arXiv subjects

Omar Osenda

Publications and source records attributed to Omar Osenda.

At least 19 recordsLinked to original sources

arXiv2026

Engineering Perfect State Transfer Graphs via Givens Transformations

Perfect quantum state transfer is achievable in different settings, including linear qubit chains, bi-dimensional arrays, ladders, etc. The most studied case contemplates transferring arbitrary one-qubit pure states in systems with homogeneous interactions. These restrictions allow finding numerous examples of systems that show perfect transfer but in geometries that are not implementable or are very difficult to implement in actual experimental settings. Relaxing the homogeneity of the interactions and inspired by the $XX$ qubit chains that show perfect transmission, we present a simple scheme based on the Givens Transformations to analyse and obtain a class of qubit graphs that possess perfect quantum state transmission. We present some simple examples and show how it is possible to generalize them for longer transmission lengths.

quant-ph↗

arXiv2026

The pros and cons of using deep reinforcement learning or genetic algorithms to design control schemes for quantum state transfer on qubit chains

In recent years, control methods based on different optimization techniques have shed light on the possibilities of processing information in many quantum systems. When exploring the transmission of quantum states, faster transmission times are mandatory to avoid the deleterious effects of multiple sources of decoherence that spoil the transmission process. In particular, using Reinforcement Learning to devise sequences of step-wise external controls provides good transfer policies at short transmission times. We present two approaches to control the transmission of quantum states in qubit chains using external controls to force the dynamical evolution of the chain state. The first approach relies on the well-known Genetic Algorithm to generate a sequence of external controls, while the second approach uses a variant of Reinforcement Learning. The Genetic algorithm achieves excellent transmission fidelity at as short transmission times as Reinforcement Learning, surpassing the fidelities achieved by the latter method. Nevertheless, the Reinforcement Learning method offers robust control policies when the control pulses are noisy enough, owing to an imperfect timing of the pulses, deficient control devices, or other sources of phase decoherence. We present the regime where each method is best suited to control the transmission of arbitrary qubit states.

quant-ph↗

arXiv2025

Optimización de la Transmisión de Estados Cuánticos en Cadenas de Qubits usando Deep Reinforcement Learning y Algoritmos Genéticos

Quantum state transfer (QST) via homogeneous spin chains plays a crucial role in building scalable quantum hardware. A basic quantum state transmission protocol prepares a state in one qubit and transfers it to another through a channel, seeking to minimize the time and avoid information loss. The fidelity of the process is measured by functions proportional to the transition probability between both states. We approach this optimization problem using constant magnetic pulses and two complementary strategies: deep reinforcement learning, where an agent learns pulse sequences through rewards, and genetic algorithms, which develop candidate solutions through selection and mutation. We analyze the efficiency of both methods and their ability to incorporate physical constraints.

quant-ph↗

arXiv2025

Implementing a Universal Set of Geometric Quantum Gates through Dressed-State assisted STA

Geometric quantum computation relies on the geometric phase that arises in adiabatic cyclic evolutions of non-degenerate quantum systems, enabling the design of robust quantum gates. However, the adiabatic condition requires long evolution times, making the system vulnerable to decoherence. In this work, we propose a scheme to realize fast and high-fidelity geometric quantum gates by applying the Superadiabatic Transitionless Driving (SATD) protocol within the dressed-state framework. We analyze the implementation of single-qubit gates in a two-level system driven by a microwave field, focusing in particular on the NV center in diamond. We show how the dynamical phase can be canceled to obtain purely geometric operations. The robustness of the gates is assessed under systematic errors and environmental decoherence, demonstrating high fidelities even in regimes with strong fluctuations. Finally, we extend the protocol to construct nontrivial two-qubit gates, highlighting its feasibility for scalable quantum information processing.

