# Outlook

How far quantum physics reaches into our macroscopic world is an open question. Until now, not a single known experiment contradicts the predictions of quantum physics.

As we humans see ourselves in a classical world, several theoretical models assume limits for the quantum superposition principle. Some relate this to the increasing complexity, but most on the increasing mass of the objects.

## The quantum nature of complex biological matter?

The complexity argument raises the question, if one could provide evidence or even usage of the quantum nature of biological matter. This question has a philosophical background and many opportunities for applications. Will we be able to show the wave nature of vitamins, amino acids, peptides, proteins or even self replicating structures such as plasmids or viroids? If yes, can we use the fine interference pattern to learn something about these objects – e.g. if we use interferometry in external electrical, optical or magnetic fields? Interferometric methods allow the measurement of very small interactions and serve a large potential as sensors. Such questions are currently studied in the ERC project Probiotiqus and the research platform QuNaBioS.

## Mass limits for quantum interference?

The mass argument is particularly interesting, as today, there is no unified theory of quantum physics and gravity. There are also elaborated mathematical models dealing with the possibility that the delocalization of massive objects would be reduced by random collapses of the wave function at a fixed rate (Continuous Spontaneous Localization, CSL). Such questions are currently being pursued in the EU project NanoQuestFit in close collaboration between theory and experiment. The experiments at the University Vienna currently  hold the mass record with $$m > 10’000 \, \mathrm{amu}$$ (in the year 2014).

## Challenges?

A particular practical challenge in the exploration of very massive quantum systems is their small de Broglie wavelength. The smaller the wavelength, the closer are the diffraction fringes. Recent interferometers at the Viennese laboratories are compatible with $$\lambda_{dB} \ge 200\, \mathrm{fm}$$. This is already 10.000 times smaller than the typical size of a single organic molecule. To keep the wavelength in this region, the molecular momentum $$p=h/\lambda_{dB}$$ needs to stay also in the region of $$p = 2\times 10^6\, \mathrm{amu\cdot m/s}$$.

An important step in the research is also the development of new sources and efficient detectors for slow, massive and mass selected, neutral molecules and nano particles; the theoretical description of these particles and their electrical, optical and magnetic properties; as well as the understanding of their quantum mechanical interactions with diffractive elements.

In any case, in this interdisciplinary research field, many synergies between quantum optics, synthetic chemistry, molecular biology and nanotechnology are arising.