arXiv subjects

Jared H. Cole

Publications and source records attributed to Jared H. Cole.

At least 19 recordsLinked to original sources

arXiv2026

Antidot superlattices in two-dimensional topological insulators

We investigate the electronic properties of a two-dimensional topological insulator patterned with an array of circular holes. The band structures of the topological insulator superlattices are calculated using the Bernevig-Hughes-Zhang model, discretized with the finite element method. The band topology is studied using the Fukui-Hatsugai-Suzuki method, exploiting the fact that topological charge is conserved when a band gap closes and reopens. We find that when the holes are close to each other and the edge states overlap significantly, the material loses its topological character and becomes a trivial insulator. The results show that patterning topological insulators changes their properties, and this can be achieved with a feature size compatible with current lithographic techniques. This shows the potential to incorporate patterned topological insulators in future electronics.

cond-mat.mes-hall↗

arXiv2026

Automating detection of Two-Level Systems in Superconducting Qubits

Microscopic two-level system (TLS) defects remain a primary mechanism of decoherence and operational instability in superconducting transmon qubits, necessitating scalable and automated methods for their characterization. Here, we present and benchmark two complementary analysis pipelines for extracting TLS statistics directly from time-resolved SWAP spectroscopy: one-dimensional decay-rate fitting (1D-DRF), which detects defects via localized enhancements in the qubit relaxation rate, and a deterministic, non-parametric computer-vision framework (2D-CV) that achieves two-dimensional spectral localization by exploiting the temporal persistence of coherent population suppression. We deploy both methods on SWAP spectroscopy measurements from 52 flux-tunable transmon qubits on Rigetti processors with and without moderate ($\sim 10\%$) post-fabrication frequency trimming via Alternating-Bias Assisted Annealing (ABAA). We show that both pipelines converge on a consistent global characterization of the defect landscape while exhibiting complementary sensitivity across distinct coupling regimes. Crucially, both methods independently reveal a count--loss decoupling under moderate annealing: while the total detectable TLS defect density remains statistically unchanged, the span-integrated dielectric loss is reduced by approximately a factor of two, demonstrating selective suppression of the most strongly dissipative defect channels. These results establish an automated, non-parametric analysis framework for high-throughput hardware diagnostics and provide a statistical baseline for post-fabrication defect engineering in large-scale superconducting quantum processors.

quant-ph↗

arXiv2026

Optimal operating temperature for industry-compatible silicon spin quantum computing: colder is not necessarily better

Silicon spin qubits are a leading candidate for large-scale quantum computing owing to their compatibility with semiconductor manufacturing. However, scaling to useful fault-tolerant processors will likely generate thermal loads that exceed the cooling power available at millikelvin temperatures. Raising the operating temperature eases cooling requirements but reduces gate fidelity, increasing the overhead of quantum error correction. Identifying the operating temperature that minimizes total power consumption is therefore a key challenge for commercially viable quantum computers. Here, we use gate set tomography to benchmark two-qubit silicon chips fabricated in both industrial and academic environments over a range of temperatures. Elevated temperatures substantially shorten coherence times and increase gate and state-preparation-and-measurement infidelities. Based on these measurements, we develop a general power model for silicon quantum computers that combines cryogenic cooling requirements with error-correction overheads. We show that a finite optimal operating temperature exists and is strongly influenced by a crossover temperature near 1 K in current devices, above which gate fidelity degrades rapidly. These results connect device-level fidelity limitations to system-level power requirements, providing design guidelines for large-scale silicon quantum computers.

quant-ph↗

arXiv2026

Quantum simulations of ultrafast optical spectroscopy of semiconductors on digital quantum computers in the semi-classical approximation