quant-ph↗

arXiv2025

Anisotropic Heisenberg Su-Schrieffer-Heeger spin chain as a quantum channel

Quantum state transmission in spin chains is a fundamental problem within quantum technologies. The Su-Schrieffer-Heeger (SSH) model, first introduced in the context of polyacetylene, provides a paradigmatic example of a system exhibiting topological and non-topological phases. We explore the transmission of one and two excitations in anisotropic Heisenberg SSH spin chains and analyze the relationship between topological properties and state transfer efficiency. We examine the robustness of quantum state transmission against static disorder in the trivial and topological regimes, exploring how topological protection influences transmission fidelity. We also consider the effect of dipolar interactions, introducing long-range couplings and breaking the conservation of total magnetization. Furthermore, we employ optimal control theory to design driving pulses for state transmission, finding substantial differences between optimizing in the trivial and topological regimes. Our results provide insights about the interplay between topology, disorder, interactions, and control strategies in quantum state transfer.

quant-ph↗

arXiv2025

Perfect, Pretty Good and Optimized Quantum State Transfer in Transmon qubit chains

Chains of transmon qubits are considered promising systems to implement different quantum information tasks. In particular as channels that perform high-quality quantum state transfer. We study how changing the interaction strength between the chain qubits allows us to obtain perfect or pretty good state transfer and present explicit analytic expressions for their transmission fidelity. For particular values of the interactions between the qubits, transmon chains are equivalent to generalized SSH chains and show the traditional traits observed in chains with topological states, localized states at the extremes of the chain, and eigenvalues that lie inside the spectral gap. Consequently, we study the quantum state transfer on chains with dimerized interactions, looking for chains with fast transfer times. We show that, in many cases, asking for fast transfer times results in chains with dimerized interactions that do not have topological states.

quant-ph↗

arXiv2024

Quantum State Transfer in a Magnetic Atoms Chain Using a Scanning Tunneling Microscope

The electric control of quantum spin chains has been an outstanding goal for the few last years due to its potential use in technologies related to quantum information processing. In this work, we show the feasibility of the different steps necessary to perform controlled quantum state transfer in a $S=1/2$ titanium atoms chain employing the electric field produced by a Scanning Tunneling Microscope (STM). Our results show that the initialization and transmission of a single excitation state is achievable in short times, and with high fidelity. Our study uses spin Hamiltonians to model the magnetic atoms chain, the tip of the STM, the interaction between it and the atoms chain and the electronic response to the fields applied by the tip, employing sets of parameters compatible with the latest experiments and ab initio calculations. The time dynamical evolution is considered in the full Hilbert space and the control pulses frequencies exerted by the tip of the microscope are within the reach of present day technology.

quant-ph↗

arXiv2024

Quantum state transfer performance of Heisenberg spin chains with site-dependent interactions designed using a generic genetic algorithm

Designing a good transfer channel for arbitrary quantum states in spin chains implies optimizing a cost function, usually the averaged fidelity of transmission. The fidelity of transmission measures how much the transferred state resembles the state prepared at the beginning of the transfer protocol. When averaged over all the possible initial states, the figure of merit quantifies the quality of the protocol. There are proposals for optimizing a given Hamiltonian to accomplish a particular task. The transfer of quantum states is one of them. In particular, we consider the design of Heisenberg spin chains using a genetic algorithm. This very efficient algorithm allows us to study different properties of Hamiltonians with good to excellent transfer ability. One apparent drawback of using a random search method is that it results in exchange coefficient strengths that change abruptly from site to site. Modifying the cost function, we obtain Hamiltonians with exchange coefficients varying smoothly along the chain length. Our results show that the smoothed Hamiltonians have the same, or less, transfer ability than the rough ones, and both kinds show similar robustness against static disorder. By studying the statistical properties of the eigenvalues of Hamiltonians with varying transfer abilities, we determine the ensemble of random matrices to which the spectra belong.

quant-ph↗

arXiv2023

The scaling law of the arrival time of spin systems that present pretty good transmission

The pretty good transmission scenario implies that the probability of sending one excitation from one extreme of a spin chain to the other can reach values arbitrarily close to the unity just by waiting a time long enough. The conditions that ensure the appearance of this scenario are known for chains with different interactions and lengths. Sufficient conditions for the presence of pretty good transmission depend on the spectrum of the Hamiltonian of the spin chain. Some works suggest that the time $t_{\varepsilon}$ at which the pretty good transmission takes place scales as $1/(|\varepsilon|)^{f(N)}$, where $\varepsilon$ is the difference between the probability that a single excitation propagates from one extreme of the chain to the other and the unity, while $f(N)$ is an unknown function of the chain length. In this paper, we show that the exponent is not a simple function of the chain length but a power law of the number of linearly independent irrational eigenvalues of the one-excitation block of the Hamiltonian that enter into the expression of the probability of transmission of one excitation. We explicitly provide examples of a chain showing that the exponent changes when the couplings between the spins change while the length remains fixed. For centrosymmetric spin chains the exponent is at most $N/2$.

