Space-time density matrix for continuous variables
Tian Zhang, University of Oxford
In ordinary, non-relativistic quantum theory, especially in quantum information, space and time are treated differently. For example, time is a parameter rather than an operator; states are defined across the whole space but only at one time, and then evolve under the prescribed dynamics. These go against our intuition from relativity. Thus, space-time density matrices have been introduced and here we discuss one of these formulations called pseudo-density matrix (PDM) which treats space and time indiscriminately.