arXiv subjects

A. Zamora

Publications and source records attributed to A. Zamora.

13 recordsLinked to original sources

arXiv2022

Searching for the Kardar-Parisi-Zhang phase in microcavity polaritons

Recent approximate analytical work has suggested that, at certain values of the external pump, the optical parametric oscillator (OPO) regime of microcavity polaritons may provide a long sought realisation of Kardar-Parisi-Zhang (KPZ) physics in 2D. Here, by solving the full microscopic model numerically using the truncated Wigner method, we prove that this predicted KPZ phase for OPO is robust against the appearance of vortices or other effects. For those pump strengths, spatial correlations in the direction perpendicular to the pump, and the distribution of phase fluctuations, match closely to the forms characteristic of the KPZ universality. This strongly indicates the viability of observing KPZ behaviour in future polariton OPO experiments.

cond-mat.quant-gas↗

arXiv2020

Kibble-Zurek mechanism in driven-dissipative systems crossing a non-equilibrium phase transition

The Kibble-Zurek mechanism constitutes one of the most fascinating and universal phenomena in the physics of critical systems. It describes the formation of domains and the spontaneous nucleation of topological defects when a system is driven across a phase transition exhibiting spontaneous symmetry breaking. While a characteristic dependence of the defect density on the speed at which the transition is crossed was observed in a vast range of equilibrium condensed matter systems, its extension to intrinsically driven-dissipative systems is a matter of ongoing research. In this work we numerically confirm the Kibble-Zurek mechanism in a paradigmatic family of driven-dissipative quantum systems, namely exciton-polaritons in microcavities. Our findings show how the concepts of universality and critical dynamics extend to driven-dissipative systems that do not conserve energy or particle number nor satisfy a detailed balance condition.

cond-mat.mes-hall↗

arXiv2020

Vortex dynamics in a compact Kardar-Parisi-Zhang system

We study the dynamics of vortices in a two-dimensional, non-equilibrium system, described by the compact Kardar-Parisi-Zhang equation, after a sudden quench across the critical region. Our exact numerical solution of the phase-ordering kinetics shows that the unique interplay between non-equilibrium and the variable degree of spatial anisotropy leads to different critical regimes. We provide an analytical expression for the vortex evolution, based on scaling arguments, which is in agreement with the numerical results, and confirms the form of the interaction potential between vortices in this system.

cond-mat.stat-mech↗

arXiv2018

Properties of the signal mode in the polariton OPO regime

Theoretical analyses of the polariton optical parametric oscillator (OPO) regime often rely on a mean field approach based on the complex Gross-Pitaevskii equations in a three-mode approximation, where only three momentum states, the signal, pump and idler, are assumed to be significantly occupied. This approximation, however, lacks a constraint to uniquely determine the signal and idler momenta. In contrast, multimode numerical simulations and experiments show a unique momentum structure for the OPO states. In this work we show that an estimate for the signal momentum chosen by the system can be found from a simple analysis of the pump-only configuration. We use this estimate to investigate how the chosen signal momentum depends on the properties of the drive.

cond-mat.quant-gas↗

arXiv2017

Dynamical critical exponents in driven-dissipative quantum systems

We study the phase-ordering of parametrically and incoherently driven microcavity polaritons after an infinitely rapid quench across the critical region. We confirm that the system, despite its driven-dissipative nature, fulfils dynamical scaling hypothesis for both driving schemes by exhibiting self-similar patterns for the two-point correlator at late times of the phase ordering. We show that polaritons are characterised by the dynamical critical exponent z ~ 2 with topological defects playing a fundamental role in the dynamics, giving logarithmic corrections both to the power-law decay of the number of vortices and to the associated growth of the characteristic length-scale.

cond-mat.quant-gas↗

arXiv2017

Tuning across Universalities with a Driven Open Condensate

Driven-dissipative systems in two dimensions can differ substantially from their equilibrium counterparts. In particular, a dramatic loss of off-diagonal algebraic order and superfluidity has been predicted to occur due to the interplay between coherent dynamics and external drive and dissipation in the thermodynamic limit. We show here that the order adopted by the system can be substantially altered by a simple, experimentally viable, tuning of the driving process. More precisely, by considering the long-wavelength phase dynamics of a polariton quantum fluid in the optical parametric oscillator regime, we demonstrate that simply changing the strength of the pumping mechanism in an appropriate parameter range can substantially alter the level of effective spatial anisotropy induced by the driving laser, and move the system into distinct scaling regimes. These include: (i) the classic algebraically ordered superfluid below the Berezinskii-Kosterlitz-Thouless (BKT) transition, as in equilibrium; (ii) the non-equilibrium, long-wave-length fluctuation dominated Kardar-Parisi-Zhang (KPZ) phase; and the two associated topological defect dominated disordered phases caused by proliferation of (iii) entropic BKT vortex-antivortex pairs or (iv) repelling vortices in the KPZ phase. Further, by analysing the renormalization group flow in a finite system, we examine the length scales associated with these phases, and assess their observability in current experimental conditions.

