SearcharxivSearch

arXiv subjects

Alejandro Kunold

Publications and source records attributed to Alejandro Kunold.

16 recordsLinked to original sources

A Lie-Jordan Geometric Formulation of Lindblad Dynamics

We develop a Lie-Jordan geometric formulation of finite-dimensional open quantum dynamics, building on the algebraic framework introduced in our previous work (arXiv:2606.26477). The Hilbert-Schmidt operator space is endowed with an orthonormal Hermitian basis, in which the commutator and anticommutator are encoded by the structure tensors \(C_{\mu\nu}{}^\lambda\) and \(B_{\mu\nu}{}^\lambda\). Within this formulation, the von Neumann and Gorini-Kossakowski-Lindblad-Sudarshan equations admit a direct component representation. Our central result is the identification of a basis-independent universal trilinear dissipative map, \( \mathcal D(X,Y)Z=XZY-\frac12\{YX,Z\}, \) whose components define a universal operator-space tensor depending only on the Lie-Jordan structure tensors. The physical dissipator is obtained by contracting this tensor with the expansion coefficients of the Lindblad operators and the Kossakowski matrix, thereby separating the universal algebraic structure from the model-dependent physical information. We further show that the combinations \((B+C)\) and \((B-C)\) generate internal left and right transports, allowing the elementary dissipative map to be expressed as a left-right bimodule action corrected by an ordered Jordan contribution. The universal map satisfies basis-independent trace and Hermitian-conjugation identities, from which trace preservation, Hermiticity preservation of the complete dissipator, and the reality of its component representation in a Hermitian Hilbert-Schmidt basis follow. We also derive its Hilbert-Schmidt adjoint and illustrate the formalism for a qubit with pure dephasing and amplitude-damping channels. This construction provides a tensorial and affine-geometric interpretation of the universal superoperator structure derived in arXiv:2606.26477 while keeping the algebraic and model-dependent sectors explicitly separated.

quant-ph

Algebraic structures of the Lindblad equation

We investigate the algebraic structure underlying the Lindblad equation for finite-dimensional open quantum systems. By introducing a suitable operator representation of the Liouville superoperator, we show that the dynamics can be formulated in terms of a closed algebra of Hermitian operators that is independent of the particular physical model. This formulation reveals that dissipative dynamics requires a substantially richer algebraic structure than purely unitary evolution, thereby providing a clear characterization of the additional complexity introduced by the Lindbladian. The resulting framework naturally leads to parametrizations of the dynamical map and to differential equations governing its evolution. We further derive recursion relations that enable the efficient construction of the algebra for systems of increasing dimension. Because the algebraic basis is universal, while all model-dependent information enters through a single set of coefficients, the proposed approach significantly reduces the computational cost of constructing the Liouville superoperator compared with direct methods. To facilitate the implementation of the method, we provide a Mathematica notebook containing a one-qubit example that can be systematically extended to an arbitrary number of qubits. The proposed framework therefore provides both a general mathematical description of finite-dimensional Lindblad dynamics and a practical foundation for efficient analytical and numerical implementations.

quant-ph

MultiAtomLiouvilleEquationGenerator: A Mathematica package for Liouville superoperators and master equations of multilevel atomic systems

MulAtoLEG (Multi-Atom Liouville Equation Generator) is an open-source Mathematica package for generating Liouville superoperators and Liouville equations, specialized for multilevel atomic systems comprising an arbitrary number of atoms. This scheme is based on an extension to multilevel atomic systems, originally developed by Lehmberg [R. H. Lehmberg, Phys. Rev. A 2, 883 (1970)] as an adjoint master equation for ensembles of two-level emitters and later reformulated by Genes [M. Reitz, C. Sommer and C. Genes, PRX Quantum 3, 010201 (2022)] as a master equation. The package facilitates the generation of equations for complex transition configurations in alkali atoms. Although primarily designed for atomic systems, it can also generate the master and adjoint master equations for general Hamiltonians and Lindbladians. In addition, it includes functionalities to construct the differential equations in the dressed-state basis, where, in many cases, the non-unitary evolution operator can be determined explicitly. To maximize computational efficiency, the package leverages Mathematica's vectorization and sparse linear algebra capabilities. Since MulAtoLEG produces exact equations without approximations, the feasible system size is naturally limited by the available computational resources.

