Demonstrating multipartite entanglement of single-particle W states: linear optical schemes

We present two linear optical schemes using nonideal photodetectors to demonstrate inseparability of W-type N-partite entangled states containing only a single photon. First, we show that the pairwise entanglement of arbitrary two modes chosen from N optical modes can be detected using the method proposed by Nha and Kim [Phys. Rev. A 74, 012317 (2006)], thereby suggesting the full inseparability among N parties. In particular, this scheme is found to succeed for any nonzero quantum efficiency of photodetectors. Second, we consider a quantum teleportation network using linear optics without auxiliary modes. The conditional teleportation can be optimized by a suitable choice of the transmittance of the beam splitter in the Bell measurement. Specifically, we identify the conditions under which maximum fidelity larger than classical bound 2/3 is achieved only in cooperation with other parties. We also investigate the case of on-off photodetectors that cannot discriminate the number of detected photons.Comment: 5.5 pages, 2 figures, published version with slight modification

Enhanced multipartite quantum correlations by non-Gaussian operations

We study how conditional photon operations can affect multipartite quantum correlations, specifically nonlocality and entanglement, of the continuous variable GHZ states. We find that the violation of the Mermin-Klyshko inequality revealing the multipartite nonlocality can be made stronger with photon subtraction applied on each mode of the original GHZ states, particularly in a weak squeezing regime. Photon addition applied on local modes also turns out to enhance the degree of multipartite nonlocality in a broad range of parameters. We further investigate the effects of the photon operations on the degree of multipartite entanglement by looking into the Gaussian tangle, the fidelity of teleportation network, and the quadrature correlations. We find that photon subtraction applied on two modes enhances those entanglement characteristics in a practical squeezing regime while there is no improvement made by photon addition.Comment: 11 pages, 10 figures, to appear in Phys. Rev.

Numerical study on hydrodynamics of a ship advancing in confined waterways

This thesis was previously held under moratorium from 22nd August 2019 to 22nd August 2021.Error on title page. Date reads 2018. This is incorrect. Degree was awarded in 2019.The prediction of ship hydrodynamics in the confined waterways is challenging. It may involve both ship-bottom and ship-bank interactions. When a ship is advancing in shallow water, the hydrodynamic behaviours may vary significantly due to the hydrodynamic interaction between the bottom of the ship hull and the seabed, or so called shallow water effects. The flow velocity in the gap between the ship bottom and the seabed increases, which will lead to an increase in ship’s sinkage, trim and resistance. Also, the asymmetric flow around a ship induced by the vicinity of banks causes pressure differences between port and starboard sides, which is known as the bank effects. Therefore, an accurate prediction of shallow water and bank effects is essential to minimize the risk of the collision and the grounding for the ships. Flanders Hydraulics Research (FHR) in cooperation with the Maritime Technology Division of Ghent University has carried out shallow model tests in a towing tank equipped with surface-piercing banks and a vertical quay wall with a 1/75 scale model of the KRISO Very Large Crude carrier (KVLCC2). The forces and moments on the KVLCC2 model were obtained at various water depths, lateral distances to the banks. Additionally, the wave elevation was measured between the quay wall and the ship model. The main objective of the present paper is to simulate the complex flow around the ship and predict the hydrodynamic behaviours of a ship when advancing in the confined waterways. To simulate ship hydrodynamics in confined waterways, the CFD programme should be used to get a reliable result. In the present study, a widely used CFD programme, Star-CCM+, will be used to simulate the complex flow phenomena induced by a ship advancing in confined waterways. To evaluate the capability of the CFD software, the numerical data will be compared with the experimental data conducted by FHR. The free surface effect will be taken into account. The results will include the forces and moments acting on the ship, as well as the wave elevation between the quay wall and the ship model. The parametric study will be conducted to investigate the effects of the ship speed, the water depths and the positions in a channel. Discussions will be highlighted on the ship-bank interaction when the water depth Froude number approaches critical value.The prediction of ship hydrodynamics in the confined waterways is challenging. It may involve both ship-bottom and ship-bank interactions. When a ship is advancing in shallow water, the hydrodynamic behaviours may vary significantly due to the hydrodynamic interaction between the bottom of the ship hull and the seabed, or so called shallow water effects. The flow velocity in the gap between the ship bottom and the seabed increases, which will lead to an increase in ship’s sinkage, trim and resistance. Also, the asymmetric flow around a ship induced by the vicinity of banks causes pressure differences between port and starboard sides, which is known as the bank effects. Therefore, an accurate prediction of shallow water and bank effects is essential to minimize the risk of the collision and the grounding for the ships. Flanders Hydraulics Research (FHR) in cooperation with the Maritime Technology Division of Ghent University has carried out shallow model tests in a towing tank equipped with surface-piercing banks and a vertical quay wall with a 1/75 scale model of the KRISO Very Large Crude carrier (KVLCC2). The forces and moments on the KVLCC2 model were obtained at various water depths, lateral distances to the banks. Additionally, the wave elevation was measured between the quay wall and the ship model. The main objective of the present paper is to simulate the complex flow around the ship and predict the hydrodynamic behaviours of a ship when advancing in the confined waterways. To simulate ship hydrodynamics in confined waterways, the CFD programme should be used to get a reliable result. In the present study, a widely used CFD programme, Star-CCM+, will be used to simulate the complex flow phenomena induced by a ship advancing in confined waterways. To evaluate the capability of the CFD software, the numerical data will be compared with the experimental data conducted by FHR. The free surface effect will be taken into account. The results will include the forces and moments acting on the ship, as well as the wave elevation between the quay wall and the ship model. The parametric study will be conducted to investigate the effects of the ship speed, the water depths and the positions in a channel. Discussions will be highlighted on the ship-bank interaction when the water depth Froude number approaches critical value

