arXiv subjects

Ahmad R. T. Nugraha

Publications and source records attributed to Ahmad R. T. Nugraha.

At least 19 recordsLinked to original sources

arXiv2026

Algebraic power scaling in a slowly-quenched bosonic quantum battery

Bosonic modes provide a promising platform for quantum batteries as a result of their unbounded energy spectrum. However, the energy that can be stored during a coherent charging process is limited due to coherent oscillations between the charger and battery. In this work, we show that by introducing a slow quench in the interaction between a coherently driven charger mode and a quadratic oscillator battery, the maximum stored energy and maximum battery power scale algebraically with the quench duration, with exponents controlled by the ramp profile. This finding implies that, quite counterintuitively, slower quenches lead to faster charging. Such a quench suppresses coherent energy oscillations between the battery and the charger, allowing an unbounded increase in power. We further show that, in the ideal closed protocol, the stored energy is fully extractable as ergotropy, while charger dissipation converts the algebraic enhancement into a finite-time scaling window with an optimal quench duration. We also show that the temporal-extensive scaling occurs in a broader context by mapping the system to a coherently driven Tavis-Cummings battery. Finally, we discuss experimentally accessible signatures in superconducting circuit quantum electrodynamics and organic microcavity platforms.

quant-ph↗

arXiv2026

Unified Spectral, Dynamical, and Correlation Signatures of an Exceptional Point in Cavity Optomechanics

We investigate how the exceptional-point structure of a dissipative cavity optomechanical system is inherited by experimentally accessible dynamical, spectral, and quantum-statistical observables. At optical-mechanical resonance, the effective non-Hermitian first-moment dynamics exhibits a second-order exceptional point, where two eigenvalues and their eigenvectors coalesce and the eigenvalue splitting follows the characteristic square-root dependence on perturbations. We show that the same square-root feature also governs transient photon and phonon populations, first-order coherence, spectral poles, and second-order intensity correlations. Below the exceptional point, the dynamics is non-oscillatory, whereas above it damped oscillations emerge together with frequency splitting of the spectral poles. At the exceptional point, the Jordan-block structure produces polynomial-exponential relaxation and a second-order spectral pole. Using the quantum regression theorem and Gaussian moment factorization, we further show that the stationary fluctuations satisfy the Siegert relation linking first- and second-order correlations. Although the zero-delay autocorrelations retain their thermal value, the finite-delay intensity correlations exhibit clear exceptional point signatures. This finding connects non-Hermitian mode coalescence with measurable dynamical and correlation observables in cavity optomechanics.

quant-ph↗

arXiv2026

SymQuPS: Symbolic Quantum Phase Space Algebra in Python

We present \texttt{SymQuPS}, a SymPy-based algebra system in Python mainly aimed toward the phase space representation of quantum mechanics within the Cahill-Glauber formalism (including the Glauber-Sudarshan $P$, Wigner, and Husimi $Q$ representations). By extension, the package serves as an algebraic venue for canonical quantization. A key feature is the phase space representation of an arbitrary Lindblad master equation, which gives the phase space equation of motion of the quantum system. We describe the core functionalities of the package, consisting of $s$-ordered operators, the star products, and the phase space representation. Some examples of use are given to illustrate the application of the package, and the package's performance in typical use cases is discussed.

quant-ph↗

arXiv2026

Spin Response Properties in Electronically Robust Ferromagnetic Strained CrSiSe$_3$ Monolayer under External Electric Fields

Integrating two-dimensional van der Waals magnets into field-effect spintronic devices requires robust charge stability and tunable spin responses. In this study, we investigate the electronic, topological, magnonic, and magneto-optical properties of the strain-engineered ferromagnetic CrSiSe$_3$ monolayer under out-of-plane external electric fields by using first-principles calculations. We find that for this material, the intrinsic charge sector, including the indirect band gap, charge Berry curvature, optical conductivities, and magneto-optical Kerr effect spectra, exhibits exceptional robustness against applied fields up to 0.3 V/$Å$. Conversely, the spin degrees of freedom demonstrate highly sensitive tunability. Electrostatic gating significantly modulates the spin Berry-like curvature, driving a non-monotonic enhancement in the spin Hall conductivity. Furthermore, external fields effectively tune collective magnon excitations by modifying microscopic Heisenberg exchange interactions. Such coexistence of robust charge immunity and flexible spin manipulation establishes the strained CrSiSe$_3$ monolayer as a promising platform for stable spintronic devices.

