arXiv subjects

Boris Kiefer

Publications and source records attributed to Boris Kiefer.

14 recordsLinked to original sources

arXiv2026

Wyckoff-Resolved Oxidation-State Atlas and Anion-Conditioned Priors for Materials Discovery

We introduce a Wyckoff-resolved oxidation-state atlas and assignment utility for probabilityranked, charge-neutral assignment from compositions or Wyckoff grammars. The atlas is constructed from a May 2026 snapshot of 154,879 Materials Project-derived structures by staged exact-neutral enumeration over common and known nonzero oxidation states. The learned prior assigns 106,053 materials in composition mode and 114,403 in Wyckoff mode, compared with a broad MP all-integer possible species count of 108,642. A matched MP baseline requiring at least one charge-neutral assignment with exactly one nonzero integer oxidation state per element contains 89,374 materials; relative to this baseline, composition and Wyckoff modes increase coverage by 18.7% and 28.0%. Of the 14,665 materials recovered only in Wyckoff mode, 99.98% exhibit distinct formal oxidation states for the same element on different site tokens. The CSV/Python workflow provides a reproducible prior for structure decoration, generative crystal models, and symbolic Wyckoff-grammar workflows.

cond-mat.mtrl-sci↗

arXiv2026

Photon-Conditioned Squeezed States for Directional Displacement Response in Continuous-Variable Photonics

Squeezed Fock states, photon-subtracted squeezed states, and optical cat states are established non-Gaussian resources in continuous-variable quantum optics. Here we compare these known state families from a task-oriented perspective: matched mean photon number, scalar Wigner negativity, and directional displacement-fidelity response. Starting from squeezed vacuum, single-photon subtraction prepares a state proportional to $S(r,\theta)\ket{1}$, while two-photon subtraction prepares an even-parity squeezed Fock superposition rather than a pure $S(r,\theta)\ket{2}$. We benchmark photon-conditioned squeezed states against Fock and coherent-cat references using the integrated Wigner negativity $\delta$, the energy-normalized metric $\delta/\langle n\rangle$, and fidelity-threshold displacement radii $R_F(\phi)$. Cat benchmarks remain strong scalar Wigner-negativity resources, whereas photon-conditioned squeezed states provide an origin-centered alternative with tunable anisotropic displacement response. In particular, the two-photon-subtracted squeezed state shows favorable displacement-fidelity radii over selected quadrature directions at matched $\langle n\rangle$. These results identify a regime relevant to homodyne-aligned continuous-variable control and anisotropic displacement-noise mitigation, with directional sensing as a natural dual application.

quant-ph↗

arXiv2026

Beyond the HOM Dip: A Multi-Metric Module for Teaching Two-Mode Quantum Optical Interference

The Hong--Ou--Mandel (HOM) effect is often introduced through a single benchmark: coincidence suppression for $\ket{1}\otimes\ket{1}$ at a balanced beam splitter. We present a classroom-oriented instructional module that broadens this treatment by comparing three output metrics -- on/off coincidence probability $P_c$, cross-correlation $g^{(2)}_{12}$, and noise-reduction factor NRF -- across four input families: Fock, superposition, coherent, and squeezed light. The module targets three instructional challenges in upper-division quantum optics: treating interference quality as a single observable, weakly connecting quantum--classical distinctions to output statistics, and limiting transfer from two-mode HOM reasoning to broader photonic benchmarking questions. A common beam-splitter sweep shows that different metrics probe different statistical properties of the same output state and can therefore support different source choices depending on the physical objective. The module combines a Jupyter/QuTiP simulator, guided activities, specification-style summary tables, and a grading rubric for use in a single upper-division or early graduate class meeting.

physics.ed-ph↗

arXiv2026

A Research-Informed Module on Quantum Superposition for Rapid Classroom Adoption

We present an adoption-ready instructional module for introducing quantum superposition in a two-state system. The package combines a five-activity classroom sequence with grading-ready assessment materials organized around six conceptual barriers documented in the physics education research literature: interpreting superposition as physical splitting, confusing coherent superposition with classical mixture, making basis-change errors, misreading finite-sample fluctuations as changes in the underlying state, using inconsistent notation, and, in an optional extension, reasoning about ordered operations. The main claim is that the bottleneck for introductory quantum instruction is rarely the absence of a usable simulator, but rather the absence of a coherent activity sequence, barrier-targeted prompts, and aligned assessment tools that an instructor can deploy without additional development work. We make the instructional rationale explicit through backward mapping from documented barriers to activity prompts and rubric-based evidence. The resulting module is designed for a single 50-minute class meeting and can be implemented with the included notebook or adapted to comparable two-state quantum simulators.

