TY - JOUR
T1 - Uniqueness of Quantum States Compatible with Given Measurement Results
JF - Physical Review A
Y1 - 2013
A1 - Jianxin Chen
A1 - Hillary Dawkins
A1 - Zhengfeng Ji
A1 - Nathaniel Johnston
A1 - David Kribs
A1 - Frederic Shultz
A1 - Bei Zeng
AB - We discuss the uniqueness of quantum states compatible with given results for measuring a set of observables. For a given pure state, we consider two different types of uniqueness: (1) no other pure state is compatible with the same measurement results and (2) no other state, pure or mixed, is compatible with the same measurement results. For case (1), it is known that for a d-dimensional Hilbert space, there exists a set of 4d-5 observables that uniquely determines any pure state. We show that for case (2), 5d-7 observables suffice to uniquely determine any pure state. Thus there is a gap between the results for (1) and (2), and we give some examples to illustrate this. The case of observables corresponding to reduced density matrices (RDMs) of a multipartite system is also discussed, where we improve known bounds on local dimensions for case (2) in which almost all pure states are uniquely determined by their RDMs. We further discuss circumstances where (1) can imply (2). We use convexity of the numerical range of operators to show that when only two observables are measured, (1) always implies (2). More generally, if there is a compact group of symmetries of the state space which has the span of the observables measured as the set of fixed points, then (1) implies (2). We analyze the possible dimensions for the span of such observables. Our results extend naturally to the case of low rank quantum states.
VL - 88
UR - http://arxiv.org/abs/1212.3503v2
CP - 1
J1 - Phys. Rev. A
U5 - 10.1103/PhysRevA.88.012109
ER -