Distinguishability of complete and unextendible product bases

It is not always possible to distinguish multipartite orthogonal states if only local operation and classical communication (LOCC) are allowed. We prove that we cannot distinguish the states of an unextendible product basis (UPB) by LOCC even when infinite resources (infinite-dimensional ancillas, infinite number of operations). Moreover we give a necessary and sufficient condition for the LOCC distinguishability of complete product bases.Comment: added necessary and sufficient condition for complete product bases, example Lagarias-Shor ten-parties complete basi

Exciton-exciton interaction engineering in coupled GaN quantum dots

We present a fully three-dimensional study of the multiexciton optical response of vertically coupled GaN-based quantum dots via a direct-diagonalization approach. The proposed analysis is crucial in understanding the fundamental properties of few-particle/exciton interactions and, more important, may play an essential role in the design/optimization of semiconductor-based quantum information processing schemes. In particular, we focus on the interdot exciton-exciton coupling, key ingredient in recently proposed all-optical quantum processors. Our analysis demonstrates that there is a large window of realistic parameters for which both biexcitonic shift and oscillator strength are compatible with such implementation schemes.Comment: 3 two-column pages, 3 figure

Local degradation of selectively oxidized AlGaAs/AlAs distributed Bragg reflectors in lateral-injection vertical-cavity surface-emitting lasers

We show the local degradation of a selectively oxidized top distributed Bragg reflector (DBR) in a lateral-junction vertical-cavity surface-emitting laser (LJ-VCSEL) working at room temperature in continuous-wave operation. The measurements were carried out by a scanning microluminescence system used in reflection mode. The injection of a few milliamps in continuous-wave operation at room temperature in the LJ-VCSEL induces damage both in the DBRs and in the active area. The submicron resolution maps of the reflected laser intensity, recorded from the top surface of the LJ-VCSEL, show a strong local change in the top DBR reflectivity before and after current injection. The μ-photoluminescence map, recorded after the device failure, shows that the radiative recombination is strongly decreased in the damaged area of the device