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arXiv:2606.01588

Higher-order exceptional points and enhanced quantum squeezing in a pseudo-Hermitian semiconductor optomechanical system

Zi-Wei Jiang, Yan-Zi Jing, Zhen-Sen Lin, Rui Zhang, Wen-Quan Yang, Ya-Feng Jiao, Le-Man Kuang

quant-phSubmitted Jun 1, 2026• Announced Jun 2, 2026
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Abstract

We investigate higher-order exceptional points and quantum squeezing of exciton polaritons in a pseudo-Hermitian semiconductor optomechanical system. We show that a third-order exceptional point (EP3) can emerge from the tripartite coupling among photons, excitons, and phonons under pseudo-Hermitian conditions. A pronounced two-mode quantum squeezing of exciton polaritons is revealed, and we demonstrate that this squeezing is significantly enhanced in the vicinity of the EP3. Furthermore, we find that in the PT-symmetric phase, the squeezing dynamics produce a frequency comb of exciton polaritons, whereas the squeezing remains constant over time in the PT-symmetry broken phase and exactly at the EP3. The sudden change in quantum squeezing dynamics can be used to probe the phase transition and the EP3. Our work opens a pathway to manipulate quantum squeezing in semiconductor optomechanical platforms, offering potential advantages for quantum sensing and metrology.

