Waveguide quantum electrodynamics with multiple atoms provides an important way to study photon transport. In this work, we study the photon transport in a one-dimensional waveguide coupled to a topological atom array. The interaction between light and topology-dressed atoms yields a rich variety of photon scattering phenomena. We find that the nonreciprocal photon reflection originates from the quantum interference of photons scattered by the dissipative edge and bulk modes in the topological atom array. The largest nonreciprocity is found at the magic atomic spacing $d=3\lambda_0/4$, where $\lambda_0$ is the characteristic wavelength of the waveguide. For an odd number of atoms with an extremely small free space decay, the broken inversion and time-reversal symmetries induce a giant anomalous photon loss from the waveguide to free space. Our model can be implemented in superconducting quantum circuits. This work opens a new avenue to manipulate photons via the interaction between light and topological quantum matter.
Waveguide quantum electrodynamics with multiple atoms provides an important way to study photon transport. In this work, we study the photon transport in a one-dimensional waveguide coupled to a topological atom array. The interaction between light and topology-dressed atoms yields a rich variety of photon scattering phenomena. We find that the nonreciprocal photon reflection originates from the quantum interference of photons scattered by the dissipative edge and bulk modes in the topological atom array. The largest nonreciprocity is found at the magic atomic spacing d=3λ0/4, where λ0 is the characteristic wavelength of the waveguide. For an odd number of atoms with an extremely small free space decay, the broken inversion and time-reversal symmetries induce a giant anomalous photon loss from the waveguide to free space. Our model can be implemented in superconducting quantum circuits. This work opens a new avenue to manipulate photons via the interaction between light and topological quantum matter.
Abstract We explore the scattering and nonreciprocal transmission of single photons in an array of N coherently coupled two-level atoms, with only the two end atoms interacting with a waveguide at distinct spatial points. The chain serves as a giant-atom-like scatterer with internal collective modes. Using the real-space approach, analytical expressions for the scattering amplitudes are obtained. For the ideal case without atomic loss, the transmission is reciprocal and can be modulated by the relative local coupling phase, the accumulated propagation phase, the interatomic hopping strength, and the photon–atom detuning. We further observe that the oscillatory behavior of the transmission spectrum becomes more pronounced as the number of atoms increases. When atomic loss into nonguided modes is included, phase-dependent interference gives rise to dissipation-assisted nonreciprocal transmission. By appropriately tuning the phase factors, the atomic loss rate, and the hopping strength, one can achieve maximal nonreciprocity, corresponding to complete suppression of transmission for one incident direction. These results establish a flexible platform for engineering directional single-photon transport in guided-wave quantum electrodynamics.
Abstract The phase-controlled single-photon transport properties of a giant atom coupled to a one-dimensional waveguide are investigated. The coupling between the giant atom and the waveguide is modeled as a multi-point interaction. The coupling strengths between the giant atom and the waveguide are represented as complex numbers with associated phases. Analytical expressions for the scattering amplitudes are obtained using the real-space Hamiltonian method. The results show that the characteristics of the scattering spectra, including the positions of peaks (or dips) and the full width at half maximum, can be tuned by adjusting the phase difference between the coupling strengths. Further calculations reveal that the scattering spectra can be either super-broadened or sub-broadened. The conditions for achieving perfect nonreciprocal single-photon transport in the Markovian regime are also discussed. Moreover, we demonstrate the control of single-photon transport through phase differences in the non-Markovian regime. Our results may find applications in the design of quantum devices operating at the single-photon level, based on waveguide quantum electrodynamics.
