Airbridges for scalable microwave control of superconducting qubits

Zijun Chen, A. Megrant, J. Kelly +16 more

Kunliang Bu, Sainan Huai, Zhenxing Zhang +8 more

The unique property of tantalum, particularly its exceptional resistance to both acid and alkali, makes it promising for superconducting quantum processors. Here, we propose a novel lift-off method for fabricating tantalum airbridges with separate or fully-capped structures. This method introduces an aluminum film as a barrier layer to separate two layers of photoresist, which is then etched away before depositing tantalum film. We experimentally characterize these tantalum airbridges as control line jumpers, ground plane crossovers and coupling elements, and further validate the overall adaptability by a 13-qubit quantum processor with a median T 1 exceeding 100 μs. The median single-qubit gate fidelity is measured at 99.95(2)% for isolated Randomized Benchmarking and 99.94(2)% for the simultaneous one. Additionally, the experimental achievement of airbridge coupling with a controlled-Z gate fidelity surpassing 99.2(2)% in a separate two-qubit quantum chip may facilitate scalable quantum computation and quantum error correction with entirely tantalum elements.

Damon S. Russell, Jean-Philip Paquette, Mehrnoosh Vahidpour +2 more

Guihem Ribeill, Diana Lee, Brian Donovan +3 more

Danny Wan, Massimo Mongillo, Yann Canvel +8 more

Superconducting Nb airbridges were fabricated in imec’s 300 mm pilot line utilizing an advanced production toolset. An optimized process flow, which does not rely on liftoff or shadow evaporation, results in high airbridge yield across full wafers, and is compatible with trilayer-based superconducting qubit fabrication methods. Airbridges integrated with resonators were characterized at millikelvin temperatures, showing that the addition of airbridges can have minimal contribution to microwave losses. This work demonstrates that airbridges can be incorporated into foundry compatible qubit fabrication flows.

Zijun Chen, A. Megrant, J. Kelly +16 more

Superconducting microwave circuits based on coplanar waveguides (CPW) are susceptible to parasitic slotline modes which can lead to loss and decoherence. We motivate the use of superconducting airbridges as a reliable method for preventing the propagation of these modes. We describe the fabrication of these airbridges on superconducting resonators, which we use to measure the loss due to placing airbridges over CPW lines. We find that the additional loss at single photon levels is small, and decreases at higher drive powers.