Welcome and Conference Opening

• Francesco Campaioli (University of Padova)
• simone montangero

What does it take to cool many-body quantum systems? (Theme 2. Quantum effects in energy processes and materials)

• Christiane Koch (Freie Universität Berlin)

The development of efficient techniques to cool quantum systems has been instrumental for the emergence of quantum technologies. Preparing a many-body quantum system in a pure target state is, for example, a prerequisite for its use to study complex interactions or implement quantum computations. State preparation needs to work irrespective of the initial state of the quantum system and thus requires reduction of both system energy and entropy. A powerful way to engineer such desired dissipative dynamics is by coupling to auxiliary qubits. While protocols where the number of auxiliary qubits increases with the system size are of limited practical usefulness, "dilute" cooling is possible for certain many-body quantum systems. I will discuss two examples of frustration-free one-dimensional spin chains and show that they can be driven into their (topological) ground state by measuring two adjacent system sites only. I will then ask what it takes to make the auxiliary qubits resemble a cold bath in nature. A natural cold bath will cool a quantum system without any knowledge of the system’s spectrum or quantization axis. Assuming a reservoir of auxiliary qubits prepared in their ground state, I will introduce a protocol for universal cooling of many-body quantum systems.

Tracking correlations in the Optical Bloch Equations: Dynamics, Energetics (Theme 1. Energy advantage and cost of quantum technology)

• Maria Maffei (Dipartimento di Fisica, Universita di Bari)

Optical Bloch Equations (OBEs) describe the dynamics of atoms that are classically driven on the one hand and coupled to thermal baths on the other, situations ubiquitous in quantum optics, quantum thermodynamics and quantum technologies. OBEs have given rise to consistent thermodynamic analyses, where work (heat) flows from the drive (the bath), yet, in these descriptions, the role played by the correlations between the atom and the field has remained elusive. At the fundamental level, the OBEs can be derived from the Hamiltonian evolution of closed and isolated emitter-field systems captured by a Collision Model (CM), where the fields encompass both drives and baths. In Ref. [ “Tracking light-matter correlations in the Optical Bloch Equations: Dynamics, Energetics”, S.P. Prasad, M. Maffei, P.A. Camati, C. Elouard, A. Auffèves, arXiv:2404.09648], we used the CM description to explicitly keep track of the atom-field correlations formed during single collisions and exploit this model to shed new light on the energy exchanges between atom and field. From a dynamical viewpoint, our model yields a splitting between effective Hamiltonian processes and correlating processes in the dynamical equations respectively ruling the atom and the field evolutions. On the atom side, we single out a self-driving term proportional to the atom coherences in the energy basis. On the field side, we show that Hamiltonian and correlating processes leave their respective imprints on the field amplitude and fluctuations, which can be measured through dyne or spectroscopic measurements. We then define work-like (heat-like) flows as the energy changes stemming from the effective Hamiltonian processes (the correlating processes). This novel sorting gives a tighter expression of the second law, an effect that we quantitatively relate to the extra knowledge acquired on the field state and that could lead to better energy management at fundamental scales.

Energy consumption of a repetition code based on superconducting cat-qubits (Theme 1. Energy advantage and cost of quantum technology)

• Jeremy Stevens (Alice & Bob)

Developing a quantum computer is the subject of intense academic and industrial research, due to its promise to solve classically intractable problems. As a consequence, quantum computing is developing rapidly, with recent advances suggesting the feasibility of quantum error correction on a large scale [1]. As with any nascent technology though, many questions remain, regarding the engineering feasibility of such a machine or its place in a world of finite resources for example. In both cases, a typical concern are the energy needs of a future quantum computer. Here we focus on superconducting cat-qubits, which are presumed to use fewer physical qubits for error correction than other platforms thanks to their noise bias, a property named ‘hardware- efficiency’ [2,3]. As of yet, no effort has been made to quantify the energy consumption of such an approach, leaving the question of energy efficiency unanswered. In this talk, we detail how to approach the energy consumption of a quantum error correction code running on a superconducting cat-qubit based processor. Using the Metric – Noise – Resource methodology developed in [4] we show how individual cat qubit gates can be optimized for their energy consumption at fixed fidelity. The simulation of a noisy repetition code [5] based on these gates allows us to analyze the resource efficiency of a logical qubit. Finally, we identify the overhead cost of current enabling hardware, pointing to a future research direction for the community at large. [1] R. Acharya et al., Quantum Error Correction below the Surface Code Threshold, arXiv:2408.13687. [2] É. Gouzien, D. Ruiz, F.-M. Le Régent, J. Guillaud, and N. Sangouard, Performance Analysis of a Repetition Cat Code Architecture: Computing 256-bit Elliptic Curve Logarithm in 9 Hours with 126 133 Cat Qubits, Phys. Rev. Lett. 131, 040602 (2023). [3] U. Réglade et al., Quantum control of a cat qubit with bit-flip times exceeding ten seconds, Nature 629, 778 (2024). [4] M. Fellous-Asiani, J. H. Chai, Y. Thonnart, H. K. Ng, R. S. Whitney, and A. Auffèves, Optimizing Resource Efficiencies for Scalable Full-Stack Quantum Computers, PRX Quantum 4, 040319 (2023). [5] J. Guillaud and M. Mirrahimi, Repetition Cat Qubits for Fault-Tolerant Quantum Computation, Phys. Rev. X 9, 041053 (2019).

Neural Quantum Simulation of Quantum Dynamics: Recent advances and limitations (Theme 3. Theoretical and experimental methods for quantum effects in energy processes)

• Filippo Vicentini (Ecole Polytechnique)

Neural-network encodings of quantum states have been shown in recent years to be powerful tools to tackle the quantum many body problem. While several outstanding results have been shown, especially when tackling spin systems such as the J1-J2 model, simulating variational dynamics is proving to be much challenging. In this talk, I will discuss recent advances in simulating dynamics by using a multitude of approaches, ranging from repeated state compression approaches (pt-VMC), discussing global optimisation ones that yield the full solution with a single optimisation problem, and finishing with the variational representation of full 'Krylov-like' subspaces. Then, I will discuss our recent understanding of what is limiting those simulations, how this is related to the limits of Tensor Network methods, and what are the advantages of those neural-network based approaches.

Quantum Kinetic Uncertainty Relations in Mesoscopic Conductors at Strong Coupling (Theme 2. Quantum effects in energy processes and materials)

• Gianmichele Blasi (Department of Applied Physics, Université de Genève, Geneva 1211, Switzerland)

Kinetic Uncertainty Relations (KURs) establish quantum transport precision limits by linking signal-to-noise ratio (SNR) to the system's dynamical activity, valid in the weak-coupling regime where particle-like transport dominates. At strong coupling, quantum coherence challenges the validity of KURs and questions the meaning of the concept of activity itself. Here, we introduce a generalized dynamical activity valid at arbitrary coupling and derive a steady-state quantum KUR (QKUR) expressed in terms of this generalized activity. Explicit expressions are obtained within Green's function and Landauer-Büttiker formalisms. This QKUR ensures that uncertainty relations are valid across all coupling strengths, offering a general framework for out-of-equilibrium quantum transport precision analysis. We illustrate these concepts for paradigmatic quantum-coherent mesoscopic devices: a single quantum channel pinched by a quantum point contact and open single- and double-quantum dot systems. Link al preprint: [https://arxiv.org/abs/2505.13200](https://arxiv.org/abs/2505.13200)

Finite temperature criticality in a quantum annealer (Theme 1. Energy advantage and cost of quantum technology)

• Gianluca Teza (Max Planck Institute for the Physics of Complex Systems)

