Frequency allocation strategy in parametric-gate-based fixed-frequency qubit systems

The parametric gates implemented with flux-tunable transmons as couplers offer flexibility and access to larger native gate sets for fixed-frequency qubits. However, frequency crowding becomes an increasingly complicated issue to handle in scaled-up devices with more qubits. In this talk, we discuss a possible frequency-allocation scheme to avoid crowding in a square lattice of qubits. The design is based on grouping the qubits in two sublattices, such that the frequencies and anharmonicities of each sublattice are centered around different values. This allows us to scale up to square lattices of arbitrary size, provided that crosstalk between physically distant transmons is minimal. Furthermore, we discuss a simplified model of the gate dynamics that allows us to quantitatively set constraints on the frequencies and anharmonicities of the qubits, and determine how robust the scheme is to the impact of crosstalk and frequency variations of the qubits.