Quantum reservoir engineering leverages dissipative processes to achieve desired behaviour, with applications ranging from entanglement generation to quantum error correction. Therein, a structured environment acts as an entropy sink for the system and no time-dependent control over the system is required. We develop a theoretical framework for active reservoir engineering, where time-dependent control over a quantum system is used to manipulate its environment. In this case, the system may act as an entropy sink for the environment. Our framework captures the dynamical interplay between system and environment, and provides an intuitive picture of how finite-size effects and system-environment correlations allow for manipulating the environment by repeated initialisation of the quantum system. We illustrate our results with two examples: a superconducting qubit coupled to an environment of two-level systems and a semiconducting quantum dot coupled to nuclear spins. In both scenarios, we find qualitative agreement with previous experimental results, illustrating how active control can unlock new functionalities in open quantum systems.
Quantum reservoir engineering leverages dissipative processes to achieve desired behaviour, with applications ranging from entanglement generation to quantum error correction. Therein, a structured environment acts as an entropy sink for the system and no time-dependent control over the system is required. We develop a theoretical framework for active reservoir engineering, where time-dependent control over a quantum system is used to manipulate its environment. In this case, the system may act as an entropy sink for the environment. Our framework captures the dynamical interplay between system and environment, and provides an intuitive picture of how finite-size effects and system-environment correlations allow for manipulating the environment by repeated initialisation of the quantum system. We illustrate our results with two examples: a superconducting qubit coupled to an environment of two-level systems and a semiconducting quantum dot coupled to nuclear spins. In both scenarios, we find qualitative agreement with previous experimental results, illustrating how active control can unlock new functionalities in open quantum systems.
In this work, we're looking at a simplified Hamiltonian model for information erasure in Quantum Internet of Things (QIoT) systems - basically just two qubits that interact with each other. We've set up a toy model where we continuously measure one qubit and use that info to control the other one. This basically lets us engineer the reservoir entropy before the environment starts messing things up. The feedback we engineer through the reservoir connects directly to how much energy it costs to erase information, and this lets us control how much mutual information the qubits share. We discuss both so-called ‘conditional’ (i.e., stochastic) and ‘unconditional’ (ensemble-averaged) master equations to describe the dynamics of the system under measurement-and-feedback protocol. This mutual information is quantified and embedded into a correlation-corrected Landauer bound, showing that quantum correlations can help us erase information using less work than the usual Landauer limit. A simple stability analysis shows the existence of an optimal feedback gain that maximizes the entropy transfer while maintaining system stability. So, our simple model here connects the quantum-level processes with the bigger thermodynamic picture - things like heat flow, entropy, and free energy when the system's out of equilibrium. We link explicitly feedback strength, dissipation rates, and correlation dynamics to provides a toy but physically intuitive model for the control in QIoT. Our model is based on the recent advances in quantum thermodynamics, reservoir engineering, and feedback-controlled quantum systems. This gives us a new way to think about building energy-efficient QIoT systems and opens some interesting possibilities for scaling more nodes, dealing with memory effects in the environment, and optimizing control across entire networks.
Quantum communication provides essentially secure transmission of information and quantum sensing provides measurement sensitivities better than classical. These powers come because of unique quantum processes, especially superposition and entanglement. Although there is a significant theoretical and experimental development, the phenomenon of decoherence is still one of the main limiting factors in performance and scalability of quantum devices. The importance of this study is that it considers an active approach to decoherence as one of the key impediments to scalable quantum technologies. Although the research on the noise sources and error mechanisms has been done extensively, the characterization is not enough to be applied to the real world. This study makes use of a theoretical and computation effort to explore scalable quantum technologies integrated decoherence control strategies. The research paper is based on the open quantum systems framework, in which quantum systems are represented as finite-dimensional systems that interact with the external environment. The findings of the study highlight that active decoherence control plays an important role in enhancing performance of open quantum systems. Without any control, the simulated quantum system is characterized by a fast decoherence time, coherence times are short, about 20 u ms, and the physical error rate is about 2.5%. The hybrid strategy is a feasible way to achieve fault-tolerant quantum operation and the transition point between theory-based control architectures and experimental hardware limitations, thus speeding up the development of reliable large-scale quantum technologies. The findings affirm that each of the isolated methods like dynamical decoupling, quantum error correction, or reservoir engineering can only be a partial solution when used alone. Adaptive and real-time control schemes responding dynamically to changing noise environments also require further research to develop them.
