Bulletin of the American Physical Society
2023 APS March Meeting
Volume 68, Number 3
Las Vegas, Nevada (March 510)
Virtual (March 2022); Time Zone: Pacific Time
Session Y71: Improving Qubit Readout with Parametric AmplifiersFocus

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Sponsoring Units: DQI Chair: Ted Thorbeck, IBM Quantum Room: Room 407/408 
Friday, March 10, 2023 8:00AM  8:12AM 
Y71.00001: FluxPumped Josephson TravelingWave Parametric Amplifier with Reverse Isolation Maxime Malnou, Jose A Estrada, Benton T Miller, Jose Aumentado, Florent Q Lecocq Travelingwave parametric amplifiers (TWPAs) have emerged as one of the leading technologies to amplify signals coming from frequencymultiplexed readout resonators. As such, they are a cornerstone in scaling up the readout architecture of superconducting quantum computers. 
Friday, March 10, 2023 8:12AM  8:24AM 
Y71.00002: Perfect phase matching via a nonlocal pump in topological Josephson travelingwave parametric amplifiers Tomas Ramos, Álvaro GómezLeón, Juan Jose GarciaRipoll, Alejandro GonzalezTudela, Diego Porras We propose a realization of a truly directional and broadband Josephson travelingwave parametric amplifier (JTWPA) using a homogeneous Josephson junction (JJ) array coupled to an auxiliary array of linear superconducting resonators [1]. We send the strong pump on the auxiliary array, which distributes an effective nonlocal pump on all sites of the JJ array. Tuning the spatial dependence of pump’s phase, we can compensate for the momentum mismatch due to the nonlinear dispersion of the JJ array and thereby achieve perfect phase matching without dispersion engineering. 
Friday, March 10, 2023 8:24AM  8:36AM 
Y71.00003: Microwave quantum optics with Josephson traveling wave parametric amplifiers : generation of twomode squeezed states Arpit Ranadive, Gwenael Legal, Giulio Cappelli, Sina Böhling, Luca Planat, Sebastien Leger, Dorian Fraudet, Olivier Buisson, Wiebke Guichard, Cécile Naud, Jose Aumentado, Florent Q Lecocq, Anja Metelmann, Nicolas Roch, Martina Esposito Josephson traveling wave parametric amplifiers have recently emerged as very promising platform for novel quantum optics experiments in microwave domain [1]. Engineering them at subwavelength scales can allow complete control over wave dispersion and nonlinear interactions [2]. We will present observation of broadband twomode squeezing generated by exciting a Josephson TWPA [3]. We will further discuss the hindrance posed by spurious processes in generation of these nonclassical states. Engineering the dispersion of the TWPA can offer efficient solutions for suppressing these spurious processes. We will highlight our efforts towards understanding and mitigating the degradation of twomode squeezing by higher order processes. 
Friday, March 10, 2023 8:36AM  8:48AM 
Y71.00004: Intermodulation Distortion in a Josephson Traveling Wave Parametric Amplifier Ants Remm, Sebastian Krinner, Nathan Lacroix, Christoph Hellings, François Swiadek, Graham J Norris, Christopher Eichler, Andreas Wallraff Josephson traveling wave parametric amplifiers enable the amplification of weak microwave signals close to the quantum limit with large bandwidth, which has a broad range of applications in superconducting quantum computing and in the operation of singlephoton detectors. While the large bandwidth allows for their use in frequencymultiplexed detection architectures, an increased number of readout tones per amplifier puts more stringent requirements on the dynamic range to avoid saturation. Here, we characterize the undesired mixing processes between the different frequencymultiplexed tones applied to a Josephson traveling wave parametric amplifier, a phenomenon also known as intermodulation distortion. The effect becomes particularly significant when the amplifier is operated close to its saturation power. Furthermore, we demonstrate that intermodulation distortion can lead to significant crosstalk and reduction of fidelity for multiplexed readout of superconducting qubits. We suggest using large detunings between the pump and signal frequencies to mitigate crosstalk. Our work provides insights into the limitations of current Josephson traveling wave parametric amplifiers and highlights the importance of performing further research on these devices. 