physics.comp-ph

When Adiabaticity Is Not Enough to Study Topological Phases in Solid-State Physics: Comparing the Berry and Aharonov-Anandan Phases in 2D Materials

Topological phases emerge as the parameters of a quantum system vary with time. Under the adiabatic approximation, the time dependence can be eliminated, allowing the Berry topological phase to be obtained from a closed trajectory in parameter space. In solid-state physics, this approach is commonly applied by taking a reciprocal space wavevector as the parameter, which is assumed to be varied by electromagnetic fields.The Berry curvature is then obtained by computing the derivatives of Bloch wavefunctions in reciprocal space. However, in many systems-especially gapless ones-the adiabatic approximation is never satisfied. This is particularly true in Dirac and Weyl materials, where the Berry curvature is often calculated without considering the breakdown of the adiabatic condition. In this work, we demonstrate how other time-dependent topological quantities, specifically the Aharonov-Anandan phase, can be used to extract information not only about topology but also about band transitions in 2D materials. In particular, a relationship between the current and the Aharonov-Anandan phase is proved, showing that photon-induced transitions produce current vortices. To illustrate this, we analyze graphene under electromagnetic radiation from a time-driven perspective, showing how the Aharonov-Anandan and Berry phases provide complementary insights into topology, interband transitions, and currents. This is achieved by using the Dirac-Bloch formalism and by solving the time-dependent equations within Floquet theory.

cond-mat.mes-hall

Vectorization of the density matrix and quantum simulation of the von Neumann equation of time-dependent Hamiltonians

Based oh the properties of Lie algebras, in this work we develop a general framework to linearize the von-Neumann equation rendering it in a suitable form for quantum simulations. We show that one of these linearizations of the von-Neumann equation corresponds to the standard case in which the state vector becomes the column stacked elements of the density matrix and the Hamiltonian superoperator takes the form $I\otimes H-H^\top \otimes I$ where $I$ is the identity matrix and $H$ is the standard Hamiltonian. It is proven that this particular form belongs to a wider class of ways of linearizing the von Neumann equation that can be categorized by the algebra from which they originated. Particular attention is payed to Hermitian algebras that yield real density matrix coefficients substantially simplifying the quantum tomography of the state vector. Based on this ideas, a quantum algorithm to simulate the dynamics of the density matrix is proposed. It is shown that this method, along with the unique properties of the algebra formed by Pauli strings allows to avoid the use of Trotterization hence considerably reducing the circuit depth. Even though we have used the special case of the algebra formed by the Pauli strings, the algorithm can be readily adapted to other algebras. The algorithm is demonstrated for two toy Hamiltonians using the IBM noisy quantum circuit simulator.

quant-ph

The role of elastic and inelastic processes in the temperature dependence of Hall induced resistance oscillations in strong magnetic fields

We develop a model of magnetoresistance oscillations induced by the Hall field in order to study the temperature dependence observed in recent experiments. The model is based on the solution of the von Neumann equation incorporating the exact dynamics of two-dimensional damped electrons in the presence of arbitrarily strong magnetic and dc electric fields, while the effects of randomly distributed neutral and charged impurities are perturbatively added. Both the effects of elastic impurity scattering as well as those related to inelastic processes play an important role. The theoretical predictions correctly reproduce the main experimental features provided that the inelastic scattering rate obeys a $T^2$ temperature dependence, consistent with electron-electron interaction effects.

cond-mat.mes-hall

Symmetry breaking as the origin of zero-differential resistance states of a 2DEG in strong magnetic fields

Zero resistance differential states have been observed in two-dimensional electron gases (2DEG) subject to a magnetic field and a strong dc current. In a recent work we presented a model to describe the nonlinear transport regime of this phenomenon. From the analysis of the differential resistivity and the longitudinal voltage we predicted the formation of negative differential resistivity states, although these states are known to be unstable. Based on our model, we derive an analytical approximated expression for the Voltage-Current characteristics, that captures the main elements of the problem. The result allow us to construct an energy functional for the system. In the zero temperature limit, the system presents a quantum phase transition, with the control parameter given by the magnetic field. It is noted that above a threshold value ($B>B_{th}$), the symmetry is spontaneously broken. At sufficiently high magnetic field and low temperature the model predicts a phase with a non-vanishing permanent current; this is a novel phase that has not been observed so far.