physics.ed-ph↗

arXiv2025

Band Alignment Tuning from Charge Transfer in Epitaxial SrIrO$_3$/SrCoO$_3$ Superlattices

Understanding charge transfer at oxide interfaces is crucial for designing materials with emergent electronic and magnetic properties, especially in systems where strong electron correlations and spin-orbit coupling coexist. SrIrO$_3$/SrCoO$_3$ (SIO/SCO) superlattices offer a unique platform to explore these effects due to their contrasting electronic structures and magnetic behaviors. Building on past theory based on continuity of O 2p band alignment, we employ density functional theory (DFT) to model electron transfer from Ir to Co across the SIO/SCO interface. To characterize these effects, we synthesized epitaxial SIO/SCO superlattices via molecular beam epitaxy. Structural and transport measurements confirmed high crystallinity, metallic behavior, and suppression of Kondo scattering that has been reported in uniform SIO films. Further characterization via X-ray absorption spectroscopy (XAS) revealed orbital anisotropy and valence changes consistent with interfacial charge transfer. Co K- and L$_{2,3}$-edge and Ir L$_2$-edge spectra verified electron donation from Ir to Co, stabilizing the perovskite SCO phase and tuning the electronic structure of SIO via hole-doping. O K-edge XAS showed band alignment shifts in the SIO layer consistent with DFT predictions. Our work here provides a pathway for engineering oxide heterostructures with tailored magnetic and electronic properties.

cond-mat.mtrl-sci↗

arXiv2025

Monopole Traps for Position-Based Information Coding

We propose a spin-ice-based heterostructure capable of encoding magnetic monopole quasiparticle positions for non-volatile information storage applications. Building upon two-dimensional magnetic monopole gases formed at the interface between 2-in-2-out spin ice and all-in-all-out antiferromagnetic pyrochlore iridate, the design introduces a 3-in-1-out/1-in-3-out fragmented barrier layer into the spin-ice matrix, defining two energetically stable monopole traps. The occupancy of these traps can be deterministically controlled by an externally applied magnetic field. Monte Carlo simulations reveal robust bistable switching, thermal stability below 0.22 K, and fully reversible field-driven transitions, demonstrating the system's potential for reliable, repeatable memory operation. Crucially, the heterostructure exhibits emergent ferromagnetism linked to monopole position, enabling non-destructive readout of the memory state via spatially resolved magnetic imaging. Unlike topological carriers such as skyrmions, monopoles confined at the sub-nanometer scale offer three orders of magnitude higher information density. These results establish these monopole-trap heterostructures as a scalable platform for next-generation ultra-compact memory technologies.

cond-mat.str-el↗

arXiv2024

Strain Effects in SrHfO$_{3}$ Films Grown by Hybrid Molecular Beam Epitaxy

Perovskite oxides hetero-structures are host to a large number of interesting phenomena such as ferroelectricity and 2D-superconductivity. Ferroelectric perovskite oxides have been of significant interest due to their possible use in MOSFETs and FRAM. SrHfO$_3$ (SHO) is a perovskite oxide with pseudo-cubic lattice parameter of 4.1 $\mathring{A}$ that previous DFT calculations suggest can be stabilized in a ferroelectric P4mm phase, similar to STO, when stabilized with sufficient compressive strain. Additionally, it is insulating, possesses a large band gap, and a high dielectric constant, making it an ideal candidate for oxide electronic devices. In this work, SHO films were grown by hybrid molecular beam epitaxy with a tetrakis(ethylmethylamino)hafnium(IV) source on GdScO$_3$ and TbScO$_3$ substrates. Equilibrium and strained SHO phases were characterized using X-ray diffraction, X-ray absorption spectroscopy, and scanning transmission electron microscopy to determine the perovskite phase of the strained films, with the results compared to density functional theory models of phase stability versus strain. Contrary to past reports, we find that compressively-strained SrHfO$_3$ undergoes octahedral tilt distortions and most likely takes on the I4/mcm phase with the a$^0$a$^0$c$^-$ tilt pattern.

