Direct all-to-all controlled-Z operation mediated via a central element on a star topology quantum processor - part 2

A major challenge in scaling superconducting quantum computers is enhancing qubit connectivity without sacrificing the speed and fidelity of the gate operations required to execute quantum algorithms.

To improve connectivity, we investigate the direct CZ gate between two peripheral qubits on a superconducting quantum processor in a star topology that uses a central element to implement effective all-to-all connectivity between the qubits [1]. To tune the interaction between any qubit and the central element while simultaneously suppressing the residual interaction to the spectator qubits, we employ flux-tunable transmon qubits as active coupling elements. In the considered topology, every qubit pair is linked by a chain of two tunable couplers and a central element. This enables direct connectivity between any pair of qubits and is used to implement the aforementioned CZ gate.

In the second part of this two-part talk, we transition from the theoretical analysis of the CZ gate to its experimental implementation, and present gate fidelity statistics of different qubit pairs. We anticipate that the obtained results pave the way towards high-connectivity architectures that strike a good balance between increased connectivity and available parallelism.

[1] https://arxiv.org/abs/2503.10903