Beta Tantalum Transmon Qubits with Quality Factors Approaching 10 Million

Tantalum-based transmon qubits are a promising platform for building large-scale quantum processors. So far, these qubits have been made from tantalum films grown exclusively in the alpha phase (α-Ta). The beta phase of tantalum ({beta}-Ta) readily nucleates at room temperature, making it attractive for scalable qubit fabrication. However, {beta}-Ta is widely believed to be detrimental to qubit performance because it has a lower superconducting critical temperature than α-Ta. We challenge this prevailing belief by fabricating low-loss transmon qubits from {beta}-Ta films on sapphire. Across 11 qubits, the mean time-averaged quality factor is (5.6 +/- 2.3) x 10^6, with the best qubit recording a time-averaged quality factor of (10.1 +/- 1.3) x 10^6. Resonator studies demonstrate that the dominant microwave loss channel is surface two-level systems, with the surface loss contribution for {beta}-Ta being about twice that of α-Ta. {beta}-Ta films exhibit significant kinetic inductance, consistent with an estimated magnetic penetration depth of (1.78 +/- 0.02) μm. This work establishes {beta}-Ta on sapphire as a material platform for realizing low-loss transmon qubits and other superconducting devices such as compact resonators, kinetic inductance detectors, and quasiparticle traps.

Source: arXiv:2603.13174v1 - http://arxiv.org/abs/2603.13174v1 PDF: https://arxiv.org/pdf/2603.13174v1 Original Link: http://arxiv.org/abs/2603.13174v1