Anomalous decay of coherence in a dissipative many-body system

Decoherence plays a major role in our current understanding of the conceptual foundations of quantum physics(1). In many instances, decoherence is also a threat that must be countered (for instance, in quantum information processing or quantum technologies). While decoherence has been extensively studied for simple, well-isolated systems such as single atoms or ions(2), much less is known for many-body systems where interparticle correlations and interactions can drastically alter the dissipative dynamics(3-6). Here, we study experimentally the decoherence of a gas of strongly interacting bosons in an optical lattice exposed to near-resonant light and spontaneous emission. We observe an anomalous subdiffusion in momentum space, associated with a universal slowing down proportional to 1/t(1/2) of the loss of spatial coherence. This algebraic decay reflects the emergence of slowly relaxing many-body states(5), akin to the subradiant states of many excited emitters(4). These results, supported by theoretical predictions, provide an important benchmark in the understanding of open many-body systems. Strongly interacting bosons in an optical lattice exhibit anomalous subdiffusive evolution when subjected to a dissipative process. The experimental observations are attributed to a mechanism termed 'interaction-impeding of decoherence'.