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physics.opticsCross-listedarXiv:2605.27536•May 28, 2026
We investigate higher-order exceptional points and quantum squeezing of exciton polaritons in a pseudo-Hermitian semiconductor optomechanical system. We show that a third-order exceptional point (EP3) can emerge from the tripartite coupling among photons, excitons, and phonons under pseudo-Hermitian conditions. A pronounced two-mode quantum squeezing of exciton polaritons is revealed, and we demonstrate that this squeezing is significantly enhanced in the vicinity of the EP3. Furthermore, we find that in the PT-symmetric phase, the squeezing dynamics produce a frequency comb of exciton polaritons, whereas the squeezing remains constant over time in the PT-symmetry broken phase and exactly at the EP3. The sudden change in quantum squeezing dynamics can be used to probe the phase transition and the EP3. Our work opens a pathway to manipulate quantum squeezing in semiconductor optomechanical platforms, offering potential advantages for quantum sensing and metrology.
Higher-order exceptional points (EPs) in non-Hermitian systems have attracted great interest due to their advantages in sensitive enhancement and distinct topological features. However, realization of such EPs is still a challenge because more fine-tuning parameters are generically required in quantum systems, compared to the second-order EP (EP2). Here, we propose a non-Hermitian three-mode optomechanical system in the blue-sideband regime for predicting the third-order EP (EP3). By deriving the pseudo-Hermitian condition for the proposed system, one cavity with loss and the other with gain must be required. Then we show that EP3 or EP2 can be observed when the mechanical resonator (MR) is neutral, loss, or gain. For the neutral MR, we find that two degenerate or two nondegenerate EP3s can be predicted by tuning system parameters in the parameter space, while four nondegenerate EP2s can be observed when the system parameters deviate from EP3s, which is distinguished from the previous study in the red-detuned optomechanical system. For the gain (loss) MR, we find that only two degenerate EP3s or EP2s can be predicted by tuning enhanced coupling strength. Our proposal provides a potential way to predict higher-order EPs or multiple EP2s and study multimode quantum squeezing around EPs using blue-detuned non-Hermitian optomechanical systems.
Higher-order exceptional points (EPs), resulting from non-Hermitian degeneracies, have shown greater advantages in sensitive enhancement than second-order EPs (EP2s). Therefore, seeking higher-order EPs in various quantum systems is important for quantum information science. Here we propose a benchmark cavity optomechanical (COM) system consisting of a mechanical resonator coupled to two cavities via radiation pressure for predicting the third-order exceptional point (EP3). We first give the pseudo-Hermitian condition for the non-Hermitian COM system by taking the bath effects into account. Then we consider the mechanical gain effect, and we find that the pseudo-Hermitian COM system without PT\mathcal{PT}PT symmetry can host both EP3 and EP2 for symmetric and asymmetric cavities. In the symmetric case, only EP3 or EP2 can be predicted in the parameter space, but EP3 and EP2 can be transformed into each other by tuning the optomechanical coupling strength in the asymmetric case. We further consider the case of one cavity with gain. For this case, the pseudo-Hermitian COM system is PT\mathcal{PT}PT symmetric and can also host EP3 or EP2. The influence of system parameters on them is discussed. Our proposal provides a potential way to realize sensitive detection and study other physical phenomena around higher-order EPs in non-Hermitian COM systems.
The exotic entanglement dynamics associated with exceptional points (EP) have been explored in a ring mechanical system, which consists of a phase-dependent phonon-hopping interaction and two phonon-squeezing interactions. By modulating the gauge-invariant phase of the system, the spontaneous PT\mathcal{PT}PT-symmetry breaking can be generated, enabling the realization of higher-order EPs, such as second- and third-order EPs. The entanglement dynamics are strongly dependent on the orders of the EP. Specifically, both bipartite and tripartite entanglements emerge near the second-order EP, while the third-order EP leads to optimal bipartite entanglement with vanishing tripartite entanglement. Moreover, the asymmetric feature of the bipartite entanglement can be controlled by tuning the parity of the third-order EP through modulation of the system's gauge-invariant phase. The work indicates that the entanglement dynamics associated with EPs may provide a useful platform for realizing non-Hermiticity-enhanced quantum information processing.
The emergence of parity-time (PT) symmetry has greatly enriched our study of symmetry-enabled non-Hermitian physics, but the realization of quantum PT symmetry faces an intrinsic issue of unavoidable symmetry-breaking Langevin noises. Here we construct a quantum pseudo-anti-PT (pseudo-APT) symmetry in a two-mode bosonic system without involving Langevin noises. We show that the spontaneous pseudo-APT symmetry breaking leads to an exceptional point, across which there is a transition between different types of quantum squeezing dynamics; i.e., the squeezing factor increases exponentially (oscillates periodically) with time in the pseudo-APT-symmetric (broken) region. Such dramatic changes of squeezing factors and quantum dynamics near the exceptional point are utilized for ultraprecision quantum sensing. These exotic quantum phenomena and sensing applications can be experimentally observed in two physical systems: spontaneous wave mixing nonlinear optics and atomic Bose-Einstein condensates. Our Letter offers a physical platform for investigating exciting APT symmetry physics in the quantum realm, paving the way for exploring fundamental quantum non-Hermitian effects and their quantum technological applications.
Quantum physics can be extended into the complex domain by considering non-Hermitian Hamiltonians that are PT\mathcal{PT}PT-symmetric. These exhibit exceptional points (EPs) where the eigenspectrum changes from purely real to purely imaginary values and have useful properties enabling applications such as accelerated entanglement generation and the delay of the sudden death of entanglement in noisy systems. An interesting question is whether similar beneficial effects can be achieved away from EPs, since this would extend the available parameter space and make experiments more accessible. We investigate this by considering a PT\mathcal{PT}PT-symmetric optomechanical system but also consider what happens when two-mode squeezing interactions are included, taking us into the pseudo-Hermitian regime. The addition of squeezing is motivated by an attempt to extend the lifetime of the system's entanglement. While this does not prove to be the case, rich dynamics are nonetheless observed in both the pseudo-Hermitian and PT\mathcal{PT}PT-symmetric systems, including the sudden death and revival of entanglement under certain conditions. In both cases, we find that the sudden disappearance of entanglement can be mitigated at EPs, and also show that the revival of entanglement is quite robust to thermal noise in a group of parameters away from the EPs. This investigation extends our understanding of non-Hermitian systems and opens a new perspective for the development of quantum devices in non-Hermitian systems even away from EPs.
Multimode cavity optomechanical systems allow light to couple otherwise non-interacting mechanical resonators, enabling non-Hermitian phenomena such as exceptional points, where eigenfrequencies and eigenvectors of coupled modes coalesce. Accessing an exceptional point and its nearby parameter space is a first step towards chiral mode dynamics and topological state transfer. Diamond optomechanical devices support strong coherent optomechanical coupling required to tune resonances to an exceptional point, as well as strain-coupling to spin-defects for hybrid quantum technologies, but have not yet been used for multimode non-Hermitian physics. Here we tune to an exceptional point in a diamond optomechanical crystal, which uses structural symmetry breaking to produce two high-frequency mechanical resonances coupled to an optical cavity. The exceptional point is reached within a stable operating window below the phonon-lasing threshold, and we observe asymmetric redistribution of optomechanical damping and anti-damping between hybridized modes. These results establish diamond optomechanical crystals as a platform for non-Hermitian optomechanics, opening routes to topological mechanical dynamics in hybrid spin-phonon interfaces.