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QI: Fachverband Quanteninformation

QI 6: Poster I (joint session QI/Q)

QI 6.7: Poster

Montag, 6. März 2023, 16:30–19:00, Empore Lichthof

What channels can be implemented without a reference frame? — •Fynn Otto — University of Siegen, Germany

Quantum reference frames are needed for communication tasks for which the method of information encoding matters. In contrast to – for example – sending integers, reference frames are needed for communicating, e.g. quantum phases or directional information. Even if a classical communication link between two parties is established, it is not possible to send a direction in space.

Lacking a reference frame limits the set of operations that can be performed deterministically. Changing reference frames is equivalent to the passive evolution of a state under the unitary operator U(g) , representing the transformation g . The transformations between reference frames form a group G , and allowed frame-agnostic channels turn out to be G -covariant: the channel E must commute with every U(g).

Here we investigate the reachable states for two important cases: lacking a phase reference (corresponding to the group G=U(1) ) and lacking a Cartesian frame alignment (G=SU(2) ). Examples of G-covariant state transformation are provided along with possible classification and interpretation of the reachability structure.