Atoms up! A heated quantum system can be used as a universal probe for exotic states of matter

From Pythagoras’ work on harmonics to the identification of the Balmer series in atomic physics, the quantization of physical observables plays a central role in our understanding and appreciation of the world around us.

Research supported by the EU has predicted a novel form of quantization involving the heating rate of a quantum system upon external shaking. Published in the journal ‘ScienceAdvances’, the paper ‘Probing topology by “heating”: Quantized circular dichroism in ultracold atoms’, sets out what the authors call an ‘intriguing manifestation of topology’.

To communicate their work, researchers put forward the following analogy: when an ice cube is placed in a microwave oven the water molecules are excited. This causes the ice to melt progressively and it passes through phases from solid to liquid. During the heating process the number of molecules that form the ice decrease over time. This process can be quantified by a heating rate. The research set out in the paper indicates that, in specific circumstances, such heating rates must satisfy an elegant and precise quantization law.

They show that when a physical system is heated up in a controlled manner, particles are ejected from the topological phase (in direct analogy with the melting of ice described above) and the corresponding heating rate demonstrably satisfies a novel quantization law. A crucial aspect of this novel quantization law is that it is dictated by the topological nature of the initial phase of the system.

Building on their universal nature, topological properties are currently studied in broad context, ranging from ultracold atomic gases and photonics to mechanical systems. These complementary and versatile domains offer the possibility of revealing unique topological properties, such as those emanating from engineered dissipation and other controllable interactions. For example, ultracold gasses have been explored by visualising the transverse displacement of an atomic cloud in response to an applied force.

The research conducted by the TOPOCOLD project, working under the auspices of the EU-funded UQUAM project, has fed into the findings presented in the paper, the most important of which is that depletion rate of filled Bloch bands can satisfy a quantization law imposed by topology.

The team maintains that the depletion rate measurements are a powerful and universal probe for topological order in quantum matter due to the quantized effect. Their results point to the need to isolate the bulk response from any detrimental effects associated with the edge mode, which is where ultracold atom setups come into play. The authors propose the use of a physical platform consisting of an ultracold gas of atoms trapped in an optical lattice (a periodic landscape created by light). Such setups are known to constitute an ideal toolbox for the quantum engineering of topological matter and for implementing new types of measurements.

Support to TOPOCOLD (Manipulation of topological phases with cold atoms) is helping to identify realistic, optical-lattice setups hosting novel topologically-ordered phases, based on those technologies that are currently developed in cold-atom experiments. UQUAM (Ultracold Quantum Matter), gather together researchers with well-recognised and complementary expertise in the domains of quantum optics, atomic and condensed matter physics, and information science. Their goal is to take the interdisciplinary field of quantum technologies further, by taking advantage of the most recent spectacular advances in the control of ultracold atomic and molecular systems.

For more information, please see:
TOPOCOLD CORDIS project web page
UQUAM CORDIS project web page
UQUAM project website