Time (BST) Monday June 27 Tuesday June 28 Wednesday June 29 Thursday June 30 Friday July 1 7:50 PaternostroWelcome Chair Nazir Ng Campisi 8:00 Splettstoesser Funo Allahverdyan 8:45 Subero Ford Gyhm 9:15 Chiaracane Ferraro (chair)flash-talks9:30-10:00 Agarwalla Fraenkel 9:45 Abah Poster I10:00-12:30 Hammam Moreira 10:15 Coffee break Coffee break Coffee break Chair Karimi Poletti Auffèves 10:45 Huard Pekola Alhambra 11:30 Kosloff Auffèves Rolandi 12:00 Thingna Hernández-Gómez Campisi 12:30 Korzekwa Manzano Mehboudi 13:00 Lunch break Lunch break Lunch break Lunch break Chair Lostaglio Anders D’Amico 14:00 Publishing Discussion14:00-16:00 Senellart Ferraro (chair)flash-talks14:00-14:30 Maniscalco Esslinger 14:45 Marín Suárez Poster II 14:30 – 17:00 Soret De Chiara (chair)Quo Vadis14:45-16:00 15:15 Perarnau-Llobet Zawadzki 15:45 Bhandari Nimmrichter 16:15 Coffee break Coffee break Chair Lopez Brantut 16:45 Ciampini Lasek 17:15 Bresque Karmakar 17:45 Arrachea Vuletic 18:30 Murch Yunger Halpern

Notice: the displayed time is BST, i.e. London time.

To facilitate networking, we have created a Discord server where you can leave messages, questions for speakers etc. You can access it here

# Monday June 27

• ## Janine Splettstoesser

Faculty @ Chalmers University, Sweden

Monday June 27 – 8.00 BST

##### Heat and charge currents across a QPC: opportunities for thermoelectrics and readout of screening effects

Quantum point contacts have a prominent role in electronic devices and act as beam splitters and energy filters. They are therefore simple examples for thermoelectric mesoscopic devices, where they were shown to maximise the possible power output. In this talk, I will present some of their properties for thermoelectric steady state heat engines and hot-carrier photovoltaics. In particular, I will show, how QPC-based thermoelectric heat engines perform in terms of precision, demonstrating a novel constraint of the “thermodynamic uncertainty relation” in the linear response regime of an operating engine [1]. I will furthermore show how the efficiency of energy conversion is influenced when the energy distribution of the heat source is described by a non thermal state as it is the case for example in hot-carrier solar cells [2].

When the QPC based thermoelectric device is operated at large voltage and/or temperature biases, the transmission of the QPC is modified due to screening effects. These modifications, which can have electrostatic as well as quantum origin, strongly depend on different conductor properties and are typically hard to access from experiments. In the second part of my talk, I will present a proposal how to readout these screening effects by exploiting tunable corrections to the thermoelectric linear-response coefficients, which occur when an additional ac signal is applied via a third terminal [3].

[1] S. Kheradsoud, N. Dashti, M. Misiorny, P. P. Potts, J. Splettstoesser, P. Samuelsson: Entropy 21, 777 (2019).

[2] L. Tesser. R. S. Whitney, J. Splettstoesser, in preparation.

[3] N. Dashti, M. Acciai, S. Kheradsoud, M. Misiorny, P. Samuelsson, J. Splettstoesser: Phys. Rev. Lett. 127, 246802 (2021).

• ## Diego Subero

Monday June 27 – 8.45 BST

##### Effect of high impedance environment on photonic heat transport

Due to the fast growth of quantum technologies, heat transport, regardless of its carriers in such systems, has become an intensive subject of study. This work focuses on studying microwave photon-mediated heat transport and its deviation from the quantum limit in systems with a small Josephson junction immersed into a high impedance environment. The variations of the quantum limit are due to Coulomb blockade effects caused by the high impedance environment. For our purpose, the environment’s resistance is greater than the resistance quantum 6.45 KΩ. Therefore, these platforms are suitable for studying exchange heat between the two environments, thanks to the correspondence between Plank’s black body radiation and Johnson-Nysquist noise yielding from the resistive elements. Photonic heat transport in this type of superconducting circuit has been studied theoretically [1-4] and experimentally [5,6] in the low impedance regime. The experimental work succeeded by Meschke et al. [5] was demonstrated heat conductance due to photons. However, the maximum limit imposed by the universal quantum limit of thermal conductance did not reach due to the impedance mismatch provided by the element used to tune the heat flow. Afterward, Timofeev et al. [6] experimentally demonstrated the vital role of impedance matching to get the heat transport quantum limited. In the present work, we study phenomena that limit quantum heat conductance when a better impedance matching for a tunable circuit such as Ref [5] is implemented. We have obtained the photonic heat conduction closer to the quantum limit by introducing higher impedance resistors.

1.      D. R. Schmidt, R. J. Schoelkopf, and A. N. Cleland, Photon-mediated thermal relaxation of electrons in nanostructures, Phys. Rev. Lett. 93, 045901 (2004).
2.      T. Ojanen and A. P. Jauho, Mesoscopic photon heat transistor, Phys. Rev. Lett. 100, 155902  (2008).
3.      L. M. Pascal, H. Courtois, and F. W. Hekking, Circuit approach to photonic heat transport, Phys. Rev. B 83, 125113 (2011).
4.      G. Thomas, J. P. Pekola, and D. S. Golubev, Photonic heat transport across a Josephson junction, Phys. Rev. B 100, 94508 (2019).
5.      M. Meschke, W. Guichard, and J. P. Pekola, Single-mode heat conduction by photons, Nature 444, 187 (2006).
6.      A. V. Timofeev, M. Helle, M. Meschke, M. Möttönen, and J. P. Pekola, Phys. Rev. Lett. 102, 200801 (2009).

• ## Cecilia Chiaracane

Monday June 27 – 9.15 BST

##### Dephasing-enhanced performance in quasiperiodic thermal machines

Understanding and controlling quantum transport in low-dimensional systems is pivotal for heat management at the nanoscale. One promising strategy to obtain the desired transport properties is to engineer particular spectral structures. In this work we are interested in quasiperiodic disorder — incommensurate with the un- derlying periodicity of the lattice — which induces fractality in the energy spectrum. A well known example is the Fibonacci model which, despite being non-interacting, yields anomalous diffusion with a continuously varying dynamical exponent smoothly crossing over from superdiffusive to subdiffusive regime as a function of potential strength. We study the finite-temperature electric and heat transport of this model in linear response in the absence and in the presence of dephasing noise due to inelastic scattering. The dephasing causes both thermal and electric transport to become diffusive, thereby making thermal and electrical conductivities finite in the thermodynamic limit. Thus, in the subdiffusive regime it leads to enhancement of transport. We find that the thermal and electric conductivities have multiple peaks as a function of dephasing strength. Remarkably, we observe that the thermal and electrical conductivities are not proportional to each other, a clear violation of Wiedemann-Franz law, and the position of their maxima can differ. We argue that this feature can be utilized to enhance performance of quantum thermal machines. In particular, we show that by tuning the strength of the dephasing noise we can enhance the performance of the device in regimes where it acts as an autonomous refrigerator.

