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Quantum simulators permit the study of quantum systems that are difficult to study in the laboratory and impossible to model with a supercomputer. In this instance, simulators are special purpose devices designed to provide insight about specific physics problems.〔 〕〔 〕〔 Note: This manuscript is a contribution of the US National Institute of Standards and Technology and is not subject to US copyright.〕 A universal quantum simulator is a quantum computer proposed by Richard Feynman in 1982.〔 〕 Feynman showed that a classical Turing machine would experience an exponential slowdown when simulating quantum phenomena, while his hypothetical universal quantum simulator would not. David Deutsch in 1985, took the ideas further and described a universal quantum computer. In 1996, Seth Lloyd showed that a standard quantum computer can be programmed to simulate any local quantum system efficiently. A quantum system of many particles is described by a Hilbert space whose dimension is exponentially large in the number of particles. Therefore, the obvious approach to simulate such a system requires exponential time on a classical computer. However, it is conceivable that a quantum system of many particles could be simulated by a quantum computer using a number of quantum bits similar to the number of particles in the original system. As shown by Lloyd, this is true for a class of quantum systems known as ''local'' quantum systems. This has been extended to much larger classes of quantum systems. Quantum simulators have been realized on a number of experimental platforms, including but not limited to systems of ultracold quantum gases, trapped ions, photonic systems and superconducting circuits. 〔(Nature Physics Insight – Quantum Simulation ). Nature.com. April 2012.〕 ==Solving physics problems== A trapped-ion simulator, built by a team that included the NIST and reported in April 2012, can engineer and control interactions among hundreds of quantum bits (qubits). Previous endeavors were unable to go beyond 30 quantum bits. As described in the scientific journal Nature, the capability of this simulator is 10 times more than previous devices. Also, it has passed a series of important benchmarking tests that indicate a capability to solve problems in material science that are impossible to model on conventional computers. Furthermore, many important problems in physics, especially low-temperature physics, remain poorly understood because the underlying quantum mechanics is vastly complex. Conventional computers, including supercomputers, are inadequate for simulating quantum systems with as few as 30 particles. Better computational tools are needed to understand and rationally design materials, such as high-temperature superconductors, whose properties are believed to depend on the collective quantum behavior of hundreds of particles.〔〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「quantum simulator」の詳細全文を読む スポンサード リンク
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