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Gregg Jaeger carries out research in quantum computing, quantum cryptography, foundations of quantum mechanics, quantum metrology, history and philosophy of science and population genetics.

RESEARCH INTERESTS:

"In my earliest work, I explored ways in which quantum two-level systems ("qubits") can be used to probe physical systems to perform quantum metrology (click here to see a review article). From this basis, I have gone to study increasing larger quantum systems through a broader array of techniques and to find more adequate concepts for conceiving of them as being and consisting of physical objects.

During the period 2001-2006, the Quantum Imaging Laboratory and collaborators at Harvard University and BBN Technologies built a practical metro area quantum cryptographic network, known as the DARPA Quantum Network Testbed, to which I contributed as the principal quantum entanglement theorist. During this project, for the first time 1550 nm (the main telecomm. wavelength) entangled photon pairs were shown to violate Bell inequalities (using superconducting single-photon detectors) and to be of practical use for quantum cryptography in a real-world computer network environment. (See the "Patents and News" section for more information.) We later pursued a new, coherent-state based approach that will allow much greater rates and distances of secure QKD to be achieved through the use of entanglement witnesses and related quantities as an eavesdropping indicators.

As mentioned above, my early work focused on two new, fundamental quantum complementarity relations. These are the relation between single-particle interference visibility and path distinguishability and the relation between single-particle and two-particle interference visibilities. Together with Abner Shimony, I also found a fundamental bound on the distinguishability of non-orthogonal quantum states. (See the "Articles" section for articles in .pdf format.) The quantum metrology techniques currently being developed in the Quantum Imaging Lab primarily use such systems.

More recently, I have been investigating coherence and entanglement in the larger quantum mechanical systems used for quantum information processing. This involves clarifying the character of entanglement in many-particle systems, such as by determining the relationship between entanglement and mixedness in arbitrarily large quantum systems.

My students, collaborators and I have often pursued the question of the general relationship between quantum entanglement and decoherence in multiple-qubit and mulitiple qu-d-it systems and inducing entanglement death.

I have most recently also been explicitly investigating the issues of probabilistic causation, quantum measurement, and the nature of quantum objects, particularly in quantum field theory. In particular, I have investigated the operation of exchange forces via virtual particles and the relationship of particles to quantum fields." Back to main page