Remarkable progress has been made in developing materials that can manipulate electromagnetic waves in a way that is impossible with natural structures, culminating in the design of spatial cloaks with the potential to hide an object within a 'hole in space'. Such devices currently have limited functionality. An analogous, conceptually intriguing idea is to devise a 'time cloak' that artificially creates a hole in time rather than in space, by accelerating and slowing down, respectively, the front and rear parts of a probe light beam. Fridman et al . demonstrate such a time cloak in a fibre-based system, in which an event that causes a clear disturbance to a probe beam appears not to occur at all when the time cloak is turned on. This effect is achieved using a split time lens that breaks light up into its slower (red) and faster (blue) components, thereby creating a temporal gap. The time cloaking is achieved on a picosecond timescale — trillionths of a second — but could be a significant step towards full spatio-temporal cloaking.
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