414 research outputs found
Symmetrical clock synchronization with time-correlated photon pairs
We demonstrate a point-to-point clock synchronization protocol based on
bidirectionally exchanging photons produced in spontaneous parametric down
conversion (SPDC). The technique exploits tight timing correlations between
photon pairs to achieve a precision of 51ps in 100s with count rates of order
200s. The protocol is distance independent, secure against symmetric
delay attacks and provides a natural complement to techniques based on Global
Navigation Satellite Systems (GNSS). The protocol works with mobile parties and
can be augmented to provide authentication of the timing signal via a Bell
inequality check.Comment: 5 pages, 5 figure
Towards resolved-sideband Raman cooling of a single 87Rb atom in a FORT
Master'sMASTER OF SCIENC
Interaction of light with a single atom in the strong focusing regime
We consider the near-resonant interaction between a single atom and a focused
light mode, where a single atom localized at the focus of a lens can scatter a
significant fraction of light. Complementary to previous experiments on
extinction and phase shift effects of a single atom, we report here on the
measurement of coherently backscattered light. The strength of the observed
effect suggests combining strong focusing with the well-established methods of
cavity QED. We consider theoretically a nearly concentric cavity, which should
allow for a strongly focused optical mode. Simple estimates show that in a such
case one can expect a significant single photon Rabi frequency. This opens new
perspectives and a possibility to scale up the system consisting of many
atom+cavity nodes for quantum networking due to a significant technical
simplification of the atom--light interfaces.Comment: 7 pages, 6 figures, followup of workshop "Single photon technologies"
in Boulder, CO, 200
Absolute clock synchronization with a single time-correlated photon pair source over 10km
We demonstrate a point-to-point clock synchronization protocol based on
bidirectionally propagating photons generated in a single spontaneous
parametric down-conversion (SPDC) source. Tight timing correlations between
photon pairs are used to determine the single and round-trip times measured by
two separate clocks, providing sufficient information for distance-independent
absolute synchronization secure against symmetric delay attacks. We show that
the coincidence signature useful for determining the round-trip time of a
synchronization channel, established using a 10\,km telecommunications fiber,
can be derived from photons reflected off the end face of the fiber without
additional optics. Our technique allows the synchronization of multiple clocks
with a single reference clock co-located with the source, without requiring
additional pair sources, in a client-server configuration suitable for
synchronizing a network of clocks.Comment: 5 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1812.0845
Mobility based energy efficient and multi-sink algorithms for consumer home networks
With the fast development of the Internet, wireless communications and semiconductor devices, home networking has received significant attention. Consumer products can collect and transmit various types of data in the home environment. Typical consumer sensors are often equipped with tiny, irreplaceable batteries and it therefore of the utmost importance to design energy efficient algorithms to prolong the home network lifetime and reduce devices going to landfill. Sink mobility is an important technique to improve home network performance including energy consumption, lifetime and end-to-end delay. Also, it can largely mitigate the hot spots near the sink node. The selection of optimal moving trajectory for sink node(s) is an NP-hard problem jointly optimizing routing algorithms with the mobile sink moving strategy is a significant and challenging research issue.
The influence of multiple static sink nodes on energy consumption under different scale networks is first studied and an Energy-efficient Multi-sink Clustering Algorithm (EMCA) is proposed and tested. Then, the influence of mobile sink velocity, position and number on network performance is studied and a Mobile-sink based Energy-efficient Clustering Algorithm (MECA) is proposed. Simulation results validate the performance of the proposed two algorithms which can be deployed in a consumer home network environment
A wide-range wavelength-tunable photon-pair source for characterizing single-photon detectors
The temporal response of single-photon detectors is usually obtained by
measuring their impulse response to short-pulsed laser sources. In this work,
we present an alternative approach using time-correlated photon pairs generated
in spontaneous parametric down-conversion (SPDC). By measuring the
cross-correlation between the detection times recorded with an unknown and a
reference photodetector, the temporal response function of the unknown detector
can be extracted. Changing the critical phase-matching conditions of the SPDC
process provides a wavelength-tunable source of photon pairs. We demonstrate a
continuous wavelength-tunability from 526 nm to 661 nm for one photon of the
pair, and 1050 nm to 1760 nm for the other photon. The source allows, in
principle, to access an even wider wavelength range by simply changing the pump
laser of the SPDC-based source. As an initial demonstration, we characterize
single photon avalance detectors sensitive to the two distinct wavelength
bands, one based on Silicon, the other based on Indim Gallium Arsenide.Comment: 10 pages, 8 figure
Evidence of Weyl Fermion Enhanced Thermal Conductivity Under Magnetic Fields in Antiferromagnetic Topological Insulator Mn(Bi(1-x)Sb(x))2Te4
We report thermal conductivity and Seebeck effect measurements on
Mn(Bi1-xSbx)2Te4 (MBST) with x = 0.26 under applied magnetic fields below 50 K.
Our data shows clear indications of the electronic structure transition induced
by the antiferromagnetic (AFM) to ferromagnetic (FM) transition driven by
applied magnetic field as well as significant positive magnetothermal
conductivity in the Weyl semimetal state of MBST. Further, by examining the
dependence of magnetothermal conductivity on field orientation for MBST and
comparison with the magnetothermal conductivity of MnBi2Te4 we see evidence of
a contribution to thermal conductivity due to Weyl fermions in the FM phase of
MBST. From the temperature dependence of Seebeck coefficient under magnetic
fields for MBST, we also observed features consistent with the Fermi surface
evolution from a hole pocket in the paramagnetic state to a Fermi surface with
coexistence of electron and hole pockets in the FM state. These findings
provide further evidence for the field-driven topological phase transition from
an AFM topological insulator to a FM Weyl semimetal.Comment: 10 pages, 3 figure
Segment Everything Everywhere All at Once
Despite the growing demand for interactive AI systems, there have been few
comprehensive studies on human-AI interaction in visual understanding e.g.
segmentation. Inspired by the development of prompt-based universal interfaces
for LLMs, this paper presents SEEM, a promptable, interactive model for
Segmenting Everything Everywhere all at once in an image. SEEM has four
desiderata: i) Versatility: by introducing a versatile prompting engine for
different types of prompts, including points, boxes, scribbles, masks, texts,
and referred regions of another image; ii) Compositionality: by learning a
joint visual-semantic space for visual and textual prompts to compose queries
on the fly for inference as shown in Fig 1; iii)Interactivity: by incorporating
learnable memory prompts to retain dialog history information via mask-guided
cross-attention; and iv) Semantic-awareness: by using a text encoder to encode
text queries and mask labels for open-vocabulary segmentation
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