Superconducting microstrip amplifiers with sub-Kelvin noise temperature near 4 GHz

We present measurements of an amplifier operating at 3.8 GHz with 150 MHz of bandwidth based on the microstrip input-coil resonance of a dc superconducting quantum interference device (SQUID) with submicron Josephson junctions. The noise temperature is measured using two methods: comparing the signal-to-noise ratio of the system with and without the SQUID in the amplifier chain, and using a modified Y-factor technique where calibrated narrowband noise is mixed up to the SQUID amplifier operating frequency. With the SQUID cooled to 0.35 K we observe a minimum system noise temperature of 0.55 $\pm~0.13$ K, dominated by the contribution from the SQUID amplifier

Flux Qubits and Readout Device with Two Independent Flux Lines

We report measurements on two superconducting flux qubits coupled to a readout Superconducting QUantum Interference Device (SQUID). Two on-chip flux bias lines allow independent flux control of any two of the three elements, as illustrated by a two-dimensional qubit flux map. The application of microwaves yields a frequency-flux dispersion curve for 1- and 2-photon driving of the single-qubit excited state, and coherent manipulation of the single-qubit state results in Rabi oscillations and Ramsey fringes. This architecture should be scalable to many qubits and SQUIDs on a single chip

Reducing microwave loss in superconducting resonators due to trapped vortices

Microwave resonators with high quality factors have enabled many recent breakthroughs with superconducting qubits and photon detectors, typically operated in shielded environments to reduce the ambient magnetic field. Insufficient shielding or pulsed control fields can introduce vortices, leading to reduced quality factors, although increased pinning can mitigate this effect. A narrow slot etched into the resonator surface provides a straightforward method for pinning enhancement without otherwise affecting the resonator. Resonators patterned with such a slot exhibited over an order of magnitude reduction in the excess loss due to vortices compared with identical resonators from the same film with no slot

Transient dynamics of a superconducting nonlinear oscillator

We investigate the transient dynamics of a lumped-element oscillator based on a dc superconducting quantum interference device (SQUID). The SQUID is shunted with a capacitor forming a nonlinear oscillator with resonance frequency in the range of several GHz. The resonance frequency is varied by tuning the Josephson inductance of the SQUID with on-chip flux lines. We report measurements of decaying oscillations in the time domain following a brief excitation with a microwave pulse. The nonlinearity of the SQUID oscillator is probed by observing the ringdown response for different excitation amplitudes while the SQUID potential is varied by adjusting the flux bias. Simulations are performed on a model circuit by numerically solving the corresponding Langevin equations incorporating the SQUID potential at the experimental temperature and using parameters obtained from separate measurements characterizing the SQUID oscillator. Simulations are in good agreement with the experimental observations of the ringdowns as a function of applied magnetic flux and pulse amplitude. We observe a crossover between the occurrence of ringdowns close to resonance and adiabatic following at larger detuning from the resonance. We also discuss the occurrence of phase jumps at large amplitude drive. Finally, we briefly outline prospects for a readout scheme for superconducting flux qubits based on the discrimination between ringdown signals for different levels of magnetic flux coupled to the SQUID.Comment: 15 pages, 9 figure

Diagnostic Patterns and Immunohistochemical Stain Usage in Extended Core Prostate Biopsies: Comparisons Between Genitourinary and Non-Genitourinary Pathologists

Background: Ancillary immunohistochemical (IPOX) stains are useful in clarifying diagnostically challenging pathologic specimens. In diagnostic workup of prostate needle biopsies, stains for basal cells and α-methylacyl coenzyme A racemase are routinely used to support or refute the diagnosis of prostate cancer. Although useful, these stains add cost and must be used judiciously. There is a lack of firm guidelines establishing the proper utilization of IPOX studies in prostate pathology. Therefore, differences in patterns of stain use and diagnoses may exist, related to expertise of the pathologist. Objectives: The purpose of this study was to compare patterns of diagnoses and IPOX stain use in extended core prostate biopsies between genitourinary (GU) and non-genitourinary (NGU) pathologists in the University of Massachusetts Medical Center Pathology department. Methods: By computer search of medical records, consecutive extended core prostate biopsies (6+ cores) from years 2006-2011 were identified. Using Current Procedural Terminology (CPT) billing data, the number of cores and number of IPOX stains were retrieved. Diagnoses were recorded. Pathologists were divided into two groups based on expertise: genitourinary and non-genitourinary. Differences in the patterns of IPOX use and diagnoses between the two groups were analyzed. Results: GU pathologists diagnose significantly higher rates of prostate cancer (43.8% vs. 35.8%, p Conclusion: Significant differences exist in patterns of IPOX usage between GU and NGU pathologists in extended core prostate biopsy in this single institution study. This suggests the need for guidelines and continuing education focused on this issue to standardize practice, an intervention likely to improve quality of diagnoses and to reduce unnecessary costs

Vortex dynamics in superconducting channels with periodic constrictions

Vortices confined to superconducting easy flow channels with periodic constrictions exhibit reversible oscillations in the critical current at which vortices begin moving as the external magnetic field is varied. This commensurability scales with the channel shape and arrangement, although screening effects play an important role. For large magnetic fields, some of the vortices become pinned outside of the channels, leading to magnetic hysteresis in the critical current. Some channel configurations also exhibit a dynamical hysteresis in the flux-flow regime near the matching fields