Implications of qudit superselection rules for the theory of decoherence-free subsystems
Mark Byrd · Physical Review A · 2006
The use of $d$-state systems, or qudits, in quantum information processing is discussed. Three-state and higher-dimensional quantum systems are known to have very different properties from two-state systems---i.e., qubits. In particular there exist qudit states which are not equivalent under local unitary transformations unless a selection rule is violated. This observation is shown to be an important factor in the theory of decoherence-free, or noiseless, subsystems. Experimentally observable consequences and methods for distinguishing these states are also provided, including the explicit construction of new decoherence-free or noiseless subsystems from qutrits. Implications for simulating quantum systems with quantum systems are also discussed.