Topological nanoelectronics

Topological insulators are materials with astonishing properties: Electric current flows only along their surfaces or edges, whereas the interior of the material behaves as an insulator. In 2007, Professor Laurens Molenkamp ...

Small magnets reveal big secrets

An international research team led by a physicist at the University of California, Riverside, has identified a microscopic process of electron spin dynamics in nanoparticles that could impact the design of applications in ...

Building single-atom qubits under a microscope

Our team at IBM Research made a breakthrough in controlling the quantum behavior of individual atoms, demonstrating a versatile new building block for quantum computation.

Extracting hidden quantum information from a light source

Current super-resolution microscopes or microarray laser scanning technologies are known for their high sensitivities and very good resolutions. However, they implement high light power to study samples, samples that can ...

A cavity leads to a strong interaction between light and matter

Researchers have succeeded in creating an efficient quantum-mechanical light-matter interface using a microscopic cavity. Within this cavity, a single photon is emitted and absorbed up to 10 times by an artificial atom. This ...

Tunable optical chip paves way for new quantum devices

Researchers have created a silicon carbide (SiC) photonic integrated chip that can be thermally tuned by applying an electric signal. The approach could one day be used to create a large range of reconfigurable devices such ...

Introducing quantum convolutional neural networks

Machine learning techniques have so far proved to be very promising for the analysis of data in several fields, with many potential applications. However, researchers have found that applying these methods to quantum physics ...

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Quantum information

In 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.

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