1,721,215 research outputs found
On the properties of circular beams: normalization, Laguerre–Gauss expansion, and free-space divergence
No full textCircular beams were introduced as a very general solution to the paraxial wave equation carrying orbital angular momentum. Here, we study their properties by looking at their normalization and their expansion in terms of Laguerre–Gauss modes. We also study their far-field divergence and, for particular cases of the beam parameters, their possible experimental generation
Einstein-Podolsky-Rosen steering: Closing the detection loophole with non-maximally-entangled states and arbitrary low efficiency
No full text
Strong Measurements Give a Better Direct Measurement of the Quantum Wave Function
Full text linkWeak measurements have thus far been considered instrumental in the so-called direct measurement of the quantum wave function [J. S. Lundeen, Nature (London) 474, 188 (2011).]. Here we show that a direct measurement of the wave function can be obtained by using measurements of arbitrary strength. In particular, in the case of strong measurements, i.e., those in which the coupling between the system and the measuring apparatus is maximum, we compared the precision and the accuracy of the two methods, by showing that strong measurements outperform weak measurements in both for arbitrary quantum states in most cases. We also give the exact expression of the difference between the original and reconstructed wave function obtained by the weak measurement approach; this will allow one to define the range of applicability of such a method
Optimizing Measurements Sequences for Quantum State Verification
Full text linkWe consider the problem of deciding whether a given state preparation, i.e.,
a source of quantum states, is accurate, namely produces states close to a
target one within a prescribed threshold. We show that, when multiple
measurements need to be used, the order of measurements is critical for quickly
assessing accuracy. We propose and compare different strategies to compute
optimal or suboptimal measurement sequences either relying solely on a priori
information, i.e., the target state for state preparation, or actively adapting
the sequence to the previously obtained measurements. Numerical simulations
show that the proposed algorithms reduce significantly the number of
measurements needed for verification, and indicate an advantage for the
adaptive protocol especially assessing faulty preparations
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