arXiv subjects

Hugo Terças

Publications and source records attributed to Hugo Terças.

At least 19 recordsLinked to original sources

arXiv2025

Tunable Magnetic Order in Chiral Coupled Spin Chains

We obtain the ground-state phase diagram of two spin chains consisting in a set two-level systems asymmetrically coupled to an XX chain through a chiral interaction. The interaction is parametrized by its magnitude and an angle defined by the relative orientation of the spins in different chains. From the entanglement spectrum, we identify the critical lines separating distinct magnetically ordered phases, with the interaction angle able to shift or fully suppress the transition. By increasing the coupling strength, the systems is driven through a quantum phase transition, leading to the formation of two types of in-plane antiferromagnetic stripes. The interaction strength sets stripe formation, while the angle controls the spins orientations. The chiral interaction also induces a non-trivial finite vector spin chirality with opposite orientation on the chains. We show that the vector spin chirality emerges smoothly from the decoupled limit and occurs for angles different from zero and $π/2$, where collinear order is favored instead.

quant-ph↗

arXiv2025

Photon Bose-Einstein Condensation in Semiconductors: A Quantum Kinetic Theory

Photon condensation in semiconductor microcavities is a transformative technique for engineering quantum states of light at room temperature by tailoring strong but incoherent light-matter interactions. While continuous-wave and electrical pumping offer exceptional prospects for miniaturized quantum photonic technologies, harnessing these requires conceptual advances in understanding nonequilibrium light-matter dynamics in semiconductors. We resolve this challenge through an \textit{ab initio} quantum kinetic theory capturing how Coulomb interactions of optically excited carriers and phonon scattering mediate photon thermalization and condensation in semiconductors. Our microscopic model shows that at high carrier densities, thermalization is dominated by carrier-carrier Coulomb scattering, in clear contrast to the rovibrational relaxation that governs dye-based photon condensates. The theory predicts a rich nonequilibrium phase diagram with thermal, Bose-condensed, multimode, and lasing phases, quantitatively in agreement with recent experiments. Crucially, we identify how cavity detuning controls transitions between equilibrium and gain-dominated regimes, enabling tailored design of coherent light sources. This work thus provides the foundation for semiconductor-based quantum photonic devices operating beyond conventional laser paradigms.

physics.optics↗

arXiv2025

Anisotropy-Induced Magnetic Field Generation in Bidimensional Materials

We investigate an electromagnetic instability in two-dimensional materials arising from an anisotropy of the Fermi surface, utilizing a kinetic model accounting for the effects of the values of temperature, chemical potential and anisotropy ratio, as well as considering both linear and quadratic low-energy band structures. The wavenumber-dependent growth-rate of these modes is derived in the linear regime, and their confinement, contrasting with stable electromagnetic waves in these systems, is described. The generation of structured out-of-plane magnetic fields, as well as their behaviour in saturation, is shown using fully kinetic and non-linear simulations.

cond-mat.mtrl-sci↗

arXiv2025

Normal modes and shockwaves in cold atoms

Numerical methods are developed to simulate the dynamics of atoms in a Magneto-Optic Trap (MOT), based on the fluid description of ultracold gases under laser cooling and magnetic trapping forces. With this model, equilibrium hydrostatic profiles and normal modes are calculated, and numerical results are validated against theoretical predictions. As a test case, shock wave formation due to rapid gas expansion and contraction of the ultracold gas is simulated. The latter is caused by a sudden change of the value of its effective collective charge. Limitations of the current methods and future improvements are discussed. This work provides a foundation for studying numerically complex MOT behaviors and their use as analog simulators for astrophysical phenomena.

