Bandwidth and dynamic range of a widely tunable Josephson parametric amplifier

The ability to manipulate quantum information encoded in microwave fields has led to a renewed interest in Josephson parametric amplifiers (JPAs). For these applications the ability of JPAs to amplify signals with the least amount of added noise is critical. Unfortunately JPAs are typically narrow band amplifiers with small dynamic range. It is therefore important to understand the bandwidth and dynamic range of any particular JPA in order to determine if it is appropriate for these applications. We recently introduced a new kind of JPA. Although it is still narrow band, the amplified band can be tuned over a full octave. We have shown that it has good noise performance and can squeeze the vacuum noise by 10 dB. Here we characterize other important parameters of this amplifier, specifically the signal-bandwidth, dynamic range and saturation power.Comment: Accepted for publication in IEEE Transactions on Applied Superconductivity; Special Issue from the Applied Superconductivity Conferenc

Strongly quadrature-dependent noise in superconducting micro-resonators measured at the vacuum-noise limit

We measure frequency- and dissipation-quadrature noise in superconducting lithographed microwave resonators with sensitivity near the vacuum noise level using a Josephson parametric amplifier. At an excitation power of 100~nW, these resonators show significant frequency noise caused by two-level systems. No excess dissipation-quadrature noise (above the vacuum noise) is observed to our measurement sensitivity. These measurements demonstrate that the excess dissipation-quadrature noise is negligible compared to vacuum fluctuations, at typical readout powers used in micro-resonator applications. Our results have important implications for resonant readout of various devices such as detectors, qubits and nano-mechanical oscillators.Comment: 13 pages, 4 figure

Phase preserving amplification near the quantum limit with a Josephson Ring Modulator

Recent progress in solid state quantum information processing has stimulated the search for ultra-low-noise amplifiers and frequency converters in the microwave frequency range, which could attain the ultimate limit imposed by quantum mechanics. In this article, we report the first realization of an intrinsically phase-preserving, non-degenerate superconducting parametric amplifier, a so far missing component. It is based on the Josephson ring modulator, which consists of four junctions in a Wheatstone bridge configuration. The device symmetry greatly enhances the purity of the amplification process and simplifies both its operation and analysis. The measured characteristics of the amplifier in terms of gain and bandwidth are in good agreement with analytical predictions. Using a newly developed noise source, we also show that our device operates within a factor of three of the quantum limit. This development opens new applications in the area of quantum analog signal processing

Josephson junction microwave amplifier in self-organized noise compression mode

The fundamental noise limit of a phase-preserving amplifier at frequency is the standard quantum limit . In the microwave range, the best candidates have been amplifiers based on superconducting quantum interference devices (reaching the noise temperature at 700 MHz), and non-degenerate parametric amplifiers (reaching noise levels close to the quantum limit at 8 GHz). We introduce a new type of an amplifier based on the negative resistance of a selectively damped Josephson junction. Noise performance of our amplifier is limited by mixing of quantum noise from Josephson oscillation regime down to the signal frequency. Measurements yield nearly quantum-limited operation, at 2.8 GHz, owing to self-organization of the working point. Simulations describe the characteristics of our device well and indicate potential for wide bandwidth operation

Measurement of the full distribution of the persistent current in normal-metal rings

We have measured the persistent current in individual normal metal rings over a wide range of magnetic fields. From this data, we extract the first six cumulants of the single-ring persistent current distribution. Our results are consistent with the theoretical prediction that this distribution should be nearly Gaussian (i.e., that these cumulants should be nearly zero) for diffusive metallic rings. This measurement highlights the particular sensitivity of persistent current to the mesoscopic fluctuations within a single coherent volume.Comment: 14 pages, 4 figures and supplementary on-line information (31 pages