This concept is similar to quantum teleportation due to entanglement, although even that does not imply a possibility of faster-than-light communication.

* The no-cloning theorem does not prevent superluminal communication via quantum entanglement, as cloning is a sufficient condition for such communication, but not a necessary one.

Recently, photons have been studied as elements of quantum computers and for sophisticated applications in optical communication such as quantum cryptography.

The prerequisites for quantum teleportation are a qubit that is to be teleported, a conventional communication channel capable of transmitting two classical bits ( i. e., one of four states ), and means of generating an entangled EPR pair of qubits, performing a Bell measurement on the EPR pair, and manipulating the quantum state of one of the pair.

Many of the successes of quantum computation and communication, such as quantum teleportation and superdense coding, make use of entanglement, suggesting that entanglement is a resource that is unique to quantum computation.

In standard quantum mechanics, it is generally accepted that the no cloning theorem prevents superluminal communication via quantum entanglement alone, leading to the no-communication theorem.

Although such communication is prohibited in the thought experiment described above, some argue that superluminal communication could be achieved via quantum entanglement using other methods that don't rely on cloning a quantum system.

As the quantum eraser experiments rely on a classical, subluminal channel for coincidence detection, it is unclear whether superluminal communication would be possible by this method.

Because a wormhole time-machine introduces a type of nonlinearity into quantum theory, this sort of communication between parallel universes is consistent with Joseph Polchinski ’ s discovery of an “ Everett phone ” in Steven Weinberg ’ s formulation of nonlinear quantum mechanics.

Quantum key distribution ( QKD ) uses quantum mechanics to guarantee secure communication.

By using quantum superpositions or quantum entanglement and transmitting information in quantum states, a communication system can be implemented which detects eavesdropping.

Quantum communication involves encoding information in quantum states, or qubits, as opposed to classical communication's use of bits.

The sender ( traditionally referred to as Alice ) and the receiver ( Bob ) are connected by a quantum communication channel which allows quantum states to be transmitted.

Practical applications are made impossible due to the no-cloning theorem, and the fact that quantum field theories preserve causality, so that quantum correlations cannot be used to transfer information.

* Bell state, in quantum information science

In quantum mechanics it often occurs that little or no information about the inner product of two arbitrary ( state ) kets is present, while it is possible to say something about the expansion coefficients and of those vectors with respect to a chosen ( orthonormalized ) basis.

The information that is lost includes every quantity that cannot be measured far away from the black hole horizon, including approximately conserved quantum numbers such as the total baryon number and lepton number.

Condensed matter systems can be tuned to provide the conditions of coherence and phase-sensitivity that are essential ingredients for quantum information storage.

See the discussion on the relationship between key lengths and quantum computing attacks at the bottom of this page for more information.

In analyzing quantum states and black holes, physicist Don Page writes that " determining experimentally whether or not information is lost down black holes of solar mass ... would require more than measurements to give a rough determination of the final density matrix after a black hole evaporates ".

This work showed that the black hole information paradox is resolved when quantum gravity is described in an unusual string-theoretic way.

Imperfect cloning can be used as an eavesdropping attack on quantum cryptography protocols, among other uses in quantum information science.

Quantum mechanics has since branched out into almost every aspect of 20th century physics and other disciplines, such as quantum chemistry, quantum electronics, quantum optics, and quantum information science.

Whereas the absolute value of the probability amplitude encodes information about probabilities, its phase encodes information about the interference between quantum states.

Efforts are being made to more fully develop quantum cryptography, which will theoretically allow guaranteed secure transmission of information.

Another active research topic is quantum teleportation, which deals with techniques to transmit quantum information over arbitrary distances.

* Experimental quantum chemists rely heavily on spectroscopy, through which information regarding the quantization of energy on a molecular scale can be obtained.

* Quantiki – Wiki and portal with free-content related to quantum information science.

In quantum mechanics, quantum information is physical information that is held in the " state " of a quantum system.

Further investigation and theoretical work showed that the effect was a radiationless effect more than an internal conversion effect by use of elementary quantum mechanics and transition rate and transition probability calculations.

Another way to define the quantum yield of fluorescence, is by the rate of excited state decay:

Thus, if the rate of any pathway changes, both the excited state lifetime and the fluorescence quantum yield will be affected.

If the error rate is small enough, it is thought to be possible to use quantum error correction, which corrects errors due to decoherence, thereby allowing the total calculation time to be longer than the decoherence time.

# The rapid rate at which quantum descriptions become more complicated as the size of a system increases.

In July 2011, researchers from University of British Columbia and University of California, Santa Barbara were able to reduce environmental decoherence rate " to levels far below the threshold necessary for quantum information processing " by applying high magnetic fields in their experiment.

Many further results may be obtained, such as Fermi's golden rule, which relates the rate of transitions between quantum states to the density of states at particular energies, and the Dyson series, obtained by applying the iterative method to the time evolution operator, which is one of the starting points for the method of Feynman diagrams.

Now Fermi's golden rule gives a master equation for the average rate of quantum jumps from state α to β ; and from state β to α.

That these codes allow indeed for quantum computations of arbitrary length is the content of the threshold theorem, found by Michael Ben-Or and Dorit Aharonov, which asserts that you can correct for all errors if you concatenate quantum codes such as the CSS codes — i. e. re-encode each logical qubit by the same code again, and so on, on logarithmically many levels — provided the error rate of individual quantum gates is below a certain threshold ; as otherwise, the attempts to measure the syndrome and correct the errors would introduce more new errors than they correct for.

In quantum physics, Fermi's golden rule is a way to calculate the transition rate ( probability of transition per unit time ) from one energy eigenstate of a quantum system into a continuum of energy eigenstates, due to a perturbation.

In quantum mechanics, an adiabatic change is one that occurs at a rate much slower than the difference in frequency between energy eigenstates.

The opinion of the above mentioned relevant experts in the field of noise is that, until the publication rate on the non-existent quantum 1 / f noise effect stays around 1 paper / year, it is more economical to refer to the old denials than to write up new refusals.

At any rate, special relativity is not in conflict with quantum mechanics.