In quantum field theory (QFT), the concept of particles existing in multiple states simultaneously is accommodated through the framework of superposition. Superposition is a fundamental principle in quantum mechanics that allows a quantum system, such as a particle, to exist in a combination of different states until a measurement is made.
In QFT, particles are described as excitations or disturbances in their respective quantum fields. Each type of particle corresponds to a specific quantum field, and the field can be in a superposition of different states. For example, in the case of a photon, which is a quantum of light, it is associated with the electromagnetic field.
According to the principles of QFT, particles are created and annihilated by interactions with their respective fields. When a measurement is made, the system collapses into one of the possible states, or eigenstates, associated with the observable being measured. Until that measurement occurs, the particle can exist in a superposition of these eigenstates, each with a certain probability amplitude.
The superposition principle allows for interference effects between different states. This interference can result in phenomena such as wave-particle duality and the famous double-slit experiment. It is through the combination of superposition and interference that QFT provides a framework to describe the behavior of particles existing in multiple states simultaneously.
It's important to note that the notion of particles existing in multiple states simultaneously should not be confused with the idea of particles being in multiple places at the same time. Rather, it refers to the particle being in a superposition of different states until a measurement is made, at which point it is found in one of those states with a certain probability. The actual observation collapses the superposition into a definite state.