cond-mat.quant-gas↗

arXiv2013

Spin liquid phases of alkaline-earth-metal atoms at finite temperature

We study spin liquid phases of spin-5/2 alkaline earth atoms on a honeycomb lattice at finite temperatures. Our analysis is based on a Gutzwiller projection variational approach recast to a path-integral formalism. In the framework of a saddle-point approximation we determine spin liquid phases with lowest free energy and study their temperature dependence. We identify a critical temperature, where all the spin liquid phases melt and the system goes to the paramagnetic phase. We also study the stability of the saddle-point solutions and show that a time-reversal symmetry breaking state, a so called chiral spin liquid phase is realized even at finite temperatures. We also determine the spin structure factor, which, in principle, is an experimentally measurable quantity and is the basic tool to map the spectrum of elementary excitations of the system.

cond-mat.quant-gas↗

arXiv2013

Optical Abelian Lattice Gauge Theories

We discuss a general framework for the realization of a family of abelian lattice gauge theories, i.e., link models or gauge magnets, in optical lattices. We analyze the properties of these models that make them suitable to quantum simulations. Within this class, we study in detail the phases of a U(1)-invariant lattice gauge theory in 2+1 dimensions originally proposed by Orland. By using exact diagonalization, we extract the low-energy states for small lattices, up to 4x4. We confirm that the model has two phases, with the confined entangled one characterized by strings wrapping around the whole lattice. We explain how to study larger lattices by using either tensor network techniques or digital quantum simulations with Rydberg atoms loaded in optical lattices where we discuss in detail a protocol for the preparation of the ground state. We also comment on the relation between standard compact U(1) LGT and the model considered.

cond-mat.quant-gas↗

arXiv2011

Layered Quantum Hall Insulators with Ultracold Atoms

We consider a generalization of the 2-dimensional (2D) quantum-Hall insulator to a non-compact, non-Abelian gauge group, the Heisenberg-Weyl group. We show that this kind of insulator is actually a layered 3D insulator with nontrivial topology. We further show that nontrivial combinations of quantized transverse conductivities can be engineered with the help of a staggered potential. We investigate the robustness and topological nature of this conductivity and connect it to the surface modes of the system. We also propose a simple experimental realization with ultracold atoms in 3D confined to a 2D square lattice with the third dimension being mapped to a gauge coordinate.

cond-mat.quant-gas↗

arXiv2010

Electrodynamics a la Horava

We study an electrodynamics consistent with anisotropic transformations of space-time with an arbitrary dynamic exponent $z$. The equations of motion and conserved quantities are explicitly obtained. We show that the propagator of this theory can be regarded as a quantum correction to the usual propagator. Moreover we obtain that both the momentum and angular momentum are not modified, but their conservation laws do change. We also show that in this theory the speed of light and the electric charge are modified with $z$. The magnetic monopole in this electrodynamics and its duality transformations are also investigated. For that we found that there exists a dual electrodynamics, with higher derivatives in the electric field, invariant under the same anisotropic transformations.

hep-th↗

arXiv2010

Two-Loop Crossover Scaling Functions of the O(N) Model

Using Environmentally Friendly Renormalization, we present an analytic calculation of the series for the renormalization constants that describe the equation of state for the $O(N)$ model in the whole critical region. The solution of the beta-function equation, for the running coupling to order two loops, exhibits crossover between the strong coupling fixed point, associated with the Goldstone modes, and the Wilson-Fisher fixed point. The Wilson functions $γ_λ$, $γ_ϕ$ and $γ_{ϕ^2}$, and thus the effective critical exponents associated with renormalization of the transverse vertex functions, also exhibit non-trivial crossover between these fixed points.

cond-mat.stat-mech↗

arXiv2005

Correlation lengths for vortex-liquid freezing in a model of layered high-temperature superconductor

We present results from extensive numerical simulations on the Lawrence-Doniach model within the lowest Landau level approximation in the unconventional spherical geometry. We study the in-layer pancake vortex density-density correlation function (intra-layer structure factor) and the layer-to-layer order-parameter correlation function along the direction perpendicular to the layers. Our results show strong evidence for the existence of a single first-order phase transition at which both inter-layer coupling and appearance of crystalline order in the in-layer vortex correlations take place as temperature is lowered.

cond-mat.supr-con↗

arXiv2005

The one-loop elastic coefficients for the Helfrich membrane in higher dimensions

Using a covariant geometric approach we obtain the effective bending couplings for a 2-dimensional rigid membrane embedded into a $(2+D)$-dimensional Euclidean space. The Hamiltonian for the membrane has three terms: The first one is quadratic in its mean extrinsic curvature. The second one is proportional to its Gaussian curvature, and the last one is proportional to its area. The results we obtain are in agreement with those finding that thermal fluctuations soften the 2-dimensional membrane embedded into a 3-dimensional Euclidean space.

cond-mat.soft↗