Research provides speed boost to quantum computers

A new finding by researchers at the University of Chicago promises to improve the speed and reliability of current and next generation quantum computers by as much as ten times. By combining principles from physics and computer ...

'Featherweight oxygen' discovery opens window on nuclear symmetry

Researchers at Washington University in St. Louis have discovered and characterized a new form of oxygen dubbed "featherweight oxygen"—the lightest-ever version of the familiar chemical element oxygen, with only three neutrons ...

Matter waves and quantum splinters

Physicists in the United States, Austria and Brazil have shown that shaking ultracold Bose-Einstein condensates (BECs) can cause them to either divide into uniform segments or shatter into unpredictable splinters, depending ...

Immunizing quantum computers against errors

Building a quantum computer requires reckoning with errors—in more than one sense. Quantum bits, or "qubits," which can take on the logical values zero and one simultaneously, and thus carry out calculations faster, are ...

A faster method to read quantum memory

The potential computing revolution that quantum computers have long promised is based on their weird property called superposition. Namely, qubits can take both logical states 0 and 1 simultaneously, on top of any value in ...

Near ground-state cooling of 2-D trapped ion crystals

Researchers have been trying to cool macroscopic mechanical oscillators down to their ground state for several decades. Nonetheless, past studies have merely attained the cooling of a few selected vibrational modes of such ...

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Quantum state

In quantum physics, a quantum state is a mathematical object that fully describes a quantum system. One typically imagines some experimental apparatus and procedure which "prepares" this quantum state; the mathematical object then reflects the setup of the apparatus. Quantum states can be statistically mixed, corresponding to an experiment involving a random change of the parameters. States obtained in this way are called mixed states, as opposed to pure states, which cannot be described as a mixture of others. When performing a certain measurement on a quantum state, the result generally described by a probability distribution, and the form that this distribution takes is completely determined by the quantum state and the observable describing the measurement. However, unlike in classical mechanics, the result of a measurement on even a pure quantum state is only determined probabilistically. This reflects a core difference between classical and quantum physics.

Mathematically, a pure quantum state is typically represented by a vector in a Hilbert space. In physics, bra-ket notation is often used to denote such vectors. Linear combinations (superpositions) of vectors can describe interference phenomena. Mixed quantum states are described by density matrices.

In a more general mathematical context, quantum states can be understood as positive normalized linear functionals on a C* algebra; see GNS construction.

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