QFE-1N is the numerical companion to QFE-1, providing reproducible null tests for a superconducting-circuit implementation of the proposed quantum-fluctuation engine framework. The study models a transmon-like two-level system coupled to a truncated resonator battery and an equilibrium thermal reservoir using a detailed-balance Lindblad master equation. The simulations show thermal energy transfer into the resonator without the appearance of anomalous ergotropy or non-equilibrium free energy, consistent with standard quantum thermodynamics. The package includes the numerical model, simulation code, data, figures, reproducibility environment and verification files. No violation of the second law or experimental evidence of single-reservoir work extraction is claimed.
QFE-1N is the numerical companion to QFE-1, providing reproducible null tests for a superconducting-circuit implementation of the proposed quantum-fluctuation engine framework. The study models a transmon-like two-level system coupled to a truncated resonator battery and an equilibrium thermal reservoir using a detailed-balance Lindblad master equation. The simulations show thermal energy transfer into the resonator without the appearance of anomalous ergotropy or non-equilibrium free energy, consistent with standard quantum thermodynamics. The package includes the numerical model, simulation code, data, figures, reproducibility environment and verification files. No violation of the second law or experimental evidence of single-reservoir work extraction is claimed.
Quantum thermodynamics sits at the intersection of quantum mechanics and thermodynamics, aiming to understand how key thermodynamic concepts such as heat, work, and entropy behave in quantum systems. A primary interest in this field is the study and development of quantum heat engines, devices that convert the flow of thermal energy into work using a quantum system as the working medium. Conventional quantum heat engines require consistent external control to drive their operating cycle. In contrast, autonomous quantum heat engines operate without such external control, instead, their cyclic behavior emerges entirely from internal dynamics and the coupling to thermal reservoirs. In this thesis, we study an autonomous quantum heat engine circuit based on superconducting quantum circuits, in which thermal noise from heat reservoirs drives cyclic energy exchange between two superconducting resonators coupled with a superconducting quantum interference device (SQUID). In this thesis, classical circuit simulations of the autonomous quantum heat engine are implemented in AWR Design Environment using lumped-element resonators, coupling capacitors, and Josephson junction models. By mapping quantum components to their classical analogues and varying the external magnetic flux threading the superconducting quantum interference device, the resonance frequencies, quality factors, and coupling dynamics of the circuit are analyzed across two parameter sets. The simulated quality factor of the second resonator exceeded the threshold required for negative dissipation in both parameter sets, consistent with conditions favorable for coherent microwave generation. Transient simulations further revealed that above a threshold drive power, energy builds up at the second resonator’s resonance frequency through SQUID-mediated coupling. This provides qualitative evidence that the classical model captures the essential inter-resonator coupling mechanism. However, systematic quantitative discrepancies in resonance frequencies and dissipation rates are identified, attributed primarily to the linearized SQUID representation used in the classical model. These results demonstrate that classical circuit simulations can qualitatively reproduce key dynamical features of the studied autonomous quantum heat engine, while also revealing the limitations of classical approximations in capturing its full quantum behavior.
This repository contains the numerical data and computational codes supporting the results presented in the manuscript: "Engineered non-Gaussian Coherence as a Thermodynamic Resource for Quantum Batteries". The archive (data_QB.zip) includes all datasets, Jupyter notebooks, and figure files required to reproduce the results reported in both the main text and the Supplemental Material. Each figure is organised in a separate directory containing the corresponding data (.txt), code (.ipynb), and generated plots (.png/.pdf). The provided materials are sufficient to reproduce all figures and results without restriction. Detailed instructions and directory structure are described in the accompanying README.txt file. This dataset is made openly available to ensure transparency and reproducibility of the reported results.
