Physics:Quantum many-body problem
The quantum many-body problem is the challenge of describing systems containing many interacting quantum particles. Because the state space grows extremely rapidly with particle number, exact solutions are usually impossible except for small or specially structured systems.[1]
Many-body physics appears in atoms, molecules, nuclei, solids, quantum fluids, plasmas, and quantum information systems. It connects microscopic quantum laws with collective behavior such as magnetism, superconductivity, phase transitions, and emergent quasiparticles.
State-space growth
For a single particle, a wavefunction may be described over ordinary space. For many particles, the wavefunction depends on all particle coordinates and internal degrees of freedom. The number of amplitudes needed to represent the state can grow exponentially.
This growth makes approximation methods central. Mean-field theory, perturbation theory, density functional theory, tensor networks, Monte Carlo methods, and effective models are all ways to reduce or reorganize the complexity.
Collective behavior
Many-body systems often display properties not obvious from individual particles alone. Examples include superconductivity, spin liquids, Fermi liquids, and topological phases.
The many-body problem is therefore both a technical challenge and a source of new physical phenomena.
See also
- Physics:Quantum Approximation Methods
- Physics:Quantum Statistical mechanics
- Physics:Quantum Fock space
- Physics:Quantum Exchange interaction
References
Source attribution: Physics:Quantum many-body problem