15,140 research outputs found
Joint optimal measurement for locating two incoherent optical point sources near the Rayleigh distance
The simultaneous optimization of the centroid estimation and the separation
estimation of two incoherent optical point sources is restricted by a tradeoff
relation through an incompatibility coefficient. At the Rayleigh distance the
incompatibility coefficient vanishes and thus the tradeoff relation no longer
restricts the simultaneous optimization of measurement for a joint estimation.
We construct such a joint optimal measurement by an elaborated analysis on the
operator algebra of the symmetric logarithmic derivative. Our work not only
confirms the existence of a joint optimal measurement for this specific imaging
model, but also gives a promising method to characterize the condition on
measurement compatibility for general multiparameter estimation problems.Comment: 5 pages, 2 figure
Quantum gates with weak van der Waals interactions of neutral Rydberg atoms
Neutral atoms are promising for large-scale quantum computing, but accurate
neutral-atom entanglement depends on large Rydberg interactions which strongly
limit the interatomic distances. Via a phase accumulation in detuned Rabi
cycles enabled by a Rydberg interaction of similar magnitude to the Rydberg
Rabi frequency, we study a controlled-phase gate with an arbitrary phase and
extend it to the controlled-NOT gate. The gates need only three steps for
coupling one Rydberg state, depend on easily accessible van der Waals
interaction that naturally arises between distant atoms, and have no rotation
error in the weak interaction regime. Importantly, they can work with very weak
interactions so that well-separated qubits can be entangled. The gates are
sensitive to the irremovable fluctuation of Rydberg interactions, but can still
have a fidelity over 98\% with realistic position fluctuation of qubits
separated over 20~m.Comment: 7 pages, 3 figure
Submodular Load Clustering with Robust Principal Component Analysis
Traditional load analysis is facing challenges with the new electricity usage
patterns due to demand response as well as increasing deployment of distributed
generations, including photovoltaics (PV), electric vehicles (EV), and energy
storage systems (ESS). At the transmission system, despite of irregular load
behaviors at different areas, highly aggregated load shapes still share similar
characteristics. Load clustering is to discover such intrinsic patterns and
provide useful information to other load applications, such as load forecasting
and load modeling. This paper proposes an efficient submodular load clustering
method for transmission-level load areas. Robust principal component analysis
(R-PCA) firstly decomposes the annual load profiles into low-rank components
and sparse components to extract key features. A novel submodular cluster
center selection technique is then applied to determine the optimal cluster
centers through constructed similarity graph. Following the selection results,
load areas are efficiently assigned to different clusters for further load
analysis and applications. Numerical results obtained from PJM load demonstrate
the effectiveness of the proposed approach.Comment: Accepted by 2019 IEEE PES General Meeting, Atlanta, G
N′-[1-(2-Hydroxyphenyl)ethylidene]-2-methoxybenzohydrazide
There are two independent molecules in the asymmetric unit of the title compound, C16H16N2O3, in which the dihedral angles between the two aromatic rings are 13.0 (3) and 6.4 (3)°. Intramolecular O—H⋯N and N—H⋯O hydrogen bonds are observed in both molecules, forming S(6) rings in all cases
Persistent Ballistic Entanglement Spreading with Optimal Control in Quantum Spin Chains
Entanglement propagation provides a key routine to understand quantum
many-body dynamics in and out of equilibrium. In this work, we uncover that the
``variational entanglement-enhancing'' field (VEEF) robustly induces a
persistent ballistic spreading of entanglement in quantum spin chains. The VEEF
is time dependent, and is optimally controlled to maximize the bipartite
entanglement entropy (EE) of the final state. Such a linear growth persists
till the EE reaches the genuine saturation with the total number of spins. The EE
satisfies for the time , with the
velocity. These results are in sharp contrast with the behaviors without VEEF,
where the EE generally approaches a sub-saturation known as the Page value
in the long-time limit, and the
entanglement growth deviates from being linear before the Page value is
reached. The dependence between the velocity and interactions is explored, with
, , and for the spin chains with Ising, XY, and
Heisenberg interactions, respectively. We further show that the nonlinear
growth of EE emerges with the presence of long-range interactions.Comment: 5 pages, 4 figure
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