arXiv subjects

Michael H. Kolodrubetz

Publications and source records attributed to Michael H. Kolodrubetz.

At least 19 recordsLinked to original sources

arXiv2026

Robust qubit interactions mediated by photonic topological edge states

We investigate the coupling of two spatially separated qubits via topologically protected edge states in a two-dimensional Hofstadter lattice. In this hybrid platform, the qubits are coupled to distinct edge sites of the lattice, enabling long-range interactions mediated by topological edge modes. We solve the full system Hamiltonian and analyze the resulting eigenstate structure to uncover the conditions under which coherent qubit interactions emerge. Our analysis reveals that the effective coupling is highly sensitive to the qubit placement, energy detuning, and the topological character of the edge spectrum. We obtain an analytical solution that goes beyond the perturbative regime, capturing the full interplay between the qubits and edge modes. These results provide a foundation for exploring information transport and many-body effects in engineered quantum systems where interactions are mediated by topological edge modes.

quant-ph↗

arXiv2025

QISCIT: A validated concept inventory assessment for quantum information science

Quantum information science (QIS) is a critical interdisciplinary field that requires a well-educated workforce in the near future. Numerous researchers and educators have been actively investigating how to best educate and prepare such a workforce. An open issue has been the lack of a validated tool to asses QIS understanding without requiring college-level math. In this paper, we present the systematic development and content validation of a new assessment instrument called the Quantum Information Science Concept Introductory Test (QISCIT). With feedback from 11 QIS experts, we have developed and validated a 31-item version of QISCIT that covers concepts like quantum states, quantum measurement, qubits, entanglement, coherence and decoherence, quantum gates and computing, and quantum communication. In addition to openly sharing our new concept inventory, we discuss how introductory QIS instructors can use it in their courses.

physics.ed-ph↗

arXiv2025

Phases and phase transition in Grover's algorithm with systematic noise

While limitations on quantum computation by Markovian environmental noise are well-understood in generality, their behavior for different quantum circuits and noise realizations can be less universal. Here we consider a canonical quantum algorithm - Grover's algorithm for unordered search on $L$ qubits - in the presence of systematic noise. This allows us to write the behavior as a random Floquet unitary, which we show is well-characterized by random matrix theory (RMT). The RMT analysis enables analytical predictions for phases and phase transitions of the many-body dynamics. We find two separate transitions. At moderate disorder $δ_{c,\mathrm{gap}}\sim L^{-1}$, there is a ergodicity breaking transition such that a finite-dimensional manifold remains non-ergodic for $δ< δ_{c,\mathrm{gap}}$. Computational power is lost at a much smaller disorder, $δ_{c,\mathrm{comp}} \sim L^{-1/2}2^{-L/2}$. We comment on relevance to non-systematic noise in realistic quantum computers, including cold atom, trapped ion, and superconducting platforms.

quant-ph↗

arXiv2024

Topological anomalous Floquet photon pump

There is a close theoretical connection between topological Floquet physics and cavity QED, yet this connection has not been realized experimentally due to complicated cavity QED models that often arise. We propose a simple, experimentally viable protocol to realize non-adiabatic topological photon pumping mediated by a single qubit, which we dub the anomalous Floquet photon pump. For both quantized photons and external drive, the system exhibits a non-trivial topological phase across a broad range of parameter space. Transitions out of the topological phase result from frequency-space delocalization. Finally, we argue that the protocol can be implemented in existing experiments via driven qubit non-linearities, with topological pumping witnessed in measurements of the cavity Wigner distribution functions.

cond-mat.mes-hall↗

arXiv2024

Probing topological phases in a perturbed Kane-Mele model via RKKY interaction: Application to monolayer jacutingaite Pt$_2$HgSe$_3$