quant-ph↗

arXiv2023

Quantum entropies of realistic states of a topological insulator

Nanowires of BiSe show topological states localized near the surface of the material. The topological nature of these states can be analyzed using well-known quantities. In this paper, we calculate the topological entropy suggested by Kitaev and Preskill for these states together with a new entropy based on a reduced density matrix that we propose as a measure to distinguish topological one-electron states. Our results show that the topological entropy is a constant independent of the parameters that characterize a topological state as its angular momentum, longitudinal wave vector, and radius of the nanowire. The new entropy is always larger for topological states than for normal ones, allowing the identification of the topological ones. We show how the reduced density matrices associated with both entropies are constructed from the pure state using positive maps and explicitly obtaining the Krauss operators.

quant-ph↗

arXiv2022

Characterization of helical states in semiconductor quantum wells using quantum information quantities

The information content of one-electron bulk and edge states in semiconductor quantum wells is calculated in the inverted regime, where edge states, topologically protected, are responsible for the conduction in Spin Quantum Hall effect experiments. To study the information content of these states we first calculate realistic two dimensional one-electron states, solving first the eight-band $\mathbf{k}\cdot\mathbf{p}$ Hamiltonian to obtain the bulk states and then a four band effective Hamiltonian to obtain the edge states. The behavior of information-like quantities, as a function of the different parameters that define the quantum well, is analyzed. The results presented show that the helical edge states can be singled out using different quantities that characterize the rich phenomenology of these states.

cond-mat.mes-hall↗

arXiv2022

Exact solution of a family of staggered Heisenberg chains with conclusive pretty good quantum state transfer

We construct the exact solution for a family of one-half spin chains explicitly. The spin chains Hamiltonian corresponds to an isotropic Heisenberg Hamiltonian, with staggered exchange couplings that take only two different values. We work out the exact solutions in the one-excitation subspace. Regarding the problem of quantum state transfer, we use the solution and some theorems concerning the approximation of irrational numbers, to show the appearance of conclusive pretty good transmission for chains with particular lengths. We present numerical evidence that pretty good transmission is achieved by chains whose length is not a power of two. The set of spin chains that shows pretty good transmission is a subset of the family with an exact solution. Using perturbation theory, we thoroughly analyze the case when one of the exchange coupling strengths is orders of magnitude larger than the other. This strong coupling limit allows us to study, in a simple way, the appearance of pretty good transmission. The use of analytical closed expressions for the eigenvalues, eigenvectors, and transmission probabilities allows us to obtain the precise asymptotic behavior of the time where the pretty good transmission is observed. Moreover, we show that this time scales as a power law whose exponent is an increasing function of the chain length. We also discuss the crossover behavior obtained for the pretty good transmission time between the regimes of strong coupling limit and the one observed when the exchange couplings are of the same order of magnitude.

quant-ph↗

arXiv2021

Understanding the propagation of excitations in quantum spin chains with different kind of interactions

The dynamical behaviour of the quantum state of different quantum spin chains, with designed site dependent interaction strengths, is analyzed when the initial state belongs to the one excitation subspace. It is shown that the inhomogeneous chains are able to transfer excitations with near perfect fidelity. This behaviour is found for two very different spin chain Hamiltonians. The first one is the ferromagnetic Heisenberg Hamiltonian with nearest neighbor interactions, the second one describes a chain with long range anisotropic interactions which are ferromagnetic in the $z$ direction and antiferromagnetic in the $(x,y)$ plane. It is shown that both designed chains have in common a partially ordered spectrum and well localized eigenvectors. This physical trait unifies the description of both kind of systems.

quant-ph↗

arXiv2021

Pretty good quantum state transfer on isotropic and anisotropic Heisenberg spin chains with tailored site dependent exchange couplings

