September 2023
Abstracts of the Quantum Center Lunch Seminar
Date: Thursday, September 7, 2023
Place: ETH Zurich, Hönggerberg, HPF G 6
Time: 12:00 - 13:30
Distributed Authentication for a Post-Quantum World
Cecilia Boschini - Foundations of Cryptography (Hofheinz group), ETH Zurich
Distributed authentication has seen a wide deployment in the last few years, mainly as a fundamental building block of blockchain-based products. However, existing protocols cannot guarantee security in case an attacker exploits a quantum computer. As such, it is currently an open question to design practical protocols that allow for distributed authentication in the so called post-quantum world, that is, distributed authentication protocols that retain security even if attacked with a quantum computer. In this talk we will present the state of the art and some recent advancements, in light of the NIST standardization process that will start next year.
Spin- and momentum-correlated atom pairs mediated by photon exchange
Fabian Finger - Quantum Optics (Esslinger group), ETH Zurich
Mechanisms generating correlated pairs of particles are at the core of diverse fields of physics such as Hawking radiation, phonon-mediated superconductivity or photon entanglement resulting from parametric down-conversion (PDC). Similar approaches have been explored with ultracold atomic gases to correlate massive particles either in their internal or external degrees of freedom, offering prospects for matter-wave interferometry, Bell tests and bipartite entanglement. Many of the aforementioned applications benefit from a rapid pair production in well-defined modes, however existing schemes relying on collisions are limited by the timescales of contact interactions. To overcome this, strong light-matter coupling can be used as a building block to correlate matter pairs.
In our work, we use a Bose-Einstein condensate (BEC) coupled to a high-finesse optical cavity to generate photon-mediated atom pairs that are simultaneously correlated in their spin and momentum. Our mechanism is, much like spontaneous PDC (SPDC), dominated by vacuum fluctuations and allows us to generate matter-wave beams of twin atoms with the potential of controllable spin entanglement. The fast timescales associated with the strong, tunable light-matter coupling are on the order of tens of microseconds, allowing us to separate this process from typical dissipative mechanisms in atomic systems, such as heating, three-body losses, and trapping effects. We observe coherent many-body pair oscillations, explore their quantum statistics and demonstrate density-density correlations in momentum space, akin to photon correlation techniques in quantum optics experiments. In conclusion, our results offer an exciting route for loophole-free Bell tests using massive particles, fast entanglement generation in spatially separated atomic clouds, and quantum simulation of photon-induced Cooper pairs.