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Standard quantum mechanics predicts the non-conservation of state norms and probability when the fundamental requirement of the Hermiticity of the Hamiltonian is relaxed. Biorthogonal quantum mechanics, or the more general metric formalism,…

Quantum Physics · Physics 2025-07-18 Mario Gonzalez , Karin Sim , R. Chitra

Quantum metric, a probe to spacetime of the Hilbert space, has been found measurable in the nonlinear electronic transport thus has attracted tremendous interest. However, without comparing with mechanisms tied to disorder, it is still…

Mesoscale and Nanoscale Physics · Physics 2025-03-25 Zhen-Hao Gong , Z. Z. Du , Hai-Peng Sun , Hai-Zhou Lu , X. C. Xie

Over the last two decades, advances in fabrication have led to significant progress in creating patterned heterostructures that support either carriers, such as electrons or holes, with specific band structure or electromagnetic waves with…

Non-Hermitian dynamics in quantum systems have unveiled novel phenomena, yet the implementation of valid non-Hermitian quantum measurement remains a challenge, because a universal quantum projective mechanism on the complete but skewed…

It is shown that the standard formulation of quantum mechanics in terms of Hermitian Hamiltonians is overly restrictive. A consistent physical theory of quantum mechanics can be built on a complex Hamiltonian that is not Hermitian but…

Quantum Physics · Physics 2008-12-18 Carl M. Bender , Dorje C. Brody , Hugh F. Jones

We experimentally observe the quantum geometric tensor, namely the quantum metric and the Berry curvature, for a square lattice of radiatively coupled plasmonic nanoparticles. We observe a non-zero Berry curvature and show that it arises…

We demonstrate how Quantum Cognition Machine Learning (QCML) encodes data as quantum geometry. In QCML, features of the data are represented by learned Hermitian matrices, and data points are mapped to states in Hilbert space. The quantum…

A review is given on the foundations and applications of non-Hermitian classical and quantum physics. First, key theorems and central concepts in non-Hermitian linear algebra, including Jordan normal form, biorthogonality, exceptional…

Mesoscale and Nanoscale Physics · Physics 2021-04-28 Yuto Ashida , Zongping Gong , Masahito Ueda

In this work we intend to study a class of time-dependent quantum systems with non-Hermitian Hamiltonians, particularly those whose Hermitian counterpart are important for the comprehension of posed problems in quantum optics and quantum…

Quantum Physics · Physics 2007-05-23 A. de Souza Dutra , M. B. Hott , V. G. C. S dos Santos

The description of states and dynamics in non-Hermitian systems is fundamentally linked to the choice of an appropriate theoretical framework -- a point of ongoing debate in the field. This work addresses this issue by proposing a…

Quantum Physics · Physics 2026-05-07 Fei Wang , Guoying Liang , Zecheng Zhao , Bao-Ming Xu

This topical review article reports rapid progress on the generalization and application of entanglement in non-Hermitian free-fermion quantum systems. We begin by examining the realization of non-Hermitian quantum systems through the…

Quantum Physics · Physics 2026-01-14 Li-Mei Chen , Yao Zhou , Shuai A. Chen , Peng Ye

Open classical and quantum systems with effective parity-time ($\mathcal{PT}$) symmetry, over the past five years, have shown tremendous promise for advances in lasers, sensing, and non-reciprocal devices. And yet, how such effective…

Quantum Physics · Physics 2020-10-21 Archak Purkayastha , Manas Kulkarni , Yogesh N. Joglekar

Quantum geometry plays a pivotal role in the second-order response of $\cal PT$-symmetric antiferromagnets. Here we study the nonlinear response of 2D altermagnets protected by $C_n\cal T$ symmetry and show that their leading nonlinear…

Mesoscale and Nanoscale Physics · Physics 2025-05-13 Yuan Fang , Jennifer Cano , Sayed Ali Akbar Ghorashi

Evolutions under non-Hermitian Hamiltonians with unbroken $\mathcal{PT}$ symmetry can be considered unitary under appropriate choices of inner products, facilitated by the so-called metric operator. While it is understood that the choice of…

Quantum Physics · Physics 2025-12-04 Himanshu Badhani , C. M. Chandrashekar

In this paper, we present a unifying analytical framework for identifying conditions for transport effects such as reflectionless and transparent transport, lasing, and coherent perfect absorption in non-Hermitian nonreciprocal systems…

Mesoscale and Nanoscale Physics · Physics 2023-03-29 Hamed Ghaemi-Dizicheh

In Hermitian topological systems, the bulk-boundary correspondence strictly constraints boundary transport to values determined by the topological properties of the bulk. We demonstrate that this constraint can be lifted in non-Hermitian…

Mesoscale and Nanoscale Physics · Physics 2019-11-26 Bastian Höckendorf , Andreas Alvermann , Holger Fehske

Recent studies have shown that the nonlinear optical response of crystalline systems is fundamentally a quantum geometric property. In this work, we propose two-dimensional coherent spectroscopy (2DCS), which measures the nonlinear…

Mesoscale and Nanoscale Physics · Physics 2025-07-08 Paul Froese , Mark R. Hirsbrunner , Yong Baek Kim

The ordinary time-dependent perturbation theory of quantum mechanics, that describes the interaction of a stationary system with a time-dependent perturbation, predicts that the transition probabilities induced by the perturbation are…

Quantum Physics · Physics 2017-10-11 S. Longhi , G. Della Valle

Based on empirical evidence, quantum systems appear to be strictly linear and gauge invariant. This work uses concise mathematics to show that quantum eigenvalue equations on a one dimensional ring can either be gauge invariant or have a…

Quantum Physics · Physics 2014-07-15 Arthur Davidson

Information exchange between two distant parties, where information is shared without physically transporting it, is a crucial resource in future quantum networks. Doing so with high-dimensional states offers the promise of higher…

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