arXiv subjects

Miguel Bello

Publications and source records attributed to Miguel Bello.

18 recordsLinked to original sources

arXiv2025

Mesoscopic cavity quantum electrodynamics with phase-disordered emitters in a Kerr nonlinear resonator

The field of cavity quantum electrodynamics (QED) has seen a recent resurgence of interest in few- and many-body physics owing to the realization that the breaking of symmetries and the presence of disorder can give rise to entirely new phenomena. Here we demonstrate a few-emitter cavity QED system capable of realizing new Hamiltonians in quantum optics based on breaking of symmetries and the realization of an in situ Kerr nonlinearity. Our experiment relies on a high-finesse silicon carbide whispering gallery mode resonator hosting an ensemble of silicon vacancy color centers. The simultaneous presence of spectral and spatial disorder of the mesoscopic atom system gives rise to emergent chirality, and the optical nonlinearity of the silicon carbide host crystal enables the observation of atom-photon correlations induced by a four-photon nonlinear process. This work demonstrates the potential for solid state defect systems to realize emerging proposals and to study fundamental physics in quantum electrodynamics.

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arXiv2024

Effects of retardation on many-body superradiance in chiral waveguide QED

We study the superradiant decay of a chain of atoms coupled to a chiral waveguide, focusing on the regime of non-negligible photon propagation time. Using an exact master equation description which accounts for delay effects, we obtain evidence to suggest that competition between collective decay and retardation leads to the emergence of an effective maximum number of atoms able to contribute to the superradiant dynamics, resulting in a plateau of the peak emission rate. To develop this analysis further, we investigate the inter-atomic correlations to find features consistent with the formation of individual superradiant domains. Moreover, we find that retardation can also result in persistent oscillatory atomic dynamics accompanied by a periodic sequence of emission bursts.

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arXiv2023

Fermionic matter-wave quantum optics with cold-atom impurity models

Motivated by recent cold-atom realisations of matter-wave waveguide QED, we study simple fermionic impurity models and discuss fermionic analogues of several paradigmatic phenomena in quantum optics, including formation of non-trivial bound states, (matter-wave) emission dynamics, and collective dissipation. For a single impurity, we highlight interesting ground-state features, focusing in particular on real-space signatures of an emergent length scale associated with an impurity screening cloud. We also present novel non-Markovian many-body effects in the quench dynamics of single- and multiple-impurity systems, including fractional decay around the Fermi level and multi-excitation population trapping due to bound states in the continuum.

quant-ph↗

arXiv2023

Hermitian and Non-Hermitian Topology from Photon-Mediated Interactions

Light can mediate effective dipole-dipole interactions between atoms or quantum emitters coupled to a common environment. Exploiting them to tailor a desired effective Hamiltonian can have major applications and advance the search for many-body phases. Quantum technologies are mature enough to engineer large photonic lattices with sophisticated structures coupled to quantum emitters. In this context, a fundamental problem is to find general criteria to tailor a photonic environment that mediates a desired effective Hamiltonian of the atoms. Among these criteria, topological properties are of utmost importance since an effective atomic Hamiltonian endowed with a non-trivial topology can be protected against disorder and imperfections. Here, we find general theorems that govern the topological properties (if any) of photon-mediated Hamiltonians in terms of both Hermitian and non-Hermitian topological invariants, thus unveiling a system-bath topological correspondence. The results depend on the number of emitters relative to the number of resonators. For a photonic lattice where each mode is coupled to a single quantum emitter, the Altland-Zirnbauer classification of topological insulators allows us to link the topology of the atoms to that of the photonic bath: we unveil the phenomena of topological preservation and reversal to the effect that the atomic topology can be the same or opposite to the photonic one, depending on Hermiticity of the photonic system and on the parity of the spatial dimension. As a consequence, the bulk-edge correspondence implies the existence of atomic boundary modes with the group velocity opposite to the photonic ones in a 2D Hermitian topological system. If there are fewer emitters than photonic modes, the atomic system is less constrained and no general photon-atom topological correspondence can be found. We show this with two counterexamples.

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arXiv2022

Topological Effects in Two-Dimensional Quantum Emitter Systems

In this work we discuss particular effects that take place in systems of quantum emitters coupled to two-dimensional bosonic topological insulators. For a single emitter coupled to the Haldane model, we find a "fragile" quasibound state that makes the emitter dynamics very sensitive to the model's parameters, and gives rise to effective long-range interactions that break time-reversal symmetry. We then discuss one-dimensional arrangements of emitters, emitter line defects, and how the topology of the bath affects the effective polariton models that appear in the weak-coupling regime when the emitters are spectrally tuned to a bandgap. In the Harper-Hofstadter model we link the non-monotonic character of the effective interactions to the Chern numbers of the surrounding energy bands, while in the Haldane model we show that the effective models are either gapless or not depending on the topology of the bath. Last, we discuss how the presence of emitters forming an ordered array, an emitter superlattice, can produce polariton models with non-trivial Chern numbers, and also modify the topology of the photonic states in the bath.

