Weakly Tunable Qubit: Part I

Performing fast, high-fidelity two-qubit gates is an important requirement of quantum computers. Cross-resonance gates applied to pairs of transmons satisfy this requirement with the added advantage of being fully controlled by microwave signals. However, applying these gates to a large transmon lattice is quite challenging. This is because cross-resonance gates set stringent requirements on the frequency landscape of neighboring qubits, which are difficult to satisfy with fixed-frequency transmons due to their relatively large frequency spread. To solve this problem, we realize a new flux-tunable qubit, compatible with cross-resonance gates, which can be tuned by less than 150 MHz. Such a weakly tunable qubit is useful for avoiding frequency collisions in a large lattice while limiting its susceptibility to flux noise. In this talk, we will introduce the qubit circuit and theory.