Mixed State Discrimination Using Optimal Control

Mixed state discrimination using optimal control.

We present theory and experiment for the task of discriminating two nonorthogonal states, given multiple copies. We implement several local measurement schemes, on both pure states and states mixed by depolarizing noise. We find that schemes which are optimal (or have optimal scaling) without noise perform worse with noise than simply repeating the optimal single-copy measurement. Applying opti...

Optimal Control Problems with Mixed Control-State Constraints

Semilinear elliptic optimal control problems with pointwise control and mixed control-state constraints are considered. Necessary and sufficient optimality conditions are given. The equivalence of the SQP method and Newton’s method for a generalized equation is discussed. Local quadratic convergence of the SQP method is proved.

Optimal unambiguous discrimination of two subspaces as a case in mixed state discrimination

We show how to optimally unambiguously discriminate between two subspaces of a Hilbert space. In particular we suppose that we are given a quantum system in either the state |ψ1〉, where |ψ1〉 can be any state in the subspace S1, or |ψ2〉, where |ψ2〉 can be any state in the subspace S2, and our task is to determine in which of the subspaces the state of our quantum system lies. We do not want to m...

Optimal unambiguous filtering of a quantum state: An instance in mixed state discrimination

Deterministic discrimination of nonorthogonal states is forbidden by quantum measurement theory. However, if we do not want to succeed all the time, i.e., allow for inconclusive outcomes to occur, then unambiguous discrimination becomes possible with a certain probability of success. A variant of the problem is set discrimination: the states are grouped in sets and we want to determine to which...

Optimal discrimination of single-qubit mixed states