Quantum sensing with high precision and sensitivity plays an important role in quantum technologies and quantum information processing. Here, we propose a nonreciprocal quantum metrological scheme for estimating rotational angular velocity in a hybrid light-matter platform, where the setup consists of a spinning ring cavity coupled to a two-level system and an auxiliary bosonic mode. Through the Sagnac effect, the angular velocity is converted into a direction-dependent detuning, which modifies the effective light-matter dressing of the hybrid system. As a result, the angular velocity is encoded not only into the renormalized hybrid-mode spectrum, but also into the virtual excitations generated by ultrastrong coupling. These virtual excitations modify the polaritonic frequency response to rotation and enhance the quantum Fisher information (QFI) associated with angular velocity estimation, without requiring direct extraction of virtual excitations. Moreover, since the Sagnac-Fizeau shift enters the virtual-transition energy denominators, the metrological response becomes intrinsically different for opposite driving directions, leading to a tunable nonreciprocal sensitivity contrast. In addition, we also discuss a readout scheme and show that bundle emission coincidence counting can serve as an auxiliary direction-dependent readout channel. Our results provide a route toward exploiting nonreciprocal light-matter dressing and virtual excitations as resources for quantum rotation sensing.
Quantum sensing with high precision and sensitivity plays an important role in quantum technologies and quantum information processing. Here, we propose a nonreciprocal quantum metrological scheme for estimating rotational angular velocity in a hybrid light-matter platform, where the setup consists of a spinning ring cavity coupled to a two-level system and an auxiliary bosonic mode. Through the Sagnac effect, the angular velocity is converted into a direction-dependent detuning, which modifies the effective light-matter dressing of the hybrid system. As a result, the angular velocity is encoded not only into the renormalized hybrid-mode spectrum, but also into the virtual excitations generated by ultrastrong coupling. These virtual excitations modify the polaritonic frequency response to rotation and enhance the quantum Fisher information (QFI) associated with angular velocity estimation, without requiring direct extraction of virtual excitations. Moreover, since the Sagnac-Fizeau shift enters the virtual-transition energy denominators, the metrological response becomes intrinsically different for opposite driving directions, leading to a tunable nonreciprocal sensitivity contrast. In addition, we also discuss a readout scheme and show that bundle emission coincidence counting can serve as an auxiliary direction-dependent readout channel. Our results provide a route toward exploiting nonreciprocal light-matter dressing and virtual excitations as resources for quantum rotation sensing.
We propose a scheme for nonreciprocal quantum rotation sensing in two coupled microring resonators, one of which rotates in a clockwise direction. Driving the rotating resonator in two directions induces the opposite Sagnac-Fizeau shifts. By pumping the other nonlinear resonator via classical field, directional squeezing is generated along the pump direction due to the phase-matching condition, which leads to an asymmetric detuning and chiral photon interaction between the two resonators. As a result, the estimation of the Sagnac-Fizeau shift is shown to be nonreciprocal, i.e., the estimation precision is dramatically enhanced for the forward-input case, where most of the accessible information is predominantly stored in the primary resonator, but not for the backward-input one. Further, we evaluate the performance of several Gaussian measurements and analyze how measurements of the second-order coherence g (2) (0) can extract quantum-enhanced information and improve measurement precision. The proposed scheme offers what we believe to be a new perspective for the design of a nonreciprocal quantum gyroscope.
We propose a scheme to realize nonreciprocal multiphoton bundle emission in a spinning resonator. The system consists of a rotating two-mode cavity directly coupled to a two-level atom, enabling efficient excitation of the desired multiphoton bundle states. These photon bundles originate from leapfrog transitions between dressed states, established through the coherent atom-cavity coupling under multiphoton resonance conditions. When the rotating resonator is driven in different directions, it generates opposite Sagnac-Fizeau shifts, making the resonant conditions dependent on the direction. As a consequence, distinct multiphoton transition channels can be selectively activated by tuning the driving direction and frequency. The nonreciprocal two-photon or three-photon bundle emission with the same and different modes can be implemented with a high tunability. This scheme provides a feasible route toward direction-controlled multiphoton emitters with potential applications in chiral quantum information processing.
ABSTRACT We propose a scheme for realizing nonreciprocal photon–phonon entanglement in a hybrid cavity magnomechanical system, where the Barnett effect and the Sagnac effect are used. By changing the rotation direction of the cavity field and the direction of the bias magnetic field or the direction of rotation of the YIG sphere, we can induce an opposite Sagnac–Fizeau frequency shift on the cavity and a Barnett frequency shift of the magnon mode, which lead to nonreciprocity. Our results indicate that through selecting appropriate parameters, such as frequency detuning or magnomechanical coupling strength or bath temperature, the nonreciprocity of photon–phonon entanglements in this system can be correspondingly manipulated (such as switched off or on). And through combining the Barnett effect with the Sagnac effect, the entanglement nonreciprocity can be significantly enhanced. We find that nonreciprocal entanglement exhibits excellent tolerance to elevated bath temperature. Our paper provides a promising approach for engineering various nonreciprocal devices with the Barnett and the Sagnac effects.