cond-mat.quant-gas↗

arXiv2024

Multiplexed quantum repeaters with hot multimode alkali-noble gas memories

We propose a non-cryogenic optical quantum memory for noble-gas nuclear spins based on the Atomic Frequency Comb (AFC) protocol. Owing to the hours-long coherence lifetimes of the noble-gas spins and the large bandwidth provided by the AFC independently of the optical depth, we estimate a time-bandwidth product of up to $9.7 \times 10^{15}$ for a realistic experimental configuration, using alkali-metal atoms as mediators. Leveraging this long-lived multimode memory, we propose a fiber-based quantum repeater scheme that could enable entanglement distribution across distances over $2000 \ \mathrm{km}$ with only $8$ elementary links, operating fully without cryogenics. Finally, we discuss how these quantum memories can enhance rates in satellite quantum communication networks.

quant-ph↗

arXiv2023

Spontaneous Symmetry Breaking of Time-Reversal-Symmetry and Time-Crystal States in Chiral Atomic Systems

We present a theoretical study of the interaction between an atom characterized by a degenerate ground state and a reciprocal environment, such as a semiconductor nanoparticle, without the presence of external bias. Our analysis reveals that the combined influence of the electron's intrinsic spin magnetic moment on the environment and the chiral atomic dipolar transitions may lead to either the spontaneous breaking of time-reversal symmetry or the emergence of time-crystal-like states with remarkably long relaxation times. The different behavior is ruled by the handedness of the precession motion of the atom's spin vector, which is induced by virtual chiral-dipolar transitions. Specifically, when the relative orientation of the precession angular velocity and the electron spin vector is as in a spinning top, the system manifests time-crystal-like states. Conversely, with the opposite relative orientation, the system experiences spontaneous symmetry breaking of time-reversal symmetry. Our findings introduce a novel mechanism for the spontaneous breaking of time-reversal symmetry in atomic systems, and unveil an exciting opportunity to engineer a nonreciprocal response at the nanoscale, exclusively driven by the quantum vacuum fluctuations.

quant-ph↗

arXiv2023

Nonlinear density waves on graphene electron fluids

In graphene, where the electron-electron scattering is dominant, electrons collectively act as a fluid. This hydrodynamic behaviour of charge carriers leads to exciting nonlinear phenomena such as solitary waves and shocks, among others. In the future, such waves might be exploited on plasmonic devices, either for modulation or signal propagation along graphene waveguides. We study the nature of nonlinear perturbations by performing the reductive perturbation method on the hydrodynamic description of graphene electrons, taking into consideration the effect of Bohm quantum potential and odd viscosity. Thus, deriving a dissipative Kadomtsev-Petviashvili equation for the bidimensional flow as well as its unidimensional limit in the form of Korteweg-de Vries-Burgers. The stability analysis of these equations unveils the existence of unstable modes that can be excited and launched through graphene plasmonic devices.

cond-mat.mes-hall↗

arXiv2022

Conductance suppression due to two-stream instability in bilayer graphene

We investigate the electron-hole two-stream instability (or Coulomb drag) in intrinsic bilayer graphene in the hydrodynamic regime, accounting for the effects of temperature, initial drift velocity, magnetic field, and collisions. The threshold drift speed for the onset of instabilities is of the order of the thermal velocity of the carriers. We put in evidence an unprecedented purely electrostatic mechanism leading to current relaxation, giving rise to a well-defined dc longitudinal conductivity $\propto T^{3/2}$. Due to competition between electrostatic and collisional processes, two distinct transport regimes are identified. An analysis on the Hall conductivity revealed that the two-stream instability effects also correct the most recent results obtained within the linear response theory.

cond-mat.mes-hall↗

arXiv2022

B-field induced mixing between Langmuir waves and axions

We present an analytic study of the dispersion relation for an isotropic magnetized plasma interacting with axions. We provide a quantitative picture of the electromagnetic plasma oscillations in both the ultrarelativistic and nonrelativistic regimes and considering both non-degenerate and degenerate media, accounting for the dispersion curves as a function of the plasma temperature and the ratio of the plasma phase velocity to the characteristic velocity of particles. We include the modifications on the Landau damping of plasma waves induced by the presence of the axion field, and we comment on the effects of damping on subluminal plasma oscillations.

