arXiv subjects

Daniel Domínguez

Publications and source records attributed to Daniel Domínguez.

12 recordsLinked to original sources

arXiv2026

Time-optimal quantum gates with bang-bang control in multilevel systems

We determine the optimal quantum manipulation protocols for implementing high-fidelity, fast single-qubit gates. We demonstrate that the time-optimal pulse sequence is a ``bang-bang'' sequence: discrete pulses of either positive or negative maximum amplitude or zero. The non-adiabatic bang-bang pulse sequence minimizes gate duration providing a speedup for low-frequency architectures. We first derive the protocol for a transversally driven two-level system, extracting exact analytic expressions for minimum gate times. We then extend this framework to general multilevel architectures, identifying conditions that enable the coherent suppression of leakage errors. Using the fluxonium circuit as a representative case study, we optimize $X/2$ and $Y/2$ gates through a combination of discrete bang sequences and continuous waveform smoothing. This approach preserves near-optimal execution speeds while mitigating transitions outside the computational subspace. Open-system simulations demonstrate that these sequences outperform commensurate and resonant pulse schemes across different fluxonium regimes, achieving low-error manipulation significantly faster than standard resonant control, even in the presence of $1/f$ flux noise and dissipation.

quant-ph↗

arXiv2024

Stability limits in two-band superconductor rings

This study explores transitions between states with different winding number in two-band superconducting rings. From the time-dependent Ginzburg-Landau (TDGL) equations for two-component superconductors, we apply linear instability theory and develop a semi-analytical method that provides the critical flux for phase-slip occurrence. The developed method was applied to investigate how the critical flux depends on physical properties, such as band parameters and temperature. Finally, we show the possible existence of a soliton state, in which the phase winding number is different in each condensate.

cond-mat.supr-con↗

arXiv2021

Efficient steady state entanglement generation in strongly driven coupled qubits

We report on a mechanism to optimize the generation of steady-state entanglement in a system of coupled qubits driven by microwave fields. Due to the interplay between Landau-Zener-Stückerlberg pumping involving three levels and a subsequent fast relaxation channel, which is activated by tuning the qubits-reservoir couplings, a maximally entangled state can be populated. This mechanism does not require from the fine-tuning of multiphoton-resonances but depends on the sign of the qubit-qubit coupling. In particular, we find that by a proper design of the system parameters and the driving protocol, the two-qubits steady-state concurrence can attain values close to 1 in a wide range of driving amplitudes. Our results may be useful to gain further insight into entanglement control and manipulation in dissipative quantum systems exposed to strong driving.

quant-ph↗

arXiv2020

Quantum emulation of coherent backscattering in a system of superconducting qubits

In condensed matter systems, coherent backscattering and quantum interference in the presence of time-reversal symmetry lead to well-known phenomena such as weak localization (WL) and universal conductance fluctuations (UCF). Here we use multi-pass Landau-Zener transitions at the avoided crossing of a highly-coherent superconducting qubit to emulate these phenomena. The average and standard deviation of the qubit transition rate exhibit a dip and peak when the driving waveform is time-reversal symmetric, analogous to WL and UCF, respectively. The higher coherence of this qubit enabled the realization of both effects, in contrast to earlier work arXiv:1204.6428, which successfully emulated UCF, but did not observe WL. This demonstration illustrates the use of non-adiabatic control to implement quantum emulation with superconducting qubits.

cond-mat.mes-hall↗

arXiv2020

Landau-Zener-Stückelberg Interferometry in dissipative Circuit Quantum Electrodynamics

We study Landau-Zener-Stückelberg (LZS) interferometry in a cQED architecture under effects of dissipation. To be specific, we consider a superconducting qubit driven by a dc+ac signal and coupled to a transmission line resonator, but our results are valid for general qubit-resonators devices. To take the environment into account, we assume that the resonator is coupled to an ohmic quantum bath. The Floquet-Born-Markov master equation is numerically solved to obtain the dynamics of the system for arbitrary amplitude of the drive and different time scales. We unveil important differences in the resonant patterns between the Strong Coupling and Ultra Strong Coupling regimes in the qubit-resonator interaction, which are mainly due to the magnitude of photonic gaps in the energy spectrum of the system. We identify in the LZS patterns the contribution of the qubit gap and the photonic gaps, showing that for large driving amplitudes the patterns present a weaving structure due to the combined intercrossing of the different gaps contributions.

