The quantum noise in photocurrent fluctuations usually gives incomplete information about the quantum state of spectral sideband modes of bright light beams involved in the detection. Each frequency component of the noise spectrum corresponds to two sideband modes symmetrically located around the bright optical field. In the case of the usual homodyne detection, it limits the ability to recover discriminated information of each mode involved. We theoretically show that complete reconstruction of the two-mode quantum state can be obtained by using phase-locked (coherent) resonator detection, even for non-Gaussian states. We experimentally demonstrate the technique by measuring a two-mode displaced coherent state.

We measure the complete quantum state for six modes of the electromagnetic field produced by an optical parametric oscillator. The investigation involves the sideband of the intense pump, signal, and idler fields generated by stimulated parametric downconversion inside a triply resonant optical resonator. We develop a theoretical model to successfully interpret the experimental results. The model takes into account the coupling of the field modes to the phonon bath of the nonlinear crystal, clearly showing the roles of different physical effects in shaping the structure of the quantum correlations between the six optical modes.

O seminário descreverá métodos analíticos baseados na espectroscopia no infravermelho próximo (NIR) desenvolvidos pelo grupo de pesquisa da palestrante para análise de combustíveis (diesel, biodiesel e gasolinas). Para tanto, serão consideradas as ferramentas quimiométricas utilizadas para construção dos modelos de calibração multivariada, bem como ferramentas para seleção de variáveis espectrais e transferência de modelos de calibração.

We demonstrate, theoretically and experimentally, the generation of hexapartite modal entanglement by the optical parametric oscillator (OPO) operating above the oscillation threshold. We show that the OPO generates a rich structure of entanglement among sets of six optical sideband modes interacting through the nonlinear crystal. The class of quantum states thus produced can be controlled by a single parameter, the power of the external laser that pumps the system. Our platform allows for the generation of massive entanglement among many optical modes with well defined but vastly different frequencies, potentially bridging nodes of a multicolor quantum network.

We consider the quantum processor based on a chain of trapped ions to propose an architecture wherein the motional degrees of freedom of trapped ions (position and momentum) could be exploited as the computational Hilbert space. We adopt a continuous-variables approach to develop a toolbox of quantum operations to manipulate one or two vibrational modes at a time. Together with the intrinsic non-linearity of the qubit degree of freedom, employed to mediate the interaction between modes, arbitrary manipulation and readout of the ionic wave function could be achieved.

The optical parametric oscillator (OPO) is a non-linear optical device capable of producing an effective interaction among optical modes with different colors. Up to now, it was believed that only three modes would be involved in the interaction. By developing a new theoretical model to analyze the sideband structure of entanglement, we show that in fact six modes are involved in the stimulated parametric interaction. We experimentally investigate how those modes are entangled to one another, in particular showing that the hexapartite entanglement can be thought of as being generated by a combination of two-mode squeezers and beam splitter Hamiltonians acting on six different colors of light.

The introduction of phase coherence in the detection of quantum noise of light yields a pure quantum measurement of spectral modes. We theoretically show that such coherent quantum measurement performed with the technique of resonator detection (RD) is able to access any direction in the two-mode phase space of spectral sidebands under appropriate conditions, thus furnishing a complete measurement of the four-dimensional Wigner function. We obtain a realistic measurement operator for coherent RD by including the effects of imperfect resonator mode matching in our analysis. Moreover, we experimentally demonstrate the realization of phase coherent RD to characterize a two-mode displaced quantum state.

Gaussian quantum states hold special importance in the continuous variable (CV) regime. In quantum information science, the understanding and characterization of central resources such as entanglement may strongly rely on the knowledge of the Gaussian or non-Gaussian character of the quantum state. However, the quantum measurement associated with the spectral photocurrent of light modes consists of a mixture of quadrature observables. Within the framework of two recent papers [Phys. Rev. A 88, 052113 (2013) and Phys. Rev. Lett. 111, 200402 (2013)], we address here how the statistics of the spectral photocurrent relates to the character of the Wigner function describing those modes. We show that a Gaussian state can be misidentified as non-Gaussian and vice-versa, a conclusion that forces the adoption of tacit \textit{a priori} assumptions to perform quantum state reconstruction. We experimentally analyze the light beams generated by the optical parametric oscillator (OPO) operating above threshold to show that the data strongly supports the generation of Gaussian states of the field, validating the use of necessary and sufficient criteria to characterize entanglement in this system.

