318 research outputs found
An Optimal Design for Universal Multiport Interferometers
Universal multiport interferometers, which can be programmed to implement any
linear transformation between multiple channels, are emerging as a powerful
tool for both classical and quantum photonics. These interferometers are
typically composed of a regular mesh of beam splitters and phase shifters,
allowing for straightforward fabrication using integrated photonic
architectures and ready scalability. The current, standard design for universal
multiport interferometers is based on work by Reck et al (Phys. Rev. Lett. 73,
58, 1994). We demonstrate a new design for universal multiport interferometers
based on an alternative arrangement of beam splitters and phase shifters, which
outperforms that by Reck et al. Our design occupies half the physical footprint
of the Reck design and is significantly more robust to optical losses.Comment: 8 pages, 4 figure
Gaussian Optical Ising Machines
It has recently been shown that optical parametric oscillator (OPO) Ising
machines, consisting of coupled optical pulses circulating in a cavity with
parametric gain, can be used to probabilistically find low-energy states of
Ising spin systems. In this work, we study optical Ising machines that operate
under simplified Gaussian dynamics. We show that these dynamics are sufficient
for reaching probabilities of success comparable to previous work. Based on
this result, we propose modified optical Ising machines with simpler designs
that do not use parametric gain yet achieve similar performance, thus
suggesting a route to building much larger systems.Comment: 6 page
Exploratory Combinatorial Optimization with Reinforcement Learning
Many real-world problems can be reduced to combinatorial optimization on a
graph, where the subset or ordering of vertices that maximize some objective
function must be found. With such tasks often NP-hard and analytically
intractable, reinforcement learning (RL) has shown promise as a framework with
which efficient heuristic methods to tackle these problems can be learned.
Previous works construct the solution subset incrementally, adding one element
at a time, however, the irreversible nature of this approach prevents the agent
from revising its earlier decisions, which may be necessary given the
complexity of the optimization task. We instead propose that the agent should
seek to continuously improve the solution by learning to explore at test time.
Our approach of exploratory combinatorial optimization (ECO-DQN) is, in
principle, applicable to any combinatorial problem that can be defined on a
graph. Experimentally, we show our method to produce state-of-the-art RL
performance on the Maximum Cut problem. Moreover, because ECO-DQN can start
from any arbitrary configuration, it can be combined with other search methods
to further improve performance, which we demonstrate using a simple random
search.Comment: In Proceedings of the 34th National Conference on Artificial
Intelligence, AAAI 202
Image-guided liver surgery: intraoperative projection of computed tomography images utilizing tracked ultrasound
AbstractBackgroundUltrasound (US) is the most commonly used form of image guidance during liver surgery. However, the use of navigation systems that incorporate instrument tracking and three-dimensional visualization of preoperative tomography is increasing. This report describes an initial experience using an image-guidance system with navigated US.MethodsAn image-guidance system was used in a total of 50 open liver procedures to aid in localization and targeting of liver lesions. An optical tracking system was employed to localize surgical instruments. Customized hardware and calibration of the US transducer were required. The results of three procedures are highlighted in order to illustrate specific navigation techniques that proved useful in the broader patient cohort.ResultsOver a 7-month span, the navigation system assisted in completing 21 (42%) of the procedures, and tracked US alone provided additional information required to perform resection or ablation in six procedures (12%). Average registration time during the three illustrative procedures was <1min. Average set-up time was approximately 5min per procedure.ConclusionsThe Explorerâ„¢ Liver guidance system represents novel technology that continues to evolve. This initial experience indicates that image guidance is valuable in certain procedures, specifically in cases in which difficult anatomy or tumour location or echogenicity limit the usefulness of traditional guidance methods
Ecological integrity and western water management: a Colorado perspective
Sept. 1995.Includes bibliographical references
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