cond-mat.mes-hall↗

arXiv2022

Bound states and photon emission in non-Hermitian nanophotonics

We establish a general framework for studying the bound states and the photon-emission dynamics of quantum emitters coupled to structured nanophotonic lattices with engineered dissipation (loss). In the single-excitation sector, the system can be described exactly by a non-Hermitian formalism. We have pointed out in the accompanying letter [Gong \emph{et al}., arXiv:2205.05479] that a single emitter coupled to a one-dimensional non-Hermitian lattice may already exhibit anomalous behaviors without Hermitian counterparts. Here we provide further detail on these observations. We also present several additional examples on the cases with multiple quantum emitters or in higher dimensions. Our work unveils the tip of the iceberg of the rich non-Hermitian phenomena in dissipative nanophotonic systems.

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arXiv2022

Anomalous Behaviors of Quantum Emitters in Non-Hermitian Baths

Both non-Hermitian systems and the behaviour of emitters coupled to structured baths have been studied intensely in recent years. Here we study the interplay of these paradigmatic settings. In a series of examples, we show that a single quantum emitter coupled to a non-Hermitian bath displays a number of unconventional behaviours, many without Hermitian counterpart. We first consider a unidirectional hopping lattice whose complex dispersion forms a loop. We identify peculiar bound states inside the loop as a manifestation of the non-Hermitian skin effect. In the same setting, emitted photons may display spatial amplification markedly distinct from free propagation, which can be understood with the help of the generalized Brillouin zone. We then consider a nearest-neighbor lattice with alternating loss. We find that the long-time emitter decay always follows a power law, which is usually invisible for Hermitian baths. Our work points toward a rich landscape of anomalous quantum emitter dynamics induced by non-Hermitian baths.

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arXiv2021

Spin many-body phases in standard and topological waveguide QED simulators

Quantum spin models find applications in many different areas, such as spintronics, high-Tc superconductivity, and even complex optimization problems. However, studying their many-body behaviour, especially in the presence of frustration, represents an outstanding computational challenge. To overcome it, quantum simulators based on cold, trapped atoms and ions have been built, shedding light already on many non-trivial phenomena. Unfortunately, the models covered by these simulators are limited by the type of interactions that appear naturally in these systems. Waveguide QED setups have recently been pointed out as a powerful alternative due to the possibility of mediating more versatile spin-spin interactions with tunable sign, range, and even chirality. Yet, despite their potential, the many-body phases emerging from these systems have only been scarcely explored. In this manuscript, we fill this gap analyzing the ground states of a general class of spin models that can be obtained in such waveguide QED setups. Importantly, we find novel many-body phases different from the ones obtained in other platforms, e.g., symmetry-protected topological phases with large-period magnetic orderings, and explain the measurements needed to probe them.

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arXiv2021

Entangling nuclear spins in distant quantum dots via an electron bus

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.

cond-mat.mes-hall↗

arXiv2021

Qubit-photon bound states in topological waveguides with long-range hoppings

Quantum emitters interacting with photonic band-gap materials lead to the appearance of qubit-photon bound states that mediate decoherence-free, tunable emitter-emitter interactions. Recently, it has been shown that when these band-gaps have a topological origin, like in the photonic SSH model, these qubit-photon bound states feature chiral shapes and certain robustness to disorder. In this work, we consider a more general situation where the emitters interact with an extended SSH photonic model with longer range hoppings that displays a richer phase diagram than its nearest-neighbour counterpart, e.g., phases with larger winding numbers. In particular, we first study the features of the qubit-photon bound states when the emitters couple to the bulk modes in the different phases, discern its connection with the topological invariant, and show how to further tune their shape through the use of giant atoms, i.e., non-local couplings. Then, we consider the coupling of emitters to the edge modes appearing in the different topological phases. Here, we show that giant atoms dynamics can distinguish between all different topological phases, as compared to the case with local couplings. Finally, we provide a possible experimental implementation of the model based on periodic modulations of circuit QED systems. Our work enriches the understanding of the interplay between topological photonics and quantum optics.

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arXiv2020

Quantum dynamics in low-dimensional topological systems

The discovery of topological matter has revolutionized the field of condensed matter physics giving rise to many interesting phenomena, and fostering the development of new quantum technologies. In this thesis we study the quantum dynamics that take place in low dimensional topological systems, specifically 1D and 2D lattices that are instances of topological insulators. First, we study the dynamics of doublons, bound states of two fermions that appear in systems with strong Hubbard-like interactions. We also include the effect of periodic drivings and investigate how the interplay between interaction and driving produces novel phenomena. Prominent among these are the disappearance of topological edge states in the SSH-Hubbard model, the sublattice confinement of doublons in certain 2D lattices, and the long-range transfer of doublons between the edges of any finite lattice. Then, we apply our insights about topological insulators to a rather different setup: quantum emitters coupled to the photonic analogue of the SSH model. In this setup we compute the dynamics of the emitters, regarding the photonic SSH model as a collective structured bath. We find that the topological nature of the bath reflects itself in the photon bound states and the effective dipolar interactions between the emitters. Also, the topology of the bath affects the single-photon scattering properties. Finally, we peek into the possibility of using these kind of setups for the simulation of spin Hamiltonians and discuss the different ground states that the system supports.

