263 research outputs found
Adaptive quantum metrology under general Markovian noise
We consider a general model of unitary parameter estimation in presence of
Markovian noise, where the parameter to be estimated is associated with the
Hamiltonian part of the dynamics. In absence of noise, unitary parameter can be
estimated with precision scaling as , where is the total probing time.
We provide a simple algebraic condition involving solely the operators
appearing in the quantum Master equation, implying at most scaling
of precision under the most general adaptive quantum estimation strategies. We
also discuss the requirements a quantum error-correction like protocol must
satisfy in order to regain the precision scaling in case the above
mentioned algebraic condition is not satisfied. Furthermore, we apply the
developed methods to understand fundamental precision limits in atomic
interferometry with many-body effects taken into account, shedding new light on
the performance of non-linear metrological models.Comment: 13 pages, see also arXiv:1706.0244
Optimal state for keeping reference frames aligned and the Platonic solids
The optimal N qubit states featuring highest sensitivity to small
misalignment of cartesian reference frames are found using the Quantum
Cramer-Rao bound. It is shown that the optimal states are supported on the
symmetric subspace and hence are mathematically equivalent to a single spin
J=N/2. Majorana representation of spin states is used to reveal a beautiful
connection between the states optimal for aligning reference frames and the
platonic solids
Quantum phase estimation with lossy interferometers
We give a detailed discussion of optimal quantum states for optical two-mode
interferometry in the presence of photon losses. We derive analytical formulae
for the precision of phase estimation obtainable using quantum states of light
with a definite photon number and prove that maximization of the precision is a
convex optimization problem. The corresponding optimal precision, i.e. the
lowest possible uncertainty, is shown to beat the standard quantum limit thus
outperforming classical interferometry. Furthermore, we discuss more general
inputs: states with indefinite photon number and states with photons
distributed between distinguishable time bins. We prove that neither of these
is helpful in improving phase estimation precision.Comment: 12 pages, 5 figure
Quantum-enhanced gyroscopy with rotating anisotropic Bose–Einstein condensates
High-precision gyroscopes are a key component of inertial navigation systems. By considering matter wave gyroscopes that make use of entanglement it should be possible to gain some advantages in terms of sensitivity, size, and resources used over unentangled optical systems. In this paper we consider the details of such a quantum-enhanced atom interferometry scheme based on atoms trapped in a carefully-chosen rotating trap. We consider all the steps: entanglement generation, phase imprinting, and read-out of the signal and show that quantum enhancement should be possible in principle. While the improvement in performance over equivalent unentangled schemes is small, our feasibility study opens the door to further developments and improvements
Optimal Quantum Phase Estimation
By using a systematic optimization approach we determine quantum states of
light with definite photon number leading to the best possible precision in
optical two mode interferometry. Our treatment takes into account the
experimentally relevant situation of photon losses. Our results thus reveal the
benchmark for precision in optical interferometry. Although this boundary is
generally worse than the Heisenberg limit, we show that the obtained precision
beats the standard quantum limit thus leading to a significant improvement
compared to classical interferometers. We furthermore discuss alternative
states and strategies to the optimized states which are easier to generate at
the cost of only slightly lower precision.Comment: 4 pages, 4 figures. Replaced with final versio
Geometric quality assurance for 3D concrete printing and hybrid construction manufacturing using a standardised test part for benchmarking capability
The need for quality control and assurance in 3D Concrete Printing (3DCP) is widely recognised. Achieving geometric accuracy to a specified tolerance is a cornerstone of component-based production and assembly. Although published work within the field recognises such issues, these fall short of proposing systematic methods to evaluate, diagnose, improve, monitor and compare system performance. This work takes inspiration from the test geometry approach readily deployed in Additive Manufacturing and develops a full-scale test part to establish a reproducible benchmark for evaluating and assuring part geometric quality of 3DCP systems. The approach is used to evaluate the benefits of a new fabrication approach that combines subtractive milling on green cement mortar in combination with 3DCP. It was demonstrated to yield useful information for direct comparison of different processes and diagnosing problems for performance improvement. The test part and measurement approach offer the 3DCP community a means of cross-platform benchmarking of 3DCP system performance
Entanglement production in Quantized Chaotic Systems
Quantum chaos is a subject whose major goal is to identify and to investigate
different quantum signatures of classical chaos. Here we study entanglement
production in coupled chaotic systems as a possible quantum indicator of
classical chaos. We use coupled kicked tops as a model for our extensive
numerical studies. We find that, in general, presence of chaos in the system
produces more entanglement. However, coupling strength between two subsystems
is also very important parameter for the entanglement production. Here we show
how chaos can lead to large entanglement which is universal and describable by
random matrix theory (RMT). We also explain entanglement production in coupled
strongly chaotic systems by deriving a formula based on RMT. This formula is
valid for arbitrary coupling strengths, as well as for sufficiently long time.
Here we investigate also the effect of chaos on the entanglement production for
the mixed initial state. We find that many properties of the mixed state
entanglement production are qualitatively similar to the pure state
entanglement production. We however still lack an analytical understanding of
the mixed state entanglement production in chaotic systems.Comment: 16 pages, 5 figures. To appear in Pramana:Journal of Physic
Microstructure, magnetic and mechanical properties of Ni-Zn ferrites prepared by Powder Injection Moulding
Nowadays, the electronic industry demands small and complex parts as a consequence of the miniaturization of electronic devices. Powder injection moulding (PIM) is an emerging technique for the manufacturing of magnetic ceramics. In this paper, we analyze the sintering process, between 900 °C and 1300 °C, of Ni–Zn ferrites prepared by PIM. In particular, the densification behaviour, microstructure and mechanical properties of samples with toroidal and bar geometry were analyzed at different temperatures. Additionally, the magnetic behaviour (complex permeability and magnetic losses factor) of these compacts was compared with that of samples prepared by conventional powder compaction. Finally, the mechanical behaviour (elastic modulus, flexure strength and fracture toughness) was analyzed as a function of the powder loading of feedstock. The final microstructure of prepared samples was correlated with the macroscopic behaviour. A good agreement was established between the densities and population of defects found in the materials depending on the sintering conditions. In general, the final mechanical and magnetic properties of PIM samples were enhanced relative those obtained by uniaxial compaction
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