The main observation in favor of BEC is the clear evidence for long-range spatial coherence of the whole polariton gas. This measurement is obtained through the use of a specially designed Michelson interferometer. Although many of the properties that we have observed might show similar behavior for a VCSEL-like laser, some of the differences clearly allow to differentiate a polariton condensate from a standard laser. According to the accepted terminology, as we are observing a thermalized distribution below threshold, what we observe is not a polariton laser but a Bose-Einstein condensate indeed.

Eventually, we study some of the consequences of the inherent disorder in semiconductor microstructures. This brings along some important observations. The first one is mode synchronization that allows the condensate to overcome residual disorder. The second one is the observation of pinned vortices, an indication of possible superfluid-like effects in the presence of disorder.

## Coherent spectroscopy for sensing inside photonic devices

In the last decade, a two-dimensional bosonic system called microcavity exciton-polariton has emerged as a new, promising candidate of Bose Einstein Condensation BEC in solids. Many pieces of important evidence of polariton BEC have been established very recently in GaAs and CdTe microcavities at liquid-helium temperature, opening a door to rich many-body physics inaccessible in experiments before. In parallel with experimental progresses, theory and numerical simulations are developed, and our understanding of the system has greatly advanced.

In this article, we review the recent experimental and theoretical results obtained at Stanford University. We derive a theory of polariton Bose-Einstein condensation based on the many-body quantum field theory of interacting Bose particles. In particular, we describe self-consistently the linear exciton-photon coupling and the exciton-non-linearities, by generalizing the Hartree-Fock-Popov description of BEC to the case of two coupled Bose fields at thermal equilibrium. In this way, we compute the density-dependent one-particle spectrum, the energy occupations and the phase diagram.

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The results quantitatively agree with the existing experimental findings. We discuss the conditions under which polaritons can be considered as a dilute Bose gas at thermal equilibrium. While the diluteness is enforced by the very peculiar energy-momentum dispersion, thermal equilibrium is only partially achieved in common experiments.

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A basic tool to model the kinetics of polariton BEC is then derived in terms of Boltzmann equations, including polariton-phonon and polariton-polariton scattering. We discuss under which conditions thermal equilibrium condensation can be reached and how to design future microcavity samples in order to reach this goal. Coupled electron-nuclear spins are promising physical systems for quantum information processing: By combining the long coherence times of the nuclear spins with the ability to initialize, control, and measure the electron spin state, the favorable properties of each spin species are utilized.

We present a vision of how these systems could be used as the fundamental processor of a quantum computer, in which the nuclear spins are analogous to local memory units, whereas the electron spins act as buses. In particular, we focus on control of a system in which a single electron spin is coupled to N nuclear spins via resolvable anisotropic hyperfine interactions.

High-fidelity universal control of this 1-electron—N-nuclei system is possible exclusively using excitations on a single electron spin transition. This electron spin actuator control is implemented by using optimal control theory to find the modulation sequences that generate the desired unitary operations. A model to fully characterize decoherence of the nuclear qubits in this context is currently under investigation. Up to now, coherent control using an electron spin actuator in an ensemble of anisotropic hyperfine-coupled 1-electron—1-nucleus systems has been achieved, providing evidence that we can generate any unitary operation on such systems while sitting on a single transmitter frequency Hodges J.

A, 78 Data was acquired using a custom-built pulsed electron spin resonance spectrometer. We have introduced a quasi—one-dimensional 1D bosonic gas of indirect excitons in semiconductor nanotubes of type-II quantum wells and studied theoretically the coherent properties of this interacting gas.

We firstly obtain the spectrum of a single exciton in such cylindrical geometry. Thus, we calculate the exciton-exciton interaction at the ground state and show that the excitons form a quasi-1D bosonic gas with repulsion interaction. Finally, by mapping the exciton gas onto an exactly solvable quasi-1D bosonic gas at the low temperature and low density limit where the bosonic features of the gas are dominant, we show that the gas is in the strong-coupling regime, and the excitons become fermions.

We have theoretically studied the radiative decay of excitons in a film with nano-to-macro crossover thickness. Under the phase matching condition between exciton center-of-mass motion and the radiation field, the exciton radiative decay rate gets larger with increasing thickness because of the increment of the interaction volume. This is called exciton superradiance. However, it is suppressed at thickness over a particular length because the Fermi's golden rule is broken in exciton-photon interaction, i. Its suppression condition is the main result of our study. We define an apparent propagation speed of the superradiant exciton as an effective thickness, which renormalizes the multiple reflection effect in the film, divided by the radiative decay time.

This propagation speed also increases together with the thickness, and the exciton superradiance is suppressed when it reaches the group velocity of exciton polaritons. Afterward, the exciton radiative decay rate decreases inversely proportional to the thickness. Since the birth of quantum mechanics, interference effects between different paths have represented one of the most fascinating signatures of this theory.

Systems of three-level atoms show a remarkable example of this effect. If one couples a long-living metastable state to an excited state by means of a strong laser field and one then probes the ground-excited transition of the dressed atom by means of another weak laser field, one will see no absorption and all the radiation will be transmitted through the atomic medium. This phenomenon is called Electromagnetically Induced Transparency EIT and it can be explained in terms of quantum interference between different atomic excitation schemes.

An atomic medium under EIT conditions shows a polaritonic dispersion, with three branches near the Raman two-photon transition between the ground and metastable states. The central polariton is characterized by a huge reduction of the group velocity of light which can be controlled by the intensity of the dressing field. The energy of the incoming radiation then coherently oscillates between electromagnetic field and atomic excitations: this gives rise to a trapping effect which eventually slows down the radiation, as can be seen in a full quantum treatment.

