68 research outputs found
Gaussian entanglement distribution with gigahertz bandwidth
The distribution of entanglement with Gaussian statistic can be used to
generate a mathematically-proven secure key for quantum cryptography. The
distributed secret key rate is limited by the {entanglement strength, the
entanglement bandwidth and the bandwidth of the photo-electric detectors}. The
development of a source for strongly, bi-partite entangled light with high
bandwidth promises an increased measurement speed and a linear boost in the
secure data rate. Here, we present the experimental realization of a Gaussian
entanglement source with a bandwidth of more than 1.25\,GHz. The entanglement
spectrum was measured with balanced homodyne detectors and was quantified via
the inseparability criterion introduced by Duan and coworkers with a critical
value of 4 below which entanglement is certified. Our measurements yielded an
inseparability value of about 1.8 at a frequency of 300\,MHz to about 2.8 at
1.2\,GHz extending further to about 3.1 at 1.48\,GHz. In the experiment we used
two 2.6\,mm long monolithic periodically poled potassium titanyl phosphate
(PPKTP) resonators to generate two squeezed fields at the telecommunication
wavelength of 1550\,nm. Our result proves the possibility of generating and
detecting strong continuous-variable entanglement with high speed.Comment: 5 pages, 3 figures, published in Optics Letter
High-bandwidth squeezed light at 1550 nm from a compact monolithic PPKTP cavity
We report the generation of squeezed vacuum states of light at 1550 nm with a
broadband quantum noise reduction of up to 4.8 dB ranging from 5 MHz to 1.2 GHz
sideband frequency. We used a custom-designed 2.6 mm long biconvex
periodically-poled potassium titanyl phosphate (PPKTP) crystal. It featured
reflectively coated end surfaces, 2.26 GHz of linewidth and generated the
squeezing via optical parametric amplification. Two homodyne detectors with
different quantum efficiencies and bandwidths were used to characterize the
non-classical noise suppression. We measured squeezing values of up to 4.8 dB
from 5 to 100 MHz and up to 3 dB from 100 MHz to 1.2 GHz. The squeezed vacuum
measurements were limited by detection loss. We propose an improved detection
scheme to measure up to 10 dB squeezing over 1 GHz. Our results of GHz
bandwidth squeezed light generation provide new prospects for high-speed
quantum key distribution.Comment: 8 pages, 4 figure
New approaches in squeezed light generation : quantum states of light with GHz squeezing bandwidth and squeezed light generation via the cascaded Kerr effect
[no abstract
An ultrahigh-vacuum cryostat for simultaneous scanning tunneling microscopy and magneto-transport measurements down to 400mK
We present the design and calibration measurements of a scanning tunneling
microscope setup in a 3He ultrahigh-vacuum cryostat operating at 400 mK with a
hold time of 10 days. With 2.70 m in height and 4.70 m free space needed for
assembly, the cryostat fits in a one-story lab building. The microscope
features optical access, an xy table, in situ tip and sample exchange, and
enough contacts to facilitate atomic force microscopy in tuning fork operation
and simultaneous magneto-transport measurements on the sample. Hence, it
enables scanning tunneling spectroscopy on microstructured samples which are
tuned into preselected transport regimes. A superconducting magnet provides a
perpendicular field of up to 14 T. The vertical noise of the scanning tunneling
microscope amounts to 1 pmrms within a 700 Hz bandwidth. Tunneling spectroscopy
using one superconducting electrode revealed an energy resolution of 120 mueV.
Data on tip-sample Josephson contacts yield an even smaller feature size of 60
mueV, implying that the system operates close to the physical noise limit.Comment: 12 pages, 11 figure
Continuous-wave squeezed states of light via ‘up-down’ self-phase modulation
Continuous-wave (cw) squeezed states of light have applications in sensing, metrology and secure communication. In recent decades their efficient generation has been based on parametric down-conversion, which requires pumping by externally generated pump light of twice the optical frequency. Currently, there is immense effort in miniaturizing squeezed-light sources for chip-integration. Designs that require just a single input wavelength are favored since they offer an easier realization. Here we report the first observation of cw squeezed states generated by self-phase modulation caused by subsequent up and down conversions. The wavelengths of input light and of balanced homodyne detection are identical, and 1550 nm in our case. At sideband frequencies around 1.075 GHz, a nonclassical noise reduction of (2.4 ± 0.1) dB is observed. The setup uses a second-order nonlinear crystal, but no externally generated light of twice the frequency. Our experiment is not miniaturized, but might open a route towards simplified chip-integrated realizations. © 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen
Fiber backscatter under increasing exposure to ionizing radiation
The Laser Interferometer Space Antenna (LISA) will measure gravitational waves by utilizing inter-satellite laser links between three triangularly-arranged spacecraft in heliocentric orbits. Each spacecraft will house two separate optical benches and needs to establish a phase reference between the two optical benches which requires a bidirectional optical connection, e.g. a fiber connection. The sensitivity of the reference interferometers, and thus of the gravitational wave measurement, could be hampered by backscattering of laser light within optical fibers. It is not yet clear if the backscatter within the fibers will remain constant during the mission duration, or if it will increase due to ionizing radiation in the space environment. Here we report the results of tests on two different fiber types under increasing intensities of ionizing radiation: SM98-PS-U40D by Fujikura, a polarization maintaining fiber, and HB1060Z by Fibercore, a polarizing fiber. We found that both types react differently to the ionizing radiation: The polarization maintaining fibers show a backscatter of about 7 ppm·m−1 which remains constant over increasing exposure. The polarizing fibers show about three times as much backscatter, which also remains constant over increasing exposure. However, the polarizing fibers show a significant degradation in transmission, which is reduced to about one third. © 2020 OSA - The Optical Society. All rights reserved
