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Creating and shaping light at single photon level

Supratik Sarkar

Published May 26, 2021• 1 citation
OpenAlex

Abstract

The ability to control light at the single photon level is essential for fully harnessing the power of quantum information theory, and precision measurements. In this thesis, we study two phenomena which can help us to create, and shape light at the smallest scale. In the first part of the thesis, we explore deterministic single photon subtraction based upon single photon Raman interaction of a single three-level Λ-type quantum emitter in a bi-modal cavity or coupled with a chiral waveguide. We study the effect of photon subtraction from different types of optical inputs –- continuous-wave or pulsed coherent states and Fock states, and dependence of the fidelity of subtraction upon key system parameters. We also discuss the suitability and prospects of using different emitter-waveguide systems reported in literature to successfully extract a single photon from an optical input. We find that a quantum dot coupled with a photonic crystal waveguide with high group index could subtract photons with fidelity close to unity. Moreover, we explore how such a SPRINT-based single photon subtraction process can be used to create non-Gaussian states with negative values of Wigner distribution, and negative conditional entropies. Such states can be used as quantum resources in various fields of quantum information theory. Finally, as an interesting example, we also discuss how this mechanism can also be used to create non-classical Fock states of arbitrary photon number. \nIn the second part of this thesis, we study how to shape the emission from a single solid-state quantum emitter, in particular an NV⁻ center in diamond, using two dimensional patterns with sub-wavelength features. We propose a pattern etched on the surface of a diamond sample that enhances the NV's emission in a particular direction, and maximizes coupling with a waveguide substantially far away from the diamond-air interface. Our proposed structure was designed using the adjoint optimization technique, which significantly reduces the amount of computational resources compared to brute-force methods to design an optical element with desired properties. Our structure exhibits a higher directionality of emission compared to other nanophotonic structures reported in the literature -- solid immersion lenses, nanopillars, and bull's eye structures. Finally, we also discuss in details the steps pertaining to setting up a confocal microscope in our laboratory for imaging NV centers, and characterizing our proposed device.

