Study of loss in superconducting coplanar waveguide resonators

Superconducting coplanar waveguide (SCPW) resonators have a wide range of applications due to the combination of their planar geometry and high quality factors relative to normal metals. However, their performance is sensitive to both the details of their geometry and the materials and processes that are used in their fabrication. In this paper, we study the dependence of SCPW resonator performance on materials and geometry as a function of temperature and excitation power. We measure quality factors greater than $2\times10^6$ at high excitation power and $6\times10^5$ at a power comparable to that generated by a single microwave photon circulating in the resonator. We examine the limits to the high excitation power performance of the resonators and find it to be consistent with a model of radiation loss. We further observe that while in all cases the quality factors are degraded as the temperature and power are reduced due to dielectric loss, the size of this effect is dependent on resonator materials and geometry. Finally, we demonstrate that the dielectric loss can be controlled in principle using a separate excitation near the resonance frequencies of the resonator.Comment: Replacing original version. Changes made based on referee comments. Fixed typo in equation (3) and added appendi

Sub-micrometer epitaxial Josephson junctions for quantum circuits

We present a fabrication scheme and testing results for epitaxial sub-micrometer Josephson junctions. The junctions are made using a high-temperature (1170 K) "via process" yielding junctions as small as 0.8 mu m in diameter by use of optical lithography. Sapphire (Al2O3) tunnel-barriers are grown on an epitaxial Re/Ti multilayer base-electrode. We have fabricated devices with both Re and Al top electrodes. While room-temperature (295 K) resistance versus area data are favorable for both types of top electrodes, the low-temperature (50 mK) data show that junctions with the Al top electrode have a much higher subgap resistance. The microwave loss properties of the junctions have been measured by use of superconducting Josephson junction qubits. The results show that high subgap resistance correlates to improved qubit performance

Functional interaction of human Ssu72 with RNA polymerase II complexes.

Phosphorylation of the C-terminal domain (CTD) of the large subunit of human RNA polymerase II (Pol II) is regulated during the transcription cycle by the combined action of specific kinases and phosphatases. Pol II enters into the preinitiation complex (PIC) unphosphorylated, but is quickly phosphorylated by Cdk7 during initiation. How phosphatases alter the pattern and extent of CTD phosphorylation at this early stage of transcription is not clear. We previously demonstrated the functional association of an early-acting, magnesium-independent phosphatase with early elongation complexes. Here we show that Ssu72 is responsible for that activity. We found that the phosphatase enters the transcription cycle during the formation of PICs and that Ssu72 is physically associated with very early elongation complexes. The association of Ssu72 with elongation complexes was stable to extensive washing with up to 200 mM KCl. Interestingly, Ssu72 ceased to function on complexes that contained RNA longer than 28 nt. However, when PICs were washed before initiation, the strict cutoff at 28 nt was lost. This suggests that factor(s) are important for the specific regulation of Ssu72 function during the transition between initiation and pausing. Overall, our results demonstrate when Ssu72 can act on early transcription complexes and suggest that Ssu72 may also function in the PIC prior to initiation

Mycotic aneurysm in a child with history of coarctation of the aorta repair

A mycotic aneurysm is a rare condition occasionally seen in patients with a history of prior cardiac or vascular surgery. Here we report the presentation of a mycotic aneurysm in a pediatric patient at the site of prior aortic coarctation repair. This patient′s initial presentation suggested rheumatologic or oncologic disease, and after diagnosis he continued to show evidence of splenic, renal and vascular injury distal to the mycotic aneurysm site while being treated with antibiotics. We discuss the diagnosis, treatment and management of this condition

Acquired ventricular septal defect due to infective endocarditis

Acquired intracardiac left-to-right shunts are rare occurrences. Chest trauma and myocardial infection are well-known causes of acquired ventricular septal defect (VSD). There have been several case reports describing left ventricle to right atrium shunt after infective endocarditis (IE). We present here a patient found to have an acquired VSD secondary to IE of the aortic and tricuspid valves in the setting of a known bicuspid aortic valve. This is the first case reported of acquired VSD in a pediatric patient in the setting of IE along with literature review of acquired left-to-right shunts

Enabling Much Higher Power Densities In Aerospace Power Electronics With High Temperature Evaporative Spray Cooling