Commercially viable **quantum annealers** have proven as reliable tools to seek the groundstates of disordered many body systems mappable to an Ising spin-glass Hamiltonian. An advantage over simulated annealing techniques is given by the intrinsic quantum nature of the spins (superflux qubits) which, thanks to a **transverse magnetic field**, can more easily and quickly escape metastable configurations and provide solutions closer to the true groundstate. Potentially, they can also be used as samplers for classical equilibrium (Boltzmann) configurations at finite temperatures. However, their reliability as such a tool is subject to several issues, mainly due to the temperature fluctuations of the QPU, analogical implementation errors, and freezouts of the relaxation dynamics for large networks. We have investigated the potential use of **D-Wave** quantum annealers as **finite-temperature** Boltzmann samplers through an embedding of the **2D Ising ferromagnetic model**. This paradigmatic model exhibits a continuous phase transition at a finite temperature, which can be used to benchmark the performance of D-wave in these difficult scenarios – both in the neighborhood of the critical region and when quenching through the phase transition. To underpin criticality, we developed an **experimental protocol** that allows us to account for systematic biases and temperature fluctuations of the QPU. This allowed us to perform reliably and consistently experiments across different system sizes making use of the whole qubits network ($\sim 3000$ spins), ultimately pinning criticality in the thermodynamic limit and recovering the universal critical exponents of a 2D classical ferromagnet. On one hand, these results set the grounds for **reliable Boltzmann sampling** on these experimental devices, while also offering the 2D Ising ferromagnet as a tool to finely benchmark the features of D-Wave quantum annelers. As a case in point, we are able to prove and quantify an explicit **advantage provided by the transverse field** in finding true Hamiltonian’s groundstate throughout an annealing schedule.

Solving the unit commitment problems with quantum annealers. (Theme 1. Energy advantage and cost of quantum technology)

• Filippo Orazi (Alma Mater Studiorum, università di Bologna)

The Unit Commitment problem (UC) is a well known problem in the context of energy engineering and optimization. Generally described as a family of optimization problems where the energy production of some generators is coordinated based on an objective function, typically the minimization of costs or maximization of revenue. There exist many different versions that take into consideration one or multiple specifics depending on the practical case study considered. The problems in this family presents some common elements such as generators, consumption forecast, rules or laws (physical or legislative), error tolerance and a temporal horizon. In literature there are many classical and quantum techniques that solve this problem with varying degrees of success. In this article we will utilize a quantum annealing approach to solve a specific instance of the problem where we consider the presence of batteries and the performance of the energy market. We will first describe our problem in its general form, then move it to a quadratic programming, and lastly to a QUBO formulation. The latter problem will be solved by a quantum annealer and the result will be compared to a classical solution obtained through simulated annealing.

Charging a quantum spin network towards Heisenberg-limited precision (Theme 2. Quantum effects in energy processes and materials)

• Beatrice Donelli (CNR-INO Istituto Nazionale di Ottica)

We present a cooperative protocol to charge quantum spin networks up to the highest-energy configuration, in terms of the network's magnetization. The charging protocol leverages spin-spin interactions and the crossing of a phase transition's critical point to achieve superextensive charging precision. The cooperative protocol guarantees a precision advantage over any local charging protocol and leads to fluctuations (standard deviation) of the magnetization that scale as $1/N$, with $N$ being the number of spins in the network, i.e., the size of the spin battery. This precision scaling mirrors the Heisenberg limit for parameter estimation in quantum metrology. We test our protocol on the D-Wave's Advantage quantum processing unit by charging sub-lattices with sizes ranging from $40$ to $5612$ spins, achieving the highest-energy configuration with a sizeable superextensive charging precision scaling, and outperforming the local charging precision by four orders of magnitude. Phys. Rev. E - Accepted 22 May, 2025 DOI: [10.1103/lffq-ylgz](https://doi.org/10.1103/lffq-ylgz)

Detecting entanglement from work extraction (Theme 3. Theoretical and experimental methods for quantum effects in energy processes)

• BEATRIZ POLO RODRÍGUEZ (Institut de Ciències Fotoniques, (ICFO) Barcelona)

Whereas correlations among the constituent parts of a quantum system are often described from an information theoretical perspective, Quantum Thermodynamics provides an alternative framework for the certification and quantification of entanglement in terms of potential work extraction. In this work we investigate the relationship between separability and ergotropic gap in Continuous-Variable systems, more specifically within the restriction to the Gaussian bipartite case. We identify important differences with respect to de DV case, arising as a consequence of the infinite-dimensional nature of the Hilbert space. Moreover, we derive a bound on the maximum relative ergotropic gap (relative with respect to the global passive state's energy) for separable mixed states, which turns this energy-related quantity into a valid entanglement witness. Finally, we identify a parametric family of Gaussian states for which the violation of our bound constitutes not only a sufficient, but also a necessary condition for entanglement. Apart from being interesting from a fundamental point of view, as an approach to bridge quantum information and statistical mechanics and to understand the role of quantum correlations in both contexts; our results pave the way to new schemes for entanglement detection, which could potentially be less resource-consuming than the traditionally-used quantum state tomography. Furthermore, since entanglement is a crucial resource both for information processing and energy processing, understanding how thermodynamical quantities can reveal entanglement is key to optimize heat transfer, work extraction, and performance of thermal machines.

Exploiting quantum effects for energy storage and spectroscopy (Theme 3. Theoretical and experimental methods for quantum effects in energy processes)

• Giulio Cerullo (Politecnico di Milano)

Quantum effects promise to disrupt many technologies, from energy storage to sensing. In this talk, I will present preliminary results towards an organic Dicke quantum battery, consisting of an ensemble of two-level systems embedded within a microcavity. I will report evidence of superextensive charging in a microcavity consisting of two dielectric mirrors enclosing a film of molecular semiconductor molecules dispersed within a polymer matrix, and discuss several approaches for storing the absorbed light energy. I will also show how quantum entanglement can be used to perform ultrafast optical spectroscopy at the lowest possible excitation level by resolving, upon single-photon absorption, excitation energy transfer cascades between light-harvesting complexes in a photosynthetic membrane. These experiments, which are performed without compromising acquisition time, may provide a completely new approach to ultrafast optical spectroscopy, where experiments are performed under conditions comparable to real-world sunlight illumination.

Benchmarking Energy Consumption in Neutral-Atom Quantum Simulators (Theme 1. Energy advantage and cost of quantum technology)

• Tiago Mendes-Santos (Pasqal)

Quantum computing has the potential to deliver exponential speedups for computational tasks in specific problem domains. While digital quantum computing remains a long-term goal due to challenges in scalability and error correction, analog quantum computing offers a promising near-term alternative. In this work, we investigate the energy consumption and runtime of analog neutral-atom quantum processing units (QPUs) in applications involving the simulation of quantum many-body dynamics. We also compare their performance against state-of-the-art classical approaches. In particular, we examine the scaling behavior of classical methods—such as Matrix Product States (MPS) and time-dependent variational Monte Carlo (VMC)—and compare their energy footprints with those of neutral-atom QPUs. Our results highlight a potential advantage of quantum computing in terms of both energy efficiency and runtime for near-term devices.

