Generating high-quality single photons for quantum computing

MIT researchers have designed a way to generate, at room temperature, more single photons for carrying quantum information. The design, they say, holds promise for the development of practical quantum computers.

New holographic technique opens the way for quantum computation

Photography measures how much light of different color hits the photographic film. However, light is also a wave, and is therefore characterized by the phase. Phase specifies the position of a point within the wave cycle ...

Quantum sensor for photons

A photodetector converts light into an electrical signal, causing the light to be lost. Researchers led by Tracy Northup at the University of Innsbruck have now built a quantum sensor that can measure light particles non-destructively. ...

Scientists connect quantum bits with sound over record distances

Scientists with the Institute for Molecular Engineering at the University of Chicago have made two breakthroughs in the quest to develop quantum technology. In one study, they entangled two quantum bits using sound for the ...

New insights into quantum measurements

Researchers from the University of Bristol have shed new light on the process of quantum measurement, one of the defining, and most quantum features of quantum mechanics.

Nanocomponent is a quantum leap for Danish physicists

University of Copenhagen researchers have developed a nanocomponent that emits light particles carrying quantum information. Less than one-tenth the width of a human hair, the miniscule component makes it possible to scale ...

New method enables quantum simulations on larger systems

Through randomly selected measurements, Austrian physicists can now determine the quantum entanglement of many-particle systems. With the newly developed method, quantum simulations can be extended to a larger number of quantum ...

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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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