cond-mat.mes-hall

Impact of heavy hole-light hole coupling on optical selection rules in GaAs quantum dots

We report strong heavy hole-light mixing in GaAs quantum dots grown by droplet epitaxy. Using the neutral and charged exciton emission as a monitor we observe the direct consequence of quantum dot symmetry reduction in this strain free system. By fitting the polar diagram of the emission with simple analytical expressions obtained from k$\cdot$p theory we are able to extract the mixing that arises from the heavy-light hole coupling due to the geometrical asymmetry of the quantum dot.

cond-mat.mes-hall

Microwave induced negative resistance states in 2D electron gas with periodic modulation

We study the microwave-induced photoconductivity of a two-dimensional electron system (2DES) in the presence of a magnetic field and a two-dimensional modulation. The microwave and Landau contributions are exactly taken into account, while the periodic potential is treated perturbatively. The longitudinal resistivity exhibits oscillations, periodic in $ω/ ω_c$. Negative resistance states (NRS) develop for sufficiently high electron mobility and microwave power. This phenomenon appears in a narrow window region of values of the lattice parameter ($a$), around $a \sim l_B$, where $l_B$ is the magnetic length. It is proposed that these phenomena may be observed in artificially fabricated arrays of periodic scatterers at the interface of ultraclean heterostructures. {73.20.At,05.60.-k, 72.15.Rn}

cond-mat.mes-hall

Zero-resistance States Induced by Bichromatic Microwaves

We have studied the bichromatic photoresistance states of a two dimensional electron gas in the regime of microwave induced resistance oscillations. Zudov and coworkers found clear experimental evidence of zero-resistance states by measuring the bichromatic resistance in a bidimensional gas of electrons. They found that the bichromatic resistance closely replicates the superposition of the two monochromatic components provided that both contributions are positive. However, the superposition principle is no longer valid if one of the two contributions give rice to a zero-resistance state. The experiments by Zudov and coworkers confirm that negative resistance states are rapidly driven into zero-resistance states through A. V. Andreev's symmetry breaking. In this work we present a model for the bichromatic-photoconductivity of a two dimensional electron system subjected to a uniform magnetic field. Our model includes both components of the microwave radiation, a uniform magnetic field and impurity scattering effects. The conductivity is calculated from a Kubo-like formula. Our calculations reproduce the main features of Zudov's experimental results.

cond-mat.mes-hall

Photoconductivity in AC-driven modulated two dimensional electron gas in a perpendicular magnetic field

In this work we study the microwave photoconductivity of a two-dimensional electron system (2DES) in the presence of a magnetic field and a two-dimensional modulation (2D). The model includes the microwave and Landau contributions in a non-perturbative exact way, the periodic potential is treated perturbatively. The Landau-Floquet states provide a convenient base with respect to which the lattice potential becomes time-dependent, inducing transitions between the Landau-Floquet levels. Based on this formalism, we provide a Kubo-like formula that takes into account the oscillatory Floquet structure of the problem. The total longitudinal conductivity and resistivity exhibit strong oscillations, determined by $ε= ω/ ω_c$ with $ω$ the radiation frequency and $ω_c$ the cyclotron frequency. The oscillations follow a pattern with minima centered at $ω/ω_c =j + {1/2} (l-1) + δ$, and maxima centered at $ω/ω_c =j + {1/2} (l-1) - δ$, where $j=1,2,3.......$, $δ\sim 1/5$ is a constant shift and $l$ is the dominant multipole contribution. Negative resistance states (NRS) develop as the electron mobility and the intensity of the microwave power are increased. These NRS appear in a narrow window region of values of the lattice parameter ($a$), around $a \sim l_B$, where $l_B$ is the magnetic length. It is proposed that these phenomena may be observed in artificially fabricated arrays of periodic scatterers at the interface of ultraclean $GaAs/Al_xGa_{1-x} As$ heterostructures.

cond-mat.mes-hall

Photoconductivity in Ac-driven lateral superlattice in the presence of a magnetic field

