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Z. Hradil

Publications and source records attributed to Z. Hradil.

60 records · Page 4Linked to original sources
arXiv1999

Analogy between optimal spin estimation and interferometry

Scheme for optimal spin state estimation is considered in analogy with phase detection in interferometry. Recently reported coherent measurements yielding the average fidelity (N+1)/(N+2) for N particle system corresponds to the standard limit of phase resolution 1/\sqrt{N}. It provides the bound for incoherent measurements when each particle is detected separately and information is used optimally. For specific states, improvement up to the value 1/N is possible in quantum theory. The best results are obtained combining sequentially coherent measurements on fractional groups of particles.

quant-ph↗
arXiv1999

Reconstruction of the spin state

System of 1/2 spin particles is observed repeatedly using Stern-Gerlach apparatuses with rotated orientations. Synthesis of such non-commuting observables is analyzed using maximum likelihood estimation as an example of quantum state reconstruction. Repeated incompatible observations represent a new generalized measurement. This idealized scheme will serve for analysis of future experiments in neutron and quantum optics.

quant-ph↗
arXiv1999

Testing operational phase concepts in quantum optics

An experimental comparison of several operational phase concepts is presented. In particular, it is shown that statistically motivated evaluation of experimental data may lead to a significant improvement in phase fitting upon the conventional Noh, Fouge'res and Mandel procedure. The analysis is extended to the asymptotic limit of large intensities, where a strong evidence in favor of multi--dimensional estimation procedures has been found.

quant-ph↗
arXiv1998

Quantum tomography as normalization of incompatible observations

Quantum states are successfully reconstructed using the maximum likelihood estimation on the subspace where the measured projectors reproduce the identity operator. Reconstruction corresponds to normalization of incompatible observations. The proposed approach handles the noisy data corresponding to realistic incomplete observation with finite resolution.

quant-ph↗
arXiv1998

Reconstruction of diagonal elements of density matrix using maximum likelihood estimation

The data of the experiment of Schiller et al., Phys. Rev. Lett. 77 (1996) 2933, are alternatively evaluated using the maximum likelihood estimation. The given data are fitted better than by the standard deterministic approach. Nevertheless, the data are fitted equally well by a whole family of states. Standard deterministic predictions correspond approximately to the envelope of these maximum likelihood solutions.

quant-ph↗