Superconducting circuits provide a controllable and versatile platform for studying quantum phenomena and advancing quantum technologies. Josephson junctions and resonators are the central circuit elements, as they enable the realization of macroscopic quantum systems—such as qubits—that can be conveniently controlled, probed, and integrated with non-superconducting components. The implementation of a thermal reservoir through the integration of a dissipative element, such as a normal-metal resistor, offers an experimental platform for investigating quantum thermodynamics, heat management in circuits, on-chip thermal detectors, and the realization of quantum thermal machines. In this thesis, we integrate a mesoscopic normal metal and its associated thermometers as an on-chip bolometer within circuit quantum electrodynamics devices for thermal detection and quantum thermodynamics experiments. The on-chip bolometer is utilized as a sensitive and broadband thermal spectrometer to characterize the properties of a superconducting resonator and to investigate its dominant loss channels. We demonstrate the capability of our thermal detector to resolve the resonator modes over a wide frequency range extending above 20 GHz. When two thermal baths are connected through a qubit–resonator system, a quantum heat valve can be realized. This device has been demonstrated using both transmon and flux qubits. Photonic heat transport between the two baths is controlled by tuning the qubit energy via an applied static magnetic field. To model these experiments, we propose an approach based on electromagnetic simulation and microwave circuit theory, restricted to the linear-response regime. Despite this limitation, the method successfully captures the experimental observations and provides a practical tool for analysing and designing circuits for future experiments. A periodically driven qubit coupled to two unequal resonators, each terminated by a heat reservoir, enables the realization of a quantum Otto refrigerator. The use of a transmon qubit for this purpose is limited by its weak anharmonicity. We therefore explore alternative platforms for the experimental implementation of a quantum refrigerator based on charge and flux qubits, which exhibit strong anharmonicity. As an important step, we perform experiments on a driven flux qubit galvanically coupled to a resonator that is, in turn, weakly capacitively coupled to a heat reservoir. We observe interference patterns in the heat current arising from driving-induced coherence. In particular, resonance peaks in the heat transferred to the bath appear at driving frequencies that are integer fractions of the resonator frequency. These quantum features are governed by the relative phase accumulated by the qubit states under driving.
TSR-Q-1 presents a preregistered and falsifiable experimental protocol designed to test for structured late-time coherence residuals in superconducting transmon qubits. The protocol does not treat generic recoherence, non-exponential decay, or non-Markovian behavior as evidence for the proposed framework, since such phenomena may arise from conventional open-system mechanisms. Instead, it targets a specific normalized temporal scaling law, tₙ/T₂ = nᵏ, with the preregistered theoretical value k* = 1.4706, corresponding to the first two target locations t₂/T₂ = 2.7714 and t₃/T₂ = 5.0310. If the associated amplitude-scaling hypothesis is retained, the predicted ratio is A₃/A₂ ≈ 0.551. The accompanying computational validation package develops the analysis pipeline through five stages: preliminary signal injection, blind null testing, blind injection-recovery, multi-qubit global-k inference, and sensitivity mapping. The synthetic null models include stretched-exponential decay, 1/f^α correlated noise, random-telegraph/TLS-like contributions, slow drift, white noise, and device-to-device variability. These simulations validate the detectability, specificity, and sensitivity of the proposed analysis procedure under the tested synthetic noise families. They do not constitute experimental evidence for the existence of the predicted physical effect. The next stage is a preregistered hardware implementation using superconducting qubits, with device-specific null calibration, blind analysis, systematic controls, held-out replication, and, ultimately, independent experimental replication.
Quantum heat engines provide attractive means in quantum thermodynamics for studying the fundamentals of the flow of heat and work. Previous experimental implementations of heat engines operating at the level of a few excitation quanta have utilized external driving, which has made the observation of the produced work challenging. Conversely, autonomous quantum heat engines only require a flow of heat to operate and generate work. However, autonomous quantum heat engines have not yet been experimentally demonstrated in any system despite numerous theoretical investigations. Here, we experimentally realize an autonomous quantum heat engine based on superconducting circuits. We construct the engine circuit implementing an approximate Otto cycle by coupling two superconducting resonators with a superconducting quantum interference device, and coupling this system to spectrally filtered hot and cold reservoirs. By varying the experimental conditions, we observe coherent microwave power generation arising from the internal dynamics of the system driven only by the thermal reservoirs. Our results validate previous theoretical predictions for this circuit and pave the way for detailed studies of quantum effects in heat engines and for using heat-generated coherent microwaves in circuit quantum electrodynamics.
We develop a simulator for quantum computers composed of superconducting transmon qubits. The simulation model supports an arbitrary number of transmons and resonators. Quantum gates are implemented by time-dependent pulses. Nontrivial effects such as crosstalk, leakage to non-computational states, entanglement between transmons and resonators, and control errors due to the pulses are inherently included. The time evolution of the quantum computer is obtained by solving the time-dependent Schrödinger equation. The simulation algorithm shows excellent scalability on high-performance supercomputers. We present results for the simulation of up to 16 transmons and resonators. Additionally, the model can be used to simulate environments, and we demonstrate the transition from an isolated system to an open quantum system governed by a Lindblad master equation. We also describe a procedure to extract model parameters from electromagnetic simulations or experiments. We compare simulation results to experiments on several NISQ processors of the IBM Q Experience. We find nearly perfect agreement between simulation and experiment for quantum circuits designed to probe crosstalk in transmon systems. By studying common gate metrics such as the fidelity or the diamond distance, we find that they cannot reliably predict the performance of repeated gate applications or practical quantum algorithms. As an alternative, we find that the results from two-transmon gate set tomography have an exceptional predictive power. Finally, we test a protocol from the theory of quantum error correction and fault tolerance. We find that the protocol systematically improves the performance of transmon quantum computers in the presence of characteristic control and measurement errors.