Session S34: Quantum Photonics and Nonlinear Optics I

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Waves traveling in weakly disordered media possessing long-range correlations experience a universal phenomenon known as branched flow, where the waves split and form channels (branches) of enhanced intensity that keeps dividing as the waves propagate. We explore this fascinating phenomenon in thin liquid soap membranes – soap bubbles. This phenomenon is naturally emerging in this system because soap films naturally have thickness variations whose parameters can be tuned to act as a weakly correlated potential, as required for branched flow.  Thus far, branched flow effects have been studied experimentally in various systems, but always with coherent waves. Here, we present the first experimental observation of the branched flow of spatially-incoherent light. We show that the primary effect of branching occurs for both coherent and incoherent light, but secondary branching arises from interference effects and disappears when the waves become incoherent. The location of the first caustic, where the branches reach peak intensity, remains the same as the coherence is reduced, but a close look at the branch statistics reveals a very different distribution arising from the incoherence.   

Metalens-based optical levitation in vacuum

Optical levitation is a powerful technique for a range of applications including novel sensors and manipulation of quantum signals for precise measurements. However, conventional optical tweezers require a dramatically bulky and high numerical-aperture objective for trapping and an extra condenser lens to collect the scattering light for detection. Here, we show a dielectric planar metalens consisting of 500-nm-thick high-vacuum-compatible silicon nanopillars. The flat metalens has a high numerical aperture of 0.88 at 1064 nm in vacuum. We realize the first metalens-based optical levitation of nanoparticles in vacuum. Due to its flat surface, the scattered light of the trapped particle can directly interfere with the back reflection of the incident beam, making measurement more convenient. We also study the transferring of trapped nanoparticles between two separated optical trapping wells. Optical levitation with an ultrathin metalens in vacuum has the potential to be applied to on-chip sensing and trapping ultracold atoms and molecules.   

Pushing Photons with Electrons: Observation of the Polariton Drag Effect

Exciton-polaritons are quasiparticles that are a superpositions of excitons and photons. In a microcavity, exciton-polaritons have an effective mass and can form a Bose-Einstein condensate (BEC). Experimentally, this condensate can be generated by pumping light into a microcavity structure with quantum wells at the antinodes of the light field. The features of the polaritons, such as energy, real-space, and momentum-space distributions, are carried by the light they emit, so we can measure those by using conventional optical methods.

In our experiment, we observed a change in the angle of emission of the photons when injecting electrons to the system, which indicates that the interaction of electrons with the polaritons changes the momentum of the polariton condensate. The condensate flow was accelerated when electrons flow with the same direction, while the condensate was slowed down when electrons flow in the opposite direction. Because the experiment is a photon-in, photon-out system, this is equivalent to steering photons using a DC electrical current. A theoretical model is also built to describe the effect.   

Bose-Einstein Condensation of Microcavity Exciton-Polaritons in Thermal Equilibrium

Strong coupling of cavity photons and quantum-well excitons gives rise to new bosonic quasiparticles called exciton-polaritons or polaritons. In this experiment, we measure the distribution function of polaritons inside an annular optical trap in a GaAs microcavity under non-resonant pumping for different detunings and bath temperatures. The annular optical trap forms a repulsive potential originating from the interactions of polaritons with the excitonic reservoir, hence trapping the polaritons inside. We explore the conditions needed for equilibration of the polaritons and the sensitivity to the density of states of the trap. We also report the observation of critical fluctuations of the polariton photoluminescence near the critical density of condensation.   

Asymmetric Localization by Second Harmonic Generation

In this talk, we introduce a nonlinear photonic system that enables asymmetric localization and unidirectionally transfers an electromagnetic wave through the second harmonic generation process. To achieve this, we propose a scattering setup consisting of a non-centrosymmetric nonlinear slab with nonlinear susceptibility (d) placed to the left of a one-dimensional periodic linear photonic crystal with an embedded defect. We engineered the linear lattice to allow the localization of frequency 2ω_* while frequency ω_* is in the gap. Thus in our proposed scattering setup, a left-incident coherent transverse electric wave with frequency ω_* exponentially decays through the lattice. In contrast, a generated second harmonic wave with frequency 2ω_* localizes at the defect layer. For a right-incident wave, our optical setup acts as a mirror and wholly reflects the incident wave. Our proposed structure will find application in designing new optical components such as optical sensors, switches, transistors, and logic elements.   

Photon-phonon entanglement and frequency upconversion with molecular oscillators

I will show that molecular vibrations, with oscillation frequencies in the tens of THz, can sustain quantum effects such as superposition and entanglement at room temperature. I will also present a new application of molecular oscillators for frequency upconversion from mid-infrared to visible light. Molecules are embedded inside a dual-resonant plasmonic nanocavity offering deep-sub-wavelength light confinement both at mid-infrared to visible frequencies  and resulting in about 13 orders of magnitude enhancement in upconversion efficiency compared to the same molecules in free space. This work demonstrates the untapped potential of molecular cavity optomechanics for coherent signal transduction.   

