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
Study Shows Time Traveling May Not Increase Computational Power
Oct 22, 2009 |
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(PhysOrg.com) -- For more than 50 years, physicists have been intrigued by the concept of closed time-like curves (CTCs). Because a CTC returns to its starting point, it raises the possibility of traveling backward in time. ...
Physicists Propose Scheme for Teleporting Light Beams
Jul 14, 2009 |
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(PhysOrg.com) -- Usually when physicists talk about quantum teleportation, they're referring to the transfer of quantum states from one particle to another without a physical link. Now, physicists have investigated ...
Too much entanglement can render quantum computers useless
May 25, 2009 |
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(PhysOrg.com) -- "For certain tasks, quantum computers are more powerful than their classical counterparts. The task to be performed is the same for quantum or classical systems. However, the former ones can do it in a more ...
Long-Lasting Quantum Memory Leads to Long-Distance Quantum Communication
Oct 07, 2008 |
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(PhysOrg.com) -- Physicists have taken a step closer to realizing long-distance quantum communication, in which a quantum state is transferred from one location to another by becoming entangled with a traveling ...
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 ...
Researchers make breakthrough in the quantum control of light
May 29, 2009 |
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Researchers at UC Santa Barbara have recently demonstrated a breakthrough in the quantum control of photons, the energy quanta of light. This is a significant result in quantum computation, and could eventually ...
Physicists detect entanglement of one photon shared among four locations
May 08, 2009 |
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Scientists at the California Institute of Technology (Caltech) have developed an efficient method to detect entanglement shared among multiple parts of an optical system. They show how entanglement, in the form of beams of ...
From three to four: a quantum leap in few-body physics
Apr 07, 2009 |
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Scientists from the University of Innsbruck, Austria, led by Rudolf Grimm offer new insights into the extremely complex few-body problem. For the first time, the quantum physicists provide evidence of universal ...
Quantum technologies move a step closer with the demonstration of an 'entanglement' filter
Jan 22, 2009 |
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(PhysOrg.com) -- A team of physicists and engineers has demonstrated an optical device that filters two particles of light (or photons) based on the correlations between their polarisation that are only allowed in the seemingly ...
Long-Distance Teleportation Between Two Atoms: First between atoms 1 meter apart
Jan 22, 2009 |
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(PhysOrg.com) -- For the first time, scientists have successfully teleported information between two separate atoms in unconnected enclosures a meter apart - a significant milestone in the global quest for ...
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 ...
Life Expectancy on the Rise -- Even for Quantum States
Apr 14, 2009 |
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(PhysOrg.com) -- For the first time, scientists have succeeded in measuring and controlling the lifetime of quantum states with potential use in optoelectronic chips. This achievement is highly significant ...
Unknown molecule opens the door to quantum computing
Jun 27, 2008 |
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The odd behavior of a molecule in an experimental silicon computer chip has led to a discovery that opens the door to quantum computing in semiconductors.
