Non-stoquastic interactions of superconducting circuits in the low frequency regime

Non-stoquastic interactions are hard to realize in experimental setups using superconducting qubits. On the other hand they are important or even necessary for the construction of adiabatic quantum computers wich show a real quantum speedup. In ArXiv:1903.06139, Ozfidan et al. show that they can realize non-stoquastic qubit-qubit interactions in a superconducting circuit architecture. The non-stoquastic nature only appears when the system is restricted to the low energy qubit subspace, since the full circuit Hamiltonian itself is stoquastic. Here we study the origin of these non-stoquastic interactions arising when projecting stoquastic Hamiltonians to the low energy spectrum. For this we use different theoretical tools, e.g. renormalization group techniques.