Detecting single-photon level signals—carriers of both classical and quantum information—is particularly challenging for low-energy microwave frequency excitations. Here we introduce a superconducting amplifier based on a Josephson junction transmission line. Unlike current standing-wave parametric amplifiers, this traveling wave architecture robustly achieves high gain over a bandwidth of several gigahertz with sufficient dynamic range to read out 20 superconducting qubits. To achieve this performance, we introduce a subwavelength resonant phase-matching technique that enables the creation of nonlinear microwave devices with unique dispersion relations. We benchmark the amplifier with weak measurements, obtaining a high quantum efficiency of 75% (70% including noise added by amplifiers following the Josephson amplifier). With a flexible design based on compact lumped elements, this Josephson amplifier has broad applicability to microwave metrology and quantum optics.
Detecting single-photon level signals—carriers of both classical and quantum information—is particularly challenging for low-energy microwave frequency excitations. Here we introduce a superconducting amplifier based on a Josephson junction transmission line. Unlike current standing-wave parametric amplifiers, this traveling wave architecture robustly achieves high gain over a bandwidth of several gigahertz with sufficient dynamic range to read out 20 superconducting qubits. To achieve this performance, we introduce a subwavelength resonant phase-matching technique that enables the creation of nonlinear microwave devices with unique dispersion relations. We benchmark the amplifier with weak measurements, obtaining a high quantum efficiency of 75% (70% including noise added by amplifiers following the Josephson amplifier). With a flexible design based on compact lumped elements, this Josephson amplifier has broad applicability to microwave metrology and quantum optics.
We propose a technique to overcome phase mismatch in Josephson-junction traveling wave parametric amplifiers in order to achieve high gain over a broad bandwidth. Using "resonant phase matching," we design a compact superconducting device consisting of a transmission line with subwavelength resonant inclusions that simultaneously achieves a gain of 20 dB, an instantaneous bandwidth of 3 GHz, and a saturation power of -98 dBm. Such an amplifier is well suited to cryogenic broadband microwave measurements such as the multiplexed readout of quantum coherent circuits based on superconducting, semiconducting, or nanomechanical elements, as well as traditional astronomical detectors.
Bringing signals from quantum to classical, from few-photon to many-photon levels for further processing, is a common challenge in rising quantum technologies. These include quantum computing, quantum communication, quantum sensing, radio astronomy, and dark matter searches, typically operating at microwave frequencies and millikelvin temperatures. Superconducting parametric amplifiers, as the first piece in the readout chain, have become a cornerstone of these technologies, since they offer unrivaled noise performance near the quantum-mechanical limit and high gain to surpass the noise of subsequent amplifiers. A notable implementation is the Josephson traveling-wave parametric amplifier (TWPA), which stands out due to its bandwidth of several Gigahertz and high saturation power, often larger than -100 dBm. These key properties come at the cost of complexity in design and fabrication: TWPA metamaterials often contain several thousands of Josephson junctions. Designing high-gain TWPAs involves three major challenges: ensuring impedance-matching, phase-matching of parametric amplification, and suppressing unwanted processes, all achievable through sub-wavelength dispersion engineering. This thesis covers the circuit design and analysis, implementation, and experimental characterization of a dispersion-engineered TWPA based on radio-frequency superconducting interference devices (rf-SQUIDs). It focuses on a detailed investigation of dispersion-engineering techniques and their effects on amplifier performance, particularly through the use of time-domain circuit simulations to analyze the multimode dynamics of the circuit. The experimentally realized device features 18 dB of gain, an instantaneous bandwidth spanning from 2.2 to 6.7 GHz, a system noise of 2.5 quanta, and a saturation power of (−86.5 ± 4.0) dBm. With these characteristics, it is suitable for frequency-multiplexed readout of detector arrays or qubits. Its high saturation power, about 10 dB higher than other reported Josephson-junction-based TWPAs, allows increasing the number of qubits per readout line, or decreasing the intermodulation between frequency-multiplexed qubits, both crucial for scaling up quantum computation.
Ultralow-noise microwave amplification and detection play a central role in different applications, going from fundamental physics experiments to the deployment of quantum technologies. In many applications the necessity of reading multiple detectors, or cavities or qubits, calls for large bandwidth amplifiers with the lowest possible noise. Current technologies are based on High Electron Mobility Transistors and Josephson Parametric Amplifiers. Both have limitations, the former in terms of the minimum noise, the latter in terms of bandwidth. Superconducting Traveling Wave Parametric Amplifiers (TWPAs) have the potential of offering quantum limited noise and large bandwidth. These amplifiers are based on the parametric amplification of microwaves traveling along a transmission line with embedded nonlinear elements. We are developing superconducting TWPAs based both on Josephson junction arrays (Traveling Wave Josephson Parametric Amplifiers) and on nonlinear kinetic inductance (Dispersion Engineered Traveling Wave Kinetic Inductance Amplifiers). Our goal is to achieve large bandwidth (in the 5 to 10 GHz range), large gain (more than 20 dB), large saturation power (more than −50 dBm), and near quantum limited noise (noise temperature less than 600 mK). Current achievements in the design and development of the high performance TWPAs are here reported and discussed, together with current limitations and possible future developments.