cond-mat.mtrl-sci↗

arXiv2024

Entropy-induced confinement in two-dimensional magnetic monopole gases

Magnetic monopole quasiparticles in spin ice materials hold the potential for exploring new frontiers of physics that extend beyond Maxwell's equations. We have previously proposed a two-dimensional magnetic monopole gas (2DMG), confined at the interface between spin-ice ($R_2$Ti$_2$O$_7$, $R$ = Dy, Ho) and antiferromagnetic iridate ($R_2$Ir$_2$O$_7$, $R$ = Dy, Ho), which hosts monopoles with a net charge. The mechanism behind the 2D confinement of the monopole gas remains unclear. In this work, we demonstrate that entropy is a key factor in the 2D confinement of this monopole gas. We reveal that the competition between the entropy of spin-ice, which favors the 2D confinement, and the entropy of the monopoles' random walks, which favors the deconfinement, dictates the distribution of the monopoles within a few layers close to the interface. Our entropy-based model accurately reproduces the monopole distribution obtained from the spin model, affirming that 2D confinement is entropy-driven. We further employ both models to show that the monopole distribution can be manipulated by an external magnetic field and temperature, holding promise for next-generation devices based on magnetic monopoles. Our findings reveal the entropic mechanisms in 2DMG, enabling the manipulation of emergent quasiparticles at material interfaces.

cond-mat.mtrl-sci↗

arXiv2024

Probing Quantum Telecloning on Superconducting Quantum Processors

Quantum information can not be perfectly cloned, but approximate copies of quantum information can be generated. Quantum telecloning combines approximate quantum cloning, more typically referred as quantum cloning, and quantum teleportation. Quantum telecloning allows approximate copies of quantum information to be constructed by separate parties, using the classical results of a Bell measurement made on a prepared quantum telecloning state. Quantum telecloning can be implemented as a circuit on quantum computers using a classical co-processor to compute classical feed forward instructions using if statements based on the results of a mid-circuit Bell measurement in real time. We present universal, symmetric, optimal $1 \rightarrow M$ telecloning circuits, and experimentally demonstrate these quantum telecloning circuits for $M=2$ up to $M=10$, natively executed with real time classical control systems on IBM Quantum superconducting processors, known as dynamic circuits. We perform the cloning procedure on many different message states across the Bloch sphere, on $7$ IBM Quantum processors, optionally using the error suppression technique X-X sequence digital dynamical decoupling. Two circuit optimizations are utilized, one which removes ancilla qubits for $M=2, 3$, and one which reduces the total number of gates in the circuit but still uses ancilla qubits. Parallel single qubit tomography with MLE density matrix reconstruction is used in order to compute the mixed state density matrices of the clone qubits, and clone quality is measured using quantum fidelity. These results present one of the largest and most comprehensive NISQ computer experimental analyses on (single qubit) quantum telecloning to date. The clone fidelity sharply decreases to $0.5$ for $M > 5$, but for $M=2$ we are able to achieve a mean clone fidelity of up to $0.79$ using dynamical decoupling.

quant-ph↗

arXiv2023

Quantum Computing, Math, and Physics (QCaMP): Introducing quantum computing in high schools

The nascent but rapidly growing field of Quantum Information Science and Technology has led to an increased demand for skilled quantum workers and an opportunity to build a diverse workforce at the outset. In order to meet this demand and encourage women and underrepresented minorities in STEM to consider a career in QIST, we have developed a curriculum for introducing quantum computing to teachers and students at the high school level with no prerequisites. In 2022, this curriculum was delivered over the course of two one-week summer camps, one targeting teachers and another targeting students. Here, we present an overview of the objectives, curriculum, and activities, as well as results from the formal evaluation of both camps and the outlook for expanding QCaMP in future years.