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New Journal of Physics•Nov 1, 2024•13 citations
The ability to control light at the single photon level is essential for fully harnessing the power of quantum information theory, and precision measurements. In this thesis, we study two phenomena which can help us to create, and shape light at the smallest scale. In the first part of the thesis, we explore deterministic single photon subtraction based upon single photon Raman interaction of a single three-level Λ-type quantum emitter in a bi-modal cavity or coupled with a chiral waveguide. We study the effect of photon subtraction from different types of optical inputs –- continuous-wave or pulsed coherent states and Fock states, and dependence of the fidelity of subtraction upon key system parameters. We also discuss the suitability and prospects of using different emitter-waveguide systems reported in literature to successfully extract a single photon from an optical input. We find that a quantum dot coupled with a photonic crystal waveguide with high group index could subtract photons with fidelity close to unity. Moreover, we explore how such a SPRINT-based single photon subtraction process can be used to create non-Gaussian states with negative values of Wigner distribution, and negative conditional entropies. Such states can be used as quantum resources in various fields of quantum information theory. Finally, as an interesting example, we also discuss how this mechanism can also be used to create non-classical Fock states of arbitrary photon number. \nIn the second part of this thesis, we study how to shape the emission from a single solid-state quantum emitter, in particular an NV⁻ center in diamond, using two dimensional patterns with sub-wavelength features. We propose a pattern etched on the surface of a diamond sample that enhances the NV's emission in a particular direction, and maximizes coupling with a waveguide substantially far away from the diamond-air interface. Our proposed structure was designed using the adjoint optimization technique, which significantly reduces the amount of computational resources compared to brute-force methods to design an optical element with desired properties. Our structure exhibits a higher directionality of emission compared to other nanophotonic structures reported in the literature -- solid immersion lenses, nanopillars, and bull's eye structures. Finally, we also discuss in details the steps pertaining to setting up a confocal microscope in our laboratory for imaging NV centers, and characterizing our proposed device.
Engineering photon-photon interactions is fundamentally challenging because photons in vacuum do not interact with each other. While their interactions can be mediated using optical nonlinearities, these effects are negligible for individual photons. This thesis explores two topics related to optical nonlinearities in waveguides. In the first part, we perform a numerical simulation study of hollow core antiresonant reflecting optical waveguides (ARROWs) fabricated using standard lithographic techniques in the context of their suitability as a platform for on-chip photonic quantum information processing. We investigate the effects of the core size, the number of pairs of antiresonant layers surrounding the hollow core, and the refractive index contrast between cladding materials on propagation losses in the waveguide. Additionally, we explore the feasibility of integrating these waveguides with Bragg gratings and dielectric metasurface mirrors to form on-chip cavities, that when loaded with atomic ensembles could act as nonlinear optical devices controllable with single photons. \n \nThe second part of this thesis studies the application of a 3 level quantum emitter coupled to a directional optical waveguide to deterministically subtract a single photon from a propagating optical pulse. Subtracting a single photon from a light state is one of the most fundamental operations with important applications in quantum information processing. However, current methods to subtract a photon such as using a low reflectivity beam splitter suffer from inherently low success probabilities as well as a strong dependence on the number of photons in the input. We explore implementing this single photon subtraction operation in our proposed system when the optical input is a continuous wave coherent state, coherent pulsed state containing a finite number of photons, or a Fock state.
Abstract We propose a scheme for deterministic single photon subtraction based on Single Photon Raman Interaction (SPRINT) with a three-level quantum emitter coupled to a chiral waveguide and present an analytical and numerical study of its feasibility. We show that single photon subtraction probability for pulsed input light in a coherent or a Fock state can approach unity in the ideal limit and discuss the potential of various reported quantum emitter-waveguide platforms as candidates for experimental realization of our scheme. The use of chiral slow-light photonic crystal waveguides coupled to Λ -type emitters can perform efficient photon subtraction. While integrating cold atoms to such systems remains technically challenging, solid-state emitters offer a potentially practical path to realize such photon subtraction.
In this thesis we investigate two domains of control over the photonic emission from NV centers. In the first part of the thesis, which focuses on emission control in the spatial domain, we will be exploring the design of a nanophotonic structure that would be able to control the directionality of photon emission from NV centers. We will be using the inverse design methodology known as adjoint optimization to design the structure. Furthermore we will present FDTD simulations to assess the performance of the designed structure and compare its performance with existing structures. We then present some preliminary experimental results from a confocal microscopy setup we built in our lab. \n \nIn the second part of the thesis, which focuses on emission control in the spectral domain, we investigate the potential of using single NV centers for photon conversion between the microwave and optical regimes. The conversion between the microwave photons, that couple to superconducting qubits, and optical photons, that are used in long range communication and memories, is an important component in realizing an extended quantum network. In our proposed scheme, we explore the use of Λ system in NV centers coupled to optical and microwave cavities as a platform for efficient conversion between the microwave and optical regimes. We present analytical and numerical simulations to identify the required characteristics of the system to achieve high conversion efficiencies.
This Thesis is focused on the study of quantum electrodynamics in photonic crystal waveguides. We investigate the interplay between a single quantum dot and the fundamental mode of the photonic crystal waveguide. We demonstrate experimental coupling eciencies for the spontaneous emission into the mode exceeding 98% for emitters spectrally close to the band-edge of the waveguide mode. In addition we illustrate the broadband nature of the underlying eects, by obtaining coupling eciencies above 90% for quantum dots detuned from the band edge by as far as 20nm. These values are in good agreement with numerical simulations. Such a high coupling eciency implies that the system can be considered an articial 1D-atom, and we theoretically show that this system can generate strong photon-photon interaction, which is an essential functionality for deterministic optical quantum information processing. We present the progress towards the experimental demonstration of such a strong photon-photon nonlinearity. We present the rst signatures of resonant transmission in photonic crystal waveguides and discuss some of the encountered diculties and future directions of the experiments. In the nal part of this Thesis we discuss a novel type of photonic crystal waveguide and show its applications for on-chip quantum information processing. This structure was designed for the ecient mapping of two orthogonal circular dipole transitions to dierent propagation paths of the emitted photon, i.e. exhibits chiral quantum-dot-waveguide coupling. Such a structure is ideally suited for a number of applications in quantum information processing and among others we propose an on-chip spin-photon interface, a single photon transistor, and a deterministic cNOT gate.
Realising a platform for efficiently guiding and manipulating light at the singlephoton level lies at the heart of optical quantum information processing. In this thesis we aid in the pursuit of this goal by analysing few-photon transport properties in photonic devices while keeping in mind possible applications and experimental challenges. We especially focus on single and two-photon transport properties in one-dimensional waveguides coupled to (artificial) atoms modelled as two and three-level emitters. We begin by introducing key concepts relevant for this thesis and then explain how to model such waveguide geometries. We show how directional-dependent coupling between a waveguide and a localized quantum system can be modelled from a chain of harmonic oscillators by allowing the system to couple to more than one site. Using the input-output formalism and scattering matrix theory we determine a general form for the single and two-photon S-matrices for a waveguide coupled to a two-level system. We also explain how to engineer a quantum optical Fanoresonance waveguide geometry and calculate how this modifies the S-matrices, the few-photon scattering probabilities, and the scattered output spectra. We show that the nonlinear effects in such a system generates highly correlated directional scattering probabilities. We device a protocol that can generate maximal entanglement between two spectrally distinct solid-state emitters by the use of multi-photon scattering. The results also reveal a rich structure for multi-photon states interacting with non-identical emitters. As a final investigation, we quantify how spectral diffusion in quantum dots affects finite-width single and two-photon scattering. Single-photon scattering probabilities are described by a simple convolution but this is not the case for a two-photon state scattering off a two-level emitter. We show that the effect of spectral wandering depletes the nonlinear scattering properties, but that it affects co and counter-propagating output probabilities differently.
Abstract We explore a recently demonstrated deterministic photon subtraction scheme, based on single-photon Raman interaction with a Λ-type three-level atom, as a tool for manipulating quantum state of few-photon light pulses. We establish a comprehensive theoretical framework using input–output formalism and quantum regression theorem, enabling calculation of the first order autocorrelation matrices of the output light and identification of the temporal modes present in the generated light via their eigendecomposition. By modeling the entire system as a quantum network consisting multiple virtual cavities and a lambda-type emitter cascaded in two parallel guided modes of opposite propagation directions, we extract the quantum state occupying the modes of interest. For both squeezed vacuum and coherent light input pulses, the Wigner function of the output light after photon subtraction clearly reveals its non-Gaussian character. Furthermore, we propose a measurement-based scheme on the subtracted photon which can lead to conditional generation of quantum states resembling Schrodinger’s kitten state directly from coherent input light with fidelities above 99%. This result is particularly nothworthy, as coherent pulses, unlike the squeezed vacuum inputs commonly used in previous studies, are readily available in most experimental setups.