In the limit of a vanishing coupling field, all the radiation energy is stored as a coherent collective atomic excitation. We have first studied the dispersion of light for a lattice of three-level atoms in the linear regime by means of the semi-classical Transfer Matrix technique: we have obtained the different polariton bands and the reflection spectrum at the interface of the atomic medium. The latter shows a dip in correspondence of the Raman resonance which is associated to the refractive index going to 1.

We have verified that this feature still holds in the case of a hole lack of one atom in the lattice. Instead, in the case of an impurity consisting of an undressed two-level atom, a peak appears at Raman resonance and the radiation is fully scattered back.

This case can be important for the behaviour of the system in the non-linear regime. Beyond the steady-state picture, the slow propagation of light opens the possibility of modulating the dressing laser field in order to manipulate in real time a travelling polariton. This is an example of a dynamical photonic structure; similar schemes have been suggested for photon lifter applications. We are presently investigating the effect of dynamical changes of the dressing field on the scattering amplitude from a defect: this problem is of interest in the perspective of probing the new quantum phases of ultracold gases by means of slow light.

The competition between the Zeeman energy and the Rashba and Dresselhaus spin-orbit couplings is studied for ferromagnetic states in the fractional quantum Hall regime. A transition of the spin-polarization direction, which acquires an in-plane component even if the magnetic field is perpendicular to the quantum well, is predicted to occur at small values of the Zeeman energy, as an effect of the spin-orbit interaction.

For a given fractional state, we theoretically investigate this phenomenon in the perturbative limit of high magnetic fields. We consider the Laughlin wave functions and the Pfaffian state as specific examples of possible ground states, and show that the quantitative features of this transition provide valuable information about the nature of the correlated ground-state. In particular, a relation to the pair-correlation function is derived. We also discuss indications of non-analytic features around the fractional states and include effects of the nuclear bath polarization, which are significant in a relevant range of temperatures and magnetic fields.

Recent mid-infrared absorption Anappara A. We theoretically investigated the effect of this strong light-matter coupling on intersubband electroluminescence. In a first work De Liberato S. B, 77 , using a cluster factorization method, we derived a closed set of dynamical equations for the quantum well carrier and cavity photon occupation numbers, the correlation between the cavity field and the intersubband polarization, as well as polarization-polarization contributions.

Solving the resulting set of equations in the stationary regime, we were able to fully characterize the transport and electroluminescence properties as a function of the applied voltage. In a second work De Liberato S. We were thus able to investigate how the electronic states are modified by the coupling to the microcavity vacuum field and showed that resonant electron tunneling from a narrow-band injector can selectively excite superradiant states and produce ultraefficient polariton electroluminescence. Guest Access. Register Log in. As a guest user you are not logged in or recognized by your IP address.

Description This volume gives an overview of the manifestations of quantum coherence in different solid state systems, including semiconductor confined systems, magnetic systems, crystals and superconductors. Order hardcopy.

## Coherent spectroscopy for sensing inside photonic devices

Front Matter. Quattropani, B. Download PDF. Exploring the quantum dynamics of atoms and photons in cavities. Abstract These lecture notes review microwave cavity experiments in which Rydberg atoms interact one by one with superconducting cavities. Generation of entangled photons in semiconductors. Abstract We review the recent progress in the generation of entangled photons in semiconductors. Quantum optics with single-electron charged quantum dots.

Abstract A quantum dot with an excess conduction band electron constitutes a new paradigm for solid-state quantum optics.

Quantum computing with electron spins in quantum dots. Abstract Several topics on the implementation of spin qubits in quantum dots are reviewed. Quantum interferometry with complex molecules. Abstract This paper reviews recent experiments on matter wave interferometry with large molecules. Decoherence and entanglement of quantum states. Amplifying quantum signals with Josephson tunnel junction circuits. Abstract Amplifiers are crucial in every experiment carrying out a very sensitive measurement. Electromagnetically induced transparency in semiconductors. Abstract Controlling quantum coherence in light-matter interactions is a key step for advanced ultra-fast and quantum information technology.

Coherent optical spectroscopy of semiconductor nanostructures. Abstract Coherent optical spectroscopy of semiconductor nanostructures is a well-established field with several decades of history. Quantum polaritonics in semiconductor microcavities. Quantum correlations in exciton systems. Abstract Here we present a microscopic quantum theory able to describe the quantum optical effects originating from nonlinear optical interactions involving excitons. Introduction to Bose-Einstein condensation.

Abstract We present a short introduction to a series of review papers and books published in the last 10 years, relative to the theoretical and experimental developments in the field of ultracold atomic gases. Quantum coherence due to Bose-Einstein condensation of parametrically driven magnons.

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Abstract Magnons are Bose particles, therefore under particular conditions they should demonstrate Bose-Einstein condensation. Optical manipulation of excitonic particles into a quantum degenerate regime. Abstract Collective quantum mechanical phenomena such as superfluidity and superconductivity are observed for particles at a high density and low temperature.

Bose-Einstein condensation of polaritons in microcavities. Baas, K. Lagoudakis, M. Wouters, S. Kundermann, B. Pietka, D. Sarchi, V. Savona, M. Richard, R. Dang, J. Kasprzak, I. Search for books, journals or webpages All Pages Books Journals. View on ScienceDirect. Authors: Toshihide Takagahara. Hardcover ISBN: Imprint: Academic Press. Published Date: 10th February Page Count: For regional delivery times, please check When will I receive my book? Sorry, this product is currently out of stock.

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Institutional Subscription. Free Shipping Free global shipping No minimum order. The first up-to-date review articles on various aspects on quantum coherence, correlation and decoherence in semiconductor nanostructures. Kyoto Institute of Technology, Japan. Powered by.