Optimal estimation of entanglement in optical qubit systems
Giorgio Brida,Ivo Pietro Degiovanni,Angela Florio,Marco Genovese,Paolo Giorda,Alice Meda,Matteo G. A. Paris,Alexander Shurupov +7 more
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In this article, the experimental determination of entanglement for systems made of a pair of polarization qubits is addressed, where the authors exploit quantum estimation theory to derive optimal estimators, which are then implemented to achieve the ultimate bound to precision.Abstract:
We address the experimental determination of entanglement for systems made of a pair of polarization qubits. We exploit quantum estimation theory to derive optimal estimators, which are then implemented to achieve ultimate bound to precision. In particular, we present a set of experiments aimed at measuring the amount of entanglement for states belonging to different families of pure and mixed two-qubit two-photon states. Our scheme is based on visibility measurements of quantum correlations and achieves the ultimate precision allowed by quantum mechanics in the limit of Poissonian distribution of coincidence counts. Although optimal estimation of entanglement does not require the full tomography of the states we have also performed state reconstruction using two different sets of tomographic projectors and explicitly shown that they provide a less precise determination of entanglement. The use of optimal estimators also allows us to compare and statistically assess the different noise models used to describe decoherence effects occurring in the generation of entanglement.read more
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Qubit thermometry for micromechanical resonators
TL;DR: In this paper, the authors consider the estimation of temperature for a micromechanical oscillator lying arbitrarily close to its quantum ground state and exploit local quantum estimation theory to assess and optimize the precision of estimation procedures based on the measurement of qubit population and compare their performances with the ultimate limit posed by quantum mechanics.
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Statistical estimation of the quality of quantum-tomography protocols
Yu. I. Bogdanov,Giorgio Brida,I. D. Bukeev,Marco Genovese,K. S. Kravtsov,Sergei P. Kulik,Ekaterina Moreva,A. A. Soloviev,Alexander Shurupov +8 more
TL;DR: In this article, a complete methodology for testing the performances of quantum tomography protocols is presented, validated by several numerical examples and by the comparison with experimental results achieved with various protocols for whole families of polarization states of qubits and ququarts including pure, mixed, entangled, and separable.
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Quantum probes for the cutoff frequency of Ohmic environments
TL;DR: In this paper, the estimation of the cutoff frequency of the Ohmic spectral density of a harmonic reservoir by quantum probes was studied and it was shown that for most of the values, a simple probe such as a single qubit is already optimal for the precise estimation.
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Self-calibrating quantum state tomography
Agata M. Brańczyk,Dylan H. Mahler,Lee A. Rozema,Ardavan Darabi,Aephraim M. Steinberg,Daniel F. V. James +5 more
TL;DR: In this article, a technique for performing quantum state tomography (QST) on multiple-qubit states despite incomplete knowledge about the unitary operations used to change the measurement basis is presented.
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Spatial and temporal characterization of polarization entanglement
Andrei Nomerotski,Dimitrios Katramatos,Paul Stankus,Peter Svihra,Guodong Cui,Sonali Gera,Mael Flament,Eden Figueroa +7 more
TL;DR: In this paper, the authors describe the full temporal and spatial characterization of polarization-entangled photons produced by spontaneous parametric down conversations using an intensified high-speed optical camera, Tpx3.
References
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