Construction of a Non-Linear Entanglement Witness Operator in Arbitrary Dimension Using a Given Linear Witness Operator

TL;DR

This paper develops methods to construct non-linear entanglement witnesses from linear ones, enhancing detection capabilities for various entangled states in arbitrary dimensions.

Contribution

It introduces a constructive approach to derive non-linear entanglement witnesses from any linear witness, capable of detecting a broader class of entangled states, including PPT and NPT states.

Findings

Constructed NLEW operators can detect states missed by LEW.

NLEW operators can identify both PPT and NPT entangled states.

Constructed NLEW operators are decomposable into local observables for experimental realization.

Abstract

Entanglement detection is one of the important problems in quantum information theory. To deal with this problem, many entanglement detection criteria have been proposed. Among the proposed criteria, the detection of entanglement through witness operator (also known as linear entanglement witness (LEW) operator) may be considered as the most practical. Although the witness operator approach to detect entanglement is experimentally friendly, the construction of these operators is not a very simple task. Even if we are able to construct a LEW operator, our problem is not solved as it may either detect a few entangled states or not a single entangled state from a given family of entangled states. Thus, we need a constructive approach in order to tackle this type of problem. In this work, we provide a few constructions of the non-linear entanglement witnesses (NLEW) for $d_1\otimes d_2$ dimensional system from any linear entanglement witness (LEW) operator. The advantage of these constructions is that, if a LEW is unable to detect any particular entangled state described by the density operator $\rho^{ent}$ then our construction of NLEW may detect the same entangled state $\rho^{ent}$. Further, we have constructed NLEW operator that may detect not only a class of bipartite negative partial transpose entangled state (NPTES), but also positive partial transpose entangled state (PPTES). Moreover, we have shown that the constructed NLEW operators may be decomposed in terms of the tensor product of local observables and hence may be realizable in an experiment.