Quantum scale anomaly and spatial coherence in a 2D Fermi superfluid

          @misc{ pirsa_PIRSA:19070028,
            doi = {10.48660/19070028},
            url = {https://pirsa.org/19070028},
            author = {Defenu, Nicolo},
            keywords = {Condensed Matter},
            language = {en},
            title = {Quantum scale anomaly and spatial coherence in a 2D Fermi superfluid},
            publisher = {Perimeter Institute},
            year = {2019},
            month = {jul},
            note = {PIRSA:19070028 see, \url{https://pirsa.org}}
          }
          

Abstract

Quantum anomalies are violations of classical scaling symmetries caused by quantum fluctuations. Although they appear prominently in quantum field theory to regularize divergent physical quanti- ties, their influence on experimental observables is difficult to discern. Here, we discovered a striking manifestation of a quantum anomaly in the momentum-space dynamics of a 2D Fermi superfluid of ultracold atoms. We measured the position and pair momentum distribution of the superfluid during a breathing mode cycle for different interaction strengths across the BEC-BCS crossover. Whereas the system exhibits self-similar evolution in the weakly interacting BEC and BCS limits, we found a violation in the strongly interacting regime. The signature of scale-invariance breaking is enhanced in the first-order coherence function. In particular, the power-law exponents that char- acterize long-range phase correlations in the system are modified due to this effect, indicating that the quantum anomaly has a significant influence on the critical properties of 2D superfluids.