Session C07: Cavity QED and Nanophotonics I

Cavity Tools for Topological Quantum Optics with Rydberg Polaritons: Part I

Probing strongly interacting quantum systems is a goal spanning diverse questions and experimental platforms.  Hybrid particles known as Rydberg polaritons have emerged as a platform to study quantum many-body physics. These particles are part photon and part atomic Rydberg excitation, combining the strong interactions of Rydberg atoms with the quantum optics toolkit.

In this talk, I will describe the development of a novel optical resonator for use with cavity Rydberg polaritons. Aspheric lenses are used inside the cavity to sculpt the spectrum to degeneracy of many modes. Despite these intracavity lenses, backreflections are suppressed to the part-per-billion level. The features of this cavity, with Rydberg atoms inside of it, will allow for direct studies of topologically ordered materials. I will discuss the mechanisms behind these cavity properties, as well as experimental results.   

Cavity Tools for Topological Quantum Optics with Rydberg Polaritons: Part II

Strongly-interacting photons are a fruitful platform for quantum many-body physics and exploring properties of topologically ordered materials. We make photons interact strongly by turning them into cavity Rydberg polaritons, quasiparticles of an optical cavity photon hybridized with an interacting atomic Rydberg excitation. Using these polaritons, we have previously prepared the first two-particle Laughlin state of light that was limited in size by the number of degenerate cavity modes. We will describe recent upgrades of our experimental apparatus including a highly degenerate multimode cavity that will allow for preparation of highly correlated states of a mesoscopic number of particles. Aside from providing technical details of our integrated cavity setup, we will show first experimental results using this platform on the way to bigger Quantum Hall states.   

A Cavity-Coupled Rydberg Atom Array Platform for Quantum Computing

Rydberg arrays are an attractive platform for quantum computing due to rapid increases in gate fidelities (≲99.9%), qubit number (256), and qubit connectivity (any-to-any). Two main challenges remain: fast nondestructive state readout and scaling beyond individual modules. We present our hardware platform for Rydberg quantum computing to eventually address both by coupling a 1D array of Rb⁸⁷ atoms to a high-finesse optical cavity system. We then propose a fast readout method for error diagnosis that will take advantage of our platform’s unique capabilities. This proposal relies on dynamically coupling atoms to the cavity, nondestructive μs global cavity readout and binary search to identify errors. We will validate the efficacy of our error diagnosis proposal with fluorescence imaging. In future work, single qubit rotations for error correction, helper qubits and Rydberg-mediated CNOT gates will be developed.

    

Subwavelength optical guiding for coupling cold atoms to a nanophotonic microring resonator

Cold atoms trapped and interfaced with guided light in nanophotonic circuits form exciting new platforms for fundamental research on atom-light interactions and applications in quantum optics, quantum many-body physics and quantum networks. Experimental demonstrations to date have primarily focused on suspended 1D nanostructures. In this talk, we report an extension of atom-light coupling in a 2D nanophotonic device. Our system is based on silicon nitride microring resonators fabricated on a transparent membrane substrate, which is compatible with cold atom laser cooling. We present a simple and efficient optical guiding technique for trapping cold atoms in the near field of a planar nanophotonic structure with subwavelength precision, which leads to the observation of atom-photon coupling to a whispering-gallery mode in a microring resonator. We extract a cooperativity parameter of C~0.9 based on a microring with a moderate quality factor of Q=5x10⁴. We discuss our on-going effort for reaching higher-Q above 10⁶ and for trapping and further cooling a single to an array of guided atoms on a microring resonator that would promise a scalable on-chip cavity QED system with strong and cooperative atom-light coupling.    