quant-ph↗

arXiv2017

Driving controlled entanglement in coupled flux qubits

We study the manipulation of quantum entanglement by periodic external fields. As an entanglement measure we compute numerically the concurrence of two flux qubits coupled inductively and/or capacitively, both driven by a dc+ac magnetic flux. Also we find an analytical lower bound for the concurrence, where the dominant terms correspond to the concurrence in the Floquet states. We show that it is possible to create or destroy entanglement in a controlled way by tuning the system at or near multiphoton resonances. We find that when the driving term of the Hamiltonian does not commute with the qubit-qubit interaction term, the control of the entanglement induced by the driving field is more robust in parameter space. This implies that capacitively coupled two flux qubits are more convenient for controlling entanglement through ac driving fluxes.

cond-mat.mes-hall↗

arXiv2016

Mesoscopic fluctuations in biharmonically driven flux qubits

We investigate flux qubits driven by a biharmonic magnetic signal, with a phase lag that acts as an effective time reversal broken parameter. The driving induced transition rate between the ground and the excited state of the flux qubit can be thought as an effective transmitance, profiting from a direct analogy between interference effects at avoided level crossings and scattering events in disordered electronic systems. For time scales prior to full relaxation but large compared to the decoherence time, this characteristic rate has been accessed experimentally and its sensitivity with both the phase lag and the dc flux detuning explored. In this way signatures of Universal Conductance Fluctuations-like effects have recently been analized in flux qubits and compared with a phenomenological model that only accounts for decoherence, as a classical noise. We here solve the full dynamics of the driven flux qubit in contact with a quantum bath employing the Floquet Markov Master equation. Within this formalism relaxation and decoherence rates result strongly dependent on both the phase lag and the dc flux detuning. Consequently, the associated pattern of fluctuations in the characteristic rates display important differences with those obtained within the mentioned phenomenological model. In particular we demonstrate the Weak Localization-like effect in the averages values of the relaxation rate. Our predictions can be tested for accessible, but longer time scales than the current experimental times.

cond-mat.mes-hall↗

arXiv2014

Symmetry for the duration of entropy-consuming intervals

We introduce the violation fraction $\upsilon$ as the cumulative fraction of time that a mesoscopic system spends consuming entropy at a single trajectory in phase space. We show that the fluctuations of this quantity are described in terms of a symmetry relation reminiscent of fluctuation theorems, which involve a function, $Φ$, which can be interpreted as an entropy associated to the fluctuations of the violation fraction. The function $Φ$, when evaluated for arbitrary stochastic realizations of the violation fraction, is odd upon the symmetry transformations which are relevant for the associated stochastic entropy production. This fact leads to a detailed fluctuation theorem for the probability density function of $Φ$. We study the steady-state limit of this symmetry in the paradigmatic case of a colloidal particle dragged by optical tweezers through an aqueous solution. Finally, we briefly discuss on possible applications of our results for the estimation of free-energy differences from single molecule experiments.

cond-mat.stat-mech↗

arXiv2014

Duration of local violations of the second law of thermodynamics along single trajectories in phase space

We define the {\it violation fraction} $ν$ as the cumulative fraction of time that the entropy change is negative during single realizations of processes in phase space. This quantity depends both on the number of degrees of freedom $N$ and the duration of the time interval $τ$. In the large-$τ$ and large-$N$ limit we show that, for ergodic and microreversible systems, the mean value of $ν$ scales as $\langleν(N,τ)\rangle\sim\big(τN^{\frac{1}{1+α}}\big)^{-1}$. The exponent $α$ is positive and generally depends on the protocol for the external driving forces, being $α=1$ for a constant drive. As an example, we study a nontrivial model where the fluctuations of the entropy production are non-Gaussian: an elastic line driven at a constant rate by an anharmonic trap. In this case we show that the scaling of $\langle ν\rangle$ with $N$ and $τ$ agrees with our result. Finally, we discuss how this scaling law may break down in the vicinity of a continuous phase transition.

