Protected qubits, Floquet engineering and crosstalk suppression with superconducting circuits

Pranav Mundada, Gengyan Zhang, Andrew Houck

Andrey R. Klots, R. McDermott, L. B. Ioffe

Anuj Aggarwal, Jorge Fernández-Pendás, Simon Pettersson Fors +9 more

As superconducting quantum processors scale to large qubit counts, unwanted microwave drive crosstalk becomes an important source of coherent errors. Here, we investigate the role of parasitic coupling paths in the suppression of drive crosstalk in a processor with two fixed-frequency transmon qubits and a tunable coupler. To account for the many different coupling paths, we develop a detailed circuit model to capture the dependence of crosstalk on the coupler frequency. We experimentally demonstrate suppression of crosstalk, finding that the suppression does not originate solely from cancellation of the effective qubit-qubit coupling, but also is a result of interference between other coupling paths. Building on these insights, we show that drive crosstalk can be suppressed with the right choice of parasitic capacitances, which otherwise often are treated as unwanted design imperfections. Our results provide practical guidance for low-crosstalk device design of superconducting quantum processors and point toward a broader strategy in which parasitic coupling paths are engineered rather than simply minimized.

Camille Le Calonnec, Alexandru Petrescu, Agustín Di Paolo +6 more

Phillipe Campagne-Ibarcq, Mazyar Mirrahimi, Michel Devoret

Catherine Leroux, Agustín Di Paolo, Alexandre Blais

A significant challenge in the design of large-scale quantum processors is the presence of unwanted qubit-qubit crosstalk, which leads to uncontrollable accumulation of correlated errors. This work introduces a superconducting device that can controllably turn qubit-qubit interactions on and off. The design takes hints from noise-protected bosonic qubits to obtain $e\phantom{\rule{0}{0ex}}x\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l$ suppression of crosstalk in the off state. These results offer the possibility to keep crosstalk under control in large superconducting processors. Notably, this approach complements the recently introduced protected qubits; an architecture based on them and the proposed coupler would have built-in protection.