164 research outputs found
Quantum correlations and violation of Bell inequality induced by External Field in a two photon radiative cascade
We study the polarization dependent second order correlation of a pair of
photons emitted in a four level radiative cascade driven by an external field.
It is found that the quantum correlations of the emitted photons, degraded by
the energy splitting of the intermediate levels in the radiative cascade can be
efficiently revived by a far detuned external field. The physics of this
revival is linked to an induced stark shift and the formation of dressed states
in the system by the non-resonant external field. Further, we investigated the
competition between the effect of the coherent external field and incoherent
dephasing of the intermediate levels. We found that the degradation of quantum
correlations due to the incoherent dephasing can be content for small dephasing
with the external field. We also studied the non-locality of the correlations
by evaluating the Bell's inequality in the linear polarization basis for the
radiative cascade. We find that the Bell parameter decreases rapidly with
increase in the intermediate level energy splitting or incoherent dephasing
rate to the extent that there is no violation. However, the presence of an
external field leads to control over the degrading mechanisms and preservation
of nonlocal correlation among the photons. This in turn can induce, violation
of Bell's inequality in the radiative cascade for arbitrary intermediate level
splitting and small incoherent dephasing
Synthetic gauge potential and effective magnetic field in a Raman medium undergoing molecular modulation
We theoretically demonstrate non-trivial topological effects for a probe
field in a Raman medium undergoing molecular modulation processes. The medium
is driven by two non-collinear pump beams. We show that the angle between the
pumps is related to an effective gauge potential and an effective magnetic
field for the probe field in the synthetic space consisting of a synthetic
frequency dimension and a spatial dimension. As a result of such effective
magnetic field, the probe field can exhibit topologically-protected one-way
edge state in the synthetic space, as well as Landau levels which manifests as
suppression of both diffraction and sideband generation. Our work identifies a
previously unexplored route towards creating topological photonics effects, and
highlights an important connection between topological photonics and nonlinear
optics
Effects of non-Hermitian perturbations on Weyl Hamiltonians with arbitrary topological charges
We provide a systematic study of non-Hermitian topologically charged systems.
Starting from a Hermitian Hamiltonian supporting Weyl points with arbitrary
topological charge, adding a non-Hermitian perturbation transforms the Weyl
points to one-dimensional exceptional contours. We analytical prove that the
topological charge is preserved on the exceptional contours. In contrast to
Hermitian systems, the addition of gain and loss allows for a new class of
topological phase transition: when two oppositely charged exceptional contours
touch, the topological charge can dissipate without opening a gap. These
effects can be demonstrated in realistic photonics and acoustics systems.Comment: 11 pages, 9 figure
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