Field-theoretical space-time position operator of the Dirac electron
  A field-theoretical space-time position operator can be properly introduced for the Dirac field, it plays the role of a generalized Noether charge associated with a local symmetry, and its second-quantized form shows that quantum fields possess zero-point time, which implies that a zero-point fluctuation of energy must be accompanied with a zero-point fluctuation of time, and then in agreement with the time-energy uncertainty principle. In practice, some possible physical effects owing to zero-point time remain to be found. 
Zhi-Yong Wang, Cai-Dong Xiong, Bing He