Entanglement and Experimental Tests of Quantum Mechanics

F.J. Duarte, T S Taylor

Shady M. Alserwy

This thesis presents a study of Bell’s inequality and its experimental tests, with a focus on their implications for the concepts of locality and realism in quantum mechanics. The work reviews the theoretical framework underlying Bell’s inequality, the assumptions of hidden variable theories, and the contrasting predictions of quantum mechanics. It further provides an overview of landmark experimental tests of Bell’s inequality, emphasizing their role in shaping the modern understanding of quantum entanglement and nonlocality. The aim of the study is to offer a clear and pedagogical introduction to the subject, bridging the mathematical formalism with experimental verification of one of the most fundamental results in the foundations of quantum theory.

Magnus Rådmark

Entanglement is a key resource in many quantum information schemes and in the last years the research on multi-qubit entanglement has drawn lots of attention. In this thesis the experimental generation and characterisation of multi-qubit entanglement is presented. Specifically we have prepared entangled states of up to six qubits. The qubits were implemented in the polarisation degree of freedom of single photons. We emphasise that one type of states that we produce are rotationally invariant states, remaining unchanged under simultaneous identical unitary transformations of all their individual constituents. Such states can be applied to e.g. decoherence-free encoding, quantum communication without sharing a common reference frame, quantum telecloning, secret sharing and remote state preparation schemes. They also have properties which are interesting in studies of foundations of quantum mechanics. In the experimental implementation we use a single source of entangled photon pairs, based on parametric down-conversion, and extract the first, second and third order events. Our experimental setup is completely free from interferometric overlaps, making it robust and contributing to a high fidelity of the generated states. To our knowledge, the achieved fidelity is the highest that has been observed for six-qubit entangled states and our measurement results are in very good agreement with predictions of quantum theory. We have also performed another novel test of the foundations of quantum mechanics. It is based on an inequality that is fulfilled by any non-contextual hidden variable theory, but can be violated by quantum mechanics. This test is similar to Bell inequality tests, which rule out local hidden variable theories as possible completions of quantum mechanics. Here, however, we show that non-contextual hidden variable theories cannot explain certain experimental results, which are consistent with quantum mechanics. Hence, neither of these theories can be used to make quantum mechanics complete.

F. J. Duarte

Bradley Christensen, Nicolas Gisin, Nicolas Brunner +2 more

We report on a variety of Bell tests performed with a high-quality photonic entanglement source. These tests begin to quantify nonlocal resources available in quantum mechanics, as well as place bounds on beyond-quantum theories.

F.J. Duarte