Non-Hermitian Squeezed Polarons

Abstract

Recent experimental breakthroughs in non-Hermitian ultracold atomic lattices have dangled tantalizing prospects in realizing exotic, hitherto unreported many-body non-Hermitian quantum phenomena. In this work, we discover and propose an experimental platform for a radically new non-Hermitian phenomenon dubbed polaron squeezing. It is marked by a dipole-like accumulation of fermions arising from an interacting impurity in a background of non-Hermitian reciprocitybreaking hoppings. Unlike Hermitian polarons which are symmetrically localized around impurities, non-Hermitian squeezed polarons localize asymmetrically in the direction opposite to conventional non-Hermitian pumping, and non-perturbatively modify the entire spectrum, despite having a manifestly local profile. Also, unlike well-known topological or skin localized states, squeezed polarons exist in the bulk, independently of boundary conditions. We base our calculations on a proposed ultracold atomic setup where a squeezed polaron can be readily detected and characterized by imaging the spatial fermionic density.

Designing non-Hermitian real spectra through electrostatics

“…Condensed matter physics has traditionally been studied in the Hermitian context, since real energies are necessary for observing stable quantum states. Yet, with intense recent research in non-Hermitian systems [1], it has become apparent that many of the most exciting contemporary phenomena -exceptional points [2][3][4], non-Hermitian skin localization and modified bulk-boundary correspondence [5][6][7][8][9][10][11], nontrivial spectral topology [12][13][14][15][16][17][18], negative entanglement entropy [19,20], effective non-Hermitian curved spaces [21], amplified Rabi frequencies [22] -exist only in the non-Hermitian realm. Fortunately, non-Hermitian systems are not necessarily unstable, since they can still possess real eigenenergies if appropriately designed.…”

Real non-Hermitian energy spectra without any symmetry

“…Non-Hermitian systems have recently inspired intense research efforts for their unconventional mathematical properties and physical robustness, such as enlarged topological symmetries, [1][2][3][4][5][6][7][8] exceptional point sensing, [9][10][11][12][13][14][15] quantized classical responses, [16] modified bulk-boundary correspondences, [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] unconventional entanglement entropy scaling, [4,[33][34][35][36][37][38][39] enhanced Rabi oscillations, [26,40,41] and effective non-Hermitian curved space. [42,43] Yet, many of these exciting phenomena are often difficult to probe experimentally due to their intrinsically unstable nature from complex eigenenergies.…”