Coherence-Driven Phenomena in Quantum & Hybrid Systems

Updated 2 January 2026

Coherence-driven phenomena are processes characterized by the maintenance and manipulation of quantum superpositions and dynamical alignments, enabling new behaviors in diverse systems.
They underpin advancements in quantum information, dynamical processes in condensed matter, and the engineering of quantum heat engines and coherence-induced forces.
These phenomena also extend to classical networks and AI inference, where feedback, memory effects, and topologically protected states enhance system performance.

Coherence-driven phenomena refer to physical, mathematical, and informational processes in which the presence, generation, or manipulation of coherence—quantified as the maintenance of quantum superpositions or persistent dynamical alignment—introduces qualitatively new behaviors, enables or limits performance, or decisively shapes emergent properties of a system. These phenomena span from foundational resource-theoretic aspects of coherence in quantum information to its role in dynamical processes in condensed matter, quantum engines, open quantum systems, network theory, and even the structure of argumentation and AI inference. Below is a comprehensive technical overview anchored in significant research contributions.

1. Coherence as a Quantifiable Resource

Quantum coherence embodies the existence of nonclassical superpositions, formally defined with respect to a chosen orthonormal basis. The rigorous resource-theoretic framework fixes the set of incoherent (diagonal) states and classifies operations (IO, MIO, SIO, etc.) incapable of generating coherence from incoherent inputs (Streltsov et al., 2016). Core quantitative measures include the $\ell_1$ –norm of coherence $C_{\ell_1}(\rho)=\sum_{i\ne j}|\rho_{ij}|$ and relative-entropy coherence $C_r(\rho)=S(\Delta[\rho])-S(\rho)$ , where $\Delta$ is full dephasing in the reference basis.

Resource theories prescribe conversion rates (distillable coherence, coherence cost), and reveal the operational significance: coherence is the parent resource from which both entanglement (communication) and "magic" (universal computation) can be derived, unifying these quantum advantages (Mukhopadhyay et al., 2018). Asymptotic distillation protocols, catalytic processes, and monotone properties anchor coherence as a nonclassical resource underpinning quantum information processing and error-resilient computation.

2. Coherence-Driven Dynamical Phenomena in Quantum Systems

Spin Qubits and Active Noise Suppression

In electron spin qubits hosted in semiconductor quantum dots, the coherence time ( $T_2^*$ ) is often limited by low-frequency (quasi-static) environmental noise—predominantly due to nuclear spin diffusion. Feedback control based on real-time Bayesian estimation can suppress these fluctuations, extending $T_2^*$ by more than an order of magnitude (from ~28 ns to ~767 ns), while uncovering a new coherence limit set by high-frequency charge noise at the Rabi frequency (Nakajima et al., 2020). This active decoupling strategy makes it possible to separate and diagnose distinct decoherence regimes, guiding material and control improvements to achieve gate fidelities exceeding 99%.

Electron-Hole Coherence in Solids

High-harmonic generation (HHG) in strongly driven solids is directly governed by the coherence between electron and hole states during the light-driven excursion. Doping-dependent ultrafast dephasing, characterized via suppression in HHG yields of higher orders, quantifies coherence lifetimes and reveals density-dependent decoherence arising from many-body interactions (Heide et al., 2021). This platform enables direct, subcycle-resolved measurement of electronic coherence in condensed phases, informing the engineering of attosecond quantum light sources and probes.

Coherence-Induced Quantum Forces

The spatial first-order coherence $g^{(1)}(x,x')$ between spatially separated matter fragments gives rise to effective quantum forces, which can be attractive or repulsive depending on the phase structure. This "coherence force" is maximal for perfect superfluid states ( $g=1$ ) and vanishes in Mott insulators ( $g=0$ ), scaling linearly with condensate fraction (Elsayed, 2021). It provides a mechanism for enhanced or suppressed tunneling in potential landscapes, directly accessible and measurable in ultracold atom setups.

3. Coherence in Quantum Thermodynamics and Engines

Coherence is not merely a byproduct but a direct contributor to irreversibility in driven quantum thermodynamic processes. Experiments in NMR platforms show that when a system is driven out of equilibrium, the irreversible entropy production $\Delta S_{\mathrm{irr}}$ decomposes into a coherence term (relative-entropy of coherence created by the drive) and a population-mismatch term, both computable via full state tomography (Shende et al., 2024). Enhanced nonequilibrium entropy due to coherence has been experimentally verified to saturate generalized Clausius bounds.