hep-ph↗

arXiv2021

Hydrodynamic electrons in Graphene: a viscous boundary-layer description

In this paper we dwell over the study of the boundary layer problem in a hydrodynamical description of the electrons in gated graphene. It has been verified experimentally that this fluid can display non-Poiseuille like flow as reproduced in our numerical simulation. In fact, the velocity profile displays a maximum value close to the boundary and then decreases as it approaches the bulk of the graphene layer. This work aims to present a satisfactory theoretical description of the boundary layer problem in graphene. We found that by using the fluid equations and following a method similar to that for deriving Blasius' equation, a non-linear model can be obtained whose solutions display the maximum values of velocity near the edges of the graphene layer. We argue that such a non-monotonic model and behaviour can shed some light on the subject of non-topological edge currents in graphene.

cond-mat.mes-hall↗

arXiv2021

Hydrodynamical study of Terahertz emission in magnetized graphene field-effect transistors

Several hydrodynamic descriptions of charge transport in graphene have been presented in the late years. We discuss a general hydrodynamic model governing the dynamics of a two-dimensional electron gas in a magnetized field-effect transistor in the slow drift regime. The Dyakonov--Shur instability is investigated including the effect of weak magnetic fields (i.e. away from Landau levels). We show that the gap on the dispersion relation prevents the instability to reach the lower frequencies thus imposing a limit on the Mach number of the electronic flow. Furthermore, we discuss that the presence of the external magnetic field decreases the growth rate of the instability, as well as the saturation amplitude. The numerical results from our simulations and the presented higher order dynamic mode decomposition support such reasoning.

cond-mat.mes-hall↗

arXiv2020

Turbulence Excitation in Counter-Streaming Paraxial Superfluids of Light

Turbulence in the quantum (superfluid) regime, similarly to its classical counterpart, continues to attract a great deal of scientific inquiry, due to the yet high number of unresolved problems. While turbulent states can be routinely created in degenerate atomic gases, there is no generic scheme to produce turbulence in fluids of light. Under paraxial propagation, light in bulk nonlinear media behaves as a two-dimensional superfluid, described by a nonlinear Schrödinger equation formally equivalent to the Gross-Pitaevskii model of a weakly interacting Bose gas, where photon-photon interactions are mediated by a third order (Kerr) nonlinearity. Here, we develop the theory describing the onset of a kinetic instability when two paraxial optical fluids with different streaming velocities interact via the optical nonlinearity. From numerical simulations of the nonlinear Schrödinger equation, we further characterize the onset of the instability and describe its saturation in the form of vortex nucleation and excitation of turbulence. The experimental observation of such effects is also discussed. The class of instabilities described here thus provide a natural route towards the investigation of quantum (superfluid) turbulence, structure formation and out-of-equilibrium dynamics in superfluids of light.

quant-ph↗

arXiv2019

Terahertz Laser Combs in Graphene Field-Effect Transistors

Electrically injected terahertz (THz) radiation sources are extremely appealing given their versatility and miniaturization potential, opening the venue for integrated-circuit THz technology. In this work, we show that coherent THz frequency combs in the range $0.5~\mathrm{THz}<ω/2π<10~\mathrm{THz}$ can be generated making use of graphene plasmonics. Our setup consists of a graphene field-effect transistor with asymmetric boundary conditions, with the radiation originating from a plasmonic instability that can be controlled by direct current injection. We put forward a combined analytical and numerical analysis of the graphene plasma hydrodynamics, showing that the instability can be experimentally controlled by the applied gate voltage and the injected current. Our calculations indicate that the emitted THz comb exhibits appreciable temporal coherence ($g^{(1)}(τ)>0.6$) and radiant emittance ($10^{7}\,\mathrm{Wm^{-2}}$). This makes our scheme an appealing candidate for a graphene-base THz laser source. Moreover, a mechanism for the instability amplification is advanced for the case of substrates with varying electric permitivitty, which allows to overcome eventual limitations associated with the experimental implementation.