Quantum spin Hall insulators (QSHIs) are promising for spintronics, leveraging strong spin-orbit coupling for efficient spin manipulation via electrical and optical methods, with potential applications in memory storage, quantum computing, and spin-based logic. While the Kane-Mele model effectively captures the low-energy physics of these materials, the impact of perturbations driving phase transitions is less well understood. Developing approaches to describe these phases is crucial. Here, we study the noncollinear Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between two magnetic impurities in a \textit{perturbed} Kane-Mele model with strong spin-orbit coupling, relevant to monolayer jacutingaite Pt$_2$HgSe$_3$ as a prominent QSHI. By analyzing RKKY interactions, we reveal distinct, relative (rather than absolute) signatures of the different phase transitions induced by static and dynamic perturbations based on their impact on magnetic impurities. We then employ these perturbations to switch between ferromagnetic and antiferromagnetic or clockwise and counterclockwise magnetic interactions for control processes. Our results offer a practical way to track topological phases via magnetic properties.

cond-mat.mes-hall↗

arXiv2024

Terahertz high-harmonic generation in gapped antiferromagnetic chains

The nonlinear dynamics of magnetization in antiferromagnets, resulting in high-frequency spin waves (high-order harmonics) as signal carriers, enable fast magnetic state switching in spintronic devices. More harmonic orders potentially allow more information to be conveyed by the spins. Developing theoretical models to describe these waves in antiferromagnets is essential for predicting their properties and guiding experimental efforts. Here, we consider the role of linear and quadratic spin-phonon couplings (SPCs) in achieving high-order harmonics in the THz magnetization of a gapped antiferromagnetic spin chain. A THz steady laser's electric field indirectly drives spins via phonons. Using spin-wave theory, mean-field theory, and the Lindblad formalism, we analyze the resulting nonlinear dynamics. We highlight the distinct mechanisms for harmonic generation when a phonon is coupled to the easy-plane and easy-axis of spins. Moreover, we observe that quadratic SPC blocks odd harmonics due to invariant inversion symmetry, while linear SPC generates both odd and even harmonics. We also investigate the effects of drive frequency, drive amplitude, phonon damping, and spin damping on the number of harmonics. Our findings offer an alternative pathway for developing nonlinear magnonics.

cond-mat.str-el↗

arXiv2024

Optimal Control and Glassiness in Quantum Sensing

Quantum systems are powerful detectors with wide-ranging applications from scanning probe microscopy of materials to biomedical imaging. Nitrogen vacancy (NV) centers in diamond, for instance, can be operated as qubits for sensing of magnetic field, temperature, or related signals. By well-designed application of pulse sequences, experiments can filter this signal from environmental noise, allowing extremely sensitive measurements with single NV centers. Recently, optimal control has been used to further improve sensitivity by modification of the pulse sequence, most notably by optimal placement of $π$ pulses. Here we consider extending beyond $π$ pulses, exploring optimization of a continuous, time-dependent control field. We show that the difficulty of optimizing these protocols can be mapped to the difficulty of finding minimum free energy in a classical frustrated spin system. While most optimizations we consider show autocorrelations of the sensing protocol that grow as a power law -- similar to an Ising spin glass -- the continuous control shows slower logarithmic growth, suggestive of a harder Heisenberg-like glassy landscape.

quant-ph↗

arXiv2024

Spin high-harmonic generation through terahertz laser-driven phonons

In the realm of open quantum systems, steady states and high-harmonic generation (HHG) existing far from equilibrium have become core pillars of ultrafast science. Most solid-state research explores charge HHG with limited investigations into spin degrees of freedom. In this study, we theoretically address spin HHG in the steady state resulting from the terahertz laser-driven spin-phonon coupling in a dissipative dimerized spin-1/2 chain. Instead of directly driving spins using time-dependent magnetic fields, we employ the magnetophononic mechanism, where the laser first drives the lattice, and then the excited lattice subsequently drives the spins. We investigate the role of various model parameters for optimizing HHG. Increasing the laser's amplitude amplifies spin HHG beyond the perturbative regime, enhancing both harmonic amplitudes and orders. We find that configuring the drive frequency far below the spin band yields the highest harmonic order. Additionally, we provide a theory matching the numerical results under weak spin-phonon coupling and propose an experimental procedure to probe the emission spectrum of spin HHG.

