1,435 research outputs found
Generation of Narrow-Band Polarization-Entangled Photon Pairs for Atomic Quantum Memories
We report an experimental realization of a narrow-band polarization-entangled
photon source with a linewidth of 9.6 MHz through cavity-enhanced spontaneous
parametric down-conversion. This linewidth is comparable to the typical
linewidth of atomic ensemble based quantum memories. Single-mode output is
realized by setting a reasonable cavity length difference between different
polarizations, using of temperature controlled etalons and actively stabilizing
the cavity. The entangled property is characterized with quantum state
tomography, giving a fidelity of 94% between our state and a maximally
entangled state. The coherence length is directly measured to be 32 m through
two-photon interference.Comment: 4 pages, 4 figure
Denoising Magnetic Resonance Spectroscopy (MRS) Data Using Stacked Autoencoder for Improving Signal-to-Noise Ratio and Speed of MRS
Background: Magnetic resonance spectroscopy (MRS) enables non-invasive
detection and measurement of biochemicals and metabolites. However, MRS has low
signal-to-noise ratio (SNR) when concentrations of metabolites are in the range
of the million molars. Standard approach of using a high number of signal
averaging (NSA) to achieve sufficient NSR comes at the cost of a long
acquisition time. Purpose: We propose to use deep-learning approaches to
denoise MRS data without increasing the NSA. Methods: The study was conducted
using data collected from the brain spectroscopy phantom and human subjects. We
utilized a stack auto-encoder (SAE) network to train deep learning models for
denoising low NSA data (NSA = 1, 2, 4, 8, and 16) randomly truncated from high
SNR data collected with high NSA (NSA=192) which were also used to obtain the
ground truth. We applied both self-supervised and fully-supervised training
approaches and compared their performance of denoising low NSA data based on
improved SNRs. Results: With the SAE model, the SNR of low NSA data (NSA = 1)
obtained from the phantom increased by 22.8% and the MSE decreased by 47.3%.
For low NSA images of the human parietal and temporal lobes, the SNR increased
by 43.8% and the MSE decreased by 68.8%. In all cases, the chemical shift of
NAA in the denoised spectra closely matched with the high SNR spectra,
suggesting no distortion to the spectra from denoising. Furthermore, the
denoising performance of the SAE model was more effective in denoising spectra
with higher noise levels. Conclusions: The reported SAE denoising method is a
model-free approach to enhance the SNR of low NSA MRS data. With the denoising
capability, it is possible to acquire MRS data with a few NSA, resulting in
shorter scan times while maintaining adequate spectroscopic information for
detecting and quantifying the metabolites of interest
Characterizing Kirkwood-Dirac nonclassicality and uncertainty diagram based on discrete Fourier transform
In this paper, we investigate the Kirkwood-Dirac nonclassicality and
uncertainty diagram based on discrete Fourier transform (DFT) in a
dimensional system. The uncertainty diagram of complete incompatibility bases
are characterized by De Bi\`{e}vre [arXiv:
2207.07451]. We show that for the uncertainty diagram of the DFT matrix which
is a transition matrix from basis to basis , there
is no ``hole" in the region of the -plane
above and on the line , whether the
bases are not complete incompatible bases or not.
Then we present that the KD nonclassicality of a state based on the DFT matrix
can be completely characterized by using the support uncertainty relation
, where and count the number of nonvanishing
coefficients in the basis and representations,
respectively. That is, a state is KD nonclassical if and only if
, whenever is prime or
not. That gives a positive answer to the conjecture in [Phys. Rev. Lett.
\textbf{127}, 190404 (2021)]
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