Revealing the fuel of a quantum continuous measurement-based refrigerator (Theme 1. Energy advantage and cost of quantum technology)

• Géraldine Haack (Department of Applied Physics, University of Geneva, 1211 Geneva, Switzerland)

While quantum measurements have been shown to constitute a resource for operating quantum thermal machines, the nature of the energy exchanges involved in the interaction between system and measurement apparatus is still under debate. In this talk, I will show that a microscopic model of the apparatus is necessary to unambiguously determine whether quantum measurements provide energy in the form of heat or work. This result will be illustrated by considering a measurement-based refrigerator, made of a double quantum dot embedded in a two-terminal device, with the charge of one of the dots being continuously monitored. Tuning the parameters of the measurement device interpolates between a heat- and a work-fueled regimes with very different thermodynamic efficiency. Notably, there is a trade-off between a maximal thermodynamic efficiency when the measurement-based refrigerator is fueled by heat and a maximal measurement efficiency quantified by the signal-to-noise ratio in the work-fueled regime. This analysis offers a new perspective on the nature of the energy exchanges occurring during a quantum measurement, paving the way for energy optimization in quantum protocols and quantum machines. Work based on the preprint [arXiv:2502.10349](https://arxiv.org/abs/2502.10349)

What can I do with a quantum computer today? (Theme 1. Energy advantage and cost of quantum technology)

• Brad Mitchell (IBM Quantum)

Quantum computers can offer dramatic speed-ups over their classical counterparts for certain problems. However, noise remains the biggest impediment to realizing the full potential of quantum computing. While the solution to this challenge has been known for almost 30 years with the theory of quantum error correction, a large scale realization of fault tolerance is still pending. What can one hope to do then, with existing noisy processors? Superconducting quantum processors now exist with over 1000 qubits, at a scale that is well beyond direct, brute-force classical simulation. In this talk, I will present methods to learn and manipulate noise in these devices to obtain noise-free computations. These methods, dubbed “error mitigation”, do not require the large qubit overheads of quantum error correction, and are immediately accessible to current devices. I will then present experiments that demonstrate the accurate execution of quantum circuits at a scale that is only accessible with classical approximate methods. I shall argue that these experiments present the first evidence that useful information can be obtained from current quantum computers even before the advent of fault tolerance.

Quantification of energy consumption of quantum resource distribution (Theme 1. Energy advantage and cost of quantum technology)

• Karol Horodecki (University of Gdańsk)

One of the main tasks of quantum information processing is generating, manipulating, and using quantum resources. Prominent examples of such resources are quantum entanglement and quantum secret key, which are planned to be used in future quantum networks, e.g., for distributed quantum computing and secret communication, respectively. In these networks, quantum resources will be distributed via quantum channels. Due to channels imperfections, this process is expected to involve energy consumption. The consumption takes place during both passing input to the channel and the distillation of imperfect resources taken from the channel’s output to its almost perfect form. For this reason, we propose estimating and minimizing this consumption as one of the important tasks on the way to resource aware quantum information processing. We then establish a quantitative study of energy expenditure in producing quantum resources via quantum channels. We distinguish technological and fundamental energy costs. Technological cost depends on hardware; hence, it is not a fixed quantity. We then focus mostly on the fundamental one. We provide a general definition for the minimal, i.e., unavoidable fundamental energy consumption in creating a maximally resourceful state expressed in units of Jule per rbit (energy invested while generating a unit of resource). We then provide an upper bound on this quantity in case of generated quantum entanglement encoded as polarization on photons, based on three quantum entanglement distillation protocols including original BBPSSW protocol. We further derive a lower bound on the fundamental energy cost of the standard procedures of entanglement distribution (taking maximally entangled states as input to the channels). Hence, under the current design, we provide a quantitative estimate (a lower bound) of the inevitable energy consumption in future quantum networks.

A methodology for characterising and benchmarking quantum devices for resource usage (Theme 1. Energy advantage and cost of quantum technology)

• Jessica Park (University of York)

Quantum Computing (QC) is undergoing a high rate of development, investment and research devoted to its improvement. However, before one can decide how to improve something, it is first necessary to define the criteria for success: what are the metrics or statistics that are relevant to the problem and the domain of use? As well as computational metrics, understanding resource requirements is also key in moving towards quantum utility. For practical use of quantum computers, there are likely to be strict resource constraints in terms of programming/optimisation time, runtime, environmental stability and power/energy consumption. The authors have developed a benchmarking methodology that uses the principles of Practice Based Research to highlight the need for detailed planning and adequate documentation in this area [1]. The methodology considers the full-stack architecture and guides the user to consider all hidden assumptions and parameter choices that are being made. This talk will present this methodology as a framework by which any user, developer or researcher can define, articulate and justify the success criteria, resource requirements and associated benchmarks that have been used to solve their problem or make their claim. 1. Park, J., Stepney, S. & D’Amico, I. A methodology for comparing and benchmarking quantum devices. in Unconventional Computation and Natural Computation 28–42 (Springer Nature Switzerland, Cham, 2024).

A full-stack assessment of fault-tolerant quantum computing energetics challenges (Theme 1. Energy advantage and cost of quantum technology)

• Olivier Ezratty (EPITA and QEI cofounder)

Adopting a long-term view, the presentation shows how recent scientific progress in scaling quantum computing is bringing new solutions and new questions on the energetics of these systems, particularly when considering fault-tolerant quantum computing roadmaps. It starts with refining the definition of an energetic quantum advantage, laying out the interconnection between the economics of quantum computing and its viable applications, which impacts the notion of energy consumption acceptability. It shows how utility-grade algorithms resource and time estimates bring new questions on the energetic and power costs of quantum computing, highlighting the contrast between theoretical and practical quantum advantages. It then identifies key emerging scalability challenges and their related potential energetic costs and constraints like quantum processors scaling limits, qubit non-local connectivity and quantum error correction overhead, qubit gate and readout times and the new critical role of quantum processor interconnect. It shows how systems architecture design strongly influences the energetic footprint of FTQC quantum computers. The overarching role of the presentation is to propose new research questions and avenues connecting quantum science and engineering with the Quantum Energy Initiative goals.

Minimizing the energy consumed by large-scale quantum computers (Theme 1. Energy advantage and cost of quantum technology)

• Marco Fellous-Asiani (Centre of New Technologies University of Warsaw)

In the race to build scalable quantum computers, minimizing the resource consumption of their full stack to achieve a target performance becomes crucial. It mandates a synergy of fundamental physics and engineering: the former for the microscopic aspects of computing performance and the latter for the macroscopic resource consumption. For this, we propose a holistic methodology dubbed metric noise resource (MNR) that is able to quantify and optimize all aspects of the full-stack quantum computer, bringing together concepts from quantum physics (e.g., noise on the qubits), quantum information (e.g., computing architecture and type of error correction), and enabling technologies (e.g., cryogenics, control electronics, and wiring). This holistic approach allows us to minimize their resource consumption. As a proof of concept, we use MNR to minimize the power consumption of a full-stack quantum computer, performing fault-tolerant computing with a target performance for the task of interest. Comparing this with a classical processor performing the same task, we identify a quantum energy advantage in regimes of parameters distinct from the commonly considered quantum computational advantage. This provides a previously overlooked practical argument for building quantum computers. While our illustration uses highly idealized parameters inspired by superconducting qubits with concatenated error correction, the methodology is universal—it applies to other qubits and error correcting codes—and it provides experimenters with guidelines to build energy efficient quantum computers. In some extreme cases, our methodology can reduce the consumption of the computer from 10 nuclear reactors (10GW) to a few megawatts. Overall, our approach lays the foundations for resource-efficient quantum technologies.

Industry Roundtable (Theme 1. Energy advantage and cost of quantum technology)

• Sabrina Maniscalco (Algorithmiq | University of Helsinki)
• Marco Barbieri (Roma Tre)
• Andrea Tabacchini (Quantum Brilliance)
• Michael Marthaler (HQS Quantum Simulations)
• Olivier Ezratty (EPITA and QEI cofounder)
• Tiago Mendes-Santos (Pasqal)

This roundtable will explore the role of quantum science and technology in energy management today. Can quantum technologies make a tangible impact now, or are they still years away from practical application? Is industry’s influence on academic research driving progress or limiting fundamental exploration? Our panel—featuring voices from across the sector—will examine these pressing questions while discussing key strategies, challenges, and opportunities for integrating quantum technologies into the energy landscape. Prof Marco Barbieri (Roma Tre) will moderate the discussion.

