83 research outputs found
Bright squeezed vacuum in a nonlinear interferometer: frequency/temporal Schmidt-mode description
Control over the spectral properties of the bright squeezed vacuum (BSV), a
highly multimode non-classical macroscopic state of light that can be generated
through high-gain parametric down conversion, is crucial for many applications.
In particular, in several recent experiments BSV is generated in a strongly
pumped SU(1,1) interferometer to achieve phase supersensitivity, perform
broadband homodyne detection, or tailor the frequency spectrum of squeezed
light. In this work, we present an analytical approach to the theoretical
description of BSV in the frequency domain based on the Bloch-Messiah reduction
and the Schmidt-mode formalism. As a special case we consider a strongly pumped
SU(1,1) interferometer. We show that different moments of the radiation at its
output depend on the phase, dispersion and the parametric gain in a nontrivial
way, thereby providing additional insights on the capabilities of nonlinear
interferometers. In particular, a dramatic change in the spectrum occurs as the
parametric gain increases
Phase sensitivity of spatially broadband high-gain SU(1,1) interferometers
Nonlinear interferometers are promising tools for quantum metrology, as they
are characterized by an improved phase sensitivity scaling compared to linear
interferometers operating with classical light. However, the multimodeness of
the light generated in these interferometers results in the destruction of
their phase sensitivity, requiring advanced interferometric configurations for
multimode light. Moreover, in contrast to the single-mode case, time-ordering
effects play an important role for the high-gain regime in the multimode
scenario and must be taken into account for a correct estimation of the phase
sensitivity. In this work, we present a theoretical description of spatially
multimode SU(1,1) interferometers operating at low and high parametric gains.
Our approach is based on a step-by-step solution of a system of
integro-differential equations for each nonlinear interaction region. We focus
on interferometers with diffraction compensation, where focusing elements such
as a parabolic mirror are used to compensate for the divergence of the light.
We investigate plane-wave and Gaussian pumping and show that for any parametric
gain, there exists a region of phases for which the phase sensitivity surpasses
the standard shot-noise scaling and discuss the regimes where it approaches the
Heisenberg scale. Finally, we arrive at insightful analytical expressions for
the phase sensitivity that are valid for both low and high parametric gain and
demonstrate how it depends on the number of spatial modes of the system
Properties of bright squeezed vacuum at increasing brightness
A bright squeezed vacuum (BSV) is a nonclassical macroscopic state of light, which is generated through high-gain parametric down-conversion or four-wave mixing. Although the BSV is an important tool in quantum optics and has a lot of applications, its theoretical description is still not complete. In particular, the existing description in terms of Schmidt modes with gain-independent shapes fails to explain the spectral broadening observed in the experiment as the mean number of photons increases. Meanwhile, the semiclassical description accounting for the broadening does not allow us to decouple the intermodal photon-number correlations. In this work, we present a new generalized theoretical approach to describe the spatial properties of a multimode BSV. In the multimode case, one has to take into account the complicated interplay between all involved modes: each plane-wave mode interacts with all other modes, which complicates the problem significantly. The developed approach is based on exchanging the (k, t ) and (ω, z) representations and solving a system of integrodifferential equations. Our approach predicts correctly the dynamics of the Schmidt modes and the broadening of the angular distribution with the increase in the BSV mean photon number due to a stronger pumping. Moreover, the model correctly describes various properties of a widely used experimental configuration with two crystals and an air gap between them, namely, an SU(1,1) interferometer. In particular, it predicts the narrowing of the intensity distribution, the reduction and shift of the side lobes, and the decline in the interference visibility as the mean photon number increases due to stronger pumping. The presented experimental results confirm the validity of the new approach. The model can be easily extended to the case of the frequency spectrum, frequency Schmidt modes, and other experimental configurations
Projective filtering of a single spatial radiation eigenmode
Lossless filtering of a single coherent (Schmidt) mode from spatially
multimode radiation is a problem crucial for optics in general and for quantum
optics in particular. It becomes especially important in the case of
nonclassical light that is fragile to optical losses. An example is bright
squeezed vacuum generated via high-gain parametric down conversion or four-wave
mixing. Its highly multiphoton and multimode structure offers a huge increase
in the information capacity provided that each mode can be addressed
separately. However, the nonclassical signature of bright squeezed vacuum,
photon-number correlations, are highly susceptible to losses. Here we
demonstrate lossless filtering of a single spatial Schmidt mode by projecting
the spatial spectrum of bright squeezed vacuum on the eigenmode of a
single-mode fiber. Moreover, we show that the first Schmidt mode can be
captured by simply maximizing the fiber-coupled intensity. Importantly, the
projection operation does not affect the targeted mode and leaves it usable for
further applications.Comment: 10 pages, 9 figure
Spatial entanglement and state engineering via four-photon Hong-Ou-Mandel interference
The phenomenon of entanglement is the basis of quantum information and
quantum communication processes. Entangled systems with a large number of
photons are of great interest at present because they provide a platform for
streaming technologies based on photonics. In this paper we present a device
which operates with four-photons and based on the Hong-Ou-Mandel (HOM)
interference. The presented device allows to maximize the degree of spatial
entanglement and generate the highly entangled four-dimensional Bell states.
Furthermore, the use of the interferometer in different regimes leads to fast
interference fringes in the coincidence probability with period of oscillations
twice smaller than the pump wavelength. We have a good agreement between
theoretical simulations and experimental results.Comment: 20 pages, 7 figur
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