Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy XI
Design of high compression point Josephson junction travelling wave parametric amplifier for readout of millimetre/sub-millimetre astronomical receivers
Supra-THz heterodyne mixers generally have higher conversion loss compared to the millimetre-wave mixers. Hence, the overall receiver noise temperature becomes increasingly dominated by the first-stage semiconductor low noise amplifier (LNA), which still struggles to achieve quantum-limited noise performance. Here, we aim to develop a Josephson junction travelling wave parametric amplifier (JTWPA) that can achieve high gain over broad bandwidth but with better noise performance to replace these Intermediate Frequency (IF) amplifiers. JTWPAs are typically considered not suitable for astronomical receivers due to their low power handling capability. However, the critical current of the Josephson junctions (JJ) can be easily engineered to match the output power of the front-end detectors. Nevertheless, this may results in the requirement of a higher number of JJs as the junction inductance is in reverse relation with the critical current. Therefore, in this paper, we aim to explore the different design parameters required for developing a JTWPA with a dynamic range compatible for readout a Superconductor-Insulator-Superconductor (SIS) mixer, as an example. Here, we present two JTWPA models that are suitable for the objective, one requiring 3,142 Nb/Al-AlOx/Nb junctions with a maximum gain of 23 dB, and the other with a lower gain at 16 dB but requires only 1,317 JJs. We then compare the SIS receiver noise performance utilising these JTWPAs with that of using a conventional high gain High Electron Mobility Transistor (HEMT) amplifier. We show that we can improve the receiver sensitivity significantly by either cascading two 23 dB gain JTWPA or using a combination of a 16 dB gain JTWPA and a HEMT amplifier. We conclude that the former option more suitable for large detector array applications as it completely replaces the high heat dissipation HEMT amplifiers; while the latter option is favourable at this stage for low pixel count application as it is easier to fabricate a lower number of junctions JTWPA.
Supra-THz heterodyne mixers generally have higher conversion loss compared to the millimetre-wave mixers. Hence, the overall receiver noise temperature becomes increasingly dominated by the first-stage semiconductor low noise amplifier (LNA), which still struggles to achieve quantum-limited noise performance. Here, we aim to develop a Josephson junction travelling wave parametric amplifier (JTWPA) that can achieve high gain over broad bandwidth but with better noise performance to replace these Intermediate Frequency (IF) amplifiers. JTWPAs are typically considered not suitable for astronomical receivers due to their low power handling capability. However, the critical current of the Josephson junctions (JJ) can be easily engineered to match the output power of the front-end detectors. Nevertheless, this may results in the requirement of a higher number of JJs as the junction inductance is in reverse relation with the critical current. Therefore, in this paper, we aim to explore the different design parameters required for developing a JTWPA with a dynamic range compatible for readout a Superconductor-Insulator-Superconductor (SIS) mixer, as an example. Here, we present two JTWPA models that are suitable for the objective, one requiring 3,142 Nb/Al-AlOx/Nb junctions with a maximum gain of 23 dB, and the other with a lower gain at 16 dB but requires only 1,317 JJs. We then compare the SIS receiver noise performance utilising these JTWPAs with that of using a conventional high gain High Electron Mobility Transistor (HEMT) amplifier. We show that we can improve the receiver sensitivity significantly by either cascading two 23 dB gain JTWPA or using a combination of a 16 dB gain JTWPA and a HEMT amplifier. We conclude that the former option more suitable for large detector array applications as it completely replaces the high heat dissipation HEMT amplifiers; while the latter option is favourable at this stage for low pixel count application as it is easier to fabricate a lower number of junctions JTWPA.
Recent progress in physics has increased the necessity for ultra-low noise amplifiers capable of operating at the quantum limit performance. These amplifiers are essential to enhance astronomical detection, dark-matter search, and qubit readout in quantum computing, among other applications. Superconducting Josephson junction Travelling Wave Parametric Amplifiers (JTWPAs) operated in the microwave range, have demonstrated high gain over several gigahertz (GHz) bandwidth, with quantum-limited noise performance and minimal heat dissipation. These excellent properties make JTWPAs an ideal solution for ultra-low noise amplification. This thesis delves into the design, fabrication and characterisation of JTWPAs operated in the microwave (1-16 GHz) and the W-band (70-115GHz) regimes. A generalised coupled-mode equations (CME) framework describing JTWPAs based on Josephson junctions and DC superconducting quantum interference devices (SQUIDs) is introduced. This framework can be combined with electromagnetic (EM) simulation softwares to model the JTWPAs, facilitating their design. It is therefore used to model two microwave JTWPA designs, using parallel plate capacitors (PPCs) and interdigitated capacitors (IDCs). The fabrication and characterisation of both designs are presented, and possible fabrication and design issues are carefully discussed. Despite these issues, we observed broadband gain in the JTWPA with PPCs, achieving > 20 dB gain at several frequency points, and a measured P1dB = −95.8dBm when operated at 17.3 dB. The RF properties of a 500-junction Josephson array are also presented in this manuscript. The device creates a Fabry-Perot cavity, leading to non-travelling wave parametric effects, such as narrow-band gain. We also observed indications of efficient phase-sensitive amplification. The thesis is concluded with the first — to the best of our knowledge — experimental attempt to extend the operational frequency of a JTWPA to the W-band. The novel design, fabrication techniques and characterisation of the W-band JTWPA are discussed in detail in this manuscript, leading to promising results suggesting that JTWPA could operate at high frequencies.
