arXiv subjects

Ramakrishna Podila

Publications and source records attributed to Ramakrishna Podila.

10 recordsLinked to original sources

arXiv2026

Lithium-Projected Phonon Spectral Distributions as Robust Descriptors of Ionic Conductivity in Solid Electrolytes

Lattice dynamics are widely invoked in the design of solid electrolytes, yet phonon information is commonly compressed into a band center or another scalar softness measure. Here we test whether the complete lithium-projected phonon density of states (Li-PDOS) provides a reproducible descriptor of experimental room-temperature ionic conductivity. MatterSim forces and Phonopy were used to generate harmonic total and Li-projected spectra for crystallographically resolved entries in the OBELiX dataset. A composition and structure audit defined a primary cohort of 260 materials (212 train and 48 test), a strict cohort of 241, and an exact-composition cohort of 168. Across 20 independently generated phonon-calculation database comparisons, the mean Wasserstein-1 distance was 0.542 THz for total DOS and 0.731 THz for Li-PDOS, revealing broad agreement but systematic, projection-dependent softening. Higher conductivity was associated with redistribution of normalized Li spectral weight toward low frequencies: in the untouched test set, the Li fractions below 2 and 5 THz had Spearman coefficients of 0.333 and 0.374, while the 5$\%$ cumulative-frequency quantile had a coefficient of $-0.393$. A Wasserstein kernel on the full Li-PDOS achieved held-out $R^2=0.444$, compared with 0.012 for total DOS and 0.181 for a static composition--structure kernel. The Li model remained stable in the strict ($R^2=0.462$) and exact ($R^2=0.451$) cohorts. Family adjustment attenuated scalar associations, and Li-versus-total whole-spectrum dependence was cohort sensitive. The results therefore support mobile-ion-resolved spectral distributions as useful comparative screening descriptors, not as a universal causal softness law.

cond-mat.mtrl-sci↗

arXiv2026

Loophole-Robust Certification of Quantum Advantage

Claims of quantum advantage should remain robust even when classical strategies have access to side information correlated with the benchmark under evaluation, just as Bell certification must account for measurement dependence. We formalize such correlations as benchmark dependence, a task-level generalization of measurement dependence. For every bounded-reward task, we show that the optimal benchmark-dependent classical score obeys $S_\eta\leq\min\{1,S_{\mathrm{cl}}+\eta\}$, and construct a family of tasks that saturates this bound, showing that the linear dependence on $\eta$ is tight without further assumptions. For repeated product tasks with roundwise dependence, we obtain the stronger multiplicative bound $S_\eta^{(n)}\leq(\omega_{\mathrm c}+\eta)^n$, and extend the framework to finite-sample data, mutual-information constraints, multipartite tasks, and correlations distributed along a causal path. Applying these results to aggregated IBM hardware data, we obtain positive raw-count cycle-product certificates of 0.0812 for CHSH and 0.2178 for Mermin--GHZ, while the nine-context magic-square construction remains uncertified; readout-mitigated values are reported separately as sensitivity estimates. We also analyze a non-Bell quantum-kernel benchmark, where a label-construction variable has measured conditional dependence $\widehat{\eta}_{\lambda}^{(Y)}=0.5$, above the threshold $\eta_{\mathrm{req}}=0.375$, required to close the reported score gap, and yields perfect classical classification. The framework therefore converts a quantum--classical score separation into a quantitative lower bound on the benchmark-correlated classical information required to explain the score separation.

quant-ph↗

arXiv2026

Sector-memory obstruction to probe-level bath emergence in finite programmable qubit environments