We show that quantum noise in the spectral domain usually corresponds to a mixed quantum measurement, and cannot attain complete information about the quantum state of spectral modes [PRL 111, 200402 (2013).]

In the spectral domain, the quantum state of the three beams emitted by an above-threshold optical parametric oscillator encompasses six modes. We use resonator detection to characterize hexapartite entanglement.

We revisit the problem of quantum state reconstruction of light beams from the photocurrent quantum noise. As is well known, but often overlooked, two longitudinal field modes contribute to each spectral component of the photocurrent (sideband modes). We show that spectral homodyne detection is intrinsically incapable of providing all the information needed for the full reconstruction of the two-mode spectral quantum state. Such a limitation is overcome by the technique of resonator detection. A detailed theoretical description and comparison of both methods is presented, as well as an experiment to measure the six-mode quantum state of pump-signal-idler beams of an optical parametric oscillator above the oscillation threshold.

Spectral homodyne detection, a widely used technique for measuring quantum properties of light beams, cannot retrieve all the information needed to reconstruct the quantum state of spectral field modes. We show that full quantum state reconstruction can be achieved with the alternative measurement technique of resonator detection. We experimentally demonstrate this difference by engineering a quantum state with features that go undetected by homodyne detection but are clearly revealed by resonator detection.

We demonstrated the direct generation of multipartite continuous-variable entanglement and investigated its robustness against losses. This led to the development of experimental capabilities to fully characterize a six-mode quantum optical state.

The ability to precisely manipulate an isolated quantum system opens new avenues in the simulation of more complicated quantum systems, using the tools of quantum computation. While the paradigm of quantum computation nowadays considers a collection of two-level systems known as qubits, it is also possible to generalize the basic logic quantum units to multi-level or even continuous systems.

We experimentally investigate quantum entanglement among three beams of light produced by the optical parametric oscillator. We aim to understand how entanglement is distributed among the light beams and associated optical sideband field modes.

In recent years we have investigated pump-signal-idler entanglement in the above-threshold optical parametric oscillator. Spectral homodyne-type detection probes two sidebands at a given analysis frequency per beam. Hexapartite entanglement is observed.

Interferometric techniques, combined with electronic signal processing, have provided powerful tools for the precise reconstruction of quantum states of the field. Nevertheless, in most cases the completeness of the measurement relies in strong assumptions about its symmetry. In the present work, I will show how the use of optical cavities as a tool for state reconstruction can provide a complete description of the state, relaxing a priori assumptions and revealing a broad distribution of entanglement among sidebands of different optical beams, as in the case of those generated by an optical parametric oscillator.

Today the interaction of light and matter on the single quantum level is a wide research field. Strong coupling between a single photon and a single atom has already been achieved with optical cavities. Here, we treat strong interaction in free space, i.e. strong interaction whilst maintaining the free space density of states of the electromagnetic field. We pursue the coupling of a properly designed single photon wave packet to a single ion aiming at an excitation probability close to unity. For this purpose a linear dipole transition of an ion localized in the focal point of a deep parabolic mirror is addressed by a collimated laser beam focused onto the ion from nearly the full solid angle. In order to reach the highest possible coupling strength, the incident vectorial light field must be matched to the radiation pattern of the corresponding atomic transition both in the spatial and in the temporal domain. Here the generation of such an incident light mode is presented.

We report on progress towards achieving a full 4pi solid angle strong coupling between a single trapped ion and a light field using a deep parabolic mirror enabling both efficient photon collection and ion excitation.