Practical issues in theoretical descriptions of experimental quantum state and entanglement estimation

Hoshang Heydari

Junaid ur Rehman, Seongjin Hong, Seung-Woo Lee +7 more

Quantum multiple parameter estimation can achieve an enhanced sensitivity beyond the classical limit. Although a theoretical ultimate sensitivity bound for multiple phase estimation is given by the quantum Cramer-Rao bound (QCRB), experimental implementations to saturate the QCRB typically require an impractical setup including entangled measurements. Since it is experimentally challenging to implement an entangled measurement, the practical sensitivity is given by the Cramer-Rao bound (CRB) relevant to the measurement probabilities. Here, we consider the problem of practical sensitivity bound for multiple phase estimation with quantum probe states and a measurement setup without entanglement, which consists of a beam splitter followed by the photon-number-resolving measurement. In this practical measurement scheme, we show that lower CRB can be achieved with a quantum probe state even with higher QCRB.

Matej Peranić, Martin Lončarić, Anton Radman +1 more

Alexandru Dima

In this thesis activity the candidate has explored the main aspects of Bell Inequalities theory and eventually executed an experimental Violation test. This work contains a brief overview of the theoretical aspects around Bell Inequalities: the doubts arisen by Einstein, Podolski and Rosen about Quantum Theory completeness; the hidden variable theories and the bounds on classical correlations; quantum correlations and violation of Bell inequalities; the response given by Bell to the EPR paradox by introducing its famous theorem. In addition, the entanglement phenomenon has been studied, in particular in those dof that are given an important role in the violation of Bell Inequalities. Some documentation work was also done on non linear optics in order to understand fundamental effects that is common practice to exploit in the photon entanglement generation: SHG for the pump photons, SPDC in non-linear crystals. Moreover, the candidate also explored in this thesis some issues more closely related to the experimental aspect:loopholes that could affect the integrity of Bell inequalities proofs; efficiency threshold estimates regarding detection loophole; loophole-free configurations. Eventually, here in this report are also showed, along with the experimental setup brief description and some comments on the apparatus and its setting, the results of an experimental test of the CHSH inequality violation using photons entangled at first in polarization and then in a time-bin entanglement configuration.

Kentaro Ohki

Past quantum state estimation is a controversial issue, and it has been studied from both theoretical curiosity and practical necessity. Some studies propose quantum state smoothing methods, yet it is still an open problem in what situations ensure the past quantum states. This paper discusses conditions that the past quantum observable estimation becomes a past quantum state estimation and proposes two recursive methods of quantum state smoother.

Daniel R. Bes