Momentum space entanglement of fermions: results and measurement protocols

In recent decades, entanglement has emerged as a prominent diagnostic of a broad range of physical phenomena in many-body systems. While one typically considers entanglement in association with partitions of a many-body system in real-space, it is in fact possible to compute the entanglement of a quantum state by partitioning it in any single-particle basis. Here we take on the problem of computing the entanglement properties of translation-invariant systems of fermions in momentum space. We present perturbative calculations for both Fermi liquids and mean-field s-wave superconductors which reveal universal aspects of their Renyi entropies. We will also discuss measurement protocols that should allow for the measurement of momentum-space entanglement, including the case in which global symmetries are present.