the dominant characteristic of these data so far is the remarkable structure in the emission rate from the excited species produced by the recombination of atomic oxygen. The latitudinal and temporal variability has been noted before by many others. In this preliminary report on WINDII results we draw attention to the dramatic longitudinal variations of planetary wave character in atomic oxygen concentration, as reflected in the OI 557.7 nm emission, and to similar variations seen in the Meine1 hydroxyl band emission.
Shepherd, G. G.↗
Electron temperature and concentration in a thermal atomic oxygen source
A thermal atomic oxygen source for materials screening was built for NASA by Boeing Aerospace. The objective here was to use a microwave interferometer and Langmuir probe to characterize the electron concentration in this thermal atomic oxygen source. Typical operating conditions in the thermal atomic oxygen source were found to produce electron concentrations that were well below the detection threshold of the interferometer (10(exp 8) cm (sup -3)). The researchers calibrated (with the interferometer) the Langmuir probe at an artificially high plasma density and then used the circular and the square Langmuir probes to measure the low electron concentrations that exist during materials exposure tests. Electron concentration was measured as a function of power and position. The electrons were lost to the walls through ambipolar diffusion, and their concentration was accurately described by an equation. The electron concentration was proportional to power squared and decayed exponentially with distance.
Pedrow, Patrick Dennis↗
Measurements of the E region neutral wind field
The neutral E-region wind field was measured at Calgary, Canada (51 N, 114 N) during 75 nights in 1982. Observations of the Doppler shift of the 5577-A emission line of atomic oxygen using a Fabry-Perot interferometer were converted to horizontal wind vectors. From the analysis of the data, four categories of wind characteristics were identified. In order of increasing magnetic activity these categories are: (1) wind field mostly variable in space and time; (2) predominantly equatorward flow throughout the night, (3) predominantly poleward flow throughout the night and (4) north-westward flow before midnight and southward after midnight. The wind magnitude was also variable and on some disturbed days exceeded 200 m/s.
Cogger, L. L.↗
Detecting gravitational signatures of dark matter with atom gradiometers
We study the purely gravitational signatures of dark matter from the ultralight to the ultraheavy mass range in proposed long-baseline atom gradiometers, focusing on terrestrial designs, such as AION-km and MAGIS-km, as well as space-based concepts, such as MAGIS-space, AEDGE and AEDGE+. Due to its exceptional acceleration sensitivity and depending on astrophysical backgrounds, a detector similar to AEDGE+ could detect a dark matter subcomponent which constitutes 𝒪(10%) of the local dark matter energy density and is populated by compact clumps of mass between 10 6 kg and 10 10 kg (10 −25 𝑀⊙ ≲ 𝑀 ≲10 −21 𝑀⊙) in an otherwise unexplored region of dark matter model space. Furthermore, because the gravitational observable depends on the relative gravitational time delay measured by spatially separated atomic clouds, we find that atom gradiometers are parametrically more sensitive than laser interferometers, such as LIGO and LISA, to fast-oscillating spacetime perturbations sourced by energy density and pressure fluctuations of ultralight dark matter. Depending on astrophysical backgrounds, a detector akin to AEDGE+ could probe a DM overdensity of 𝒪(10) times the local dark matter energy density for masses 𝑚 ≲10 −17 eV.
79 ASTRONOMY AND ASTROPHYSICS↗
Optical study of the hyperfine structure of the rubidium resonance lines
Optical hyperfine splitting of Rb resonance lines of atomic beam light source, using Fabry-Perot interferometer
Andrew, K. L.↗
Comparing Laser Interferometry and Atom Interferometry Approaches to Space-Based Gravitational-Wave Measurement
Thoroughly studied classic space-based gravitational-wave missions concepts such as the Laser Interferometer Space Antenna (LISA) are based on laser-interferometry techniques. Ongoing developments in atom-interferometry techniques have spurred recently proposed alternative mission concepts. These different approaches can be understood on a common footing. We present an comparative analysis of how each type of instrument responds to some of the noise sources which may limiting gravitational-wave mission concepts. Sensitivity to laser frequency instability is essentially the same for either approach. Spacecraft acceleration reference stability sensitivities are different, allowing smaller spacecraft separations in the atom interferometry approach, but acceleration noise requirements are nonetheless similar. Each approach has distinct additional measurement noise issues.