The giant-atom topological-waveguide-QED systems have recently emerged as a promising platform for manipulating light-matter interactions. The combination of the multiple-point couplings and topological phase effect could lead to rich physical phenomena and effects. Here, we study single-photon scattering in a Su-Schrieffer-Heeger (SSH) waveguide coupled to either one or two two-level giant atoms. We assume that each giant atom is coupled to the waveguide via two coupling points and hence there exist four and sixteen coupling configurations for the single-giant-atom case and two-giant-atom separate coupling case, respectively. By solving the single-photon scattering problem in the real space, we obtain the exact expressions of the single-photon scattering amplitudes. It is found that a single photon in the SSH waveguide can be completely reflected or transmitted by choosing proper coupling configurations, coupling-point distances, atomic resonance frequency, and dimerization parameter. In addition, under proper parameter conditions, the scattering spectra are periodically modulated by the coupling-point distances. We also find that the collective behavior of the two giant atoms can be adjusted by quantum interference effect and topological effect and that the single-photon scattering spectra can exhibit the Lorentzian, super-Gaussian, electromagnetically induced transparencylike, and asymmetric Fano line shapes for some coupling configurations. This work will inspire the development of controllable single-photon devices based on the giant-atom topological-waveguide-QED systems.
We investigate coherent single-photon transport in a waveguide quantum electrodynamics structure containing multiple giant atoms. The single-photon scattering amplitudes are solved using a real-space method. The results give rise to a clear picture of the multichannel scattering process. In the case of identical and equally spaced giant atoms in a separate configuration, we also use the transfer-matrix method to express the scattering amplitudes in terms of compact analytical expressions, which allow us to conveniently analyze the properties of the scattering spectra. Based on these theoretical results, we find that the nondipole effects of giant atoms, which are relevant to the design of the setup, can strongly manipulate several types of collective properties of the output fields, including the superradiant phenomenon, the multiple Fano interference, and the photonic band gap. This makes it possible to manipulate the photon transport in a more versatile way than with small atoms. We also make a proposal to probe the topological states of a chain of braided giant atoms by using photon scattering spectra, showing that waveguide quantum electrodynamics systems with giant atoms are ideal platforms to merge topological physics and on-chip quantum optics.
The ordered atomic array emerges as a versatile atom-photon interface for exquisite control of light-matter interaction at the nanoscale. In particular, the one-dimensional atom-waveguide system can achieve strong coupling between a single atom and a photon, where two atomic mirrors coupled to waveguide act as a high-finesse cavity. In this work we show that under the strong-coupling regime, the mirror atoms arranged in the form of a Su-Schrieffer-Heeger chain are advantageous in decoherence suppression compared to a nontopological Bragg configuration, manifesting a significant increase in the lifetime of dressed states, substantial narrowing of the spectral linewidth, and order-of-magnitude enhancement of the cooperativity of light-matter interaction. Furthermore, subradiant dressed states with a decay rate smaller than the emission rate of a free-space atom are found in the dissipationless atomic cavity with a few mirror atoms, which cannot be achieved with a Bragg atomic mirror. A theory of the local density of states (LDOS) of the atomic cavity is presented and reveals that the decoherence suppression is directly related to the negative LDOS in a wide frequency range contributed by the bulk modes of the topological atomic cavity. This peculiar feature of the LDOS indicates the destructive quantum interference of photon scattering by the topological edge- and bulk-state channels. Our work demonstrates the great potential of topology in engineering quantum states and enhancing quantum coherence for future applications in quantum computing and quantum information processing.
Atom arrays are a new type of quantum light-matter interface.Here we propose to employ one-dimensional ordered arrays as atomic waveguides.These arrays support optical guided modes that do not decay into free space.We show that these modes can be harnessed to mediate tunable, long-range interactions between additional "impurity qubits" coupled to the chain, without need for photonic structures.The efficient coupling between qubits and atomic waveguides enables the realization of tunable qubit-qubit interactions, which can be short or long range, dissipative or coherent, as well as chiral.Moreover, owing to the two-level nature of atoms, these waveguides are intrinsically quantum.In contrast to classical waveguides, where photons do not interact with each other, atomic waveguides display strong nonlinearities, which create a tunable dissipative channel for qubit-qubit interactions, and opens the door to the exploration of many-body physics between guided photons.This physics is universal as it only relies on photon interference and can also be observed with other types of quantum emitters, such as those in molecular or solid-state systems.