Recursive algorithm for constructing antisymmetric fermionic states in first quantization mapping
Evan Rule, I. A. Chernyshev, Ionel Stetcu, Joseph Carlson, R. Weiss · Quantum · 2026
We devise a deterministic quantum algorithm to produce antisymmetric states of single-particle orbitals in the first quantization mapping. Unlike sorting-based antisymmetrization algorithms, which require ordered input states and high Clifford-gate overhead, our approach initializes the state of each particle independently. For a system of η particles and N single-particle states, our algorithm prepares antisymmetrized states of non-trivial localized (e.g., Hartree-Fock) orbitals using O ( η 2 N ) T -gates, outperforming alternative algorithms when η ≲ N . To achieve such scaling, we require O ( N ) dirty ancilla qubits for intermediate calculations. Knowledge of the single-particle states to be antisymmetrized can be leveraged to further improve the efficiency of the circuit, and a measurement-based variant reduces gate cost by roughly a factor of two. We show example circuits for two- and three-particle systems and discuss the generalization to an arbitrary number of particles. For a specific three-particle example, we decompose the circuit into Clifford + T gates and study the impact of noise on the prepared state.