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
JQI researchers create entangled photons from quantum dots
Nov 18, 2009 |
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To exploit the quantum world to the fullest, a key commodity is entanglement—the spooky, distance-defying link that can form between objects such as atoms even when they are completely shielded from one another. Now, physicists ...
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 ...
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 ...
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 ...
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. ...
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 ...
Entangled Light in Bose-Einstein Condensates
Apr 08, 2009 |
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(PhysOrg.com) -- When physicists entangle light, they usually use nonlinear crystals as the source. However, it’s difficult to control the entanglement generation process in a bulk crystal, and so scientists ...
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 ...
Quantum communication through synergy
Jan 19, 2009 |
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(PhysOrg.com) -- When most people think of quantum communication, they think in terms of private communication channels - the ability to send messages without a third-party deciphering them. Indeed, quantum cryptography represents ...
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.
Sustained quantum information processing demonstrated
Aug 06, 2009 |
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Raising prospects for building a practical quantum computer, physicists at the National Institute of Standards and Technology have demonstrated sustained, reliable information processing operations on electrically ...
Diamonds May Be the Ultimate MRI Probe, Say Quantum Physicists
Sep 22, 2009 |
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(PhysOrg.com) -- Diamonds, it has long been said, are a girl's best friend. But a research team including a physicist from the National Institute of Standards and Technology has recently found that the gems ...
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 ...
Making quantum computing scalable
Mar 20, 2009 |
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(PhysOrg.com) -- Quantum information processing is one of the hottest areas of science and technology right now. Making quantum information processing scalable is an important part of the efforts involved with regard to practical ...
