请您介绍一下量子力学的基本概念，包含3个要点，每个要点位于不同的段落，并且全部小写，禁用任何特殊符号和数值。
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quantum mechanics is a fundamental theory in physics

it describes nature at the smallest scales such as atomic and subatomic levels

the theory introduces the concept of wave-particle duality and the uncertainty principle
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