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.
Abstract A Josephson traveling-wave parametric amplifier (JTWPA) is indispensable for the high-fidelity readout of superconducting qubits, owing to its broadband gain and near-quantum-limited noise performance. Conventional JTWPAs implemented with 0-Josephson junctions (0-JTWPAs) avoid magnetic-flux bias but rely on Kerr nonlinearity, which leads to pump-power-dependent phase mismatch, gain ripple, and a limited dynamic range. More recently, three-wave-mixing (3WM) JTWPAs employing flux-biased rf-SQUIDs have been proposed to suppress Kerr effects. However, these designs require a significant external flux bias per unit cell, which complicates cryogenic hardware, introduces sensitivity to flux noise, and limits scalability in large arrays. In this study, we propose and analyze a π -junction-based JTWPA ( π -JTWPA) in which the intrinsic π phase shift of the junction effectively displaces the operating point of the current–phase relation. This approach aims to realize 3WM-type nonlinearity with reduced flux bias while preserving broadband amplification, thereby simplifying flux-bias distribution, enhancing robustness against flux noise, and providing a pathway toward scalable, multiplexed quantum readout architectures. In addition, we examine the potential applicability of the π -JTWPA in four-wave-mixing (4WM) operation.
Broadband ultra-low noise amplification is important for many fundamental physics experiments. In our case, we aim to develop a quantum limited Josephson Travelling Wave Parametric Amplifier (JTWPA) for dark matter search experiments. In this paper, we focus on the development of the JTWPA, in particular to optimise the performance of the amplifier with a simplified fabrication prospect. We present our methodology for the optimisation process, focusing on three important aspects, namely utilising the minimal number of tunnel junction required, maximising the operational bandwidth and achieving a 50 Ω characteristic impedance. We first explore the relations between the important circuit parameters of the JTWPA and its performance indicators. Using the information obtained, we perform our optimisation process to search for the optimal design parameters. We then compare the gain bandwidth performance of the different optimised models, and present our findings with further analyses. We demonstrate that our optimised model requires 4 less tunnel junctions compared to the conventional model, and we are able to improve the operational bandwidth by 68% while maintaining the characteristic impedance of the device at 50 Ω.
Abstract Superconducting Parametric Amplifiers (SPAs) with near-quantum-limited added noise are crucial for weak signal detection applications such as astronomical receivers, quantum computation, and fundamental physics experiments. Commercially available SPAs include Josephson Parametric Amplifiers (JPAs), which offer high gain but narrow bandwidth performance; and Josephson-junction Travelling Wave Parametric Amplifiers (JTWPAs), which provide broader bandwidth at the cost of a complicated fabrication procedure, lower fabrication yield, and larger footprint area. In this paper, we investigate the parametric amplification of microwave signals in a Josephson array embedded in a low-Q Fabry-Pérot cavity. We fabricated a 500-junction array device and measured >15 dB phase-preserving gain over a ∼350 MHz bandwidth, while offering almost two orders of magnitude improvement in compression point (P 1dB = −106.2 dBm) compared to standard JPAs. Furthermore, using a novel measurement technique, we configured our device to operate in the phase-sensitive mode, measuring a phase-sensitive extinction ratio (PSER) of 42.3 ± 2.81 dB, in line with state-of-the-art values for JPAs. These promising performances, combined with the ease of fabrication and improved yield compared with JTWPAs, underscore the potential of these devices for applications in advanced detection schemes.
In order to build a large-scale quantum computer, one of the requirements is high-fidelity
multiplexed qubit readout, which in turn relies on the use of ultralow-noise
amplifiers. While Josephson Parametric Amplifiers (JPAs), using a cavity with
few Josephson junctions, have shown promising results for single qubit readout,
they have limitations such as low saturation power and a gain-bandwidth product
restriction. This makes them less suited for frequency multiplexed qubit readout. A
current-pumped Josephson Travelling-Wave Parametric Amplifier (JTWPA), using
4-wave mixing in a lumped-element transmission line, features both high saturation
power as well as no restriction on large bandwidth and high gain. This is possible
due to multiple junctions and the lack of a cavity. However, also this current pumped
JTWPA has an inherent problem, namely phase mismatch between the pump and
the signal. This prevents exponential gain. In this thesis, a current pumped JTWPA
using the resonant phase matching (RPM) technique to reduce the phase mismatch
problem is studied and characterised. The JTWPA shows high gain, high saturation
power and a large signal-to-noise ratio improvement. The JTWPA is also used for
qubit readout, for which it clearly improves the readout fidelity.