A requirement for quantum information experiments using superconducting quantum circuits is the readout of extremely weak microwave signals. Quantum limited amplifiers are essential for such task and this is precisely why they occupy an always-growing importance in such experiments, particularly for superconducting quantum bits readout.In this thesis, we present two quantum limited amplifiers architectures: the first one is based on a resonator while the second one leverages a traveling-wave construction. These amplifiers both take advantage of tunable Josephson junctions (squid). It is the ideal component for quantum limited parametric amplification: it is both nonlinear and dissipationless (given its superconducting nature). This thesis demonstrates the operation of these Josephson quantum limited amplifiers and how they go beyond the state-of-the-art thanks to original design choices.An important limitation of resonant Josephson parametric amplifiers is their poor dynamic range. We identified the Kerr nonlinearity as the main cause, and we successfully managed to tailor it using Josephson junction arrays. We also developed a model in good agreement with the experimental data, therefore validating our initial assumption that the Kerr nonlinearity and saturation are linked. However, most of the resonant Josephson parametric amplifiers suffer from a fundamental issue, arising from their architecture. It is the conservation of the gain bandwidth product, therefore limiting their bandwidth. Traveling-wave architectures are well suited to overcome this limitation. However, two new issues must be dealt with: impedance matching and phase matching. To tackle the former, we developed an original and simple fabrication process in order to obtain a 50ohm matched 2000 squid array. As for the phase, we matched it by periodically modulating the impedance of the squid transmission line in order to open a photonic band gap. Therefore, we locally distort the dispersion relation. This step does not add any complexity to the initial fabrication process. Moreover, we developed a model in good agreement with experimental data while considering the nonlinear behavior of the photonic gap in a Josephson metamaterial. In addition to demonstrating high performance amplifiers poised for numerous quantum technological applications, this thesis opens the door to more fundamental quantum optics experiments taking advantage of these highly nonlinear transmission lines.With the resonant amplifiers, we measured a 1dB compression point around -117dBm and 45MHz bandwidth (at 20 db gain). With the traveling-wave amplifiers, we measured 18dB gain on a 2.25GHz bandwidth, a 1dB compression point reaching -103dBm and near quantum-limited noise performances.
Coherent circuits based on superconducting elements hold tremendous promise for the practical implementation of quantum information technology: advanced computation, cryptography, and hardware simulation of complex materials systems are envisioned applications. Such circuits are essentially engineered atoms with level transitions in the 4-8 GHz regime; as such “read” and “write” operations are performed with the aid of fast microwave pulses and low-noise amplifiers, respectively. Recent advances in cavity-based superconducting parametric amplifiers have enabled real-time measurement and feedback in one and two qubits. We demonstrate a novel Josephson junction transmission-line based traveling-wave amplifier which employs sub-wavelength phase matching resonators to achieve high gain, several GHz of bandwidth, and near quantum-noise limited performance. Such devices will enable multiplexed qubit readout in integrated architectures comprised of a variety of microwave frequency analog and digital superconducting technologies: signal sources, multiplexers, ADCs, DACs, mixers, and amplifiers.
Superconducting traveling-wave parametric amplifiers have emerged as highly promising devices for near-quantum-limited broadband amplification of microwave signals and are essential for high quantum-efficiency microwave readout lines. Built-in isolation, as well as gain, would address their primary limitation: lack of true directionality due to potential backward travel of electromagnetic radiation to their input port. Here, we demonstrate a Josephson-junction-based traveling-wave parametric amplifier isolator. It utilizes third-order nonlinearity for amplification and second-order nonlinearity for frequency upconversion of backward propagating modes to provide reverse isolation. These parametric processes, enhanced by a novel phase matching mechanism, exhibit gain of up to 20~dB and reverse isolation of up to 30~dB over a static 3~dB bandwidth greater than 500~MHz, while keeping near-quantum limited added noise. This demonstration of a broadband truly directional amplifier ultimately paves the way towards broadband quantum-limited microwave amplification lines without bulky magnetic isolators and with inhibited back-action.