## Quantum Seismology

## Quantum Clocks and Quantum Causality

Firstly, I will consider spatial interference of a “clock” – a time-evolving (internal) degree of freedom of a particle – that ticks at different rates in different regions of background space-time. While the “time as shown by the clock” is not a common parameter for different amplitudes in the superposition, there is still the notion of global time.

Secondly, I will introduce a quantum framework where no reference is made to any global time or causal order, and show that the framework allows for quantum correlations for which one cannot say that one event is taking place before or after another.

## Relativistic Quantum Clocks

In this talk, we discuss an implementation of the twin paradox in superconducting circuits with velocities as large as a few percent of the speed of light. Ultrafast modulation of the boundary conditions for the electromagnetic field in a microwave cavity simulates a clock moving at relativistic speeds. While previous demonstrations of this effect involve point-like clocks, our superconducting cavity has a finite length, allowing us to investigate the role of clock size as well as interesting quantum effects on time dilation. In particular, our theoretical results show that the travelling twin ages slower for larger cavity lengths and that quantum particle creation, known in this context as the dynamical Casimir effect, increases time dilation.

Finally, we will discuss how the accuracy of a clock is affected by the Dynamical Casimir Effect and other phenomena generated by relativistic motion.

## Non-perturbative cavity quantum electrodynamics: ultrastrong coupling and beyond

S. De Liberato, Phys. Rev. Lett. 112, 016401 (2014)

G. Scalari et al., Science 335,1323 (2012)