We present a digital quantum simulation framework for ultrafast optical spectroscopy of semiconductor materials. The framework is based on Brillouin-zone discretization and the second-quantization formalism, and is designed as a quantum alternative to classical simulations based on the semiconductor Bloch equations. Its current capabilities include quantum simulations of linear absorption and optical gain spectra, incorporating Lorentzian broadening, finite-temperature band-filling effects, and reduced-dimensionality effects. Benchmark comparisons with classical simulations for GaAs demonstrate quantitative agreement in the noiseless limit. The inclusion of realistic hardware noise of NISQ-era quantum computers effectively manifests itself as an additional source of scattering processes, resulting in increased spectral broadening. While no exponential quantum advantage is expected in the single-particle approximation, the framework naturally extends to many-body regimes where classical simulations face the hierarchy problem and exponential scaling and provable quantum advantage will be possible. The quantum simulations considered in this work capture central elements of semiconductor spectroscopy, the aspects such as open quantum systems, light-matter interactions, statistical mechanics, non-equilibrium quantum dynamics, and many-body physics. As such, it provides a physically motivated and scalable model for benchmarking quantum computers in applications to complex, real-world problems.

quant-ph↗

arXiv2026

Hybrid Six-Level Rydberg Atomic Quantum Receiver for Multi-Band Wireless Communications

Rydberg atomic quantum receivers (RAQRs) have recently emerged as a promising technology for radio-frequency (RF) reception by directly transducing incident RF fields into optical signals. Existing receiver architectures, however, exploit only subsets of the dipole-allowed transitions within a given atomic manifold, limiting the number of simultaneously accessible RF channels. In this paper, a hybrid six-level Rydberg atomic quantum receiver (H-RAQR) is proposed by integrating parallel and cascaded RF coupling pathways within a single vapor-cell receiver. A communication-oriented analytical framework is developed by deriving a closed-form steady-state atom--field interaction model and establishing an equivalent baseband signal representation. The achievable ergodic sum rate is analyzed, and a resource-efficiency metric is introduced to quantify throughput per unit optical receiver resource. The analytical model is validated against full Lindblad master-equation simulations over its identified operating region. Numerical results show that the proposed H-RAQR supports four simultaneous RF channels within a single atomic system, achieves higher ergodic sum rate than conventional parallel Rydberg state (PRS) and cascade Rydberg state (CRS) receivers, and provides about 29% higher resource efficiency than a combined PRS-CRS deployment with equivalent four-band coverage. The proposed framework provides a scalable foundation for multi-band atomic wireless receivers.

quant-ph↗

arXiv2026

Gate Stack Engineering for High-Mobility and Low-Noise SiMOS Quantum Devices

We systematically investigate the interplay between materials engineering, quantum transport, and low-frequency charge noise in silicon metal--oxide--semiconductor (SiMOS) quantum devices. By combining Hall-bar transport measurements with charge-noise spectroscopy of gate-defined quantum dots, we identify correlations between gate-stack design, carrier mobility, and electrostatic noise, providing an experimental case study of material and process dependencies relevant to low-noise, high-mobility operation. Hall-bar studies reveal that increasing the atomic-layer-deposition temperature of Al$_2$O$_3$ markedly enhances mobility, whereas the choice of oxidant has little impact. Devices incorporating HfO$_2$ exhibit improved carrier mobility, an interesting observation that can plausibly be attributed to defect passivation associated with aluminum diffusion from the gate metal into the HfO$_2$ layer. Charge-noise measurements show a strong correlation between higher mobility and reduced noise, with TiPd-gated devices displaying both degraded transport and elevated charge noise. In contrast, the poly-Si-gated CMOS-foundry device achieves the lowest noise levels. Finally, dual-feedback dot--sensor stability mapping demonstrates enhanced charge stability in devices with the gate stacks studied here, underscoring their promise for scalable, high-fidelity silicon spin-qubit platforms.

cond-mat.mes-hall↗

arXiv2025

Direct measurement of coherent nodal and antinodal dynamics in underdoped Bi-2212

