Modelling Open Quantum Systems - Perspectives and Challenges

Dr. Gernot Schaller (FWZ)

2022, December 13th

The promise of the gate model of quantum computation is that by perfectly controlling many-qubit quantum systems, one can perform certain computational tasks with unprecedented speed. For imperfect control however, the quantum (computing) system becomes quickly entangled with the uncontrollable environment, and the computational advantage is turned into the exact antipode by decoherence. I will discuss our mathematical tools for treating the dynamics of open quantum systems with some focus on the numerical challenges arising from the exponential scaling of complexity with the number of qubits.

Despite the complexity, one can show that reservoirs in thermal equilibrium tend to thermalize the quantum system, explaining their detrimental influence on quantum computers. As a possible remedy, I will review the adiabatic model of quantum computation, where this property can turn out to be an advantage rather than an obstacle.

Furthermore, if one can couple the open quantum system to multiple reservoirs, one may exploit quantum benefits in heat engines, which I will discuss at the example of a collective quantum absorbtion refrigerator.