Quantum state
hideIn 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.
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News tagged with quantum state
Straightening messy correlations with a quantum comb
Nov 23, 2009 |
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Quantum computing promises ultra-fast communication, computation and more powerful ways to encrypt sensitive information. But trying to use quantum states as carriers of information is an extremely delicate ...
UCSB physicists move one step closer to quantum computing
Nov 20, 2009 |
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Physicists at UC Santa Barbara have made an important advance in electrically controlling quantum states of electrons, a step that could help in the development of quantum computing. The work is published ...
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Creating a six-qubit cluster state
Nov 02, 2009 |
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(PhysOrg.com) -- Many scientists believe that quantum entanglement is required in order for effective quantum computing. Entanglement takes place when there is a connection that exists between two objects - even when they ...
Using superconducting probes to get a picture of what it's like inside CNTs
Nov 20, 2009 |
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(PhysOrg.com) -- "Carbon nanotubes are exciting for fundamental physics, and for potential technological applications," Nadya Mason tells PhysOrg.com. "However, we are generally limited in the way that we can study them. ...
First Bose-Einstein condensation of strontium
Nov 09, 2009 |
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In an international first, scientists from the Institute of Quantum Optics and Quantum Information (IQOQI, Austria) produced a Bose-Einstein condensate of the alkaline-earth element strontium, thus narrowly ...
Rice ties in race for atomic-scale breakthrough
Nov 17, 2009 |
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Everybody loves a race to the wire, even when the result is a tie. The great irony is the ultraprecise clocks that could result from this competition could probably break any tie.
Turning heat to electricity... efficiently
Nov 18, 2009 |
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(PhysOrg.com) -- In everything from computer processor chips to car engines to electric powerplants, the need to get rid of excess heat creates a major source of inefficiency. But new research points the way ...
Spin polarization achieved in room temperature silicon
Nov 27, 2009 |
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(PhysOrg.com) -- A group in The Netherlands has achieved a first: injection of spin-polarized electrons in silicon at room temperature. This has previously been observed only at extremely low temperatures, ...
New funding will stimulate alternative energy research
Nov 16, 2009 |
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Initiatives to provide geothermal heating or power at the Pueblo of Jemez and the New Mexico Institute of Mining and Technology campus are receiving Los Alamos National Laboratory assistance, thanks to recent American Reinvestment ...
More than powerful: German research computer QPACE is the most energy efficient in the world
Nov 20, 2009 |
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At the 2009 Supercomputing Conference in Portland, Oregon, the high-performance computer QPACE (QCD Parallel Computing on the Cell) was recognized today as the most energy-efficient supercomputer in the world.
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