A power electronics module was equipped with an evaporative spray cooling nozzle assembly that served to remove waste heat from the silicon devices. The spray cooling nozzle assembly took the place of the standard heat sink, which uses single phase convection. The purpose of this work was to test the ability of spray cooling to enable higher power density in power electronics with high temperature coolant, and to be an effective and lightweight system level solution to the thermal management needs of aerospace vehicles. The spray cooling work done here was with 95 °C water, and this data is compared to 100 °C water/propylene glycol spray cooling data from a previous paper so as to compare the spray cooling performance of a single component liquid to that of a binary liquid such as WPG. The module used during this work was a COTS module manufactured by Semikron, Inc., with a maximum DC power input of 180 kW (450 VDC and 400 A). With single phase convective cooling, the coolant must be kept at 25 °C in order to prevent the insulated gate bipolar transistor (IGBT) die temperatures from exceeding acceptable limits at full power. If the coolant temperature is higher (100 °C, for example) the module power rating is reduced by a factor of 4 to 45 kW. Due to the high heat transfer coefficient of the evaporative spray cooling nozzles, the module was run at full load while maintaining satisfactory die temperatures even with the coolant at high temperature. The temperatures of the IGBT dies were measured by electrically insulated type T thermocouples that were placed on the die surfaces by Semikron during the manufacturing process. It was found that water spray cooling yielded IGBT device temperatures about 10 °C lower than WPG did, and both offer a substantial improvement over single phase convective cooling. The ability to cool power electronics with high temperature coolant means that a large ΔT is available for heat rejection to ambient conditions, which translates into a small and lightweight condenser. This higher coolant temperature also means it is possible to reject heat to warm ambient air. Also, the use of lower coolant flow rates enables the use of a smaller and lighter liquid pump. These factors, combined with the higher power density achieved, mean that evaporative spray cooling has significant potential to yield a lightweight thermal management system for aerospace applications. Copyright © 2008 SAE International

Evaporative Spray Cooling Of Power Electronics Using High Temperature Coolant

A pressure atomized evaporative spray cooling nozzle array was used to thermally manage the power electronics of a 3 phase inverter module. The module tested was a COTS module manufactured by Semikron, Inc., and has a maximum DC power input of 180 kW (450 VDC and 400 A) with 25°C coolant. However, the standard heat sink that the module uses is a single phase liquid heat sink and when 100°C coolant is used (as in automotive applications), the maximum module power is de-rated to 45 kW so that the IGBT chips will not overheat. The module tested here incorporated a custom heat sink that allowed for the use of spray cooling nozzles, which were designed and developed by RTI. The spray liquid was a 50/50 mixture of water and propylene glycol (WPG) at a temperature of 100°C. The sprays impinged directly onto the bottom surface of the DBC boards to which the power electronics were mounted. This arrangement, combined with the high heat transfer coefficient of evaporative spray cooling, greatly reduced the thermal resistance of the power electronics material stack up, but did so without directly wetting the electronics. The results of this work were that the unique evaporative spray cooling nozzle design and patented electronics interface design allowed the module to be run to full power while keeping the IGBT junction temperatures acceptable, despite the high coolant temperature. The junction temperatures of the IGBT\u27s were measured by electrically insulated type T thermocouples placed on top of the devices, and the thermocouple readings at the full load were within several degrees of one another. Consistent and uniform junction temperatures are an important factor in long term device reliability. For the standard heat sink, which uses single phase liquid cooling, the pressure drop and flow rate required for maximum heat removal would be 17 psi and 5.3 GPM. For the pressure atomizer spray nozzles, the module would require a pressure drop and flow rate of 40 psi and only 2.7 GPM. ©2008 IEEE

Research data supporting: The Crucial Role of Charge in Thermoresponsive-Polymer-Assisted Reversible Dis/Assembly of Gold Nanoparticles

Research data supporting The Crucial Role of Charge in Thermoresponsive-Polymer-Assisted Reversible Dis/Assembly of Gold Nanoparticle

Backaction effects of a SSET measuring a qubit spectroscopy and ground State measurement

We investigate the backaction of superconducting single-electron transistor (SSET) continuously measuring a Cooper-pair box. Due to the minimized backaction of the SSET, we observe a 2e periodic Coulomb staircase according to the two-level system Hamiltonian of the Cooper-pair box. We demonstrate that we can control the quantum broadening of the ground state in-situ. We perform spectroscopy measurements and demonstrate that we have full control over the Cooper-pair box Hamiltonian. The ability to reduce the backaction is a necessary condition to use the SSET as a quantum state readout for the CPB as a qubit