Josephson parametric amplifiers (JPAs) are crucial devices for readout of solid-state qubits. We review how to optimize the compression power and bandwidth of JPAs, necessary for realizing large-scale quantum information processors. We also discuss recent work to realize JPAs with a Josephson Junction Field Effect Transistor made from InAs-Al heterostructures.
Josephson parametric amplifiers (JPAs) are crucial devices for readout of solid-state qubits. We review how to optimize the compression power and bandwidth of JPAs, necessary for realizing large-scale quantum information processors. We also discuss recent work to realize JPAs with a Josephson Junction Field Effect Transistor made from InAs-Al heterostructures.
Near-quantum-limited amplifiers are essential building blocks for high-fidelity readout of superconducting qubits. Josephson parametric amplifiers (JPAs) have been developed to achieve this ultra-low-noise performance [1] in the last two decades by exploiting the quartic term in the nonlinear energy-phase relation of Al-AlO X superconductor-insulator-superconductor Josephson Junctions (SIS JJs). An ongoing research focus is to enhance JPAs’ compression power for processing readout signals in large-scale quantum processors. One approach is to optimize circuit designs to minimize parasitic higher-order nonlinear terms while preserving the quartic nonlinearity for the amplification process. An alternative approach is to make use of new types of JJ devices with small quartic nonlinearity such that parasitic nonlinearities are inherently even lower. Here, we demonstrate that superconductor-semiconductor-superconductor (SSmS) JJs, realized with Al-InAs heterostructures are a promising device to realize quantum-limited amplifiers for superconducting quantum computing. Al-InAs JJs have been used to realize qubits [2] , voltage-tunable resonators [3] , and parametric amplifiers [4] by exploiting critical current tunability via gate voltage ( Fig. 1(a–b) ). In this work, for the first time, we experimentally studied the nonlinear energy-phase relation of Al-InAs JJs and revealed their inherently low quartic nonlinearity. Next, we demonstrate a four-wave-mixing (4WM) parametric amplifier made with an Al-InAs junction that achieves greater than 20 dB of gain, 6 MHz of bandwidth and −119 dBm of compression power.
Superconducting quantum circuits are a leading platform for building a large-scale quantum processor [1]. A crucial component necessary for the high-fidelity readout of qubits in this framework, is an ultra-low-noise microwave amplifier. Thus, over the past two decades, superconducting Josephson parametric amplifiers (JPAs) have been developed that achieve near quantum-limited noise performance, an order of magnitude lower than competing microwave amplifiers based on semiconductor transistors [2]. Nevertheless, JPAs suffer from drawbacks such as limited bandwidth and compression power that makes them difficult to use in an eventual large-scale quantum processor. Thus, an ongoing theme in JPA development is to optimize the circuit to improve these specifications without sacrificing other desirable properties such as the noise performance, ease of construction and operation, etc. Here, we review some results of optimizing a specific JPA circuit called the SNAIL parametric amplifier [3]–[5], shown in Fig. 1, where the acronym SNAIL refers to the Superconducting Nonlinear Asymmetric Inductive eLement. The SNAIL is a composite element made from conventional Al/AlOx/Al Josephson junctions, which has a nonlinear current-phase relation that can be approximated as a nonlinear inductance. By applying a strong microwave frequency pump to modulate the nonlinear inductance, parametric amplification can be realized. By device and circuit engineering we have demonstrated two orders of magnitude improvement in compression power (Fig. 2) in such devices without sacrificing other desirable characteristics.
Josephson Parametric Amplifiers (JPAs) are key components in quantum information processing due to their ability to amplify weak quantum signals with near-quantum-limited noise performance. This is essential for applications such as qubit readout, quantum sensing, and communication, where signal fidelity and coherence preservation are critical. Unlike CMOS and HEMT amplifiers used in conventional RF systems, JPAs are specifically optimized for millikelvin (mK) cryogenic environments. CMOS amplifiers offer good integration but perform poorly at ultra-low temperatures due to high noise. HEMT amplifiers provide better noise performance but are power-intensive and less suited for mK operation. JPAs, by contrast, combine low power consumption with ultra-low noise and excellent cryogenic compatibility, making them ideal for quantum systems. The first part of this study compares these RF amplifier types and explains why JPAs are preferred in cryogenic quantum applications. The second part focuses on the design and analysis of JPAs based on both single Josephson junctions and junction arrays. While single-junction JPAs utilize nonlinear inductance for amplification, they suffer from gain compression, limited dynamic range, and sensitivity to fabrication variations. To overcome these challenges, this work explores JPA designs using Josephson junction arrays. Arrays distribute the nonlinear response, enhancing power handling, linearity, impedance tunability, and coherence while reducing phase noise. Several advanced JPA architectures are proposed, simulated, and compared using quantum theory and CAD tools to assess performance trade-offs and improvements over conventional designs.
Josephson parametric amplifiers (JPAs) are important tools in quantum information technology, and traveling-wave JPAs with extended bandwidth are especially desired for frequency multiplexing, e.g. in qubit readout. So far these devices have required the four-wave mixing condition to operate. The author shows, however, that there is a way to realize $t\phantom{\rule{0}{0ex}}h\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}e-w\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}v\phantom{\rule{0}{0ex}}e$ mixing, with negligible phase mismatch. This simple traveling-wave amplifier would offer large gain, wide bandwidth, and ultimately quantum-limited characteristics, outperforming its state-of-the-art four-wave counterparts.
Josephson parametric amplifiers (JPAs) with nearly quantum-limited noise performance have become indispensable devices for the measurements of superconducting quantum information. We have developed an all-Nb lumped-element flux-driven JPA operating in the three-wave mixing mode. Our Nb-based JPA comprises Nb/Al-AlO x /Nb Josephson junctions, a parallel-plate capacitor with SiO2 dielectric sandwiched between two Nb layers, a bottom coplanar waveguides layer, and a top Nb wiring layer. We experimentally demonstrate a 20 dB gain over a 190 MHz bandwidth, a mean 1 dB compression of –123 dBm, and near quantum-limited noise performance. This fabrication process can be further used to design impedance transformed parametric amplifiers for multiple-qubit readout.
We report a fabrication process and characterization of the Josephson parametric amplifier (JPA) for the single-shot quantum state measurement of superconducting multiqubit system. The device is prepared using Nb film as its base layer, which is convenient in the sample patterning process like e-beam lithography and film etching. Our results show that the JPA has a bandwidth up to 600 MHz with gain above 15 dB and noise temperature approaching the quantum limit. The qubit state differentiation measurements demonstrate the signal-to-noise ratio around 3 and the readout fidelity above 97% and 91% for the ground and first-excited states, respectively.