Logarithmic negativity

The logarithmic negativity1 is an entanglement measure which is easily computable and an upper bound to the distillable entanglement. It is defined as

EN(ρ) :  = log2∣∣ρΓA∣∣1 where ΓA is the partial transpose operation and ∣∣ ⋅ ∣∣1 denotes the trace norm.

It relates to the negativity 2 as follows:

EN(ρ) :  = log2(2N + 1).


The logarithmic negativity

  • can be zero even if the state is entangled (if the state is PPT entangled)
  • does not reduce to the entropy of entanglement on pure states like most other entanglement measures
  • is additive on tensor products: EN(ρ ⊗ σ) = EN(ρ) ⋅ EN(σ)
  • is not asymptotically continuous. That means that for a sequence of bipartite Hilbert spaces H1, H2, … (typically with increasing dimension) we can have a sequence of quantum states ρ1, ρ2, … which converges to ρ ⊗ n1, ρ ⊗ n2, … (typically with increasing ni) in the trace distance, but the sequence EN(ρ1)/n1, EN(ρ2)/n2, … does not converge to EN(ρ).
  • is an upper bound to the distillable entanglement

See also

Category:Quantum Information Theory Category:Handbook of Quantum Information Category:Entanglement

  1. quant-ph/0505071
  2. quant-ph/0102117
Last modified: 
Monday, October 26, 2015 - 17:56