cond-mat.mtrl-sci↗

arXiv2026

Geometry-controlled magnon-polaritons of double magnetic films in planar cavities

Planar cavity magnonics has been developed mainly for a single magnetic film, leaving multilayer behavior in spatially resolved cavity scattering largely unexplored. Here, we introduce a double layer planar cavity with two magnetic films embedded in the same microwave cavity to derive a full two-film scattering theory in the macrospin ($J = 0$) limit and recover the exact zero-gap half-thickness limit, thereby benchmarking the model against the known one-film result. We find that the double layer model actively enables geometry-controlled bright-channel enhancement, demonstrating that the magnon-photon coupling depends on spatial placement rather than just total magnetic volume. Antinode-compatible placements increase the coupling, while node-compatible placements suppress it. Weak symmetry breaking also transfers finite cavity weight to a mode dark in the symmetric limit, producing an additional branch without destroying the main avoided crossing. Finally, a reduced multimode theory for $J\neq 0$ predicts family-resolved bright and dark channels for odd standing-spin-wave modes.

cond-mat.mes-hall↗

arXiv2025

Transient dynamics of the quantum Stuart-Landau oscillator

We investigate the transient dynamics of the quantum Stuart-Landau oscillator, a paradigmatic quantum system exhibiting a quantum limit cycle and synchronization. From the energy dynamics, we determine a condition for the classical regime of transient dynamics and the limit cycle. Additionally, we formulate a guess function that fits the classical-regime steady-state Wigner function. The equation of motion for the Wigner function is derived and compared to the Kramers-Moyal equation for stochastic processes. We then characterize the classical-like behavior as the system evolves from a coherent state, noting the slow decay of neighboring-level coherence. We also study the evolution of the Wigner negativity as an indicator of nonclassicality, showing its temporary increase for some specific cases. To quantify the evolution speed, we examined the system's Lindbladian spectra, particularly the Liouvillian gap. Finally, we record the time it takes to reach the steady state for some Fock, thermal, and coherent states. The parameter dependence of the steady-state time may differ from the Liouvillian gap, and the limit-cycle attraction is significantly slower for coherent states compared to Fock or thermal states. For the diagonal states, there are \revision{fast convergence regimes} for which the steady-state time is locally minimized. This study provides a deeper insight into the transient behavior of self-sustained quantum systems.

quant-ph↗

arXiv2025

Noise-induced Zeno-like effect in a spin-chain quantum battery

Quantum batteries, which are energy-storage or state-storage devices that exploit unique quantum effects, are sensitive to environmental noise. Here, we demonstrate that suitably engineered noise can induce a "Zeno-like" stabilization effect of the charging process in a spin-chain quantum battery within the Heisenberg XYZ model. Focusing on a system size N=6, which balances computational cost and storage capacity, we find that the ergotropy-to-energy ratio W(t)/E_B(t) attains a maximum value of about 0.99 at a certain time parameter value. Then, by varying the noise strength in each channel, we find that not only does decoherence merely degrade performance but it may also stabilize stored energy and ergotropy in the high noise strength regime. For instance, the phase-flip channel slows charging and reduces charging power, but its discharging behavior releases energy and ergotropy more slowly, allowing the battery to be used for longer times compared to bit-flip and bit-phase-flip channels. In contrast, the bit-flip channel enables fast charging, but yields low storage and rapid energy release. Remarkably, the bit-phase-flip channel can combine the advantages of both bit-flip and phase-flip channels in the high-noise-strength regime. The bit-phase-flip channel supports accelerated charging together with enhanced storage capacity, while its discharging behavior resembles that of the bit-flip channel with rapid energy release. These results reveal that, under sufficiently strong noise, environmental decoherence induces a Zeno-like stabilization, allowing it to achieve enhanced charging performance and to stabilize stored energy and ergotropy in the spin-chain quantum battery.

quant-ph↗

arXiv2025

pyBoLaNO: A Python symbolic package for normal ordering involving bosonic ladder operators

