The double-slit experiment, which demonstrates the wave-particle duality of matter and light, can indeed be performed with specially prepared particles, such as single photons or electrons. These particles are often used in experiments because they are more easily controllable and their quantum nature is well-understood.
However, the wave-particle duality is not limited to these specially prepared particles. It is a fundamental concept of quantum mechanics that applies to all particles, including "ordinary" matter. In fact, experiments have demonstrated wave-like behavior even with macroscopic objects, such as large molecules or clusters of atoms.
The key point is that the wave-particle duality is a property inherent to quantum systems, regardless of their preparation or manipulation. It arises from the mathematical formalism of quantum mechanics, which describes the behavior of particles in terms of wavefunctions. The wavefunction of a particle represents a superposition of possible states, allowing for both wave-like and particle-like behavior.
In the case of the double-slit experiment, when particles are sent through two closely spaced slits onto a screen, an interference pattern is observed, characteristic of waves. This pattern emerges because the particle's wavefunction can interfere with itself, leading to regions of constructive and destructive interference. This behavior is not limited to specially prepared particles but is a consequence of the underlying quantum nature of matter and light.
While it is true that macroscopic objects in our everyday experience appear to exhibit purely classical behavior, this is due to a phenomenon called decoherence. Macroscopic objects interact with their environment and quickly lose their quantum coherence, making their wave-like behavior effectively undetectable at macroscopic scales. However, in carefully controlled experimental conditions, it is possible to observe quantum behavior in macroscopic systems as well.
Therefore, the wave-particle duality is a fundamental aspect of quantum mechanics that applies to all particles, including those in the "classical" world. While the behavior may be more easily observable and manipulated in specially prepared particles, the wave-particle duality remains a foundational principle that underlies our understanding of the quantum nature of matter and light.