Dynamic Cooling of Qubits on Contemporary Quantum Computers (Theme 1. Energy advantage and cost of quantum technology)

• Lindsay Oftelie (CNR-NANO)

Quantum computers require qubits to be initialized in a pure (i.e., cold) state for successful computation. Dynamic cooling offers a route to effectively lower qubit temperatures beyond what is possible with direct, physical cooling techniques in an energy efficient manner. It works by cooling a subset of qubits, at the expense of heating others, by applying certain logic gates to the entire system. While it was initially dismissed as impractical for the high-temperature NMR-based quantum computers available at the time of its inception, we show how dynamic cooling is substantially more effective and efficient on the low-temperature quantum computers available today. In this talk, we will examine how optimal dynamic cooling scales with total system size, in terms of the minimal achievable final temperature, the work cost, and the complexity of the associated quantum circuits. We will observe the effect of hardware noise on cooling and share results of a successful demonstration of dynamic cooling with a 3-qubit system on a real quantum processor. Finally, we will propose a sub-optimal dynamic cooling scheme with fixed (low) complexity to improve the feasibility of implementation on noisy quantum hardware.

Speed versus temperature for energy-efficient quantum computing: learning from existing spin-qubits (Theme 1. Energy advantage and cost of quantum technology)

• Robert Whitney (Universite Grenoble Alpes & CNRS)

As quantum technologies advance, it will be important to have methods to minimize their resource consumption without impact-ing their performance. Here, we show how to use experimental data to build and optimize a system-level (full-stack) model of a quantum computer, within the Metric-Noise-Resource approach [1]; a model that contains everything from the qubits to the end-user. We use it to explore the interplay of qubit temperature and gate-operation speed, while maintaining a target fidelity for the noisy qubit circuit to perform a desired algorithm. The resource minimized is the energy consumption of the algorithm. While a given target fidelity can be achieved by either (i) calculating slowly with cold qubits, or (ii) calculating fast with hot qubits, we show that both come at a large energy cost. Minimal energy con-sumption is at a sweet-spot of intermediate speed and temperature [2]. We demonstrate the approach [2] by building a system-level model of using experimental data for silicon spin-qubits taken from recent publications, such as [3]. We use the model to optimize a NISQ computer containing a few dozen qubits. We thereby find the speed-temperature sweet-spot for such a NISQ computer. We show that this sweet-spot depends on: • Algorithm factors: the number of qubits needed by the algorithm. • Microscopic hardware factors: type of noise felt by the qubits. • Macroscopic hardware factors: type of cryogenics and wiring. We consider various examples of these, to find which are most suitable for energy-efficient quantum computing. [1] M. Fellous-Asiani, J.H. Chai, Y. Thonnart, H.K. Ng, R.S. Whitney, A. Auffèves, PRX Quantum 4, 040319 (2023)  [2] K. Koteva, A. Auffèves & R.S. Whitney, in preparation (2025). [3] J.Y. Huang et al., Nature 627, 772 (2024).

Energetic Analysis of Emerging Quantum Communication Protocols (Theme 1. Energy advantage and cost of quantum technology)

• Raja Yehia (ICFO)

In a world with finite resources where energy demands outgrow energy generation, it is crucial to estimate how much energy quantum networks will consume prior to their deployment. Such a study can reveal limiting factors for future implementations of networks, or even show the energetic advantages of certain quantum technologies over classical ones. This work presents the foundations of a framework to estimate the energy cost of quantum network protocols. We give a first estimation of the energy requirements of basic network functionalities, namely Quantum Key Distribution (QKD) and Conference Key Agreement (CKA), whose goals are to generate a secret private key among end users of a quantum network. The methods and hardware they use are generic to most protocols based on photonic implementations. In particular, the creation and sharing of entangled states among distant parties, believed to be the main goal of most quantum network architectures, are the building blocks of many other network protocols. To obtain concrete figures of merit, we take a hardware-dependent approach to compare different implementations of some common protocols. Namely, different QKD implementations are compared, and the implementation of networks of $N$ nodes are analyzed, since their scaling in resources with the number of nodes is non-trivial. Using the energetic cost as a benchmark, instead of the rate or the fidelity, gives a unique perspective. For example, our simulations suggest that there exists regimes of parameters for QKD protocols where using less efficient but more energy effective detectors results in huge energy savings at the cost of increased execution time. Another example of results from this work are the discovery of distance regimes for which the usage of different wavelengths results in energy savings, and the identification of optimal protocols to achieve multipartite tasks as a function of the number of parties. See pdf for an example result and see arxiv for more info : https://arxiv.org/abs/2410.10661

Bosonic thermodynamics: Linear versus nonlinear interactions (Theme 1. Energy advantage and cost of quantum technology)

• Armen Allahverdyan (Alikhanyan National Laboratory)

We carried out a quantum thermodynamic analysis of linear versus non-linear interactions in bosonic systems (phonon, photons, etc). We show that linear dynamics (e.g. linear optics) imposes a relation that is more general than the second law of thermodynamics: for modes undergoing a linear evolution, the full mean occupation number, i.e., the photon number for optical modes, does not decrease, provided the evolution starts from a (generalized) diagonal state. This relation connects to noise increasing (or heating), is akin to the second law, and holds for a wide set of initial states. We show that heating can be reversed via nonlinear interactions between the modes. They can cool, i.e., decrease the full mean occupation number and the related noise, an equilibrium system of modes provided their frequencies are different. Such an effect cannot exist in energy cooling, where only a part of an equilibrium system is cooled. We describe the cooling setup via both efficiency and coefficient of performance and relate the cooling effect to the Manley-Rowe theorem in nonlinear physics and electrodynamics. Together with noise also the Bose entropy of modes increases during a linear evolution, though this relation imposes additional limitations on the initial states and on linear evolution. We deduce from this result that the formation of Bose-Einstein condensate is impossible in a closed system undergoing linear evolution if this condensate was not present in the system initially. We conclude that non-linear interactions in bosonic systems is an important thermodynamic resource.

Dynamical blockade of a reservoir for optimal performances of a quantum battery (Theme 2. Quantum effects in energy processes and materials)

• Dario Ferraro (University of Genova)

The development of fast and efficient quantum batteries is crucial for the prospects of quantum technologies. We show that both requirements are accomplished in the paradigmatic model of a harmonic oscillator strongly coupled to a highly non-Markovian thermal reservoir [1]. At short times, a dynamical blockade of the reservoir prevents the leakage of energy towards its degrees of freedom, promoting a significant accumulation of energy in the battery with high efficiency. The possibility of implementing these conditions in LC quantum circuits opens up new avenues for solid-state quantum batteries. F. Cavaliere, G. Gemme, G. Benenti, D. Ferraro, M, Sassetti. arXiv:2407.16471

Non-adiabaticity and irreversible entropy production in the quantum regime (Theme 1. Energy advantage and cost of quantum technology)

• Francesco Plastina (Dip. Fisica Università della Calabria)

Finite-time thermodynamic transformations typically lead to the generation of energetic coherence in the out-of-equilibrium state of a quantum system; indeed, it is possible to identify a contribution to the irreversible entropy production that is due to coherence generation. On the other hand, coherence is connected also to the non-adiabaticity of a processes, for which it gives the dominant contribution for slow-enough transformations. With the help of fluctuation theorems, we will provide a full characterization of the irreversible entropy generated because of deviation from adiabaticity (i.e., diabatic transition), and because of coherence production.

