Quantum information
hideIn quantum mechanics, quantum information is physical information that is held in the "state" of a quantum system. The most popular unit of quantum information is the qubit, a two-level quantum system. However, unlike classical digital states (which are discrete), a two-state quantum system can actually be in a superposition of the two states at any given time.
Quantum information differs from classical information in several respects, among which we note the following:
However, despite this, the amount of information that can be retrieved in a single qubit is equal to one bit. It is in the processing of information (quantum computation) that a difference occurs.
The ability to manipulate quantum information enables us to perform tasks that would be unachievable in a classical context, such as unconditionally secure transmission of information. Quantum information processing is the most general field that is concerned with quantum information. There are certain tasks which classical computers cannot perform "efficiently" (that is, in polynomial time) according to any known algorithm. However, a quantum computer can compute the answer to some of these problems in polynomial time; one well-known example of this is Shor's factoring algorithm. Other algorithms can speed up a task less dramatically - for example, Grover's search algorithm which gives a quadratic speed-up over the best possible classical algorithm.
Quantum information, and changes in quantum information, can be quantitatively measured by using an analogue of Shannon entropy. Given a statistical ensemble of quantum mechanical systems with the density matrix S, it is given by
Many of the same entropy measures in classical information theory can also be generalized to the quantum case, such as the conditional quantum entropy.
For more information about Quantum information, read the full article at
Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.
News tagged with quantum information
Qubits and Branes Share Surprising Features
Jul 03, 2008 |
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What do black holes and entangled particles have in common? Until about a year ago, physicists thought that the two entities existed in completely separate worlds. Then, in 2007, physicist Michael Duff from ...
Quantum computing: Entanglement may not be necessary
Dec 05, 2008 |
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(PhysOrg.com) -- It is a truth universally acknowledged that quantum computing must have entanglement.
Scientists create first electronic quantum processor
Jun 28, 2009 |
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A team led by Yale University researchers has created the first rudimentary solid-state quantum processor, taking another step toward the ultimate dream of building a quantum computer.
Memoirs of a qubit: Hybrid memory solves key problem for quantum computing
Oct 22, 2008 |
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An international team of scientists has performed the ultimate miniaturisation of computer memory: storing information inside the nucleus of an atom. This breakthrough is a key step in bringing to life a quantum ...
A broadband single-photon source
Sep 19, 2008 |
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As science makes progress toward practical quantum computing, improved quantum cryptography and scalable quantum communications systems, single photon sources will become more important. Until now, though, ...
First-ever calculation performed on optical quantum computer chip
Sep 03, 2009 |
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(PhysOrg.com) -- A primitive quantum computer that uses single particles of light (photons) whizzing through a silicon chip has performed its first mathematical calculation. This is the first time a calculation ...
New concept for creating quantum states in many-body systems
Sep 07, 2008 |
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(PhysOrg.com) -- In the online edition of Nature Physics, theoretical physicists from the Institute for Quantum Optics and Quantum Information (IQOQI) and the University of Innsbruck today are presenting a compl ...
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 ...
Physicists Demonstrate Three-Color Entanglement
Oct 07, 2009 |
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(PhysOrg.com) -- For the first time, physicists have demonstrated the quantum entanglement of three light beams, all of different wavelengths. Entanglement of two light beams of different wavelengths has already ...
An oblivious transfer protocol for quantum cryptography
Jul 01, 2008 |
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“It's hard to beat the noise that you have with quantum information,” Barbara Terhal tells PhysOrg.com. “So our security protocol relies on the fact that storing quantum bits noiselessly is hard to do with current technology.”
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 ...
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 ...
Physicists Investigate Unusual Four-Qubit Entanglement
Sep 30, 2009 |
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(PhysOrg.com) -- For the first time, physicists have experimentally demonstrated a four-qubit bound-entangled state - a peculiar form of entanglement that cannot be distilled (optimized) by the usual means. ...
Researchers Design Triple Quantum Dot for Quantum Information Applications
Nov 30, 2009 |
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(PhysOrg.com) -- While quantum dots have existed since the 1980s, only in the past decade have physicists successfully created lateral few-electron single quantum dots. These quantum dots enable physicists ...
Quantum measurements: Common sense is not enough
Jul 22, 2009 |
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(PhysOrg.com) -- In comparison to classical physics, quantum physics predicts that the properties of a quantum mechanical system depend on the measurement context, i.e. whether or not other system measurements ...
