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A plain lowercase a, removing one quantum.
Also known as: Lowering operator, Destruction operator, Annihilation operator
The annihilation operator lowers a state by one quantum, and applied to the vacuum it gives zero rather than a negative-occupancy state. That single property is what defines the vacuum in quantum field theory.
Denotes the annihilation operator, lowering a quantum state's occupation number by one.
Contexts: Laboratory
Annihilates the vacuum state — gives zero rather than an unphysical result — which is how the vacuum is defined operationally.
Contexts: Laboratory
A plain italic lowercase letter a, a bowl with a vertical stroke on its right.