Ultrafast modulation of polaritonic systems to control photon statistics in a Fabry-Perot cavity at mid-infrared frequencies

Controlling the quantum statistics of the electromagnetic field is one of the biggest challenges in quantum optics and nanophotonics in the mid-infrared regime. In this work, we propose that by coupling molecular vibrations with the vacuum in a Fabry-Perot cavity, the photon number and quadratures of the intracavity electromagnetic field can be modified by pumping one cavity mirror with ultrafast UV pulses. We show that modulating the cavity frequency by ~15% leads to strong variations of the Mandel Q-factor and squeezing of order ~1 dB of the intracavity field, for a system initially prepared in the experimentally relevant ground or lower polariton state. The adiabatic modulation of the cavity frequency produces sub-Poissonian infrared light when the system is initialized in a super-Poissonian ground polariton state. We also describe the dependence of the cavity field statistics with the electric dipole behavior and the spectral anharmonicity of molecular vibrations. This proposal opens new routes in the development of mid-infrared quantum optical devices at room temperature using molecular vibrations in confined electromagnetic fields.    

Optical mode conversion via modulated atomic samples

Atomic systems are appealing in large part for the tunability of their parameters, such as energy levels. In this talk, I explore the conversion of photons between optical modes of a twisted cavity enabled by spatiotemporal modulation of a cloud of ⁸⁷Rb atoms. This modulation is induced by a varying Stark shift which “carves out” an effective, rotating optic from the atomic cloud, coupling transverse modes of the twisted cavity. We observe conversion between angular momentum modes and achieve the maximum theoretical conversion efficiency, demonstrating the versatility of atomic samples and prospects for engineering couplings between arbitrary modes.   

A platform for rapid integration of cold atoms and exotic optical resonators

Cavity QED—the interaction between cavity-confined photons and atoms—is a powerful platform for exploring quantum manybody physics and quantum information science. Here we focus on developing a tool for rapid testing of exotic optical cavities, including those with twist to induce gauge fields for light, those with lenses to reduce aberrations and improve mode degeneracy, and those with small waists to directly boost their single-atom cooperativity. An ultra-high vacuum (UHV) environment is essential for integration with a laser-cooled atomic gas, but limits our ability to rapidly benchmark the performance of new cavity models. We address this challenge with a next-gen vacuum chamber design incorporating a load-lock architecture that isolates the loading chamber from the science chamber, and allows us to install and bake new cavities in the loading chamber without compromising the vacuum in the science chamber, thereby facilitating faster project turnaround. I will introduce this new apparatus, describe relevant design challenges, and present our progress towards integration with atoms and optical resonators.   

Self-oscillating geometric pump in a dissipative atom-cavity system

The time evolution of a quantum system can be strongly affected by dissipation. Although this mainly implies that the system relaxes to a steady state, in some cases it can make new phases appear and trigger emergent dynamics. In our experiment, we study a Bose-Einstein Condensate dispersively coupled to a high finesse resonator. The cavity is pumped via the atoms, such that the sum of the coupling beam(s) and the intracavity standing wave gives an optical lattice potential. When the dissipation and the coherent timescales are comparable, we find a regime of persistent oscillations where the cavity field does not reach a steady state. In this regime the atoms experience an optical lattice that periodically deforms itself, even without providing an external time dependent drive. Eventually, the dynamic lattice triggers a geometric pumping mechanism. We show complementary measurements of the light field dynamic and of the particle transport, proving the connection between the emergent non-stationarity and the geometric pump.   

Extreme parametric sensitivity of steady-state transport in quantum Rabi model

We numerically investigate the steady-state transport properties of the quantum Rabi model, commonly employed to study atom-cavity interactions, subject to phenomenological dissipation. It is found that the steady-state transport depends sensitively on the system parameters, specifically it is significantly enhanced when the parameters are carefully tuned. We attribute this enhancement of open system transport to the resonance between specific energy levels of the corresponding closed system. The connection to quantum chaos and the effects of dissipation is briefly discussed.   

Exponentially fast generating and utilizing quantum entanglement in cavity QED system

An ensemble of atomic spin interacting with an optical cavity mode is widely studied and attracts many interests from quantum metrology to quantum many-body physics. The optical cavity can generate a coherent long-ranged spin-spin interaction among atomic ensembles via the one-axis twisting Hamiltonian. The dynamics of the spin system are significantly affected and exhibit rich quantum many-body phenomena by exposing the ensemble to an additional transverse field. In addition, by using a recently achieved time-reversal toolbox, one also has a probe of more non-trivial collective spin states, especially those with high quantum Fisher information. We will report here our experimental and theoretical progress in this direction and an outlook for exploring other exotic quantum properties.