We have recently shown that Alkali atoms contained in a vapor cell can serve as a highly accurate standard for microwave electric field strength as well as polarization using the principles of Rydberg atom electromagnetically induced transparency. Here, we show, for the first time, that Rydberg atom electromagnetically induced transparency can be used to image microwave electric fields with unprecedented precision. The spatial resolution of the method is far into the sub-wavelength regime. The electric field resolutions are similar to those we have demonstrated in our prior experiments. Our experimental results agree with finite element calculations of test electric field patterns.Atomic standards are important because they enable stable and uniform measurements and often link physical quantities to each other via universal constants [1]. We have demonstrated in our prior work that atoms contained in a vapor cell can be used for a practical and, in principle, portable microwave (MW) electric field standard using Rydberg atom electromagnetically induced transparency (EIT) [2, 3]. The accurate measurement of MW electric field strength and polarization can lead to advances in applications such as antenna design, device development, characterization of electro-magnetic interference, advanced radar applications and materials characterization [4-9], including metamaterials [10][11][12].To our knowledge, no other work exists on imaging MW electric fields with atoms in vapor cells. Even in the field of magnetometry, where vapor cell magnetometers have played a central part [13], absorption imaging for vapor cell MW magnetometry has only been recently reported [14, 15]. Many of the technical issues of imaging a MW magnetic field as opposed to an electric field with a vapor cell are different. Knowledge of both fields is important. Despite the rather straightforward connection between the electric and magnetic fields in free space, there is not always a simple relation between them in the near field. The absolute measurement of MW electric fields at sub-wavelength resolutions and in the near field is necessary for many MW applications.To meet the need for sub-wavelength imaging of MW electric fields, we demonstrate a scheme for subwavelength MW electrometry using Rydberg atom EIT [16, 17] in Cesium (Cs) atomic vapor cells at room temperature. In contrast to scanning probe technology [18, 19], our approach avoids cryogenics and eliminates the presence of conducting materials near the sample, therefore minimizing field disturbances. We achieve a 2-dimensional spatial resolution of ∼ λ MW /650, ∼ 66 µm at ∼ 6.9 GHz, using a test MW electric field in the form of a standing wave and image the MW electric field di- * Corresponding author: shaffer@nhn.ou.edu rectly above a co-planar waveguide (CPW) to demonstrate near field imaging. The electric field resolution is ∼ 50 µV cm −1 limited by our detection setup. The measurements are compatible with our prior work where we attained a minimum detectable electric field amplitude of ...

We present a very sensitive and scalable method to measure the population of highly excited Rydberg states in a thermal vapor cell of rubidium atoms. We detect the Rydberg ionization current in a 5 mm electrically contacted cell. The measured current is found to be in excellent agreement with a theory for the Rydberg population based on a master equation for the three level problem including an ionization channel and the full Doppler distributions at the corresponding temperatures. The signal-to-noise ratio of the current detection is substantially better than purely optical techniques.PACS numbers: 32.80. Rm, 03.67.Lx, 42.50.Gy Coherent phenomena involving strongly interacting Rydberg atoms have recently led to the demonstration of first quantum devices like quantum logic gates [1][2][3] and single photon sources [4] based on ultracold atoms. All these experiments require precise control over the highly excited states populations, which can be probed directly by field ionization [5,6] or by fluorescence techniques involving Rydberg shielding [7]. Since the strong vdW interaction has recently also been observed in vapor cells [8], scalable quantum devices based on the Rydberg blockade in above room temperature ensembles seem to be also within reach [9]. However, ion detectors as electron multipliers or multi-channel plates cannot be used in dense thermal vapors. For this reason, in thermal cells, most studies today use an indirect measurement of the excited state population by analyzing light fields leaving the atomic ensemble. Nevertheless, it is desirable to study not only the back-action of the vapor on the light, typically via electromagnetically induced transparency (EIT) [10], but also to measure directly the number of excited Rydberg states. One method, developed almost a century ago [11,12], makes use of thermionic diodes [13][14][15]. There, one of the electrodes is heated to emit electrons, which produce space charge limited gain for the amplification of ionized Rydberg atoms. The need of long ion trapping times requires large geometries for the space charge region, and an additional shielded excitation region to minimize the effect of disturbing electric fields during excitation of the highly polarizable Rydberg atoms. Despite its high sensitivity, this drawback sets a practical limitation for further applications where size and scalability play a role.Here we demonstrate that, in a symmetric configuration of atomic vapor between two transparent field plates, sizable currents in the nA regime reflect directly the Rydberg population and can be used as a probe with very good signal-to-noise ratio. This opens unique possibilities to probe very efficiently small spectroscopic features involving Rydberg states in thermal vapor but also might be used to stabilize lasers. By extending this concept to an array of pixel-wise arranged electrodes, high resolution spatial information on the Rydberg population can be obtained.The experiments were performed with the setup schematically shown in Fig. 1. The Rb va...

