We report the design, fabrication, and characterization of parametric amplifiers based on nonlinearities arising from current-induced pair-breaking in high kinetic inductance superconducting nanowires. We call these devices microwave entangler circuits (MEC), as they are intended for use in cluster state generation. The MECs are implemented as high quality factor lumped-element LC resonators and designed to support three-wave mixing, targeting a resonance frequency of 4.5 GHz and total loss rates below 2 MHz. Fabrication involved sputtering of 14 nm NbTiN films followed by lithography and reactive ion etching to define the nanoscale circuits. Resonator properties were characterized in a rapid thermal cycle cryostat at temperatures down to 1.7 K to extract the resonant frequency, and both internal and external loss rates. Parametric amplification from three-wave mixing was demonstrated with the application of a combined DC bias and high-frequency pump. Both signal and idler gain were observed, with gain up to 18 dB. A theoretical framework was also developed to model the operation of the MECs. The models help explain the observed gain and nonlinear response. This work lays the groundwork for future cluster state generation experiments.
We report the design, fabrication, and characterization of parametric amplifiers based on nonlinearities arising from current-induced pair-breaking in high kinetic inductance superconducting nanowires. We call these devices microwave entangler circuits (MEC), as they are intended for use in cluster state generation. The MECs are implemented as high quality factor lumped-element LC resonators and designed to support three-wave mixing, targeting a resonance frequency of 4.5 GHz and total loss rates below 2 MHz. Fabrication involved sputtering of 14 nm NbTiN films followed by lithography and reactive ion etching to define the nanoscale circuits. Resonator properties were characterized in a rapid thermal cycle cryostat at temperatures down to 1.7 K to extract the resonant frequency, and both internal and external loss rates. Parametric amplification from three-wave mixing was demonstrated with the application of a combined DC bias and high-frequency pump. Both signal and idler gain were observed, with gain up to 18 dB. A theoretical framework was also developed to model the operation of the MECs. The models help explain the observed gain and nonlinear response. This work lays the groundwork for future cluster state generation experiments.
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.
Abstract We study the response of several microwave resonators made from superconducting NbTiN thin-film meandering nanowires with large kinetic inductance, having different circuit topology and coupling to the transmission line. Reflection measurements reveal the parameters of the circuit and analysis of their temperature dependence in the range 1.7–6 K extract the superconducting energy gap and critical temperature. The lumped-element LC resonator, valid in our frequency range of interest, allows us to predict the quasiparticle (QP) contribution to internal loss, independent of circuit topology and characteristic impedance. Our analysis shows that the internal quality factor is limited not by thermal-equilibrium QP, but an additional temperature-dependent source of internal microwave loss.
Parametric converters are parametric amplifiers that mix two spatially separate nondegenerate modes and are commonly used for amplifying and squeezing microwave signals in quantum computing and sensing. In Josephson parametric converters, the strong localized nonlinearity of the Josephson junction limits the amplification and squeezing, as well as the dynamic range, in current devices. In contrast, a weak distributed nonlinearity can provide higher gain and dynamic range, when implemented as a kinetic inductance (KI) nanowire of a dirty superconductor, and has additional benefits such as resilience to magnetic field, higher-temperature operation, and simplified fabrication. Here, we propose, demonstrate, and analyze the performance of a KI parametric converter that relies on the weak distributed nonlinearity of a Nb-Ti-N KI nanowire. The device utilizes three-wave mixing induced by a dc current bias. We demonstrate its operation as a nondegenerate parametric amplifier with high phase-sensitive gain, reaching two-mode amplification and deamplification of approximately 30 dB for two resonances separated by 0.8 GHz, in excellent agreement with our theory of the device. We observe a dynamic range of $\ensuremath{-}108$ dBm at 30 dB gain. Our device can significantly broaden applications of quantum-limited signal processing devices including phase-preserving amplification and two-mode squeezing.
We study the temperature-dependent microwave response of high-kinetic-inductance superconducting resonators fabricated in Albanova's Nanolab as a part of the LKIPA device project. The investigated devices are based on circuit layouts designed for kinetic-inductance parametric amplification but are characterized using single-tone microwave measurements. We first compare the resonance parameters of different circuit designs to discuss and evaluate the performance of some fabricated resonators. A selected device is then measured in a cryostat, between 1.7 K and 3.0 K, to investigate how the resonance frequency, internal and external loss rates, and Kerr nonlinearity depend on temperature. The results show that the temperature dependence of the resonance frequency and external loss rate can be well described using a Mattis-Bardeen approach for linear responses in the investigated temperature interval. The internal loss rate, however, requires additional resistive channels beyond quasiparticle losses. By investigating near-resonance nonlinearities, we also demonstrate that nonlinear effects are less prominent when the temperature is increased. Deviations between the scattering fit and measured data are also discussed to evaluate possible limitations of the scattering model.
Abstract Superconducting resonators and parametric amplifiers are important components in scientific systems such as kinetic inductance detector arrays, frequency-domain multiplexers for other superconducting bolometers, spin-ensemble based memories, and circuit quantum electrodynamics demonstrators. In this paper, we report microwave measurements of superconducting Ti, Nb, and NbN resonators and their use as parametric amplifiers. These half-wave resonators were fabricated under near identical sputtering and lithographic conditions to ensure a like-for-like comparison of material properties. We report a wide range of properties and behaviours in terms of transition temperatures, resistivities, rate-limiting nonlinear response times, nonlinear dissipation, signs of the nonlinear inductances and their dependences on temperature and resonance harmonic. We have successfully operated Nb and NbN resonators as high gain parametric amplifiers, achieving greater than 20 dB of power amplification. We have shown that for a half-wave resonator, amplification can be realised not only in the fundamental resonance but also in the higher harmonic resonances. Further, for materials with high transition temperatures, e.g. Nb and NbN, amplification can be achieved at ∼ 4 K, i.e. a temperature maintained by a pulse tube cooler. Finally, in materials systems that have very fast response times, e.g. NbN, we have found that a cross-harmonic type of amplification can be achieved by placing pump tone in a different resonant mode as the signal and the idler. This wide range of observations will have important implications on the design and application of superconducting parametric amplifiers.
Traveling-wave parametric amplifiers may be fabricated from superconducting films that exhibit highly nonlinear kinetic inductance. The coplanar waveguide of such a microwave device, extending to a meter or more in length but compacted to reside on a chip of the order of a square centimeter, is engineered with periodic variations in its width. These width variations, or loadings, alter the dispersion characteristics of a nonlinear current propagating along the waveguide, changing its group velocity and modulation behavior. A strong pump and a small signal injected into one end of the waveguide mix parametrically in the presence of the nonlinear kinetic inductance. Engineered dispersion induces the favorable conditions of overall phase matching, leading to generation of idler products as well as signal amplification of wide bandwidth, high dynamic range, and low noise, making the device of particular use in quantum computing and photon detection. The authors present a theoretical framework in which signal gain may be calculated solely from loading design. This involves construction of a metamaterial band theory of the engineered dispersion, which is used as a basis to describe the mixing of nonlinear traveling waves.