We show how to reliably encode quantum information and send it between two arbitrary generalrelativistic observers without a shared reference frame. Information stored in a quantum field will inevitably be destroyed by an unknown Bogolyubov transformation relating the observers. However certain quantum correlations between different, independent fields will be preserved, no matter what transformation is applied. We show how to efficiently use these correlations in communication between arbitrary observers. -Introduction. The central question of the quantum information theory: how to reliably encode, send and decode information In this work we propose a general method of overcoming the problems of mutual communication with quantum states between two observers without a shared reference frame. When one party wishes to send a quantum state to the other, the state becomes distorted due to relative motion. However, following the idea of Ref. [5] we note that any type of motion affects states of all quantum fields in an analogous way. Consider a number of independent, non-interacting quantum fields. Although the states of individual fields will be affected by the relative motion in a certain way, some correlations between different fields will remain unaffected. Therefore if the sender and the receiver have access to at least two independent quantum fields, they can securely encode information into correlations between the fields and such information will not be affected by their relative motion. We show how the ability to create and measure these correlations allows the observers to reliably communicate even without sharing a common reference frame. The same method finds application also in more general schemes. For example, this approach can be applied to dynamical space-times that are asymptotically flat, such as the scenario of a collapsing star forming a black hole or an expanding universe modeled by Robertson-Walker space-time The idea presented in this work is closely related to the common concept of decoherence-free subspaces used in non-relativistic quantum information to avoid or at least minimize the effect of correlated noise onto communication -The model. In quantum field theory any change of the coordinate system, for example due to motion of the observer, leads to a certain transformation of all quantum state
