Quantum-limited parametric amplifiers based on superconducting circuits are essential for the readout of microwave quantum systems. They are typically realized by exploiting the nonlinearity of Josephson junctions (JJs), which can be modulated through the application of strong pump tones. Despite the remarkable progress achieved over the past decade, JJ-based amplifiers still suffer from two major limitations that hinder their applicability in next-generation quantum technologies: sensitivity to magnetic fields beyond the millitesla range and non-negligible higher-order nonlinearities. Disordered superconductors have recently emerged as an alternative nonlinear medium capable of overcoming these limitations. Among them, granular aluminum (grAl) offers a particularly rich and versatile source of nonlinearity, well suited for the implementation of parametric devices. In this work, we leverage the intrinsic properties of grAl to develop a practical standing-wave parametric amplifier, called grAlPA, with a design resembling a superconducting Bose–Hubbard dimer. We demonstrate the magnetic-field resilience of the grAlPA, achieving near quantum-limited performance for in-plane magnetic fields up to 1 T. Furthermore, by exploiting the interplay between the intrinsically diluted higher-order nonlinearities and the low self-capacitance of grAl, we realize an amplifier exhibiting unconventional gain–bandwidth scaling up to gain levels of 25 dB. These results positions grAl as a compelling nonlinear platform for the next-generation of parametric amplifiers and open new opportunities for future quantum technologies.
Quantum-limited parametric amplifiers based on superconducting circuits are essential for the readout of microwave quantum systems. They are typically realized by exploiting the nonlinearity of Josephson junctions (JJs), which can be modulated through the application of strong pump tones. Despite the remarkable progress achieved over the past decade, JJ-based amplifiers still suffer from two major limitations that hinder their applicability in next-generation quantum technologies: sensitivity to magnetic fields beyond the millitesla range and non-negligible higher-order nonlinearities. Disordered superconductors have recently emerged as an alternative nonlinear medium capable of overcoming these limitations. Among them, granular aluminum (grAl) offers a particularly rich and versatile source of nonlinearity, well suited for the implementation of parametric devices. In this work, we leverage the intrinsic properties of grAl to develop a practical standing-wave parametric amplifier, called grAlPA, with a design resembling a superconducting Bose–Hubbard dimer. We demonstrate the magnetic-field resilience of the grAlPA, achieving near quantum-limited performance for in-plane magnetic fields up to 1 T. Furthermore, by exploiting the interplay between the intrinsically diluted higher-order nonlinearities and the low self-capacitance of grAl, we realize an amplifier exhibiting unconventional gain–bandwidth scaling up to gain levels of 25 dB. These results positions grAl as a compelling nonlinear platform for the next-generation of parametric amplifiers and open new opportunities for future quantum technologies.
Josephson junction parametric amplifiers have become essential tools for microwave quantum circuit readout with minimal added noise. Even after improving at an impressive rate in the past decade, they remain vulnerable to magnetic fields, which limits their use in many applications such as spin qubits, Andreev and molecular magnet devices, dark matter searches, etc. Kinetic inductance materials, such as granular aluminum (grAl), offer an alternative source of nonlinearity with innate magnetic field resilience. We present a nondegenerate amplifier made of two coupled grAl resonators resilient to in-plane magnetic fields up to 1T. It offers 20 dB of gain close to the quantum limit of added noise, with a gain-bandwidth product of 28 MHz and -110 dBm input saturation power.
Superconducting circuits based on high kinetic inductance materials are promising candidates for future quantum technologies, owing to their magnetic field resilience, low microwave losses, and lithographic scalability. In this thesis, we explore the properties of granular aluminum (grAl) resonators in two distinct geometries, using the nonlinear kinetic inductance of grAl for applications in superconducting quantum circuits. In the first part, we present compact meandered ring resonators fabricated using a single-step electron-beam lithography and lift-off process. By optimizing film resistivity and geometry, we achieve superinductors with characteristic impedances exceeding 100kΩ, corresponding to total inductances of several microhenries, while maintaining internal quality factors on the order of 105 in the single-photon regime. In the second part, we investigate DC-tunable resonators based on a 3λ/4 fractal geometry that allows direct current injection for in-situ tuning of the resonance frequency. We achieve frequency tunability up to 4.5% and analyze the nonlinear kinetic inductance using models based on Ginzburg-Landau, Mattis-Bardeen-BCS, and an effective Josephson-junction-array model. This work establishes granular aluminum as a material for realizing high-impedance and frequency-tunable superconducting circuits, offering new opportunities for advanced applications in protected qubits, hybrid quantum systems, broadband phase shifters, and three-wave mixing parametric amplifiers.
