Seminars from 2014

We will explore a quantum mechanical method of detecting weak vibrational disturbances inspired by the protocol of entanglement farming, which is itself inspired in the harvesting of entanglement from the vacuum state of a quantum field. This setup consists of inherently non-relativistic quantum optics elements, where small relativistic effects (which are usually neglected) build up to give a non-negligible effect over long times. We will comment on the sensitivity of the setup and its prospects to be used in different fields from seismology to gravitational wave detection.

Quantum physics differs from classical physics in that no definite values can be attributed to observables independently of the measurement context. However, the notion of time and of casual order preserves such an objective status in the theory: all events are assumed to be ordered according to “time flow” such that every event is either in the future, in the past or space-like separated from any other event. The possible interplay between quantum mechanics and general relativity may, however, require superseding such a paradigm. I will approach this problem in two step.

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.

Time dilation, a striking prediction of Einstein’s relativity, plays an important role in applications such as the Global Positioning System. One of the most compelling consequences of time dilation is known as the twin paradox, where a twin at rest ages more than her sibling travelling at relativistic speeds.

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.

Cavity quantum electrodynamics (CQED) studies the interaction of light and matter in confined geometries. Improvements both in the photonic confinement and in the emitter design have led to a steady increase in the strength of the light-matter coupling in CQED experiments. This has allowed to access interaction-dominated regimes, in which many fascinating non-perturbative physical phenomena become observable: from quantum vacuum radiation to quantum phase transitions. After a general introduction to CQED, I will introduce some of these fascinating phenomena and I will give an overview of the experimental efforts that are been conducted to observe them.

S. De Liberato, Phys. Rev. Lett. 112, 016401 (2014)
G. Scalari et al., Science 335,1323 (2012)