Doblesplitteksperimentet

Doblesplitteksperimentet, commonly known in English as the double-slit experiment, is a foundational demonstration in quantum mechanics that reveals the wave–particle duality of light and matter. It shows that particles can display interference when not observed in a way that determines their path, illustrating the superposition principle at the heart of quantum theory.

Origin and setup: The earliest form was demonstrated by Thomas Young in 1801 using light and two closely spaced slits, producing an alternating pattern of bright and dark fringes on a screen. In modern versions, particles such as electrons, atoms, or molecules pass one at a time through two slits, and over many trials the detection pattern forms an interference figure, implying wave-like behavior of individual particles.

Key findings: When both slits are open and no measurement provides which-path information, the probability distribution on the detection screen shows interference. If a measurement determines through which slit a particle passes, the interference disappears and the pattern becomes a sum of two single-slit distributions, revealing particle-like behavior.

Variants and implications: Delayed-choice and quantum eraser variants test the role of measurement in real time and show that the interference pattern can be restored by erasing which-path data under certain conditions. The experiment underpins core quantum concepts such as superposition, complementarity, and the probabilistic nature of the theory; it has influenced interpretations of quantum mechanics and the development of quantum optics and quantum information.

Applications: The core ideas inform experimental techniques in interferometry, precision measurement, and studies of quantum coherence across photons, electrons, atoms, and larger molecules.