Session H07: Cavity QED and Nanophotonics II

Emitter Coupled to One-Dimensional Waveguide: Physics Beyond the Rotating Wave Approximation

One-dimensional waveguide systems are ubiquitous in the study of nanophotonics and quantum optics. When coupled to an impurity such as, e.g., a quantum dot or an atom, waveguide systems have been utilized for photon routing and as quantum switches, which constitute important building blocks of quantum networks. We report our progress in theoretically investigating a three-level quantum emitter coupled to a one-dimensional cavity resonator waveguide. Such systems have received attention in the context of chiral waveguide dynamics and photon transport via electromagnetically induced transparency. We focus on the strong coupling regime, where the rotating wave approximation breaks down and the number of excitations is not conserved. We present our observations of the radiation dynamics in this system and identify quantum states of interest.   

Continuous-wave virtual-state lasing without ground state population inversion

We present a theoretical description of a lasing scheme of cooled and trapped ytterbium atoms in an optical cavity. Here, continuous-wave lasing is achieved on the semi-forbidden intercombination line ${}^1 S_0 \longleftrightarrow {}^3 P_1$, therefore producing coherent light directly from a narrow-linewidth transition.  Lasing is realized by pumping the atoms to the ${}^3 P_1$ state that subsequently can emit a cavity photon by decaying to a virtual state. This process is enhanced by a two-photon transition induced by a second driving field that quasi-resonantly couples the virtual state to the broad-linewidth ${}^1 P_1$ state. We study this system using mean-field equations for the coupled atom-cavity dynamics. With this we determine the lasing threshold and the emission frequencies. The non-linear nature of this device is highlighted by its ability to form bistable lasing and non-lasing states and to show a hysteresis when slowly ramping the pump power above threshold and back. We discuss how our analysis can be extended to calculate the linewidth of the laser and how we could incorporate motional effects to describe lasing, trapping, and cooling.    

Cavity Modification of the Quantum Hall Effects

Cavity modification of materials is a novel research field motivated by the advances in strong light-matter interactions. In this talk we present how the strong coupling of Landau levels (in a two-dimensional electron gas) to the cavity field leads to the emergence of quasiparticles between the Landau levels and the photons, known as Landau polaritons [1]. The Landau polaritons have direct implications for the transport properties of the electron gas [3,4]. Further, we will present how our theory predicts that the cavity field can alter the fundamental quantization of the Hall conductance in the integer regime [4], as it has been also recently observed experimentally [3]. Connections of our theoretical prediction to these experiments will be discussed. Finally, in the case where the electron gas is replaced by a 2D periodic material we show that our theory predicts the emergence of polaritonic fractal energy spectra as a function of the cavity coupling strength [4]. The polaritonic fractal spectra are a polaritonic extension of the well-known Hofstadter butterfly [5]. 

[1] V. Rokaj, M. Penz, M. A. Sentef, M. Ruggenthaler, and A. Rubio, Phys. Rev. Lett. 123, 047202 (2019)

[2] G. L. Paravicini-Bagliani et al., Nat. Phys. 15, 186-190 (2019)

[3] F. Appugliese et al., arXiv:2107.14145 (2021)

[4] V. Rokaj, M. Penz, M. A. Sentef, M. Ruggenthaler, and A. Rubio, arXiv:2109.15075 (2021)

[5] D. R. Hofstadter, Phys. Rev. B 14, 2239 (1976)   

Non paraxial resonator mode calculations in the small-waist limit: a local ray expansion for wave physics

The field of optical cavity QED has long relied on ABCD matrices to describe propagation, mode structure, and resonator stability. This works extremely well for low NA resonators with parabolic mirrors. Going to higher NA, or introducing non-quadratic optics, breaks this paradigm. In this talk, we present a local ray expansion that dramatically reduces the numerical complexity of mode calculations in the non-paraxial regime. By expanding the Huygen's integral about a ray-traced eikonal field, we arrive at a technique capable of fast mode calculations for not only beyond-paraxial resonators, but also for resonators with intracvity opticsc. We explore implications for near-concentric resonators, near degenerate resonators, cavities containing aspheric surfaces, axicon cavities, and more.   

Withdrawn

Utilizing a simple and original approach to Gaussian quantum fluctuations around the Lindblad dynamics, we explore theoretically the spectral properties of the non-equilibrium photonic phases hosted by a lattice of coupled cavities in the presence of non-Markovian driving and dissipation, as well as strong photon interactions. In particular, we analyze how the elementary excitations of the system evolve across the Mott/superfluid-like dynamical transition exhibited by the model and point out the emergence of a diffusive Goldstone mode in the symmetry-broken phase whose structure indicates a close intertwining between dissipation and coherence as a consequence of strong correlations. Moreover, we investigate the one-body coherence of the insulating phase, showing how the dynamical properties of quasiparticles make this regime significantly different from its equilibrium counterpart. Our study goes in the direction of investigating the potential of driven-dissipative photonic fluids to quantum simulate a wider range of many-body scenarios.   