• ## Obinna Abah ￼

Faculty @ School of Mathematics, Statistics and Physics, Newcastle

Monday June 27 – 9.45 BST

##### Quantum critical battery: Harnessing non-adiabatic excitations

Crossing a quantum critical point in finite time challenges the adiabatic condition due to the closing of the energy gap, which ultimately results in the formation of excitations. Such non-adiabatic excitations are typically deemed detrimental in many scenarios, and consequently several strategies have been put forward to circumvent their formation.  Here, however, we show how these non-adiabatic excitations — originated from the failure to meet the adiabatic condition due to the presence of a quantum critical point — can be controlled and thus harnessed to perform certain tasks advantageously. We focus on closed cycles reaching the quantum critical point of fully-connected model to analyse a quantum battery that is loaded by approaching a quantum critical point. We show that the stored and extractable work increases exponentially via repeating cycles. Our results can readily be implemented in different experimental platforms as well as highlight the rich interplay between quantum thermodynamics and critical nonequilibrium dynamics.

O. Abah,  G. De Chiara, M. Paternostro and R. Puebla, Harnnessing non-adiabatic excitations promoted by a quantum critical point, arXiv:2105.00362

• ## Benjamin Huard

Faculty @ Ecole Normale Supérieure, Lyon, France

Monday June 27 – 10.45 BST

##### Energetics of the driving field during a single qubit gate and a measurement powered engine

Qubits are physical, a quantum gate thus not only acts on the information carried by the qubit but also on its energy. What is then the corresponding flow of energy between the qubit and the controller that implements the gate? In this talk, we exploit a superconducting platform to answer this question in the case of a quantum gate realized by a resonant drive field. During the gate, the superconducting qubit becomes entangled with the microwave drive pulse so that there is a quantum superposition between energy flows. We measure the energy change in the drive field conditioned on the outcome of a projective qubit measurement. We demonstrate that the drive’s energy change associated with the measurement backaction can exceed by far the energy that can be extracted by the qubit. This can be understood by considering the qubit as a weak measurement apparatus of the driving field.

In the second part of the talk, we will discuss an experiment that realizes an engine able to extract work from the measurement backaction of a qubit. The extracted work is directly measured in the reflection of a resonant field that drives the qubit.

• ## Ronnie Kosloff

Faculty @ Hebrew University

Monday June 27 – 11.30 BST

##### Controlling the uncontrollable: Quantum control of open system dynamics

Control of an open quantum system is essential in contemporary science and technology. We demonstrate such control employing a thermodynamically consistent framework. We specifically address the fact that the control drive modifies the interaction with environment. The effect is incorporated within the dynamical equation, leading to control dependent dissipation. Thermodynamics is reflected by a unidirectional flow of energy to the environment. The dynamical equations of motion serves as the key element for open system control. The control paradigm is displayed by analyzing
entropy changing state to state transformations, heating and cooling N-levels systems. A crucial task is generating quantum gates under dissipative conditions. We demonstrate both non-unitary reset maps with complete memory loss and a universal set of single and double qubit unitary gates.

• ## Juzar Thingna

Faculty @ Institute for Basic Science

Monday June 27 – 12.00 BST

##### Effects of measurements on quantum devices

In this talk, I’ll introduce a method, known as repeated contacts, that allows us to infer the sum of the values of an observable taken during contacts with a pointer state [1]. I’ll first show the superiority of this approach with the results of the same number of generalized Gaussian measurements of the considered observable. The proposed repeated contact approach could be beneficial to measure the work output of a quantum Otto heat engine and I’ll demonstrate this using a two-level system as the working substance [2]. I’ll discuss the imperfect thermalizing engine under Landau-Zener work strokes and show that the repeated contact scheme is minimally invasive and gives enhanced performance metrics (efficiency, power output, and reliability) as compared to the standard repeated generalized Gaussian measurements. Lastly, I’ll consider the charging of a quantum battery using an Otto engine and demonstrate that periodic measurement on the battery speeds up its charging of internal energy, but sacrifices the ergotropy [3]. Overall, I’ll show the importance of considering the effects of quantum measurements using different measurement protocols on the performance of a machine.

[1] J. Thingna and P. Talkner, Phys. Rev. A 102, 012213 (2020).
[2] J. Son, P. Talkner, and J. Thingna Phys. Rev. X Quantum 2, 040328 (2021).
[3] J. Son, P. Talkner, and J. Thingna (in preparation).

• ## Kamil Korzekwa

Postdoc @ Jagiellonian University, Kraków

Monday June 27 – 12.30 BST

##### Optimizing thermalizations

The standard dynamical approach to quantum thermodynamics is based on Markovian master equations describing the thermalization of a system weakly coupled to a large environment. Here, based on the newly introduced notion of continuous thermomajorization, we obtain necessary and sufficient conditions for the existence of such a thermalization process transforming between given initial and final energy populations of the system. These include standard entropy production relations as a special case, but also yield a complete, continuous family of entropic functions that need to monotonically increase during the dynamics. Importantly, we significantly simplify these conditions by identifying a finitely verifiable set of constraints governing non-equilibrium transformations under master equations. What is more, the framework is also constructive, i.e., it returns an explicit set of elementary controls realizing any allowed transformation. We also present an algorithm that in a finite number of steps allows one to construct all energy distributions achievable from a given initial state via Markovian thermalization processes. The algorithm can be deployed to solve complex optimization problems in out-of-equilibrium setups and it returns explicit elementary control sequences realizing optimal transformations. We illustrate this by finding optimal protocols in the context of cooling, work extraction and catalysis. The same tools also allow one to quantitatively assess the role played by memory effects in the performance of thermodynamic protocols. We obtained exhaustive solutions on a laptop machine for systems with dimension d ≤ 7, but with heuristic methods one could access much higher d.

arXiv:2111.12130

# Tuesday June 28

• ## Pascale Senellart

Faculty @ CNRS, University Paris-Sud, University Paris-Saclay, France

Tuesday June 28 – 14.00 BST

##### Coherence-powered work exchanges between a solid-state qubit and light fields

We explore how quantum coherence impacts energy exchanges between a solid-state quantum bit and light fields. Following pioneering theoretical frameworks, we first experimentally study the work transferred during the spontaneous emission of a solid-state qubit into a reservoir of modes of the electromagnetic field. This step energetically corresponds to the charging of a quantum battery and we show that the amount of transferred work is proportional to the initial quantum coherence of the qubit, and is reduced at higher temperatures. In a second step, we study the discharge of the battery and its energy transfer to a classical- i.e.- laser field using homodyne-type measurements. We demonstrate that the amount of energy and work transferred to the laser field is controlled by the relative classical optical phase between the two fields, the quantum purity of the charged battery field as theoretically predicted, as well as long-term fluctuations in the qubit solid-state environment.

• ## Marco Marín Suárez

Tuesday June 28 – 14.45 BST

##### An electron turnstile for frequency-to-power conversion

Nanometric normal-metal islands coupled to superconducting leads through insulating tunnel junctions are suitable as single-electron turnstiles, when its excess charge is periodically driven through a capacitively coupled gate electrode. The superconducting leads extend the stability zone along the whole gate-voltage parameter space making it possible to create single-electron currents by only allowing one tunnelling event per cycle per junction [1]. In this device, electric charge is carried by superconducting excitations which are injected into the leads in each tunnelling event. These excitations are created close to the superconducting gap edge. Consequently, the energy current, that is, power injected to the leads is given by a simple frequency-to-power conversion relation, namely the superconducting energy gap times the driving signal frequency $\left( P=\Delta f\right)$. Such a simple relation enables this device as a candidate for a power standard, analogue to the frequency-to-current conversion of single-electron turnstiles. This is experimentally demonstrated [2] as a first proof-of-concept. The power production is shown to be possible even in the absence of particle current. Moreover, the dynamics of power repartition among both junctions is studied. Further improvements in the accuracy of the power emission are proposed.

