The anisotropic Rabi model (ARM), which features tunable Jaynes-Cummings (JC) and anti-Jaynes-Cummings (AJC) interactions, has remained challenging to realize fully. We present a circuitQED implementation that provides static control over the ARM parameters. By simultaneously coupling a qubit to a resonator’s voltage and current antinodes, we geometrically tune the interaction from pure JC to pure AJC. This control enables novel quantum measurement capabilities, including dispersive shift cancellation and Purcell-suppressed readout. Our work establishes a direct platform for exploring the ARM’s full parameter space and its applications in quantum information processing.
Josephson Parametric Amplifiers (JPAs) are key components in quantum information processing due to their ability to amplify weak quantum signals with near-quantum-limited noise performance.This is essential for applications such as qubit readout, quantum sensing, and communication, where signal fidelity and coherence preservation are critical. Unlike CMOS and HEMT amplifiers used in conventional RF systems, JPAs are specifically optimized for millikelvin (mK) cryogenic environments. CMOS amplifiers offer good integration but perform poorly at ultra-low temperatures due to high noise. HEMT amplifiers provide better noise performance but are power-intensive and less suited for mK operation. JPAs, by contrast, combine low power consumption with ultra-low noise and excellent cryogenic compatibility, making them ideal for quantum systems. The first part of this study compares these RF amplifier types and explains why JPAs are preferred in cryogenic quantum applications. The second part focuses on the design and analysis of JPAs based on both single Josephson junctions and junction arrays. While single-junction JPAs utilize nonlinear inductance for amplification, they suffer from gain compression, limited dynamic range, and sensitivity to fabrication variations. To overcome these challenges, this work explores JPA designs using Josephson junction arrays. Arrays distribute the nonlinear response, enhancing power handling, linearity, impedance tunability, and coherence while reducing phase noise. Several advanced JPA architectures are proposed, simulated, and compared using quantum theory and CAD tools to assess performance trade-offs and improvements over conventional designs.
In this work, we design an advanced quantum readout architecture that integrates a four qubit superconducting chip with a novel parametric amplifier ended with analog front-end circuit.Unlike conventional approaches, this design eliminates the need for components such as Purcell filters. Instead, a Josephson Parametric Amplifier is engineered to simultaneously perform quantum-limited signal amplification and suppress qubit energy leakage. The design features a tailored gain profile across C-band, with sharp peaks (24 dB) and troughs (0 dB), enabling qubit frequencies to align with gain minima and resonator frequencies with gain maxima.
The Purcell effect, a common issue in qubit-resonator systems leading to fidelity loss is studied while its suppression is achieved using a novel qubit readout circuit design. Our approachutilizes a unique coupling architecture in which, the qubit first interacts with a filter resonator before linking to the readout resonator. This configuration enables precise control over the Purcell decay rate and ac Stark factor without impacting on measuring time. The mentioned factor is highly sensitive to the coupling strength between the readout resonator and the filter, meaning that the factor adjustment directly impacts the qubit state detection. A major advantage of this design is that tuning the resonator-filter coupling strength is relatively straightforward, offering flexibility in fine-tuning ac Stark factor.