Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session T3: Keithley Award Session (GIMS) |
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Sponsoring Units: GIMS Chair: James Matey, US Naval Academy Room: 301/302 |
Wednesday, March 18, 2009 2:30PM - 3:06PM |
T3.00001: Joseph F. Keithley Award Talk: Microwave Measurements of Mesoscopic Devices Invited Speaker: Typical measurements of mesoscopic devices at low temperatures suffer from annoyingly low speeds and the presence of excess low-frequency noise that can try the experimentalist's patience. Even though these devices are not well-matched to the fifty ohm world of microwaves, the ability to listen to signals coming from a cryogenic nanostructure with a wideband amplifier at gigahertz frequencies has proven quite beneficial. These techniques can be surprising precise and powerful, allowing access to high-speed dynamics, the collection of information from wideband signals such as noise, and an entry into the domain of quantum electrical signals. I will review some of our early experiments at Yale in this area, especially the development of the Radio-Frequency Single-Electron Transistor (RF-SET), which is still the most sensitive electrometer known. Today we find that microwave measurements are proving highly beneficial for solid-state quantum computing, which in turn is leading to a new wave of capabilities for generating and measuring microwave signals at the single photon level. [Preview Abstract] |
Wednesday, March 18, 2009 3:06PM - 3:42PM |
T3.00002: Near-Quantum-Limited SQUID Amplifier Invited Speaker: The SET (Single-Electron Transistor), which detects charge, is the dual of the SQUID (Superconducting QUantum Interference Device), which detects flux. In 1998, Schoelkopf and co-workers introduced the RFSET, which uses a resonance circuit to increase the frequency response to the 100-MHz range. The same year saw the introduction of the Microstrip SQUID Amplifier$^{1}$ (MSA) in which the input coil forms a microstrip with the SQUID washer, thereby extending the operating frequency to the gigahertz range. I briefly describe the theory of SQUID amplifiers involving a tuned input circuit with resonant frequency f. For an optimized SQUID at temperature T, the power gain and noise temperature are approximately G = f$_{p}$/$\pi $f and T$_{N}$ = 20T(f/f$_{p})$, respectively; f$_{p}$ is the plasma frequency of one of the Josephson junctions. Because the SQUID voltage and current noise are correlated, however, the optimum noise temperature is at a frequency below resonance. For a phase-preserving amplifier, T$_{N}$ = ($\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $ + A)hf/k$_{B}$, where Caves' added noise number A = $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $ at the quantum limit. Simulations based on the quantum Langevin equation (QLE) suggest that the SQUID amplifier should attain A = $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $. We have measured the gain and noise of an MSA in which the resistive shunts of the junctions are coupled to cooling fins to reduce hot electron effects. The minimum value A = 1.1 $\pm $ 0.2 occurs at a frequency below resonance. On resonance, the value A = 1.5 $\pm $ 0.3 is close to the predictions of the QLE, suggesting that this model may fail to predict the cross-correlated noise term correctly. Indeed, recent work suggests that a fully quantum mechanical theory is required to account properly for this term$^{2}$. This work is in collaboration with D. Kinion and supported by DOE BES. $^{1}$M. Mueck, \textit{et al}., \textit{Appl. Phys. Lett.} \textbf{72}, 2885 (1998). $^{2}$A. Clerk, \textit{et al.,} http://arxiv.org/abs/0810.4729. [Preview Abstract] |
Wednesday, March 18, 2009 3:42PM - 4:18PM |
T3.00003: Optomechanics with microwave light Invited Speaker: Recently, superconducting circuits resonant at microwave frequencies have revolutionized the measurement of astrophysical detectors [1] and superconducting qubits [2]. In this talk, I will describe how we extend this technique to measuring and manipulating nanomechanical oscillators. By strongly coupling the motion of a nanomechanical oscillator to the resonance of the microwave circuit we create structures where the dominant dissipative force acting on the oscillator is the radiation pressure of microwave ``light'' [3]. These devices are ultrasensitive force detectors and they allow us to cool the oscillator towards its motional ground state. \\[4pt] [1] P. K. Day \emph{et al}., Nature \textbf{425}, 817 (2003).\\[0pt] [2] A. Wallraff \emph{et al}., Nature \textbf{431}, 162 (2004).\\[0pt] [3] J. D. Teufel, J. W. Harlow, C. A. Regal and K.~W. Lehnert, Phys. Rev. Lett., \textbf{101}, 197203 (2008). [Preview Abstract] |
Wednesday, March 18, 2009 4:18PM - 4:54PM |
T3.00004: Noise in Mesoscopic, Quantum, and Nano-Systems Invited Speaker: Studies of fluctuations and noise have been pursued for over a century. These allow investigation of basic physical concepts, dynamics of small systems, internal electronic structure of mesoscopic and nano systems, and quantum limits on detection. We review recent studies at Yale that illustrate these topics. We discuss quantum and classical noise in mesoscopic systems, noise in normal and superconducting tunnel junctions, higher moments of noise, and electrothermal fluctuations in superconducting nanosystems. We conclude by outlining a detector that utilizes many of these concepts, and should allow efficient detection and energy measurement of single microwave and higher-energy photons, at high count rates. [Preview Abstract] |
Wednesday, March 18, 2009 4:54PM - 5:30PM |
T3.00005: Nonlinear Dispersive Measurement with Superconducting Circuits Invited Speaker: Superconducting circuit elements can be used to form high quality factor harmonic and anharmonic oscillators. When coupled to a pseudospin system, these oscillators can be used for quantum state measurement. In the dispersive limit, the oscillator resonant frequency depends on the spin state. The case of a linear transmission line resonator coupled to a superconducting qubit was demonstrated by R. Schoelkopf and co-workers [1]. We will describe quantum measurement performed using a nonlinear resonator consisting of a Josephson tunnel junction shunted with a reactive impedance. As the Josephson oscillator is excited with an increasing number of photons, its resonant frequency progressively decreases. Under appropriate bias conditions, it is also possible to access a bifurcation where two dynamical states exist. We will show that with a nonlinear Josephson oscillator, it is possible to realize both analog and digital quantum state measurement with variable gain. We will discuss two protocols for accessing the nonlinear response of the junction, amplitude modulation and frequency modulation, and describe in detail two applications---superconducting qubit readout and high speed magnetometry of single molecule magnets. \\[4pt] [1] A. Wallraff et al, \textit{Physical Review Letters} \textbf{95}, 060501 (2005). [Preview Abstract] |
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