Quantum nonlinear optics using single atom

[ANGLÈS] In this thesis we tried to investigate the non-linear effects introduced by a generalized interaction of a two-level atom coupled to two photons. Scattering matrices were used to calculate the non-linear effects introduced and the dependence of outgoing frequencies of quantum light on these effects was found. It was seen as quite opposed to typical classical theories, that the non-linear susceptibility for an atom dictates very precise output frequencies from it. As a next step this work probes into quantum computing in which the two-photon bound state problem was mathematically established to show that a single two-level atom cannot be used in realization of non-linear logical operations in quantum computations. In the end a possible intuitive solution, involving dissimilar decay rates in three level systems, was thought of and shown that it can be effectively applied to quantum logic.[CASTELLÀ] En esta tesis hemos tratado de investigar los efectos no lineales introducidos por una interacción generalizada de un átomo de dos niveles acoplado a dos fotones. Matrices de dispersión se utilizaron para calcular los efectos no lineales introducidos y fue encontrada la dependencia de las frecuencias de salida de luz cuántica de estos efectos. Fue visto como totalmente opuesta a las típicas teorías clásicas, que la susceptibilidad no lineal para un átomo determina de una forma muy precisa las frecuencias de salida. Como paso siguiente este trabajo sondea en la computación cuántica en el que se estableció el problema de dos fotones estado ligado matemáticamente para mostrar que un solo átomo de dos niveles no se puede utilizar en la realización de operaciones no lineales lógicas en cálculos cuánticos. Al final, una posible solución intuitiva, relativa a tipos diferentes de descomposición en tres sistemas de nivel, fue pensada y demostrada que puede ser efectivamente aplicada a una lógica cuántica.[CATALÀ] En aquesta tesi hem intentat investigar els efectes no lineals introduïts per una interacció generalitzada d'un àtom de dos nivells acoblat a dos fotons. Es van utilitzar matrius de dispersió per calcular els efectes no lineals introduïts i es va trobar la dependència de les freqüències de sortida de llum quàntica d'aquests efectes. Va ser vist com totalment oposada a les típiques teories clàssiques, que la susceptibilitat no lineal per a un àtom determina d'una forma molt precisa les freqüències de sortida. Com a pas següent aquest treball sondeja en la computació quàntica en què es va establir que el problema de dos fotons està lligat matemàticament per mostrar que un sol àtom de dos nivells no es pot utilitzar en la realització d'operacions no lineals lògiques en càlculs quàntics. Al final, una possible solució intuïtiva, relativa a tipus diferents de descomposició en tres sistemes de nivell, va ser pensat i demostrat que pot ser efectivament aplicat a una lògica quàntica

Quantum nonlinear optics using single atom

[ANGLÈS] In this thesis we tried to investigate the non-linear effects introduced by a generalized interaction of a two-level atom coupled to two photons. Scattering matrices were used to calculate the non-linear effects introduced and the dependence of outgoing frequencies of quantum light on these effects was found. It was seen as quite opposed to typical classical theories, that the non-linear susceptibility for an atom dictates very precise output frequencies from it. As a next step this work probes into quantum computing in which the two-photon bound state problem was mathematically established to show that a single two-level atom cannot be used in realization of non-linear logical operations in quantum computations. In the end a possible intuitive solution, involving dissimilar decay rates in three level systems, was thought of and shown that it can be effectively applied to quantum logic.[CASTELLÀ] En esta tesis hemos tratado de investigar los efectos no lineales introducidos por una interacción generalizada de un átomo de dos niveles acoplado a dos fotones. Matrices de dispersión se utilizaron para calcular los efectos no lineales introducidos y fue encontrada la dependencia de las frecuencias de salida de luz cuántica de estos efectos. Fue visto como totalmente opuesta a las típicas teorías clásicas, que la susceptibilidad no lineal para un átomo determina de una forma muy precisa las frecuencias de salida. Como paso siguiente este trabajo sondea en la computación cuántica en el que se estableció el problema de dos fotones estado ligado matemáticamente para mostrar que un solo átomo de dos niveles no se puede utilizar en la realización de operaciones no lineales lógicas en cálculos cuánticos. Al final, una posible solución intuitiva, relativa a tipos diferentes de descomposición en tres sistemas de nivel, fue pensada y demostrada que puede ser efectivamente aplicada a una lógica cuántica.[CATALÀ] En aquesta tesi hem intentat investigar els efectes no lineals introduïts per una interacció generalitzada d'un àtom de dos nivells acoblat a dos fotons. Es van utilitzar matrius de dispersió per calcular els efectes no lineals introduïts i es va trobar la dependència de les freqüències de sortida de llum quàntica d'aquests efectes. Va ser vist com totalment oposada a les típiques teories clàssiques, que la susceptibilitat no lineal per a un àtom determina d'una forma molt precisa les freqüències de sortida. Com a pas següent aquest treball sondeja en la computació quàntica en què es va establir que el problema de dos fotons està lligat matemàticament per mostrar que un sol àtom de dos nivells no es pot utilitzar en la realització d'operacions no lineals lògiques en càlculs quàntics. Al final, una possible solució intuïtiva, relativa a tipus diferents de descomposició en tres sistemes de nivell, va ser pensat i demostrat que pot ser efectivament aplicat a una lògica quàntica