TBA (Theme 1. Energy advantage and cost of quantum technology)

• Sabrina Maniscalco (Algorithmiq | University of Helsinki)

Exploring decoherence and energy transfer with tensor network wave functions (Theme 2. Quantum effects in energy processes and materials)

• Alex W. Chin (Sorbonne Université, INSP)

The non-perturbative and non-Markovian dynamics of open quantum systems are highly challenging to simulate, due to the extensive quantum correlations that appear in both time and space between the observable systems and their environments. However, understanding and exploiting these rich - and often cooperative - physics could provide novel ways to optimise dissipative processes, particularly in the intrinsically ‘open' conditions related to energy harvesting and transduction. In this talk I will present a numerically exact approach to such problems based on the Time-Evolving Density with Orthogonal Polynomials (TEDOPA) technique, as it is currently implemented in the open source code MPSDynamics.jl [1,2]. Through a series of examples covering photosynthetic light-harvesting, organic photovoltaic materials and molecular photphysics, I’ll demonstrate how this approach provides direct insights into the microscopic, multi-scale interplay of dissipative processes that drive advanced functionalities in such systems, and suggest how these tools and emerging concepts could be exploited in designing future quantum devices. [1] MPSDynamics.jl: Tensor network simulations for finite-temperature (non-Markovian) open quantum system dynamics. Thibaut Lacroix, Brieuc Le Dé, Angela Riva, Angus J. Dunnett, Alex W. Chin J. Chem. Phys. 161, 084116 (2024) [2] [https://github.com/shareloqs/MPSDynamics.jl](https://github.com/shareloqs/MPSDynamics.jl)

Spin-polarized electron transport through nanojunctions (Theme 3. Theoretical and experimental methods for quantum effects in energy processes)

• Susanne Leitherer-Stenger (University of Copenhagen)

The conductance properties of nanojunctions connected to macroscopic electrodes can be explored through quantum transport calculations that employ non-equilibrium Green's functions (NEGF) alongside density functional theory (DFT). When these systems exhibit electron spin polarization, the theoretical analysis often incorporates spin-polarized or unrestricted DFT. In this contribution, we present several examples of nanostructures where this approach has proven effective. First, we examine spin-polarized currents in zigzag graphene nanoribbons (zGNRs) subjected to electric fields and finite bias voltages.[1] Next, we explore electron transport through molecules with unpaired electrons, in particular oxidized molecules that demonstrate highly conductive low-energy states, classified as one-dimensional topological insulators.[2] It is well-known that DFT can encounter difficulties with open-shell structures due to their multiconfigurational nature. We illustrate how a selection of polycyclic aromatic hydrocarbons— such as those previously studied in recent scanning probe experiments [3]—can have their ground state accurately determined using a multi- configurational short-range DFT approach.[4] Our findings underscore both the effectiveness and the limitations of integrating DFT with NEGF calculations.

Detecting and mitigating the effect of dissipation in quantum circuits (Theme 1. Energy advantage and cost of quantum technology)

• Clemens Winkelmann (Grenoble INP)

The operation of quantum logical devices is necessarily accompanied by irreversibility and therefore dissipation. In practice, this leads to temperature fluctuations in the device and its immediate environment, which can lead to decoherence and fidelity reduction. Measuring the time-resolved temperature fluctuations in a heat absorber then allows estimating the timing and the magnitude of the dissipative events. In a first experiment, we detect in real time the heat dissipated by individual 2π slips of the phase difference in an overdamped Josephson junction, which allows quantifying the major role played by thermal effects in superconducting quantum circuits [1]. We then move to semiconducting silicon and germanium nanostructures (quantum dots and Josephson junctions) and highlight their potential as heat detectors in the vicinity of qubit architectures [2]. Eventually, we discuss an unexpected recently reported temperature dependence of the Larmor frequency fL in electron spin qubits down to the lowest temperatures [3], which leads to reduced coherence times at high drive powers. We show this effect to exist with similar magnitude in hole spin qubits in silicon. We further unveil the temperature susceptibility of fL to be governed by spin-orbit interactions and that qubit operation under well chosen conditions (at so-called thermal sweet spots) allows its complete cancellation. [1] E. Gümüs et al., Nat. Phys. 19, 196 (2023). [2] V. Champain et al., Phys. Rev. Appl. 21, 064039 (2024). [3] B. Undseth et al., Phys. Rev. X 13, 041015 (2023).

Quantum enhancement of precision in photonic energy harvesters (Theme 1. Energy advantage and cost of quantum technology)

• Federico Centrone (ICFO, UBA)

We investigate quantum energy harvesters—systems designed to convert an external quantum source, such as an electromagnetic potential, into useful work, in the form of a measurable electric current. The latter can be utilized to power thermal machines or stored in a quantum battery. Our study focuses on multimode continuous-variable (CV) quantum systems, which provide a natural framework for describing and manipulating energy fluctuations at the quantum scale. A key challenge in energy harvesting is optimizing the precision of work extraction. We show that this depends on the interplay between quantum coherence, entanglement, and non-Gaussianity. To prove it, we establish a hierarchy of analytical upper bounds on the signal-to-noise ratio (SNR) of the harvested energy. These bounds provide fundamental insights into how quantum resources enhance energy transfer. Our results reveal that when the external energy source exhibits nonclassical properties, significant improvements in precision can be achieved. Moreover, if the source is also non-Gaussian, entanglement can be leveraged to further optimize the SNR, leading to near-optimal work extraction. We demonstrate that entangled multimode states can be engineered to maximize energy harvesting efficiency, finding the optimal parameters that enhance the precision of energy conversion. This suggests that non-Gaussian quantum correlations serve as a resource not only for quantum computation and communication but also for energy processing. By exploiting these quantum effects, we establish a deeper link between the flow of energy and information in quantum systems. Our theoretical framework can be experimentally realized with current photonic technologies, making it feasible for near-term implementations in quantum laboratories. The ability to precisely control quantum energy transfer is particularly relevant for emerging nanotechnologies, where energy fluctuations at the quantum level start to play a crucial role. Moreover, our findings open new avenues for precision charging in quantum batteries, ensuring that energy is delivered with minimal loss and maximum efficiency. This work highlights the potential of quantum energy harvesters as a novel platform for energy-efficient quantum technologies. By bridging concepts from quantum thermodynamics, quantum optics, and information theory, we provide a blueprint for designing energy-harvesting systems that harness uniquely quantum advantages. Future research will explore how these principles extend to more complex networked systems and investigate their integration with quantum computing architectures. Our findings suggest that quantum-enhanced energy processing could revolutionize the way energy is distributed and utilized at the nanoscale, paving the way for next-generation sustainable power solutions in quantum technologies.

Nucleonics: Toward the Precise Control of Nuclear States (Theme 2. Quantum effects in energy processes and materials)

• Florian Metzler (Massachusetts Institute of Technology)

In 2023, we published “The Emergence of Quantum Energy Science,” which laid out how quantum principles well-known in the realm of Quantum Information Science have been put to use in various energy fields, including solar cell engineering, batteries, and nuclear engineering [1]. Since then, our focus has remained on nuclear applications, collecting theoretical and experimental evidence that suggests the possibility of precisely manipulating nuclear states. Just as the semiconductor revolution of the 1940s enabled precise control over electronic states—giving rise to modern *electronics*—we anticipate that *nucleonics*, the precise manipulation of nuclear states, will be similarly transformative. Historically, nuclear state manipulation has been coarse, relying on high-energy sources such as particle accelerators or nuclear chain reactions. As a result, nuclear engineering has focused on engineering *around* nuclear reactions, rather than engineering the reactions *themselves*. Nuclear decay and reaction parameters have been regarded as fixed and immutable, limiting possibilities for highly controlled nuclear processes. In this presentation, we outline key theoretical and experimental findings supporting nucleonics. At the core of this approach is the coupling of nuclear states with their environment, particularly through quasi-particles in solid-state lattices such as phonons and magnons (as explored by Matt Lilley in his presentation). Such couplings may enable nonradiative transfer of energy between nuclear donor and receiver systems under conditions of resonance and aided by well-known quantum phenomena such as Dicke enhancement [2]. In parallel to model development, we pursue experimental work to test corresponding hypotheses under a research program funded by the US Department of Energy (see my colleague Matt DeCapua’s presentation) [3]. We also motivated and designed extensions to well-established experiments, such as Chumakov et al.’s demonstration of nuclear superradiance (see Jonah Messinger’s presentation on nuclear supertransfer) [4]. Nucleonics promises fundamentally new approaches to the exploitation of nuclear energy, the remediation of nuclear waste and the transmutation of materials. Key challenges involve bridging the gap between traditionally disconnected fields such as solid-state physics and nuclear physics as well as quantum engineering and nuclear engineering [5]; and the continued integration of model development with experiments reporting nuclear anomalies. This presentation concludes with a roadmap for the field of nucleonics, outlining key experimental and theoretical milestones. Our goal is to establish a rigorous scientific foundation for this emerging field and to pave the way for its technological realization. We invite researchers across the quantum energy community to contribute to this effort, as advancing nucleonics will require broad interdisciplinary collaborations. [1] Metzler et al. (2023). The emergence of quantum energy science. J. Phys. Energy, 5(4), 041001. [2] Metzler et al. (2024). Known mechanisms that increase nuclear fusion rates in the solid state. New J. Phys., 26(10), 101202. [3] US DOE (2023). US Department of Energy announces funding to projects studying low-energy nuclear reactions. https://arpa-e.energy.gov [4] Chumakov et al. (2018). Superradiance of an ensemble of nuclei excited by a free electron laser. Nat. Phys., 14(3), 261–264. [5] Aleta et al. (2019). Explore with caution: Mapping the evolution of scientific interest in physics. EPJ Data Sci., 8(1), Art. 1.