Squeezed light at 1550 nm with a quantum noise reduction of 12.3 dB
Continuous-wave squeezed states of light at the wavelength of 1550 nm have
recently been demonstrated, but so far the obtained factors of noise
suppression still lag behind today's best squeezing values demonstrated at 1064
nm. Here we report on the realization of a half-monolithic nonlinear resonator
based on periodically-poled potassium titanyl phosphate which enabled the
direct detection of up to 12.3 dB of squeezing at 5 MHz. Squeezing was observed
down to a frequency of 2 kHz which is well within the detection band of
gravitational wave interferometers. Our results suggest that a long-term stable
1550 nm squeezed light source can be realized with strong squeezing covering
the entire detection band of a 3rd generation gravitational-wave detector such
as the Einstein Telescope
SOX5 is involved in balanced MITF regulation in human melanoma cells
Background: Melanoma is a cancer with rising incidence and new therapeutics are needed. For this, it is necessary to understand the molecular mechanisms of melanoma development and progression. Melanoma differs from other cancers by its ability to produce the pigment melanin via melanogenesis; this biosynthesis is essentially regulated by microphthalmia-associated transcription factor (MITF). MITF regulates various processes such as cell cycling and differentiation. MITF shows an ambivalent role, since high levels inhibit cell proliferation and low levels promote invasion. Hence, well-balanced MITF homeostasis is important for the progression and spread of melanoma. Therefore, it is difficult to use MITF itself for targeted therapy, but elucidating its complex regulation may lead to a promising melanoma-cell specific therapy. Method: We systematically analyzed the regulation of MITF with a novel established transcription factor based gene regulatory network model. Starting from comparative transcriptomics analysis using data from cells originating from nine different tumors and a melanoma cell dataset, we predicted the transcriptional regulators of MITF employing ChIP binding information from a comprehensive set of databases. The most striking regulators were experimentally validated by functional assays and an MITF-promoter reporter assay. Finally, we analyzed the impact of the expression of the identified regulators on clinically relevant parameters of melanoma, i.e. the thickness of primary tumors and patient overall survival. Results: Our model predictions identified SOX10 and SOX5 as regulators of MITF. We experimentally confirmed the role of the already well-known regulator SOX10. Additionally, we found that SOX5 knockdown led to MITF up-regulation in melanoma cells, while double knockdown with SOX10 showed a rescue effect; both effects were validated by reporter assays. Regarding clinical samples, SOX5 expression was distinctively up-regulated in metastatic compared to primary melanoma. In contrast, survival analysis of melanoma patients with predominantly metastatic disease revealed that low SOX5 levels were associated with a poor prognosis. Conclusion: MITF regulation by SOX5 has been shown only in murine cells, but not yet in human melanoma cells. SOX5 has a strong inhibitory effect on MITF expression and seems to have a decisive clinical impact on melanoma during tumor progression
Single-cell genomics reveal low recombination frequencies in freshwater bacteria of the SAR11 clade
Zaremba-Niedzwiedzka K, Viklund J, Zhao W, et al. Single-cell genomics reveal low recombination frequencies in freshwater bacteria of the SAR11 clade. Genome biology. 2013;14(11): R130.BACKGROUND: The SAR11 group of Alphaproteobacteria is highly abundant in the oceans. It contains a recently diverged freshwater clade, which offers the opportunity to compare adaptations to salt- and freshwaters in a monophyletic bacterial group. However, there are no cultivated members of the freshwater SAR11 group and no genomes have been sequenced yet. RESULTS: We isolated ten single SAR11 cells from three freshwater lakes and sequenced and assembled their genomes. A phylogeny based on 57 proteins indicates that the cells are organized into distinct microclusters. We show that the freshwater genomes have evolved primarily by the accumulation of nucleotide substitutions and that they have among the lowest ratio of recombination to mutation estimated for bacteria. In contrast, members of the marine SAR11 clade have one of the highest ratios. Additional metagenome reads from six lakes confirm low recombination frequencies for the genome overall and reveal lake-specific variations in microcluster abundances. We identify hypervariable regions with gene contents broadly similar to those in the hypervariable regions of the marine isolates, containing genes putatively coding for cell surface molecules. CONCLUSIONS: We conclude that recombination rates differ dramatically in phylogenetic sister groups of the SAR11 clade adapted to freshwater and marine ecosystems. The results suggest that the transition from marine to freshwater systems has purged diversity and resulted in reduced opportunities for recombination with divergent members of the clade. The low recombination frequencies of the LD12 clade resemble the low genetic divergence of host-restricted pathogens that have recently shifted to a new host
- …