cond-mat.str-el↗

arXiv2024

Ultrafast dynamics of a fermion chain in a terahertz field-driven optical cavity

We study the effect of a terahertz field-driven single cavity mode for ultrafast control of a fermion chain with dissipation-induced nonlinearity and quadratic coupling to an infrared-active phonon mode. Without photon loss from the cavity, we uncover a first-order phase transition in the nonequilibrium steady state only for the lower phonon-polariton, accompanied by polaritons whose frequency response is asymmetric with respect to the photon frequency due to the direct laser-induced dressing effect on the photon. A weak laser field fails to induce the phase transition but renders the polaritons symmetrical. Finally, we show that sufficiently strong photon loss from the cavity eliminates the polaritons and the associated phase transition. The experimental feasibility of these phenomena is also proposed.

cond-mat.str-el↗

arXiv2023

Laser-enhanced magnetism in SmFeO$_3$

To coherently enhance inherent weak magnetic interactions in rare-earth orthoferrite SmFeO$_3$ as a functional material for spintronic applications, we simulate the dissipative spin dynamics that are linearly and quadratically coupled to laser-driven infrared-active phonons. When linear coupling dominates, we discover a magnetophononic dynamical first-order phase transition in the nonequilibrium steady state which can inhibit strong enhancement of magnetic interactions. By contrast, when quadratic spin-phonon coupling dominates, no phase transition exists at experimentally relevant parameters. By utilizing a chirp protocol, the phase transition can be engineered, enabling stronger magnetic interactions. We also discuss the route for experimental observation of our results.

cond-mat.mtrl-sci↗

arXiv2023

Nonequilibrium phononic first-order phase transition in a driven fermion chain

We study the direct laser drive of infrared-active phonons that are quadratically coupled to a spinless fermion chain. Feedback is incorporated by phonon dressing of the electronic dispersion, which enables effective non-linearities in the phonon dynamics. We uncover a first-order phase transition in the phononic steady state in which hysteretic effects allow either large or small phonon occupation depending on the drive protocol. We discuss the implications of these findings for probing phase transitions in real driven materials.

cond-mat.str-el↗

arXiv2023

Cavity induced many-body localization

In this manuscript, we explore the feasibility of achieving many-body localization in the context of cavity quantum electrodynamics at strong coupling. Working with a spinless electronic Hubbard chain sitting coupled to a single-mode cavity, we show that the global coupling between electrons and photons -- which generally would be expected to delocalize the fermionic excitations -- can instead favor the appearance of localization. This is supported by a novel high-frequency expansion that correctly accounts for electron-photon interaction at strong coupling, as well as numerical calculations in both single particle and many-bod regimes. We find evidence that many-body localization may survive strong quantum fluctuations of the photon number by exploring energy dependence, seeing signatures of localization down to photon numbers as small as $n\sim2$.

cond-mat.mes-hall↗

arXiv2023

Tunable superdiffusion in integrable spin chains using correlated initial states

Although integrable spin chains only host ballistically propagating particles they can still feature diffusive spin transport. This diffusive spin transport originates from quasiparticle charge fluctuations inherited from the initial state's magnetization Gaussian fluctuations. We show that ensembles of initial states with quasi-long range correlations lead to superdiffusive spin transport with a tunable dynamical exponent. We substantiate our prediction with numerical simulations and explain how deviations arise from finite time and finite size effects.

cond-mat.stat-mech↗

arXiv2022

Noncollinear twisted RKKY interaction on the optically driven SnTe(001) surface

The nontrivial spin texture on the (001) surface of topological crystalline insulator SnTe hosts exotic scientific importance and spintronic applications. Here, we study the effects of weak Floquet optical driving on the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between two magnetic impurities on a doped SnTe(001) surface. Due to peculiar spin-orbit hybridization, we find a noncollinear twisted RKKY interaction comprising XYZ-Heisenberg, symmetric in-plane, and asymmetric Dzyaloshinskii-Moriya (DM) terms. We see that contributions from the $z$ ($x$)-component of the XYZ-Heisenberg (DM) interaction are dominant for most parameters. The interactions, including DM terms that are responsible for interesting spin textures, require doping in most cases. We propose to modify the interactions in situ via optical control of band structure, and thereby doping. A notable aspect of this control protocol is breaking of electron-hole symmetry, which stems from the DM interaction.