Superconducting standing−wave parametric amplifiers are crucial for the readout of microwave quantum devices. Despite significant improvements in recent years, the need to operate near an instability point imposes a fundamental constraint: the instantaneous bandwidth decreases with increasing amplifier gain. Here we show that it is possible to obtain parametric amplification without instability by using two simultaneous drives that activate phase-preserving gain and frequency conversion. Realized in a granular aluminum dimer with Kerr nonlinearity, our method demonstrates a sixfold bandwidth increase at 20 dB gain, surpasses the conventional gain−bandwidth scaling up to 25 dB, and remains near the quantum limit.
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.
Parametric amplification is essential for quantum measurement, enabling the amplification of weak microwave signals with minimal added noise. While Josephson-junction-based amplifiers have become standard in superconducting quantum circuits, their magnetic sensitivity, limited saturation power, and sub-kelvin operating requirements motivate the development of alternative nonlinear platforms. Here we demonstrate a two-mode kinetic-inductance parametric amplifier based on a pair of capacitively coupled Kerr-nonlinear resonators fabricated from NbTiN and NbN thin films. The distributed Kerr nonlinearity of these materials enables nondegenerate four-wave-mixing amplification with gains approaching 40 dB, gain-bandwidth products up to 6.9 MHz, and 1-dB compression powers two to three orders of magnitude higher than those of state-of-the-art Josephson amplifiers. A coupled-mode theoretical model accurately captures the pump-induced modification of the hybridized modes and quantitatively reproduces the observed signal and idler responses. The NbN device exhibits a significantly larger Kerr coefficient and superior gain-bandwidth performance, highlighting the advantages of high-kinetic-inductance materials. Our results establish coupled kinetic-inductance resonators as a robust platform for broadband, high-power, and magnetically resilient quantum-limited amplification, offering a scalable route for advanced readout in superconducting qubits, spin ensembles, quantum dots, and other microwave-quantum technologies.
With a large portfolio of elemental quantum components, superconducting quantum circuits have contributed to dramatic advances in microwave quantum optics. Of these elements, quantum-limited parametric amplifiers have proven to be essential for low noise readout of quantum systems whose energy range is intrinsically low (tens of µeV). They are also used to generate non classical states of light that can be a resource for quantum enhanced detection. Superconducting parametric amplifiers, like quantum bits, typically utilize a Josephson junction as a source of magnetically tunable and dissipation-free nonlinearity. The magnetic control is not an industry standard for devices and starts already to be an issue in large scale circuits. In recent years, efforts have been made to introduce semiconductor weak links as electrically tunable nonlinear elements, with demonstrations of microwave resonators and quantum bits using semiconductor nanowires, a two dimensional electron gas, carbon nanotubes and graphene. However, given the challenge of balancing nonlinearity, dissipation, participation, and energy scale, parametric amplifiers have not yet been implemented with a semiconductor weak link. The work presented in this PhD thesis demonstrates the design, fabrication and performances of a parametric amplifier leveraging a graphene Josephson junction.The graphene is encapsulated in between hBN flakes in order to improve its quality. Using such high quality junctions, we demonstrate amplification with 20 dB gain which is the milestone for overcoming noise of the classical amplifiers in the rest of the amplification chain. The Josephson parametric amplifier being based on a resonant structure (around 6 GHz) suffers from the gain bandwidth product limiting the amplification to a few MegaHertz frequency range. The use of a side gate to electrically tune the graphene gives control of the Josephson junction inductance and thus the resonant frequency of the amplifier. We demonstrate a near 1 GHz tunability of the amplification frequency with the use of a side gate which is as good as the tunability offered by using a magnetic flux on a SQUID for similar amplifier designs. Moreover, graphene has shown to exhibit nonlinear loss under a strong microwave irradiation arising because of dynamics in the Andreev states. Dissipation is known to add intrinsic noise on quantum amplifiers and could be a problem for quantum limited parametric amplification. We demonstrate that despite the presence of nonlinear loss, graphene based Josephson parametric amplifiers can reach near quantum limited amplification. A two photon loss model was used to describe the behaviour of the device but we show that a more complex model is required in order to take into account the nonlinear dissipation and the non-sinusoidal current phase relation. We also studied the dynamic range and showed that the graphene based Josephson parametric amplifier can reach a 1 dB compression point of -123 dBm which is as good as single tunnel junctions based parametric amplifiers. Our results expand the toolset for electrically tunable superconducting quantum circuits and offer new opportunities for the development of quantum technologies such as quantum computing, quantum sensing and fundamental science.