On-demand, photonic entanglement synthesizer

Quantum information protocols are based on a variety of entanglement modes such as Einstein-Podolsky-Rosen (EPR), Greenberger-Horne-Zeilinger (GHZ) and other cluster states. For on-demand preparation, these states can be ...

Generating multiphoton quantum states on silicon

In a recent study now published in Light: Science & Applications, Ming Zhang, Lan-Tian Feng and an interdisciplinary team of researchers at the departments of quantum information, quantum physics and modern optical instrumentation ...

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 ...

18-qubit entanglement sets new record

Physicists have experimentally demonstrated 18-qubit entanglement, which is the largest entangled state achieved so far with individual control of each qubit. As each qubit has two possible values, the 18 qubits can generate ...

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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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