Friday, March 10, 2023 8:48AM  9:00AM 
Y71.00005: LowLoss Floquet Mode Josephson TravelingWave Parametric Amplifiers with Broadband NearIdeal Intrinsic Quantum Efficiency Kaidong Peng, Jennifer Wang, Mahdi Naghiloo, Jeffrey Knecht, Jack Qiu, Alec Yen, Yufeng Ye, Gregory D Cunningham, Katrina M Sliwa, Bethany M Niedzielski, Max Tan, Alicia J Zang, Kyle Serniak, Mollie E Schwartz, William D Oliver, Kevin P O'Brien We experimentally demonstrate a lowloss, Floquet mode travelingwave parametric amplifier (Floquet TWPA) using a superconducting qubit compatible aluminum process. With 20 dB gain and less than 1 dB of insertion loss over a several GHz bandwidth, our Floquet TWPAs are ideal for a wide range of informationcritical applications such as multiplexed qubit readout. We present noise characterization and superconducting qubit measurement using a Floquet TWPA. 
Friday, March 10, 2023 9:00AM  9:12AM 
Y71.00006: Noise in TravelingWave Parametric Amplifiers Matthew T Bell, Francesco Vischi We discuss experimental results of noise in a broadband travelingwave parametric amplifier (TWPA) utilizing a fourwave mixing process. The TWPA measured utilizes a phase matching approach which does not require dispersion engineering and is based on the Kerr reversal technique [1]. We have fabricated and measured two nominally identical TWPAs with different dielectrics of the grounding capacitors, one with higher loss SiO_{2} dielectric and the second with low loss SiNx dielectric. Noise measurements of the two TWPAs show amplifier added noise near the quantum limit and to be primarily dominated by higher parametric mixing products. These results agree with numerical simulations which will be discussed. 
Friday, March 10, 2023 9:12AM  9:48AM 
Y71.00007: Parametric amplifiers for high fidelity, QND qubit measurement Invited Speaker: Michael J Hatridge Quantum information processing requires highfidelity, quantum nondemolition (QND) readout of quantum bits. In superconducting circuits, qubits are coupled to shortlived 'readout' oscillators and measured via coherent pulses which gain qubit information as they pass through the readout mode. A central challenge is that these pulses must be very short compared to qubit lifetimes (to achieve high fidelity) and contain relatively few photons (to remain QND due to poorly understood measurementinduced qubit transitions). Given these limitations, the amplifier which processes these pulses is of vital importance. We desire these amplifiers to have high saturation power, large bandwidth, achieve the quantum limit on added noise, and be directional so that we can connect them directly to quantum circuits. In this talk I will discuss our efforts to master all these requirements in cavitybased, parametrically driven amplifiers. I will show a simple singlemode, nondirectional amplifier which is nearlyquantum limited with good bandwidth and a very high saturation power (90 dBm), and demonstrate high fidelity qubit readout with this device. I will also describe our efforts to build socalled 'embedded amplifiers' which can act directionally and be directly integrated into quantum processors without the use of bulky ferritebased microwave circulators. Finally, I will discuss how close we are to the point where further amplifier improvements cease to benefit us and further readout fidelity increase must come from the qubit's increased tolerance for strong, short readout pulses. 
Friday, March 10, 2023 9:48AM  10:00AM 
Y71.00008: Progress towards a near quantumlimited Josephson travelling wave parametric amplifier based on NbAl/Al_{2}O_{3}Nb trilayer technology. Evgenii Guzovskii, Hao Li, Yang Xu, Marco Scigliuzzo, Shingo Kono, Tobias J Kippenberg The interest in travelling wave parametric amplifiers (TWPAs) has dramatically increased over the past decade due to their ability to enhance quantum efficiency of measurements while retaining a large bandwidth and dynamic range essential for the operation of largescale frequencymultiplexed systems. Here we report on the developments in the fabrication of a TWPA based on Josephson transmission line periodically loaded with resonators for phasematching. We present the optimized process for the fabrication of the NbAl/Al_{2}O_{3}Nb trilayerbased Josephson circuits and the results of the characterization of the fabricated devices. 
