No quantum systems is entirely isolated from its environment. This basic yet important fact is ultimately responsible for classical features to emerge in quantum systems. We work on how such classical features arise and can lead to exact instances of decohering systems. We are also interested in the mathematical foundations of the study of the dynamics of open quantum systems related to the theory of dynamical semi-groups, asking, for example, for the precise degree of Markovianity of quantum dynamics. A core interest in the context of quantum systems interacting with complex baths is the study of quantum "mechanical" effects in opto-mechanical systems that are cooled by means of exploiting radiation pressure. We think of probing actual quantum effects in such exciting mechanical systems.

**Selected group publications**

- Observation of non-Markovian micro-mechanical Brownian motion

Nature Communications 6, 7606 (2015) - Cooling by heating

Physical Review Letters 108, 120602 (2012) - A positive tensor network approach for simulating open quantum many-body systems

Physical Review Letters 116, 237201 (2016) - The complexity of relating quantum channels to master equations

Communications of Mathematical Physics 310, 383 (2012) - Assessing non-Markovian dynamics

Physical Review Letters 101, 150402 (2008) - Gently modulating opto-mechanical systems

Physical Review Letters 103, 213603 (2009) - Creating and probing macroscoping entanglement with light

Physical Review Letters 99, 250401 (2007) - Towards mechanical entanglement in nano-electromechanical devices

Physical Review Letters 93, 190402 (2004) - Exact decoherence to pointer states in free open quantum systems is universal

Physical Review Letters 92, 210401 (2004) - Hot entanglement in a simple dynamical model

Journal of Modern Optics 50, 881 (2003) - Quantum and classical correlations in quantum Brownian motion

Physical Review Letters 89, 137902 (2002) - Extracting dynamical equations from experimental data is NP-hard

Physical Review Letters 108, 120503 (2012) - Entanglement of nanoelectromechanical oscillators by Cooper-pair tunneling

Physical Review B 88, 035441 (2013)