Dynamically encircling an exceptional point in anti-parity-time symmetric systems: asymmetric mode switching for symmetry-broken modes

Abstract

Dynamically encircling an exceptional point (EP) in parity-time (PT) symmetric waveguide systems exhibits interesting chiral dynamics that can be applied to asymmetric mode switching for symmetric and anti-symmetric modes. The counterpart symmetry-broken modes (i.e., each eigenmode is localized in one waveguide only), which are more useful for applications such as on-chip optical signal processing, exhibit only non-chiral dynamics and therefore cannot be used for asymmetric mode switching. Here, we solve this problem by resorting to anti-parity-time (anti-PT) symmetric systems and utilizing their unique topological structure, which is very different from that of PT-symmetric systems. We find that the dynamical encircling of an EP in anti-PT-symmetric systems with the starting point in the PT-broken phase results in chiral dynamics. As a result, symmetry-broken modes can be used for asymmetric mode switching, which is a phenomenon and application unique to anti-PT-symmetric systems. We perform experiments to demonstrate the new wave-manipulation scheme, which may pave the way towards designing on-chip optical systems with novel functionalities.

Coherent Perfect Absorption Laser Points in One-Dimensional Anti-Parity–Time-Symmetric Photonic Crystals

“…It is the unique property of CPA-LPs usually utilized for confirming CPA-LP in non-Hermitian systems. In the vicinity of the CPA-LP, the curves of the imaginary part are crossing, while the curves of the real part are anti-crossing [52]. The CPA-LPs are connected with the surface mode localized at the gain-loss boundary.…”

“…However, studies on non-Hermitian photonics have shown that loss and gain, satisfied with PT symmetry, provide a new degree of freedom for the system, which can effectively control photons and generate new optical effects, such as unidirectional reflectionless resonance, which can be used to prepare chip-level semiconductor lasers [48].Anti-PT-symmetric systems, in which the refractive index of material obeys n(x) = −n*(−x), have been proposed and attracted much attention [49][50][51]. Many interesting phenomena are found in anti-PT-symmetric systems, such as flat broadband light transport [50], and chiral mode conversion [52]. Actually, anti-PT symmetry belongs to a more fundamental symmetry called charge-conjugation symmetry [53,54], which consists of two sublattices.…”

“…Anti-PT-symmetric systems, in which the refractive index of material obeys n(x) = −n*(−x), have been proposed and attracted much attention [49][50][51]. Many interesting phenomena are found in anti-PT-symmetric systems, such as flat broadband light transport [50], and chiral mode conversion [52]. Actually, anti-PT symmetry belongs to a more fundamental symmetry called charge-conjugation symmetry [53,54], which consists of two sublattices.…”

Robust mode conversion in NV centers using exceptional points

“…A new class of adiabatic protocols enables robust mode conversion in open systems that possess a special degeneracy called an exceptional point (EP)-where multiple modes of the system coalesce [1][2][3]. EP-based mode switches have intriguing physical properties, such as topological protection and non-reciprocity [4][5][6][7][8], which were demonstrated experimentally in optical waveguides and optomechanics [9][10][11][12][13][14] and theoretically proposed for several additional systems [15][16][17][18]. Realizing robust nonreciprocal mode switching in quantum systems has far reaching consequences in quantum information processing and quantum control, as well as in quantum technology.…”

“…Typically, small perturbations in the operational details only slightly distort the loop or move the location of the EP, but do not lift the degeneracy. The possibility of creating a non-reciprocal switches between pure states has attracted considerable attention [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] and, here, we generalize this concept for mixed states. Our protocol includes (i) finding an isolated EP in the eigenvalue spectrum of the NV center ( Fig.…”