Detecting and generating quantum correlations with thermal processes (Theme 2. Quantum effects in energy processes and materials)

• Jonatan Bohr Brask (Technical University of Denmark DTU)

Heat and thermal noise disturb fragile quantum systems and are often enemies of those who strive to realise quantum advantages in computing, sensing, or communication. Nevertheless, there are intricate links between thermodynamic quantities and quantum correlations, and thermodynamic processes can in certain cases be harnessed to support quantum information processing and to reveal properties of quantum systems. In this talk, I will discuss relations between thermal processes and quantum correlations. In particular, thermal entanglement engines that harness heat flows to generate entanglement, when such machines are possible and impossible, as well as how measurements of heat exchange can be used to witness the presence of quantum correlations and coherence.

Quantum Machine Learning Applications in High Energy Physics and Beyond (Theme 1. Energy advantage and cost of quantum technology)

• Konstantin Matchev (University of Alabama)

This talk will review recent applications of quantum machine learning to problems in high energy particle physics motivated by the analysis of data from the Large Hadron Collider at CERN, Geneva. Typical tasks include the classifications of jets as quarks or gluons; the classification of calorimeter clusters as electrons or photons; generative modelling of fragmentation and hadronization in jets; and representation learning. The explored hybrid quantum architectures include: quantum equivariant deep neural networks, quantum equivariant graph neural networks, quantum transformers, quantum diffusion models, quantum GANs, etc.

Funding and Policy Roundtable (Theme 1. Energy advantage and cost of quantum technology)

• John Goold (Trinity College Dublin)
• Chris Vale (CSIRO)
• Stefano Lodi (University of Bologna)
• Luis Fariña Busto (European Research Council Executive Agency)
• Raphaël Bodin (Quantonation)

This roundtable will examine the challenges and opportunities of investing in and regulating quantum energy research. It will bring together experts from diverse sectors, including private investors and public funding bodies. The discussion will highlight key insights, share lessons learned, and explore future directions for advancing the field. Prof John Goold (Trinity College Dublin) will moderate the discussion.

Theory of Spin Effects in Triplet–Triplet Annihilation Upconversion: Modelling Magneto–Photoluminescence (Theme 2. Quantum effects in energy processes and materials)

• Roslyn Forecast (RMIT University, Australia)

In triplet-triplet annihilation (TTA) the molecular energy of two photons is pooled and emitted as fluorescence of a single photon of higher energy. TTA is a promising means of accessing solar irradiance below the silicon bandgap and surpassing the thermodynamic limit for single-junction solar cells. In addition, TTA allows the output light wavelength to be tailored to a specific application via choice of molecule and functionalisation. As TTA is a spin-selective process it exhibits a magnetic field response, which has traditionally been described and modelled in the context of Atkins & Evans’ Theory.1 Here, we revisit the theory, motivating the origin of key equations and evaluating the assumptions behind them. We rederive the theory, which captures the typical situation for TTA in solution. We compute the relative contributions of all spin channels,2 not only the singlet as in the original, but also triplet and quintet channels. These new conditions change the evolution of decoherence in the system, and thus the final magnetic field response equations. The ramifications of these updates are discussed in light of recent magneto-photoluminescence experimental results.3,4 $^1$ Atkins P, Evans G. M*ol. Phys.* **1975**, 29, 921–935. $^2$ Forecast R, Campaioli F, Cole JH. *J. Chem. Theory Comput* **2023**, 19, 7816–7824. $^3$ Gholizadeh EM, Prasad SKK, Teh ZL, Ishwara T, Norman S, Petty AJ, Cole JH, Cheong S, Tilley RD, Anthony JE, Huang S, Schmidt TW. *Nat. Photonics* **2020**, 14, 585–590. $^4$ Forecast R, Campaioli F, Schmidt TW, Cole JH. *J. Phys. Chem. A* **2023**, 127, 1794–1800.

Thermoelectric energy conversion close to a phase transition (Theme 2. Quantum effects in energy processes and materials)

• Ilia Khomchenko (University of Malta)

From a thermodynamic viewpoint, thermoelectric systems are akin to heat engines producing electricity through direct conversion of heat into electrical power. Since the conduction electron gas is the system's working fluid, its properties influence the energy conversion efficiency. Here, we study thermoelectric energy conversion close to an electronic phase transition, focusing on the superconducting fluctuating regime in a 2D system just above the critical temperature. While in the normal phase, the conversion efficiency remains small even in idealized cases, we find that it increases sharply in the fluctuating regime, where 2D fluctuating Cooper pairs strongly influence the ability of the thermoelectric system to convert heat into electrical power. This occurs due to the behavior of the electron gas compressibility in this regime, which leads to the divergence of the isentropic expansion factor. The closer the temperature of the fluctuating Cooper pairs system is to the critical temperature, the larger the values of the power factor, reflecting the increase of the conversion efficiency. These theoretical results are backed up by experimental data obtained with a pnictide thin film, which shows that, close to the superconducting phase transition, the power factor is 300 times larger than it is in the normal phase at room temperature. While these increases of power factor and conversion efficiency are drastic, they are possible only in a very small range above the critical temperature. This indicates that, for practical applications, thermoelectric systems close to an electronic phase transition are not useful for electricity generation, but may serve more effectively as heat pumps.

Electrically-driven superextensivity for energy-efficient quantum technologies (Theme 2. Quantum effects in energy processes and materials)

• Kieran Hymas (Commonwealth Scientific and Industrial Research Organisation (CSIRO))

By leveraging quantum mechanical effects such as quantum coherence and entanglement, physical systems can be engineered to exhibit superextensive properties that scale greater than the sum of their parts. This offers distinct advantages over classical technologies and ushers in a desperately needed wave of energy-efficient quantum devices. Here we present the experimental realisation and theoretical characterisation of two such devices that exhibit a quantum advantage over traditional energy storage and display technologies. In both cases, the cavity-induced molecular correlations enabling superextensivity, are intimately linked to the application of an electrical current to each device. To facilitate the discussion, we will present a heretofore unpublished theoretical model of charge transport in microcavity architectures. These devices serve as an impactful example for how quantum effects can be employed to address aspects of global energy consumption without compromising device performance.

