In quantum mechanics, an electron in a superposition state exists in multiple possible states simultaneously until a measurement collapses it into a definite state. However, the concept of mass remains well-defined even in superposition.
The mass of an electron is an intrinsic property, meaning it does not change whether the electron is in a definite state or a superposition state. Unlike position or momentum, which can be in a probabilistic combination of values, mass remains constant at approximately 9.109 × 10-31 kg.
In cases involving relativistic quantum mechanics, such as in quantum field theory, mass arises from interactions with the Higgs field, which does not depend on the state of superposition. Therefore, an electron in superposition retains its fundamental mass, even though its other properties (like position and momentum) may be indeterminate.
Just like charge, the mass of an electron remains well-defined even when the electron is in a superposition state. Mass is a fundamental property of the electron, and it does not become "spread out" or uncertain due to superposition, just as charge does not.
Even if an electron exists in a superposition of different positions, momenta, or energy states, each possible outcome still corresponds to an electron with the same intrinsic mass (me). This is because mass, like charge, is a conserved quantity in quantum mechanics and is not subject to quantum uncertainty in the same way as position or momentum.
However, in certain relativistic and quantum field theory contexts (such as in interacting quantum fields or virtual particles in quantum electrodynamics), the concept of "effective mass" can change due to interactions with the vacuum or external fields. But for a free electron in superposition, its rest mass remains constant at approximately 9.109 × 10-31 kg.