Composite states and entanglement
A joint pure state can fail to factor into subsystem states.
Key knowledge
For specified finite-dimensional subsystems, the joint space is H_A⊗H_B. A pure state is entangled when it cannot be written as ψ_A⊗ψ_B; its subsystem state is obtained by partial trace.
Values and equations
H = H_A⊗H_B; ρ_A = Tr_B(|ψ⟩⟨ψ|)
- H, H_A, H_B
- Joint and subsystem Hilbert spaces
- ψ
- Normalized joint pure state
- ρ_A
- Reduced density operator
- Tr_B
- Partial trace over subsystem B
Conditions and scope
- The subsystem partition is specified.
- Nonfactorization of a mixed density operator alone does not establish entanglement.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Section 4.1: tensor space, product-state exception and reduced density matrix.
2026-10-10 · Bipartite pure-state criterion only; mixed-state separability tests excluded.
Entry details
Permanent link to this entry ↗- Record identity
- physics-tensor-product-entanglement
- Revision
- university-reference.1
- Structured reference record
- University reference · University core expansion