We present pyBoLaNO, a Python symbolic package based on SymPy to quickly normal-order (Wick-order) any polynomial in bosonic ladder operators. By extension, this package offers the normal ordering of commutators of any two polynomials in bosonic ladder operators and the evaluation of the normal-ordered expectation value evolution in the Lindblad master equation framework for open quantum systems. The package also supports multipartite descriptions and multiprocessing. We describe the package's workflow, show examples of use, and discuss its computational performance. All codes and examples are available on our GitHub repository.

quant-ph↗

arXiv2024

Thermoelectric Properties of Type-I and Type-II Nodal Line Semimetals: A Comparative Study

We investigate the thermoelectric (TE) properties of nodal line semimetals (NLSs) using a combination of semi-analytical calculations within Boltzmann's linear transport theory and the relaxation time approximation, along with first-principles calculations for the so-called type-I and type-II NLSs. We consider the conduction and valence bands that cross near the Fermi level of these materials through first-principles calculations of typical type-I (TiS) and type-II (Mg$_3$Bi$_2$) NLSs and use the two-band model fit to find the Fermi velocity $v_{F}$ and effective mass $m$ that will be employed as the initial energy dispersion parameters. The optimum curvature value for each energy band is searched by tuning both $v_{F}$ and $m$ to improve the TE properties of the NLSs. By systematically comparing all of our calculation results, we observe that tuning $v_{F}$ significantly improves TE properties in both types of NLS compared to tuning $m$. We also find that in all TE metrics, the type-I NLS surprisingly can surpass the type-II NLS, which seems counter-intuitive to the fact that within the two-band model, the type-I NLS contains a parabolic band while the type-II NLS possesses a higher-order, Mexican-hat band. Our study demonstrates that optimizing the curvature of energy bands by tuning $v_F$ can significantly improve the TE performance of NLSs. This approach could guide future efforts in exploring other semimetals as potential TE materials by manipulating their band structures.

cond-mat.mtrl-sci↗

arXiv2023

High-performance Kerr quantum battery

We propose and investigate the performance of a hybrid quantum battery, the so-called Kerr quantum battery, which consists of two interacting quantum oscillators, i.e., the charger is a harmonic oscillator and the battery is an anharmonic oscillator involving the Kerr nonlinearity. Such a setup creates nonuniform spacing between energy levels of the quantum oscillator that increases with the energy level. We find that the Kerr quantum battery can store more energy than the qubit battery and reaches maximum stored energy faster than the harmonic oscillator battery. In particular, the average charging power of the Kerr quantum battery is larger than the qubit battery. Furthermore, most of the stored energy in the Kerr quantum battery can be extracted for work. All of the properties of the Kerr quantum battery are controlled by the strength of nonlinearity, in which the enhancement of the nonlinearity transforms the battery from a harmonic oscillator to a qubit.

quant-ph↗

arXiv2023

Phase transition in the majority rule model with the nonconformist agents

Independence and anticonformity are two types of social behaviors known in social psychology literature and the most studied parameters in the opinion dynamics model. These parameters are responsible for continuous (second-order) and discontinuous (first-order) phase transition phenomena. Here, we investigate the majority rule model in which the agents adopt independence and anticonformity behaviors. We define the model on several types of graphs: complete graph, two-dimensional (2D) square lattice, and one-dimensional (1D) chain. By defining $p$ as a probability of independence (or anticonformity), we observe the model on the complete graph undergoes a continuous phase transition where the critical points are $p_c \approx 0.334$ ($p_c\approx 0.667$) for the model with independent (anticonformist) agents. On the 2D square lattice, the model also undergoes a continuous phase transition with critical points at $p_c \approx 0.0608$ ($p_c \approx 0.4035$) for the model with independent (anticonformist) agents. On the 1D chain, there is no phase transition either with independence or anticonformity. Furthermore, with the aid of finite-size scaling analysis, we obtain the same sets of critical exponents for both models involving independent and anticonformist agents on the complete graph. Therefore they are identical to the mean-field Ising model. However, in the case of the 2D square lattice, the models with independent and anticonformist agents have different sets of critical exponents and are not identical to the 2D Ising model. Our work implies that the existence of independence behavior in a society makes it more challenging to achieve consensus compared to the same society with anticonformists.

