# What is the deep physical reason behind the existence of bound entanglement? [closed]

In Quantum Information processing, we can extract entanglement from $$n$$-copies of a weakly entangled state to produce a fully or highly entangled states in $$d$$-dimensions, using the known distillation protocols.

However, there are states from which no entanglement can be extracted out using the known distillation protocols for no value of $$n$$. Such states contain bound entanglement.

For qubits, PPT is a necessary and sufficient criterion for separability. In higher dimensions, i.e qudits, there are states which satisfy PPT but are entangled and such states contain bound i.e non-distillable entanglement. I am not sure but I guess there are states which are NPT but bound entangled.

What is the deep physical reason behind the existence of bound entanglement?

• What is your question? Jul 20 '20 at 1:01
• Whether there is any deep physical reason for existence of bound entanglement or not Jul 20 '20 at 4:32
• "deep physical reason" is a bit subjective. Can you be more specific?
– glS
Jul 21 '20 at 15:52
• "I am not sure but I guess there are states which are NPT but bound entangled." -- That's one of the big open questions in quantum information theory. Jul 21 '20 at 19:37