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arXiv2020

Quantum electrodynamics in a topological waveguide

While designing the energy-momentum relation of photons is key to many linear, non-linear, and quantum optical phenomena, a new set of light-matter properties may be realized by employing the topology of the photonic bath itself. In this work we investigate the properties of superconducting qubits coupled to a metamaterial waveguide based on a photonic analog of the Su-Schrieffer-Heeger model. We explore topologically-induced properties of qubits coupled to such a waveguide, ranging from the formation of directional qubit-photon bound states to topology-dependent cooperative radiation effects. Addition of qubits to this waveguide system also enables direct quantum control over topological edge states that form in finite waveguide systems, useful for instance in constructing a topologically protected quantum communication channel. More broadly, our work demonstrates the opportunity that topological waveguide-QED systems offer in the synthesis and study of many-body states with exotic long-range quantum correlations.

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arXiv2019

Sublattice dynamics and quantum state transfer of doublons in two-dimensional lattices

We study the dynamics of two strongly-interacting fermions moving in 2D lattices under the action of a periodic electric field, both with and without a magnetic flux. Due to the interaction, these particles bind together forming a doublon. We derive an effective Hamiltonian that permits us to understand the interplay between the interaction and the driving, revealing surprising effects that constrain the movement of the doublons. We show that it is possible to confine doublons to just the edges of the lattice, and also to a particular sublattice, if different sites in the unit cell have different coordination numbers. Contrary to what happens in 1D systems, here we observe the coexistence of both topological and Shockley-like edge states when the system is in a non-trivial phase.

cond-mat.quant-gas↗

arXiv2019

Doublon lifetimes in dissipative environments

We study the dissipative decay of states with a doubly occupied site in a two-electron Hubbard model, known as doublons. For the environment we consider charge and current noise which are modelled as a bosonic heat bath that couples to the onsite energies and the tunnel couplings, respectively. It turns out that the dissipative decay depends qualitatively on the type of environment as for charge noise, the life time grows with the electron-electron interaction. For current noise, by contrast, doublons become increasingly unstable with larger interaction. Numerical studies within a Bloch-Redfield approach are complemented by analytical estimates for the decay rates. For typical quantum dot parameters, we predict that the doublon life times up to 50 ns.

cond-mat.mes-hall↗

arXiv2019

Simulation of 1D topological phases in driven quantum dot arrays

We propose a driving protocol which allows to use quantum dot arrays as quantum simulators for 1D topological phases. We show that by driving the system out of equilibrium, one can imprint bond-order in the lattice (producing structures such as dimers, trimers, etc) and selectively modify the hopping amplitudes at will. Our driving protocol also allows for the simultaneous suppression of all the undesired hopping processes and the enhancement of the necessary ones, enforcing certain key symmetries which provide topological protection. In addition, we have discussed its implementation in a 12-QD array with two interacting electrons and found correlation effects in their dynamics, when configurations with different number of edge states are considered.

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arXiv2019

Unconventional quantum optics in topological waveguide QED

The discovery of topological materials has challenged our understanding of condensed matter physics and led to novel and unusual phenomena. This has motivated recent developments to export topological concepts into photonics to make light behave in exotic ways. Here, we predict several unconventional quantum optical phenomena that occur when quantum emitters interact with a topological waveguide QED bath, namely, the photonic analogue of the Su-Schrieffer-Hegger model. When the emitters frequency lies within the topological band-gap, a chiral bound state emerges, which is located at just one side (right or left) of the emitter. In the presence of several emitters, it mediates topological, long-range tunable interactions between them, that can give rise to exotic phases such as double Néel ordered states. On the contrary, when the emitters' optical transition is resonant with the bands, we find unconventional scattering properties and different super/subradiant states depending on the band topology. We also investigate the case of a bath with open boundary conditions to understand the role of topological edge states. Finally, we propose several implementations where these phenomena can be observed with state-of-the-art technology.

cond-mat.mes-hall↗

arXiv2019

Interplay between long range hopping and disorder in topological systems

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.

cond-mat.mes-hall↗

arXiv2018

SSH model with long-range hoppings: topology, driving and disorder

The Su-Schrieffer-Heeger (SSH) model describes a finite one-dimensional dimer lattice with first-neighbour hoppings populated by non-interacting electrons. In this work we study a generalization of the SSH model including longer-range hoppings, what we call the extended SSH model. We show that the presence of odd and even hoppings has a very different effect on the topology of the chain. On one hand, even hoppings break particle-hole and sublattice symmetry, making the system topologically trivial, but the Zak phase is still quantized due to the presence of inversion symmetry. On the other hand, odd hoppings allow for phases with a larger topological invariant. This implies that the system supports more edge states in the band's gap. We propose how to engineer those topological phases with a high-frequency driving. Finally, we include a numerical analysis on the effect of diagonal and off-diagonal disorder in the edge states properties.

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