physics.ed-ph↗

arXiv2023

Enhanced piezoelectric response at nanoscale vortex structures in ferroelectrics

The piezoelectric response is a measure of the sensitivity of a material's polarization to stress or its strain to an applied field. Using in-operando x-ray Bragg coherent diffraction imaging, we observe that topological vortices are the source of a five-fold enhancement of the piezoelectric response near the vortex core. The vortices form where several low symmetry ferroelectric phases and phase boundaries coalesce. Unlike bulk ferroelectric solid solutions in which a large piezoelectric response is associated with coexisting phases in the proximity of the triple point, the largest responses for pure BaTiO3 at the nanoscale are in spatial regions of extremely small spontaneous polarization at vortex cores. The response decays inversely with polarization away from the vortex, analogous to the behavior in bulk ceramics as the cation compositions are varied away from the triple point. We use first-principles-based molecular dynamics to augment our observations, and our results suggest that nanoscale piezoelectric materials with large piezoelectric response can be designed within a parameter space governed by vortex cores. Our findings have implications for the development of next-generation nanoscale piezoelectric materials.

cond-mat.mtrl-sci↗

arXiv2022

Quantum Telecloning on NISQ Computers

Due to the no-cloning theorem, generating perfect quantum clones of an arbitrary unknown quantum state is not possible, however approximate quantum clones can be constructed. Quantum telecloning is a protocol that originates from a combination of quantum teleportation and quantum cloning. Here we present $1 \rightarrow 2$ and $1 \rightarrow 3$ quantum telecloning circuits, with and without ancilla, that are theoretically optimal (meaning the clones have the highest fidelity allowed by quantum mechanics), universal (meaning the clone fidelity is independent of the state being cloned), and symmetric (meaning the clones all have the same fidelity). We implement these circuits on gate model IBMQ and Quantinuum NISQ hardware and quantify the clone fidelities using parallel single qubit state tomography. Quantum telecloning using mid-circuit measurement with classical feed-forward control (i.e. real time if statements) is demonstrated on the Quantinuum H1-2 device. Two alternative implementations of quantum telecloning, deferred measurement and post selection, are demonstrated on ibmq\_montreal, where mid-circuit measurements with real time if statements are not available. Our results show that NISQ devices can achieve near-optimal quantum telecloning fidelity; for example the Quantinuum H1-2 device running the telecloning circuits without ancilla achieved a mean clone fidelity of $0.824$ with standard deviation of $0.024$ for two clone circuits and $0.765$ with standard deviation of $0.022$ for three clone circuits. The theoretical fidelity limits are $0.8\overline{3}$ for two clones and $0.\overline{7}$ for three clones. This demonstrates the viability of performing experimental analysis of quantum information networks and quantum cryptography protocols on NISQ computers.

quant-ph↗

arXiv2022

High Mobility Two-Dimensional Electron Gas at the BaSnO$_{3}$/SrNbO$_{3}$ Interface

Oxide two-dimensional electron gases (2DEGs) promise high charge carrier concentrations and low-loss electronic transport in semiconductors such as BaSnO$_{3}$ (BSO). ACBN0 computations for BSO/SrNbO$_{3}$ (SNO) interfaces show Nb-4$\textit{d}$ electron injection into extended Sn-5$\textit{s}$ electronic states. The conduction band minimum consists of Sn-5$\textit{s}$ states ~1.2 eV below the Fermi level for intermediate thickness 6-unit cell BSO/6-unit cell SNO superlattices, corresponding to an electron density in BSO of ~10$^{21}$ cm$^{-3}$. Experimental studies of analogous SNO/BSO interfaces grown by molecular beam epitaxy confirm significant charge transfer from SNO to BSO. $\textit {In situ}$ angle-resolved X-ray photoelectron spectroscopy studies show an electron density of ~4 $\times$ 10$^{21}$ cm$^{-3}$. The consistency of theory and experiment shows that BSO/SNO interfaces provide a novel materials platform for low loss electron transport in 2DEGs.

cond-mat.mtrl-sci↗

arXiv2001

Evidence of local magnetic order in hcp iron from Raman mode splitting

Experimental measurements of Raman spectra for hcp iron at high pressure show two modes over a considerable pressure range in contrast to the prediction of one doubly degenerate mode for the hcp lattice. We use density functional theory to investigate the influence of magnetic order on the Raman active modes of hcp iron. We find an antiferromagnetic state that lifts the degeneracy of the transverse optical mode, and yields stable antiferromagnetic moments up to approximately 60 GPa (55 Bohr$^3$). The resulting frequencies of the two transverse optical modes are in good agreement with the experimental Raman shifts, lending support to the existence of local antiferromagnetic order in hcp iron.

cond-mat.mtrl-sci↗