2013/08/21 by Bo Peng, Sahin Kaya Ozdemir, Fuchuan Lei +7 · 1 citation
Physics and Astronomy · Mathematics · #physics.optics #cond-mat.mtrl-sci #math-ph #math.MP #physics.class-ph #quant-ph
paper · pdf · doi:10.1038/nphys2927
published as Nature Physics, 10, 394 (2014) · 13 Pages, 5 figures, 35 References
arxiv created 2013/08/21 · arxiv updated 2014/06/26
Optical systems combining balanced loss and gain profiles provide a unique platform to implement classical analogues of quantum systems described by non-Hermitian parity-time- (PT-) symmetric Hamiltonians and to originate new synthetic materials with novel properties. To date, experimental works on PT-symmetric optical systems have been limited to waveguides in which resonances do not play a role. Here we report the first demonstration of PT-symmetry breaking in optical resonator systems by using two directly coupled on-chip optical whispering-gallery-mode (WGM) microtoroid silica resonators. Gain in one of the resonators is provided by optically pumping Erbium (Er3+) ions embedded in the silica matrix; the other resonator exhibits passive loss. The coupling strength between the resonators is adjusted by using nanopositioning stages to tune their distance. We have observed reciprocal behavior of the PT-symmetric system in the linear regime, as well as a transition to nonreciprocity in the PT symmetry-breaking phase transition due to the significant enhancement of nonlinearity in the broken-symmetry phase. Our results represent a significant advance towards a new generation of synthetic optical systems enabling on-chip manipulation and control of light propagation.