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arXiv:1909.08005 · Physical Review Applied

Josephson Array-Mode Parametric Amplifier

Volodymyr Sivak, Shyam Shankar, Guangtong Liu, José Aumentado, Michel Devoret

Published Feb 7, 2020• 57 citations
arXivHTMLPDF

Abstract

We introduce a near-quantum-limited amplifier with a large tunable bandwidth and high dynamic range---the Josephson array-mode parametric amplifier (JAMPA). The signal and idler modes involved in the amplification process are realized by the array modes of a chain of 1000 flux-tunable Josephson-junction-based nonlinear elements. The frequency spacing between the array modes is comparable to the flux tunability of the modes, ensuring that any desired frequency can be occupied by a resonant mode, which can further be pumped to produce high gain. We experimentally demonstrate that the device can be operated as a nearly quantum-limited parametric amplifier with 20 dB of gain at almost any frequency within a 4--12-GHz band. On average, it has a 3-dB bandwidth of 11 MHz and an input 1-dB compression power of $\ensuremath{-}108\phantom{\rule{0.2em}{0ex}}\mathrm{dBm}$, which can go as high as $\ensuremath{-}93\phantom{\rule{0.2em}{0ex}}\mathrm{dBm}$. We envision the application of such a device to the time- and frequency-multiplexed readout of multiple qubits, as well as to the generation of continuous-variable cluster states.

