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Abstract:

A novel compact implementation is introduced, providing contiguous multiplexing of channels with extreme bandwidth differences. It relies on the combination of the direct branching approach with the ‘all-resonator’ multiplexing method. It accommodates the implementation of nearly arbitrary filter functions for different channels, incorporating transmission zeros (TZs) to meet the rejection demands between contiguous channels with a reasonable filter order. The proposed approach has been applied to a contiguous Ka-band multiplexer design with 15.5% overall bandwidth, serving four channels with three different channel bandwidths: 11.7%, 2.1%, and two channels of 0.6% each. Accordingly, different filter functions are applied - namely, 12th-, 8th-, and 6th-order filters - each providing two TZs. The wideband channel is separated at the common branching from the other three channels, which are served by an adapted all-resonator multiplexing method. The final multiplexer design proves high RF performance with a very compact implementation.

Abstract:

We present a framework for implementing two-qubit entangling operations between distant superconducting qubits using a space-time modulated Josephson junction (JJ) metasurface. By modulating the surface in both space and time, we engineer sidebands with controllable wavevectors that selectively couple target qubits. The metasurface acts as a reconfigurable coupling medium, where the interaction strength is determined by engineered transmission coefficients $T_{\mu}\left(\mathrm{k}_{\mu} \cdot \mathrm{r}\right)$ rather than by exponentially decaying near-field coupling, thus reducing the dependence on physical proximity. We investigated the implementation of two-qubit interactions via iSWAP gates driven resonantly through the metasurface and controlled phase gates via geometric phase accumulation. Simulations show entangling fidelity exceeding 98% maintained over centimeter-scale separations.