New Method Reveals Hidden Order in Complex Systems

Scientists have developed a novel spectroscopic technique, termed dissipative spectroscopy, to extract spectral information from complex systems by harnessing controlled dissipation. Xudong He and Yu Chen, from the University of Science and Technology of China, present this framework, establishing a general dissipative response applicable to both Markovian and non-Markovian environments. Their research details a protocol to access the dissipative spectrum through driven oscillation-dissipation resonance, revealing previously hidden signatures of critical behaviour and macroscopic order. This work is significant because it identifies two-particle soft modes near critical points and predicts power-law growth following a dissipation quench, even in quasiparticle-dominant regimes often dismissed as trivial. By introducing extended dissipative susceptibilities and demonstrating their utility in a fermionic model, the authors offer a versatile tool for probing both equilibrium properties and predicting non-equilibrium dissipative dynamics.

Scientists have devised a novel technique for understanding complex materials by carefully controlling how energy fades away within them. This method reveals hidden details about a material’s behaviour, even when traditional approaches fail to detect changes, and promises a fresh perspective on predicting how systems evolve and respond to external stimuli. This work introduces dissipative spectroscopy, a technique that extracts spectral information from quantum materials through controlled dissipation, opening avenues to study phenomena previously hidden from view. The research details how this approach can identify subtle changes within materials near critical points, moments of dramatic transformation, and even predict the emergence of order in seemingly disordered systems. Probing quantum dynamics often requires distinguishing between external influences and inherent noise. Equipped with recent advances in dissipation engineering, researchers are now able to isolate and analyse the contributions from these different sources. By treating environmental coupling as a controlled perturbation, a non-Hermitian linear response theory has been developed, providing a generalised susceptibility that encodes spectral information via early-time dissipative transients. The resulting dissipative spectrum (DS) uncovers soft modes near quantum critical points, indicating a propensity for change. Strikingly, even when the DS exhibits well-defined quasiparticle excitations, their scaling behaviour signals the emergence of macroscopic order on the disordered side of the transition, a phenomenon not observed in conventional, unitary quenches. Thus, DS exposes a distinct form of dissipation-induced quantum criticality, offering a new perspective on how order arises from disorder. Furthermore, the study demonstrates that extended dissipative susceptibilities capture memory effects, clarifying the conditions under which the DS remains valid. At the heart of this work lies a general dissipative response theory, where a series of generalised susceptibilities and spectroscopies can be defined. This framework extends beyond conventional Hermitian spectroscopy, providing an alternative pathway for spectral diagnostics in open quantum settings, and offers a versatile tool for probing equilibrium properties and predicting nonequilibrium dissipative dynamics. Mapping energy loss via driven dissipation and extended susceptibilities Dissipative spectroscopy serves as the central technique employed in this work to characterise systems through controlled dissipation. This method establishes a general dissipative response applicable to both Markovian and non-Markovian environments, allowing access to the dissipative spectrum (DS) via driven oscillation-dissipation resonance. By driving the system and simultaneously monitoring its decay, researchers can map out the energy landscape and identify key features indicative of underlying physical phenomena. This approach differs from traditional spectroscopy, which typically relies on observing absorption or emission of energy, instead focusing on how energy is lost from the system. Establishing a protocol to access the DS required careful consideration of the system’s response to external stimuli. The research team implemented extended dissipative susceptibilities, tools that capture leading memory effects within the system, and demonstrated their utility within a dissipative fermionic model. These susceptibilities provide a more accurate description of the system’s behaviour when past interactions influence present states, a common occurrence in many physical systems. Such detailed analysis allows for the identification of two-particle soft modes near critical points, subtle changes in the system’s behaviour that signal an impending phase transition. The study reveals the emergence of macroscopic order exhibiting power-law growth following a dissipation quench. A dissipation quench involves abruptly changing the rate at which energy is removed from the system, allowing researchers to observe how the system reorganises itself. This dynamic observation is made possible by the precise