Efficient control of fluxonium qubits via nonadiabatic transitions

The fluxonium qubit is a promising platform for quantum operations due to its large anharmonicity and long coherence time. However, conventional resonant driving methods often require long operation times and complex implementation. As an alternative, nonadiabatic transitions induced by a time-dependent external flux <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>ϕ</a:mi><a:mi>ext</a:mi></a:msub><a:mrow><a:mo>(</a:mo><a:mi>t</a:mi><a:mo>)</a:mo></a:mrow></a:mrow></a:math> can enable faster and simpler control by exploiting quantum interference between multiple transition paths. Existing approaches typically impose periodicity or symmetry on <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:msub><b:mi>ϕ</b:mi><b:mi>ext</b:mi></b:msub><b:mrow><b:mo>(</b:mo><b:mi>t</b:mi><b:mo>)</b:mo></b:mrow></b:mrow></b:math>, which can limit control efficiency. We propose a design strategy for <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:msub><c:mi>ϕ</c:mi><c:mi>ext</c:mi></c:msub><c:mrow><c:mo>(</c:mo><c:mi>t</c:mi><c:mo>)</c:mo></c:mrow></c:mrow></c:math> that relaxes these constraints. We demonstrate the effectiveness of this approach in two key scenarios: population inversion and adiabatic passage. Numerical simulations show that our method achieves higher control efficiency than existing schemes, emphasizing the advantage of breaking periodicity and symmetry. Furthermore, by incorporating decoherence effects using the Lindblad master equation, we confirm that the proposed scheme remains robust under realistic conditions.