In this review we present the problem of time in quantum physics, including a short history of
the problem and the known objections about considering time as a quantum observable …

In physics, every observation is made with respect to a frame of reference. Although
reference frames are usually not considered as degrees of freedom, in all practical situations …

All physical observations are made relative to a reference frame, which is a system in its own
right. If the system of interest admits a group symmetry, the reference frame observing it must …

Treating reference frames fundamentally as quantum systems is inevitable in quantum
gravity and also in quantum foundations once considering laboratories as physical systems …

We develop an operational framework, combining relativistic quantum measurement theory
with quantum reference frames (QRFs), in which local measurements of a quantum field on …

We describe a completely general and fully non-perturbative framework for constructing
dynamical reference frames in generally covariant theories, and for understanding the …

Experiments are beginning to probe the interaction of quantum particles with gravitational
fields beyond the uniform-field regime. In nonrelativistic quantum mechanics, the …

One of the most basic notions in physics is the partitioning of a system into subsystems and
the study of correlations among its parts. In this Letter, we explore this notion in the context of …

In general relativity, the description of spacetime relies on idealised rods and clocks, which
identify a reference frame. In any concrete scenario, reference frames are associated to …

We challenge the view that there is a basic conflict between the fundamental principles of
Quantum Theory and General Relativity and, in particular, the fact that a superposition of …