arXiv subjects

Kieran Hymas

Publications and source records attributed to Kieran Hymas.

9 recordsLinked to original sources

arXiv2026

Collective Enhancement of Nuclear Excitation for a Nuclear Quantum Battery

Current implementations of quantum batteries are constrained by limited energy density and short retention times associated with the electronic or molecular excitations. Here we propose a nuclear quantum battery based on collective excitation of the $^{57}$Fe nuclei of density $n$ embedded in a planar hard X-ray waveguide. Using a Green function waveguide-QED description, we study charging via excitation beyond linear response, where saturation and drive back-action reshape the incident pulse. We introduce a self-consistent waveform-engineering protocol that inhibits local radiative decay in the waveguide thus promoting absorption into high-lying collective nuclear excitation manifolds. We show an enhanced excitation cross section of the nuclear ensemble which yields superlinear charging, with maximum studied energy density scaling approximately like $n \sqrt{n}$. Our results provide a route to high-energy-density quantum charging at hard X-ray energies using contemporary X-ray sources and waveguide architectures by identifying nonlinear, collectively enhanced absorption as a key mechanism for nuclear quantum battery operation.

quant-ph↗

arXiv2026

Quantum entanglement provides a competitive advantage in adversarial games

Whether uniquely quantum resources confer advantages in fully classical, competitive environments remains an open question. Competitive zero-sum reinforcement learning is particularly challenging, as success requires modelling dynamic interactions between opposing agents rather than static state-action mappings. Here, we conduct a controlled study isolating the role of quantum entanglement in a quantum-classical hybrid agent trained on Pong, a competitive Markov game. An 8-qubit parameterised quantum circuit serves as a feature extractor within a proximal policy optimisation framework, allowing direct comparison between separable circuits and architectures incorporating fixed (CZ) or trainable (IsingZZ) entangling gates. Entangled circuits consistently outperform separable counterparts with comparable parameter counts and, in low-capacity regimes, match or exceed classical multilayer perceptron baselines. Representation similarity analysis further shows that entangled circuits learn structurally distinct features, consistent with improved modelling of interacting state variables. These findings establish entanglement as a function resource for representation learning in competitive reinforcement learning.

quant-ph↗

arXiv2026

Quenching Speculation in Quantum Markets via Entangled Neural Traders

Speculative trading can drive pronounced market instabilities, yet existing regulatory and macroprudential tools intervene only after such dynamics emerge. Quantum technologies offer a fundamentally new means of shaping economic behavior by introducing non-classical correlations between decision-makers. Here we demonstrate a prototype quantum stock market in which entanglement between traders' valuations mitigates the runaway devaluation characteristic of speculative busts. Using reinforcement-learning agents trading a single commodity, we show that replacing classical valuations with quantum-correlated qubit-encoded valuations stabilizes prices and increases the AI traders' net worth relative to a classical market, where instead agents rapidly converge to liquidation strategies that collapse the asset value. To explain this behavior, we formulate and analyze a quantized version of the $p$-guessing game, a canonical model of speculative dynamics. Quantum entanglement and phase coherence reshape the strategic landscape, eliminating the pathological pure-strategy Nash equilibrium that drives market collapse in the classical game, while mixed-strategy equilibria remain non-degenerate and avoid bust-type outcomes. These results identify quantum correlations as a novel, endogenous mechanism for market stabilization and, more broadly, demonstrate the utility of multi-agent reinforcement learning algorithms for uncovering optimal strategies in complex decision-making frameworks with quantum degrees of freedom.

quant-ph↗

arXiv2025

Preparation and coherent manipulation of toroidal moments in molecules

Molecules with an odd number of electrons typically display paramagnetic behaviour in a uniform magnetic field. Single-molecule toroics -- a family of open shell lanthanide complexes -- instead display an unprecedented vanishing magnetization. The anomaly is reconciled by degenerate quantum states where electron spins and orbital currents give rise to time-odd and space-odd magnetic vortices known as toroidal moments, that carry a vanishing magnetic dipole. Resilient to stray magnetic fields and susceptible to electric manipulation, toroidal moments have attracted interest for spintronic, magnonic, and photonic applications. While macroscopic toroidal moments feature in some extended systems, molecular toroidal states have yet to be observed, as it remains unclear how existing experimental set-ups could split degenerate states carrying counter-rotating vortices. We propose a realistic pulsed radiation protocol to polarise and observe molecular toroidal moments in a class of MDy$_6$ (M = Al$^{3+}$, Cr$^{3+}$) molecules with coupled Dy$_3$ toroidal moieties. Three resonant MW-pulses -- delivered sequentially or simultaneously -- selectively and coherently transfers population to a long-lived toroidally-polarised state whose ensuing magneto-electric properties provide a read-out mechanism. Our results provide a strategy to measure and coherently manipulate toroidal states in molecular systems, which is expected to trigger applications of molecular toroidal states to quantum technologies.

cond-mat.mes-hall↗

arXiv2025

Finite-Temperature Toroidal Moment Amenable to Direct Observation in an Fe$_{10}$Dy$_{10}$ Molecular Ring

