On-chip waste recovery in quantum and nanoscale devices guided by novel performance quantifiers

Projektinformationen

NanoRecycle

ID Finanzhilfevereinbarung: 101088169

DOI

10.3030/101088169

EK-Unterschriftsdatum 6 Juni 2023

Startdatum 1 Januar 2024

Enddatum 31 Dezember 2028

Finanziert unter

• European Research Council (ERC)

Gesamtkosten

€ 1 998 784,00

EU-Beitrag

€ 1 998 784,00

Koordiniert durch

CHALMERS TEKNISKA HOGSKOLA AKTIEBOLAG
Sweden

Periodic Reporting for period 1 - NanoRecycle (On-chip waste recovery in quantum and nanoscale devices guided by novel performance quantifiers)

Berichtszeitraum: 2024-01-01 bis 2026-06-30

Zusammenfassung vom Kontext und den Gesamtzielen des Projekts

Recent years have seen a boom in both fundamental research and development towards quantum technologies, which provide dramatic improvements in computing, sensing, communications and information applications. Simultaneously, classical technologies are quickly advancing, interfacing with the quantum ones.

Management of heat and dissipation is crucial for all of these technologies as they rely to a large extent on micro- or nanoscale devices operated at cryogenic temperatures. This is even more so since any on-chip operation leaves behind waste, such as, e.g. dissipated heat, that is not used any further or could even be detrimental for the device. However, the on-chip waste of small-scale, low-temperature devices is not only dissipated heat, but also fluctuations and nonthermal/nonequilibrium states, which could even have quantum properties. Besides heat, fluctuations can furthermore be highly detrimental in small-scale devices.

The project NanoRecycle aims at exploiting the waste in the broadest possible sense, arising from on-chip operations, and to convert it into useful resources – such as electrical power, cooling, or advantageous nonthermal energy-distributions – adapted for further on-chip tasks. Already small gains on-chip can avoid large power expenses from external control. On-chip energy conversion has the intriguing advantage that the fundamental and distinctive properties of these devices can be exploited in order to transform on-chip "waste" of an operation into a useful resource.

We will tackle this comprehensive study based on three paradigmatic devices, which incorporate major characteristics and key opportunities of nano-scale and quantum technologies. They are close to realistic experiments yet well-described by relatively simple models allowing for a largely analytical treatment and generalizations to larger classes of relevant experiments. These devices are (A) multi-terminal, coherent conductors, (B) capacitively coupled quantum dots in contact with several baths and (C) quantum-dot systems coupled to a bosonic quantum cavity - again each of them coupled to environments.

The main aims of NanoRecycle are:
• to set up a holistic performance analysis, by identifying and quantifying the waste occurring in nanoscale and quantum devices, as well as the desired output, and inter-relating them in novel types of efficiencies and constraints on dedicated conversion processes. The developed novel performance quantifiers will serve as basis for the following aims of NanoRecycle and as guide for sustainable future technologies.
• to develop optimal processes for the conversion of nonthermal distributions that are ubiquitous in small-scale devices, into power or other useful resources.
• to harvest different types of fluctuations for power production and to optimise waste-recovery processes with the performance goal of suppressing output power fluctuations or in other words of increasing precision.
•to identify quantum properties of waste and to develop dedicated processes to exploit or counteract them.

Arbeit, die ab Beginn des Projekts bis zum Ende des durch den Bericht erfassten Berichtszeitraums geleistet wurde, und die wichtigsten bis dahin erzielten Ergebnisse

WP1: To quantify the performance of energy conversion processes using (1) alternative resources as compared to (only) heat and work and (2) aiming at optimising not only output power and efficiencies, one needs to identify meaningful and generic performance quantifiers. We have made significant progress of relevance for the ongoing and future development of the subsequent WPs.
For the characterization of nonthermal resources, we have put forward an optimization scheme where we allow for arbitrary transport currents as the desired “task” and optimize for different goals: the output current, efficiencies with respect to an arbitrary resource current (for example entropy), precision, as well as to trade-offs combining these goals.
Important for the characterisation of nonthermal resources is furthermore the possibility to include mutual information or correlations between subsystems as a resource. To fully capture the role of information in conversion processes with nonthermal resources, we have introduced a way to analyse information at the level of stochastic trajectories. Based on this we also introduced efficiencies where information flow or entropy currents feature as resources.
To quantify the performance of engines exploiting quantum measurement, we have focussed on ergotropy – namely the maximum amount of energy that can be extracted by a unitary transformation – conditioned on measurement outcomes as performance quantifier. We have furthermore explicitly highlighted measurement time, which we used as starting point for a multi-objective Pareto optimization.