Using a global optimization algorithm we obtain spin chains with site-dependent exchange coefficients which allow almost perfect quantum state transfer between the extremes of the chains without any further time-dependent external control. We consider chains with isotropic and anisotropic Heisenberg Hamiltonian with up to 100 spins. The method allow us to choose the arrival of the transferred state by changing the range available to the exchange coupling strengths. We consider short transferred times, in particular shorter than those achievable with known time-dependent control schemes. The chains obtained with the optimization method show some remarkable and interesting traits as, for instance, the scaling of the magnitude of the exchange couplings needed to achieve near perfect state transfer with the length of the chain and the arrival time. This scaling makes it possible to decide if the chain with site-dependent coefficients can be implemented in an actual system according to the range of interactions allowed in it. We compare the robustness of the transmission protocol against static disorder on the exchange coefficients using different figures of merit, which allow us to conclude that the isotropic Heisenberg chain is the best option when compared with anisotropic chains. This comparison is relevant since the method allow us to start with chains that all achieve near perfect quantum state transfer, regime that was not available previously in these chains without time-dependent external control.

quant-ph↗

arXiv2020

Controlled quantum state transfer in $XX$ spin chains at the Quantum Speed Limit

The Quantum Speed Limit can be found in many different situations, in particular in the propagation of information through quantum spin chains. In homogeneous chains it implies that taking information from one extreme of the chain to the other will take a time $O(N/2)$, where $N$ is the chain length. Using Optimal Control Theory we design control pulses that achieve near perfect population transfer between the extremes of the chain at times on the order of $N/2$, or larger, depending on which features of the transfer process are to be studied. Our results show that the control pulses that govern the dynamical behaviour of chains with different lengths are closely related, that larger control times imply more complicated control pulses than those found at times on the order of $N/2$ and also larger driving energies. The pulses were constructed for control schemes involving one or two actuators in chains with exchange couplings without static disorder. Our results also show that the two actuator scheme is considerably more robust against the presence of static disorder than the scheme that uses just a single one.

quant-ph↗

arXiv2019

Excitonic states in spherical layered quantum dots

he properties of excitons formed in spherical quantum dots are studied using the $\mathbf{k}\cdot\mathbf{p}$ method within the Hartree approximation. The spherical quantum dots considered have a central core and several concentric layers of different semiconductor materials that are modeled as a succession of potential wells and barriers. The $\mathbf{k}\cdot\mathbf{p}$ Hamiltonian and the Coulomb equations for the electron-hole pair are solved using a self-consistent iterative method. The calculation of the spectrum of the empty quantum dot and the electron-hole pair is performed by means of a very accurate numerical approximation. It is found that the exciton binding energy as a function of the core radius of the quantum dot shows a strong non-linear behaviour. In particular, for quantum dots with two potential wells, the binding energy presents a large steep change. This last behaviour is explained in terms of the polarization charges at the interfaces between different materials and the matching conditions for the eigenfunctions.

cond-mat.mes-hall↗

arXiv2019

Convexity properties of superpositions of degenerate bipartite eigenstates

The entanglement content of superpositions of pairs of degenerate eigenstates of a bipartite system are considered in the case that both are also eigenstates of the $z$ component of the total angular momentum. It is shown that the von Neumann entropy of the state that is obtained tracing out one of the parts of the system has a definite convexity (concavity) as a function of the superposition parameter and that its convexity (concavity) can be predicted using a quantity of information that measures the entropy shared by the states at the extremes of the superposition. Several examples of two particle system, whose eigenfunctions and density matrices can be obtained exactly, are analyzed thoroughly.

quant-ph↗

arXiv2018

Fast optical control of a coded qubit in a triple quantum dot

In this work, we study strategies for the optical control, within the dipole approximation, of a qubit encoded in the three-electron states of a triple quantum dot. The system is described by effective confining potentials, and its electronic structure by the configuration interaction method. Optimal control theory (OCT) was applied to design low-fluence time-dependent electric fields controlling the qubit in times shorter than a nanosecond. The resulting pulses produce transitions between the qubit states for experimentally available field amplitudes with high fidelity. Their frequency spectra are related to transitions to some lower-lying excited states and a simplified pulse based on those sequential transitions is presented. The limitations of an extended Hubbard description for the type of strategy analyzed here are also discussed.

cond-mat.mes-hall↗