In this work we present a model for the photoconductivity of two-dimensional electron system in a perpendicular homogeneous magnetic field, a weak lateral superlattice, and exposed to millimeter irradiation. The model includes the microwave and Landau contributions in a non-perturbative exact way, the periodic potential is treated perturbatively. The Landau-Floquet states provide a convenient base with respect to which the lattice potential becomes time-dependent, inducing transitions between the Landau-Floquet levels. Based on this formalism, we provide a Kubo-like formula that takes into account the oscillatory Floquet structure of the problem. The total conductivity exhibits strong oscillations, determined by $ε= ω/ ω_c$ with $ω$ the radiation frequency and $ω_c$ the cyclotron frequency. The oscillations follow a pattern with minima centered at $ω/ω_c =j + {1/2} (l-1) + δ$, and maxima centered at $ω/ω_c =j + {1/2} (l-1) - δ$, where $j=1,2,3.......$, $δ$ is a constant phase shift and $l$ is the dominant multipole contribution. Negative conductance states develop as the electron mobility and the intensity of the microwave power are increased. It is proposed that, depending on the geometry, negative conductance sates or negative resistance states may be observed in lateral superlattices fabricated in $GaAs/AlGa As$ heterostructures.

cond-mat.mes-hall

Kubo formula for Floquet states and photoconductivity oscillations in a 2D electron gas

The recent discovery of the microwave induced vanishing resistance states in a two dimensional electron system (2DES) is an unexpected and surprising phenomena. In these experiments the magnetoresistance of a high mobility 2DES under the influence of microwave radiation of frequency $ω$ at moderate values of the magnetic field, exhibits strong oscillations with zero-resistance states (ZRS) governed by the ratio $ω/ω_c$, where $ω_c$ is the cyclotron frequency. In this work we present a model for the photoconductivity of a two dimensional electron system (2DES) subjected to a magnetic field. The model includes the microwave and Landau contributions in a non-perturbative exact way, impurity scattering effects are treated perturbatively. In our model, the Landau-Floquet states act coherently with respect to the oscillating field of the impurities, that in turn induces transitions between these levels. Based on this formalism, we provide a Kubo-like formula that takes into account the oscillatory Floquet structure of the problem. We study the effects of both short-range and long-range disorder on the photoconductivity. Our calculation yields a magnetoresistance oscillatory behavior with the correct period and phase. It is found that, in agreement with experiment, negative dissipation can only be induced in very high mobility samples. We analyze the dependence of the results on the microwave power and polarization. For high-intensity radiation multi-photon processes take place predicting new negative-resistance states centered at $ ω/ ω_c=1/2$, and $ ω/ ω_c= 3/2$.

cond-mat.mes-hall

A model for the microwave assisted zero resistance states

In this work we present a model for the photoconductivity of a two dimensional electron system (2DES) subjected to a magnetic field. The model includes the microwave and Landau contributions in a non-perturbative exact way, Impurity scattering effects are treated perturbatively. Based on this formalism, we provide a Kubo-like formula that takes into account the oscillatory Floquet structure of the problem. We discuss results related with the recently discovered zero-resistance states.

cond-mat.mes-hall

Hofstadter spectrum in electric and magnetic fields

The problem of Bloch electrons in two dimensions subject to magnetic and intense electric fields is investigated. Magnetic translations, electric evolution and energy translation operators are used to specify the solutions of the Schrödinger equation. For rational values of the magnetic flux quanta per unit cell and commensurate orientations of the electric field relative to the original lattice, an extended superlattice can be defined and a complete set of mutually commuting space-time symmetry operators is obtained. Dynamics of the system is governed by a finite difference equation that exactly includes the effects of: an arbitrary periodic potential, an electric field orientated in a commensurable direction of the lattice, and coupling between Landau levels. A weak periodic potential broadens each Landau level in a series of minibands, separated by the corresponding minigaps. The addition of the electric field induces a series of avoided and exact crossing of the quasienergies, for sufficiently strong electric field the spectrum evolves into equally spaced discreet levels, in this "magnetic Stark ladder" the energy separation is an integer multiple of $ h E / a B $, with $a$ the lattice parameter.

cond-mat.mes-hall

Bloch electrons in electric and magnetic fields

We investigate Bloch electrons in two dimensions subject to constant electric and magnetic fields. The model that results from our pursuit is governed by a finite difference equation with a quasienergy spectrum that interpolates between a butterfly-like structure and a Stark ladder structure. These findings ensued from the use of electric and magnetic translation operators.

cond-mat.mes-hall