With recent developments in the field of quantum computing and cryptography, establishing quantum networks would allow for the implementation of post-quantum cryptographic protocols, distributed quantum computing, and quantum sensor networks. Though, quantum networks require the use of quantum repeaters to preserve the transmitted quantum information over long distances. This work focuses on the implementations of quantum frequency conversion which is used to ensure the signal is of a suitable frequency for transmission between the different optical components in the system.
We present an assortment of experiments exploring loading, control, and probing of laser-cooled caesium atoms inside a hollow-core photonic-bandgap fiber.
Metasurface presents itself as a method to create flat optical devices that generate customizable wavefronts at the nanoscale. The traditional metasurface design process involves solving Maxwell’s equations through forward simulations and implementing trial-and-error to achieve the desired spectral response. This approach is computationally expensive and typically requires multiple iterations. In this study, we propose a reverse engineering solution that utilizes a deep learning artificial neural network (DNN). The ideal phase and transmission spectrums are inputted into the neural network, and the predicted dimensions which correspond to these spectrums are outputted by the network. The prediction process is less computationally expensive than forward simulations and is orders of magnitude faster to execute. Our neural network aims to identify the dimensions of elliptical nanopillars that will create the ideal phase response with a near unity transmission in a 20 nm wavelength interval surrounding the center wavelength of the spectral response. We have trained such a reverse DNN to predict the optimal dimensions for a birefringent metasurface composed of elliptical nanopillars.
We report on the experimental observation of chiral resonant modes via a free-space spin-preserving Fabry-Pérot cavity using Pancharatnam-Berry phase reflecting dielectric metasurface mirrors. Such meta-mirrors focus one spin state while diverging the other and preserve the helicity upon reflection.
We show the first demonstration of a hybrid external cavity diode laser (ECDL) using aluminum nitride (AlN) as the wave-guiding material. Two devices are presented, a near-infrared (NIR) laser using a 850 nm diode and a red laser using a 650 nm diode. The NIR laser has ≈1 mW on chip power, 6 nm of spectral coverage, instantaneous linewidth of 720±80 kHz, and 12 dB side mode suppression ratio (SMSR). The red laser has 15 dB SMSR.
Laser locking is a crucial tool in various scientific applications, especially in the field of atomic physics, where the laser's frequency must be stable with respect to the frequencies of atomic transitions. This work aims to leverage the advantages of 3D printed push-fit slots to achieve an inexpensive, compact, and highly customizable optical setup for locking lasers to the frequency of transition between two excited, and thus unpopulated, electron states of a neutral atom. In our approach, the optical components are mounted in custom 3D printed slots instead of traditional optical posts to decrease costs and overall size. The error signal is then created by an Electromagnetically Induced Transparency (EIT) signal in a Two-Photon Dichroic Atomic Vapor Laser Lock (T-P DAVLL), corresponding to the 6S1/2, 6P1/2, and 8S1/2 states of Cesium.
We describe a method for fabricating inline lenses by splicing a graded-index multi-mode (GRIN) fiber to a single-mode fiber (SMF), with a core-less fiber segment controlling focal length and spot size. Based on the experimental results and precision of our glass cleaving and processing equipment, we demonstrate the feasibility of producing fiber lenses with focal lengths ranging from 10 μm to 1 mm, spot sizes from sub-μm to 30 μm, and numerical apertures from 0.10 to 0.30, showcasing potential applications in compact spaces.
Here we report on our recent experimental efforts towards the design, fabrication and characterization of various metasurface structures that would allow spatial and temporal control of photon emission from atomic ensembles, as well as state preparation of solid state and atomic quantum emitters. The emphasis is placed on the development of two distinct categories of structures: (i) Micro- and meso-scale free-space self-polarizing confocal cavities formed by dielectric metasurfaces. (ii) flat hyper-gratings fabricated on the surface of a diamond, which would make the radiation pattern from NV centers in the diamond to be highly directional so that the emitted photons can be collected with high efficiency.
We describe the development and applications of a single-photon source based on a quantum dot embedded in a semiconductor nanowire, which can be precision-tuned to emit ∼1ns long photons at wavelengths that match the transitions of caesium D1 line. We discuss interfacing such single-photon source with atomic ensembles and present our experimental results demonstrating a new method of tuning the emission of the quantum dot by condensing inert gas (N2) on the nanowire. Next, we describe how these single photons at ∼895nm can be efficiently converted to wavelength suitable for satellite QKD links (∼794 nm) and optical fiber links (∼1469 nm) using a laser-cooled atomic ensemble that is loaded and confined inside a hollow-core optical fiber. Lastly, we inroduce our proposal of integrating the semiconductor nanowire with a lensed fiber to create a compact single-photon source with improved photon-collection efficiency compared to conventional setups.
We describe the experimental progress and the challenges of integrating a single photon source based on quantum dots embedded in semiconductor nanowires with a cold-atom experiment in which laser-cooled caesium atoms are loaded and confined inside a hollow-core micro-structured optical fiber. We focus in particular on wavelength conversion of the photons between 895nm and wavelengths suitable for satellite links (~794nm).
We explore Fabry-Perot cavities formed by a pair of photonic-crystal slabs acting as mirrors as a platform for quantum optics at low light levels. We present our recent experimental demonstrations of polarization dichroic mirrors for both linearly and circularly polarized light and propose schemes in which cavities formed by such mirrors can be used to create single-photon optical nonlinearities in atomic ensembles.
We report loading of laser-cooled caesium atoms into a hollow-core photonic-bandgap fiber and confining the atoms in the fiber’s 7μm diameter core with a red-detuned dipole trap. In this system, the atom-photon interaction probability is in the range of 0.5% and optical depths exceeding 100 can be achieved. We discuss the outlooks for photon storage and nonlinear optics at low light levels, such as cross-phase modulation and single-photon wavelength conversion, in this system.
A monolithic compound semiconductor phototransducer optimized for narrow-band light sources was designed for and has achieved conversion efficiencies exceeding 50%. The III-V heterostructure was grown by MOCVD, based on the vertical stacking of a number of partially absorbing GaAs n/p junctions connected in series with tunnel junctions. The thicknesses of the p-type base layers of the diodes were engineered for optimal absorption and current matching for an optical input with wavelengths centered in the 830 nm to 850 nm range. The device architecture allows for improved open-circuit voltage in the individual base segments due to efficient carrier extraction while simultaneously maintaining a complete absorption of the input photons with no need for complicated fabrication processes or reflecting layers. Progress for device outputs achieving in excess of 12 V is reviewed in this study.
We study the dynamics of the interaction between two weak light beams mediated by a strongly coupled quantum dot-photonic crystal cavity system. We demonstrate switching between two weak pulsed beams (40 ps pulses), observing an increase of the systems transmission when the signal and the control pulses overlap inside the cavity. Our results show that the quantum dot-nanocavity system enables fast, controllable optical switching at the single-photon level.
Cold atoms confined inside a hollow-core photonic-crystal fiber with core diameters of a few photon wavelengths
are a promising medium for studying nonlinear optical interactions at extremely low light levels. The high electric
field intensity per photon and interaction lengths not limited by diffraction are some of the unique features of
this system. Here, we present the results of our first nonlinear optics experiments in this system including a
demonstration of an all-optical switch that is activated at energies corresponding to few hundred optical photons
per pulse.
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