Is it correct to visualize the vacuum as the superposition of various quantum fields (photonic field, electronic field, etc.) in the ground state with each quantum field producing a quantum particle (photons, electrons, etc.) when excited?

We should establish some terminology. The vacuum is the state of lowest energy density of a quantum field theory - it is synonymous with the ground state in ordinary quantum mechanics. In quantum field theories, what were classical fields become instead field operators. This means roughly that the coefficients of the Fourier expansion of the fields are promoted to operators which do not commute with each other. In general, the field operators are operators on a linear space. The Fourier coefficients of the classical fields thus become operators which do not commute, and certain combinations of these operators will act to create, or to destroy, particles in the vacuum. So particles are the quanta of fields. They are created by the action of the creation and annihilation operators on the vacuum, and these operators in the classical theory were just the amplitudes of certain normal mode oscillations of the fields. If the field theory is weakly interacting, then you can imagine that the vacuum state is simply one that is empty of all quanta of the fields - it has no particles in it, and it is a simply a direct product of the vacuum states for all of the interacting fields in the theory. QED at low energies is an example of this type of theory. Excited states become a bit mixed up a bit when you have a state in which a few electrons and photons are interacting with each other. But basically the electron and photon catch the idea of what is going on. But if the theory is strongly interacting, then things become much more complicated - it may even be that the fields which are used to create the perturbative vacuum, when expanded into creation and annihilation operators,  do not create particles that can propagate freely to infinity ... in this case the degrees of freedom in the imaginary perturbative vacuum do not exist in the theory, because the interactions are so strong that they don't allow the particles to escape. So in such a theory, the vacuum structure is much more complicated. And there are such theories which seem to describe the world, QCD being an example .... quarks are the natural quanta of the fields which emerge from the Fourier expansion of the classical fields. The actual vacuum state of QCD is not known, though many physicists have made attempts to describe it: Ken Johnson being among my favorites. Yet the particles corresponding to the original field operators in QCD can't propagate to infinity, because the interactions with the gluon fields are too strong. The quarks are confined and don't propagate to infinite distances ... instead the theory forms new degrees of freedom that can propagate out to infinity. So the vacuum structure of a quantum field theory can be more complicated than what you suggest.

I'm not sure I'm with your term "quantum field". AIUI the fields themselves are not quantised but pervade space to a degree dependent on the type of field in question. To obtain a particle from a field you have to excite it above the level necessary to bring a particle into being, in other words a quantum. So by energising the Higgs field above a certain level you can obtain a Higgs particle. The energy necessary to cause the particle to appear closely defines the particle in question. Provably the electromagnetic field pervades all space and the photons from the big bang detected by COBE show that must be so. Presumably other fields (if there are other fields and not other manifestations of the same field) permeate all space in a similar way. I find it healthy to remind oneself that these are mathematical models which many times give accurate results. As to whether they help describe the system under consideration is open to question. After all, the average American family once upon a time had 2.4 children. Sounds nonsense looked at from an absolutist perspective, but gave undeniably useful results. For a really quality grasp of the issues, get a copy of Feynman's lectures. His ability to describe a mathematical concept in system's terms was, simply, unbelievable. When he'd finished even I thought I understood.

and pretty much! Of course, David's was a detailed explanation  Even though I haven't studied Quantum Field Theries and Quantum Mechanics very much but both their answers made quite a lot of sense. Sorry I'm not quite qualified enough to write this answer! Thanks for A2A Edward!

My best answer is that you should read http://plato.stanford.edu/entries/quantum-field-theory/ and if you come away fully understanding it and able to answer your question definitively, then please tell me what the answers are. :-)

It's been 2500 years since the fakers are trying to ban the vacuum to be empty! If this is the vacuum is that it is empty. If they want to reinvent a kind of ether or other lucubrations, they stop using the word "vacuum"! The fundamentals from which this science is demonstrated are either called definitions somehow; or axioms and postulates (that) are by no one not conceded. And these I treat forthwith. Definitions The names, quantity, duration. and space, are known for as much as they are able to be defined by other names. Def. 1: Place is part of space which things fill evenly. Def. 2: Body is that which fills place. Def.3: Rest is remaining in the same place. Def. 4: Motion is change of place. NOTE: I have said that body fills place; that is that it so fills it that another thing of the same kind or some other body is completely excluded, forasmuch as it is impenetrable. Let it be, however, that place is called the part of space in which things inhere evenly, but so far as here bodies and not penetrable things are being examined, I have chosen to define (that to be) a part of space which something fills.