cond-mat.mes-hall↗

arXiv2019

Slow sound in matter-wave dark soliton gases

We demonstrate the possibility of drastically reducing the velocity of phonons in quasi one-dimensional Bose-Einstein condensates. Our scheme consists of a dilute dark-soliton "gas" that provide the trapping for the impurities that surround the condensate. We tune the interaction between the impurities and the condensate particles in such a way that the dark solitons result in an array of {\it qutrits} (three-level structures). We compute the phonon-soliton coupling and investigate the decay rates of these three-level qutrits inside the condensate. As such, we are able to reproduce the phenomenon of acoustic transparency based purely on matter wave phononics, in analogy with the electric induced transparency (EIT) effect in quantum optics. Thanks to the unique properties of transmission and dispersion of dark solitons, we show that the speed of an acoustic pulse can be brought down to $\sim 5$ $μ$m/s, $\sim 10^3$ times lower than the condensate sound speed. This is a record value that greatly underdoes most of the reported studies for phononic platforms. We believe the present work could pave the stage for a new generation of "stopped-sound" based quantum information protocols.

quant-ph↗

arXiv2019

Spontaneous generation of phononic entanglement in quantum dark-soliton qubits

We show that entanglement between two solitary qubits in quasi-one-dimensional Bose-Einstein condensates can be spontaneously generated due to quantum fluctuations. Recently we have shown that dark solitons are an appealing platform for qubits thanks to their appreciable long lifetime. We investigate the spontaneous generation of entanglement between dark-soliton qubits in the dissipative process of spontaneous emission. By driving the qubits with the help of oscillating magnetic field gradients, we observe the formation of long distance steady-state concurrence. Our results suggest that dark-soliton qubits are good candidates for quantum information protocols based purely on matter-wave phononics.

quant-ph↗

arXiv2018

Roton-Induced Trapping in Strongly Correlated Rydberg Gases

Atoms excited into high-lying Rydberg states and under strong dipole-dipole interactions exhibit phenomena associated with highly correlated and complex systems. We perform first principles numerical simulations on the dynamics of such systems. The emergence of a roton minimum in the excitation spectrum, as expected in strongly correlated gases and accurately described by Feynman's theory of liquid helium, is shown to significantly inhibit particle transport, with a strong suppression of the diffusion coefficient, due to the emerging spatial order. We also demonstrate how the ability to temporally tune the interaction strength among Rydberg atoms can be used in order to overcome the effects of disorder induced heating, allowing the study of unprecedented highly coupled regimes.

physics.atom-ph↗

arXiv2018

Entanglement sudden death and revival in quantum dark-soliton qubits

We study the finite time entanglement dynamics between two dark soliton qubits due to quantum fluctuations in a quasi one dimensional Bose-Einstein condensates. Recently, dark solitons are proved to be an appealing platform for qubits due to their appreciably long life time. We explore the entanglement decay for an entangled state of two phonon coherences and the qubits to be in the diagonal basis of so called Dicke states. We observe the collapse and revival of the entanglement, depending critically on the collective damping term but independent of the qubit-qubit interaction for both the initial states. The collective behavior of the dark soliton qubits demonstrate the dependence of entanglement evolution on the interatomic distance.

quant-ph↗

arXiv2017

Emergence of Spatial Order in Highly Interacting Rydberg Gases

We describe the emergence of strong spatial correlations, akin to liquid-like behavior and crystallization effects, in low (one and two) dimensional gases of cold Rydberg atoms. The presence of an external electric field permanently polarizes the atoms, which became highly correlated due to the long-range dipole-dipole interaction. We describe a theoretical approach particularly suited for strongly coupled systems and numerically obtain both the two-particle distribution function and the static structure factor. The experimental implementation of such highly interacting systems is discussed, including detailed calculations of the interaction strength for different Rydberg states. The results provide new insights into many-body effects associated with strongly interacting Rydberg atoms, including the possibility of observing novel highly ordered phases.

physics.atom-ph↗