Generation of Flying Logical Qubits using Generalized Photon Subtraction with Adaptive Gaussian Operations

The generation of a logical qubit called the Gottesman-Kitaev-Preskill qubit in an optical traveling wave is a major challenge for realizing large-scale universal fault-tolerant optical quantum computers. Recently, probabilistic generation of elementary GKP qubits has been demonstrated using photon number measurements and homodyne measurements. However, the generation rate is only a few Hz, and it will be difficult to generate fault-tolerant GKP qubits at a practical rate unless success probability is significantly improved. Here, we propose a method to efficiently synthesize GKP qubits from several quantum states by adaptive Gaussian operations. In the initial state preparation that utilizes photon number measurements, an adaptive operation allows any measurement outcome above a certain threshold to be considered as a success. This threshold is lowered by utilizing the generalized photon subtraction method. The initial states are synthesized into a GKP qubit by homodyne measurements and a subsequent adaptive operation. As a result, the single-shot success probability of generating fault-tolerant GKP qubits in a realistic scale system exceeds 10$\%$, which is one million times better than previous methods. This proposal will become a powerful tool for advancing optical quantum computers from the proof-of-principle stage to practical application.Comment: 9 pages, 3 figure

Hybrid free-surface flows in a two-dimensional channel

Hybrid free-surface flows past disturbances in a two-dimensional channel are identified and studied. The fluid is assumed to be inviscid and incompressible, and the flow to be steady and irrotational. The disturbances consist of a step in the bottom of the channel and a flat object lying on the free-surface (e.g., a sluice gate). A weakly nonlinear one-dimensional analysis is used to classify the possible types of solutions, and nonlinear solutions are obtained numerically by a boundary integral equation method.Benjamin James Binder and Jean-Marc Vanden-Broec

High grid resolution and parallelized tsunami simulation with fully nonlinear Boussinesq equations

Numerical simulation of tsunami propagation in large basin across the ocean demands significantly high computational capability in terms of CPU time and memory allocation. Due to this limitation, the use of sequential codes in a single scientific workstation is possible only for small-scale tsunami problem. To overcome this difficulty, a parallel Boussinesq wave model is developed based on the original FUNWAVE sequential model for efficient simulation of long wave propagation, coastal inundation and runup. The numerical resolution is decomposed into small sub-domains using domain decomposition technique for each processor to perform the calculations. The wave information is exchanged between processors via message passing interface (MPI). We show the effectiveness of this parallel code on distributed- and shared-memory computer clusters in simulating two tsunami events: the 2004 Indian Ocean and the 1999 Vanuatu tsunamis. Communication in the overlapping domains and load balancing in the partitioned domains are considered to ensure the efficiency of this method. It is found that the performance of the parallel model for both large- and small-scale tsunami problems is very satisfactory. Finally, the parallel model is applied to a spatial hierarchical grids methodology for a location-specific numerical simulation. Grid sensitivity and improved simulation results for runups along Phang Nga coastline from Takua Thung to Khao Lak are presented

On the weak impact of the 26 December Indian Ocean tsunami on the Bangladesh coast

The 26 December 2004 Indian Ocean tsunami damaged severely most of the Gulf of Bengal's coastal areas, but the coast of Bangladesh which stands at the edge of an extraordinarily extended continental shelf. This latter feature has been built through huge discharges of river sediments along the Brahmaputra and Ganges rivers. As a result of this enormous discharge, another interesting feature of the area is the deep underwater Canyon, connected with the estuaries, running NE-SW from 25 km off the coast towards the continental slope. We investigate here how these two geological features may have modified/perturbed the Indian ocean tsunami propagation and impact on the Coast of Bangladesh. For that purpose we have realized an ensemble of numerical simulations based on Funwave Boussinesq numerical model and a validated coseismic source. It is found, at first order, that the extended shallow bathymetric profile of the continental shelf plays a key role in flattening the waveform through a defocussing process while the Canyon delays the process. The wave evolution seems to be related at first order to the bathymetric profile rather than to dynamical processes like nonlinearity, dispersion or bottom friction

Modeling the 26 December 2004 Indian Ocean tsunami: Case study of impact in Thailand

