Álvaro Gómez-León, Gloria Platero
Sep 24, 2012·quant-ph·PDF In this work we study the geometrical and topological properties of non-equilibrium quantum systems driven by ac fields. We consider two tunnel coupled spin qubits driven by either spatially homogeneous or inhomogeneous ac fields. Our analysis is an extension of the classical model introduced by Berry with he addition of the spatial degree of freedom. We calculate the Berry and Aharonov-Anandan geometric phases, and demonstrate the influence of the different field parameters in the geometric properties. We also discuss the topological properties associated with the different driving regimes, and show that by tuning the different parameters one can induce topological phase transitions, even in the non-adiabatic regime.
Rafael Sánchez, Ernesto Cota, Ramón Aguado, Gloria Platero
Recently it has been shown that ac-driven double quantum dots can act as spin pumps and spin filters. By calculating the current through the system for each spin polarization, by means of the time evolution of the reduced density matrix in the sequential tunneling regime (Born-Markov approximation), we demonstrate that the spin polarization of the current can be controlled by tuning the parameters (amplitude and frequency) of the ac field. Importantly, the pumped current as a function of the applied frequency presents a series of peaks which are uniquely associated with a definite spin polarization. We discuss how excited states participating in the current allow the system to behave as a bipolar spin filter by tuning the ac frequency and intensity. We also discuss spin relaxation and decoherence effects in the pumped current and show that measuring the width of the current vs frequency peaks allows to determine the spin decoherence time $T_{2}$.
Gloria Platero, Ramon Aguado
In this review we focus on electronic transport through semiconductor nanostructures which are driven by ac fields. Along the review we describe the available experimental information on different nanostructures, like resonant tunneling diodes, superlattices or quantum dots, together with the theoretical tools needed to describe the observed features. These theoretical tools such as, for instance, the Floquet formalism, the non-equilibrium Green's function technique or the density matrix technique, are suitable for tackling with photon-assisted transport problems where the interplay of different aspects like nonequilibrium, nonlinearity, quantum confinement or electron-electron interactions gives rise to many intriguing new phenomena. Along the review we give many examples which demonstrate the possibility of using appropriate ac fields to control/manipulate coherent quantum states in semiconductor nanostructures.
David Sanchez, L. Brey, Gloria Platero
We perform a Hartree-Fock calculation in order to describe the ground state of a vertical double quantum dot in the absence of magnetic fields parallel to the growth direction. Intra- and interdot exchange interactions determine the singlet or triplet character of the system as the tunneling is tuned. At finite Zeeman splittings due to in-plane magnetic fields, we observe the continuous quantum phase transition from ferromagnetic to symmetric phase through a canted antiferromagnetic state. The latter is obtained even at zero Zeeman energy for an odd electron number.
Rosa Lopez, Ramon Aguado, Gloria Platero, Carlos Tejedor
We present a fully nonequilibrium calculation of the low temperature transport properties of a quantum dot in the Kondo regime when an AC potential is applied to the gate voltage. We solve a time dependent Anderson model with finite on-site Coulomb interaction. The interaction self-energy is calculated up to second order in perturbation theory in the on-site interaction, in the context of the Keldysh non-equilibrium technique, and the effect of the AC voltage is taken into account exactly for all ranges of AC frequencies and AC intensities. The obtained linear conductance and time-averaged density of states of the quantum dot evolve in a non trivial way as a function of the AC frequency and AC intensity of the harmonic modulation.
Ming Li, JunYan Luo, Gloria Platero, Georg Engelhardt
Motivated by the importance of dispersive readout in quantum technology, we study a prototypical dispersive readout setup that is probed by a squeezed vacuum in a time-reversal-symmetric fashion. To this end, we develop a full-counting-statistics framework for dispersive readout and analyze its measurement information, accompanied by a generalized mean-field approach suitable to deal with non-unitary dynamics. Distinct from conventional input-output theory, our full-counting-statistics approach enables the direct calculation of arbitrary-order cumulants for the measured cumulative (i.e., time-integrated) photonic distribution while maintaining applicability to nonlinear systems. The corresponding Fisher information exhibits an exponential dependence on the squeezing parameter and a robustness against residual nonlinearity, which can even approach the quantum Fisher information, setting an upper limit. This work introduces a conceptually streamlined and computationally efficient framework for continuous quantum measurements, making it well suited for widespread adoption in quantum technologies.
Christian Ventura Meinersen, David Fernandez-Fernandez, Gloria Platero, Maximilian Rimbach-Russ
Apr 10, 2025·quant-ph·PDF Adiabatic optimal control schemes are essential for advancing the practical implementation of quantum technologies. However, the vast array of possible adiabatic protocols, combined with their dependence on the particular quantum system and function-specific parameter ranges, complicates the task of discerning their respective strengths and limitations in arbitrary operations. In this work, we provide a unifying framework, called $(α,β)$-hypergeometries, that allows for flexible, noise-resistant, and easy-to-use implementation of enforced adiabatic dynamics for any multi-level quantum system. Moreover, this framework provides a comprehensive mapping of all adiabatic protocols through a universal cost function and offers an exact analytical characterization of the adiabatic dynamics. In particular, we derive precise expressions for infidelity resonances and establish performance guarantees in the adiabatic limit for any choice of $(α,β)$. We also discuss in detail the experimental feasibility of the resulting pulse shapes through analytical and numerical methods. Finally, we test our method for the optimal control of coherent information transfer through spin shuttling in silicon quantum dots with small valley splittings.