[1] Pekola, J. P. Vartiainen, J. J. Möttönen, M. Saira, O-P. Meschke, M. Averin, D. Hybrid single-electron transistor as a source of quantized electric current. Nat. Phys. 4, 2007.
[2] Marín-Suárez, M. Peltonen, J. T. Golubev, D. S. Pekola, J. P. An electron turnstile for frequency-to-power conversion. Nat. Nanotechnol., 2022.

• ## Marti Perarnau Llobet

Postdoc @ University of Geneva

Tuesday June 28 – 15.15 BST

##### Fundamental limits in Bayesian thermometry and attainability via adaptive strategies

We investigate the limits of quantum thermometry using quantum probes at thermal equilibrium within the Bayesian approach. We consider the possibility of engineering interactions between the probes in order to enhance their sensitivity, as well as feedback during the measurement process, i.e., adaptive protocols. On the one hand, we obtain an ultimate bound on thermometry precision in the Bayesian setting, valid for arbitrary interactions and measurement schemes, which lower bounds the error with a quadratic (Heisenberg-like) scaling with the number of probes. We develop an adaptive strategy that can saturate this limit. On the other hand, we derive a no-go theorem for non-adaptive protocols that does not allow for better than linear (shot-noise-like) scaling even if one has unlimited control over the probes, namely access to arbitrary many-body interactions. Our work highlights the crucial role of both feedback and many-body interactions in quantum thermometry. This talk is based on [1].

[1] Fundamental limits in Bayesian thermometry and attainability via adaptive strategies, Mohammad Mehboudi, Mathias R. Jørgensen, Stella Seah, Jonatan B. Brask, Jan Kołodyński, Martí Perarnau-Llobet,   arXiv:2108.05932 (2021).

• ## Bibek Bhandari

Postdoc @ Institute for Quantum Studies, Chapman University, Orange, California, 92866, USA

Tuesday June 28 – 15.45 BST

##### Continuous measurement boosted adiabatic quantum thermal machines

We present a unified approach to study continuous measurement based quantum thermal machines in static as well as adiabatically driven systems. We investigate both steady state and transient dynamics for the time-independent case. In the adiabatically driven case, we show how measurement based thermodynamic quantities can be attributed geometric characteristics. We also provide the appropriate definition for heat transfer and dissipation owing to continous measurement in the presence and absence of adiabatic driving. We illustrate the aforementioned ideas and study the phenomena of refrigeration in two different paradigmatic examples: a coupled quantum dot and a coupled qubit system, both undergoing continuous measurement and slow driving. In the time-independent case, we show that quantum coherence can improve the cooling power of measurement based quantum refrigerators. Exclusively for the case of coupled qubits, we consider linear as well as non-linear system-bath couplings. We observe that non-linear coupling produces cooling effects in certain regime where otherwise heating is expected. In the adiabatically driven case, we observe that quantum measurement can provide significant boost to the power of adiabatic quantum refrigerators. The measurement based refrigerators can have similar or better coefficient of performance (COP) in the driven case compared to the static one in the regime where heat extraction is maximum. Our results have potential significance for future application in devices ranging from measurement based quantum thermal machines to refrigeration in quantum processing networks.

B. Bhandari and A. N. Jordan arXiv:2112.03971 (2021)

• ## Mario Arnolfo Ciampini

Postdoc @ University of Vienna

Tuesday June 28 – 16.45 BST

##### Experimental nonequilibrium memory erasure beyond Landauer’s bound

Logically irreversible transformations unavoidably consume power and cause heat dissipation. On a fundamental level, Landauer’s bound provides the minimum value of these energetic costs when erasing one bit of information in equilibrium with its environment [1]. Several proof-of-concept experiments have successfully reached this limit [2-6]. Yet, real devices operate out of equilibrium, calling for a deeper understanding of the underlying thermodynamic laws in this regime [7-9]. Here, we demonstrate the possibility to control the thermodynamics of a two-state memory by separating nonequilibrium memory preparation from memory processing [10]. Specifically, we report the first experimental demonstration of the full reset of one bit of information that evades the seemingly inevitable heat dissipation when stored in an out-of-equilibrium state. To achieve this, we developed an electro-optical double-well trap for levitated nanoparticles that can be shaped dynamically, allowing for precise and fast memory state preparation and processing. Our results indicate that far-from-equilibrium thermodynamics can offer a route for heat management in computational architectures paving the road for the extension of the research question to the quantum regime.

[1] Landauer, R. Irreversibility and heat generation in the computing process. IBM J. Res. Dev. 5, 183 191 (1961).
[2] Bérut, A. et al. Experimental verification of Landauer’s principle linking information and thermodynamics. Nature 484, 187 189 (2012).
[3] Orlov, A. O., Lent, C. S., Thorpe, C. C., Boechler, G. P. & Snider, G. L. Experimental test of Landauer’s principle at the sub-kBT level. Japanese Journal of Applied Physics 51, 06FE10 (2012).
[4] Jun, Y., Gavrilov, M. & Bechhoefer, J. High-precision test of Landauer’s principle in a feedback trap. Phys. Rev. Lett. 113, 190601 (2014).
[5] Hong, J., Lambson, B., Dhuey, S. & Bokor, J. Experimental test of Landauer’s principle in single-bit operations on nanomagnetic memory bits. Science Advances 2, 3 (2016).
[6] Dago, S., Pereda, J., Barros, N., Ciliberto, S. & Bellon, L. Information and thermodynamics: Fast and precise approach to landauer’s bound in an underdamped micromechanical oscillator. Phys. Rev. Lett. 126, 170601 (2021).
[7] Esposito, M. & den Broeck, C. V. Second law and Landauer principle far from equilibrium. EPL (Europhysics Letters) 95, 40004 (2011).
[8] Wolpert, D. H. The stochastic thermodynamics of computation. J. Phys. A: Math. Theor. 52, 193001 (2019).
[9] Konopik, M., Friedenberger, A., Kiesel, N. & Lutz, E. Nonequilibrium information erasure below kTln2. EPL 131, 6004 (2020)
[10] Ciampini, M.A. et al. Experimental nonequilibrium memory erasure beyond Landauer’s bound, arXiv:2107.04429

• ## Léa Bresque

Tuesday June 28 – 17.15 BST

##### The thermodynamic cost of quantum measurements in the circuit quantum electrodynamics architecture

Since work can be extracted from coherences in the eigenenergy basis [1], conversely, measuring a state in this basis can have a cost. Theoretically, this cost is proportional to the QC-mutual information obtained from the measurement~[2], but this bound is not always reachable in the experimental context. Since some resources, such as thermal states, are much easier to produce than others, one could wonder about their measuring capabilities. Here, in a circuit quantum electrodynamics setup, we investigate the resources required to perform quantum measurements of a qubit. We compare the measurement backaction and signal-to-noise ratio of single-photon, coherent and thermal fields. We find that in the strong dispersive limit the thermal light is capable of performing quantum measurements with comparable figure of merit to coherent light. Furthermore, we analyze the energetic and entropic costs of these quantum measurements at different measurement strengths and investigate the fundamental reasons behind these experimental results. This work demonstrates a new, efficient approach to quantum measurements in circuit quantum electrodynamics and provides a new point of view to the energetic cost of a measurement.