Finite quantum environments can relax local probes without acting as canonical baths. We study this distinction for a probe qubit coupled to a programmable bath of ($N$) qubits under excitation-number-conserving dynamics. The conserved charge partitions the Hilbert space into sectors. We characterize probe-level bath emergence using the sector-resolved late-time population ($p_e^{(q)}$), the sector-memory variance ($M_N$), and a global Gibbs-fit error ($\Delta_G^{\mathrm{global}}$). Exact simulations with Haar-random pure states in each complete fixed-charge sector yield sector-dependent populations close to the maximally mixed-sector benchmark ($p_e^{(q)}=q/(N+1)$), producing a nonzero Gibbs obstruction. We then construct charge-preserving Floquet circuits using ($R_z$) phases and ($XX+YY$) exchange gates, validate them with ideal and noisy Qiskit simulations, and implement finite-depth experiments on IBM Fez. For ($N=4$) and ($\epsilon=0$), the hardware data give ($M_N \simeq 0.044$), ($\Delta_G^{\mathrm{global}} \simeq 0.558$), and charge preservation near 0.90 after readout mitigation. A paired symmetry-breaking scan using bath ($R_x(\epsilon)$) rotations reduces both diagnostics while increasing charge leakage, but does not erase sector ordering over the accessible depths. These results show that equilibration within constrained sectors is insufficient to produce a single sector-independent Gibbs state for the probe.

quant-ph↗

arXiv2026

A Preparation Nonstationarity Loophole in Superconducting-Qubit Bell Tests

Bell or Clauser-Horne-Shimony-Holt (CHSH) tests on superconducting quantum processors are commonly interpreted under the assumption that repeated circuit executions sample a single, stationary preparation ensemble. Here we show that this assumption can be violated on contemporary hardware, with direct implications for the interpretation of observed Bell violations. We introduce an ensemble-divergence framework in which slow temporal drift of the preparation process induces context-dependent effective ensembles, even when measurement independence and locality are preserved. This leads to a relaxed Bell bound $|S| \le 2 + 6\delta_{\mathrm{ens}}$, where $\delta_{\mathrm{ens}}$ quantifies preparation nonstationarity. Because $\delta_{\mathrm{ens}}$ is not directly observable, we develop an operational witness $\delta_{\mathrm{op}}$ based on bin-resolved outcome statistics for fixed measurement channels. Using Pauli-axis measurements on IBM superconducting processors, we observe statistically significant operational drift that persists after full two-qubit readout mitigation, ruling out measurement artifacts. In contrast, drift extracted from CHSH-optimal measurements is eliminated by mitigation, demonstrating that such settings are unsuitable for diagnosing preparation nonstationarity. We further show that the observed Bell violations imply only modest ensemble divergences, comparable in scale to those required in Hall-type measurement-dependence models, but arising here solely from preparation drift combined with experimental scheduling. Our results identify a preparation-dependent loophole relevant to Bell tests on noisy intermediate-scale quantum devices and highlight the necessity of drift-aware protocols for reliable quantum certification.

quant-ph↗

arXiv2017

A wireless triboelectric nanogenerator

We demonstrate a new paradigm for the wireless harvesting of mechanical energy via a 3D-printed triboelectric nanogenerator (TENG) which comprises a graphene polylactic acid (gPLA) nanocomposite and Teflon. The synergistic combination of eco-friendly PLA with graphene in our TENG exhibited an output voltage > 2 kV with an instantaneous peak power of 70 mW, which in turn generated a strong electric field to enable the wireless transmission of harvested energy over a distance of 3 m. Specifically, we demonstrate wireless and secure actuatation of smart-home applications such as smart tint windows, temperature sensors, liquid crystal displays, and security alarms either with a single or a specific user-defined passcode of mechanical pulses (e.g., Fibonacci sequence). Notably, such high electric output of a gPLA-based TENG enabled unprecedented wireless transmission of harvested mechanical energy into a capacitor, thus obviating the need for additional electronics or energy sources. The scalable additive manufacturing approach for gPLA-based TENGs, along with their high electrical output can revolutionize the present method of harnessing the mechanical energy available in our environment.

physics.app-ph↗

arXiv2016

Defect-engineered graphene for bulk supercapacitors with high energy and power densities

