Quantum sensing networks for the estimation of linear functions

The theoretical framework for networked quantum sensing has been developed to a great extent in the past few years, but there are still a number of open questions. Among these, a problem of great significance, both fundamentally and for constructing efficient sensing networks, is that of the role of inter-sensor correlations in the simultaneous estimation of multiple linear functions, where the latter are taken over a collection local parameters and can thus be seen as global properties. In this work we provide a solution to this when each node is a qubit and the state of the network is sensor-symmetric. First we derive a general expression linking the amount of inter-sensor correlations and the geometry of the vectors associated with the functions, such that the asymptotic error is optimal. Using this we show that if the vectors are clustered around two special subspaces, then the optimum is achieved when the correlation strength approaches its extreme values, while there is a monotonic transition between such extremes for any other geometry. Furthermore, we demonstrate that entanglement can be detrimental for estimating non-trivial global properties, and that sometimes it is in fact irrelevant. Finally, we perform a non-asymptotic analysis of these results using a Bayesian approach, finding that the amount of correlations needed to enhance the precision crucially depends on the number of measurement data. Our results will serve as a basis to investigate how to harness correlations in networks of quantum sensors operating both in and out of the asymptotic regime

The elusive Heisenberg limit in quantum enhanced metrology

We provide efficient and intuitive tools for deriving bounds on achievable precision in quantum enhanced metrology based on the geometry of quantum channels and semi-definite programming. We show that when decoherence is taken into account, the maximal possible quantum enhancement amounts generically to a constant factor rather than quadratic improvement. We apply these tools to derive bounds for models of decoherence relevant for metrological applications including: dephasing,depolarization, spontaneous emission and photon loss.Comment: 10 pages, 4 figures, presentation imporved, implementation of the semi-definite program finding the precision bounds adde

Study on crystallization phenomenon and thermal stability of binary Ni–Nb amorphous alloy

In this paper, a ribbon of binary Ni–Nb amorphous alloy was prepared by the melt spinning technique. Glass transition and crystallization phenomenon of the alloy were investigated by differential scanning calorimetry. Thermal properties of the ribbon of binary Ni–Nb upon heating and cooling were analysed by DTA at a heating/ cooling rate of 0.5 K s-1 under the purified argon atmosphere. The thermal stability of Ni–Nb amorphous alloy was studied by using an X-ray diffractometer equipped with an in situ heating system. The structure and fracture morphology of the ribbons were examined by X-ray diffraction and scanning electron microscopy methods

Advances in photonic quantum sensing

Quantum sensing has become a mature and broad field. It is generally related with the idea of using quantum resources to boost the performance of a number of practical tasks, including the radar-like detection of faint objects, the readout of information from optical memories or fragile physical systems, and the optical resolution of extremely close point-like sources. Here we first focus on the basic tools behind quantum sensing, discussing the most recent and general formulations for the problems of quantum parameter estimation and hypothesis testing. With this basic background in our hands, we then review emerging applications of quantum sensing in the photonic regime both from a theoretical and experimental point of view. Besides the state-of-the-art, we also discuss open problems and potential next steps.Comment: Review in press on Nature Photonics. This is a preliminary version to be updated after publication. Both manuscript and reference list will be expande

Wpływ struktury powłok PVD i CVD na trwałość spiekanych ostrzy skrawających

In the work it was demonstrated that the exploitative stability of edges from tool ceramics and sintered carbides coated with gradient and multilayer PVD and CVD coatings depends mainly on the adherence of the coatings to the substrate, while the change of coating microhardness from 2300 to 3500 HV0.05, the size of grains and their thickness affect the durability of the edges to a lesser extent. It was found that some coatings showed a fine-grained structure. The coatings which contained the AlN phase with hexagonal lattice showed a considerably higher adhesion to the substrate from sialon ceramics rather than the coatings containing the TiN phase. Better adherence of the coatings containing the AlN phase with hexagonal lattice is connected with the same kind of interatomic bonds (covalent) in material of both coating and ceramic substrate. In the paper the exploitative properties of the investigated coatings in the technological cutting trials were also determined. The models of artificial neural network, which demonstrate a relationships between the edge stability and coating properties such as: critical load, microhardness, thickness and size of grains were worked out.W pracy wykazano, że trwałość eksploatacyjna ostrzy skrawających z ceramiki narzędziowej i węglików spiekanych pokrytych gradientowymi i wielowarstwowymi powłokami PVD oraz CVD zależy głównie od przyczepności powłok do podłoża, natomiast zmiana mikrotwardości w zakresie od 2300 do 3500 HV0.05. wielkości ziarn oraz ich grubości w mniejszym stopniu wpływają na trwałość ostrzy. Powłoki wykazują drobnoziarnistą strukturę. Powłoki zawierające fazę AlN o sieci heksagonalnej wykazują lepszą przyczepność do sialonowego podłoża niż powłoki zawierające fazę TiN. Lepsza przyczepność powłok zawierających fazę A1N o sieci heksagonalnej związana jest z takim samym rodzajem wiązań międzyatomowych (kowalencyjnych) w materiale powłoki i ceramicznego podłoża. W pracy określono także własności eksploatacyjne powłok w technologicznej próbie toczenia. Zależności pomiędzy trwałością ostrza a własnościami powłok takimi jak obciążenie krytyczne, mikrotwardość, grubość i wielkość ziarna określono z zastosowaniem sztucznych sieci neuronowych