Quantum heat engines can be engineered to use coherence as the sole thermodynamic resource, with no traditional heat flow between temperature reservoirs. Jaynes-Cummings coupling to a "coherence bath" charges qubits, allowing the extraction of work proportional to the internal part of coherence, $C_{\mathrm{int}}(\rho)$ , under energy-preserving unitaries (Aimet et al., 2022). Optimizing work and efficiency involves balancing the flow and retention of coherence, and increasing system size up to a non-trivial optimum (e.g., $N=4$ qubits). Furthermore, periodically driven inelastic engines exhibit power/efficiency enhancements driven by steady-state coherence, with geometric (Berry phase) effects magnified by quantum superpositions, as seen in constructive interference terms and pumped transport (Lu et al., 2023).

Autonomous thermal machines (QATMs) can filter bath-induced decoherence and enable non-Markovian memory effects, allowing coherence injection to boost quantum battery performance (power, ergotropy) by preserving the charger's coherence and modulating the coupling between charger and battery (khoudiri et al., 3 Sep 2025).

4. Coherence-Driven Phenomena in Classical and Hybrid Systems

Complex Networks and Connectivity-Driven Coherence

The emergence of dynamical coherence in networks of coupled nonidentical elements is analytically linked to the network's spectral gap and mean degree. In random graphs, coherence enhancement is proportional to average node degree, while in locally connected (regular) networks, coherence requires the mean degree to scale rapidly with system size (Pereira et al., 2013). Introducing even a small number of random shortcuts can restore coherence in regular networks exhibiting incoherence due to insufficient connectivity, an analytically predictable analogue of the small-world effect.

Non-Markovian and Memory-Driven Coherence

Temporal coherence between agents with heterogeneous and asymmetric dynamics can be sustained via non-Markovian coupling mechanisms that break reciprocity. The Coupled Memory Graph Process (CMGP) demonstrates that directed memory kernels enable "ghost coherence," defined by high temporal cross-correlation even with mismatched mean-squared displacement scaling, a regime inaccessible to classical diffusion or generalized Langevin paradigms (Sarkar, 16 May 2025). The "memory engine"—a single agent coupled to its self-generated viscoelastic memory field—transits from diffusion to phase-locked coherent dynamics when cross-feedback surpasses a critical threshold in substrate stiffness, marked by energy saturation, transfer entropy peaks, and bifurcation in linear stability (Sarkar, 27 May 2025).

5. Topological and Many-Body Coherence Mechanisms

Kondo Insulators and Topological Materials

The emergence of robust surface states in Kondo insulators (e.g., magnetically alloyed SmB $_6$ ) is a direct consequence of many-body Kondo coherence. The opening of a direct hybridization gap at a coherence-formation temperature $T_{\mathrm{coh}}$ enables topologically protected surface conduction robust to strong magnetic disorder and antiferromagnetic order, so long as the direct gap remains open and exceeds disorder-induced broadening (Miao et al., 2019).

Floquet Systems and Interband Coherence

In adiabatic pumping of periodically driven (Floquet) systems, interband coherence in the initial state induces corrections to the net displacement of wavepackets persisting even in the adiabatic limit—beyond what is predicted by single-band Berry curvature integrals (Wang et al., 2015). The "interband coherence correction" probes Floquet band topology and is sensitive to topological transitions and degeneracies, opening control pathways for coherent transport leveraging initial-state engineering.

6. Information, Argumentation, and Coherence-Driven Inference

In symbolic and neurosymbolic AI, global rationality or coherence of arguments can be formalized as a combinatorial optimization over weighted coherence graphs. Given local, pairwise consistency/preference scores (e.g., extracted by LLMs), maximizing the global coherence of a set of propositions reduces to a weighted MAX-CUT problem (Huntsman et al., 19 Feb 2025, Huntsman, 23 Sep 2025). This coherence-driven inference mechanism enables robust resolution of inconsistencies and the identification of maximally self-supporting subsets in legal, policy, and decision contexts, blending neural "System 1" local estimation with "System 2" global search.

7. Holography, Causality, and Emergent Coherence

Foundationally, proposals in quantum gravity link the structure of classical spacetime to universal coherence on causal horizons. The phenomenology argues that the quantum information lives exclusively on causal boundaries, and decoherence at the horizon for an observer yields their classical spacetime. This principle predicts Planck-scale correlated fluctuations observable in MHz-band interferometric experiments, and may explain large-angle anomalies in the cosmological microwave background as signatures of horizon-wide coherence (Kwon, 2022).

These diverse phenomena underscore that coherence—beyond its abstract quantum-theoretic meaning—has concrete, enabling, and sometimes limiting roles in dynamical, informational, and physical properties across quantum, classical, and hybrid systems. Understanding and harnessing coherence-driven effects remain central to advances in quantum technologies, condensed matter, complex networks, nonequilibrium thermodynamics, and foundational physics.