Despite recent developments and new treatments in ophthalmology there is nothing available to cure retinal degenerations like Retinitis Pigmentosa (RP) yet. One of the most advanced approaches to treat people that have gone blind due to RP is to replace the function of the degenerated photoreceptors by a microelectronic neuroprosthetic device. Basically, this subretinal active implant transforms the incoming light into electric pulses to stimulate the remaining cells of the retina. The functional time of such devices is a crucial aspect. In this paper the laboratory and clinical reliability of the two active subretinal implants Alpha IMS and Alpha AMS is presented. Based on clinical data the median operating life of the Alpha AMS is estimated to be 3.3 years with a one-sided lower 75 % confidence level of 2.0 years. This data shows a significant improvement of the device lifetime compared to the previous device Alpha IMS which shows a median lifetime of 0.6 years with a lower confidence bound (75 %) of 0.5 years. The results are in good agreement with laboratory data from accelerated aging tests of the implant components, showing an estimated median lifetime for Alpha IMS components of 0.7 years compared to the improved lifetime of Alpha AMS of 4.7 years.

Electronic retinal implants have been developed and are marketed as a therapeutic option for blind people suffering from degenerative retinal diseases such as retinitis pigmentosa. The functionality of subretinal implants depends heavily on the performance of the electronic interface to the retina. For the RETINA IMPLANT Alpha AMS device, this interface consists of a subretinally implanted chip that samples the retinal image, like a camera chip, and stimulates the adjacent retina simultaneously at the corresponding locations. The technical functionality of the RETINA IMPLANT Alpha AMS is described and compared with the outcome of two clinical trials over an observation period of one year. The discrimination of different grey levels observed in these clinical trials confirms that the sensitivity of the implanted CMOS chip can be varied over the range of relevant light intensities. We show that accelerated aging lifetime measurements of implant components in a laboratory environment match implant lifetimes observed during clinical trials for the predecessor device, the RETINA IMPLANT Alpha IMS. By using the same model for the current technically advanced device, the RETINA IMPLANT Alpha AMS, the predicted clinical lifetime of the implant is about 5 years.

We demonstrate the use of electrically contacted vapor cells to switch the transmission of a probe laser. The excitation scheme makes use of electromagnetically induced transparency involving a Rydberg state. The cell fabrication technique involves thin-film-based electric feedthroughs, which are well suited for scaling this concept to many addressable pixels like in flat panel displays.

We demonstrate the use of an anodic bonding technique for building a vacuum tight vapor cell for the use of Rydberg spectroscopy of alkali atoms with thin film electrodes on the inside of the cell. The cell is fabricated by simultaneous triple stack glass-to-glass anodic bonding at 300• C. This glue-free, low temperature sealing technique provides the opportunity to include thin film electric feedthroughs. The pressure broadening is only limited by the vapor pressure of rubidium and the lifetime is at least four months with operating temperatures up to 230• C.Atomic vapor cells at and above room temperature are the basis for applications such as optical frequency references 1 , magnetic 2 and electric 3 field sensors, and atom clocks 4 . Due to advances in miniaturization and fabrication techniques commercial products are now available 5 . With the demonstration of Rabi flopping at GHz frequencies in a thermal vapor 6 and the possibility to excite Rydberg atoms in tight confinements 7 it has been shown that applications in nonlinear and quantum optics are possible in thermal vapor cells. The large Stark effect associated with the huge polarizability of Rydberg atoms can be exploited to switch and modulate the optical properties of such cells 8 . In fact electric field control is also important to avoid drifts, broadening, and dephasing of the spectroscopy lines. While thin film based electrical feedthroughs are compatible with microfabrication techniques and can easily be scaled up to large numbers, they are destroyed when vapor cells are sealed above the melting point of glass. Our previously demonstrated gluing technique 9 is compatible with these requirements, but the maximum operating temperature was limited to 100• C. This is a severe drawback when it comes to highly integrated cells and therefore to small vapor volumes. To achieve reasonable optical density in such thin cells, higher temperatures are required. Therefore it is necessary to develop techniques to produce high vacuum tight vapor cells with conductive, thin film based feedthroughs, that can withstand temperatures up to 200• C and under these conditions provide lifetimes that are long enough for commercial applications.Most of the currently available techniques to build high vacuum tight vapor cells are often not compatible with thin film coatings. The conventional sealing of glass cells by flame can not be used, as thin film electrodes would not survive the high temperatures required to melt glass. Other techniques like direct bonding also require high temperatures and polished surfaces with a flatness better than the height of the electrodes. For glass frit bonding a technology to print and cure the glass frit is needed a) Electronic