[1] P. Kammerlander, J. Anders, “Coherence and measurement in quantum thermodynamics”, Scientific Reports 6, (2016).
[2] T. Sagawa, M. Ueda, “Minimal Energy Cost for Thermodynamic Information Processing: Measurement and Information Erasure”, Phys. Rev. Let. 102. (2009).
*This work was supported by the John Templeton Foundation, Grant No. 61835

• ## Liliana Arrachea

Faculty @ Universidad de Buenos Aires, Argentina

Tuesday June 28 – 17.45 BST

TBA

• ## Kater Murch

Faculty @ Washington U. in St. Louis, US

Tuesday June 28 – 18.30 BST

##### Energetic cost of measurements using quantum, coherent, and thermal light

In the quantum information literature, the basic concepts are unitary operators, quantum gates, entangling operations, and measurements. These are all applied to accomplish tasks in quantum information processing. However, much like classical computers, all logical operations demand resources. In particular, dissipative operations, such as measurement and erasure, are nonconservative operations, and must also generate entropy – and are therefore connected to and constrained by the laws of thermodynamics. I will present our recent experimental work investigating quantum measurement from the perspective of thermodynamical and quantum resources. Using a superconducting qubit and the physics of cavity quantum electrodynamics, we have characterized measurement efficiency and effectiveness for different thermal, coherent, and quantum states of light. In particular, we find that thermal light is capable of performing quantum measurements with comparable efficiency to coherent light, both being outperformed by single-photon light. These experiments elucidate the physics of quantum measurement, deepening our understanding of the thermodynamics of quantum information.

# Wednesday June 29

• ## Ken Funo

Faculty @ RIKEN, Japan

Wednesday June 29 – 8.00 BST

##### Effective cancellation of the current-dissipation trade-off by quantum coherence

In recent years, various kinds of trade-off relations between the current and the entropy production have been derived in the field of stochastic thermodynamics. One of the important insights that can be gained from these trade-off relations is that a simultaneous maximization of the thermodynamic efficiency and the output power of heat engines is not possible. While the trade-off relations have been successful in many applications ranging from biomolecular processes to thermoelectric junctions, the effect of quantum coherence was not clear. Here, we focus on the current-dissipation trade-off relation which sets a bound on both enhancing the heat current and suppressing the entropy production, simultaneously. By analyzing the effect of coherence on the current-dissipation ratio, we find that coherence between different energy eigenstates always increases the entropy production, thereby worsening the current-dissipation ratio. On the other hand, we find that coherence between degenerate states may improve the current-dissipation ratio. When the amount of coherence between degenerate states is large enough, the trade-off relation is effectively cancelled, and the heat current scales at the same order as the particle number while suppressing the entropy production at a constant order. By utilizing the above scaling analysis, we show a quantum heat engine model that asymptotically reaches the Carnot efficiency with finite output power, and explain how this finding is consistent with the power-efficiency trade-off relation.

[H. Tajima and K. Funo, Phys. Rev. Lett. 127, 190604 (2021)].

• ## Ian Ford

Faculty @ UCL

Wednesday June 29 – 8.45 BST

##### Zeno effects and entropy production for Brownian trajectories of a physical density matrix

If we regard the (reduced) density matrix of an open quantum system as a representation of real-world physical properties and not merely as a provider of probabilities for strong projective measurements, then it makes sense to imagine its time evolution to be stochastic, as it responds to physical interactions with an underspecified environment with many similar degrees of freedom. The uncertain evolution of the state of any physical system may be characterised by the production of stochastic entropy, and an ensemble of evolutions of a density matrix can be similarly treated. We use the quantum state diffusion framework to describe such continuous Brownian trajectories. We show that various stochastic couplings between the density matrix and its environment can lead to behaviour that corresponds to thermalisation or to eigenstate selection by measurement of an observable, with none of the interpretational issues that often distinguish these two effects. By regarding the density matrix as a stochastic physical property, we study simple two- and three-level systems undergoing deterministic Hamiltonian evolution and stochastic environmental disturbance, and demonstrate Zeno effects and entropy production that would not be apparent in a more traditional ensemble-averaged description of density matrix evolution.

• ## Bijay Agarwalla

Faculty @ Indian Institute of Science Education and Research (IISER) Pune

Wednesday June 29 – 9.15 BST

##### Universal bounds on fluctuations in thermal machines and its connection to thermodynamic uncertainty relation

Trade-off relations involving the relative uncertainty of currents and the associated entropy production have been of enormous interest for the past few years in the field of non-equilibrium stochastic thermodynamics. It is now realized, for example, that the optimization of heat engines should balance power, efficiency as well as power fluctuations.  In this talk, I will talk about multi-affinity-driven continuous thermal machines and show that the relative fluctuations of individual currents for thermal machines are not independent but follow strict bounds, giving rise to a new universal bound for the mean efficiency of thermal machines and is tighter than the well known Carnot bound as predicted by macroscopic thermodynamics. I will also talk about the extension of this bound for time-reversal symmetry-breaking systems.

1. Universal bounds on fluctuations in continuous thermal machines, S. Saryal et al Phys. Rev. Lett, 127, 190603 (2021).
2. Bounds on fluctuations for finite-time quantum Otto cycle, S. Saryal and Bijay Agarwalla, Phys. Rev. E. Lett 103 L060103 (2021).
3. Universal bounds on fluctuations for machines with broken time-reversal symmetry, Accepted in Phys. Rev. E, arxiv: 2110.05297
S. Saryal, S. Mohanta, and Bijay Kumar Agarwalla
4. Universal bounds on fluctuations for machines with broken time-reversal symmetry, S. Saryal, S. Mohanta, and Bijay Agarwalla, arXiv: 2110.05297.

• ## Tathagata Karmakar

Wednesday June 29 – 9.45 BST

##### Stochastic path-integral analysis of the continuously monitored quantum harmonic oscillator

We look at the evolution of a quantum harmonic oscillator in general Gaussian states undergoing simultaneous weak continuous position and momentum measurements. The conditional state dynamics can be described in terms of stochastic diffusive evolution of the position and momentum expectation values. We extend the Chantasri-Dressel-Jordan stochastic path integral formalism (Chantasri et al., 2013, 2015) to this continuous variable system and construct a stochastic action and Hamiltonian, thereby characterizing the statistics of the measurement process. This stochastic path integral formalism helps us find the most-likely state dynamics and the final state probability densities of the system undergoing measurements. Numerical simulations confirm our analytical results. Our findings provide insights into the energetics of the measurement process, motivating their importance for quantum measurement engines/refrigerators construction.

[1] T. Karmakar, P. Lewalle, and A. N. Jordan, PRX Quantum, 3, 010327 (2022).
[2] A. Chantasri, J. Dressel, and A. N. Jordan, Phys. Rev. A 88, 042110 (2013).
[3] A. Chantasri and A. N. Jordan, Phys. Rev. A 92, 032125 (2015).

