My research is on quantum information science and its connections to other fields like the foundations of quantum mechanics, information theory, complexity theory, quantum field theory, quantum thermodynamics and quantum gravity. I have extensively contributed to the areas of quantum cryptography, entanglement theory, Bell inequalities, reconstructions of quantum theory and nano-scale thermodynamics. The following is a selection of my most relevant scientific contributions.
- All entangled states constitute useful resources for information processing tasks like teleportation, Bell-inequality violation and pure entanglement distillation. This result brought a sharp answer to the contemporary question "what is bound entanglement useful for?", and it has been extended to different setups by several authors.
- Reconstruction of quantum theory from physical principles having a simple and direct meaning (Nature Physics highlight, July 2011). This contrasts with the standard formulation in terms of abstract postulates with no clear meaning.
- Proof of the area law in arbitrary spatial dimensions. First general proof that the entropy of a region of a lattice system in its ground state is proportional to the boundary area of the region (instead of the volume), provided that the system has local interactions and a moderate density of low-energy levels.
- Device-independent quantum key distribution. Discovery that certain protocols for key distribution based on the violation of Bell inequalities enjoy a higher level of security than the standard quantum key distribution protocols. I also provided the first security proof for an efficient device-independent quantum key distribution protocol.
- Derivation of the Third Law of Thermodynamics. This is a model-independent lower bound on the resources that are necessary for bringing a system to any temperature. In particular, it shows the impossibility to reach absolute zero. This also puts limits how fast information can be erased.
- The quantum Chernoff bound is the quantum generalisation of a very important result in probability theory. It quantifies the statistical distinguishability between any pair of quantum states.