cond-mat.stat-mech↗

arXiv2010

Large Amplitude Harmonic Driving of Highly Coherent Flux Qubits

The device for the Josephson flux qubit (DJFQ) can be considered as a solid state artificial atom with multiple energy levels. When a large amplitude harmonic excitation is applied to the system, transitions at the energy levels avoided crossings produce visible changes in the qubit population over many driven periods that are accompanied by a rich pattern of interference phenomena. We present a Floquet treatment of the periodically time-dependent Schrödinger equation of the strongly driven qubit beyond the standard two levels approach. For low amplitudes, the average probability of a given sign of the persistent current qubit exhibits, as a function of the static flux detuning and the driving amplitude, Landau-Zener-Stückelberg interference patterns that evolve into complex diamond-like patterns for large amplitudes. In the case of highly coherent flux qubits we find that the higher order diamonds can not be simply described relying on a two-level approximations. In addition we propose a new spectroscopic method based on starting the system in the first excited state instead of in the ground state, which can give further information on the energy level spectrum and dynamics in the case of highly coherent flux qubits. We compare our numerical results with recent experiments that perform amplitude spectroscopy to probe the energy spectrum of the artificial atom.

cond-mat.supr-con↗

arXiv2006

Nonequilibrium structures and dynamic transitions in driven vortex lattices with disorder

We review our studies of elastic lattices driven by an external force $F$ in the presence of random disorder, which correspond to the case of vortices in superconducting thin films driven by external currents. Above a critical force $F_c$ we find two dynamical phase transitions at $F_p$ and $F_t$, with $F_c<F_p<F_t$. At $F_p$ there is a transition from plastic flow to smectic flow where the noise is isotropic and there is a peak in the differential resistance. At $F_t$ there is a sharp transition to a frozen transverse solid where both the transverse noise and the diffussion fall down abruptly and therefore the vortex motion is localized in the transverse direction. From a generalized fluctuation-dissipation relation we calculate an effective transverse temperature in the fluid moving phases. We find that the effective temperature decreases with increasing driving force and becomes equal to the equilibrium melting temperature when the dynamic transverse freezing occurs.

cond-mat.supr-con↗

arXiv1994

Non-equilibrium coherent vortex states and subharmonic giant Shapiro steps in Josephson junction arrays

This is a review of recent work on the dynamic response of Josephson junction arrays driven by dc and ac currents. The arrays are modeled by the resistively shunted Josephson junction model, appropriate for proximity effect junctions, including self-induced magnetic fields as well as disorder. The relevance of the self-induced fields is measured as a function of a parameter $κ=λ_L/a$, with $λ_L$ the London penetration depth of the arrays, and $a$ the lattice spacing. The transition from Type II ($κ>1$) to Type I ($κ<1$) behavior is studied in detail. We compare the results for models with self, self+nearest-neighbor, and full inductance matrices. In the $κ=\infty$ limit, we find that when the initial state has at least one vortex-antivortex pair, after a characteristic transient time these vortices unbind and {\it radiate} other vortices. These radiated vortices settle into a parity-broken, time-periodic, {\em axisymmetric coherent vortex state} (ACVS), characterized by alternate rows of positive and negative vortices lying along a tilted axis. The ACVS produces subharmonic steps in the current voltage (IV) characteristics, typical of giant Shapiro steps. For finite $κ$ we find that the IV's show subharmonic giant Shapiro steps, even at zero external magnetic field. We find that these subharmonic steps are produced by a whole family of coherent vortex oscillating patterns, with their structure changing as a function of $κ$. In general, we find that these patterns are due to a break down of translational invariance produced, for example, by disorder or antisymmetric edge-fields. The zero field case results are in good qualitative agreement with experiments

cond-mat↗