Non-reciprocal energy transfer through the quantum vacuum fluctuations

Quantum mechanics predicts random fluctuations of electromagnetic fields in vacuum which leads to the well-known Casimir force between macroscopic bodies. Efforts have been made to create various Casimir-based devices. However, the regulation of phonon transfer and dynamics between two closing surfaces by quantum vacuum fluctuations is still an unexplored frontier. In this talk, I will present the first experimental demonstration of quantum vacuum mediated non-reciprocal energy transfer between two micromechanical oscillations. The strong coupling is realized by modulating the Casimir interaction parametrically at nanoscale. We design and engineer the system’s spectrum to include an exceptional point in the parameter space and observe the topological structure near the exceptional point. By dynamically changing the parameters near the exceptional point, non-reciprocal energy transfer with high contrast is realized. In this way, we develop a flexible and robust method to regulate quantum fluctuations and build functional Casimir devices.   

On the Generation of Topological Optical Solitons

We’ve discovered that the second harmonic intensity profiles generated by Bessel like beams are solitary waves of various geometries knotted together by concentric rings. One of which, is two central spots of similar radius knotted by ellipsoidal concentric rings. We show that the spatial profile is invariant against propagation. We observe that their behavior is similar to that of screw dislocation in wave trains: they collide and rebound as they propagate. Their intensity distribution have characteristics of energy density of iso–surfaces that illustrate the right-angle scattering of two Dirac monopoles: the outgoing monopoles are moving along a line at right angles to the line of the incoming monopoles. This right–angle scattering of monopoles, is a direct consequence of the geometry of the Atiyah-Hitchin manifold.

In combining wavefront shaping methods and and ultrafast nonlinear optics, we've developed novel methods of production, study, and control of topological

quantum light for computation. We use higher order Bessel like beams in simple configurations of nonlinear light–matter interactions, to show how these can lead to optical excitations in atomic media of comparable or considerably more complex topologies.   

Non-reciprocal optical frequency shifter and polarization rotator on chip

Optical light has exhibited versatile degree of freedoms, such as frequency and polarization, that can be used for encoding information in optical quantum computing. However, controlling these degree of freedoms in integrated photonic platform has been challenging. In this work, we demonstrated a frequency domain beam-splitter, which is the building block for frequency encoded qubit in high dimensional quantum computing. By spatio-temporally modulating an optical ring resonator via three Aluminum Nitride bulk acoustic wave resonators, a pair of transverse electrical (TE) and transverse magnetic (TM) optical modes are strongly coupled. The output light shifts in both frequency and polarization, with conversion efficiency (beam splitting ratio) controlled by microwave power. Maximum of 50% energy conversion is achieved, with 15 dB suppression of carrier frequency and 12 dB sideband asymmetry. The indirect interband transition breaks the spatial reciprocity, where the conversion only happens when light inputs in phase matched direction.    

Unidirectional flow of composite bright-bright solitons through asymmetric double potential barriers and wells

We investigate the dynamics of two-component bright-bright (BB) solitons through reflectionless double barrier and double-well potentials in the framework of a Manakov system governed by the coupled nonlinear Schrödinger equations. The objective is to achieve unidirectional flow and unidirectional segregation/splitting, which may be used in the design of optical data processing devices. We observe how the propagation of composite BB soliton is affected by the presence of interaction coupling between the two components passing through the asymmetric potentials. We consider Gaussian and Rosen-Morse double potential barriers in order to achieve the unidirectional flow. Moreover, we observe a novel phenomenon that we name "Polarity Reversal" in the unidirectional flow. In this situation, the polarity of the diode is reversed. To understand the physics underlying these phenomena, we perform a variational calculation where we also achieve unidirectional segregation/splitting using an asymmetric double square potential well. Our comparative study between analytical and numerical analysis lead to an excellent agreement between the two methods.   

Manipulating the mid-infrared quantum field statistics with molecular polaritons in the strong and ultrastrong coupling regime

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.   

An atomic frequency comb memory in rare-earth doped thin-film lithium niobate

Atomic frequency comb memories that are compact and chip-integrated have broad applications in both classical and quantum information processing. Previously, atomic frequency comb memories have been achieved in rare-earth-doped ion diffused waveguides patterned in bulk lithium niobate. However, these devices have a large mode cross section which requires high optical power for coherent control and storage. Here we present a compact chip-integrated atomic frequency comb memory in rare-earth doped thin-film lithium niobate. We demonstrate both coherent control of the atomic ensemble and optical storage. Our optical memory exhibits a broad storage spectrum exceeding 100 MHz, and coherent optical storage time of over 250 ns. The strong light-matter interaction in our platform enables coherent rotations on the ions with a power that is three orders of magnitude smaller than previous results in large waveguides. We also take advantage of the thin film platform and fabricate impedance matched ring resonators using an optimized fabrication recipe to increase the storage efficiency. These results pave the way towards scalable, highly efficient, electro-optically tunable quantum photonic systems where one can store and manipulate light on chip with high bandwidth and low powers.