Publications by Cristiano Ciuti

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Superfluidity, the ability of a quantum fluid to flow without friction, is one of the most spectacular phenomena occurring in degenerate gases of interacting bosons. Since its first discovery in liquid helium-4 (refs 1, 2), superfluidity has been observed ...

Microcavity exciton polaritons, the fundamental optical excitations of semiconductor microcavities with quantum wells inside, have been proposed as promising candidates for observing stimulated scattering, condensation and other phenomena related to the bosonic nature of excitons. Having a light mass, quantum degeneracy of polaritons can be reached at low densities and high temperatures. But the radiative time of polaritons is very short (in the picosecond range) and usually prevents an efficient thermaliza

Decay of a particle into more particles is a ubiquitous phenomenon to interacting quantum systems, taking place in colliders, nuclear reactors or solids. In a nonlinear medium, even a single photon would decay by down-converting (splitting) into lower-freq ...

Modifying the photonic environment of a semiconductor quantum well by embedding it in a high-reflectivity microcavity gives rise to new fundamental optical excitations, half-quantum well excitons, half-photons. These particles, called polaritons, have a light mass, as cavity photons, meaning that they have a large De Broglie wavelength. On the other hand, polaritons, like excitons, are subject to Coulomb interaction, a feature generating strong optical nonlinearities. Such properties favour quantum degenera

Cavity polaritons, the elementary optical excitations of semiconductor microcavities, may be understood as a superposition of excitons and cavity photons(1). Owing to their composite nature, these bosonic particles have a distinct optical response, at the same time very fast and highly nonlinear. Very efficient light amplification due to polariton-polariton parametric scattering has recently been reported in semiconductor microcavities at liquid-helium temperatures(2-11). Here we demonstrate polariton param

We demonstrate a method to create potential barriers with polarized light beams for polaritons in semiconductor microcavities. The form of the barriers is engineered via the real space shape of a focalized beam on the sample. Their height can be determined ...

An investigation of the parametric amplification and its coherent control in a semiconductor micro-cavity is presented. The time and angle resolved pump and probe experiments show that several ps after pumping parametric scattering is still phase coherent. The experimental data are in qualitative agreement with the numerical data obtained from a relatively simple theoretical model based on three polarisation components, pump, probe, and idler. This model also predicts that under particular circumstances, th

In a pump-probe experiment, we have been able to control, with phase-locked probe pulses, the ultrafast nonlinear optical emission of a semiconductor microcavity, arising from polariton parametric amplification. This evidences the coherence of the polariton population near k = 0, even for delays much longer than the pulse width. The control of a large population at k = 0 is possible although the probe pulses are much weaker than the large polarization they control. With rising pump power the dynamics of the

We study the subpicosecond gain dynamics in a high-finesse semiconductor microcavity containing quantum wells by means of degenerate pump-probe spectroscopy. Tuning the optical excitation in resonance with both the exciton and the cavity modes, at high pump fields the probe pulses are strongly amplified near the energy of the empty-cavity mode. At zero probe delay, integration of the probe spectrum yields a net gain of several percents. The coherent nature of the gain is demonstrated by its oscillatory beha

In this work we present the coherent control of polariton parametric scattering with weak phase locked probe pulses. It is demonstrated that the signal emission arising from the parametric scattering is completely coherent for moderate excitation power, whereas at high pump density the dynamics appears less coherent due to the depletion of the pump polariton reservoir. It is furthermore demonstrated that the phase of the probe pulses controls the emission from signal, pump, and idler at the same time.

We have studied the femtosecond dynamics of excitonic resonances in quantum well microcavities under strong excitation. Very strong non-linearities are observed, which bear clear resemblance to the non-linearities of an atomic two-level system. The fact that the excitonic system undergoes Rabi flopping and AC Stark splitting is clearly evidenced in a number of cases. Excitation induced dephasing shows an effect much stronger than the light dressing and prevents the observation of the Rabi flopping only when

We investigate the mechanisms leading to the optical non-linearities observed on a strongly excited semiconductor microcavity containing quantum wells. This study of a coupled exciton-cavity system is possible owing to the availability of a sample of exceptionally high quality, permitting to exclude effects of disorder and inhomogeneous broadening. Sub-picosecond pump and probe experiments are performed, in the regime of an incoherent exciton gas of high density. For such a gas the dephasing due to collisio

We study an array of coupled optical cavities in the presence of two-photon driving and dissipation. The system displays a critical behavior similar to that of a quantum Ising model at finite temperature. Using the corner-space renormalization method, we c ...

