According to our current understanding in quantum field theory, the quantum fields themselves exist regardless of whether they are manifesting particles or not. The quantum fields are fundamental entities that permeate all of space and time.
In quantum field theory, particles are viewed as excitations or disturbances in their respective quantum fields. These fields are associated with specific types of particles, such as the electron field or the photon field. When a particle is "manifested," it corresponds to a localized and quantized excitation of its associated field.
However, even in the absence of particles, the fields still exist and are in a state of what we call the vacuum state. The vacuum state is not a state of nothingness but rather the lowest energy state of the fields. It is a highly dynamic state where particles and antiparticles continuously emerge from and annihilate back into the vacuum.
So, in essence, the quantum fields are always present, even when they are not manifesting particles. They are an inherent part of our current understanding of the fundamental structure of the universe.