The development of high-energy and high-power density supercapacitors (SCs) is critical for enabling next-generation energy storage applications. Nanocarbons are excellent SC electrode materials due to their economic viability, high-surface area, and high stability. Although nanocarbons have high theoretical surface area and hence high double layer capacitance, the net amount of energy stored in nanocarbon-SCs is much below theoretical limits due to two inherent bottlenecks: i) their low quantum capacitance and ii) limited ion-accessible surface area. Here, we demonstrate that defects in graphene could be effectively used to mitigate these bottlenecks by drastically increasing the quantum capacitance and opening new channels to facilitate ion diffusion in otherwise closed interlayer spaces. Our results support the emergence of a new energy paradigm in SCs with 250% enhancement in double layer capacitance beyond the theoretical limit. Furthermore, we demonstrate prototype defect engineered bulk SC devices with energy densities 500% higher than state-of-the-art commercial SCs without compromising the power density.

cond-mat.mtrl-sci↗

arXiv2014

Correlations between Chondroitin Sulfate Physicochemical Properties and its in-vitro Absorption and Anti-inflammatory Activity

Here, we investigated the influence of physicochemical characteristics of chondroitin sulfate (CS) on its in vitro absorption and anti-inflammatory activity. We used eight different synthetic and natural CS samples with a range of molecular weights (7-35 kDa) and sulfation patterns. Our studies indicate that the absorption of CS is moderately correlated to percentage of chondroitin-6-sulfate while the anti-inflammatory activity may be weakly related to the molecular weight and the amount of total sulfation in the samples. Our in vitro studies could provide helpful screening tools for quick and effective evaluation of CS samples as a preliminary step towards in vivo studies.

q-bio.TO↗

arXiv2012

Effects of surface functional groups on the formation of nanoparticle-protein corona

Herein, we examined the dependence of protein adsorption on the nanoparticle surface in the presence of functional groups. Our UV-visible spectrophotometry, transmission electron microscopy, infrared spectroscopy and dynamic light scattering measurements evidently suggested that the functional groups play an important role in the formation of nanoparticle-protein corona. We found that uncoated and surfactant-free silver nanoparticles derived from a laser ablation process promoted a maximum protein (bovine serum albumin) coating due to increased changes in entropy. On the other hand, BSA displayed a lower affinity for electrostatically stabilized nanoparticles due to the constrained entropy changes.

cond-mat.soft↗

arXiv2011

Effects of Layer Stacking on the Combination Raman modes in Graphene

We have observed new combination modes in the range from 1650 - 2300 cm-1 in single-(SLG), bi-, few-layer and incommensurate bilayer graphene (IBLG) on silicon dioxide substrates. The M band at ~1750 cm-1 is suppressed for both SLG and IBLG. A peak at ~1860 cm-1 (iTALO-) is observed due to a combination of the iTA and LO phonons. The intensity of this peak decreases with increasing number of layers and this peak is absent in bulk graphite. Two previously unidentified modes at ~1880 cm-1 (iTALO+) and ~2220 cm-1 (iTOTA) in SLG are tentatively assigned as combination modes around the K point of the graphene Brillouin zone. The peak frequencies of the iTALO+ (iTOTA) modes are observed to increase (decrease) linearly with increasing graphene layers.

cond-mat.mes-hall↗

arXiv2010

Double resonance Raman study of disorder in CVD-grown single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) with varying degrees of disorder were investigated using multiple-excitation Raman spectroscopy. The lattice disorder was imparted into the nanotubes by the addition of varying amounts of sulfur to the iron catalyst in a thermal chemical vapor deposition process. Changes in the intensities of peaks occurring due to a double resonance Raman process were studied. The intensity of the disorder-induced D band increased with a decrease in the sulfur content. Upon post-synthesis heat treatment, the double resonance process got quenched due to defect healing. The second order G' band and iTOLA bands exhibited a two-peak structure, of which one of the peaks is relatively more sensitive to defects and decreased in intensity with heat treatment.

cond-mat.mes-hall↗