• ## Jukka Pekola

Faculty @ Aalto University, Finland

Wednesday June 29 – 10.45 BST

##### Counting electrons and photons in nanocircuits – experiments on non-equilibrium thermodynamics

I describe recent experiments in our laboratory on how non-equilibrium excitations in low temperature superconductors can be observed by counting emitted electrons one-by-one [1]. Interesting statistics and long-term relaxation of rare events reveal new features of quasiparticle excitations in the system, precisely characterized in the experiment, but not fully in line with earlier understanding. In the second part of the talk I describe our current efforts to move from steady-state bolometric measurements of thermal microwave photons [2] to observation of single events by a nano-calorimeter. I describe the sensitive thermometer on the electronic absorber of this calorimeter achieving the fundamental lower bound of energy fluctuations arising from fluctuation-dissipation theorem [3]. The detector is in principle capable of detecting absorption events of single photons in a circuit in a continuous manner. We describe a recent proposal of splitting the energy of the photon to two absorbers to significantly boost the signal-to-noise ratio in a temperature cross-correlation measurement [4].

[1] E. T. Mannila, P. Samuelsson et al., Nat. Phys. 18, 145 (2022).
[2] JP and Bayan Karimi, Rev. Mod. Phys. 93, 041001 (2021).
[3] Bayan Karimi et al., Nat. Commun. 11, 367 (2020).
[4] JP and Bayan Karimi, Phys. Rev. X 12, 011026 (2022).

• ## Alexia Auffèves

Faculty @ CNRS

Wednesday June 29 – 11.30 BST

##### Quantum technologies need a quantum energy initiative

Quantum technologies are currently the object of high expectations from governments and private companies, as they hold the promise to shape safer and faster ways to exchange and treat information. However, despite its major potential impact for industry and society, the question of their energetic footprint has remained in a blind spot of current deployment strategies. In this talk, i will present why quantum technologies must urgently plan for the creation and structuration of a transverse quantum energy initiative, connecting quantum thermodynamicists, computer scientists, experimenters and engineers. Such initiative is the only path towards sustainable quantum technologies, help reducing the cost of classical information processing, and possibly bring out an energetic quantum advantage.

arXiv:2111.09241

• ## Santiago Hernández-Gómez

Postdoc @ LENS – University of Florence

Wednesday June 29 – 12.00 BST

##### Measuring negative quasiprobabilities with a diamond spin

One of the most fascinating issues of quantum thermodynamics is how to capture the effect of quantum coherence and quantum correlations on thermodynamic processes occurring at the nanoscale.
This is a challenging question, because conventional methods to study energy exchange such as the two-point-measurement (TPM) scheme unavoidably destroy quantum coherence terms in the initial state [1]. A possible solution to this problem is the introduction of Kirkwood-Dirac quasiprobabilities (KDQ). Negative and/or complex values of the KDQ have been shown to imply proofs of non-classicality [2], but such values have not been observed yet in experiments.
Here we resort to the solid-state spin platform based on optically-active NV center in diamond,  recently employed in studies on energy fluctuation relations [3-5], to demonstrate a weak-TPM protocol [6] to measure the KDQ, both in a two- and a three-level system. We also explore the possibility of implementing an interferometric scheme for the measurement of KQP and moments of their statistics, using a nuclear spin as an ancillary system. Our results represent the first experimental measurement of KDQ using a weak-TPM scheme.

[1] M. Perarnau-Llobet, E. Bäumer, K. V. Hovhannisyan, M. Huber, A. Acin, PRL 118, 070601 (2017)
[2] A. Levy, and M. Lostaglio, PRX Quantum 1, 010309 (2020)
[3] S. Hernández-Gómez, S. Gherardini, F. Poggiali, F. S.Cataliotti, A. Trombettoni, P. Cappellaro, and N. Fabbri, Phys. Rev. Research 2, 023327 (2020)
[4] S. Hernández-Gómez, N. Staudenmaier, M. Campisi, N. Fabbri, New J. Phys. 23 065004 (2021)
[5] S. Hernández-Gómez, S. Gherardini, N. Staudenmaier, F. Poggiali, M. Campisi, A. Trombettoni, F. S. Cataliotti, P. Cappellaro
[6] A. Belenchia, S. Gherardini, S. Hernández-Gómez, N. Fabbri,  A. Levy, M. Lostaglio, in preparation.

• ## Gonzalo Manzano

Postdoc @ Institute for Cross-Disciplinary Physics and Complex Systems, IFISC (UIB-CSIC)

Wednesday June 29 – 12.30 BST

##### Non-Abelian Quantum Transport and Thermosqueezing Effects

Nonequilibrium classical systems support the transport of particles (e.g., electrons) and heat. Combining these two currents can lead to interesting physical applications, known as thermoelectricity. These include the Seebeck and Peltier effects, which are used in several electronic devices. Some examples are thermocouples and thermopiles useful for measuring temperature, or thermoelectric generators, used for recycling waste heat in power plants and automobiles. Quantum systems, in addition to heat and particles, support the transport of other types of excitations, with more exotic properties. These include magnetization currents, or radiation squeezing, a widely used property in quantum technologies with roots in the uncertainty principle.
By combining heat and squeezing currents, we derive a set of thermosqueezing effects, completely analogous to the thermoelectric case [1].  Our key insight is to use generalized Gibbs ensembles with noncommuting charges as the basic building blocks and strict charge-preserving unitaries in a collisional setup, building from previous considerations on squeezed thermal reservoirs [2]. These effects may have applications for new sensing technologies and for heat-to-work conversion in the quantum regime. Furthermore, an entire theoretical formalism for studying the joint transport of currents associated with observables that do not commute at the quantum level (the so-called non-Abelian charges) is formulated. This framework develops on the theory of linear transport processes, put forth by Onsager almost nine decades ago, and extends it to more general kinds of quantum processes. Remarkably, it is demonstrated that, within this framework, quantum coherence in the form of noncommutativity can lead to a reduction in dissipation. Therefore, the results presented here open new avenues for the thermodynamic description and exploitation of quantum effects.

[1] Gonzalo Manzano, Juan M.R. Parrondo, and Gabriel T. Landi, PRX Quantum 3, 010304 (2022).
[2] Gonzalo Manzano, Phys. Rev. E 98, 042123 (2018).

# Thursday June 30

• ## Sabrina Maniscalco & Marco Cattaneo

Faculty @ University of Helsinki, Finland

Thursday June 30 – 14.00 BST

##### Quantum simulation of dissipative collective effects on noisy quantum computers

Dissipative collective effects are ubiquitous in quantum physics, and their relevance ranges from the study of entanglement in biological systems to noise mitigation in quantum computers. Here, we put forward the first fully quantum simulation of dissipative collective phenomena on a real quantum computer. The quantum simulation is based on the recently introduced multipartite collision model, which reproduces the action of a dissipative common environment by means of repeated interactions between the system and some ancillary qubits. First, we theoretically study the accuracy of this algorithm on near-term quantum computers with noisy gates, and we derive some rigorous error bounds which depend on the timestep of the collision model and on the gate errors. These bounds can be employed to estimate the necessary resources for the efficient quantum simulation of the collective dynamics. Then, we implement the algorithm on some IBM quantum computers to simulate superradiance and subradiance between a pair of qubits. Our experimental results successfully display the emergence of collective effects in the quantum simulation. Finally, we analyze the noise properties of the gates we employed in the algorithm by means of full process tomography. Using the state-of-the-art tools for noise analysis in quantum computers, we obtain the values of the average gate fidelity, unitarity and diamond error, and we establish a connection between them and the accuracy of the experimentally simulated state. Although the scaling of the error as a function of the number of gates is favorable, we observe that reaching the threshold for quantum fault tolerant computation is still orders of magnitude away.