Full vectorial mapping of the complex electric near-fields of THz resonators

Using micro-structured photo-conducting probes, we demonstrate full vectorial mapping of the complex electric fields in the near-field region of a resonant structure at THz frequencies. The investigated structure represents the simplest case of a resonator: a metallic rod. We show field amplitude as well as phase maps for the three field components at the half wavelength (λ/2) resonance of the rod. The field as well as the phase distributions are in excellent agreement with our physical understanding of local electric-field distributions in the vicinity of λ/2 resonant structures and are validated by numerical simulations. These measurements can be a platform for performance optimization of the emerging field of THz photonic and plasmonic devices with complex sub-wavelength structures

Diffraction enhanced transparency (DET) using frequency detuned and displaced resonant rods

In this contribution, we demonstrate that a periodic lattice of frequency-detuned and displaced resonant rods can suppress the THz extinction at the central resonant frequency, leading to an enhanced spectral window of near perfect transparency. The system consists of a periodic lattice of metallic rods of two different sizes. Each of the rods supports a strong half-wavelength (λ/2) resonance which are detuned with respect to each other. Furthermore, both the rods are spatially displaced within each unit cell of the lattice. The group-index obtained from far-field measurements shows that the THz field is strongly delayed by more than four orders of magnitude at the spectral transparency window. Using micro-spectroscopic measurements of the electric near fields, we show that this transparency window has its origin in the interference between two surface lattice resonances, arising from the diffractively enhanced radiative coupling of the two λ/2 resonances in the lattice. Thus, we term this phenomenon as Diffraction Enhanced Transparency (DET). Since DET does not involve near-field coupling between resonators, the fabrication tolerance to imperfections is expected to be very high. This remarkable response and ease of fabrication renders these systems as very interesting components for THz communicatio

Visualizing near-field coupling in terahertz dolmens

\u3cp\u3eStrong interactions between resonant structures in the near-field occur at length scales shorter than the wavelength, and can be exploited for modifying the propagation of electromagnetic radiation. Dolmen-like structures, formed by a rod supporting a dipolar (bright) resonance and two orthogonal rods with a quadrupolar (dark) resonance at the same frequency, represent a geometry of significant interest for near-field electromagnetic coupling. These structures demonstrate electromagnetically induced transparency (EIT) through coupling between these resonances, concurrently providing a sharp spectral selectivity in transmission and large group velocity reduction. We use near-field terahertz scanning microscopy to map the electric fields in the vicinity of a metallic dolmen in both amplitude and phase. In this way, we directly measure the interaction between bright and dark modes in the time-domain, revealing the physics resulting in EIT. We experimentally demonstrate the hybridization of bright and dark modes accompanying the near-field coupling, as well as the excitation of the dark mode at the frequency of the far-field transparency.\u3c/p\u3

Visualizing near-field coupling in terahertz dolmens

Strong interactions between resonant structures in the near-field occur at length scales shorter than the wavelength, and can be exploited for modifying the propagation of electromagnetic radiation. Dolmen-like structures, formed by a rod supporting a dipolar (bright) resonance and two orthogonal rods with a quadrupolar (dark) resonance at the same frequency, represent a geometry of significant interest for near-field electromagnetic coupling. These structures demonstrate electromagnetically induced transparency (EIT) through coupling between these resonances, concurrently providing a sharp spectral selectivity in transmission and large group velocity reduction. We use near-field terahertz scanning microscopy to map the electric fields in the vicinity of a metallic dolmen in both amplitude and phase. In this way, we directly measure the interaction between bright and dark modes in the time-domain, revealing the physics resulting in EIT. We experimentally demonstrate the hybridization of bright and dark modes accompanying the near-field coupling, as well as the excitation of the dark mode at the frequency of the far-field transparency

Diffraction Enhanced Transparency and Slow THz Light in Periodic Arrays of Detuned and Displaced Dipoles

We demonstrate that a periodic lattice of detuned resonators can suppress the THz extinction at the central resonant frequency, leading to an enhanced transparency due to diffraction. The system consists of metallic rods of two different sizes, each of them supporting a strong half-wavelength (λ/2) resonance, which are spatially displaced within the unit cell of the lattice. Using a coupled dipole model we show that the diffraction enhanced transparency (DET) window has its origin in the interference between two surface lattice resonances, arising from the diffractively enhanced radiative coupling of the λ/2 resonances in the lattice. Group-index measurements show that the THz field is strongly delayed by more than 4 orders of magnitude at the transparency window. Since DET does not involve the near-field coupling of resonators, the fabrication tolerance to imperfections is expected to be very high. This remarkable response renders these systems as very interesting components for THz communication