Dynamical decoupling applies a designed sequence of control operations to a quantum system to suppress unwanted evolution, especially coupling to an environment that causes quantum decoherence. The controls repeatedly change how the unwanted interaction acts, so its effects can average away over a cycle. This does not mean that all noise is removed or that arbitrary useful dynamics are automatically preserved.[ref]
Experimental realization of robust dynamical decoupling with bounded controls in a solid-state spin system by F. Wang and others. Introduction: slow environmental coupling and bounded controls
For a simple example, let a qubit have an unwanted constant Quantum Hamiltonian , where is the Pauli Z gate matrix. Free evolution for time gives . An ideal Pauli X gate obeys , henceThe two intervals cancel the same constant phase drift in this ideal model. This is the basic refocusing idea behind a spin echo. A changing drift, finite pulse duration or imperfect rotation can leave residual error.
A2016 solid-state experiment used nitrogen-vacancy centers in diamond to compare decoupling protocols with bounded, finite-duration controls. Long shaped control paths were tested against imposed dephasing and more general noise. The experiment matters because instantaneous perfect pulses are an idealization: a useful sequence must account for the control apparatus as well as the unwanted interaction.[ref]
Experimental realization of robust dynamical decoupling with bounded controls in a solid-state spin system by F. Wang and others. Abstract, Introduction and experimental Results: finite-width Eulerian control in NV-center spins
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Dynamical decoupling is a technique used in quantum mechanics and quantum information science to mitigate the effects of decoherence on quantum states. Decoherence is a process where a quantum system loses its quantum properties due to interactions with its environment, leading to the degradation or loss of information. The basic idea behind dynamical decoupling is to apply a sequence of carefully timed control pulses or operations to the quantum system.