1. Quantum physics beneath the everyday world

A quantum object can be described as a combination of possible states until a measurement produces a definite result. This idea, called superposition, makes quantum predictions probabilistic rather than simply uncertain—and gives quantum computing its unusual approach to information.

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Particles can sometimes cross barriers that classical physics says they should not pass. Quantum tunneling helps nuclear reactions occur in stars and plays a role in semiconductor devices and microscopes that can map individual atoms.

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Entangled particles have measurement results linked more strongly than ordinary objects allow, even when separated. Entanglement cannot send messages faster than light, but it can support secure communication, precise sensing, and new kinds of computation.

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Quantum ideas already power lasers, computer chips, solar cells, atomic clocks, and parts of medical imaging. Physicists, engineers, chemists, materials scientists, and software researchers use them in laboratories, manufacturing, energy research, sensing, and quantum technology projects.

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