Single-molecule toroics (SMTs) host closed magnetic-vortex configurations that carry toroidal moments $\boldsymbol{\tau}$, whose electric-dipole symmetry enables magnetoelectric spin control. Yet, opposite toroidal chiralities are degenerate in conventional magnetic fields, making direct detection of molecular toroidal polarisation challenging. Current approaches probe molecular toroidal dynamics only indirectly through weak residual magnetism, leaving direct interrogation of toroidal polarisation an open challenge. Moreover, the survival of toroidal polarization at finite temperature, and realistic preparation-and-readout conditions, have not been quantitatively established. Here we investigate the icosanuclear $3d$--$4f$ molecular ring Fe$_{10}$Dy$_{10}$, featuring a $\sim$62-billion-dimensional low-energy manifold with pervasive toroidal character, rendered computationally tractable via an ab initio-informed transfer-matrix framework with perturbative corrections. Our model reproduces magnetic and calorimetric measurements and reveals a maximally toroidal ground doublet with robust finite-temperature toroidal response. We introduce the toroidal susceptibility $\xi$ as a finite-temperature linear-response function to quantify toroidal polarisation induced by magnetic-field curl. We then develop a preparation-and-detection protocol in which a temporally asymmetric near-infrared waveform generates a cumulative toroidal population imbalance, while an ab initio-informed magnetoelectric tensor predicts an electric-field-induced magnetic moment within $\mu$SQUID detectability. These results establish Fe$_{10}$Dy$_{10}$ as a molecular platform where toroidal polarisation can be prepared, accumulated and read out under realistic experimental conditions.

cond-mat.mes-hall↗

arXiv2025

Superradiant Organic Light-Emitting Diodes

Organic light-emitting diodes (OLEDs) are central to modern display technologies and are promising candidates for low-cost energy-efficient lighting. Their performance is determined by numerous, intricate fabrication parameters, but not least by the number of emissive molecules N, which provide sites for electron-hole recombination and photon generation in the diode host matrix. Counterintuitively, larger concentrations of emitters do not always lead to brighter or more efficient OLEDs due to concentration quenching of luminescence meaning that rates of radiative electron-hole recombination can become severely reduced, negatively impacting charge-to-photon conversion efficiency. In this work we trigger steady-state superradiant light emission from a series of Fabry-Pérot microcavity OLEDs by scaling the operating voltage of each device with emitter concentration. We demonstrate a collective enhancement in the luminance of a microcavity OLED that scales super-extensively when compared to no-cavity controls fabricated in the same run. Triggering quantum correlations between emitters via the confined cavity field allows devices with fewer emitters to match or even exceed the brightness of control OLEDs even when driven by lower voltages. Moreover, our devices show significant narrowing of their emission spectra, offering purer colours at low applied voltages. Leveraging collective effects in microcavity OLEDs provides a new approach to enable brighter, more efficient devices paving the way for next-generation displays and lighting that do not compromise performance for operational efficiency or device lifetime.

quant-ph↗

arXiv2025

Spatiotemporal entanglement of the vacuum

We demonstrate that the future and left Rindler wedges of Minkowski spacetime are entangled, leading to the Unruh effect. Similarly, the past and right Rindler wedges are also entangled. We propose a protocol to extract this entanglement using two two-state detectors located in the past and right Rindler wedges. By scaling the detector transition frequencies inversely with Minkowski time, entanglement from the quantum field is transferred to the detectors, suggesting they may support quantum teleportation via the vacuum. Our protocol can be implemented with current quantum systems, such as flux-tunable transmon qubits. This research provides new insights into the entanglement properties of spacetime and hints at practical applications for secure quantum information transfer using the vacuum state of a quantum field.

gr-qc↗

arXiv2025

Powering Quantum Computation with Quantum Batteries

Executing quantum logic in cryogenic quantum computers requires a continuous energy supply from room-temperature control electronics. This dependence on external energy sources creates scalability limitations due to control channel density and heat dissipation. Here, we propose quantum batteries (QBs) as intrinsic quantum energy sources for quantum computation, enabling the thermodynamic limit of zero dissipation for unitary gates. Unlike classical power sources, QBs maintain quantum coherence with their load - a property that, while theoretically studied, remains unexploited in practical quantum technologies. We demonstrate that initializing a bosonic QB in a Fock state can supply the energy required for arbitrary unitary gates regardless of the circuit's depth, via the recycling of pre-charged energy. Crucially, allowing QB-qubit entanglement during computation lowers the QB initial energy requirements below established energy-fidelity bounds. This scheme facilitates a universal gate set controlled by a single parameter per qubit, its resonant frequency. The relative detuning of each qubit from the QB resonant frequency gives rise to qualitatively two gate types, off-resonance and around-resonance. The former facilitates dispersive gates which allow multi-qubit parity probing while the latter enables energy exchange between the QB and the qubits, driving both population transfer and entanglement generation. This mechanism utilizes the all-to-all connectivity of the shared resonator architecture to go beyond the standard single- and two-qubit native gates of current platforms with multi-qubit gate timescales of few pi/g, where g is the qubit-resonator coupling. The resultant speed-up includes also superextensive gates between symmetric Dicke states, characteristic of QB systems.

quant-ph↗

arXiv2025

Experimental demonstration of a scalable room-temperature quantum battery

Harnessing quantum phenomena in energy storage systems offers an opportunity to introduce a new generation of batteries with quantum-enhanced performance. Until now, the quantum battery has largely remained a theoretical concept, with little progress towards experimental realisation, due to the challenges in quantum coherent control. Here, we experimentally demonstrate a scalable room-temperature quantum battery with a multi-layered organic-microcavity design. We show that it exhibits superextensive charging, metastabilisation of stored energy, and generates superextensive electrical power, the latter an unpredicted phenomenon. The combination of these properties in a single device is the first demonstration of the full cycle of a quantum battery, laying the framework for future designs.

quant-ph↗