Baker, John↗
The 158 micron (CII) mapping of galaxies: Probing the atomic medium
Using the MPE/UCB Far-infrared Imaging Fabry-Perot Interferometer (FIFI) on the Kuiper Airborne Observatory (KAO), we have made large scale maps of (CII) in the spiral galaxies NGC 6946, NGC 891, M83 and the peculiar elliptical Cen A, thus allowing for the first time, detailed studies of the spatial distribution of the FIR line emission in external galaxies. We find that the (CII) emission comes from a mixture of components of interstellar gas. The brightest emission is associated with the nuclear regions, a second component traces the spiral arms as seen in the nearly face on spiral galaxies NGC 6946 and M83 and the largest star forming/H2 regions contained within them, and another extended component of low brightness can be detected in all of the galaxies far from the nucleus, beyond the extent of CO emission.
Madden, S. C.↗
Measurement of the specific refractivities of CF4 and C2F6
In order to relate the measured fringe shift of an interferometer to the density of a medium, the relation between density and refractive index, which is expressed by the specific refractivity, must be known. In the present paper, the specific refractivities of the wind tunnel test gases CF4 and C2F6 are determined in order to verify estimations based on the atomic refractivities of carbon and fluorine. A Twyman-Green two-beam interferometer with a 633-nm He-Ne laser light source was used to measure the specific refractivity as a function of fringe shift as the density of the gas was changed. Values of 0.122 and 0.131 cu cm/g were obtained for CF4 and C2F6 respectively at a temperature of 300 K, which are within 1% of the values computed from the atomic refractivities.
Burner, A. W.↗
Accelerating the Deployment of Space-Based Quantum Sensors
Quantum sensors rely on quantum mechanical properties, such as wave-particle duality, atomic energy levels, or entanglement, to measure physical, optical, or electromagnetic information from a target. Examples include Rydberg sensors, nitrogen-vacancy magnetometers, HOM (Hong-Ou-Mandel) interferometers, and SQUIDs (Superconducting Quantum Interference Devices). In general, as quantum sensors rely on interrogation at the atomic and photonic level rather than on classical mechanical measurements, these technologies promise advantages over their traditional counterparts in sensitivity, accuracy, and SWaP (Size, Weight, and Power). Conceptually, the use of quantum sensors unlocks the new phenomenology of sensor entanglement. While an ultra-low TRL (Technology Readiness Level) prospect for most sensor types, multi-sensor entanglement is a high risk, high reward strategy with a potential for exquisite sensitivity and SWaP improvements entirely inaccessible to classical sensors.
Grace Caroline Wusk↗
Spin Squeezing with Itinerant Magnetic Dipoles
Entanglement can improve the measurement precision of quantum sensors beyond the shot noise limit. Neutral atoms, the basis of some of the most precise and accurate optical clocks and interferometers, do not naturally exhibit the all-to-all interactions traditionally used to generate such entangled states. On the other hand, these systems exhibit exceedingly high degrees of experimental control over parameters such as temperature, spatial entropy, and itinerancy. In this work, we investigate spin squeezing in a highly coherent itinerant system of neutral atoms with magnetic dipole-dipole interactions. We achieve 7.1 dB of metrologically useful squeezing using finite-range spin-exchange interactions in an erbium quantum gas microscope, and we demonstrate that introducing atomic motion, realizing a dipolar 𝑡−𝐽 model, protects the spin sector coherence at low fillings, significantly improving the achievable spin squeezing in a 2D dipolar system. This work’s protocol can be implemented with most neutral atoms, opening the door to quantum-enhanced metrology in other itinerant dipolar systems, such as molecules or optical lattice clocks, and serves as a novel method for studying itinerant quantum magnetism with long-range interactions.
Atomic, optical & lattice clocks↗
LDEF results for polymer matrix composite experiment AO 180
This report represents a summary of the results obtained to-date on a polymer matrix composite experiment (AO 180) located at station D-12, about 82 deg off the 'ram' direction. Different material systems comprised of graphite, boron, and aramid (Kevlar) fiber reinforcements were studied. Although previous results were presented on in-situ thermal-vacuum cycling effects, particularly dimensional changes associated with outgassing, additional comparative data will be shown from ground-based tests on control and flight samples. The system employed was fully automated for thermal-vacuum cycling using a laser interferometer for monitoring displacements. Erosion of all three classes of materials due to atomic oxygen (AO) will also be discussed, including angle of incidence effects. Data from this experiment will be compared to published results for similar materials in other LDEF experiments. Composite materials' erosion yields will be presented on an AO design nomogram useful for estimating total material loss for given exposure conditions in low Earth orbit (LEO). Optical properties of these materials will also be compared with control samples. A survey of the damage caused by micrometeoroids/debris impacts will be addressed as they relate to polymer matrix composites. Correlations between hole size and damage pattern will be given. Reference to a new nomogram for estimating the number distribution of micrometeoroid/debris impacts for a given space structure as a function of time in LEO will be addressed based on LDEF data.