control offered by the experimental setup, which allows for accurate manipulation of the dissipation rate. The work highlights that these distinctive signatures are particularly prominent in quasiparticle-dominant regimes, areas previously considered less informative. Inside the experimental configuration, the team leveraged the versatility of the DS to probe both equilibrium properties and predict nonequilibrium dissipative dynamics. By carefully analysing the decay patterns, they gained insights into the fundamental characteristics of the system at rest, as well as its behaviour when driven away from equilibrium. This dual capability positions dissipative spectroscopy as a powerful tool for investigating a wide range of physical phenomena, offering a new perspective on understanding complex quantum systems. Dissipative spectra reveal soft modes and memory effects in quantum critical systems Researchers established a general dissipative response theory, revealing how to extract spectral information from systems via controlled dissipation. Initial findings demonstrate that the resulting dissipative spectrum (DS) identifies two-particle soft modes near quantum critical points, signifying instabilities in the system as it transitions between different states of matter. Moreover, the DS predicts the emergence of macroscopic order exhibiting power-law growth following a dissipation quench, even in regimes previously thought to be inert. By introducing extended dissipative susceptibilities, the study captures leading memory effects, essentially how the system ‘remembers’ its past states. These susceptibilities were then successfully applied to a dissipative fermionic model, a system of interacting particles, further validating the approach. The research indicates that the DS is not only accessible but also a versatile tool for probing both equilibrium properties and predicting nonequilibrium dissipative dynamics. At the heart of this framework lies the dissipative susceptibility, a measure of how the system responds to external perturbations. Calculations show that in the low-temperature Markovian limit, the dissipative susceptibility simplifies to a form directly related to the dissipation strength. This simplification allows for easier analysis and interpretation of the results. By modulating the dissipation strength with a cosine function, researchers were able to isolate the resonant component of the dissipative response. The oscillatory part of the response revealed a linear growth in time, proportional to the amplitude of the dissipative spectrum. This linear growth signifies resonance, where the system strongly responds to the external perturbation. The amplitude and phase of this resonant signal provide crucial information about the system’s properties, offering a new pathway for spectral diagnostics in open quantum settings. Indeed, the DS exposes a distinct form of dissipation-induced quantum criticality, extending beyond conventional Hermitian spectroscopy. Harnessing energy loss to reveal quantum material behaviour Scientists have long sought ways to observe the hidden order within complex quantum systems, often hampered by the difficulty of teasing out subtle signals from background noise. Now, a new approach, dissipative spectroscopy, offers a potential breakthrough, not simply by improving signal clarity, but by actively using dissipation itself as a tool for analysis. Rather than fighting against energy loss, this technique embraces it, revealing previously obscured features in how quantum materials behave as they approach critical points. This isn’t merely a refinement of existing methods; it represents a shift in perspective, viewing decay as informative rather than destructive. Understanding these systems remains a considerable challenge, as traditional spectroscopic techniques struggle with materials where interactions are strong and disorder is prevalent. Existing methods often assume a level of equilibrium that doesn’t exist in many real-world scenarios, limiting their ability to predict how these materials will respond to external stimuli. This new framework, however, extends beyond equilibrium, offering insights into the dynamics of systems driven far from balance, and potentially predicting their behaviour following a sudden change. It allows researchers to identify soft modes, patterns of collective excitation, that signal an impending transition to a new state of matter. While demonstrated in a fermionic model, applying it to more complex systems will require overcoming significant computational hurdles and experimental constraints. Moreover, the precise relationship between the observed dissipative spectrum and the underlying microscopic interactions remains an open question, demanding careful theoretical modelling and validation. Beyond this, future work could explore how this method integrates with other spectroscopic techniques, creating a more complete picture of quantum material behaviour. Once refined, this approach promises to accelerate the design of new materials with tailored properties, impacting fields from quantum computing to energy storage. 👉 More information 🗞 Dissipative Spectroscopy 🧠 ArXiv: https://arxiv.org/abs/2602.14557 Tags: