Switching quantum reference frames in the N-body problem and the absence of global relational perspectives

Understand

Given the importance of quantum reference frames (QRFs) to both quantum and gravitational physics, it is pertinent to develop a systematic method for switching between the descriptions of physics relative to different choices of QRFs, which is valid in both fields.

• Here we continue with such a unifying approach, begun in arxiv:1809.00556, whose key ingredient is a symmetry principle, which enforces physics to be relational.
• Thanks to gauge related redundancies, this leads to a perspective-neutral structure which contains all frame choices at once and via which frame perspectives can be consistently switched.
• Formulated in the language of constrained systems, the perspective-neutral structure is the constraint surface classically and the gauge invariant Hilbert space in the Dirac quantized theory.