The physics of strongly correlated materials is deeply rooted in electron interactions and their coupling to low-energy excitations. Unraveling the competing and cooperative nature of these interactions is crucial for connecting microscopic mechanisms to the emergence of exotic macroscopic behavior, such as high-temperature superconductivity. Here we show that polarization-resolved multidimensional coherent spectroscopy (MDCS) is able to selectively drive and measure coherent Raman excitations in different parts of the Fermi surface, where the superconducting gap vanishes or is the largest (respectively called Nodal and Antinodal region) in underdoped Bi-2212. Our evidence reveal that in the superconducting phase, the energy of Raman excitations in the nodal region is anti-correlated with the energy of electronic excitations at $\sim$1.6~eV, and both maintain coherence for over 44~fs. In contrast, excitations in the antinodal region show significantly faster decoherence ($<$18~fs) and no measurable correlations. Importantly, this long-lived coherence is specific to the superconducting phase and vanishes in the pseudogap and normal phases. This anti-correlation reveals a coherent link between the transition energy associated with the many body Cu-O bands and the energy of electronic Raman modes that map to the near-nodal superconducting gap. The different coherent dynamics of the nodal and antinodal excitations in the superconducting phase suggest that nodal fluctuations are protected from dissipation associated with scattering from antiferromagnetic fluctuations and may be relevant to sustaining the quantum coherent behaviour associated with high temperature superconductivity.

cond-mat.supr-con↗

arXiv2025

A Depinning Model for Josephson Junction Tuning

Building more powerful quantum computers requires manufacturing processes with tight tolerances. To improve the tolerances on Josephson junctions, techniques to fine tune their properties after fabrication have been developed. Understanding how tuning techniques may physically modify the tunnel barrier of a Josephson junction is important and will enable these techniques to be optimised. We develop a model of junction tuning based on depinning theory to interpret a phase diagram of tuning rate. We extract the dependence on temperature, time-varying voltages and oscillation frequency. Using depinning theory we are able to show both why time-varying annealing potentials result in controlled junction tuning and how such protocols can be optimised. We examine how tuning changes the electrical breakdown of barriers and discrepancies between modeled and measured higher energy levels of transmon qubits.

quant-ph↗

arXiv2024

The $N_2V$ color center: a ubiquitous visible and near-infrared-II quantum emitter in nitrogen-doped diamond

Photoluminescent defects in diamond, like the nitrogen-vacancy (NV) color center, are at the forefront of emerging optical quantum technologies. Most emit in the visible and near-infrared spectral region below 1000 nm (NIR-I), limiting their applications in photonics, fiber communications, and biology. Here, we show that the nitrogen-vacancy-nitrogen ($N_2V$) center, which emits in the visible and near-infrared-II (NIR-II, 1000-1700 nm), is ubiquitous in as-synthesized and processed nitrogen-doped diamond from bulk samples to nanoparticles. We demonstrate that $N_2V$ is also present in commercially available state-of-the-art NV diamond sensing chips made via chemical vapor deposition (CVD). In high-pressure high-temperature (HPHT) diamonds, the photoluminescence (PL) intensity of both $N_2V$ charge states, $N_2V^0$ in the visible and $N_2V^-$ in the NIR-II, increases with increasing substitutional nitrogen concentration. We determine the PL lifetime of $N_2V^-$ to be 0.3 ns and compare a quantum optical and density functional theory model of the $N_2V^-$ with experimental PL spectra. Finally, we show that detonation nanodiamonds (DND) show stable PL in the NIR-II, which we attribute to the $N_2V$ color center, and use this NIR-II PL to image DNDs inside skin cells. Our results will contribute to the scientific and technological exploration and development of the $N_2V$ color center and inspire more research into its effect on other color centers in diamond.

cond-mat.mes-hall↗

arXiv2024

Quantum emitter in a plasmonic field: an orientation generalised model

When a quantum emitter (QE) is placed in close proximity to a plasmonic metal nanoparticle (MNP) within an external optical field, a dipole-dipole coupling arises, resulting in a highly tunable hybrid nanosystem that surpasses the optical manipulation capabilities of the individual components. These hybrid systems enable the exploration and manipulation of optical fields at the intersection between classical and quantum phenomena. Theoretical models of this interaction have typically been limited to the extreme orientations, where the QE and plasmonic dipoles are polarised either along or perpendicular to the inter-particle axis, for analytical tractability. In this work, we generalise the semi-classical optical dipole-dipole interaction model for a two-level quantum emitter in a plasmonic field for arbitrary polarisation angles. We show that the total field experienced by the quantum emitter at intermediate angles does not necessarily align with the external input field and discuss the implications of varying the polarisation angle of the external input field.

