Rydberg atom radio-frequency sensors are a unique platform for precision electromagnetic field measurement; e.g., they have extraordinary carrier bandwidth spanning MHz to THz and can be self-calibrated. These photonic sensors use lasers to prepare and read out the atomic response to a radio-frequency electromagnetic field. Most work on Rydberg atom sensors centers on radio-frequency electric field strength because the sensor functions as a square law detector, unless an external radio-frequency heterodyning field is used. A heterodyning field acts as a local oscillator and enables phase readout at the expense of the radio-frequency equipment necessary to generate it. In order to overcome the disadvantages of a radio-frequency local oscillator, we investigate all-optical phase-sensitive detection using a five-level closed-loop excitation scheme. We show that under finite detuning of the loop fields, the atomic response oscillates at the frequency of the detuning. The oscillation is transferred to a probe laser absorption signal. The phase, frequency, and amplitude of the radio-frequency signal are imprinted on the oscillatory dynamics and can be determined using demodulation and matched filter techniques applied to the probe laser transmission signal.

In this work, we present a high-sensitivity, all-optical, atom-based radio-frequency electrometry technique, implemented via a collinear three-photon excitation scheme in a room-temperature cesium vapor cell. By employing a wave-vector matching condition unique to cesium, our approach reduces the residual Doppler broadening so that it does not dominate the electromagnetically induced absorption linewidth, achieving linewidths below 200 kHz. The narrow linewidth enables the expansion of the self-calibrated Autler-Townes sensing regime and increased sensitivity when compared to methods where Doppler broadening dominates the linewidth. In this paper, we report our latest sensitivity measurements which successfully detected radio-frequency (RF) Rabi frequencies of 2 pi x43 kHz using a 480 kHz measurement bandwidth at 10.7 GHz, corresponding to a sensitivity of 45 nV/cm/root Hz. The results of our experiment show a thirteen-fold improvement compared to our previously reported findings for all-optical atom-based electrometry. Our measurements demonstrate the ability to detect time-varying signals suitable for radar and communication applications with high sensitivity.

In this talk, we present work on a colinear three-photon approach to all-optical, atom-based electric field sensing. Atom-based radio frequency field sensors have a number of applications in communications, radar and test and measurement. All of these applications benefit from being able to improve accuracy and sensitivity. Our three-photon approach eliminates Doppler broadening, improving sensitivity and spectral resolution. Increasing spectral resolution extends the Autler-Townes region where the sensing is self-calibrated. Using a colinear three-photon configuration for preparation and readout, we present results where we obtain an $\sim 20$ times improvement in spectral resolution and $\sim 10$ times improvement in sensitivity when compared to the conventional two-photon preparation and readout. Wel address further avenues for improving sensitivity in the talk, including novel types of vapor cells.

Rydberg atom-based radio frequency electromagnetic field sensors are drawing wide-spread interest because of their unique properties, such as small size, dielectric construction, and self-calibration. These photonic sensors use lasers to prepare atoms and read out the atomic response to a radio frequency electromagnetic field based on electromagnetically induced transparency, or related phenomena. Much of the theoretical work has focused on the Autler-Townes splitting induced by the radio frequency wave. The amplitude regime, where the change in transmission observed on resonance is measured to determine electric field strength, has received less attention. In this paper, we deliver analytic expressions that are useful for calculating the absorption coefficient in the amplitude regime. Our main goal is to describe the analytic expressions for the absorption coefficient and demonstrate their validity over a large range of the interesting parameter space. The effect of the thermal motion of the atoms is explicitly addressed. The analytic formulas for the absorption coefficient for different types of Doppler broadening are compared to estimate the sensitivity under conditions where it is limited by the laser shot noise. Residual Doppler shifts are shown to limit sensitivity. The expressions, approximations and descriptions presented in the paper are important for understanding the absorption of Rydberg atom-based sensors in the amplitude regime. This provides insight into the physics of multi-level interference phenomena.

