Current Quantum Information Science and Technology

Current Quantum Information Science and Technology

Göran Pulkkis, Kaj J. Grahn
Copyright: © 2015 |Pages: 14
DOI: 10.4018/978-1-4666-5888-2.ch420
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Information Representation With Quantum States

Quantum states are energy levels of molecules, atoms, and photons. Two quantum states for which a state transition exists can be used to represent an information bit, if the energy levels of both states can be measured. A bit defined by quantum states is called a quantum bit or qubit. However, quantum states are probabilistic. When the energy level of a molecule, an atom, or a photon is measured, the outcome is one of all possible energy levels and each possible outcome is associated with a probability. The sum of the probabilities of all possible measurement outcomes is of course 1. A qubit is thus also probabilistic.

Another fundamental qubit property is the No Cloning Property, the impossibility to create a copy of an unknown quantum state. However, an unknown quantum state can be transferred between qubit platforms with teleportation, in which the original qubit state is lost.

Key Terms in this Chapter

Teleportation: Transfer of an unknown qubit state.

Adiabatic Quantum Computation (AQC): Calculation by quantum annealing.

Quantum Gate: A device for changing the state of one or of multiple qubits.

Photon: A discrete packet of electromagnetic energy.

Avalanche Photodiode: A photodetector which can be regarded as the semiconductor analog to a photomultiplier.

Decoherence Time: The time a qubit state can be maintained before it collapses.

Enlanglement: Multiple qubits are entangled, when their quantum state cannot be reached by combining single qubit quantum states.

Polarization: The plane in which an electromagnetic wave propagates.

Qubit: A two-state quantum-mechanical system allowing the qubit to be in a superposition of both states at the same time.

Quantum Private Network (QPN): Is a VPN link where session key agreement is based on a QKD protocol.

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