This work develops a control-oriented theoretical framework for the manipulation of transient emission spectra and field-state purity in a qubit interacting with a broadband squeezed reservoir. We model the joint qubit-field dynamics using a time-resolved open quantum system formalism. This establishes a direct, quantitative connection between transient spectral characteristics, quantum purity evolution, and controllable system parameters. The analysis reveals that nonclassical reservoir properties, particularly squeezing-induced correlations, strongly influence both spectral deformation and coherence redistribution during the early-time dynamics. Building on this foundation, the work explores practical control strategies aimed at engineering the system’s dynamical response. Pulse shaping and time-dependent modulation of qubit-reservoir coupling offer effective control tools. These regulate spectral broadening, suppress unwanted decoherence, and accelerate convergence toward stabilized operating regimes. In addition, feedback-assisted qubit probing protocols are investigated as a means of monitoring and controlling field purity while minimizing measurement back-action on the squeezed mode. Our results show that well-designed control loops can balance information extraction and disturbance. This enables efficient regulation of nonclassical field properties. The proposed approach highlights transient spectral measurements as a powerful diagnostic and control resource, linking observable emission features to underlying quantum correlations and purity dynamics. From an engineering perspective, the framework offers practical guidelines. These guide the design of feedback-stabilized quantum emitters and reservoir-engineered coherence control. These findings are directly relevant to emerging quantum technologies, including cavity and circuit quantum electrodynamics, quantum sensing, and quantum communication systems operating in nonclassical environments.
Quantum steering ellipsoids (QSEs) provide a geometric representation, within the Bloch picture, of all possible states to which one qubit can be steered through measuring another correlated qubit. However, in realistic settings, quantum systems are inevitably coupled to their environment, resulting in decoherence and degradation of the QSE. Here, by investigating how local dissipative environments coupled to each qubit affect the quantum steering, we find that the geometry of each party's QSE is closely tied to the non-Markovian effect and the formation of a bound state in the energy spectrum of the total qubit-environment system. The bound state provides the ability and the non-Markovian effect provides the dynamical way for preserving the QSE. We systematically examine the characteristics of QSEs under three distinct scenarios, i.e., two-sided bound states, one-sided bound states, and no bound state, revealing a diverse range of steering types. Our work establishes quantum reservoir engineering as a tunable strategy for protecting and controlling quantum steering in open systems, offering a practical pathway toward robust steering-based quantum technologies.
Squeezed thermal reservoirs, characterized by thermal noise with anisotropic fluctuations, have profound implications in quantum thermodynamics and serve as powerful resources for quantum information. However, their experimental realizations remain challenging. Existing schemes typically rely on injected squeezed light, time-dependent modulation, or driven nonlinear interactions, which introduce complexity and limit experimental feasibility. Using only time-independent linear coupling to a lossy mode within a normal thermal environment, we identify a general and experimentally accessible framework for squeezed-reservoir engineering, applicable across platforms such as circuit and cavity quantum electrodynamics as well as coupled cavity systems. We illustrate the framework through two experimentally relevant cases: directional phase coherence extension in two-level systems like qubits or atoms, and dissipative quadrature squeezing in bosonic modes like photons or phonons. By eliminating the need for active control or squeezed input, our passive linear-coupling approach provides a resource-efficient and practical pathway to dissipative squeezing, decoherence suppression, entanglement stabilization, quantum simulation, and the exploration of unconventional quantum thermodynamics and phase transitions.
Abstract We determine how to optimally reset a superconducting qubit which interacts with a thermal environment in such a way that the coupling strength is tunable. Describing the system in terms of a time-local master equation with time-dependent decay rates and using quantum optimal control theory, we identify temporal shapes of tunable level splittings which maximize the efficiency of the reset protocol in terms of duration and error. Time-dependent level splittings imply a modification of the system-environment coupling, varying the decay rates as well as the Lindblad operators. Our approach thus demonstrates efficient reservoir engineering employing quantum optimal control. We find the optimized reset strategy to consist in maximizing the decay rate from one state and driving non-adiabatic population transfer into this strongly decaying state.