88 research outputs found
Seeded and unseeded high order parametric down conversion
Spontaneous parametric down conversion (SPDC) has been one of the foremost
tools in quantum optics for over five decades. Over that time it has been used
to demonstrate some of the curious features that arise from quantum mechanics.
Despite the success of SPDC, its higher-order analogues have never been
observed, even though it has been suggested that they generate far more unique
and exotic states than SPDC. An example of this is the emergence of
non-Gaussian states without the need for post-selection. Here we calculate the
expected rate of emission for nth-order SPDC with and without external
stimulation (seeding). Focusing primarily on third-order parametric
down-conversion (TOPDC), we estimate the photon detection rates in a rutile
crystal, for both the unseeded and seeded regimes.Comment: 11 pages, 6 figure
Two-Color Bright Squeezed Vacuum
In a strongly pumped non-degenerate traveling-wave OPA, we produce two-color
squeezed vacuum with up to millions of photons per pulse. Our approach to
registering this macroscopic quantum state is direct detection of a large
number of transverse and longitudinal modes, which is achieved by making the
detection time and area much larger than the coherence time and area,
respectively. Using this approach, we obtain a record value of twin-beam
squeezing for direct detection of bright squeezed vacuum. This makes direct
detection of macroscopic squeezed vacuum a practical tool for quantum
information applications.Comment: 4 pages, 4 figure
Time-resolved purification of photon pairs from ultrasmall sources
Generation of entangled photons through spontaneous parametric
down-conversion (SPDC) from ultrasmall sources like thin films, metasurfaces,
or nanoantennas, offers unprecedented freedom in quantum state engineering.
However, as the source of SPDC gets smaller, the role of photoluminescence
increases, which leads to the contamination of two-photon states with thermal
background. Here we propose and implement a solution to this problem: by using
pulsed SPDC and time distillation, we increase the purity and the heralding
efficiency of the photon pairs. In the experiment, we increase the purity of
two-photon states generated in a 7 m film of lithium niobate from 0.002 to
0.99. With the higher purity, we were able to observe and characterize
different polarization states of photon pairs generated simultaneously due to
relaxed phase matching. In particular, we showed the presence of orthogonally
polarized photons, potentially usable for the generation of polarization
entanglement
Autonomous absolute calibration of an ICCD camera in single-photon detection regime
Intensified charge coupled device (ICCD) cameras are widely used in various
applications such as microscopy, astronomy, spectroscopy. Often they are used
as single-photon detectors, with thresholding being an essential part of the
readout. In this paper, we measure the quantum efficiency of an ICCD camera in
the single-photon detection mode using the Klyshko absolute calibration
technique. The quantum efficiency is obtained as a function of the threshold
value and of the wavelength of the detected light. In addition, we study the
homogeneity of the photon sensitivity over the camera chip area. The experiment
is performed in the autonomous regime, without using any additional detectors.
We therefore demonstrate the self-calibration of an ICCD camera.Comment: 8 pages, 3 figure
Transverse Entanglement of Biphotons
We measure the transverse entanglement of photon pairs on their propagation
from the near to the far field of spontaneous parametric downconversion (SPDC).
The Fedorov ratio, depending on the widths of conditional and unconditional
intensity measurements, is shown to be only able to characterize entanglement
in the near and far field zones of the source. Therefore we also follow a
different approach. By evaluating the first-order coherence of a subsystem of
the state we can quantify its entanglement. Unlike previous measurements, which
determine the Fedorov ratio via intensity correlations, our setup is sensitive
to both phase and modulus of the biphoton state and thus always grants
experimental access to the full transverse entanglement of the SPDC state. It
is shown theoretically that this scheme represents a direct measurement of the
Schmidt number.Comment: 11 pages, 6 figure
Wigner Function Tomography via Optical Parametric Amplification
We demonstrate a method of Wigner function tomography that is tolerant to
detection loss and noise. The method employs optical parametric amplification
to reconstruct quadrature distributions from photon-number distributions
measured via direct detection. By applying the method to a single mode filtered
from multimode squeezed vacuum, we obtained a Wigner function showing a
squeezing of 0.4 dB and a purity of despite
more than detection losses. The method can be applied to faint as well
as bright non-Gaussian states, which are very susceptible to loss. In addition,
our scheme is suitable for the tomography of spatially and temporally multimode
quantum states, and being detection loss-tolerant, the method allows for the
simultaneous tomography of multiple modes. This makes it a powerful tool for
optical quantum information
Multi-photon nonclassical correlations in entangled squeezed vacuum states
Photon-number correlation measurements are performed on bright squeezed
vacuum states using a standard Bell-test setup, and quantum correlations are
observed for conjugate polarization-frequency modes. We further test the
entanglement witnesses for these states and demonstrate the violation of the
separability criteria, which infers that all the macroscopic Bell states,
containing typically photons per pulse, are polarization entangled. The
study also reveals the symmetry of macroscopic Bell states with respect to
local polarization transformations.Comment: 5 pages, 4 figure
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