WP2: Nonthermal distributions can arise due to the experimentally relevant situations of driving or competition between different environments, which we have both considered. Also for generic nonthermal resources, we have optimized the performance of refrigeration by identifying sequences of box-car shaped filters as the ideal properties of a thermoelectric conductor.
Nonthermal resources can drive a conversion process without providing energy on average. This is reminiscent to (but not the same as) a Maxwell demon. In quantum-dot systems, we have analyzed connections and differences between use of nonthermal resources and information. We found that, while quantum-dot engines driven by information or by nonthermal resources can have similar power output and efficiencies, the precision of a nonthermal engine can be decisively higher.
We have furthermore analyzed the time-dependent decay of out-of-equilibrium quantum dots. We have identified parameter regions in which the so-called Mpemba effect is manifest, meaning that states that are initially farther away from equilibrium reach the equilibrium faster. This is of interest for (dis)charging of energy storage and for pulsed device operation.

WP3: We have reached our goal of performing a full-counting analysis of nonthermal quantum-dot heat engines, even including counting of information and activity. Combining this with an analysis of stochastic trajectories, we identified operation conditions with high precision. We also found situations where the engine reduces fluctuations from input to output, while producing power.
Importantly, we furthermore have developed a suite of bounds on precision, as described in more detail below.

WP4: To exploit and characterize resources for energy conversion that have quantum properties, we have started preparations in three directions: (1) We have set up a model and code for possibly strongly cavity-coupled quantum dots. The quantum cavity states can be exploited to generate a current through the dots, or, vice-versa, the strong coupling is used to create quantum cavity states. (2) We have set up noise bounds for arbitrary driving, which can generally create coherent energy superposition states. Its effect on precision will be explored. (3) We have started a research line exploiting quantum measurement for energy conversion and for battery (dis)charging.

Fortschritte, die über den aktuellen Stand der Technik hinausgehen und voraussichtliche potenzielle Auswirkungen (einschließlich der bis dato erzielten sozioökonomischen Auswirkungen und weiter gefassten gesellschaftlichen Auswirkungen des Projekts)

One significant methodological achievement provides a novel way of combining scattering matrix theory for quantum transport with the two-point measurement scheme of relevance for quantum stochastic thermodynamics. It is expected to heavily be used in the remainder of the project. Scattering matrix theory for quantum transport has the capability of describing strongly coupled (but weakly interacting) quantum systems. However, scattering theory does not typically deal with the system's density operator, which is instead usually needed in stochastic thermodynamics. With the approach we are currently developing, we can combine the two features. With this, we can analyze entropy production due to scattering, measurement, and dissipation in a transport setup and start an analysis of entropy currents and their full statistics.
Another major achievement concerns the characterisation of fluctuations (or equivalently precision). We have developed a suite of bounds on precision, which are valid for generic coherent conductors under a wide range of possible non-equilibrium conditions that can be strongly coupled to the environment but have weak many-body interactions. These bounds are hence complementary to the major part of currently studied bounds that are typically valid for classical and/or weakly coupled systems. Importantly, our bounds cover a wide range of observables and nonequilibrium conditions. An important asset is furthermore that the constraints we identify are always provided in terms of measurable, intuitively accessible quantities, which are directly connected to the conversion process itself. They are therefore ideal starting points for performance quantifiers of trade-off relations including precision. The developed sets of bounds provide helpful estimates of expected fluctuations, serve as guidelines to reduce them, and establish factors that can serve as precision trade-off performance quantifiers.