Topologically Protected All‐Optical Memory

The in‐memory processor has played an essential role in overcoming the von Neumann bottleneck, which arises from the partition of memory and a processing unit. Although photonic technologies have recently attracted attention for ultrafast and power‐efficient in‐memory computing, the realization of an all‐optical in‐memory processor remains a challenge. This difficulty originates from the contradiction between robustness and sensitivity in wave dynamics, requiring both noise‐immune memory states and modulation‐sensitive transitions between these states. Here, a building block that provides an all‐optical transition between topologically protected memory states is proposed. A nonlinear photonic molecule that satisfies parity‐time (PT) symmetry, revealing multiple oscillation quenching states with different degeneracies determined by PT‐symmetric phases is investigated. In terms of topology for dynamical systems, these quenching states support topologically protected dynamical trajectories suitable for stable memory states. An all‐optical bidirectional transition between these states, which allows incoherent memory switching is demonstrated. The result provides design criteria for all‐optical in‐memory processors with multilevel operations, enabling the classical‐wave counterpart of electronic memristors. An all‐optical building block for photonic in‐memory processors is demonstrated by exploiting oscillation quenching states in nonlinear parity‐time‐symmetric systems. With the achievement of topological noise immunity and all‐optical state transition in a platform that is integratable with signal processors, the topologically protected all‐optical memory composes a photonic counterpart of electronic memristors.