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In quantum physics, the squeeze operator for a single mode of the electromagnetic field is
where the operators inside the exponential are the ladder operators. It is a unitary operator and therefore obeys S S † = S † S = 1 ^ {\displaystyle SS^{\dagger }=S^{\dagger }S={\hat {1}}} , where 1 ^ {\displaystyle {\hat {1}}} is the identity operator.
Its action on the annihilation and creation operators produces
The squeeze operator is ubiquitous in quantum optics and can operate on any state. For example, when acting upon the vacuum, the squeezing operator produces the squeezed vacuum state.