cond-mat.mes-hall↗

arXiv2024

Transverse magnetic focusing in two-dimensional hole gases

Two-dimensional hole gases (2DHGs) have strong intrinsic spin-orbit coupling and could be used to build spin filters by utilising transverse magnetic focusing (TMF). However, with an increase in the spin degree of freedom, holes demonstrate significantly different behaviour to electrons in TMF experiments, making it difficult to interpret the results of these experiments. In this paper, we numerically model TMF in a 2DHG within a GaAs/Al$_{\mathrm{x}}$Ga$_{\mathrm{1-x}}$As heterostructure. Our band structure calculations show that the heavy $(\langle J_{z} \rangle = \pm\frac{3}{2})$ and light $(\langle J_{z} \rangle = \pm\frac{1}{2})$ hole states in the valence band mix at finite $k$, and the heavy hole subbands which are spin-split due to the Rashba effect are not spin-polarised. This lack of spin polarisation casts doubt on the viability of spin filtering using TMF in 2DHGs within conventional GaAs/Al$_{\mathrm{x}}$Ga$_{\mathrm{1-x}}$As heterostructures. We then calculate transport properties of the 2DHG with spin projection and offer a new perspective on interpreting and designing TMF experiments in 2DHGs.

cond-mat.mes-hall↗

arXiv2024

Modal decomposition of localized plasmon on gold nanoparticles

Localized surface plasmons (LSPs) are collective oscillations of free electrons in metal nanoparticles that confine electromagnetic waves into subwavelength regions, making them an ideal platform for light-matter coupling. To design and understand plasmonic structures, numerical computations of Maxwell's equations are commonly used. However, obtaining physical insight from these numerical solutions can be challenging, especially for complex-shaped nanoparticles. To circumvent this, we introduce mode decomposition strategies within the boundary element method (BEM). By employing singular value decomposition (SVD) and quasi-normal mode (QNM) decomposition, we break down optical responses into elementary modes. QNMs offer deeper insights into frequency and damping, while SVD modes allow for more accurate spectral reconstruction with fast computation. These techniques provide a deeper understanding of LSPs and facilitates the design of metal nanoparticles for efficient light-matter interaction.

physics.optics↗

arXiv2024

Electronic Structure at the Perovskite Rubrene Interface: The Effect of Surface Termination

Perovskite films have rapidly emerged as leading active materials in optoelectronic devices due to their strong optical absorption, high carrier mobility and ease of fabrication. Whilst proving to be promising materials for solar cells and light-emitting diodes, another application of perovskites which makes effective use of their unique properties is sensitisation for photon upconversion. Consisting of a bulk perovskite sensitiser alongside an adjacent organic semiconductor film, the upconverting system can absorb multiple low-energy photons to emit high-energy photons. In this work, density functional theory, in conjunction with GW theory, is utilised to investigate the electronic structure at the MAPbI$_3$/rubrene interface for different surface terminations of MAPbI$_3$. From this investigation, we reveal that the surface termination of the perovskite layer greatly affects the charge density at the interface and within the rubrene layer driven by the formation of interfacial dipole layers. The formation of a strong interfacial dipole for the lead-iodide terminated perovskite alters the band alignment of the heterojunction and is expected to facilitate more efficient hole transfer. For the perovskite surface terminated with the methylammonium iodide layer, the highest occupied molecular orbital of the adjacent rubrene layer lies deep within the perovskite band gap. This termination type is further characterized by a lower density of states near the band edges thereby acting as a spacer which is anticipated to decrease the probability of charge transfer across the interface. Thus based on our results, PbI$_2$-terminated perovskite surfaces are predicted to be favourable for applications where hole transfer to a rubrene layer is ideal, highlighting the significance of surface termination for all systems where the electronic environment at the interface is crucial to performance.

cond-mat.mtrl-sci↗

arXiv2024

Correlated frequency noise in a multimode acoustic resonator

Frequency instabilities are a major source of errors in quantum devices. This study investigates frequency fluctuations in a surface acoustic wave (SAW) resonator, where reflection coefficients of 14 SAW modes are measured simultaneously for more than seven hours. We report two distinct noise characteristics. Multimode frequency noise caused by interactions with two-level system (TLS) defects shows significant degrees of correlations that diminish with increased detuning. This finding agrees with the current understanding of the parasitic TLS behavior as one of the dominant noise sources in quantum devices. In addition to the TLS-induced noise, we observe strong anomalous frequency fluctuations with slow, anti-correlated dynamics. These noise bursts resemble signatures of cosmic radiation observed in superconducting quantum systems.

