Virtual state

In quantum physics, a virtual state is a very short-lived, unobservable quantum state.^[1]

In many quantum processes a virtual state is an intermediate state, sometimes described as "imaginary"^[2] in a multi-step process that mediates otherwise forbidden transitions. Since virtual states are not eigenfunctions of any operator,^[3] normal parameters such as occupation, energy and lifetime need to be qualified. No measurement of a system will show one to be occupied,^[4] but they still have lifetimes derived from uncertainty relations.^[5]^[6] While each virtual state has an associated energy, no direct measurement of its energy is possible^[7] but various approaches have been used to make some measurements (for example see^[8] and related work^[9]^[10] on virtual state spectroscopy) or extract other parameters using measurement techniques that depend upon the virtual state's lifetime.^[11] The concept is quite general and can be used to predict and describe experimental results in many areas including Raman spectroscopy,^[12] non-linear optics generally,^[5] various types of photochemistry,^[13] and nuclear processes.^[14]

See also

References

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