A Method of XML Document Fragmentation for Reducing Time of XML Fragment Stream Query Processing

As XML has been established as the standard for data exchange not just on the Web but among heterogeneous devices, systems, and applications, effective processing of XML queries is one of core components of ubiquitous computing. Most of the mobile/hand-held devices deployed in ubiquitous computing environment are still limited in memory and processing power. An effective query processing is required when the source XML document is of large volume. The framework of fragmenting an XML document and streaming the XML fragments for query processing at the mobile devices has received much attention. However, the main focus was on the memory efficiency to cope with the memory constraint in the mobile devices. Query processing time might be compromised in those techniques. Since the processing power is also limited in the mobile devices, the time optimization deserves attention. We have found out that the query processing time is significantly affected by how the source XML document is fragmented. In this paper, we propose a method of XML document fragmentation whereby query processing gets efficient in time while the size constraint for each resulting fragment is satisfied. Through implementation and a set of detailed experiments, we show that our proposed method considerably outperforms other methods

Enhancing quantum entanglement for continuous variables by a coherent superposition of photon subtraction and addition

We investigate how the entanglement properties of a two-mode state can be improved by performing a coherent superposition operation of photon subtraction and addition, proposed by Lee and Nha [Phys. Rev. A 82, 053812 (2010)], on each mode. We show that the degree of entanglement, the EPR-type correlation, and the performance of quantum teleportation can be all enhanced for the output state when the coherent operation is applied to a two-mode squeezed state. The effects of the coherent operation are more prominent than those of the mere photon subtraction and the addition particularly in the small squeezing regime, whereas the optimal operation becomes the photon subtraction in the large-squeezing regime.Comment: 6 pages, 6 figures, published versio

Loophole-free Bell test for continuous variables via wave and particle correlations

We derive two classes of multi-mode Bell inequalities under local realistic assumptions, which are violated only by the entangled states negative under partial transposition in accordance with the Peres conjecture. Remarkably, the failure of local realism can be manifested by exploiting wave and particle correlations of readily accessible continuous-variable states, with very large violation of inequalities insensitive to detector-efficiency, which makes a strong case for a loophole-free test.Comment: 4 pages, published versio

Reply to the comment on "Loophole-free Bell test for continuous variables via wave and particle correlations"

In a recent note, Cavalcanti and Scarani (CS) constructed a counter local-hidden-variable model to explain the violation of our inequalities in Phys. Rev. Lett. 105, 170404 (2010). Here, we briefly discuss some issues in response to the comments raised by CS.Comment: published versio

Memory-Efficient Query Processing over XML Fragment Stream with Fragment Labeling

The portable/hand-held devices deployed in mobile computing environment are mostly limited in memory. To make it possible for them to locally process queries over a large volume of XML data, the data needs to be streamed in fragments of manageable size and the queries need to be processed over the stream with as little memory as possible. In this paper, we report a considerable improvement of the state-of-the-art techniques of query processing over XML fragment stream in memory efficiency. We use XML fragment labeling (XFL) as a method of representing XML fragmentation, and show that XFL is much more effective than the popular hole-filler (HF) model employed in the state-of-the-art in reducing the amount of memory required for query processing. The state-of-the-art with the HF model requires more memory as the stream size increases. With XFL, we overcome this fundamental limitation, proposing the techniques to make query processing scalable in the sense that memory requirement is not affected by the size of the stream as long as the stream is bounded. The improvement is verified through implementation and a detailed set of experiments