Granular Aluminum Parametric Amplifier for Low-Noise Measurements in Tesla Fields
Nicolas Zapata, Ivan Takmakov, Simon Günzler, Simon Geisert, Soeren Ihssen, M. E. Field, Ameya Nambisan, Dennis Rieger, Thomas J.G. Reisinger, Wolfgang Wernsdorfer, Ioan M. Pop
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.
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.
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.
Superconducting parametric amplifiers are crucial components in microwave quantum circuits for enabling quantum-limited signal readout.The best-performing such amplifiers are often based on Josephson junctions, which however are sensitive to magnetic fields.Therefore, they require magnetic shields and are not easily integratable with other quantum systems that operate within magnetic fields, such as spinensemble quantum memories.To tackle this challenge, we develop a kinetic inductance-based parametric amplifier featuring a NbN nanobridge instead of Josephson junctions, which provides the desired nonlinearity for a strong parametric gain up to 42 dB.The added noise of this nanobridge kinetic-inductance parametric amplifier (hereby referred to as NKPA) is calibrated and found to be 0.59 ± 0.03 quanta for phase-preserving amplification, approaching the quantum limit of 0.5 quanta.Most importantly, we show that such excellent noise performance is preserved in an in-plane magnetic field up to 427 mT, the maximum field available in our experiment.This magnetic-field-resilient parametric amplifier presents an opportunity towards addressing single electron-spin resonance and more efficient search for axions as well as Majorana fermions.
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.
High kinetic inductance materials constitute a valuable resource for superconducting quantum circuits and hybrid architectures. Superconducting granular aluminum (grAl) reaches kinetic sheet inductances in the nH/□ range, with proven applicability in superconducting quantum bits and microwave detectors. Here, we show that the single photon internal quality factor Qi of grAl microwave resonators exceeds 105 in magnetic fields up to 1 T, aligned in-plane to the grAl films. Small perpendicular magnetic fields, in the range of 0.5 mT, enhance Qi by approximately 15%, possibly due to the introduction of quasiparticle traps in the form of fluxons. Further increasing the perpendicular field deteriorates the resonators' quality factor. These results open the door for the use of high kinetic inductance grAl structures in circuit quantum electrodynamics and hybrid architectures with magnetic field requirements.
Cryogenic parametric amplifiers are used to amplify radio-frequency signals for a range of applications in basic and applied science. Both Josephson Parametric Amplifiers and Josephson Traveling-Wave Parametric Amplifiers have been used as first-stage amplifiers enabling readout chains operating within a few quanta of the quantum limit. However, these devices are highly sensitive to magnetic fields, having critical current suppressed by the Fraunhofer effect, requiring substantial field-free zones. In a dark matter axion search experiment, axions convert to detectable microwave photons in the presence of a strong magnetic field, necessitating amplifiers that can reliably operate close to these environments. Kinetic-inductance Traveling-Wave Parametric Amplifiers (KTWPAs) may be the ideal candidate for this type of application having high critical magnetic field of the materials used throughout their construction. In this letter we demonstrate that KTWPAs can provide high gain (>20dB) over a multi-GHz bandwidth in spite of from multiple exposures to multi-Tesla fields. Further, we explore operational characteristics of these devices under harsh conditions as a function of overall field strength, device orientation within the field, applied bias current, and pump power & frequency. In so doing, we find KTWPA gain vanishes in devices oriented perpendicularly to a field of 0.02T, but gain values >10dB are achievable in fields over 1T when oriented near~parallel to the device plane, with peak gain achieved with an applied 0.25T to 0.5T field. It is our expectation that KTWPAs will expand the accessibility of quantum-limited RF measurements in the presence of Tesla-scale fields.
Advancing superconducting quantum devices to higher operating frequencies broadens their functionality and enables operation at elevated temperatures, but it also requires near-quantum-limited amplifiers beyond the few-gigahertz regime. Here we present a junction-free, kinetic-inductance parametric amplifier based on thin-film niobium nitride (NbN) operating at 23 GHz in the microwave K-band, achieving a gain up to 40 dB, a 100 MHz gain-bandwidth product, a 1 dB saturation input power of -85 dBm with 23 dB gain, and added noise no greater than 1.4 quanta for phase-preserving amplification. Leveraging the large superconducting gap of NbN, this architecture can be extended to even higher frequencies, supporting applications such as high-fidelity readout of millimeter-wave superconducting qubits and axion searches over an expanded mass window.