squeezedvacuum

A squeezed vacuum is a quantum mechanical state of the electromagnetic field that exhibits reduced quantum noise in one observable at the expense of increased noise in another, complementary observable. In quantum optics, this phenomenon is often discussed in terms of photon number and phase. A standard vacuum state, which is the lowest energy state of the electromagnetic field, has a certain amount of inherent quantum fluctuation in both its amplitude and phase. Squeezing modifies this relationship, often described by Heisenberg's uncertainty principle, which states that certain pairs of observables cannot be known with perfect accuracy simultaneously. By reducing the uncertainty in one observable, the uncertainty in its conjugate variable must increase. For the electromagnetic field, this means that if the amplitude (or photon number) is squeezed, the phase uncertainty increases, and vice versa. Squeezed vacuum states are typically generated using nonlinear optical processes, such as through a process called parametric down-conversion in a nonlinear crystal. These states have important applications in precision measurements, quantum information processing, and fundamental tests of quantum mechanics, as they can enable measurements below the standard quantum limit of sensitivity.