We present femtosecond gain measurements in microcavity-embedded quantum wells. When the excitonic transition is saturated by an intense pump field, the spectrum measured with a weak probe pulse is strongly modulated by pump-probe wave mixing processes. A giant probe amplification occurs within the bandwidth of the empty-cavity mode. The optical feedback provided by the microcavity is responsible for a net gain of the broadband probe pulse. [S0163-1829(99)50424-4].

The coherent optical response of high quality microcavities containing quantum wells is investigated. The dynamics of the ac Stark effect is investigated by degenerate pump-probe experiments, by exciting the quantum well excitons at various intensities and detunings. The evolution from a simple dynamical excitonic Stark shift to a splitting is dearly observed, even when the excitation is degenerate with the continuum states. The experimental results agree well with the predictions of a theoretical model bas

A dramatic suppression of the absorption of light by exciton polaritons is observed after resonant excitation of the polaritonic modes in a multiple quantum well Bragg structure. Time-resolved reflectivity measurements confirm that this is due to the formation of a dominant superradiant polariton mode created by the light-induced coupling of excitons in different quantum wells that suppress absorption. The stability of the superradiant mode is demonstrated at high excitation powers and at temperatures of up

We report novel oscillator strength transfer phenomena induced by the exciton-exciton correlation. A high quality semiconductor microcavity is resonantly excited by intense circularly polarised sigma(+) pump pulses (100 fs long) and probed at different delays by weak counter-polarised sigma(-) test pulses. We show that the presence of sigma(+) excitons can completely inhibit the creation of sigma(-) excitons. With increasing sigma(+) exciton density the oscillator strength of the a- transition is transferre

A microscopic theory is presented for the giant amplification from microcavities in the strong exciton-photon coupling regime, providing excellent agreement with recent angle-resolved pump-probe experiments. The analytical and numerical solutions give insight into the physics of the polariton parametric amplifier. The coherent gain, due to polariton four-wave-mixing, has a threshold dependence on the pump power and is spectrally blueshifted from the lower polariton energy. The gain shift does not depend on

We study the coherent optical response of a very high-finesse microcavity with a single quantum well by means of degenerate subpicosecond pump-probe spectroscopy. The dynamics of the ac Stark effect versus Pump intensity is investigated upon tuning the empty-cavity;mode-below and above the exciton transition energy, at the exciton continuum onset. The evolution from a simple dynamical excitonic shift to a dynamical splitting is clearly observed in both eases. The qualitative, agreement with numerical calcul

Cristiano Ciuti

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Superfluidity of polaritons in semiconductor microcavities

Towards a room-temperature polariton amplifier

Polariton amplification in semiconductor microcavities

Down-conversion of a single photon as a probe of many-body localization

Polariton parametric amplification in semiconductor microcavities

High-temperature ultrafast polariton parametric amplification in semiconductor microcavities

Light engineering of the polariton landscape in semiconductor microcavities

Quantum kinetics of parametric polariton scattering in microcavities

Coherent control of polariton parametric scattering in semiconductor microcavities

Net coherent optical gain in strongly pumped semiconductor microcavities

Coherence properties of polaritons in semiconductor microcavities

Femtosecond dynamics and non-linearities of exciton-photon coupling in semiconductor microstructures

Intrinsic non-linearities in exciton-cavity-coupled systems

Quantum Critical Regime in a Quadratically Driven Nonlinear Photonic Lattice

Strong coherent gain from semiconductor microcavities in the regime of excitonic saturation

The microcavity AC Stark triplet: Excitation in the exciton continuum

Suppression of exciton-polariton light absorption in multiple quantum well Bragg structures

Crossover from exciton to biexciton cavity polaritons

Theory of the angle-resonant polariton amplifier

Direct observation of an ac Stark splitting in semiconductor microcavities excited above the continuum onset