John Preskill is a prominent theoretical physicist known for his work in quantum information and quantum computing. He is a professor at the California Institute of Technology (Caltech) and has made significant contributions to the understanding of quantum mechanics, quantum algorithms, and the foundational aspects of quantum information theory. Preskill is perhaps most well-known for coining the term "quantum supremacy," which refers to the point at which a quantum computer can perform a calculation that is infeasible for any classical computer.
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John Preskill's quantum computation notes develop the distinction between a quantum state ray, a normalized wave function, and a density operator. This makes a practical difference for a subsystem of an entangled state: its predictions are described by a reduced density operator obtained with the partial trace, even when the joint quantum state is pure. His discussion also shows why different statistical preparations can give the same density operator and therefore identical predictions for measurements confined to that subsystem.[ref]
Foundations I: States and Ensembles by John Preskill. Section 2.1, state rays; section 2.3.1, equations (2.51)–(2.61), partial trace and ensemble interpretation
Homepage: www.preskill.caltech.edu/
Portrait of John Preskill
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