Miguel Bello, Mónica Benito, Martin J. A. Schuetz, Gloria Platero, Géza Giedke
We propose a protocol for the deterministic generation of entanglement between two ensembles of nuclear spins surrounding two distant quantum dots. The protocol relies on the injection of electrons with definite polarization in each quantum dot and the coherent transfer of electrons from one quantum dot to the other. Computing the exact dynamics for small systems, and using an effective master equation and approximate non-linear equations of motion for larger systems, we are able to confirm that our protocol indeed produces entanglement for both homogeneous and inhomogeneous systems. Last, we analyze the feasibility of our protocol in several current experimental platforms.
A. Diaz-Fernandez, E. Diaz, Álvaro Gómez-León, Gloria Platero, F. Domínguez-Adame
We propose to Floquet-engineer Dirac cones at the surface of a three-dimensional topological insulator. We show that a large tunability of the Fermi velocity can be achieved as a function of the polarization, direction and amplitude of the driving field. Using this external control, the Dirac cones in the quasienergy spectrum may become elliptic or massive, in accordance to experimental evidences. These results help us to understand the interplay of surface states and external ac driving fields in topological insulators. In our work we use the full Hamiltonian for the three-dimensional system instead of effective surface Hamiltonians, which are usually considered in the literature. Our findings show that the Dirac cones in the quasienergy spectrum remain robust even in the presence of bulk states and, therefore, they validate the usage of effective surface Hamiltonians to explore the properties of Floquet-driven topological boundaries. Furthermore, our model allows us to introduce new out-of-plane field configurations, which cannot be accounted for by effective surface Hamiltonians.
Beatriz Pérez-González, Miguel Bello, Álvaro Gómez-León, Gloria Platero
We extend the standard SSH model to include long range hopping and disorder, and study how the electronic and topological properties are affected. We show that long range hopping can change the symmetry class and the topological invariant, while diagonal and off-diagonal disorder lead to Anderson localization. Interestingly we find that the Lyapunov exponent $γ(E)$ can be linked in two ways to the topological properties in the presence of disorder: Either due to the different response of mid-gap states to increasing disorder, or due to an extra contribution to $γ$ due to the presence of edge modes. Finally we discuss its implications in realistic transport measurements.
Yue Ban, Xi Chen, Gloria Platero
Rapid and efficient preparation, manipulation and transfer of quantum states through an array of quantum dots (QDs) is a demanding requisite task for quantum information processing and quantum computation in solid-state physics. Conventional adiabatic protocols, as coherent transfer by adiabatic passage (CTAP) and its variations, provide slow transfer prone to decoherence, which could lower the fidelity to some extent. To achieve the robustness against decoherence, we propose a protocol of speeding up the adiabatic charge transfer in multi-QD systems, sharing the concept of "Shortcuts to Adiabaticity" (STA). We first apply the STA techniques, including the counterdiabatic driving and inverse engineering, to speed up the direct (long range) transfer between edge dots in triple QDs. Then, we extend our analysis to a multi-dot system. We show how by implementing the modified pulses, fast adiabatic-like charge transport between the outer dots can be eventually achieved without populating intermediate dots. We discuss as well the dependence of the transfer fidelity on the operation time in the presence of dephasing. The proposed protocols for accelerating adiabatic charge transfer directly between the outer dots in a QD array offers a robust mechanism for quantum information processing, by minimizing decoherence and relaxation processes.
Oliva G. Cantu Ros, Gloria Platero, Luis L. Bonilla
We investigate the role that noise plays in the hysteretic dynamics of a suspended nanotube or a graphene sheet subject to an oscillating force. We find that not only the size but also the position of the hysteresis region in these systems can be controlled by noise. We also find that nano-resonators act as noise rectifiers: by increasing the noise in the setup, the resonance width of the characteristic peak in these systems is reduced and, as a result, the quality factor is increased.
Fernando Domínguez, Sigmund Kohler, Gloria Platero
We investigate decoherence in a triple quantum dot in ring configuration in which one dot is coupled to a damped phonon mode, while the other two dots are connected to source and drain, respectively. In the absence of decoherence, single electron transport may get blocked by an electron falling into a superposition decoupled from the drain and known as dark state. Phonon-mediated decoherence affects this superposition and leads to a finite current. We study the current and its shot noise numerically within a master equation approach for the electrons and the dissipative phonon mode. A polaron transformation allows us to obtain a reduced equation for only the dot electrons which provides analytical results in agreement with numerical ones.