We numerically study the many-body physics of molecular Bose-Einstein condensates with strong dipole-dipole interactions. We observe the formation of self-bound droplets, and explore phase diagrams that feature a variety of exotic supersolid states. In all of these cases, the large and tunable molecular dipole moments enable the study of unexplored regimes and phenomena, including liquidlike density saturation and universal stability scaling laws for droplets, as well as pattern formation and the limits of droplet supersolidity. We discuss a realistic experimental approach to realize both the required collisional stability of the molecular gases and the independent tunability of their contact and dipolar interaction strengths. Our work provides both a blueprint and a benchmark for near-future experiments with bulk molecular Bose-Einstein condensates.

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Hyperfine effects in Rydberg atom-based sensing have been observed for sensing polarization. However, in most work to date, the hyperfine structure involved in the radio frequency transition has been ignored because the residual Doppler widths realized in experiments are larger than the hyperfine energy splittings of the Rydberg states. Recently, we have proposed and demonstrated a collinear three photon scheme for Rydberg atom-based electrometry that has a greatly reduced residual Doppler width, < 500 kHz. In these experiments, we observe the effect of optical pumping and the hyperfine structure of the Rydberg states. We compare the 42P3/2 → 41D5/2 and 42P3/2 → 41D3/2 sensing transitions to show that Rydberg atom hyperfine structure effects can be observed at our spectral resolution. Hyperfine structure and optical pumping can alter the effective transition dipole moments on the sensing transition and can be used to detect polarization of the radio frequency field so our work is important for practical Rydberg atom electric field sensing.

Phase transitions share the universal feature of enhanced fluctuations near the transition point. Here we show that density fluctuations reveal how a Bose-Einstein condensate of dipolar atoms spontaneously breaks its translation symmetry and enters the supersolid state of matter -- a phase that combines superfluidity with crystalline order. We report on the first direct in situ measurement of density fluctuations across the superfluid-supersolid phase transition. This allows us to introduce a general and straightforward way to extract the static structure factor, estimate the spectrum of elementary excitations and image the dominant fluctuation patterns. We observe a strong response in the static structure factor and infer a distinct roton minimum in the dispersion relation. Furthermore, we show that the characteristic fluctuations correspond to elementary excitations such as the roton modes, which have been theoretically predicted to be dominant at the quantum critical point, and that the supersolid state supports both superfluid as well as crystal phonons.

We observe signatures of radial and angular roton excitations around a droplet crystallization transition in dipolar Bose-Einstein condensates. In situ measurements are used to characterize the density fluctuations near this transition. The static structure factor is extracted and used to identify the radial and angular roton excitations by their characteristic symmetries. These fluctuations peak as a function of the interaction strength indicating the crystallization transition of the system. We compare our observations to a theoretically calculated excitation spectrum allowing us to connect the crystallization mechanism with the softening of the angular roton modes.

Dipolar interactions are fundamentally different from the usual van der Waals forces in real gases. Besides the anisotropy the dipolar interaction is nonlocal and as such allows for self organized structure formation. In 2005 the first dipolar effects in a quantum gas were observed in an ultracold Chromium gas. By the use of a Feshbach resonance a purely dipolar quantum gas was observed three years after [1]. Recently it became possible to study degenerate gases of lanthanide atoms among which one finds the most magnetic atoms. Similar to the Rosensweig instability in classical magnetic ferrofluids self-organized structure formation was expected. In our experiments with quantum gases of Dysprosium atoms we could observe the formation of a droplet crystal [2]. In contrast to theoretical mean field based predictions the super-fluid droplets did not collapse. We find that this unexpected stability is due to beyond meanfield quantum corrections of the Lee-Huang-Yang type [3,4]. We observe and study self-bound droplets [5] which can interfere with each other. We also observe selforganized stripes in a confined geometry [6] and collective scissors mode oscillations of dipolar droplets [7]. Very recently in the striped phase also phase coherence was observed in Dysprosium and Erbium experiments, which is evidence for a supersolid state of matter [8]. This transition to a supersolid is a beautiful example for the appearance of a Goldstone mode even in a finite system, which we have observed recently.