Probing and controlling the dynamics of a one-dimensional SSH lattice through a two-level emitter

The one-dimensional SSH (Su-Schrieffer-Heeger) model is one of the simplest model Hamiltonians that supports non-trivial topological states. It possesses a Peierls instability that leads to dimerization. In addition to serving as a paradigmatic toy model, the SSH Hamiltonian describes key features of approximately linear systems such as, e.g., polyacetylene. This work investigates the possibility of probing and controlling the SSH lattice dynamics by means of a two-level emitter theoretically. In particular, we investigate SSH lattices that are arranged in a chain, in an X-type structure, and in a star-type structure for varying coupling strengths between the emitter and the lattice; in all cases, we restrict ourselves to the weak coupling limit. Regimes where the two-level emitter plays the role of a weakly-perturbing probe are identified. In addition, regimes where the two-level emitter serves as a new edge, thus notably changing the dynamics, are identified.     

Quantum Nonreciprocity with Nonlinearity and Weyl semimetals

The emerging field of quantum computing has been rapidly growing and has shown interesting opportunities to overcome the limitations of classical computers for many currently unfeasible problems. A key technology that will be required for quantum computation devices is the unidirectional signal propagation and routing, whereby electromagnetic radiation propagates asymmetrically between two points. Most modern nonreciprocal components are realized based on the magneto-optical effect in ferrite materials. These devices are expensive, barely tunable, bulky, and incompatible with planar technologies, including transmission-line quantum circuits. In this work, we present our recent results on isolators suitable for quantum systems. We first discuss the isolation effect obtained by a suitable combination of quantum nonlinearities and symmetry breaking. By an example of a two-qubit system, we show that the presence of the dark state and its properties are crucial to establish large nonreciprocity in this class of systems. Then we discuss a novel approach to tunable isolation based on twisted bilayered Weyl semimetals. The approach enables highly efficient tuning of both direction and value of isolation with the relative rotation of Weyl semimetals.

    

Atom-Nanophotonic Quantum Network Node with Direct Telecom Operation

Practical quantum networks designed for long distance operation require the use of telecom photons to mitigate fiber losses. However, many promising qubit candidates do not have ground state telecom transitions. We propose a scheme that overcomes this limitation by strongly coupling atomic qubits to telecom nanophotonic cavities which both provide the efficient light-matter interface necessary for a quantum network node and circumvent the need for frequency conversion by exploiting excited-excited state transitions. Specifically, our scheme creates robust time-bin entanglement between the atomic hyperfine ground states and telecom photons collected via the cavity mode. We show that high fidelity entanglement can be generated with experimentally realistic parameters including cavity coupling strength, finite atomic temperature, and polarization impurity of the addressing lasers due to the nearby dielectric surface.

We will present these results with emphasis on our recent experimental progress towards realizing this network node architecture including fabrication and characterization of high quality factor nanophotonic cavities, coupling to our cavities via free space, and a compact vacuum chamber designed for integration of a photonic chip hosting many nanophotonic devices.   

Non-Markovian Collective Quantum Beats

Quantum beats are an interference phenomenon in the radiation from different excited levels in a multilevel atomic system. Recently it has been experimentally demonstrated that quantum beats can be cooperatively enhanced in a collection of multi-level atoms [1]. In this work, we study quantum beats emitted by two three-level V-type atoms coupled via a waveguide. We illustrate a crossover of the collective quantum beat dynamics from a Markovian to a non-Markovian regime as the atomic separation becomes sufficiently large to bring the memory effects of the electromagnetic environment into consideration. We show that quantum beats can be collectively enhanced or suppressed, akin to Dicke super- and sub-radiance, depending on the inter-atomic separation modulo the beat wavelength and the initial correlations between the atoms. Furthermore, in a non-Markovian regime, collective quantum beats can be enhanced beyond the Markovian limit as a result of retardation effects. Our results demonstrate the rich interplay between multilevel and multiatom quantum interference effects in a non-Markovian regime, which can be relevant to quantum communication between distant quantum network nodes.

[1] H. S. Han, A. Lee, K. Sinha, F. K. Fatemi, and S. L. Rolston, Phys. Rev. Lett. 127, 073604 (2021).