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 addition to a strong interest in the foundations of quantum theory, I investigate how information can be encoded and transformed in quantum systems, both in theory and practice, for example, for the purposes of quantum computing and quantum cryptography. I have also 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).
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.)
My early work focused on the entanglement of dichotomic quantum observables in two-particle systems, that is on entangled pairs of two-level systems. These results included 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. For example, complementarity relations were found and published in "Entanglement, mixedness, and spin-flip symmetry in multiple-qubit states." Most recent directions include the discovery of higher multipartite states most strongly exhibiting quantum behavior and the discovery of the effect of local noise on multipartite quantum systems. For example, the article "Bell gems," introduces a new generalization of the Bell basis to states of arbitarily large numbers of parties that includes maximally entangled quantum error correction code states with applications in optical quantum memory design.
Currently, my students and I are pursuing the question of the general relationship between quantum entanglement and decoherence in multiple-qubit and mulitiple qu-d-it systems. For example, our recent article "Local-dephasing-induced entanglement sudden death in two-component finite-dimensional systems" shows that local noise alone is capable of destroying all entanglement in classes of pairs of d-level systems ("qudits") in finite times, that is, of inducing entanglement sudden death.
I have just finished a monograph on the foundations of quantum theory."
His 2007 book Quantum Information: An Overview is a concise look at the new field of quantum information science.
His 2009 book, Entanglement, Information, and the Interpretation of Quantum Mechanics focuses on the relationship of information and entanglement to the foundations of quantum mechanics.
