Design of Qubit Readout Circuit for Purcell Rate Suppressing and Nonclassicality Enhancing

The Purcell effect, a common issue in qubit-resonator systems leading to both fidelity and nonclassicality losses is studied while its suppression is achieved using a novel qubit readout circuit design. Our approach utilizes a unique coupling architecture in which, the qubit first interacts with a filter resonator before coupling 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. This work extensively analyzes the system using full quantum mechanical theory, deriving the total Hamiltonian and investigates mode dynamics via quantum Langevin equations. Key parameters influencing the nonclassicality of output signals are also explored through quantum correlation metrics, including symplectic eigenvalues, quantum discord, and classical discord. The main goal is to find any compromises exsting between the ac Stark factor increasing and the quantum correlation created in the readout circuit. By optimizing the critical factors, by which the ac Stark factor mainly affected, the proposed design not only improves the distinguishability of the qubit states but also ensures robust nonclassicality in the output signals. Results demonstrate the potential of the proposed system to bridge the gap between a high fidelity readout and quantum correlation preservation in scalable quantum architectures.