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Zenith Grant Awardee

Caslav Brukner

Institute for Quantum Optics and Quantum Information (IQOQI)

Project Title

Agents in superpositions: the covariance of physical laws in quantum reference frames

Project Summary

In our laboratories, we perform experiments with single quantum particles which can be in a superposition of different states or entangled with other particles, showing features which are strikingly different to the classical world. What would be the description of the world, if we could "sit" on a particle that is in a superposition state with respect to the laboratory frame of reference? The relational approach to physics suggests that the description from such a "quantum reference frame" is exactly the opposite: while for itself, the particle appears classical, it is the laboratory that is in a quantum superposition of states. In the current project, we aim at developing a quantum theory framework for a "quantum agent" that is "attached" to a quantum particle or a quantum field. The working hypothesis of the project is that although the features of observed systems – such as entanglement and superposition – are agent-dependent, the physical laws themselves remain the same for all agents (i.e. are invariant under the transformation between quantum reference frames).

Technical Abstract

In physics, every observation is made with respect to an agent residing in a frame of reference. Although reference frames are usually considered to be abstractions, they are in practice physical systems which obey the laws of physics. If a quantum system is considered as a reference frame, which description of the world would an agent attached to such "quantum reference frame" (QRF) give? In the current project, we will develop an operational quantum framework for an agent acting in and observing from a QRF. In particular, we will introduce transformations that lead to a generalization of the notion of covariance of dynamical laws of physics under the change between QRFs, which we will explore in the case of "superpositions of Lorentz boosts" and apply to explore the spin-momentum entanglement of a relativistic particle. We will also analyse the Unruh effect from a reference frame in a "superposition of accelerations" with respect to an inertial agent. Finally, we expect to gain new insights in the famous Wigner thought experiment by finding the transformation that makes it possible to switch between the perspectives of Wigner and Wigner’s friend.

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