Controlled Optical Charging of a Symmetry-Protected Open Quantum Battery (Theme 2. Quantum effects in energy processes and materials)

• Gabriel Hanna (University of Alberta)

Quantum batteries, which store and transfer energy at the quantum level, have attracted significant interest for their potential applications in energy-efficient quantum technologies. Previous studies [1,2] demonstrated that an exciton could be stored indefinitely in a symmetry-protected dark state of an open quantum battery model, preventing environment-induced losses. However, an open question remained: how to efficiently prepare—or charge—the battery in this dark state. In this work, we address this challenge by employing a controlled optical charging mechanism. Specifically, we initialize the quantum battery in its ground state and excite it using a continuous-wave laser field to an intermediate bright state located above the target dark state. By leveraging a carefully engineered combination of coherent quantum dynamics and controlled dissipation, we drive the system toward the dark state. Once the laser field is turned off after the dark state has been fully populated, the battery remains in this symmetry-protected state, enabling indefinite energy storage. Our results offer a pathway for practical implementation of quantum batteries and contribute to the broader understanding of energy storage and transfer in open quantum systems. References [1] Liu, J., Segal, D., and Hanna, G. “Loss-free excitonic quantum battery” J. Phys. Chem. C 123, 18303-18314 (2019). [2] Liu, Z and Hanna, G. “Population and energy transfer dynamics in an open excitonic quantum battery” Molecules 29, 889 (2024).

Extending the self-discharge time of Dicke quantum batteries using molecular triplets (Theme 2. Quantum effects in energy processes and materials)

• Daniel Tibben (RMIT University)

Quantum batteries, quantum systems for energy storage, have gained interest due to their potential scalable charging power density. A quantum battery proposal based on the Dicke model has been explored using organic microcavities, which enable a cavity-enhanced energy transfer process called superabsorption. However, energy storage lifetime in these devices is limited by fast radiative emission losses, worsened by superradiance. We present a proof-of-concept device based on a multilayer optical microcavity, where an active absorption layer transfers energy to the molecular triplets of a storage layer. We experimentally realise this device and show that energy is stored for tens of microseconds--a $10^3$-fold increase in storage time compared to previous demonstrations.

Conference Dinner

Scalable quantum computing with trapped ions and selected application examples (Theme 3. Theoretical and experimental methods for quantum effects in energy processes)

• Ferdinand Schmidt-Kaler (QUANTUM, Institut für Physik, Universität Mainz)

I will describe the challenges on the way to a scalable, eventually fault tolerant quantum computers [1]. Efforts from physics, informatics [2,3] & mathematics but also engineering [4] are concentrated in demonstrator setups. As a first glance into the power of quantum computing, I will describe a couple of usecases: the VQE-simulation of a two-flavor Schwinger quark model executed on a trapped-ion quantum processor [5], and the quantum autoencoder [6], as a simple instance of machine learning on this hardware. Using, and extending the toolset of quantum computing are investigating circuits that realize quantum thermodnamic processes [7,8,9]. **References** [1] Hilder et al., Phys. Rev. X.12.011032 (2022) [2] Kreppel et al., Quantum 7, 1176 (2023) [3] Durandeau et al., Quantum 7, 1175 (2023) [4] Kaustal et al., AVS Qu. Sci. 2, 014101 (2020) [5] Melzer et al., arXiv:2504.20824 [6] Locher et al., Quantum 7, 942 (2023) [7] Fox et al., Entropy 26(11), 952 (2024) [8] Onishchenko et al., Nat. Comm. 15, 6974 (2024) [9] Stahl et al., arXiv:2404.14838

Harvesting light with polaritons (Theme 2. Quantum effects in energy processes and materials)

• Gerrit Groenhof (University of Jyväskylä)

When placing an organic material inside an optical cavity, molecular and cavity mode excitations can hybridize into polaritons that provide the coupled system with new, sometimes enhanced, photochemical properties [1]. However, the mechanism by which the light-matter interaction changes the photochemistry of the molecules, remains unknown. Here, using molecular dynamics computer simulations, we demonstrate in atomic detail how collectively coupling a mixture of photoreactive and non-photoreactive molecules to a cavity can enhance artificial light harvesting in a way that resembles natural light-harvesting. Our results suggest that collective strong coupling not only enhances photon absorption but also provides a mechanism to transfer that photon into a photoreactive molecule and trigger the photochemical reaction that ultimately captures the energy in a chemical bond. [1] F. J. Garcia-Vidal, C. Ciuti and T. Ebbesen. Manipulating matter by strong coupling to vacuum fields. Science, 373: eabd0336, 2021

Experimental detection of quantum coherent phenomena in artificial nanomaterials (Theme 3. Theoretical and experimental methods for quantum effects in energy processes)

• elisabetta collini (DiSC)

2D electronic spectroscopy (2DES) techniques have become increasingly popular due to their ability to track ultrafast coherent and non-coherent processes in real time [1]. 2DES has garnered significant attention for its role in studying energy and charge transport in complex systems (from biological light-harvesting proteins [2] to solid-state materials [3]), where it has revealed unexpected dynamics driven by quantum effects. Recently, it has also been recognized as a valuable tool for examining transport processes in artificial nanomaterials and nanodevices. This lecture will provide examples of experimental detection of coherent phenomena that drive relaxation dynamics in artificial nanomaterials [4, 5] within the sub-picosecond timescale. Despite the varying nature of the samples reviewed, quantum phenomena consistently appear to dominate the early stages of relaxation dynamics. [1] E.Fresch et al., Nature Reviews Methods Primers 2023, 3, 84; E.Collini, J Phys Chem C 2021, 125, 13096. [2] G.Marcolin et al., J Phys Chem Lett 2024, 15, 2392; E. Meneghin et al., Nature Comm 2018, 9, 3160. [3] E.Collini et al., J Phys Chem C 2020, 124, 16222; JR Hamilton et al., Adv Quantum Technol 2022, 2200060. [4] A Casotto et al., JACS 2024, 146, 14989. [5] N. Peruffo et al., Adv Opt Mater 2023, 2203010; F. Toffoletti et al., 2025, in preparation.

Thermometry based on superconductive qubit (Theme 2. Quantum effects in energy processes and materials)

• Sergei Lemziakov (Aalto University)

Thermometry of superconductive qubit attracts special attention due to prospects of monitoring temperature with minimal invasion, properties of quantum systems with high accuracy at extremely low temperatures [1]. Studies of qubit thermalization process shed light onto interaction between the qubits and their effective environment, contributing to the field of open quantum systems and quantum thermodynamics. We employ a superconducting transmon qubit for quantum thermometry at sub-kelvin temperatures [2]. The thermometry principle is based on the steady-state qubit population measurements, done by applying different sequences of π-pulses [3]. We present a comprehensive experimental study of a qubit thermometer and consider different application cases, such as measurements of the cryostat temperature, or thermometry of a weakly coupled heat bath having a variable temperature. The heat bath is comprised of a mesoscopic resistor with a controllable temperature, realized by NIS-junction thermometry [4]. We provide a thermal model for the qubit coupled to several heat baths representing the cryostat and an effective environment. We discuss various limitations of the qubit thermometer in terms of its dynamic range, sensitivity, accuracy, operation speed etc., and compare our results with previous theoretical and experimental works. We consider influence of the qubit relaxation and coherence times and, respectively, and finite fidelity of the control pulses on the accuracy of the presented method and compare it with a numerical model. **References** [1] M. Mehboudi, A. Sanpera, and L. A. Correa, Thermometry in the quantum regime: recent theoretical progress, Journal of Physics A: Mathematical and Theoretical 52, 303001 (2019). [2] Dmitrii S. Lvov, Sergei A. Lemziakov, Elias Ankerhold, Joonas T. Peltonen, and Jukka P. Pekola. Thermometry based on a superconducting qubit. arXiv:2409.02784, 2024. [3] A. Sultanov, M. Kuzmanovi´c, A. V. Lebedev, and G. S. Paraoanu, Protocol for temperature sensing using a three-level transmon circuit, Applied Physics Letters 119, 144002 (2021). [4] A. V. Feshchenko, L. Casparis, I. M. Khaymovich, D. Maradan, O.-P. Saira, M. Palma, M. Meschke, J. P. Pekola, and D. M. Zumb¨uhl, Tunnel-junction thermometry down to millikelvin temperatures, Phys. Rev. Appl. 4, 034001 (2015).