The devastating 26 December 2004 Indian Ocean tsunami stressed the need for assessing tsunami hazard in vulnerable coastal areas. Numerical modeling is but one important tool for understanding past tsunami events and simulating future ones. Here we present a robust simulation of the event, which explains the large runups and destruction observed in coastal Thailand and identifies areas vulnerable to future tsunamis, or safer for reconstruction. To do so, we use an accurate tsunami source, which was iteratively calibrated in earlier work to explain the large-scale tsunami features, and apply it over a computational domain with a finer grid and more accurate coastal bathymetry in Thailand. Computations are performed with a well-validated numerical model based on fully nonlinear and dispersive Boussinesq equations (FUNWAVE) that adequately models the physics of tsunami propagation and runup, including dissipation caused by bottom friction and wave breaking. Simulated runups in Thailand reproduce field observations with a surprising degree of accuracy, as well as their high degree of along-coast variation: a 92% correlation is found between (58) runup observations and computations, while the model explains 85% of the observed variance; overall, the RMS error is approximately 1 m or 17% of the mean observed runup value (skill of the simulation). Because we did not use runup observations to calibrate our coseismic tsunami source, these results are robust, and thus provide a uniquely accurate synoptic prediction of tsunami impact along the Andaman coast of Thailand, including those areas where no observations were made. Copyright 2007 by the American Geophysical Union

Numerical Simulation of the December 26, 2004: Indian Ocean Tsunami

The December 26, 2004 tsunami is one of the most devastating tsunami in recorded history. It was generated in the Indian Ocean off the western coast of northern Sumatra, Indonesia at 0:58:53 (GMT) by one of the largest earthquake of the century with a moment magnitude of Mw = 9.3. In the study, we focus on best fitted tsunami source for tsunami modeling based on geophysical and seismological data, and the use of accurate bathymetry and topography data. Then, we simulate the large scale features of the tsunami propagation, runup and inundation. The numerical simulation is performed using the GEOWAVE model. GEOWAVE consists of two components: the modeling of the tusnami source (Okada, 1985) and the initial tsunami surface elevation, and the computation of the wave propagation and inundation based on fully nonlinear Boussinesq scheme. The tsunami source is used as initial condition in the tsunami propagation and inundation model. The tsunami source model is calibrated by using available tide gage data and anomalous water elevations in the Indian Ocean during the tsunami event, recorded by JASON's altimeter (pass 129, cycle 109). The simulated maximum wave heights for the Indian Ocean are displayed and compared with observations with a special focus on the Thailand coastline

Reconstructions of the coastal impact of the 2004 Indian Ocean tsunami in the Khao Lak area, Thailand

International audienceKhao Lak, SW Thailand was severely affected by the tsunami on 26 December 2004. Here we present reconstructions of its coastal impact in this area. These are based on (1) eyewitness reports alone and (2) eyewitness reports supported by videos and photos of the tsunami and the damage it caused, field measurements, and satellite imagery. On the basis of eyewitness reports, we estimated that the sea began retreating at 1000 local time (LT) and, based also on photos, that the tsunami arrived at 1026–1029 LT. On the basis of videos of the tsunami, we estimated an offshore wave direction of 083 ± 3° and on the basis of the paths by which eyewitnesses were carried, we estimated an onshore direction of 088 ± 6°. On the basis of videos, we calculated that the velocity of the wavefront on its final approach was 33 ± 4 km/h. We obtained tsunami heights of 7.3 ± 0.8 m (relative to ground level) on the basis of eyewitness reports and 8.0 ± 0.6 m (relative to mean sea level) on the basis of field and photographic data. On the basis of eyewitness reports and photos, we concluded that Khao Lak experienced at least two main waves with a period >40 min. From eyewitness reports and satellite imagery, we measured maximum inundation ≤0.5 km in the southern part of the area, which is confined by a steeply sloping hinterland, and ≤1.5 km in the more gently sloping northern part. Comparison between these reconstructions supports the reliability of eyewitness reports as a source of quantitative data, and comparison with the numerical simulation by Ioualalen et al. (2007) supports the validity of the simulation