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Application of Hollow Core Photonic Crystal Fibers in Quantum Optics

Wenjia Elser

Published Jan 1, 2021• 0 citations
OpenAlex

Abstract

Non-classical states of light, such as squeezed states, enable a wide variety of scientific and engineering applications in optical communication, precision measurements and quantum computing. Therefore, engineering non-classical states of light in different systems for different purposes is interesting and appealing. Non-classical states of light, particularly squeezed states, can be generated from light in a coherent state or vacuum state by using certain optical nonlinear interactions. To efficiently introduce such optical nonlinear interactions, a high nonlinear coefficient of the medium and high intensity of light in the medium are the key factors, where the hollow core photonic crystal fibers filled with atomic vapor shows their great benefits. In this thesis, we report on our approach to apply hollow core photonic crystal fibers (HCPCFs) with the goal to generate squeezed states using strong optical nonlinearities of atomic vapor. In a HCPCF, light with high intensity has a well confined mode over long distances along the fiber. To apply the HCPCF in squeezed state generation, we experimentally investigated unexpected noise properties of the HCPCF and determined the parameter range to reduce excess noise from the fiber. Furthermore, we have filled the hollow core of a piece of HCPCF with rubidium vapor, which provides a high nonlinearity when the confined light is on resonance with the rubidium dipole transition. Fundamentally, our planned approach relies on self induced transparency (SIT), which offers high nonlinearity and absorption-free propagation at the same time. We have theoretically investigated SIT solitons in rubidium vapor to analyze the required parameters to achieve SIT solitons in our rubidium filled HCPCF. The experimental and theoretical approach presented in this thesis suggests an efficient method for generating squeezed light.

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Squeezing by self induced transparency in Rb filled hollow core fibers

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There is great interest in photonic crystal fibers (PCFs) because of their potential for hosting highly nonlinear material. Already with material of low nonlinearity such as silica for solid core PCFs, the nonlinear properties can be utilized since high intensities of light are guided within the core. To create squeezed states, we plan to exploit the high nonlinearity of resonant Rb vapor filled in the hollow fiber core and to use self-induced transparency (SIT) solitons to avoid resonant loss. High nonlinearity is induced from the self-phase modulation of a detuned 2pi soliton. Photon-phonon interactions, which cause a significant amount of excess noise in solid core fibers, will be highly reduced in our system.

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•Aug 29, 2019•0 citations

Non-linear spectroscopy of rubidium in hollow-core fibres

Christopher Perrella

[Truncated] This thesis concerns a new photonic technology based on hollow-core photonic-crystal fibre (HC-PCF) that has been loaded with an atomic vapour. It was demonstrated that this technology may have important applications in the fields of metrology and quantum optics. Furthermore, the small size and robustness of HC-PCF allows these devices to potentially be miniaturised for possible commercial and industrial applications. By filling the HC-PCF with an atomic vapour, excellent light-atom coupling can be attained as both the atoms and light are confined within the same volume. The small transverse dimensions of the fibre’s optical mode leads to high intensities at low input powers, enabling efficient driving of non-linear transitions which would otherwise be difficult with free-space optical systems. Additionally, long interaction lengths, obtained through an arbitrary length of HC-PCF, lead to large optical depths on these typically weak non-linear transitions. The non-linear transition employed here is the 5S1/2 → 5D5/2 rubidium (Rb) two-photon transition. This system is of great interest due to its non-linearity, long excited state lifetime, efficient excitation and large optical depth attained within the HC-PCF. A number of methods for loading a HC-PCF with Rb are discussed, along with proposed ideas for making this process more efficient. Spectroscopic techniques were used to investigate the effect of the fibre’s confined geometry upon the atomic spectra. Extensive theoretical modelling was employed to confirm the observed spectra and give insight to the mechanisms behind the observations. Using this experimental and theoretical knowledge, two applications were targeted: optical atomic frequency standards; and cross phase modulation for quantum logic gates.

