Research in Quantum information processing studies the potential use of quantum mechanical systems–individual atoms, ions, photons, and nanoscale solid state devices–for information-processing tasks such as computation and communication. Such quantum systems may offer large gains over classical information processing. Algorithms for quantum computers are known which outperform the best known classical algorithms for a number of problems: factoring large numbers, searching an unstructured database, and the simulation of quantum systems. Quantum communications can offer perfectly secure encryption (through quantum key distribution) and capacity gains due to purely quantum resources, such as entanglement. In the QIP group at USC, research is done on a variety of problems. Particular areas of research include: the protection of quantum computers from noise (decoherence) by error correction, decoherence-free subspaces and subsystems, and refocusing pulses; weak and continuous measurements and quantum trajectories; realistic modeling of near-term experiments; quantum random walks; quantum chaos; quantum phase transitions; optical quantum computing and quantum communications; design of single photon sources and detectors; quantum information theory; asymptotic resource inequalities; and quantum channel capacities.