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arXiv:2209.07757 · Applied Physics Letters

Readout of a quantum processor with high dynamic range Josephson parametric amplifiers

T. White, Alex Opremcak, George Sterling, Alexander N. Korotkov, D. Sank, Rajeev Acharya, M. Ansmann, Frank Arute, Kunal Arya, Joseph C. Bardin, Andreas Bengtsson, Alexandre Bourassa, Jenna Bovaird, Leon Brill, Bob B. Buckley, David A. Buell, Tim Burger, Brian Burkett, Nicholas Bushnell, Zijun Chen, B. Chiaro, J. G. Cogan, Roberto Collins, Alexander L. Crook, Ben Curtin, Sean Demura, A. Dunsworth, Catherine Erickson, Reza Fatemi, Leslie Flores Burgos, Ebrahim Forati, Brooks Foxen, William Giang, Marissa Giustina, Alejandro Grajales Dau, Michael C. Hamilton, Sean David Harrington, Jeremy Hilton, M. R. Hoffmann, Sabrina Hong, Trent Huang, Ashley Huff, Justin Iveland, Evan R. Jeffrey, Mária Kieferová, Seon Kim, Paul V. Klimov, Fedor Kostritsa, John Mark Kreikebaum, David Landhuis, Pavel Laptev, Lily Laws, Kenny Lee, Brian Lester, Alexander T. Lill, Wayne Liu, Aditya Locharla, Erik A. Lucero, Trevor McCourt, Matt McEwen, Xiao Mi, Kevin C. Miao, Shirin Montazeri, Alexis Morvan, M. Neeley, Charles Neill, Ani Nersisyan, Jiun How Ng, Anthony Nguyen, Murray Nguyen, Rebecca L. Potter, Chris Quintana, P. Roushan, Kannan Sankaragomathi, Kevin J. Satzinger, Christopher Schuster, Michael J. Shearn, Aaron Shorter, Vladimir A. Shvarts, Jindra Skruzny, W. Clarke Smith, Marco Szalay, Alfredo Torres, Bryan W. K. Woo, Zhengliang Yao, P. Yeh, Juhwan Yoo, Grayson Young, Ningfeng Zhu, Nicholas Zobrist, Yu Chen, A. Megrant, Julian Kelly, Ofer Naaman

Published Jan 2, 2023• 45 citations
arXivHTMLPDF

Abstract

We demonstrate a high dynamic range Josephson parametric amplifier (JPA) in which the active nonlinear element is implemented using an array of rf-SQUIDs. The device is matched to the 50 Ω environment with a Klopfenstein-taper impedance transformer and achieves a bandwidth of 250–300 MHz with input saturation powers up to −95 dBm at 20 dB gain. A 54-qubit Sycamore processor was used to benchmark these devices, providing a calibration for readout power, an estimation of amplifier added noise, and a platform for comparison against standard impedance matched parametric amplifiers with a single dc-SQUID. We find that the high power rf-SQUID array design has no adverse effect on system noise, readout fidelity, or qubit dephasing, and we estimate an upper bound on amplifier added noise at 1.6 times the quantum limit. Finally, amplifiers with this design show no degradation in readout fidelity due to gain compression, which can occur in multi-tone multiplexed readout with traditional JPAs.

DOI
10.1063/5.0127375

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We demonstrate a high dynamic range Josephson parametric amplifier (JPA) in which the active nonlinear element is implemented using an array of rf-SQUIDs. The device is matched to the 50 Ω environment with a Klopfenstein-taper impedance transformer and achieves a bandwidth of 250–300 MHz with input saturation powers up to −95 dBm at 20 dB gain. A 54-qubit Sycamore processor was used to benchmark these devices, providing a calibration for readout power, an estimation of amplifier added noise, and a platform for comparison against standard impedance matched parametric amplifiers with a single dc-SQUID. We find that the high power rf-SQUID array design has no adverse effect on system noise, readout fidelity, or qubit dephasing, and we estimate an upper bound on amplifier added noise at 1.6 times the quantum limit. Finally, amplifiers with this design show no degradation in readout fidelity due to gain compression, which can occur in multi-tone multiplexed readout with traditional JPAs.
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Josephson parametric amplification is a tool of paramount importance in circuit-QED especially for the quantum-noise-limited single-shot read-out of superconducting qubits. We developed a Josephson parametric amplifier (JPA) based on a lumped-element LC resonator, in which the inductance L is composed by a geometric inductance and an array of 4 superconducting quantum interference devices (SQUIDs). We characterized the main figures of merit of the device, obtaining a −3 dB bandwidth BW = 15 MHz for a gain G = 21 dB and a 1 dB compression point P1dB = −115 dBm. The obtained results are promising for the future use of such JPA as the first stage of amplification for single-shot readout of superconducting qubits.
Traveling-wave parametric amplifiers (TWPAs) have become an essential tool for the readout of quantum circuits and the search for dark matter. We report on the implementation of an rf-superconducting quantum interference device (SQUID)-based Josephson TWPA with an average saturation power of −84 dBm while providing an average power gain of 20 dB from 3.5 to 8.5 GHz. This wide bandwidth is enabled by reducing the curvature of the dispersion in the signal band while suppressing detrimental mixing processes. With 2393 rf-SQUIDs, our device has a comparable number of nonlinear elements but achieves ten times higher saturation power than previously reported devices. This shows that using rf-SQUIDs results in a more favorable trade-off between device length and saturation power. Harnessing wideband characterization techniques, we determine the TWPA’s excess noise above the quantum limit to be 0.8 to 1.5 photons. In addition, we validate the signal-to-noise ratio improvement as a practical measure for tuning the TWPA to minimize the total system noise and demonstrate that its optimum does not coincide with the highest gain.
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.