Remarks on 2–q-bit states

Berthold‐Georg Englert, Nasser Metwally, Sektion Physik

We distinguish six classes of families of locally equivalent states in a straightforward scheme for classifying all 2-q-bit states; four of the classes consist of two subclasses each. The simple criteria that we stated recently for checking a given state's positivity and separability are justified, and we discuss some important properties of Lewenstein-Sanpera decompositions. An upper bound is conjectured for the sum of the degree of separability of a 2-q-bit state and its concurrence.

A. D. Jannussis, G. Bbodimas, D. Soublas +1 more

David S. Simon

Rolf W. Landauer

Earlier work demonstrated that quantum–mechanical machinery can be used to transmit classical bits without a minimal unavoidable energy cost per bit. It is shown that a very minor variation of the earlier proposal also works for qubits. In addition, some casual remarks about error control in quantum parallelism are provided.

Yoshihito Kuno

Edge bit in an average symmetry protected topological (ASPT) mixed state is studied. The state is protected by one strong $Z_2$ and one weak (average) $Z_2$ symmetries. As analogous objects of pure symmetry protected topological (SPT) states, the ASPT possesses edge bits. In particular, the analogous operator response exists, that is, symmetry fractionalization. The fractionalization preserves the presence of the ASPT in the bulk, and the fractionalized edge operators acting on the edge bits of the ASPT. %analogous to the ones in the pure SPTs. In this work, based on the cluster model and by employing Choi mapping, we discuss generic features of the edge bits and numerically clarify the behavior of the edge bits and their robustness for varying decoherence and perturbative interactions. By using an operator-space mutual information (OSMI), we track the flow of quantum correlations between the two edges. Remarkably, even in the ASPT regime, a finite portion of the initial edge-to-edge correlation survives.

Franklin de Lima Marquezino, Renato Portugal, Carlile Lavor