The efficiency and safety of neuronal stimulation with implants strongly depend on the electrode material. Microelectrodes composed of iridium oxide are becoming increasingly important as they exhibit excellent charge injection capacity (CIC) as well as charge storage capacity (CSC). We present the development of a robust process for the fabrication of sputtered iridium oxide films (SIROF). This process has been used for the "RETINA IMPLANT Alpha AMS" for several years of subretinal stimulation. In this paper, we describe the full experimental investigation of the electrode material. The electrochemical and morphological properties were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), voltage transient measurements, and focused ion beam-scanning electron microscopy (FIB-SEM). The implementation on the CMOS chip of the retinal prosthesis is presented. The deposition process window was investigated extensively. Major changes in process parameters lead to a difference in impedance of only 10% of the mean. Accelerated aging tests revealed a long-term stability of the electrodes of at least 10 years under conditions of use. The SIROF electrodes (diameter 30 µm) show low impedance (15.9 kΩ), excellent CSC (50.9 mC/cm 2), and high CIC (4.2 mC/cm 2). In summary, the robustness of the presented deposition process and the large process window enable the integration of high-quality SIROF microelectrodes in active implants and thus long-term stability in a wide range of safe electrical stimulation.

It is clearly important to pursue atomic standards for quantities like electromagnetic fields, time, length and gravity. We have recently shown, using Rydberg states, that Rb atoms in a vapor cell can serve as a practical, compact standard for microwave electric field strength. Here, we demonstrate, for the first time, that Rb atoms excited in a vapor cell can also be used for vector microwave electrometry by using Rydberg atom electromagnetically induced transparency. We describe the measurements necessary to obtain an arbitrary microwave electric field polarization at a resolution of 0.5• . The experiments are compared to theory and found to be in excellent agreement.PACS numbers: 32.80. Rm, 42.62.Fi, 03.50.De, 07.50.Ls Quantum systems, such as atoms, have already been adopted as time and length standards because they offer significant advantages for making stable and uniform measurements of these quantities [1,2]. Atoms have also been successfully used for magnetometry, reaching impressive sensitivity and spatial resolutions [3][4][5][6][7][8]. Despite these successes, it is only recently that atoms have been used for practical microwave (MW) electrometry and achieved sensitivities below current standards by exploiting the properties of Rydberg atoms [9]. Rydberg atoms have been used for electrometry for some time, but almost exclusively in elaborate laboratory setups [10][11][12][13][14][15][16][17][18][19][20][21].The relative lag of atom based electrometry compared to magnetometry is not simply due to a lack of importance. The accurate measurement of MW electric field strength and polarization offers interesting possibilities for antenna calibration and MW electronics development, as well as for realizing an atomic candle for MW electric field stabilization [22,23], to name a few important examples. Atom based MW electrometry, therefore, has the potential to lead to revolutionary advances in the development of MW electronics, advanced radar applications, and materials used in MW systems. So far, only the magnetic field has been accessible in the near-field MW regime [24,25] and our method can be valuable for measuring MW electric fields in the near-field. Recall, there is not generally a straightforward relation between the MW magnetic and electric fields in the near-field.In this paper, we demonstrate a scheme for vector MW electrometry using Rydberg atom electromagnetically induced transparency (EIT) [26,27] in Rb atomic vapor cells. We achieve an angular resolution of 0.5• and show the method can be realized by comparing experimental data to theory. The agreement between theory and experiment is shown to be excellent. The vector measurements here are compatible with our prior work where we attained a minimum detectable electric field amplitude of ∼ 8 µV cm [9]. To date, EIT has been principly used for vector magnetometry [28,29]. To measure the strength and polarization of a MW electric field, we use the Rb level system shown in Figure 1a. In the 3-level system, 5S 1/2 − 5P 3/2 − 53D 5/2 , quantum in...