General relativity and quantum theory differ profoundly in both structure and interpretation. While each has been tested to high precision in its own regime, gravitational effects in current quantum experiments are still described by the Newtonian limit, and precision tests of general relativity remain classical. Understanding regimes in which both theories are simultaneously required is therefore of fundamental importance.

Our group investigates this interplay from several directions. We predicted novel quantum effects of relativistic time dilation in interference experiments with quantum clocks, whose internal dynamics provide an operational notion of time. For sufficiently large systems, these effects give rise to an effective decoherence mechanism, already relevant at low energies and in Earth’s gravitational field.

We also study table-top probes of phenomenological quantum-gravity models, including scenarios with modified canonical commutation relations. In addition, we have analysed gedanken experiments showing that, to avoid signaling or violations of complementarity, a quantum superposition of a Newtonian-like gravitational field must be accompanied by the quantum radiation field of gravity. This suggests that retaining the former without the latter is not consistent.

Further Reading:

1. M. Zych, F. Costa, I. Pikovski, Č. Brukner, Quantum interferometric visibility as a witness of general relativistic proper time, Nature Communication 2:505 doi: 10.1038/ncomms1498 (2011).

2. I. Pikovski, M. R. Vanner, M. Aspelmeyer, M. S. Kim and Č. Brukner, Probing Planck-scale physics with quantum optics, Nature Physics 8, 393–397 (2012).

3. I. Pikovski, M. Zych. F. Costa, C. Brukner, Universal decoherence due to gravitational time dilation, Nature Physics 11, 668–672 (2015).

4. M.  Zych, F. Costa, I. Pikovski, T. C. Ralph and Č. Brukner, General relativistic effects in quantum interference of photons, Class. Quantum Grav. 29 224010 (2012).

5. A. Belenchia, R. M. Wald, F. Giacomini, E. Castro-Ruiz, Č. Brukner and M. Aspelmeyer, Quantum superposition of massive objects and the quantization of gravity, Phys. Rev. D 98, 126009 (2018).

6. M. Zych, F. Costa, I. Pikovski, Č. Brukner, Quantum Complementarity Meets Gravitational Redshift, (at www.2physics.com).

7. I. Pikovski, M. Zych, F. Costa, Č. Brukner, How Time Dilation Affects Quantum Superpositions, (at www.2physics.com).

8. Steven K. Blau An optical probe of quantum gravity?, Physics Today (May 2012).