We show that partial transposition for pure and mixed two-particle states in a discrete N -dimensional Hilbert space is equivalent to a change in sign of a "momentum-like" variable of one of the particles in the Wigner function for the state. This generalizes a result obtained for continuous-variable systems to the discrete-variable system case. We show that, in principle, quantum mechanics allows measuring the expectation value of an observable in a partially transposed state, in spite of the fact that the latter may not be a physical state. We illustrate this result with the example of an "isotropic state", which is dependent on a parameter r, and an operator whose variance becomes negative for the partially transposed state for certain values of r; for such r, the original states are entangled.
Keywords 1 IntroductionQuantum entanglement in multipartite qubit (and qunits, i.e., N -dimensional quantum bits) states is a powerful computation and information resource [1,2]. Entanglement of pure quantum states is well understood, but entanglement of mixed quantum states, i.e., states that cannot be represented using a wave