Session N02: Cavity QED and Nanophotonics

Live

In the context of quantum metrology, optical cavity-QED platforms have primarily been focused on the generation of entangled atomic spin states useful for next-generation frequency and time standards. We report a complementary application: The use of optical cavities to generate non-classical atom-light cat-states for quantum-enhanced sensing of small field displacements. We show that even in the presence of intrinsic photon loss from the cavity, the collective enhancement of atom-light interactions allows for potential metrological gains of 10-20 dB below the standard quantum limit in state-of-the-art cavity-QED systems operating with long-lived alkaline-earth atoms. Our protocol opens a path for sub-SQL sensing of electromagnetic fields in the optical domain, and could have applications in circumventing shot-noise limitations in optical interferometry, as well as in other frequency regimes since it is applicable to a broad range of platforms featuring similar types of spin-boson couplings, such as trapped ion arrays and opto-mechanical systems.   

Live

Helium Rydberg atoms traveling in pulsed supersonic beams have been coherently coupled to microwave fields in a niobium nitride quarter-wave superconducting coplanar waveguide (CPW) resonator. The two-photon $|55\mathrm{s}\rangle\rightarrow|56\mathrm{s}\rangle$ transition between triplet Rydberg states at a frequency of 19.556 GHz was driven by the third harmonic microwave field in the resonator. This transition was selected for use in the experiments because of its low sensitivity to stray electric fields emanating from the superconducting chip surface. The detuning of the resonator frequency from the atomic transition frequency was controlled by stabilizing the superconducting chip temperature to values between 3.65 and 4.5 K. The Rydberg atoms were detected by state-selective pulsed electric field ionization. The coherence of the atom-resonator-field interaction was characterized by Rabi and Ramsey spectroscopy, with the experimental results compared to the results of numerical calculations. Coherence times of between 100 ns and 1 $\mu$s, limited by the spatial distribution and motion of the atoms above the CPW resonator, have been achieved.   

Live

Atom-light interactions in optical cavities have been proposed as emulators of quantum spin models with long-range interactions. Building on our recent experimental observation of collective spin-exchange interactions, generated by coupling a far-detuned optical cavity mode to a narrow optical transition in Sr-88 [arXiv:1910.00439 (2019)], we report progress towards the simulation of the iconic BCS Hamiltonian which describes s-wave superconductors. Theoretical studies of this model have predicted novel dynamical phases of matter including one in which the superconducting order parameter exhibits persistent and robust coherent oscillations. Leveraging the internal structure of the 1S0-3P1 optical transition we discuss protocols to realize the dynamical phases in our cavity-QED simulator. The interplay between the cavity-mediated interactions and tunable inhomogeneous energy shifts generated via Stark and magnetic Zeeman shifts allow us to explore the dynamical phase diagram. We discuss the feasibility of observing the dynamical phases under current experimental conditions, including robustness to typical sources of decoherence and experimental noise.   

Live

Strongly interacting optical photons hold great promise for exploring the exotic properties of topologically ordered materials. We make photons interact strongly by turning them into cavity Rydberg polaritons, quasiparticles hybridizing an optical cavity photon with an interacting atomic Rydberg excitation. We recently used these polaritons to create the first Laughlin states of light. However, the maximum size of such quantum materials in our system scales with the number of degenerate modes of the optical cavity. Thus, we describe our efforts to create a highly degenerate multimode twisted cavity compatible with the Rydberg gas, enabling us to explore bigger and more robust topologically-ordered Laughlin states with multiple polaritons.   

Live

We show that quantum many-body effects can appear in a single non-linear oscillator that is driven by an external field in the presence of dissipation. This simple system is a paradigmatic example of open quantum many-body systems in which there has been great interest recently due to recent experimental advances such as quantum simulation. Here, weak non-linearity plays the role of the thermodynamic limit. Using both analytical and numerical methods, we demonstrate Z2 symmetry breaking and the corresponding phase transition.   

Live

Chaotic whispering-gallery modes have significance both for optical applications and for our understanding of the interplay between wave phenomena and the classical ray limit in the presence of chaotic dynamics and openness. However, the ray patterns corresponding to such modes only exist in convex cavities [1]. We performed numerical computations of the electromagnetic fields in planar dielectric cavities that are strongly non-convex because they are coupled to waveguides, and found a family of special states which retains many features of the chaotic whispering-gallery modes [2]: an intensity pattern corresponding to near-grazing incidence along extended parts of the boundary, and comparatively high cavity Q factors. The modes are folded into a figure-eight pattern, so overlap with the boundary is reduced in the region of self-intersection. The modes combine the phenomenology of chaotic WGMs with an important technological advantage: the ability to directly attach waveguides without spoiling the Q factor of the folded mode. \newline \newline [1] J. N. Mather, Ergodic Theory and Dynamical Systems 4, 301 (1984). [2] K. Burke and J.U.Noeckel, Phys. Rev. A, 063829 (2019)   

Live

Planar microcavities filled with certain organic dyes result in vacuum Rabi splittings in the visible that are in excess of 1eV, indicating the resulting cavity polaritons are in the ultra-strongly coupled regime. A quantum optics-based theory model for the dye leads to quantitative comparison with recent Z-scan measurements of the dispersion and character of the non-linear optical response of this ultrastrongly coupled polaritonic matter. This comparison highlights the role the ultrastrongly coupled polaritonic states themselves play in the non-linear optical response, in contrast to that of a non-polaritonic loaded cavity. (Support via NSF DMR-1609077.)   

On Demand

The nitrogen-vacancy (NV) center in diamond has been explored extensively as a light-matter interface for quantum information applications, however it is limited by low coherent photon emission and spectral instability. Alternatively, group-IV diamond defects such as the germanium-vacancy (GeV) center have gained attention for their superior optical properties. Inspired by this, we explore an interface based on a single GeV in a diamond membrane coupled to a finesse 11,000 fiber cavity, obtaining a 30-fold enhancement in the spectral density of emission. This work sets the stage for cryogenic experiments, where we predict a factor of 20 increase in the spontaneous emission rate.   

On Demand

We present a method for experimentally characterizing the multi-photon scattering matrix and multi-photon correlations from the output of complex nanophotonic devices. The tomography requires the preparation of coherent state pulses and the measurement of homodyne or intensity- intensity correlations. We explain the basic steps for the reconstruction of single- and two-photon processes, and provide a first experimental test using a quantum dot inside a photonic crystal waveguide. These results open the door to explore quantum light-matter interactions in the controlled multi-photon regime.