In this Optics Express article, the authors take a source of squeezed light based on sending laser pulses through a loop of nonlinear fibre. Output pulses show a 3dB reduction in amplitude fluctuations, and initially have a Gaussian mode-shape. This beam is then reflected from a liquid crystal spatial light modulator (SLM), which converts the mode to a desired shape by applying a carefully chosen phase pattern. Since the SLM only modulates the phase of the beam, not its amplitude, this reshaping is a unitary operation and in principle should not affect the quantum state of the mode. In practice, some of the light is lost into different diffraction orders after the SLM, resulting in some reduction of the squeezing. A variety of the Laguerre-Gauss and Bessel-Gauss spatial modes were prepared whilst maintaining around 1.3dB of squeezing, as well as an ‘arbitrary pattern’ spelling “MPL” with 0.4dB of squeezing. The preparation of squeezed states with arbitrary spatial structure may be used in quantum imaging, in gravitational wave detection, where higher-order modes potentially allow higher optical power to be used, and in quantum information, for multiplexing several modes using the transverse degree of freedom.
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