TY  - JOUR
A1  - Mari, Andrea
A1  - Kieling, Konrad
A1  - Nielsen, B. Melholt
A1  - Polzik, E. S.
A1  - Eisert, Jens
T1  - Directly estimating nonclassicality
JF  - Physical review letters
N2  - We establish a method of directly measuring and estimating nonclassicality-operationally defined in terms of the distinguishability of a given state from one with a positive Wigner function. It allows us to certify nonclassicality, based on possibly much fewer measurement settings than necessary for obtaining complete tomographic knowledge, and is at the same time equipped with a full certificate. We find that even from measuring two conjugate variables alone, one may infer the nonclassicality of quantum mechanical modes. This method also provides a practical tool to eventually certify such features in mechanical degrees of freedom in opto-mechanics. The proof of the result is based on Bochner's theorem characterizing classical and quantum characteristic functions and on semidefinite programming. In this joint theoretical-experimental work we present data from experimental optical Fock state preparation.
Y1  - 2011
U6  - https://doi.org/10.1103/PhysRevLett.106.010403
SN  - 0031-9007
VL  - 106
IS  - 1
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Lemr, Karel
A1  - Cernoch, A.
A1  - Soubusta, Jan
A1  - Kieling, Konrad
A1  - Eisert, Jens
A1  - Dusek, M.
T1  - Experimental implementation of the optimal linear-optical controlled phase gate
JF  - Physical review letters
N2  - We report on the first experimental realization of optimal linear-optical controlled phase gates for arbitrary phases. The realized scheme is entirely flexible in that the phase shift can be tuned to any given value. All such controlled phase gates are optimal in the sense that they operate at the maximum possible success probabilities that are achievable within the framework of postselected linear-optical implementations with vacuum ancillas. The quantum gate is implemented by using bulk optical elements and polarization encoding of qubit states. We have experimentally explored the remarkable observation that the optimum success probability is not monotone in the phase.
Y1  - 2011
U6  - https://doi.org/10.1103/PhysRevLett.106.013602
SN  - 0031-9007
VL  - 106
IS  - 1
PB  - American Physical Society
CY  - College Park
ER  -