Production scale inert atmosphere microwave sintering has not been successful yet, mainly because of lack of suitable equipment. For sintering in air microwave furnaces are available at different industrial scale, e.g., gas-microwave hybrid heated batch kilns or microwave “adiabatic casket” tunnel kiln [1]. Inert atmosphere furnaces require vacuum and gastight coupling of microwave energy. In the State of the Art technology, microwave-coupling windows represent a heat sink inside the sintering furnace. Although, radiation heat loss at temperatures > 1600 °C can be reduced by using a thermally insulating casket inside the microwave furnace, heat loss and temperature gradients caused by the microwave transparent windows are still not acceptable. Therefore, a new concept was developed assisted heating in inert atmosphere sintering furnaces, enabling high power microwave coupling by means of high temperature resistant antennas [2]. This paper presents microwave sintering results of commercial powder metallurgical (PM)-parts, details of the antenna system and the processing technology.

First, material properties of the ultra-thin YSZ were character- ized experimentally and found to be significantly different than those of bulk YSZ (3). Second, based on the obtained proper- ties, maximum stresses in the plates at 625ºC were analyzed us- ing non-linear von Karman plate theory (4). The stresses showed three regions with sidelength variation: an un-buckled regime, a buckled regime with high stresses, and post-buckling regime with lower stresses (see Figure 1). The µSOFCs were fabricated in the post-buckling regimes with ~80-~180µm sidelength and total ~450nm thickness. With the plates buckled as shown in Figure 2, the µSOFCs produced power output of 0.008mW/cm, lower than the expected power from their electrochemical test. Given the high-performance predicted for the underlying nano-struc- tured ultra-thin electrolyte, anode, and cathode layers, additional studies are needed to improve specimens and test setup and to assess µSOFCs' long-term operational stability.

The authors report on the design, fabrication, and testing of a threshold pressure switch with mechanical hysteresis. The expansion of trapped gas in a sealed cavity formed by wafer bonding is used to plastically deform a thin silicon membrane bonded over the cavity, creating a spherically shaped cap. This deformed cap exhibits mechanical hysteresis in its deflection versus pressure characteristics at the point of buckling. It is this buckling phenomenon which is used to produce the hysteresis in the pressure switch. The authors describe the fabrication and testing of devices as well as a model to predict the onset of plastic deformation in these structures. They have tested the threshold pressure switch and found that it exhibits approximately 2 psi of hysteresis. Possible applications for this threshold pressure switch are tire pressure monitoring, tactile sensor arrays, keyboards, and scales.<>

A novel dopant selective etching technique, which uses pulsed anodizing voltages applied to silicon samples immersed in KOH:H/sub 2/O solutions, has been developed. The use of pulsed anodization causes passivation of p-type silicon while n-type silicon continues to etch, making it possible to selectively etch-stop on p-type material. These results are consistent with a process which is rate-limiting by holes in the semiconductor. To demonstrate this technique, a 12 mu m-thick p-type membrane was formed. This method differs from the conventional p-n junction etch-stop in that a diode is not required to accomplish selective anodization and etch-stop. In this way, the performance of the etch-stop does not depend on the presence or quality of the diode.<>

Three fabrication issues related to the design and fabrication of micromechanical devices using sealed cavities within bonded silicon wafers are discussed. The first concerns the resultant residual gas pressure within a sealed cavity between two bonded wafers after bonding and a high-temperature anneal. The second concerns the prediction of plastic deformation in capping layers of single-crystal s...

The authors report the complete fabrication and packaging process which yields functional pressure-balanced microvalves and report the results on the fluidic behavior of the valve using pneumatic actuation. The process to implement the valve uses three silicon wafer bonding steps to form the structure. The valve is packaged by anodically bonding a machined glass part having the appropriately sized inlet and outlet ports to the top surface of the microvalve. A chrome/platinum layer on the glass side prevents the valve plunger from bonding to the glass so that the valve can be successfully actuated. Flow rates of up to 120 ml/min were measured when the differential pressure across the valve was 35 psi and the pneumatic actuation pressure was 5 psi absolute. The on-off ratio has been estimated to be over 300. The pressure-balancing concept has been shown to be successful.<>