•Jan 1, 2013•0 citations
Non-classical states of light, such as squeezed states, enable a wide variety of scientific and engineering applications in optical communication, precision measurements and quantum computing. Therefore, engineering non-classical states of light in different systems for different purposes is interesting and appealing. Non-classical states of light, particularly squeezed states, can be generated from light in a coherent state or vacuum state by using certain optical nonlinear interactions. To efficiently introduce such optical nonlinear interactions, a high nonlinear coefficient of the medium and high intensity of light in the medium are the key factors, where the hollow core photonic crystal fibers filled with atomic vapor shows their great benefits. In this thesis, we report on our approach to apply hollow core photonic crystal fibers (HCPCFs) with the goal to generate squeezed states using strong optical nonlinearities of atomic vapor. In a HCPCF, light with high intensity has a well confined mode over long distances along the fiber. To apply the HCPCF in squeezed state generation, we experimentally investigated unexpected noise properties of the HCPCF and determined the parameter range to reduce excess noise from the fiber. Furthermore, we have filled the hollow core of a piece of HCPCF with rubidium vapor, which provides a high nonlinearity when the confined light is on resonance with the rubidium dipole transition. Fundamentally, our planned approach relies on self induced transparency (SIT), which offers high nonlinearity and absorption-free propagation at the same time. We have theoretically investigated SIT solitons in rubidium vapor to analyze the required parameters to achieve SIT solitons in our rubidium filled HCPCF. The experimental and theoretical approach presented in this thesis suggests an efficient method for generating squeezed light.
There is great interest in photonic crystal fibers (PCFs) because of their potential for hosting highly nonlinear material. Already with material of low nonlinearity such as silica for solid core PCFs, the nonlinear properties can be utilized since high intensities of light are guided within the core. To create squeezed states, we plan to exploit the high nonlinearity of resonant Rb vapor filled in the hollow fiber core and to use self-induced transparency (SIT) solitons to avoid resonant loss. High nonlinearity is induced from the self-phase modulation of a detuned 2pi soliton. Photon-phonon interactions, which cause a significant amount of excess noise in solid core fibers, will be highly reduced in our system.
Our goal is to study quantum optical phenomena in a strong nonlinear optical system. For this purpose, we create a hollow-core photonic-crystal (HCPC) fiber-based platform that confines photons and atomic ensembles together. This enables strong light-matter interactions which are crucial for implementing optical nonlinearities at single-photon levels [1]. We use an optical dipole trap at cesium's magic wavelength to guide laser cooled cesium atoms into and inside the fiber core. This approach will allow us to perform experiments with the dipole trap continuously on as opposed to the previously reported fiber-loading systems [2,3] in which the dipole trap was rapidly amplitude-modulated to avoid the effect from the spatially dependent AC Stark shift. In this system, we perform experiments on electromagnetically induced transparency (EIT) and demonstrate slow light and all optical switch. We also aim to observe large cross-phase modulation (XPM) using a three-level ladder scheme [4,5]. Lastly, the approaches to integrate a cavity into HCPCFs to increase light-matter interactions, thus the optical nonlinearities, will be described.
Strong photon-photon interactions are a key requirement for numerous protocols in quantum computing and communication. Generation of these interactions mediated by atomic vapor in a hollow waveguide has shown great promise, with efficiency enhanced by the tight transverse confinement and extended interaction length in the optical fiber. The authors investigate the strength of such interactions in a series of hollow-core photonic-crystal fibers, and show that they scale only with optical-mode diameter, not mode area (as might be expected). This insight allows targeting of specific photon-photon interaction strengths in waveguide design.
Low-light-level optical nonlinearities are of significant interest for performing operations such as single-photon switching and quantum non-demolition measurements on single-photons. To evoke strong nonlinearities from singlephotons, one can enhance the matter-photon interaction using strongly nonlinear materials such as alkali vapors in combination with an appropriate geometry such as a waveguide, which provides a long interaction length while maintaining a small light mode area. We demonstrate for the first time that such a system can be experimentally realized by loading rubidium vapor inside a hollow-core photonic band-gap fiber. Using the technique of light-induced atomic desorption in this geometry, we have generated optical depths greater than 1000. As a proof of principle, we demonstrate electromagnetically induced transparency (EIT) with control powers 1000 times lower than those used for hot vapor cells in a focused beam geometry. Working with such a high aspect ratio geometry requires us to identify and measure the various sources of decoherence via spectroscopy of desorbed atoms in the fiber. Using such techniques, we also estimate the temperature of the desorbing atoms inside the fiber. The desorption mechanism is studied, and we show that pulsed desorption beams of the right amplitude and duration can be used for generating precisely controlled optical depths. Finally, we investigate the use of various buffer gas techniques for increasing the effective transverse path of the atoms as they move across the fiber in order to reduce their ground state decoherence and map this effect as a function of buffer gas pressure.
