We present design and simulation of a Josephson parametric amplifier with bandwidth exceeding 1.6 GHz, and with high saturation power approaching -90 dBm at a gain of 22.8 dB. An improvement by a factor of roughly 50 in bandwidth over the state of the art is achieved by using well-established impedance matching techniques. An improvement by a factor of roughly 100 in saturation power over the state of the art is achieved by implementing the Josephson nonlinear element as an array of rf-SQUIDs with a total of 40 junctions. WRSpice simulations of the circuit are in excellent agreement with the calculated gain and saturation characteristics.Josephson parametric amplifiers have been in extensive use over the past few years, providing quantum limited noise performance at gains exceeding 20 dB, and enabling high fidelity qubit readout, 1-3 squeezed microwave field generation, 4 weak measurement, 5 and feedback control. 6 However, state-of-the-art devices of the eponymous JPA 7 and Josephson Parametric Converter (JPC) types 8 suffer from either narrow bandwidth ∼ 10 MHz, or low saturation power ∼ −110 dBm, or in many cases from both. Traveling-wave parametric amplifier 9,10 architectures can achieve large bandwidths of several GHz at the cost of high junction counts, typically exceeding 2000, with only modest improvement in saturation power. Here, we describe a flux-pumped JPA-type three-wave mixing amplifier with over 20 dB gain, in which we implement wellestablished impedance matching techniques to achieve over 1.6 GHz bandwidth, and a recently developed junction array design 11 to achieve high saturation power approaching -90 dBm. Overall, this work represents 50-fold improvement over the state of the art in bandwidth and 100-fold improvement saturation power, in a circuit with less than 100 junctions. We compare the calculated amplifier response to Spice simulations of the full nonlinear circuit.Both JPA and JPC, and their variants, are built with resonant structures embedding Josephson junctions or SQUIDs, which serve as the nonlinear active elements in the amplifier. Traditionally, their design has been driven by the principle that the loaded quality factor of the resonated nonlinearity must be relatively high in order to achieve high power gains. As a result, most Josephson parametric amplifiers are extremely narrow-band, and a considerable effort has been directed into making their center frequency tunable 12 to enable their practical use in the lab. This concept has been challenged recently by the work of Mutus et al. 13 and Roy et al., 14 who have shown that JPAs have been traditionally operating far from their maximum possible gain-bandwidth product, and that high gains and wide-band operation can be achieved simultaneously by improving the amplifier impedance match to the 50 Ω environment.The pumped nonlinearity in a parametric amplifier a) ofer.naaman@ngc.com presents the signal port with an effective negative resistance, giving rise to reflection gain. At the center of the amplifier band, the gain of a dev...
We demonstrate, for the first time, that a quantum flux parametron (QFP) is capable of acting as both isolator and amplifier in the readout circuit of a capacitively shunted flux qubit (CSFQ). By treating the QFP like a tunable coupler and biasing it such that the coupling is off, we show that T1 of the CSFQ is not impacted by Purcell loss from its low-Q readout resonator (Qe = 760) despite being detuned by only 40 MHz. When annealed, the QFP amplifies the qubit's persistent current signal such that it generates a flux qubit-state-dependent frequency shift of 85 MHz in the readout resonator, which is over 9 times its linewidth. The device is shown to read out a flux qubit in the persistent current basis with fidelities surpassing 98.6% with only 80 ns integration, and reaches fidelities of 99.6% when integrated for 1 µs. This combination of speed and isolation is critical to the readout of high-coherence quantum annealers.
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