physics.soc-ph↗

arXiv2023

Computational study of III-V direct-gap semiconductors for thermoradiative cell applications

We investigate the performance of thermoradiative (TR) cells using the III-V group of semiconductors, which include GaAs, GaSb, InAs, and InP, with the aim of determining their efficiency and finding the best TR cell materials among the III-V group. The TR cells generate electricity from thermal radiation, and their efficiency is influenced by several factors such as the bandgap, temperature difference, and absorption spectrum. To create a realistic model, we incorporate sub-bandgap and heat losses in our calculations and utilize density-functional theory to determine the energy gap and optical properties of each material. Our findings suggest that the effect of absorptivity on the material, especially when the sub-bandgap and heat losses are considered, can decrease the efficiency of TR cells. However, careful treatment of the absorptivity indicates that not all materials have the same trend of decrease in the TR cell efficiency when taking the loss mechanisms into account. We observe that GaSb exhibits the highest power density, while InP demonstrates the lowest one. Moreover, GaAs and InP exhibit relatively high efficiency without the sub-bandgap and heat losses, whereas InAs display lower efficiency without considering the losses, yet exhibit higher resistance to sub-bandgap and heat losses compared to the other materials, thus effectively becoming the best TR cell material in the III-V group of semiconductors.

cond-mat.mes-hall↗

arXiv2023

Trigonal warping effects on optical properties of anomalous Hall materials

The topological nature of topological insulators are related to the symmetries present in the material, for example, quantum spin Hall effect can be observed in topological insulators with time reversal symmetry, while broken time reversal symmetry may give rise to the presence of anomalous quantum Hall effect (AHE). Here we consider the effects of broken rotational symmetry on the Dirac cone of an AHE material by adding trigonal warping terms to the Dirac Hamiltonian. We calculate the linear optical conductivity semi-analytically to show how by breaking the rotational symmetry we can obtain a topologically distinct phase. The addition of trigonal warping terms causes the emergence of additional Dirac cones, which when combined has a total Chern number of $\mp 1$ instead of $\pm 1/2$. This results in drastic changes in the anomalous Hall and longitudinal conductivity. The trigonal warping terms also activates the higher order Hall responses which does not exist in a $\mathcal{R}$ symmetric conventional Dirac material. We found the presence of a non-zero second order Hall current even in the absence of Berry curvature dipole. This shift current is also unaffected by the chirality of the Dirac cone, which should lead to a non-zero Hall current in time reversal symmetric systems.

cond-mat.mes-hall↗

arXiv2022

Long-lived qubit entanglement by surface plasmon polaritons in a Weyl semimetal

We investigate spontaneous entanglement of two qubits mediated by nonreciprocal surface plasmon polaritons (SPPs) in a Weyl semimetal. In the absence of external magnetic fields, the topology of the Weyl semimetal even gives rise to nonreciprocal SPPs that are topologically protected and reside inside the photonic gap. We utilize this nonreciprocal SPP as a mediator of entanglement of two spatially-separated qubits. Our two main findings are: (1) the nonreciprocal SPP gives better quantum entanglement than the reciprocal one, and (2) the achieved entanglement is sufficiently long-lived compared to the entanglement using SPPs in conventional metals.

cond-mat.mes-hall↗

arXiv2022

Enhancement of spin mixing conductance by $s$-$d$ orbital hybridization in heavy metals

In a magnetic multilayer, the spin transfer between localized magnetization dynamics and itinerant conduction spin arises from the interaction between a normal metal and an adjacent ferromagnetic layer. The spin-mixing conductance then governs the spin-transfer torques and spin pumping at the magnetic interface. Theoretical description of spin-mixing conductance at the magnetic interface often employs a single conduction-band model. However, there is orbital hybridization between conduction $s$ electron and localized $d$ electron of the heavy transition metal, in which the single conduction-band model is insufficient to describe the $s$-$d$ orbital hybridization. In this work, using the generalized Anderson model, we estimate the spin-mixing conductance that arises from the $s$-$d$ orbital hybridization. We find that the orbital hybridization increases the magnitude of the spin-mixing conductance.

