Backup copy: Putting quantum weirdness to work: Quantum Information Science
Quantum physics, information theory, and computer science are among the crowning intellectual achievements of the 20th century. Now, a new synthesis of these themes is underway. The emerg- ing field of quantum information science is providing important insights into fundamental issues at the interface of computation and physical science, and may guide the way to revolutionary technological advances. The quantum laws that govern atoms and other tiny objects differ radically from the classical laws that govern our ordinary experience. In particular, quantum information (information en- coded in a quantum system) has weird properties that contrast sharply with the familiar properties of classical information. Physicists, who for many years have relished this weirdness, have begun to recognize in recent years that we can put the weirdness to work: There are tasks involving the acquisition, transmission, and processing of information that are achievable in principle because Nature is quantum mechanical, but that would be impossible in a less weird classical world. John Preskill will describe the properties of quantum bits ("qubits"), the indivisible units of quantum infor- mation, and explain the essential ways in which qubits differ from classical bits. For one thing, it is impossible to read or copy the state of a qubit without disturbing it. This property is the basis of "quantum cryptography," wherein the privacy of secret information can be founded on principles of fundamental physics. Qubits can be "entangled" with one another. This means that the qubits can exhibit subtle quantum correlations that have no classical analogue; roughly speaking, when two qubits are en- tangled, their joint state is more definite than the state of either qubit by itself. Because of quantum entanglement, a vast amount of classical information would be needed to describe completely the quantum state of just a few hundred qubits. Therefore, a "quantum computer" operating on just a few hundred qubits could perform tasks that ordinary digital computers could not possibly emulate.
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