• ## Ariane Soret

Postdoc @ University of Luxembourg

Thursday June 30 – 14.45 BST

##### Thermodynamic consistency in open quantum systems: from exact identities to quantum master equations

In the context of open quantum systems, a recent effort has been put in finding alternative and general derivations of master equations which do not require the secular approximation, using partial coarse graining [1] and symmetrization  techniques [2,3,4]. These generalized master equations provide an accurate dynamic description for a larger range of parameters than the standard secular Lindblad master equations. However, the question of their thermodynamic consistency has not yet been addressed.
Here, we study the thermodynamic consistency of quantum master equations from a general point of view. Starting with a discussion of the fluctuation theorem for work, heat and entropy production at the unitary level, we derive a quantum detailed balance condition that has to be fulfilled by any time-local master equation to ensure thermodynamic consistency. While the Redfield equation breaks such conditions, we show that the validity of the latter can be restored by using secular or beyond-secular approximation schemes, already proven to be effective in restoring the positivity of the dynamical evolution [2,3,4].
In addition, we study the steady state for different models of master equations, proving that the breakdown of the Redfield equation at long times is strictly connected with the violation of the quantum detailed balance condition.
We illustrate the theoretical results by a thorough numerical analysis of the paradigmatic example of a three level system.

[1] Gernot Schaller and Tobias Brandes. Preservation of positivity by dynamical coarse graining. Phys. Rev. A, 78:022106, Aug 2008
[2] Krzysztof Ptaszyński and Massimiliano Esposito. Thermodynamics of quantum information flows. Physical review letters, 122(15):150603, 2019.
[3] Gavin McCauley, Benjamin Cruikshank, Denys I Bondar, and Kurt Jacobs. Accurate lindblad-form master equation for weakly damped quantum systems across all regimes. npj Quantum Information, 6(1):1–14, 2020.
[4] Frederik Nathan and Mark S. Rudner. Universal lindblad equation for open quantum systems. Phys. Rev. B, 102:115109, Sep 2020

Postdoc @ Royal Holloway University of London

Thursday June 30 – 15.15 BST

##### Work statistics and entanglement across the superfluid-insulator transition

Out-of-equilibrium strongly correlated systems have been shown to display interesting work fluctuations across a phase transition [1,2]. The work distribution at criticality has been investigated recently in a few models, most of which are exactly solvable, with a focus on the first and second moments after a sudden quench. Very recently, results for inhomogeneous Hubbard chains driven for a finite time indicated that the skewness of the work distribution, besides being a measure of non-Gaussianity, also captures transitions between different correlated phases [3]. Here, we explore the first three moments of the work distribution across the superfluid-insulator transition (SIT), which is well described by the attractive Fermionic Hubbard model in the presence of randomly distributed impurities [4]. The SIT can be triggered by changing either (i) the concentration of impurities or (ii) the disorder strength. We study two quench protocols implementing these two paths and discuss the impact of the entanglement and of the temperature for maximal work extraction. Our results indicate that for disorder strengths sufficiently large to overcome the Coulomb attraction, all three moments of the work distribution show a kink at the critical concentration $C_C=N/2$. This is the same point in which the entanglement is minimal or vanishes. All the effects of the transition are suppressed at high temperatures, with work being absorbed by the system and very large fluctuations. The protocol in which the SIT is triggered by route (i) is more efficient for the average work extraction and its variance is minimized at $C_C$.

[1] “Statistics of the Work Done on a Quantum Critical System by Quenching a Control Parameter”
A. Silva
Phys. Rev. Lett. 101, 120603,  2008
[2] “Work statistics and symmetry breaking in an excited-state quantum phase transition”
Z. Mzaouali, R. Puebla, J. Goold, M. El Baz, and S. Campbell
Phys. Rev. E 103, 032145, 2021
[3] “Work-distribution quantumness
and irreversibility when crossing a quantum phase transition in finite time.”
K. Zawadzki, R. M. Serra, and I. D’Amico.
Phys. Rev. Research, 2(3) 033167, 2020
[4] “Superfluid-insulator transition unambiguously detected by
entanglement in one-dimensional disordered superfluids.”
G.A. Canella and V. V. França. Scientific reports, 9(1)1–6, 2019.

• ## Stefan Nimmrichter

Faculty @ University of Siegen

Thursday June 30 – 15.45 BST

##### Coherent speed-up in the collisional charging of quantum batteries

We study self-contained collisional models for the charging of a quantum battery by a stream of identical nonequilibrium qubit units, comparing the charging power for coherent and incoherent protocols on an initially empty battery. The battery can be an oscillator, a large spin, or any other linear energy ladder with a ground state, while the qubits are assumed to be resonant with the ladder, which obviates the need for additional work input as they exchange excitations with the battery.
When the qubits are prepared in a population-inverted, incoherent mixture of energy eigenstates, the energy and ergotropy gain in the battery can be described by a generalized classical random walk process with level-dependent rates. We provide an upper bound on the charging power for any incoherent protocol, including adaptive charging strategies.  We show that this bound can be broken by non-adaptive protocols with qubits that contain quantum coherence, thus demonstrating a quantum speedup at the level of a single battery.
In homogeneous ladder models with level-independent transition rates, the speedup can be attributed to quantum walk-like interference effects. In oscillator and spin batteries, the greatest speedup is reached in the limit when the charging process approximates a coherent Rabi drive.
We show that the oscillator battery model could be realized in a state-of-the-art cavity micromaser setup, and the coherent speedup could be achieved in the presence of realistic cavity damping.

• ## Aleksander Lasek

Postdoc @ University of Maryland

Thursday June 30 – 16.45 BST

##### Experimental observation of thermalisation with noncommuting charges

Noncommuting charges have recently emerged as an area at the intersection of quantum thermodynamics and quantum information. There is a flurry of papers being published in this rapidly developing subfield. Often, the global energy and particle number are conserved, and the system is prepared with a well-defined particle number. However, quantum evolution can also conserve quantities, or charges, that fail to commute with each other. As noncommutation underlies quantumness, such systems are of particular interest. Quantum simulators have recently enabled experimental observations of quantum many-body systems’ internal thermalisation. We initiate the experimental testing of its predictions with a trapped-ion simulator. We initialize 6–15 qubits in an approximate microcanonical subspace, a recently theorized generalisation of the microcanonical subspace for accommodating noncommuting charges. The noncommuting charges are the three spin components. We report the first experimental observation of an equilibrium state predicted within quantum-information thermodynamics in 2016: the non-Abelian thermal state. Despite the threat of decoherence breaking multiple conservation laws, thanks to our use of dynamical decoupling, our many-body system is shown to exhibit quantum-thermodynamical effects only described in theory until now. This work initiates the experimental testing of a recently emerged subfield that has so far remained theoretical.

