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Momentum-space non-Hermitian skin effect in an exciton-polariton system
Authors:
Yow-Ming,
Hu,
Mateusz Król,
Daria A. Smirnova,
Lev A. Smirnov,
Bianca Rae Fabricante,
Karol Winkler,
Martin Kamp,
Christian Schneider,
Sven Höfling,
Timothy C. H. Liew,
Andrew G. Truscott,
Elena A. Ostrovskaya,
Eliezer Estrecho
Abstract:
Localization of a macroscopic number of eigenstates on a real-space boundary, known as the non-Hermitian skin effect, is one of the striking topological features emerging from non-Hermiticity. Realizing this effect typically requires periodic (lattice) systems with asymmetry of intersite coupling, which is not readily available in many physical platforms. Instead, it is meticulously engineered, e.…
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Localization of a macroscopic number of eigenstates on a real-space boundary, known as the non-Hermitian skin effect, is one of the striking topological features emerging from non-Hermiticity. Realizing this effect typically requires periodic (lattice) systems with asymmetry of intersite coupling, which is not readily available in many physical platforms. Instead, it is meticulously engineered, e.g., in photonics, which results in complex structures requiring precise fabrication steps. Here, we propose a simpler mechanism: introducing an asymmetric, purely imaginary potential in a topologically trivial system induces momentum-space localization akin to the skin effect. We experimentally demonstrate this localization using exciton polaritons, hybrid light-matter quasi-particles in a simple engineered `round box' trap, pumped by a laser pump offset from the trap center. The effect disappears if the pump is concentric with the trap. The localization persists and becomes stronger at higher densities of polaritons, when a non-equilibrium Bose-Einstein condensate is formed and the system becomes nonlinear. Our approach offers a new route to realizing skin effects in continuous, non-periodic systems and exploring the interplay of non-Hermiticity, topology, and nonlinearity in macroscopic quantum states.
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Submitted 10 December, 2025;
originally announced December 2025.
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Zitterbewegung Effect and Quantum Geometry in Non-Hermitian Exciton-Polariton Systems
Authors:
Yow-Ming Robin Hu,
Elena A. Ostrovskaya,
Eliezer Estrecho
Abstract:
In this work, we analytically derive a semi-classical equation of motion describing the zitterbewegung effects arising in the dynamics of wavepackets in non-Hermitian systems. In Hermitian non-relativistic quantum systems, the zitterbewegung effects can arise due to the spin precession and spin-orbit coupling. Interestingly, the spin dynamics in non-Hermitian systems are qualitatively different be…
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In this work, we analytically derive a semi-classical equation of motion describing the zitterbewegung effects arising in the dynamics of wavepackets in non-Hermitian systems. In Hermitian non-relativistic quantum systems, the zitterbewegung effects can arise due to the spin precession and spin-orbit coupling. Interestingly, the spin dynamics in non-Hermitian systems are qualitatively different because of the effective nonlinear terms induced by the non-Hermitian part of the Hamiltonian. In this work, we show the effects from the non-Hermitian spin dynamics by generalising the description of zitterbewegung effects to non-Hermitian systems. We also uncover novel non-Hermitian correction to the group velocity, which can be expressed in terms of the non-Hermitian quantum metric tensor in the absence of out-of-plane effective field.
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Submitted 31 October, 2025;
originally announced October 2025.
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Emergent momentum-space topological pseudospin defects in non-Hermitian systems
Authors:
Yow-Ming Robin Hu,
Elena A. Ostrovskaya,
Alexander Yakimenko,
Eliezer Estrecho
Abstract:
Topological defects are central to modern physics, from spintronics to photonics, due to their robustness and potential application in information processing. In this work, we discuss topological point defects that spontaneously emerge at the imaginary Fermi arcs (degeneracy lines) in momentum space of two-dimensional systems described by non-Hermitian effective Hamiltonians. In particular, we con…
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Topological defects are central to modern physics, from spintronics to photonics, due to their robustness and potential application in information processing. In this work, we discuss topological point defects that spontaneously emerge at the imaginary Fermi arcs (degeneracy lines) in momentum space of two-dimensional systems described by non-Hermitian effective Hamiltonians. In particular, we consider a generic non-Hermitian Dirac model and a phenomenological model describing hybrid light-matter quasiparticles - exciton polaritons hosted in an optical microcavity. In both cases, the eigenenergies of the system have both real and imaginary parts and form two distinct bands corresponding to two (pseudo-)spin states. We describe the trajectories of the point defects characterized by integer-valued topological winding (vorticity) analytically and show that the defects with opposite vorticity annihilate with each other in the fully gapped phases, but are protected from annihilation by the non-Hermitian spectral degeneracies (exceptional and hybrid points) in the gapless phases. We also suggest that the signatures of these defects can be experimentally measured in an exciton-polariton system.
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Submitted 18 September, 2025;
originally announced September 2025.
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Quantum geometric tensor and wavepacket dynamics in two-dimensional non-Hermitian systems
Authors:
Y. -M. Robin Hu,
Elena A. Ostrovskaya,
Eliezer Estrecho
Abstract:
The quantum geometric tensor (QGT) characterizes the local geometry of quantum states, and its components directly account for the dynamical effects observed, e.g., in condensed matter systems. In this work, we address the problem of extending the QGT formalism to non-Hermitian systems with gain and loss. In particular, we investigate a wave-packet dynamics in two-band non-Hermitian systems to elu…
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The quantum geometric tensor (QGT) characterizes the local geometry of quantum states, and its components directly account for the dynamical effects observed, e.g., in condensed matter systems. In this work, we address the problem of extending the QGT formalism to non-Hermitian systems with gain and loss. In particular, we investigate a wave-packet dynamics in two-band non-Hermitian systems to elucidate how non-Hermiticity affects the definition of QGT. We employ first-order perturbation theory to account for non-adiabatic corrections due to interband mixing. Our results suggest that two different generalizations of the QGT, one defined using only the right eigenstates and the other one using both the left and right eigenstates, both play a significant role in wave-packet dynamics. We then determine the accuracy of the perturbative approach by simulating a wave-packet dynamics in a well studied physical non-Hermitian system -- exciton polaritons in a semiconductor microcavity. Our work aids deeper understanding of quantum geometry and dynamical behaviour in non-Hermitian systems.
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Submitted 16 February, 2025; v1 submitted 11 December, 2024;
originally announced December 2024.