The Null Flux Qubit

We discuss a superconducting flux qubit whose sensitivity to low frequency flux is reduced through a null flux geometry consisting of one closed wire loop twisted into a `figure eight' shape composed of two open loops, each with opposite circulation. This protects against global flux noise in a similar way as the gradiometer qubit, but with only one loop degree of freedom instead of the two DOF of the gradiometer. This important difference opens several possibilities for dealing with the local flux noise that causes decoherence in the gradiometer qubit. We further show that the null flux shape increases the sensitivity to high frequency flux, making the system potentially useful for superconducting transduction.