cond-mat.mes-hall↗

arXiv2022

Spin-tunable thermoelectric performance in monolayer chromium pnictides

Historically, finding two-dimensional (2D) magnets is well known to be a difficult task due to instability against thermal spin fluctuations. Metals are also normally considered poor thermoelectric (TE) materials. Combining intrinsic magnetism in two dimensions with conducting properties, one may expect to get the worst for thermoelectrics. However, we will show this is not always the case. Here, we investigate spin-dependent TE properties of monolayer chromium pnictides (CrX, where X = P, As, Sb, and Bi) using first-principles calculations of electrons and phonons, along with Boltzmann transport formalism under energy-dependent relaxation time approximation. All the CrX monolayers are dynamically stable and they also exhibit half metallicity with ferromagnetic ordering. Using the spin-valve setup with antiparallel spin configuration, the half metallicity and ferromagnetism in monolayer CrX enable manipulation of spin degrees of freedom to tune the TE figure of merit (ZT). At optimized chemical potential and operating temperature of 500 K, the maximum ZT values (= 0.22, 0.12, and 0.09) with the antiparallel spin-valve setup in CrAs, CrSb, and CrBi improve up to almost twice the original values (ZT = 0.12, 0.08, and 0.05) without the spin-valve configuration. Only in CrP, which is the lightest species and less spin-polarized among CrX, the maximum ZT (= 0.34) without the spin-valve configuration is larger than that (= 0.19) with the spin-valve one. We also find that, at 500 K, all the CrX monolayers possess exceptional TE power factors of about 0.02-0.08 W/m.K2, which could be one of the best values among 2D conductors.

cond-mat.mtrl-sci↗

arXiv2022

Thermoelectric properties of semiconducting materials with parabolic and pudding-mold band structures

We theoretically investigate the thermoelectric properties of semiconducting (gapped) materials by varying the degrees of polynomials in their energy dispersion relations, in which either the valence or conduction energy dispersion depends on the wave vector raised to the power of two, four, and six. The thermoelectric transport coefficients such as the Seebeck coefficient, electrical conductivity, and thermal conductivity are calculated within the linearized Boltzmann transport theory combined with the relaxation time approximation. We consider various effects such as band gaps, dimensionalities, and dispersion powers to understand the conditions that can give the optimal thermoelectric efficiency or figure of merit ($ZT$). Our calculations show that the so-called pudding-mold band structure produces larger electrical and thermal conductivities than the parabolic band, but no significant difference is found in the Seebeck coefficients of the pudding-mold and parabolic bands. Furthermore, we find that a high $ZT$ can be obtained by tuning the band gap of the material to an optimum value simultaneously with breaking the band symmetry. The largest $ZT$ is found in a combination of two-contrasting polynomial powers in the dispersion relations of valence and conduction bands. This band asymmetry also shifts the charge neutrality away from the undoped level and allows optimal $ZT$ to be located at a smaller chemical potential. With some reasonable values of thermal conductivity parameters, the maximum $ZT$ for the bulk systems can be larger than 1, while for one-dimensional systems it can even reach almost 4. We expect this work to trigger high-throughput calculations for screening of potential thermoelectric materials combining various polynomial powers in the energy dispersion relations of semiconductors.

cond-mat.mtrl-sci↗

arXiv2022

Opinion dynamics involving contrarian and independence behaviors based on the Sznajd model with two-two and three-one agent interactions

We investigate the opinion evolution of outflow dynamics based on the Sznajd model on a complete graph involving contrarian and independence behaviors. We consider a group of four spins representing the social agents with the following scenarios: (1) scenario two-two with contrarian agents or independence agents and (2) scenario three-one with contrarian or independence agents. All of them undergo a second-order phase transition according to our simulation. The critical point decreases exponentially as $λ$ and $f$ increases, where $λ$ and $f$ are contrarian and flexibility factors, respectively. Furthermore, we find that the critical point of scenario three-one is smaller than that of scenario two-two. For the same level of $λ$ and $f$, the critical point of the scenario involving independence is smaller than the scenario with contrarian agents. From a sociophysics point of view, we observe that scenario three-one can likely reach a stalemate situation rather than scenario two-two. Surprisingly, the scenarios involving contrarians have a higher probability of achieving a consensus than a scenario involving independence. Our estimates of the critical exponents indicate that the model is still in the same universality class as the mean-field Ising model.

physics.soc-ph↗