Tennyson, R. C.↗
Measurement of the Specific Refractivities of CF4 and C2F6
In order to relate the measured fringe shift of an interferometer to density, the relation between density rho and refractive index n must be known. For gases where the refractive index is close to unity, this relation between density and refractive index is very closely approximated by (n - 1) = K rho where K is the specific refractivity, or the Gladstone-Dale constant. The specific refractivity, which is weakly dependent on wavelength and temperature, is readily available for a number of common test gases such as N2 and air. For more unique test gases such as CF4 and C2F6 for which refractive index data at optical wavelengths is not readily available, the constants can be estimated from the atomic refractivities of carbon and fluorine. In order to verify this estimation, a two-beam interferometer was used to experimentally determine the specific refractivities of CF4 and C2F6. This data was required for holographic interferometric measurements made at the Langley Hypersonic CF4 Tunnel. A Twyman-Green interferometer with a He-Ne laser light source of vacuum wavelength lambda equal to 633 nm was used to measure the constants. One beam of the two-beam interferometer passed through an optical cell of known inside length l which could be evacuated and slowly filled with the test gas to a density of 7.2 kg/cu m for CF4 or 5.7 kg/cu m for C2F6. If the refractive index (and hence density) is constant along the optical path through the cell, the fringe shift M and density change Delta rho are related M = 2Kl Delta rho/lambda for the double pass interferometer. Thus K can be determined by measuring the fringe shift as the density is changed. The output of a photodiode used to detect the fringe shift was recorded on a strip chart recorder. The rate of pressure increase of the test gas in the cell was controlled such that the fringes shifted at a rate of 0.5 to 1 fringe per sec. The pressure in the test cell was measured with a high accuracy quartz crystal pressure transducer and recorded approximately every 20 fringe peaks. The temperature of the cell was measured with a thermocouple and recorded at the start, midpoint, and end of each test.
Burner, A. W.↗
Investigation of possible lower hybrid emission from the NASA Lewis Bumpy Torus plasma
Radio frequency emission detected near the lower hybrid frequency of the NASA Lewis Bumpy Torus plasma is studied, using a simple detection system that consists of a spectrum analyzer and a 50-ohm miniature co-axial antenna concentrically located in a re-entrant quartz tube. The frequency shift of a broad emission peak is monitored as a function of the background pressure, electrode voltage, and the strength of the dc magnetic field. Simultaneous measurements of the average plasma density are made with a polarization diplexing microwave interferometer. Information from the experiment is discussed with particular reference to the role of atomic or molecular species of deuterium in the emissions, the strength of the dc magnetic field in the emitting region, the geometric location of the emitting region of the plasma, the lower hybrid plasma density as compared with the average plasma density, and the relation of the ion spoke geometry to the lower hybrid emission.
Mallavarpu, R.↗
Compatibility of seasonal variations in mid-latitude thermospheric models at solar maximum and low geomagnetic activity
Satellite drag data, in situ mass spectrometer data, Fabry Perot interferometer data, and incoherent scatter data were used to produce models of the concentration of atomic oxygen and molecular nitrogen in the thermosphere and of the exospheric temperature. Incoherent scatter data from two stations near 45 deg N were used. The three techniques provide similar patterns for the annual variations of the atomic oxygen concentration at 400 km, and the mean annual temperatures are within 20 K of each other for five of the six models involved. Four of the models are in good agreement concerning the annual temperature variation. There is fair agreement between incoherent scatter models and mass spectrometer models for the N2 concentrations at 400 km but disagreement between these models and the satellite drag model. It is shown that most disagreements can be resolved by changing both the vertical temperature profile and the lower-thermosphere oxygen concentration in the direction indicated by previous incoherent scatter measurements.
Alcayde, D.↗
Alternative Methods of the Thermospheric Atomic Oxygen Density Determination
Atomic oxygen density in the upper thermosphere (approximately 300 km) can be calculated using ground based incoherent scatter radar and Fabry-Perot interferometer measurements. Burnside et al. [1991] was the first to try this method, but Buonsanto et al. provided an extensive treatment of the method in 1997. This paper further examines the method using 46 nights of data collected over six years and the latest information on the oxygen collision frequency. The method is compared with the MSIS-86 atomic oxygen prediction values, which are based upon in situ rocket born and satellite measurements from the 70's to the mid-80's In general, the method supports the MSIS-86 model, but indicates several areas of discrepancy. Furthermore, no direct correlation is found between the geomagnetic conditions and the difference between the method and MSIS-86 predictions.
Bennett. Adam C.↗