Quantum entanglement, according to Erwin
Schrödinger the essence of quantum mechanics, is a unique feature of the quantum world. Our research is devoted to studying its fundamental properties and implications for the foundations of physics.
Our group pioneered the realization of novel quantum states and quantum phenomena with entangled photons, such as polarization entanglement, orbital angular momentum entanglement, Greenberger-Horn-Zeilinger (GHZ) entanglement, Cluster state entanglement, and other types of multi-particle entanglement, that are designed to demonstrate the unique and counterintuitive phenomena of quantum physics.
We are also working on implementing quantum entanglement for new quantum information applications. Our group’s accomplishments include a number of applications of entanglement-based quantum information protocols such as quantum state teleportation, quantum dense coding, and entangled -photon quantum cryptography. One important aspect for future quantum communication networks, the ability to distribute entanglement over long distances, is addressed by our experiments on the distribution of entangled photons via optical fibres and via free space, and in the future, even using quantum communication satellites in Space.
Quantum Computer Technology has the potential to perform tasks utterly intractable on any conceivable classical computing hardware. The focus of our research is entanglement-based quantum computation with single photons, which have the advantage of allowing high-speed operations while undergoing negligible decoherence.
The concept of quantum entanglement leads to correlations, even if the entangled particles (e.g. photons) are distributed to far apart receiver stations. In our setups we make use of the BBM92 quantum cryptography protocol for entangled systems to create unconditional secure keys between distant parties. Disturbances due to an eavesdropping attempt result immediately in a degradation in the quality of the received quantum correlations. Furthermore it can be shown that all information leaked to the adversary must reduce the entanglement, so all attacks are detectable as a matter of principle. This is an important prerequisite for quantum key distribution (QKD), which delivers identical bit strings at two communicating parties. Ultimately, no information of the shared secret can be obtained by any possible attack on the quantum channel.
Exploring the quantum regime of mechanical systems is a thriving, interdisciplinary and growing field in physics at the boundary of quantum physics, applied physics and nanoscience. Mechanical quantum states offer fascinating new possibilities for both applied physics, such as quantum-limited mechanical sensing, and fundamental physics, such as the preparation of quantum superposition states and entangled states involving massive systems that contain up to 10^20 atoms. They might even provide the basis for completely new ways of (mechanical) quantum information processing. Our research is focused on full quantum control of mechanical systems via optomechanical coupling, i.e. the coupling of light via radiation pressure. This includes laser-cooling of mechanical modes to the quantum ground state, optomechanical quantum entanglement and hybrid approaches to scalable quantum computing as well as novel fabrication methods of high-quality micromirrors.
The properties of molecules may resemble those of atomic few-level states for very small particles at low temperatures or those of soft macroscopic matter at higher temperatures and higher levels of complexity. These dual properties turn molecules into very interesting systems for the exploration of decoherence and the transition between quantum and classical phenomena.
The Vienna team is focussing on quantum interference of macromolecules. New interference techniques have been developed with fullerenes and small biomolecules. New source and detection methods are being studied for large biomolecules and slow perfluoralkylated particles.
Recent developments have also proved that the techniques developed for interferometry will be fruitful for molecule metrology and the creation of molecular nanopatterns.
Quantum information science breaks limitations of conventional (classical) communication, cryptography, and computation. In particular, quantum information can be used to reduce the communication costs in situations where separated parties need to exchange information in order to accomplish a globally defined task, which is impossible to solve single-handedly. Examples involve the scheduling of an appointment between two parties or computing a function whose partial inputs are distributed over the parties. It turns out that the “quantum communication complexity” of these problems are provably less than its classical communication complexity. The Vienna group is focussing on investigating quantum non-locality - one of the most counter-intuitive features of quantum physics- as a useful resource for reduction of communication complexity.
