In the physics of coupled oscillators, antiresonance, by analogy with resonance, is a pronounced minimum in the amplitude of an oscillator at a particular frequency, accompanied by a large, abrupt shift in its oscillation phase. Such frequencies are known as the system's antiresonant frequencies, and at these frequencies the oscillation amplitude can drop to almost zero. Antiresonances are caused by destructive interference, for example between an external driving force and interaction with another oscillator.

Antiresonances can occur in all types of coupled oscillator systems, including mechanical, acoustical, electromagnetic, and quantum systems. They have important applications in the characterization of complicated coupled systems.

The term antiresonance is used in electrical engineering for a form of resonance in a single oscillator with similar effects.

In electrical engineering, antiresonance is the condition for which the reactance vanishes but the resistive impedance of an electrical circuit is none the less very high, approaching infinity.

In an electric circuit consisting of a capacitor and an inductor in parallel, antiresonance occurs when the alternating current line voltage and the resultant current are in phase. Under these conditions the line current is very small because of the high electrical impedance of the parallel circuit at antiresonance. The branch currents are almost equal in magnitude and opposite in phase.

The simplest system in which antiresonance arises is a system of coupled harmonic oscillators, for example pendula or RLC circuits.

Consider two harmonic oscillators coupled together with strength g and with one oscillator driven by an oscillating external force F. The situation is described by the coupled ordinary differential equations

where the ω_i represent the resonance frequencies of the two oscillators and the γ_i their damping rates. Changing variables to the complex parameters: