Waveguide QED Research Articles

Power-law-exponential interaction induced quantum spiral phases

We theoretically predict a kind of power-law-exponential (PLE) dipole-dipole interaction between quantum emitters in a 1D waveguide QED system. This unconventional long-range interaction is the combination of power-law growth and exponential decay couplings. Applying the PLE interaction to a spin model, we uncover the rich many-body phases. Most remarkably, we find that the PLE interaction can induce the ordered and critical spiral phases. These spiral phases emerge from the strong frustration generated by the power-law factor of the PLE interaction; hence they are absent for other types of long-range interaction, e.g., pure exponential and power-law decay interactions. Our work is also applicable for the higher-dimensional systems. It fundamentally broadens the realm of many-body physics and has significant applications in quantum simulation of strongly correlated matter. Published by the American Physical Society 2024

Two-photon dynamics in non-Markovian waveguide QED with a giant atom

Two-photon dynamics in non-Markovian waveguide QED with a giant atom

Non-Markovian collective emission of giant emitters in the Zeno regime

We explore the collective Zeno dynamics of giant artificial atoms that are coupled, via multiple coupling points, to a common photonic or acoustic reservoir. In this regime, the establishment of atomic cooperativity and the revivification of exponential decay are highly intertwined, which is utterly beyond the non-Markovian regime with only retarded backaction. We reveal that giant atoms build up their collective emission smoothly from the decay rate of zero to that predicted by Markovian approximation and show great disparity between different waveguide QED setups. As a comparison, the steplike growth of instantaneous decay rates in the retardation-only picture has also been shown. All of these theoretical pictures predict the same collective behavior in the long time limit. From a phenomenological standpoint, we observe that the atomic superradiance exhibits significant directional property. In addition, the subradiant photons feature prolonged oscillation in the early stage of collective radiance, where the energy is exchanged remarkably between giant emitters and the field. Our results might be probed in state-of-art waveguide QED experiments and fundamentally broaden the fields of collective emission in systems with giant atoms. Published by the American Physical Society 2024

Photon routing in disordered chiral waveguide QED ladders: interplay between photonic localization and collective atomic effects

Photon routing in disordered chiral waveguide QED ladders: interplay between photonic localization and collective atomic effects

Coherent response of inhomogeneously broadened and spatially localized emitter ensembles in waveguide QED

Coherent response of inhomogeneously broadened and spatially localized emitter ensembles in waveguide QED

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

Motivated by recent cold-atom realizations of matter-wave waveguide QED, we study simple fermionic impurity models and discuss fermionic analogs of several paradigmatic phenomena in quantum optics, including formation of nontrivial 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 non-Markovian many-body effects in the quench dynamics of single- and multiple-impurity systems, including fractional decay around the Fermi level and multiexcitation population trapping due to bound states in the continuum. Published by the American Physical Society 2024

N scaling of large-sample collective decay in inhomogeneous ensembles

We experimentally study collective decay of an extended disordered ensemble of N atoms inside a hollow-core fiber. We observe up to 300-fold enhanced decay rates, strong optical bursts, and a coherent ringing. Due to inhomogeneities limiting the synchronization of atoms, the data does not show the typical scaling with N. We show that an effective number of collective emitters can be determined to recover the N scaling known to homogeneous ensembles over a large parameter range. This provides physical insight into the limits of collective decay and allows for its optimization in extended ensembles as used, e.g., in quantum optics, precision time-keeping, or waveguide QED. Published by the American Physical Society 2024

Dynamical beats of short pulses in waveguide QED

Dynamical beats of short pulses in waveguide QED

Autonomous Distribution of Programmable Multiqubit Entanglement in a Dual-Rail Quantum Network.

We propose and analyze a scalable and fully autonomous scheme for preparing spatially distributed multiqubit entangled states in a dual-rail waveguide QED setup. In this approach, arrays of qubits located along two separated waveguides are illuminated by correlated photons from the output of a nondegenerate parametric amplifier. These photons drive the qubits into different classes of pure entangled steady states, for which the degree of multipartite entanglement can be conveniently adjusted by the chosen pattern of local qubit-photon detunings. Numerical simulations for moderate-sized networks show that the preparation time for these complex multiqubit states increases at most linearly with the system size and that one may benefit from an additional speedup in the limit of a large amplifier bandwidth. Therefore, this scheme offers an intriguing new route for distributing ready-to-use multipartite entangled states across large quantum networks, without requiring any precise pulse control and relying on a single Gaussian entanglement source only.

Biphoton routing in few-emitter chiral waveguide quantum electrodynamics ladders

We study the problem of two-photon routing in waveguide QED ladders where a few two-level quantum emitters (QEs) are simultaneously coupled with two chiral waveguides. We analyze the routing probability in two regimes, namely, under a purely plane wave approximation (scattering case) and in the presence of photon-photon bound state formation. Within the scattering case, we examine the two-photon routing in the presence of up to five QEs, considering two possibilities separately: ideal-symmetric coupling and the critical coupling scenario. We examine the photon routing up to the two QEs for the bound state situation and compare the photon redirection efficiency with the corresponding scattering case. Our findings show the potential of utilizing chiral light-matter interactions in multi-photon and multi-emitter-based quantum networking protocols where interlinking among spatially distant nodes is required.

Temperature-related single-photon transport in a waveguide QED.

We propose a scheme to realize a novel, to the best of our knowledge, scenario that the single-photon transport in a one-dimensional waveguide can be affected by the temperature. The scheme is composed by a waveguide-atom interacting structure linked to a thermal bath. The single-photon reflection (or transmission) coefficient can be controlled by adjusting the temperature of the thermal bath. This provides a thermal control of the single-photon transport. Moreover, the scheme provides an approach for implementing the optical thermometer, in which the temperature of the thermal bath is estimated by measuring the photonic transport. The thermometer can accurately measure the temperature in the low-temperature region.

Topological Inverse Band Theory in Waveguide Quantum Electrodynamics.

Topological phases play a crucial role in the fundamental physics of light-matter interaction and emerging applications of quantum technologies. However, the topological band theory of waveguide QED systems is known to break down, because the energy bands become disconnected. Here, we introduce a concept of the inverse energy band and explore analytically topological scattering in a waveguide with an array of quantum emitters. We uncover a rich structure of topological phase transitions, symmetric scale-free localization, completely flat bands, and the corresponding dark Wannier states. Although bulk-edge correspondence is partially broken because of radiative decay, we prove analytically that the scale-free localized states are distributed in a single inverse energy band in the topological phase and in two inverse bands in the trivial phase. Surprisingly, the winding number of the scattering textures depends on both the topological phase of inverse subradiant band and the odevity of the cell number. Our Letter uncovers the field of the topological inverse bands, and it brings a novel vision to topological phases in light-matter interactions.

Variational Quantum Simulators Based on Waveguide QED.

Waveguide QED simulators are analog quantum simulators made by quantum emitters interacting with one-dimensional photonic band gap materials. One of their remarkable features is that they can be used to engineer tunable-range emitter interactions. Here, we demonstrate how these interactions can be a resource to develop more efficient variational quantum algorithms for certain problems. In particular, we illustrate their power in creating wave function Ansätze that capture accurately the ground state of quantum critical spin models (XXZ and Ising) with fewer gates and optimization parameters than other variational Ansätze based on nearest-neighbor or infinite-range entangling gates. Finally, we study the potential advantages of these waveguide Ansätze in the presence of noise. Overall, these results evidence the potential of using the interaction range as a variational parameter and place waveguide QED simulators as a promising platform for variational quantum algorithms.

Effects of environment correlations on the onset of collective decay in waveguide QED

Effects of environment correlations on the onset of collective decay in waveguide QED

The single- and two-photon scattering in the waveguide QED coupling to a giant atom

The giant atom, which means the nonlocal atom-waveguide coupling, gives lots of newfangled physics. In this paper, we study the single- and two-photon scattering in the waveguide quantum electrodynamics on a two-level giant atom. For single-photon scattering, we find that the transmission rate is dependent on the atomic size. For the two-photon scattering, using a reasonable wave function hypothesis, we can get the two-photon scattering state, which consists of the symmetric and anti-symmetric plane wave functions. The other eigenstate is the two-photon bound state, which is orthogonal to the two-photon scattering state. We find that the spatial extent of the two-photon bound state is related to the detuning between waveguide and atom, which is distinguished from the character of the general atom. Our study is beneficial to photon control and the fundamental research of the two-photon scattering.

Higher-order mean-field theory of chiral waveguide QED

Waveguide QED with cold atoms provides a potent platform for the study of non-equilibrium, many-body, and open-system quantum dynamics. Even with weak coupling and strong photon loss, the collective enhancement of light-atom interactions leads to strong correlations of photons arising in transmission, as shown in recent experiments. Here we apply an improved mean-field theory based on higher-order cumulant expansions to describe the experimentally relevant, but theoretically elusive, regime of weak coupling and strong driving of large ensembles. We determine the transmitted power, squeezing spectra and the degree of second-order coherence, and systematically check the convergence of the results by comparing expansions that truncate cumulants of few-particle correlations at increasing order. This reveals the important role of many-body and long-range correlations between atoms in steady state. Our approach allows to quantify the trade-off between anti-bunching and output power in previously inaccessible parameter regimes. Calculated squeezing spectra show good agreement with measured data, as we present here.

Multichannel waveguide QED with atomic arrays in free space

We study light scattering off a two-dimensional array of atoms driven to Rydberg levels. We show that the problem can be mapped to a generalized model of waveguide QED, consisting of multiple one-dimensional photonic channels (transverse modes), each of which is directionally coupled to a corresponding Rydberg surface mode of the array. In the Rydberg blockade regime, collective excitations of different surface modes block each other, leading to multichannel correlated photonic states. Using an analytical approach, we characterize interchannel quantum correlations, and elucidate the role of collective two-photon resonances of the array. Our results open new possibilities for multimode many-body physics and quantum information with photons in a free-space platform.

Retardation Effect and Dark State in a Waveguide QED Setup With Rectangle Cross Section

AbstractThis paper investigates the dynamics of two two‐level atoms, which simultaneously couple to a quasi‐1D waveguide with rectangular cross section. The waveguide modes serve as environment, which induces the interaction and collective dissipation between the two distant atoms. When both of the two atoms are located in the middle of the waveguide, a retardation effect is observed, which can be broken by moving one of the atoms away from the center of the waveguide. To preserve the complete dissipation of the system via dark state mechanism, a scheme where the connection of the atoms is perpendicular to the axis of the waveguide is proposed.

Plasmonic spin induced Imbert–Fedorov shift

Abstract The spin angular momentums of surface plasmon polaritons (SPPs) on chiral material interfaces and the Imbert–Fedorov shifts of linearly polarized light beams are investigated. Compared to a traditional TM-polarized SPP having a transverse spin, the SPP on a chiral material interface also has a longitudinal spin component, resulting from the nature that this new kind of SPP is a hybrid of TE and TM-polarized evanescent waves. When a light beam is incident on a sandwich structure composed of chiral material, prisms, and metal layers, in which the SPP is supported, the reflection and transmission processes can be analogous to the transport of a photon in a waveguide QED system. The SPP with longitudinal spin can be excited by the incident wave and the reflected and transmitted beams carry the spin features of the SPP. Moreover, the beams exhibit large Imbert–Fedorov shifts stemming from the spin–orbit coupling even for a linearly polarized incident beam. The shifts are determined by the longitudinal spin angular momentum and excitation coefficient of the SPP. This present work extends the study of photonic spin–orbit coupling and provides an important platform to investigate the plasmonic spin.

Perfect splitting of a two-photon pulse

We employ a cascaded system approach to numerically simulate the interaction of photon pulses with a two-level scatterer in a chiral waveguide QED setup and show that the scattering of a two-photon pulse may lead to the predominant population of only two output wave packet modes in an entangled state, $|2,0\ensuremath{\rangle}--|0,2\ensuremath{\rangle}$. In a complementary wave-packet basis, this is a product state of two orthogonal single-photon wave packets. Operating this process in reverse allows a perfect merging of distinguishable single-photon wave packets into a single-mode pulse carrying two identical photons.