The focus of this thesis is to investigate and fabricate a platform that can facilitate the enhancement of light-matter interactions. By tightly confining the photons and atoms to the same region of space, the probability of interaction is drastically increased as compared to free space interactions. Specifically, we focus on forming an optical cavity (or resonator) incorporated into a hollow-core photonic crystal fiber (HCPCF) using two distinct types of reflective mirrors along the axis of the fiber while still permitting atoms to be loaded into the region of high field confinement. \n \nOne means of pursuing this goal that we explored was to propose and numerically simulate two methods for implementing Bragg gratings in a HCPCF. These two methods leave the hollow-core unobstructed and are both based on controlled selective injection of photosensitive polymers into the photonic-crystal region of the hollow-core fiber, followed by interference photolithography. We report the results of numerical simulations for the hollow core fiber with Bragg gratings formed by the two methods. We find that a reflectivity of > 99.99% should be achievable from such fiber-integrated mirrors. Such a device could support high cooperativity and strong coupling regimes to be achieved. \n \nWe also demonstrate a fiber-integrated Fabry-Pérot cavity formed by attaching a pair of dielectric metasurfaces to the ends of a hollow-core photonic-crystal fiber segment. The metasurfaces consist of perforated membranes designed as photonic-crystal slabs that act as planar mirrors but can potentially allow injection of gases through their holes into the hollow core of the fiber. We have so far observed cavities with finesse of 11 and Q-factors of ~ 4.5 × 10^5, but much higher values should be achievable with improved fabrication procedures. We expect this device to enable the advancement of new fiber lasers, enhanced gas spectroscopy, and studies of fundamental light-matter interactions and nonlinear optics. These mirrors can be designed to be polarization dichroic — transparent for one polarization and reflective for another. This unique property can be exploited to allow for all signals to be directed along the high optical depth axis of the cavity and may provide a excellent platform for applications such as optical switching. \n \nFinally, we develop a novel protocol for a single photon all-optical transistor and how it may be implemented in the above mentioned fiber cavity systems. This unique scheme utilizes a far off-resonant vacuum cavity mode to stimulate a Raman absorption process of a source photon which may be switched off by the insertion of a single gate photon into the cavity mode. Relatively high switching contrasts and ratios for the source photon transmission can be obtained in our system.
[Truncated] This thesis concerns a new photonic technology based on hollow-core photonic-crystal fibre (HC-PCF) that has been loaded with an atomic vapour. It was demonstrated that this technology may have important applications in the fields of metrology and quantum optics. Furthermore, the small size and robustness of HC-PCF allows these devices to potentially be miniaturised for possible commercial and industrial applications. By filling the HC-PCF with an atomic vapour, excellent light-atom coupling can be attained as both the atoms and light are confined within the same volume. The small transverse dimensions of the fibre’s optical mode leads to high intensities at low input powers, enabling efficient driving of non-linear transitions which would otherwise be difficult with free-space optical systems. Additionally, long interaction lengths, obtained through an arbitrary length of HC-PCF, lead to large optical depths on these typically weak non-linear transitions. The non-linear transition employed here is the 5S1/2 → 5D5/2 rubidium (Rb) two-photon transition. This system is of great interest due to its non-linearity, long excited state lifetime, efficient excitation and large optical depth attained within the HC-PCF. A number of methods for loading a HC-PCF with Rb are discussed, along with proposed ideas for making this process more efficient. Spectroscopic techniques were used to investigate the effect of the fibre’s confined geometry upon the atomic spectra. Extensive theoretical modelling was employed to confirm the observed spectra and give insight to the mechanisms behind the observations. Using this experimental and theoretical knowledge, two applications were targeted: optical atomic frequency standards; and cross phase modulation for quantum logic gates.