Designing quantum error correction codes for practical spin qudit

Abstract

The implementation of practical error correction protocols is essential for deployment of quantum information technologies. Ways of exploiting high-spin nuclei, which have multi-level quantum resources, have attracted interest in this context because they offer additional Hilbert space dimensions in a spatially compact and theoretically efficient structure. We present a quantitative analysis of the performance of a spin-qudit-based error-correctable quantum memory, with reference to the actual Hamiltonians of several potential candidate systems. First, the ideal code-word implemented on a spin-7/2 nucleus, which provides first order Pauli-$X$, $Y$ and $Z$ error correction, has intrinsic infidelity due to mixed eigenstates under realistic conditions. We confirm that expansion to a spin-9/2 system with tailored code-words can compensate this infidelity. Second, we claim that electric field fluctuations -- which are inevitable in real systems -- should also be considered as a noise source, and we illustrate an encoding/decoding scheme for a multi-spin-qudit-based error correction code that can simultaneously compensate for both electric and magnetic field perturbations. Such strategies are important as we move beyond the current noisy-intermediate quantum era, and fidelities above two or three nines becomes crucial for implementation of quantum technologies.