Collective excitations in a spin liquid can be used to encode and manipulate information. The non-linear response is also exquisitively sensitive to the ground state character for systems with competing order parameters. I will report results on spin liquids stabilized to the lowest temperatures by quantum fluctuations [Li(Ho,Y)F4] and by geometrical frustration [GGG]. We are able to burn holes in the spectral response in analogy to optical bleaching, but we use a wire loop at 1 Hertz rather than a laser at TeraHertz frequency, with an excitation field a fraction of the earth's magnetic field! The resulting spin excitations retain phase coherence with the pump pulse for many seconds after the pump is turned off, returning to their ground state via a process paralleling free induction decay in NMR experiments. Finally, we show that it is possible to simultaneously burn holes at different frequencies, making it possible to encode independent bits of information in the non-interacting eigenstates of the system.
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