Electrical control over designer quantum materials

Exploring the properties and behaviors of strongly interacting quantum particles is one of the frontiers of modern physics. Not only are there major open problems that await solutions, some of them since decades (think high-temperature ...

Cooling radio waves to their quantum ground state

Researchers at Delft University of Technology have found a new way to cool radio waves all the way down to their quantum ground state. To do so, they used circuits that employ an analog of the so-called laser cooling technique ...

Levi­tating particles in a vacuum

Levitation of both large objects and of single atoms has become a widely used technique in science and engineering. In the last years, many researchers have started to explore a new horizon: the levitation of nano- and micro-particles—still ...

Fast tool developed for quantum computing and communication

Isaac Nape, an emerging South African talent in the study of quantum optics, is part of a crack team of Wits physicists who led an international study that revealed the hidden structures of quantum entangled states. The study ...

page 1 from 40

Quantum state

In quantum physics, a quantum state is a mathematical object that fully describes a quantum system. One typically imagines some experimental apparatus and procedure which "prepares" this quantum state; the mathematical object then reflects the setup of the apparatus. Quantum states can be statistically mixed, corresponding to an experiment involving a random change of the parameters. States obtained in this way are called mixed states, as opposed to pure states, which cannot be described as a mixture of others. When performing a certain measurement on a quantum state, the result generally described by a probability distribution, and the form that this distribution takes is completely determined by the quantum state and the observable describing the measurement. However, unlike in classical mechanics, the result of a measurement on even a pure quantum state is only determined probabilistically. This reflects a core difference between classical and quantum physics.

Mathematically, a pure quantum state is typically represented by a vector in a Hilbert space. In physics, bra-ket notation is often used to denote such vectors. Linear combinations (superpositions) of vectors can describe interference phenomena. Mixed quantum states are described by density matrices.

In a more general mathematical context, quantum states can be understood as positive normalized linear functionals on a C* algebra; see GNS construction.

This text uses material from Wikipedia, licensed under CC BY-SA