Recent progress in solid state quantum information processing has stimulated the search for ultralow-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.In this article, we focus on parametric amplifiers which are powered by an ac source with frequency f p also known as the "pump". Such amplifiers operate with a minimal number of degrees of freedom and are the natural candidates for ultra low noise operation [1,2]. A single spatial and temporal mode of the electromagnetic field with carrier frequency f can be decomposed into its in-phase A cos 2πf t arXiv:0912.3407v1 [cond-mat.mes-hall]

We have constructed a new type of amplifier whose primary purpose is the readout of superconducting quantum bits. It is based on the transition of an RF-driven Josephson junction between two distinct oscillation states near a dynamical bifurcation point. The main advantages of this new amplifier are speed, high-sensitivity, low back-action, and the absence of on-chip dissipation. Pulsed microwave reflection measurements on nanofabricated Al junctions show that actual devices attain the performance predicted by theory.Quantum measurements of solid-state systems, such as the readout of superconducting quantum bits [1,2,3,4,5,6,7], challenge conventional low-noise amplification techniques. Ideally, the amplifier for a quantum measurement should minimally perturb the measured system while maintaining sufficient sensitivity to overcome the noise of subsequent elements in the amplification chain. Additionally, the characteristic drift of materials properties in solid-state systems necessitates a fast acquisition rate to permit measurements in rapid succession. To meet these inherently conflicting requirements, we propose to harness the sensitivity of a dynamical system -a single RF-driven Josephson tunnel junction -tuned near a bifurcation point. The superconducting tunnel junction is the only electronic dipolar circuit element whose nonlinearity remains unchanged at arbitrary low temperatures. As the key component of present superconducting amplifiers [8,9,10], it is known to exhibit a high degree of stability. Moreover, all available degrees of freedom in the dynamical system participate in information transfer and none contribute to unnecessary dissipation resulting in excess noise. The operation of our Josephson bifurcation amplifier is represented schematically in Fig. 1. The central element is a Josephson junction whose critical current I 0 is modulated by the input signal using an application-specific coupling scheme (input port), such as a SQUID loop [4] or a SSET [2]. The junction is driven with an sinusoidal signal i RF sin(ωt) fed from a transmission line through a directional coupler (drive port). In the underdamped regime, when the drive frequency ω is detuned form the natural oscillation frequency ω p and when the drive current IB < i RF < I B ≪ I 0 , the system has two possible oscillation states which differ in amplitude and phase [11,12]. Starting in the lower amplitude state, at the bifurcation point i RF = I B the system becomes infinitely sensitive, in absence of thermal and quantum fluctuations, to variations in I 0 . The energy stored in the oscillation can always be made larger than thermal fluctuations by increasing the scale of I 0 , thus preserving sensitivity at finite temperature. The reflected component of the drive signal, measured through another transmission line connected to the coupler (output port), is a convenient signature of the junction oscillation state which carries with it information about the input signal. This arrangement minimizes the back-action of the amplifier since the...

Cavity-optomechanics" aims to study the quantum properties of mechanical systems. A common strategy implemented in order to achieve this goal couples a high finesse photonic cavity to a high quality factor mechanical resonator. Then, using feedback forces such as radiation pressure, one can cool the mechanical mode of interest into the quantum ground state and create non-classical states of mechanical motion. On the path towards achieving these goals, many near-term applications of this field have emerged. After briefly introducing optomechanical systems and describing the current state-of-the-art experimental results, this article summarizes some of the more exciting practical applications such as ultra-sensitive, high bandwidth accelerometers and force sensors, low phase noise x-band integrated microwave oscillators and optical signal processing such as optical delay-lines, wavelength converters, and tunable optical filters. In this rapidly evolving field, new applications are emerging at a fast pace, but this article concentrates on the aforementioned labbased applications as these are the most promising avenues for near-term real-world applications. New basic science applications are also becoming apparent such as the generation of squeezed light, testing gravitational theories and for providing a link between disparate quantum systems. V C 2014 AIP Publishing LLC. [http://dx.