Maria Busl, Rafael Sánchez, Gloria Platero
We analyze coherent spin phenomena in triple quantum dots in triangular configuration under crossed DC and AC magnetic fields. In particular, we discuss the interplay between Aharonov-Bohm current oscillations, coherent electron trapping and spin blockade under electron spin resonance conditions. We demonstrate that, for certain field frequencies, AC magnetic fields induce an antiresonant behavior in the current, allowing for both removal and restoration of entangled spin blockaded states by tuning the AC field frequency. Our theoretical predictions indicate how to manipulate spin qubits in a triangular quantum dot array.
Jesus Inarrea, Gloria Platero
In this work we present a theoretical model to study the effect of microwave radiation on Weiss oscillations. In our proposal Weiss oscillations, produced by an spatial periodic potential, are modulated by microwave radiation due to an interference effect between both, space and time-dependent, potentials. The final magnetoresistance depends mainly on the spatial period of the spatial potential and the frequency of radiation. Depending on the values of these parameters, we predict that Weiss oscillations can reach zero resistance states. On the other hand, these dissipationless transport states, created just by radiation, can be destroyed by the additional presence of a periodic space-dependent potential. Then by tuning the spatial period or the radiation frequency, the magnetoresistance can be strongly modified.
Rafael Sánchez, Gloria Platero, Tobias Brandes
We study the counting statistics for electrons and photons being emitted from a driven two level quantum dot. Our technique allows us to calculate their mutual correlations as well. We study different transport configurations by tuning the chemical potential of one of the leads to find that the electronic and photonic fluctuations can be externally manipulated by tuning the AC and transport parameters. We also propose special configurations where electron-photon correlation is maximal meaning that spontaneous emission of photons with a well defined energy is regulated by single electron tunneling. Interesting features are also obtained for energy dependent tunneling.
Álvaro Gómez-León, Gloria Platero
We analyze electron dynamics and topological properties of open double quantum dots (DQDs) driven by circularly polarized ac-magnetic fields. In particular we focus on the system symmetries which can be tuned by the ac-magnetic field. Remarkably, we show that in the electron spin resonance (ESR) configuration, where the magnetic fields in each dot oscillate with a phase difference of $π$, charge localization occurs giving rise to transport blocking at arbitrary intensities of the ac field. The conditions for charge localization are obtained by means of Floquet theory and related with quasienergies degeneracy. We also demonstrate that a topological phase transition can be induced in the adiabatic regime for a phase difference of $π$, either by tuning the coupling between dots or by modifying the intensity of the driving magnetic field.
Anders Mathias Lunde, Gloria Platero
We study the hyperfine interaction between the nuclear spins and the electrons in a HgTe quantum well, which is the prime experimentally realized example of a two-dimensional topological insulator. The hyperfine interaction is a naturally present, internal source of broken time-reversal symmetry from the point of view of the electrons. The HgTe quantum well is described by the so-called Bernevig-Hughes-Zhang (BHZ) model. The basis states of the BHZ model are combinations of both S- and P-like symmetry states, which means that three kinds of hyperfine interactions play a role: (i) The Fermi contact interaction, (ii) the dipole-dipole like coupling and (iii) the electron orbital to nuclear-spin coupling. We provide benchmark results for the forms and magnitudes of these hyperfine interactions within the BHZ model, which give a good starting point for evaluating hyperfine interactions in any HgTe nanostructure. We apply our results to the helical edge states of a HgTe two-dimensional topological insulator and show how their total hyperfine interaction becomes anisotropic and dependent on the orientation of the sample edge within the plane. Moreover, for the helical edge states the hyperfine interactions due to the P-like states can dominate over the S-like contribution in certain circumstances.
Rafael Sánchez, Gloria Platero, Tobias Brandes
We study a two-level quantum dot embedded in a phonon bath and irradiated by a time-dependent ac field and develope a method that allows us to extract simultaneously the full counting statistics of the electronic tunneling and relaxation (by phononic emission) events as well as their correlation. We find that the quantum noise of both the transmitted electrons and the emitted phonons can be controlled by the manipulation of external parameters such as the driving field intensity or the bias voltage.
Rafael Sánchez, Carlos López-Monís, Gloria Platero
We analyze the charge and spin dynamics in a DC biased double quantum dot driven by crossed DC and AC magnetic fields. In this configuration, spatial delocalization due to inter-dot tunnel competes with intra-dot spin rotations induced by the time dependent magnetic field, giving rise to a complicated time dependent behavior of the tunnelling current. When the Zeeman splitting has the same value in both dots and spin flip is negligible, the electrons remain in the triplet subspace (dark subspace) performing coherent spin rotations and the current does not flow. This electronic trapping is removed either by finite spin relaxation or when the Zeeman splitting is different in each quantum dot. In the first case, our results show that measuring the current will allow to get information on the spin relaxation time. In the last case, we will show that applying a resonant bichromatic magnetic field, the electrons become trapped in a coherent superposition of states and electronic transport is blocked. Then, manipulating AC magnetic fields, electrons are driven to perform coherent spin rotations which can be unambiguously detected by direct measurement of the tunneling current.