Virtual excitations, inherent to ultrastrongly coupled light-matter systems, induce measurable modifications in system properties, offering a novel resource for quantum technologies. In this Letter, we demonstrate how these virtual excitations and their correlations can be harnessed to enhance precision measurements, without the need to extract them. Building on the paradigmatic Dicke model, which describes the interaction between an ensemble of two-level atoms and a single radiation mode, we propose a method to harness hybridized light-matter modes whose renormalized frequencies encode the effects of virtual excitations for quantum metrology. Remarkably, we find that, for a fixed squeezing parameter ξ, exploiting virtual squeezing through oscillator frequency shifts yields a quadratic enhancement in estimation precision-scaling as exp(4ξ)-compared to the conventional exp(2ξ) scaling of real squeezed states. These results show that virtual excitations, though unobservable, can drive metrological performance beyond the standard quantum limit. Our approach establishes a broadly applicable framework for high-precision measurements across a wide class of ultrastrongly coupled quantum systems.
Quantum sensing promises measurement precision beyond classical shot-noise limits, but practical implementations face a persistent gap between idealized theoretical protocols and the constraints imposed by real hardware: thermal noise, directional asymmetry in light-matter coupling, fabrication-limited mode matching, non-Hermitian spectral structure, and adversarial network channels. This paper synthesizes six recent findings—spanning quant-ph and physics.optics—to argue for a candidate structural reading: the dominant engineering bottlenecks in near-term quantum sensing are not primarily about generating nonclassical probe states, but about *preserving and certifying metrological information* across the full sensing chain from state preparation through transduction to readout and network distribution. This is offered as a heuristic reading, not a formal derivation, since the sources span distinct physical platforms and do not share a unified Hamiltonian framework. The synthesized findings are: (1) hot-state bosonic probes can match or exceed ground-state protocols under realistic decoherence, via parity-selection and coherence-between-displacements mechanisms [corpus:arxiv:2606.13650v1]; (2) nonreciprocal rotation sensing exploits virtual-excitation asymmetry in spinning cavities to encode angular velocity into direction-dependent quantum Fisher information [corpus:arxiv:2606.10984v1]; (3) fiber-cavity substrate fabrication can be pre-selected via in-situ reflectometry to achieve 95–99% mode-matching yield before expensive coating runs [corpus:arxiv:2606.12168v1]; (4) fourth-order exceptional surfaces in dissipative atomic systems provide enhanced sensitivity with improved robustness relative to isolated exceptional points [corpus:arxiv:2606.10865v1]; (5) time-frequency grid states enable model-free correction of channel-induced coordinate distortions, improving Gaussian-shape fidelity from 76.2% to 90.0% [corpus:arxiv:2606.12216v1]; and (6) bilateral Pauli-twirling forces effective channels into Bell-diagonal form, enabling simultaneous quantum-limited precision and certified eavesdropper-distinguishable estimation over insecure networks [corpus:arxiv:2606.10700v1]. The falsification path for the central thesis is: demonstrate a practical quantum sensing system in which the dominant fidelity loss is attributable to probe-state generation rather than transduction, mode-matching, or channel certification, with each loss channel independently quantified. --- Authorship: Saluca Agentic AI Research Team (Saluca LLC). AI-drafted from arXiv preprint corpus on the date in the filename. Cited arXiv preprints: 2606.09765v1, 2606.10700v1, 2606.10865v1, 2606.10984v1, 2606.11048v1, 2606.11311v1, 2606.12168v1, 2606.12216v1, 2606.12284v1, 2606.13375v1, 2606.13412v1, 2606.13521v1, 2606.13559v1, 2606.13606v1, 2606.13638v1, 2606.13641v1, 2606.13650v1
Cavity-magnon systems, combining magnons and photons, offer a versatile platform for studying quantum entanglement and advancing quantum information science. In this work, we propose a scheme for generating nonreciprocal magnon-magnon entanglement in a hybrid system consisting of two yttrium iron garnet spheres coupled to a spinning whispering-gallery-mode cavity. By leveraging the magnon Kerr nonlinearity and the Sagnac effect arising from the cavity rotation, we show that the entanglement can be substantially enhanced, and the resulting entanglement exhibits pronounced nonreciprocal characteristics. Furthermore, our scheme demonstrates that the entanglement remains robust against thermal noise and persists at bath temperatures up to 100 mK. This work underscores the potential of spinning cavity-magnon systems as a versatile platform for realizing nonreciprocal quantum devices and facilitating the development of quantum technologies.