Arxiv preprint “Experimental observation of thermalisation with noncommuting charges” (2022) available at: https://arxiv.org/abs/2202.04652
Previous theoretical work:
N.  Yunger  Halpern,  P.  Faist,  J.  Oppenheim,  and  A.  Winter,  “Microcanonical  and  resource-theoretic  derivations  of  thethermal state of a quantum system with noncommuting charges”, Nature Commun.7, 12051 (2016)

• ## Kenza Hammam

Postdoc @ Queen’s University Belfast

Thursday June 30 – 17.15 BST

##### The Thermodynamics of Quantum Coherence and Quantum Thermal Machines

The impact of quantum resources, mainly quantum coherence, on the operation of thermodynamic tasks is considered one of the leading subjects of research in quantum thermodynamics. In our work, we study the effects of quantum coherent baths on the functioning of a quantum thermal machine by using a collision model framework in the continuous time limit. We find that consuming coherences from the baths allows the machine to function with efficiencies beyond the Carnot bound and allows it to perform useful tasks simultaneously including refrigeration and  generation of work, providing a new genre of device dubbed hybrid refrigerator

K. Hammam, H. Leitch, Y. Hassouni, G. De Chiara, Exploiting coherence for quantum thermodynamic advantage, (2022), arXiv:2202.07515

Faculty @ MIT, US

Thursday June 30 – 17.45 BST

##### Machine-learning-accelerated Bose-Einstein condensation

Machine learning is emerging as a technology that can enhance physics experiment and data analysis. Here, we apply machine learning to accelerate the production of a Bose-Einstein condensate across the phase transition from a classical to a quantum gas. Starting from a room-temperature gas and optimizing laser cooling (Raman sideband cooling) using a Bayesian approach with up to 55 control parameters, we prepare a condensate of rubidium atoms in less than 0.6 seconds; the fastest condensation to date. We find that the choice of cost function for the algorithm strongly influences the trade-off between large and pure condensates. We anticipate that many other physics experiments with complex nonlinear system dynamics or involving phase transitions can be significantly enhanced by a similar machine-learning approach.

• ## Nicole Yunger Halpern

Faculty @ University of Maryland, US

Thursday June 30 – 18.30 BST

##### Towards reconciliation of completely positive open system dynamics with equilibration postulate

Why do chaotic quantum many-body systems thermalize internally? The eigenstate thermalization hypothesis (ETH) explains why if the Hamiltonian lacks degeneracies. If the Hamiltonian conserves one quantity (“charge”), the ETH implies thermalization within an eigenspace of the charge—in a microcanonical subspace. But, as was recently pointed out in quantum thermodynamics, quantum systems can have charges that fail to commute with each other and so share no eigenbasis; microcanonical subspaces may not exist. Worse, the Hamiltonian will have degeneracies, so the ETH need not imply thermalization. We adapt the ETH to noncommuting charges by positing a non-Abelian ETH and invoking the approximate microcanonical subspace introduced in quantum thermodynamics. We apply the non-Abelian ETH in calculating local observables’ time-averaged. In many cases, we prove, the time average thermalizes. However, we find anomalous corrections to thermal predictions under a physically reasonable assumption. This work bridges noncommuting charges, recently on the rise in quantum thermodynamics, to the ETH, a cornerstone of many-body physics.

Murthy, Babakhani, Iniguez, Srednicki, and NYH, arXiv:2206.05310
(2022).
NYH and Majidy, npj Quantum Information 8, 10 (2022).
Kranzl, Lasek, Joshi, Kalev, Blatt, Roos, and NYH, arXiv:2202.04652
(2022).

# Friday July 1

• ## Armen Allahverdyan

Faculty @ Yerevan Physics Institute, Armenia

Friday July 1 – 8.00 BST

##### Dissipative search of an unstructured database

The search of an unstructured database amounts to finding one element having a certain property out of $N$ elements. The classical search with an oracle checking one element at a time requires on average $N/2$ steps. The Grover algorithm for the quantum search, and its unitary Hamiltonian evolution analogue, accomplish the search asymptotically optimally in $O(\sqrt{N})$ time steps. Here we propose a new computational model based on dissipative dynamics, where the quantum search is reformulated as a problem in non-equilibrium statistical mechanics. Now the search amounts to relaxing to the ground state for a quantum system having a specific, gapped energy spectrum. We show that under proper conditions, a dissipative Markov process in the $N$-level system coupled to a thermal bath leads to the system’s relaxation to the ground state during time $O(\ln N)$.

[A. E.  Allahverdyan and D. Petrosyan, Dissipative search of an unstructured database, Phys. Rev. A 105, 032447 (2022)].

• ## Ju-Yeon Gyhm

Postgraduate @ Seoul National University (SNU)

Friday July 1 – 8.45 BST

##### Quantum Charging Advantage Cannot Be Extensive Without Global Operations

Quantum batteries are thermal devices, which store energy at quantum states and convert it to usable energy. They have numerous possibilities to be applied significant technology, due to their speed of charging and releasing energy which has at most quadratic scaling with cells over the classically achievable linear scaling. The paper, “Quantum Charging Advantage Cannot Be Extensive Without Global Operations” (going to be published at Physical Review Letters as Editors’ Suggestion) shows the general bound of charging speed and the necessary condition to reach the quadratic scaling derived from the bound.
Quantum batteries’ state storing energy at the battery Hamiltonian $\hat{H}$ is evolved by the driving Hamiltonian $\hat{V}$. This is the basic protocol of Quantum batteries and gives a crucial bound for us. We show that the maximum energy change $\Delta E$ by the first time perturbation term $\hat{V}t$ decide the bound of the power. It is simply written as equation $|P|\leq \Delta E \|\hat{V}\|$ which gives the condition to obtain quadratic scaling.
To achieve quadratic scaling, a global charging protocol, which charges all the cells collectively, needs to be employed. Meanwhile, It is not a sufficient condition. We found a case that the batteries evolved by the global operator have the power increasing with linearly with cells.
We showed the significant condition for quantum batteries. This concludes the quest on the limits of charging power of quantum batteries and adds to other results in which quantum methods are known to provide at most quadratic scaling over their classical counterparts.
cf. I changed my academic name as Ju-Yeon Gyhm from Juyeon Kim. The First author of the paper referred to in the abstract is me.
Kim, J., Rosa, D., & Šafránek, D. (2021). Quantum Charging Advantage Cannot Be Extensive Without Global Operations. arXiv preprint arXiv:2108.02491.

• ## Shachar Fraenkel

Friday July 1 – 9.15 BST

##### Extensive long-range entanglement in a nonequilibrium steady state

Entanglement measures constitute powerful tools in the quantitative description of quantum many-body systems out of equilibrium. We study entanglement in the current-carrying steady state of a paradigmatic one-dimensional model of noninteracting fermions at zero temperature in the presence of a scatterer. In our previous work [1] we found an unusual scaling law for the entanglement entropy of a subsystem that is far away from the scatterer. Our exact results showed that the entanglement entropy of such a subsystem obeys an extensive (volume-law) scaling along with an additive logarithmic correction.
In this new work, we show that disjoint intervals located on opposite sides of the scatterer and within similar distances from it display volume-law entanglement regardless of their separation, as measured by their fermionic negativity [2] and coherent information [3]. We employ several complementary analytical methods to derive exact expressions for the extensive terms of these quantities and, given a large separation, also for the subleading logarithmic terms. Remarkably, our results imply in particular that far-apart intervals which are positioned symmetrically relative to the scatterer are more strongly entangled than if we had reduced the distance between them by choosing one of these intervals to be closer to the scatterer.
The strong long-range entanglement is generated by the coherence between the transmitted and reflected parts of propagating particles within the bias-voltage window, despite the fact that only single particles are scattered independently. The generality and simplicity of the model suggest that this behavior should characterize a large class of nonequilibrium steady states.