DOI
10.1103/physrevapplied.13.024014

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We introduce a near-quantum-limited amplifier with a large tunable bandwidth and high dynamic range---the Josephson array-mode parametric amplifier (JAMPA). The signal and idler modes involved in the amplification process are realized by the array modes of a chain of 1000 flux-tunable Josephson-junction-based nonlinear elements. The frequency spacing between the array modes is comparable to the flux tunability of the modes, ensuring that any desired frequency can be occupied by a resonant mode, which can further be pumped to produce high gain. We experimentally demonstrate that the device can be operated as a nearly quantum-limited parametric amplifier with 20 dB of gain at almost any frequency within a 4--12-GHz band. On average, it has a 3-dB bandwidth of 11 MHz and an input 1-dB compression power of \ensuremath−108dBm\ensuremath{-}108\phantom{\rule{0.2em}{0ex}}\mathrm{dBm}\ensuremath−108dBm, which can go as high as \ensuremath−93dBm\ensuremath{-}93\phantom{\rule{0.2em}{0ex}}\mathrm{dBm}\ensuremath−93dBm. We envision the application of such a device to the time- and frequency-multiplexed readout of multiple qubits, as well as to the generation of continuous-variable cluster states.
We have developed and measured a high-gain quantum-limited microwave parametric amplifier based on a superconducting lumped LC resonator with the inductor L including an array of eight superconducting quantum interference devices (SQUIDs). This amplifier is parametrically pumped by modulating the flux threading the SQUIDs at twice the resonator frequency. Around 5 GHz, a maximum gain of 31 dB, a product amplitude gain $\ifmmode\times\else\texttimes\fi{}$ bandwidth above 60 MHz, and a 1 dB compression point of $\ensuremath{-}123$ dBm at 20 dB gain are obtained in the nondegenerate mode of operation. Phase-sensitive amplification-deamplification is also measured in the degenerate mode and yields a maximum gain of 37 dB. The compression point obtained is 18 dB above what would be obtained with a single SQUID of the same inductance, due to the smaller nonlinearity of the SQUID array.
Arrays of 10 or 40 series-connected small densely packed Josephson tunnel junctions were successfully operated as parametric amplifiers at 10 GHz. Between 50 and 90% of the junctions in an array were observed to work coherently in the amplification process. Signal gain exceeding 24 dB was achieved with a pump power as low as −50 to −70 dBm. A power width (i.e., the range of the pump power for a gain within 3 dB of the peak gain) of 0.25 dB and a bandwidth of 15 MHz were measured for 20-dB gain. The power width was in accordance with theory but the bandwidth was reduced, probably due to noise saturation effects. The latter effects can be reduced by lowering the input noise temperature or by including an external band limitation. The noise temperature was also increased by saturation; however, with an external bandwidth of 60 MHz, a noise temperature of 30±20 K was measured. The application of a magnetic field has proved extremely useful as a means of tuning the amplifiers to stable high-gain operating points. This tuning was also utilized in evaluating the amplifier parameters, and the theory by Feldman, Parrish, and Chiao has been verified. The upper frequency limit for a lead tunnel junction amplifier ought to be well above 300 GHz.
The weak quantum signal amplification is an essential task in quantum computing. In this study, a recently introduced structure of Josephson junctions array called Blochnium (N series Quarton structure) is utilized as a parametric amplifier. We begin by theoretical deriving the system's Lagrangian, quantum Hamiltonian, and then analyze the dynamics using the quantum Langevin equation. By transforming these equations into the Fourier domain and employing the input-output formalism, leading metric indicators of the parametric amplifier become calculated. The new proposed design offers significant advantages over traditional designs due to its ability to manipulate nonlinearity. This premier feature enhances the compression point (P1dB) of the amplifier dramatically, and also provides its tunability across a broad band. The enhanced linearity, essential for quantum applications, is achieved through effective nonlinearity management, which is theoretically derived. Also, the ability to sweep the C-band without significant spectral overlap is crucial for frequency multiplexing in scalable quantum systems. Simulation results show that Blochnium parametric amplifiers can reach to a signal gain around 25 dB with a compression point better than of −92 dBm. Therefore, our proposed parametric amplifier, with its superior degree of freedom, surpasses traditional designs like arrays of Josephson junctions, making it a highly promising candidate for advanced quantum computing applications.
Broadband quantum-limited amplifiers play a critical role in the single-shot readout of superconducting qubits, but a popular implementation, the traveling wave parametric amplifier, involves a complex design and fabrication process. Here, we present a simple design for a Josephson parametric amplifier, using a lumped element resonator comprising a superconducting quantum interference device whose useful bandwidth is enhanced with an on-chip impedance-matching circuit. We demonstrate a flux-coupling geometry that maximizes the coupling to the Josephson loop and minimizes spurious excitation of the amplifier resonant circuit. The amplifier, which operates in a flux-pumped mode, is demonstrated with a power gain of more than 20 dB over a bandwidth of about 300 MHz, where approximate noise measurements indicate quantum-limited performance. A procedure is given for optimizing the bandwidth for this kind of amplifier, using a linearized circuit simulation while minimizing non-linearities.
Operating superconducting qubits at elevated temperatures offers increased cooling power, thus system scalability, but requires suppression of thermal photons to preserve coherence and readout fidelity. This motivates migration to higher operation frequencies, which demands high-frequency amplification with near-quantum-limited noise characteristics for qubit readout. Here, we report the design and experimental realization of a wireless Josephson parametric amplifier (WJPA) operating above 20 GHz. The wireless design eliminates losses and impedance mismatches that become problematic at high frequencies. The WJPA achieves more than 20 dB of gain across a tunable frequency range of 21–23.5 GHz, with a typical 3 dB bandwidth of 3 MHz. Through Y-factor measurements and a qubit-based photon number calibration, we show that the amplifier exhibits an added noise of approximately two photons.
We demonstrate K-band nondegenerate three-wave-mixing amplification in a multimode resonator comprising an array of 500 SNAILs. Pairing K-band signal modes with lower-frequency internal idler modes enables 20 dB of gain continuously from 19.6 to 25.6 GHz with pump frequencies below 32.2 GHz. At 20 dB gain, the 3-dB bandwidth ranges from 2.6 to 11.7 MHz, and the input-referred 1-dB compression power reaches -100.9 dBm. In the 20-22 GHz band, the average added noise is 0.73 quanta. A two-mode nondegenerate parametric amplification model describes the measured gain response and gain-bandwidth behavior, while a multimode Kerr model captures the overall compression scale. Our amplifier provides a practical solution for implementing a state-of-the-art readout of superconducting qubits in the K-band.