Advanced tensor network methods for many-body physics (Theme 3. Theoretical and experimental methods for quantum effects in energy processes)

• Luka Pavesic (University of Padova)

The density matrix renormalization group was formulated three decades ago to compute the ground state of interacting one dimensional systems. Since then, tensor network methods have grown into an all-encompassing toolbox of algorithms for the low-energy physics of many body systems. This includes ground state search, evolution in real and imaginary time, dynamics of open systems, etc. Nowadays, most methods easily approach machine precision for simple cases, like quantum spin chains. However, tackling more realistic models, long-range interactions, higher dimensions, or geometric frustration requires a slightly more refined approach. One possible avenue are tree tensor networks. They are constructed to capture more entanglement, and are thus useful for problems which are out of reach for standard matrix product states. I will broadly introduce these methods, present some recent results we obtained using tree tensor networks, and sketch what might be possible in the near future.

Simulation of 2DES from ab initio quantum chemistry (Theme 3. Theoretical and experimental methods for quantum effects in energy processes)

• Giulia Dall'Osto (University of Trieste)

Bidimensional electronic spectroscopy (2DES)[1] is a nonlinear optical technique that involves the interaction of a sample with a sequence of three ultrafast pulses, each separated by a precisely controlled delay. The resulting third-order signal is collected in a phase-matching direction. 2DES has proven to be an exceptional tool for probing quantum coherence in light-harvesting systems central to photosynthetic processes.[2] Over time, its applications have expanded to encompass a wide range of systems, including organic multichromophore complexes and fully inorganic materials, with many potential applications still to be explored. The wealth of information embedded in a 2D spectrum often necessitates the use of advanced theoretical tools for accurate interpretation. Many of these approaches rely on density matrix dynamics, typically modeled through master equations and operating under the impulsive limit.[3] An alternative strategy involves wave-function propagation methods, which not only achieve results comparable to density matrix dynamics but also offer a more intuitive understanding.[4] In this case one of the possible approach which enables the extraction of the third order signal along a phase-matching direction is the phase cycling scheme.[5] Additionally, environmental effects, such as dephasing and relaxation, which lead to population and coherence decay, can be accounted for using stochastic methods like the Stochastic Schrödinger Equation.[6] I will present a theoretical approach to compute the third order signal using a real-time approach based on wave-function dynamics and starting from ab initio calculation of the system. Our aim is to present simulations not only able to represent the final 2D spectrum, but that also closely aligns with experimental setups. This strategy will be applied to benchmark molecules and extended to systems of practical relevance in order to investigate quantum effects not still clear. [1] Hybl, J. D., Albrecht, A. W., Faeder, S. M. G., & Jonas, D. M. (1998). Two-dimensional electronic spectroscopy. Chemical physics letters, 297(3-4), 307-313. [2] Schlau-Cohen, G. S., Ishizaki, A., & Fleming, G. R. (2011). Two-dimensional electronic spectroscopy and photosynthesis: Fundamentals and applications to photosynthetic light-harvesting. Chemical Physics, 386(1-3), 1-22. [3] Mukamel S. (1995) Principles of nonlinear optical spectroscopy. O.U.P, New York [4] Albert, J., Falge, M., Keß, M., Wehner, J. G., Zhang, P. P., Eisfeld, A., & Engel, V. (2015). Extended quantum jump description of vibronic two-dimensional spectroscopy. The Journal of Chemical Physics, 142(21). [5] Seibt, J., Renziehausen, K., Voronine, D. V., & Engel, V. (2009). Probing the geometry dependence of molecular dimers with two-dimensional-vibronic spectroscopy. The Journal of chemical physics, 130(13). [6] Coccia, E., Troiani, F., & Corni, S. (2018). Probing quantum coherence in ultrafast molecular processes: An ab initio approach to open quantum systems. The Journal of Chemical Physics, 148(20).

Theory of Photoinduced Excited State Proton Transfer (Theme 2. Quantum effects in energy processes and materials)

• Brieuc Le Dé (Sorbonne Université, INSP)

Photoinduced Excited State Proton Transfer (ESPT) is characterized by a transfer of a proton between two moieties of a molecule when the system is photoexcited, often seen via an exceptionally large (≥ 8000 cm-1) Stokes shift in fluorescence spectra. The efficiency of photoinduced ESPT reactions is critical for the light reactions of photosynthesis and light-driven enzyme biosynthesis [2]. Remarkably, EPST can be a truly ultrafast process that occurs on timescales at the limit of many experimental probes - just a few tens of femtoseconds. However, the theoretical understanding of ESPT at such very short timescales - and where quantum dynamical effects are likely to be important - still needs to be developed, and could open up novel opportunities for new light-harvesting applications. By developing simple prototype systems, we focused especially on short time behaviors parametrized by the photoexcitation shape and vibrations of the system. This surrounding environment is included with great accuracy through fully quantized theoretical simulation and powerful numerical Tensor-Network techniques [3], permitting us to include hundreds of vibrations modes. Studying the wavepacket propagation of test bed molecule models for ultrafast ESPT with explicit description of vibrations, we revealed the importance of the pump duration on initial conditions and on the subsequent dynamics. The presented study helps gain insight into the non-equilibrium dynamics of proton transfer and provides new design principles mimicking this natural and essential process. References [1] B. Le Dé, S. Huppert, R. Spezia and A.W. Chin : J. Chem. Theory Comput. 2024, 20, 8749−8766 . [2] P. Goyal and S. Hammes-Schiffer ACS Energy Lett. 2, 512–519 (2017). [3] A. J. Dunnett, D. Gowland, C. M. Isborn, et al. J. Chem. Phys 155, 144112 (2021).

Quantum Computation with Quantum Batteries (Theme 1. Energy advantage and cost of quantum technology)

• Yaniv Kurman (CSIRO)

The implementation of quantum logic in cryogenic quantum computers requires continuous energy supply from room-temperature control electronics. The dependence on external energy sources limits scalability due to control channel density and heat dissipation. Here, we suggest quantum batteries as an intrinsic energy source for quantum computation that facilitates quantum universal gate-set. We introduce a quantum battery that supplies energy for all unitary gates and enables all-to-all qubit connectivity. We find that the battery facilitates superextensive energy-transfer gates from the battery to the qubits and vice versa. The quantum battery plays an active role in the computation, enabling multi-qubit parity probing with a single entangling gate. We simulate a quantum error correction circuit with >98% fidelity in logical state encoding only through battery-qubit interactions. By eliminating the need for a drive line for each qubit, this architecture reduces energy consumption to readout-only and increases the number of qubits per cryogenic system by a factor of four. Quantum batteries thus offer a transformative paradigm for scalable and energy-efficient approach to next-generation quantum computation.

Frustrating quantum batteries (Theme 2. Quantum effects in energy processes and materials)

• Alberto Giuseppe Catalano (Università degli Studi di Padova)

We are at the verge of the Quantum Technology Revolution: quantum mechanics allows for phenomena that have no classical counterparts and which can be harvested for new technologies. An example of the emerging quantum technologies are quantum batteries (QB), i.e. quantum mechanical systems that can store and transfer energy in a coherent way. While the practical implementation of such devices is still far from becoming reality, a serious effort is being devoted to understanding their advantages and limitations, using different platforms and protocols. As it has been recently demonstrated that the introduction of topological frustration in one-dimensional spin-1/2 chains can strongly modify the low energy properties of these systems, we investigate the performance of a quantum battery realized through such frustrated chains and show their superiority compared to their unfrustrated counterpart in terms of both energy storage and transfer. We quantify this superiority using the notion of ergotropy, that is, the maximum amount of work that can be extracted from a quantum system with a unitary transformation.

Conference Closing

• James Quach (CSIRO)
• Francesco Campaioli (University of Padova)