quant-ph↗

arXiv2023

Plasmonically engineered nitrogen-vacancy spin readout

Ultra-precise readout of single nitrogen-vacancy (NV) spins hold promise for major advancements in quantum sensing and computing technologies. We predict significant brightness and contrast enhancements in NV spin qubit readout and optically detected magnetic resonance (ODMR) arising from plasmonic interaction. We present a rigorous theory verified using existing measurements in the literature for such predictions. Plasmonic spin readout enhancements selectively manifest in carefully engineered parameter regions, necessitating rigorous modelling prior to experimentation.

quant-ph↗

arXiv2023

Non-Drude THz conductivity of graphene due to structural distortions

The remarkable electrical, optical and mechanical properties of graphene make it a desirable material for electronics, optoelectronics and quantum applications. A fundamental understanding of the electrical conductivity of graphene across a wide frequency range is required for the development of such technologies. In this study, we use terahertz (THz) time-domain spectroscopy to measure the complex dynamic conductivity of electrostatically gated graphene, in a broad $\sim$0.1 - 7 THz frequency range. The conductivity of doped graphene follows the conventional Drude model, and is predominantly governed by intraband processes. In contrast, undoped charge-neutral graphene exhibits a THz conductivity that significantly deviates from Drude-type models. Via quantum kinetic equations and density matrix theory, we show that this discrepancy can be explained by additional interband processes, that can be exacerbated by electron backscattering. We propose a mechanism where such backscattering -- which involves flipping of the electron pseudo-spin -- is mediated by the substantial vector scattering potentials that are associated with structural deformations of graphene. Our findings highlight the significant impact that structural distortions and resulting electrostatic vector scattering potentials can have on the THz conductivity of charge-neutral graphene. Our results emphasise the importance of the planar morphology of graphene for its broadband THz electronic response.

cond-mat.mtrl-sci↗

arXiv2023

A Tutorial on Quantum Master Equations: Tips and tricks for quantum optics, quantum computing and beyond

Quantum master equations are an invaluable tool to model the dynamics of a plethora of microscopic systems, ranging from quantum optics and quantum information processing, to energy and charge transport, electronic and nuclear spin resonance, photochemistry, and more. This tutorial offers a concise and pedagogical introduction to quantum master equations, accessible to a broad, cross-disciplinary audience. The reader is guided through the basics of quantum dynamics with hands-on examples that build up in complexity. The tutorial covers essential methods like the Lindblad master equation, Redfield relaxation, and Floquet theory, as well as techniques like Suzuki-Trotter expansion and numerical approaches for sparse solvers. These methods are illustrated with code snippets implemented in python and other languages, which can be used as a starting point for generalisation and more sophisticated implementations.

quant-ph↗

arXiv2022

Exciton-polaron interactions in monolayer WS$_2$

Interactions between quasiparticles are of fundamental importance and ultimately determine the macroscopic properties of quantum matter. A famous example is the phenomenon of superconductivity, which arises from attractive electron-electron interactions that are mediated by phonons or even other more exotic fluctuations in the material. Here we introduce mobile exciton impurities into a two-dimensional electron gas and investigate the interactions between the resulting Fermi polaron quasiparticles. We employ multi-dimensional coherent spectroscopy on monolayer WS$_2$, which provides an ideal platform for determining the nature of polaron-polaron interactions due to the underlying trion fine structure and the valley specific optical selection rules. At low electron doping densities, we find that the dominant interactions are between polaron states that are dressed by the same Fermi sea. In the absence of bound polaron pairs (bipolarons), we show using a minimal microscopic model that these interactions originate from a phase-space filling effect, where excitons compete for the same electrons. We furthermore reveal the existence of a bipolaron bound state with remarkably large binding energy, involving excitons in different valleys cooperatively bound to the same electron. Our work lays the foundation for probing and understanding strong electron correlation effects in two-dimensional layered structures such as moiré superlattices.

cond-mat.mes-hall↗