Sensing with Exceptional Surfaces in Order to Combine Sensitivity with Robustness

Abstract

Exceptional points (EPs) are singularities that arise in non-Hermitian physics. Current research efforts focus only on systems supporting isolated EPs characterized by increased sensitivity to external perturbations, which makes them potential candidates for building next generation optical sensors. On the downside, this feature is also the Achilles heel of these devices: they are very sensitive to fabrication errors and experimental uncertainties. To overcome this problem, we introduce a new design concept for implementing photonic EPs that combine the robustness required for practical use together with their hallmark sensitivity. Particularly, our proposed structure exhibits a hypersurface of Jordan EPs (JEPs) embedded in a larger space, and having the following peculiar features: (1) A large class of undesired perturbations shift the operating point along the exceptional surface (ES), thus leaving the system at another EP which explains the robustness;(2) Perturbations due to back reflection/scattering force the operating point out of the ES, leading to enhanced sensitivity. Importantly, our proposed geometry is relatively easy to implement using standard photonics components and the design concept can be extended to other physical platforms such as microwave or acoustics. * ganainy@mtu.edu 1 arXiv:1810.09417v1 [physics.optics]

Weak-force sensing with squeezed optomechanics

“…In conclusion, we have investigated weak-force sensing in a squeezed cavity and theoretically showed that (i) the SQL cannot be surpassed in the case of G = 0 or θ = 0, (ii) the measurement precision of weak-force detection can be remarkably improved at the coupling strength smaller than g SQL by tuning the parametric phase and gain, and (iii) under the approximation of κ ω, quantum noise can be reduced without losing mechanical-mode information. Our work provides new insight in strengthening the sensitivity of a force sensor with the assistance of intracavity squeezing, which can be also extended into other systems of quantum sensing with e.g., waveguide [84,87], interferometer [88], or parity-time (PT ) symmetric microcavity [89][90][91]. In the future, we plan to extend our work to study the weakforce measurement with the help of two-mode squeezing or quantum entanglement [92][93][94], squeezed mechanical modes [70,95], or squeezed sources in hybrid COM devices [96,97].…”

Non-Hermitian and topological photonics: optics at an exceptional point

“…For instance, an EP sensor can also be excessively vulnerable to fabrication errors and imperfections that are inevitable in experiments. In this respect, exceptional surfaces have been suggested as a possible avenue to combine the robustness required for practical applications with the characteristic sensitivity offered by EPs [127]. One way to achieve this is to introduce a unidirectional coupling between the counterpropagating modes of a microring cavity.…”

Untying links through anti-parity-time-symmetric coupling

“…The types of non-Hermiticities and their manners of appearance are important for the non-Hermitian topological systems [34,54]. If the non-Hermiticity is = (0, 0, γ ), the topological phase transition and the existence of the edge state are unaltered because of the pseudo-anti-Hermiticity protection [34]; the topological properties of the non-Hermitian system are inherited by the EPs (exceptional rings or exceptional surfaces in 2D or 3D) [60][61][62][63][64][65][66][67]. If the non-Hermiticity is = (0, γ , 0), the non-Hermitian skin effect occurs under open boundary condition [54][55][56][57][58][59][68][69][70][71][72][73][74][75][76][77][78], the non-Hermitian Aharonov-Bohm effect under periodical boundary condition invalidates the conventional bulk-boundary correspondence [54], and the non-Bloch band theory is developed for topological characterization [77][78][79][80][81][82].…”