Friday, March 10, 2023 10:00AM  10:12AM 
Y71.00009: Threewave mixing Josephson traveling wave parametric amplifiers with integrated parametric pump coupler circuits Visa Vesterinen, Tuomas Uusnäkki, Debopam Datta, Nils Tiencken, Leif Grönberg, Renan Pires Loreto, Om Prakash, Janne Lehtinen, Mika Prunnila, Joonas Govenius We present our latest results on Josephson traveling wave parametric amplifiers (TWPAs, [1]), which are currently in testing at operation frequencies of 750 MHz and 1500 MHz. These TWPAs have potential applications in, e.g., the readout of sensors and spin qubits. Due to the unavailability of multioctave cryogenic circulators at low radio frequencies, we are considering diplexers for the coupling of a pump tone in and out of the device. We describe the integration of diplexers into our TWPA sample holders, followed by standalone testing at cryogenic temperatures. Experimental characterization of the TWPAs will also be discussed. 
Friday, March 10, 2023 10:12AM  10:24AM 
Y71.00010: K band Josephson traveling wave parametric amplifiers for neutrino mass measurement Jennifer Wang, Kaidong Peng, Wouter Van De Pontseele, Katrina Sliwa, Patrick M Harrington, Yanjie Qiu, Kyle Serniak, Joseph A Formaggio, William D Oliver, Kevin P O'Brien Josephson traveling wave parametric amplifier (JTWPAs) are highgain, broadband, and lownoise quantum amplifiers that are crucial for frequencymultiplexed superconducting qubit readout. They also hold great promise in advancing quantum sensing capabilities across many fields. In collaboration with Project 8, a nextgeneration neutrino mass experiment which measures the electron cyclotron frequency from tritium beta decay to infer the neutrino mass, we are developing highfrequency JTWPAs centered at 25 GHz. These JTPWAs are predicted to attain 20 dB of gain over a few GHz of bandwidth with approximately 85% quantum efficiency relative to an ideal phasepreserving amplifier, resulting in an order of magnitude better noise performance than that of offtheshelf HEMT amplifiers. This talk presents simulations of the frequency response and parasitics of highfrequency JTWPA chip designs, as well as how to optimize packaging to minimize extraneous modes and impedance mismatches. We also present experimental progress towards utilizing the JTWPA in the Project 8 measurement chain to detect electromagnetic signals below the femtowatt level, and highlight that the high frequency JTWPA bandwidth can be tailored to address a wide range of applications, such as quantum information processing, dark matter searches, and other fundamental physics demonstrations. 
Friday, March 10, 2023 10:24AM  10:36AM 
Y71.00011: Nonlinear amplifiers: quantum limits and generalized longitudinal readout Joshua L Combes, Birgitta Whaley, Jeffrey M Epstein Nonlinear amplifiers such as the transistor are ubiquitous in classical technology, but their quantum analogues are not well understood. We introduce a class of nonlinear amplifiers that amplify any normal operator and add only a halfquantum of vacuum noise at the output. In the largegain limit, when used in conjunction with a noisy linear detector, these amplifiers implement ideal measurements of the normal operator. It turns out a special case of these amplifiers is the longitudinal interaction. Thus longitudinal readout can be understood through the lens of nonlinear amplification. 
Friday, March 10, 2023 10:36AM  10:48AM 
Y71.00012: Quantum Nondemolition Measurement of the Transverse Component of a Qubit Using a Dissipative SNAIL Coupler Chao Zhou, Jacob J Repicky, Mingkang Xia, Maria M Mucci, Roger Mong, Michael J Hatridge Quantum NonDemolition (QND) measurements of qubit arrays along combinations of both the transverse (x, y) and longitudinal (z) axes are commonly needed in quantum error correction. In this work we have designed and implemented a QND transverse axes measurement protocol on a transmon qubit by parametrically pumping a lossy, threewave SNAIL coupler at the sum and difference frequencies between the qubit and the SNAIL mode. Such a twotone pump effectively projects the qubit onto a transverse axis determined by the pump phases, and creates coherent light in the SNAIL mode with a phase that is conditional on whether the qubit is, for instance, in the +x or x eigenstate. This resultant xbasis measurement result is collected by demodulating the SNAIL output signal. Unlike usual dispersive measurement based on the Jaynes–Cummings Hamiltonian, this interaction is off when the drives are removed, which can enhance qubit coherence by rendering the transmon insensitive to thermal photons in the readout mode. We will present the measurement frame tuneup protocol, experiment data on measurement fidelity and efficiency, as well as the prospects for measuring multiqubit operators by parametrically linking more than one qubit to a single SNAIL. 
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