A microscopic understanding of quantum systems is crucial for their engineering. Detailed knowledge about the interactions within a system as well as its coupling to external fields can provide opportunities for accurate quantum state manipulation and quantum sensing. We are interested in the microscopic description of various few-body systems which can serve as the building blocks of future quantum devices.
One example of a highly controllable quantum system are atoms, molecules and ions cooled to near absolute zero temperatures. Under such conditions the thermal fluctuations in the system are weak and quantum effects have a prominent role. Importantly, the interactions in the system can be tuned using external electromagnetic fields, e.g. by means of Fano-Feshbach resonances. Building on the properties of two-body scattering as well as the structure of few-body states, we design protocols for implementation of entangling quantum gates and derive the effective description of many-body systems with ultracold constituents. Tuning the range, strength and anisotropy of the interactions can lead to new exotic phases of matter as well as a better understanding of theoretical concepts by means of quantum simulations.
In particular, hybrid systems of cold and trapped atoms and ions can be a useful experimental platform for specific applications. For instance, a single ion immersed in a quantum degenerate gas captures the physics of polarons in the strong coupling regime. Precise manipulation of the quantum state of the ion-atom pair enables the creation of cold molecular ions and their precise spectroscopy in the ion trap which can potentially provide insight into the physics beyond the Standard Model. We are exploring the control possibilities in such systems under realistic conditions as well as designing experimental proposals for using them for quantum technological purposes.
Another example of a highly controllable quantum system that we investigate along this line of research are nitrogen-vacancy (NV) centers in diamond. Here, implanting a nitrogen atom into the crystal structure of a nano-diamond creates a defect with a free electron and surrounding nuclear spins that can be manipulated with lasers and electromagnetic fields in the radio-frequency and microwave domain. NV-centers in diamond offer a perfect playground to investigate the interaction of a controllable quantum system with its environment.
Various control pulses acting on the system and/or its environment allow to tune the system-environment interaction. In particular, NV-centers in diamond are a leading platform in the field of quantum sensing: A specific set of quantum states are chosen as system (sensor) that interacts with the environment in a desired (signal) and undesired, deleterious (noise) way. To engineer the quantum sensor, one has to tune the system-environment interaction such that the noise-generating part of the environment is suppressed (i.e. decoupled) and that the interaction with the signal is enhanced. We apply methods of quantum optimal control and dynamical decoupling to achieve the desired effects and collaborate with different experimental groups to test our solutions, especially within the EU Quantum flagship project ASTERIQS.