[1] S. Fraenkel and M. Goldstein, Entanglement measures in a nonequilibrium steady state: Exact results in one dimension, SciPost Phys. 11, 85 (2021).
[2] H. Shapourian, K. Shiozaki, and S. Ryu, Partial time-reversal transformation and entanglement negativity in fermionic systems, Phys. Rev. B 95, 165101 (2017).
[3] M. Horodecki, J. Oppenheim, and A. Winter, Partial quantum information, Nature 436, 673 (2005).

• ## Saulo V. Moreira

Postdoc @ Lund University

Friday July 1 – 9.45 BST

##### Extractable work in a Szilard engine with a finite-size reservoir

The Szilard engine is a paradigmatic protocol in thermodynamics when it comes to the question of how much work can be extracted from a system coupled to a single thermal reservoir, by means of performing measurement and feedback. Originally conceived as a thought experiment by Szilard [1], experimental realizations of the engine have been implemented over the last few years, for example in the context of nanodevices such as quantum dots [2,3]. In an ideal Szilard engine, in which the system is coupled to an infinite-size bath at constant temperature, the extractable work has an upper bound, reaching k_BT ln 2 for a quasi-static, large amplitude cycle.
Here, we aim to study how the extraction of work in a Szilard engine is impacted by finite-size reservoirs. We focus on a system constituted of a quantum dot, which is, in turn, coupled to a finite-size fermionic reservoir. Due to the exchange of heat between the quantum dot and the reservoir, the temperature of the reservoir develops fluctuations in time. We find that the maximum amount of work that can be extracted is always lower than in the ideal Szilard engine, with infinite size reservoirs. Moreover, in the limit of large but finite-size reservoirs, the difference in extractable work is inversely proportional to the heat capacity of the reservoir.
Moreover, we compare our results with previously derived upper bounds for the extractable work derived for finite-size reservoirs [4,5], and show that our results are consistent with these bounds.

[1] L. Szilard. Über die Entropieverminderung in einem thermodynamischen System bei Eingriffen intelligenter Wesen, Z. Physik 53, 840–856 (1929).
[2] J. V. Koski, V. F. Maisi, J. P. Pekola and D. V. Averin. Experimental realization of a Szilard engine with a single electron, Proc Natl Acad Sci 11, 13786 (2014).
[3] D. Barker, M. Scandi, S. Lehmann, C. Thelander, K. A. Dick, M. Perarnau-Llobet, and V. F. Maisi. Experimental Verification of the Work Fluctuation-Dissipation Relation for Information-to-Work Conversion, Phys. Rev. Lett. 128, 040602 (2022).
[4] R. Clausius. Ueber verschiedene für die Anwendung bequeme Formen der Hauptgleichungen der mechanischen Wärmetheorie, Ann. Phys. 201, 353 (1865).
[5] P. Strasberg and A. Winter. First and second law of quantum thermodynamics: A consistent derivation based on a microscopic definition of entropy. PRX Quantum 2, 030202  (2021).

• ## Alvaro Alhambra

Faculty @ Max Planck Institute for Quantum Optics, Germany

Friday July 1 – 10.45 BST

##### Quantum many-body systems in thermal equilibrium: correlations and classical simulation

There are numerous models of interacting many-body quantum systems whose physics we would like to probe and better understand. This notably includes situations in which the systems at hand are at thermal equilibrium with its environment.

Due to the inherent complexity of quantum mechanics, one might expect that those equilibrium states will typically be very complex, and hard to describe via direct means or classical algorithms. At the same time, the effect of thermal fluctuations, together with our intuition from thermodynamics, point in the opposite direction: a system at equilibrium should have a simple description.

In this talk, we aim to clarify the product of this tension. To do so, we explain how and when quantum systems in thermal equilibrium can be shown to have simpler features and descriptions than general quantum states. This includes mathematical results on the nature of the internal correlations of these systems, such as area laws, as well as provably efficient classical algorithms for their description, mostly involving tensor networks.

• ## Alberto Rolandi

Friday July 1 – 11.30 BST

##### Finite-time Landauer principle at strong coupling

Landauer’s principle gives a fundamental limit to the thermodynamic cost of erasing information. Its saturation requires a reversible isothermal process, and hence infinite time. We develop a finite-time version of Landauer’s principle for a quantum dot strongly coupled to a fermionic bath. By solving the exact non-equilibrium dynamics, we optimize erasure processes (taking both the dot’s energy and system-bath coupling as control parameters) in the slow driving regime through a geometric approach to thermodynamics. We find analytic expressions for the thermodynamic metric and geodesic equations, which can be solved numerically. Their solution yields optimal finite-time processes that allows us to characterise a fundamental finite-time correction to Landauer’s bound, fully taking into account non-markovian and strong coupling effects.

• ## Michele Campisi

Faculty @ NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Pisa

Friday July 1 – 12.00 BST

##### Observation of quantum enhanced information erasure

We study Information erasure is one of the basic operations that allow computers, classical and quantum alike, to work. Recent research has elucidated the microscopic mechanisms that are  the basis of the physics of information erasure and their energetic cost. Experiments have been carried either in the classical regime (e.g., using optically trapped colloidal particles), or in the quantum regime (e.g., using nanomagnets). Here we employ a quantum annealer to experimentally study the process of information erasure in a macroscopic register whose degree of quantumness can be tuned. This allowed the unprecedented possibility to observe the genuine impact that quantum phenomena have on the physics of information erasure. We report evidence of a triple quantum advantage: the quantum assisted erasure is more effective, faster and more energy efficient. We also observe that the quantum enhancement is so strong that it enables a cooperative erasure of the information individually carried by each qubit forming the register, and that happens with an energy dissipation close to the Landauer bound. We thus demonstrated an effective and energy efficient method to prepare ensembles of qubits in a state of high purity and long time duration, which is a promising tool for quantum computing applications.

##### https://arxiv.org/abs/2206.10230

Postdoc @ University of Geneva

Friday July 1 – 12.30 BST

##### Feasible measurements for thermometry of Gaussian quantum systems

We study the problem of estimating the temperature of Gaussian systems with feasible measurements, namely Gaussian and photo-detection-like measurements. For Gaussian measurements, we develop a general method to identify the optimal measurement numerically and derive the analytical solutions in some relevant cases. For a class of single-mode states that includes thermal ones, the optimal Gaussian measurement is either Heterodyne or Homodyne, depending on the temperature regime. This contrasts with the general setting, in which a projective measurement in the eigenbasis of the Hamiltonian is optimal regardless of temperature. In the general multi-mode case, and unlike the general unrestricted scenario where joint measurements are not helpful for thermometry (nor for any parameter estimation task), it is open whether joint Gaussian measurements provide an advantage over local ones. We conjecture that they are not useful for thermal systems, supported by partial analytical and numerical evidence. We further show that Gaussian measurements become optimal in the limit of large temperatures, while photo-detection-like measurements do it for when the temperature tends to zero. Lastly, we present an example where, despite being sub-optimal, Gaussian measurements can exploit bath induced correlations to enhance thermometry precision at extremely low temperatures. Our results therefore put forward an experimentally realizable thermometry protocol for Gaussian quantum.

1. arXiv:2110.02098
2. Phys. Rev. Lett. 128, 040502 (2022)

• ## Tilman Esslinger

Faculty @ ETH Zürich, Switzerland

Friday July 1 – 14.00 BST

TBA