Security of Quantum Key Distribution with Entangled Qutrits

The study of quantum cryptography and quantum non-locality have traditionnally been based on two-level quantum systems (qubits). In this paper we consider a generalisation of Ekert's cryptographic protocol [Ekert] where qubits are replaced by qutrits. The security of this protocol is related to non-locality, in analogy with Ekert's protocol. In order to study its robustness against the optimal individual attacks, we derive the information gained by a potential eavesdropper applying a cloning-based attack.Comment: 9 pages original version: july 2002, replaced in january 2003 (reason: minor changes

From Cooperative Scans to Predictive Buffer Management

In analytical applications, database systems often need to sustain workloads with multiple concurrent scans hitting the same table. The Cooperative Scans (CScans) framework, which introduces an Active Buffer Manager (ABM) component into the database architecture, has been the most effective and elaborate response to this problem, and was initially developed in the X100 research prototype. We now report on the the experiences of integrating Cooperative Scans into its industrial-strength successor, the Vectorwise database product. During this implementation we invented a simpler optimization of concurrent scan buffer management, called Predictive Buffer Management (PBM). PBM is based on the observation that in a workload with long-running scans, the buffer manager has quite a bit of information on the workload in the immediate future, such that an approximation of the ideal OPT algorithm becomes feasible. In the evaluation on both synthetic benchmarks as well as a TPC-H throughput run we compare the benefits of naive buffer management (LRU) versus CScans, PBM and OPT; showing that PBM achieves benefits close to Cooperative Scans, while incurring much lower architectural impact.Comment: VLDB201

A posteriori teleportation

The article by Bouwmeester et al. on experimental quantum teleportation constitutes an important advance in the burgeoning field of quantum information. The experiment was motivated by the proposal of Bennett et al. in which an unknown quantum state is `teleported' by Alice to Bob. As illustrated in Fig. 1, in the implementation of this procedure, by Bouwmeester et al., an input quantum state is `disembodied' into quantum and classical components, as in the original protocol. However, in contrast to the original scheme, Bouwmeester et al.'s procedure necessarily destroys the state at Bob's receiving terminal, so a `teleported' state can never emerge as a freely propagating state for subsequent examination or exploitation. In fact, teleportation is achieved only as a postdiction.Comment: 1 page LaTeX including 1 figure. Scientific Correspondence about: "Experimental quantum teleportation" Nature 390, 575 (1997

Interference due to Coherence Swapping

We propose a method called `coherence swapping' which enables us to create superposition of a particle in two distinct paths, which is fed with initially incoherent, independent radiations. This phenomenon is also present for the charged particles, and can be used to swap the effect of flux line due to Aharonov-Bohm effect. We propose an optical version of the experimental set-up to test the coherence swapping. The phenomenon, which is simpler than entanglement swapping or teleportation, raises some fundamental questions about true nature of wave-particle duality, and also opens up the possibility of studying the quantum erasure from a new angle.Comment: Latex file, 10 pages, Two figure

Long distance entanglement swapping with photons from separated sources

We report the first experimental realization of entanglement swapping over large distances in optical fibers. Two photons separated by more than two km of optical fibers are entangled, although they never directly interacted. We use two pairs of time-bin entangled qubits created in spatially separated sources and carried by photons at telecommunication wavelengths. A partial Bell state measurement is performed with one photon from each pair which projects the two remaining photons, formerly independent onto an entangled state. A visibility high enough to violate a Bell inequality is reported, after both photons have each travelled through 1.1 km of optical fiber.Comment: 4 pages, 3 figures, submitte

Law\u27s Racism: The Perpetuation of Settler Colonialism in Ktunaxa v. British Columbia

In considering the nexus between law, religion, and settler colonialism I consider a case in which an Indigenous freedom of religion claim under section 2(a) of the Canadian Charter of Rights and Freedoms was ruled by the majority of Supreme Court of Canada as not being a valid freedom of religion claim. In examining this decision, I will construct an analytical framework by which I will examine the decision in a way that considers the legal system in which it occurs, that legal system’s culture, and the relevance of land in this case. Using this analytical framework, I will tease out why the Ktunaxa decision occurred in the way that it did, drawing on the discourse of both the majority and concurring arguments. I argue that the Court restricting what may validly be claimed as an infringement on the Charter’s guarantee to freedom of religion is an example of continuing settler colonialism that occurs within a political culture that, superficially, places great emphasis on reconciliation with the Indigenous peoples that reside within its political-geographical confines

Photon-bunching measurement after 2x25km of standard optical fibers

To show the feasibility of a long distance partial Bell-State measurement, a Hong-Ou-Mandel experiment with coherent photons is reported. Pairs of degenerate photons at telecom wavelength are created by parametric down conversion in a periodically poled lithium niobate waveguide. The photon pairs are separated in a beam-splitter and transmitted via two fibers of 25km. The wave-packets are relatively delayed and recombined on a second beam-splitter, forming a large Mach-Zehnder interferometer. Coincidence counts between the photons at the two output modes are registered. The main challenge consists in the trade-off between low count rates due to narrow filtering and length fluctuations of the 25km long arms during the measurement. For balanced paths a Hong-Ou-Mandel dip with a visibility of 47.3% is observed, which is close to the maximal theoretical value of 50% developed here. This proves the practicability of a long distance Bell state measurement with two independent sources, as e.g. required in an entanglement swapping configuration in the scale of tens of km.Comment: 6 pages, 5 figure