cond-mat.str-el↗

arXiv2022

Anomalous Floquet-Anderson Insulator with Quasiperiodic Temporal Noise

Time-periodic (Floquet) drive can give rise to novel symmetry breaking and topological phases of matter. Recently, we showed that a quintessential Floquet topological phase known as the anomalous Floquet-Anderson insulator is stable to noise on the timing of its Floquet drive. Here, we perturb the anomalous Floquet-Anderson insulator at a single incommensurate frequency, resulting in a quasiperiodic 2-tone drive. Our numerics indicate that a robust topological phase survives at weak noise with topological pumping that is more stable than the case of white noise. Within the topological phase, we show that particles move subdiffusively, which is directly responsible for stabilizing topological transport. Surprisingly, we discover that when quasiperiodic noise is sufficiently strong to kill topology, the system appears to exhibit diffusive dynamics, suggesting that the correlated structure of the quasiperiodic noise becomes irrelevant.

cond-mat.mes-hall↗

arXiv2021

Quantized Floquet topology with temporal noise

Time-periodic (Floquet) drive is a powerful method to engineer quantum phases of matter, including fundamentally non-equilibrium states that are impossible in static Hamiltonian systems. One characteristic example is the anomalous Floquet insulator, which exhibits topologically quantized chiral edge states similar to a Chern insulator, yet is amenable to bulk localization. We study the response of this topological system to time-dependent noise, which breaks the topologically protecting Floquet symmetry. Surprisingly, we find that the quantized response, given by partially filling the fermionic system and measuring charge pumped per cycle, remains quantized up to finite noise amplitude. We trace this robust topology to an interplay between diffusion and Pauli blocking of edge state decay, which we expect should be robust against interactions. We determine the boundaries of the topological phase for a system with spatial disorder numerically through level statistics, and corroborate our results in the limit of vanishing disorder through an analytical Floquet superoperator approach. This approach suggests an interpretation of the state of the system as a non-Hermitian Floquet topological phase. We comment on quantization of other topological responses in the absence of Floquet symmetry and potential experimental realizations.

cond-mat.quant-gas↗

arXiv2020

Inverted many-body mobility edge in a central qudit problem

Many interesting experimental systems, such as cavity QED or central spin models, involve global coupling to a single harmonic mode. Out-of-equilibrium, it remains unclear under what conditions localized phases survive such global coupling. We study energy-dependent localization in the disordered Ising model with transverse and longitudinal fields coupled globally to a $d$-level system (qudit). Strikingly, we discover an inverted mobility edge, where high energy states are localized while low energy states are delocalized. Our results are supported by shift-and-invert eigenstate targeting and Krylov time evolution up to $L=13$ and $18$ respectively. We argue for a critical energy of the localization phase transition which scales as $E_c \propto L^{1/2}$, consistent with finite size numerics. We also show evidence for a reentrant MBL phase at even lower energies despite the presence of strong effects of the central mode in this regime. Similar results should occur in the central spin-$S$ problem at large $S$ and in certain models of cavity QED.

cond-mat.dis-nn↗

arXiv2019

Landau levels, Bardeen polynomials and Fermi arcs in Weyl semimetals: the who's who of the chiral anomaly

Condensed matter systems realizing Weyl fermions exhibit striking phenomenology derived from their topologically protected surface states as well as chiral anomalies induced by electromagnetic fields. More recently, inhomogeneous strain or magnetization were predicted to result in chiral electric $\mathbf{E}_5$ and magnetic $\mathbf{B}_5$ fields, which modify and enrich the chiral anomaly with additional terms. In this work, we develop a lattice-based approach to describe the chiral anomaly, which involves Landau and pseudo-Landau levels and treats all anomalous terms on equal footing, while naturally incorporating Fermi arcs. We exemplify its potential by physically interpreting the largely overlooked role of Fermi arcs in the covariant (Fermi level) contribution to the anomaly and revisiting the factor of $1/3$ difference between the covariant and consistent (complete band) contributions to the $\mathbf{E}_5\cdot\mathbf{B}_5$ term in the anomaly. Our framework provides a versatile tool for the analysis of anomalies in realistic lattice models as well as a source of simple physical intuition for understanding strained and magnetized inhomogeneous Weyl semimetals.

cond-mat.mes-hall↗