2,701 research outputs found
Nonclassicality filters and quasiprobabilities
Necessary and sufficient conditions for the nonclassicality of bosonic
quantum states are formulated by introducing nonclassicality filters and
nonclassicality quasiprobability distributions. Regular quasiprobabilities are
constructed from characteristic functions which can be directly sampled by
balanced homodyne detection. Their negativities uncover the nonclassical
effects of general quantum states. The method is illustrated by visualizing the
nonclassical nature of a squeezed state.Comment: Significantly revised version, more emphasis on practical applicatio
Operational multipartite entanglement classes for symmetric photonic qubit states
We present experimental schemes that allow to study the entanglement classes
of all symmetric states in multiqubit photonic systems. In addition to
comparing the presented schemes in efficiency, we will highlight the relation
between the entanglement properties of symmetric Dicke states and a recently
proposed entanglement scheme for atoms. In analogy to the latter, we obtain a
one-to-one correspondence between well-defined sets of experimental parameters
and multiqubit entanglement classes inside the symmetric subspace of the
photonic system.Comment: 5 pages, 1 figur
Lifelong Multi-Agent Path Finding in Large-Scale Warehouses
Multi-Agent Path Finding (MAPF) is the problem of moving a team of agents to
their goal locations without collisions. In this paper, we study the lifelong
variant of MAPF, where agents are constantly engaged with new goal locations,
such as in large-scale automated warehouses. We propose a new framework
Rolling-Horizon Collision Resolution (RHCR) for solving lifelong MAPF by
decomposing the problem into a sequence of Windowed MAPF instances, where a
Windowed MAPF solver resolves collisions among the paths of the agents only
within a bounded time horizon and ignores collisions beyond it. RHCR is
particularly well suited to generating pliable plans that adapt to continually
arriving new goal locations. We empirically evaluate RHCR with a variety of
MAPF solvers and show that it can produce high-quality solutions for up to
1,000 agents (= 38.9\% of the empty cells on the map) for simulated warehouse
instances, significantly outperforming existing work.Comment: Published at AAAI 202
Direct Sampling of Negative Quasiprobabilities of a Squeezed State
Although squeezed states are nonclassical states, so far, their
nonclassicality could not be demonstrated by negative quasiprobabilities. In
this work we derive pattern functions for the direct experimental determination
of so-called nonclassicality quasiprobabilities. The negativities of these
quantities turn out to be necessary and sufficient for the nonclassicality of
an arbitrary quantum state and are therefore suitable for a direct and general
test of nonclassicality. We apply the method to a squeezed vacuum state of
light that was generated by parametric down-conversion in a second-order
nonlinear crystal.Comment: 4 pages, 4 figures, supplementary material adde
Nonclassicality Quasiprobability of Single-Photon Added Thermal States
We report the experimental reconstruction of a nonclassicality
quasiprobability for a single-photon added thermal state. This quantity has
significant negativities, which is necessary and sufficient for the
nonclassicality of the quantum state. Our method presents several advantages
compared to the reconstruction of the P function, since the nonclassicality
filters used in this case can regularize the quasiprobabilities as well as
their statistical uncertainties. A-priori assumptions about the quantum state
are therefore not necessary. We also demonstrate that, in principle, our method
is not limited by small quantum efficiencies.Comment: 6 pages, 4 figure
Entangled Qubits in a non-Gaussian Quantum State
We experimentally generate and tomographically characterize a mixed, genuinely non-Gaussian bipartite continuous-variable entangled state. By testing entanglement in 22-dimensional two-qubit subspaces, entangled qubits are localized within the density matrix, which, firstly, proves the distillability of the state and, secondly, is useful to estimate the efficiency and test the applicability of distillation protocols. In our example, the entangled qubits are arranged in the density matrix in an asymmetric way, i.e. entanglement is found between diverse qubits composed of different photon number states, although the entangled state is symmetric under exchanging the modes
Experimental determination of a nonclassical Glauber-Sudarshan P function
A quantum state is nonclassical if its Glauber-Sudarshan P function fails to
be interpreted as a probability density. This quantity is often highly
singular, so that its reconstruction is a demanding task. Here we present the
experimental determination of a well-behaved P function showing negativities
for a single-photon-added thermal state. This is a direct visualization of the
original definition of nonclassicality. The method can be useful under
conditions for which many other signatures of nonclassicality would not
persist.Comment: 4 pages, 4 figure
Experimental test of nonclassicality criteria
We experimentally examine the nonclassical character of a class of
non-Gaussian states known as phase-diffused squeezed states. These states may
show no squeezing effect at all, and therefore provide an interesting example
to test nonclassicality criteria. The characteristic function of the
Glauber-Sudarshan representation (P function) proves to be a powerful tool to
detect nonclassicality. Using this criterion we find that phase-diffused
squeezed states are always nonclassical, even if the squeezing effect vanishes.
Testing other criteria of nonclassicality based on higher-order squeezing and
the positive semidefinitness of special matrices of normally ordered moments,
it is found that these criteria fail to reveal the nonclassicality for some of
the prepared phase-diffused squeezed states.Comment: 6 pages, 2 figure
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