Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session J3: SQUID Amplifiers: at the Quantum Limit |
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Sponsoring Units: DCMP Chair: John Clarke, University of California, Berkeley Room: 301/302 |
Tuesday, March 17, 2009 11:15AM - 11:51AM |
J3.00001: Quantum information processing with the Josephson ring modulator Invited Speaker: |
Tuesday, March 17, 2009 11:51AM - 12:27PM |
J3.00002: Nearly noiseless amplification of microwave signals with a Josephson parametric amplifier Invited Speaker: A degenerate parametric amplifier transforms an incident coherent state by amplifying one of its quadrature components while deamplifying the other. This transformation, when performed by an ideal parametric amplifier, is completely deterministic and reversible; therefore the amplifier in principle can be noiseless. We attempt to realize a noiseless amplifier of this type at microwave frequencies with a Josephson parametric amplifier (JPA). To this end, we have built a superconducting microwave cavity containing many dc-SQUIDs. This arrangement creates a non-linear medium in a cavity and it is closely analogous to an optical parametric amplifier. In my talk, I will describe the current performance of this circuit, where I show I can amplify signals with less added noise than a quantum-limited amplifier that amplifies both quadratures. In addition, the JPA also squeezes the electromagnetic vacuum fluctuations by 10 dB. Finally, I will discuss our effort to put two such amplifiers in series in order to undo the first stage of squeezing with a second stage of amplification, demonstrating that the amplification process is truly reversible.\\[4pt] M. A. Castellanos-Beltran, K. D. Irwin, G. C. Hilton, L. R. Vale and K. W. Lehnert, Nature Physics, published on line, http://dx.doi.org/10.1038/nphys1090 (2008). [Preview Abstract] |
Tuesday, March 17, 2009 12:27PM - 1:03PM |
J3.00003: Flux-driven Josephson parametric amplifier Invited Speaker: Degenerate parametric amplifiers are phase sensitive amplifiers, which can in principle amplify one of the two quadratures of a signal without introducing extra noise. Parametric amplifiers based on the nonlinear inductance of a Josephson junction have been studied for a long time. Recently, there has been a renewed interest in parametric amplifiers due in part to the increasing need for quantum- limited amplification in the field of quantum information processing using superconducting circuits. In the present work, we design a novel Josephson parametric amplifier, comprising a superconducting transmission-line resonator terminated by a dc SQUID. Contrary to the previous works, the pump is not used to directly modulate a current through the Josephson junction, but is instead used to modulate a flux through the dc SQUID. Because the dc SQUID determines the boundary condition of the resonator, the flux modulation gives the temporal variation of the resonant frequency, which leads to the parametric amplification of the signal coming into the resonator. The practical advantage of the scheme is, first, that the band center of the signal is widely controllable by a dc flux also applied to the SQUID. Second, as the pump and the signal are applied to different ports and their frequencies are twice different, it is straightforward to separate the output signal from the pump. We have operated such a flux-driven Josephson parametric amplifier at around 10 GHz and characterized its basic properties. [Preview Abstract] |
Tuesday, March 17, 2009 1:03PM - 1:39PM |
J3.00004: Optimizing the Gain and Noise Temperature of Microstrip SQUID Amplifiers Invited Speaker: Micrrostrip SQUID amplifiers (MSA) offer near quantum-limited sensitivity and gains greater than 20 dB at frequencies around 1 GHz. These properties make them desirable for applications ranging from dark-matter axion detection to dispersive readout of superconducting qubits. The input of the MSA is a microstrip transmission line in the shape of a square spiral coil surrounding the hole in the SQUID washer that serves as the ground plane. Near the fundamental resonance, there is strong flux coupling between the input coil and SQUID. To obtain maximum performance it is necessary to know the complete set of complex scattering parameters. We present measurements of the scattering parameters of MSAs cooled to 4.2 K. The input impedance is found by measuring the reverse scattering parameter (S11) and is described well by a low-loss transmission line model. We map the low-loss transmission line model into an equivalent parallel RLC circuit that accurately predicts the observed gain given by the forward scattering parameter (S21). This information is used to optimize the input and output matching circuitry to achieve optimal noise temperature and gain. We will present results for the gain, dynamic range, linearity and noise temperature of these optimized MSAs at 30-500 mK as a function of frequency and SQUID bias. We will compare the results to the prediction of the circuit model and to the theoretical expectation that the lowest noise temperature occurs off-resonance. This work is in collaboration with John Clarke and a portion of this work was supported by DOE. [Preview Abstract] |
Tuesday, March 17, 2009 1:39PM - 2:15PM |
J3.00005: Lumped-Element DC-SQUID Microwave Amplifier Invited Speaker: We report on the development at NIST of microwave amplifiers in the 6-8 GHz frequency range using DC SQUIDs. Our design approach is to use small SQUIDs which can be modeled as lumped element circuits, thus separating the design process for the SQUID from that of the microwave impedance transformers. We present our model and measurements of the impedance, gain and noise of these SQUID amplifiers. Furthermore, we discuss how our modular hardware design allows for easy deployment in labs around the world where there is a need for lower noise microwave measurement. [Preview Abstract] |
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