Matrix product states and first quantization

Abstract

Common wisdom says that the entanglement of fermionic systems can be low in the second quantization formalism but is extremely large in the first quantization. Hence Matrix Product State (MPS) methods based on moderate entanglement have been overwhelmingly formulated in second quantization. Here we introduce a first-quantized MPS approach to simulate quantum many-body systems. We show that by reformulating the way the fermionic anti-symmetry is handled, we arrive at MPS with a level of entanglement comparable to the usual one found in second quantization. We demonstrate our scheme on the one-dimensional $t$-$V$ model (spinless fermions with nearest neighbour density-density interaction) for both ground state and time evolution. For time evolution, we find that the entanglement entropy in first quantization is significantly smaller than in its second quantization counterpart.