bistate

Bistate, or bistable, describes a system that possesses two distinct, stable states and can reside in either state without continuous input. A perturbation or trigger pushes the system from one state to the other, after which it remains in that state in the absence of further input. The two states are separated by an unstable equilibrium, creating a switch-like behavior and an inherent memory: the current state encodes information.

In electronics, bistability is foundational for memory devices. A bistable multivibrator (also called a flip-flop or latch) uses feedback to maintain either of two logic levels. Common types include RS, D, JK, and T flip-flops. Such devices store one bit of information and require a clock or control signal to change state. Some implementations aim for non-volatile operation, retaining the bit without continuous power.

Beyond circuits, bistability occurs in optical systems with feedback, mechanical structures that buckle into two stable configurations, and gene regulatory networks where positive feedback yields two expression states. In physics and engineering, optical bistability and mechanical buckling are studied for switches, memory, and hysteresis-based sensing.

The term is distinct from multistability, where more than two stable states exist; bistability specifically means two stable states, and an unstable transition state between them.

Applications include digital memory, switching, and sensors with hysteresis; in biology, bistable switches underlie cell fate decisions.