Role of particle statistics in quantum mechanical decay and Fano resonance

Avi Marchewka, Er’el Granot

Andrea Crespi, Linda Sansoni, Giuseppe Della Valle +6 more

Quantum mechanical decay, Fano interference, and bound states with energy in the continuum are ubiquitous phenomena in different areas of physics. Here we experimentally demonstrate that particle statistics strongly affects quantum mechanical decay in a multiparticle system. By considering propagation of two-photon states in engineered photonic lattices, we simulate quantum decay of two noninteracting particles in a multilevel Fano-Anderson model. Remarkably, when the system sustains a bound state in the continuum, fractional decay is observed for bosonic particles, but not for fermionic ones. Complete decay in the fermionic case arises because of the Pauli exclusion principle, which forbids the bound state to be occupied by the two fermions. Our experiment indicates that particle statistics can tune many-body quantum decay from fractional to complete.

C. P. Holfeld, F. Löser, M. Sūdžius +3 more

Summary form only given.Fano resonances arise due to quantum mechanical coupling of a discrete state to a degenerate continuum. The line shape in optical absorption spectra is characterized by an intrinsic broadening of the line, strong asymmetry, and a reduced absorption at one side of the peak falling well below the pure continuum level. Intensive theoretical investigations predicted Fano resonances as a general feature of a large variety of low-dimensional semiconductors. We present the observation of Fano resonances in semiconductor superlattices (SL). In SL, discrete excitonic states of the Wannier-Stark ladder are in resonance with subband continua of lower ladder states. The coupling between discrete and continuous states is mediated by Coulomb interaction, which is also responsible for the formation of the discrete excitonic states. As a unique feature of Fano resonances in SL, the Fano coupling strength can be continuously changed in the experiment by tuning the applied electric field. We have also performed time-integrated four-wave-mixing experiments to investigate the influence of Fano coupling on the polarization decay of a Wannier-Stark exciton. We have been able to resolve the polarization decay of a Fano resonance in the time-integrated signal and to follow its changes with field.

Alexander Blech, Yuval Shagam, Nicolas Hölsch +8 more

Decay of bound states due to coupling with free particle states is a general phenomenon occurring at energy scales from MeV in nuclear physics to peV in ultracold atomic gases. Such a coupling gives rise to Fano-Feshbach resonances (FFR) that have become key to understanding and controlling interactions—in ultracold atomic gases, but also between quasiparticles, such as microcavity polaritons. Their energy positions were shown to follow quantum chaotic statistics. In contrast, their lifetimes have so far escaped a similarly comprehensive understanding. Here, we show that bound states, despite being resonantly coupled to a scattering state, become protected from decay whenever the relative phase is a multiple of π. We observe this phenomenon by measuring lifetimes spanning four orders of magnitude for FFR of spin–orbit excited molecular ions with merged beam and electrostatic trap experiments. Our results provide a blueprint for identifying naturally long-lived states in a decaying quantum system.