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Abstract
The quest to manipulate light propagation in ways not possible with natural media has driven the development of artificially structured metamaterials. One of the most striking effects is negative refraction, where the light beam deflects away from the boundary normal. However, due to material characteristics, the applications of this phenomenon, such as lensing that surpasses the diffraction limit, have been constrained. Here, we demonstrate negative refraction of light in an atomic medium without the use of artificial metamaterials, employing essentially exact simulations of light propagation. High transmission negative refraction is achieved in atomic arrays for different level structures and lattice constants, within the scope of currently realised experimental systems. We introduce an intuitive description of negative refraction based on collective excitation bands, whose transverse group velocities are antiparallel to the excitation quasi-momenta. We also illustrate how this phenomenon is robust to lattice imperfections and can be significantly enhanced through subradiance.
Highlights
Negative refraction of electromagnetic waves [1–7] is characterised by counter-intuitive phenomena, such as the bending of waves in a medium in the opposite direction to what normally occurs and the amplification of evanescent waves in the bulk [8, 9]
We have employed large atomic-scale simulations to establish a link between the microscopic quantum properties of atoms and material bulk parameters of macroscopic electromagnetism. These demonstrate that cooperative atom response in a periodic structure can lead to folding of the dispersion band, resulting in an effective negative refractive index
The simulations are based on a methodology that has been shown to describe accurately the experiments on atoms illuminated with resonant light in optical lattices [21, 22]
Summary
Negative refraction of electromagnetic waves [1–7] is characterised by counter-intuitive phenomena, such as the bending of waves in a medium in the opposite direction to what normally occurs and the amplification of evanescent waves in the bulk [8, 9]. We show that negative refraction of light can be obtained in atomic media without the use of artificially fabricated resonators This is made possible by harnessing and utilising cooperative, non-local atom responses that arise from strong light-mediated interactions at high densities. In contrast to our approach, previous proposals for utilising atomic media to achieve negative refraction have relied on quantum interference effects in multilevel systems involving inherently weak magnetic dipole transitions for independently scattering atoms [23, 24]. The simulations uncover a distinct deflection of propagating light beams in the opposite direction to what normally occurs This enables us to extract from microscopic simulations the negative value of refractive index which represents the effective macroscopic electrodynamics material parameter of the atomic sample. The effective refractive index can be significantly enhanced through coupling with more subradiant excitations
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