Design and fabrication of millimeter-wave Josephson Travelling Wave Parametric Amplifiers*

Superconducting qubits have been instrumental in advancing microwave quantum computing technology. However, building a versatile fault-tolerant quantum computer requires a two-order-of-magnitude increase in qubit numbers. Achieving this scalability is challenging due to the demands on operational temperature (below 100 mK), large qubit footprints (0.1–1 mm) etc. A potential solution to these challenges is a millimeter (mm) wave qubit technology, which could relax the strict temperature constraints. Microwave superconducting qubits are generally readout using narrow-band Josephson Parametric Amplifiers (JPAs). In recent years, Josephson Travelling Wave Parametric Amplifiers (JTWPA) have emerged as a promising alternative, offering quantum-limited noise performance across a broader microwave bandwidth, enabling the readout of a larger array of qubits. However, the potential of JTWPA at millimeter-wave frequencies has remained relatively unexplored, despite its potential impact not only in millimeter-wave quantum computing but also in fields like millimeter-wave astronomy and dark matter search. In this talk, we will present our exploration of various design parameters for operating a JTWPA in the millimeter-wave regime, which in many cases is very different compared to the microwave counterpart e.g., the power coupling strategy. We will conclude with the presentation of a realistic design of a millimeter-wave JTWPA, including some preliminary test results.