Entanglement can show fundamentally different behavior in fermionic systems. However, while bipartite measures of fermionic entanglement have been established, genuine multiparty entanglement (GME) in fermionic systems is much less understood. We introduce an efficiently computable measure (via semi-definite programming) of fermionic GME, fermion genuine multiparty negativity (fGMN), and show that it is an entanglement monotone and a natural multipartite extension of the fermionic negativity. Using this measure, we find many states which have fGMN but no non-fermionic GME, including large classes of fermionic stabilizer states. The fGMN also displays some major phenomenological differences to the bipartite fermionic negativity, such as finite sudden death points over separation and temperature.
The bipartite entanglement in Fermi gas without interaction is investigated when there are three fermions in the system. The negativity and the von Neumann entropy are employed to measure the entanglement of the system. The position of the third fermion can affect the entanglement between the first and the second fermions. The entanglement can be enhanced or suppressed when the third fermion changes its position. When the two fermions are at the same position or when their distance is more than 2.0/k F , the third fermion cannot affect them.
In this thesis the entanglement entropy of fermions on sublattices is studied and contrasted with known results for bosons. By studying a
(1+1)-dimensional periodic lattice and generalizing the notion and theory of circulant matrices to the broader class of phase circulant matrices, the results can be obtained analytically, thus providing a thorough understanding of entanglement entropy of fermion systems. To study the effect of long range coupling, a Lifshitz theory is adapted.\nTo start with, known results for the boson system have been reproduced to provide a background for the fermion results. The results for fermions show, firstly, a significant effect of the boundary conditions on the entanglement entropy. Secondly, a remarkable distinction between massive and massless fermions arises in the result that massless fermions generally have a maximal entanglement entropy. Most striking however, is the insight gained on the effect of long range coupling on the entanglement entropy, where the results for fermions strongly contrast the boson system: the entanglement entropy does not generally increase when long range coupling terms are added. We propose an explanation of this phenomenon by destructive interference. These results provide new and profound insights on entanglement of fermion systems.