New protocol to identify charges in quantum systems

22 May 2018

The increasing miniaturisation of electronic chips is enabling a technological revolution, exemplified in a growing number of applications, from powerful mobile phones to the internet of things. But as the components of our electronic devices become smaller and smaller, we need to use the unintuitive laws of quantum physics to understand their behaviour and predict, for instance, how much heat a small quantum machine will generate when driven at maximum power. Things can get event stranger when dealing with quantum systems that feature some additional conserved charges (say, spin or the number of photons). In general, it is very difficult to know how many of these ‘charges’ a quantum system has, which makes predicting their dynamics a difficult task.

A team of researchers led by Dr Mur-Petit from the Department of Physics at Oxford, in collaboration with colleagues at Complutense University in Madrid and the Institute for the Structure of Matter of the Spanish National Research Council (CSIC), have developed a set of mathematical laws –known as quantum fluctuation relations– that enable to reveal conserved charges in a quantum system. This will enable to understand how energy or current flow and fluctuate in such small quantum systems, and thus will contribute to a better modelling and improved design of new micro- and nano-meter sized devices where the interplay of thermal and quantum effects is paramount.

The researchers accompany their derivations with computer simulations that highlight the importance of these results to get accurate temperature measurements of strongly-interacting quantum systems, which is a difficult task facing the field of quantum simulations. Because of this, the researchers expect their findings will lead to new insights into long-standing questions on the relaxation and thermalisation of quantum systems.

Figure caption:
Sketch of the experimental setup proposed: a string of atoms (orange circles) is trapped by electromagnetic fields (generated by the grey endcaps). A pair of lasers (blue and red arrows) coupled the internal state of the ions to their motion in the trap (black double-headed arrows). The amplitude and fluctuations of the oscillations of the ions’ positions caused by changing the laser intensities are governed by the laws derived by the researchers. (Figure adapted from Mur-Petit et al., Nature Communications, DOI: 10.1038/s41467-018-04407-1.)

Publication reference:
J. Mur-Petit, A. Relaño, R. A. Molina, & D. Jaksch. “Revealing missing charges with generalised quantum fluctuation relations.” Nature Communications 9, 2006 (2018). DOI: 10.1038/s41467-018-04407-1