Vortices provide the elementary quanta of rotation in superfluids. Here we exploit the natural assets of open-dissipative exciton-polariton fluids to set into ultrafast spiraling motion a doubly-charged vortex, which also results in the time-varying orbital angular momentum of emitted light. The created topology comprises all the possible polariton pseudospins filling the associated Hilbert space of states, with each of them appearing twice in real space where the Bloch sphere is mapped. The intrinsic quantity characterizing the topological link between the two spaces— the Berry curvature—is reshaping in time, but always keeps a space integral of twice the solid angle.
Lorenzo Dominici, David Colas, Stefano Donati, Galbadrakh Dagvadorj, Antonio Gianfrate, Carlos Sánchez Muñoz, Dario Ballarini, Milena De Giorgi, Giuseppe Gigli, Marzena Szymańska, Fabrice Laussy, Daniele Sanvitto
Here we present different approaches to ultrafast pulse and polarization shaping, based on a “quantum fluid” platform of polaritons. Indeed we exploit the normal modes of two dimensional polariton fluids made of strong coupled quantum well excitons and microcavity photons, by rooting different polarization and topological states into their sub-picosecond Rabi oscillations. Coherent control of two resonant excitation pulses allows us to prepare the desired state of the polariton, taking benefit from its four-component features given by the combination of the two normal modes with the two degrees of polarization. An ultrafast imaging based on the digital off-axis holography technique is implemented to study the polariton complex wavefunction with time and space resolution. We show in order coherent control of the polariton state on the Bloch sphere, an ultrafast polarization sweeping of the Poincaré sphere, and the dynamical twist of full Poincaré states such as the skyrmion on the sphere itself. Finally, we realize a new kind of ultrafast swirling vortices by adding the angular momentum degree of freedom to the two-pulse scheme. These oscillating topology states are characterized by one or more inner phase singularities tubes which spirals around the axis of propagation. The mechanism is devised in the splitting of the vortex into the upper and lower polaritons, resulting in an oscillatory exchange of energy and angular momentum and in the emitted time and space structured photonic packets.
Exciton-polaritons, composite particles resulting from the strong coupling between excitons and photons, have shown the capability to undergo condensation into a macroscopically coherent quantum state, demonstrating strong non-linearities and unique propagation properties. These strongly-coupled light-matter particles are promising candidates for the realization of semiconductor all-optical devices with fast time response and small energy consumption. Recently, quantum fluids of polaritons have been used to demonstrate the possibility to implement optical functionalities as spin switches, transistors or memories, but also to provide a channel for the transmission of information inside integrated circuits. In this context, the possibility to extend the range of light-matter interaction up to room temperature becomes of crucial importance. One of the most intriguing promises is to use organic Frenkel excitons, which, thanks to their huge oscillator strength, not only sustain the polariton picture at room temperature, but also bring the system into the unexplored regime of ultra-strong coupling. The combination of these materials with ad-hoc designed structures may allow the control of the propagation properties of polaritons, paving the way towards their implementation of the polariton functionalities in actual devices for opto-electronic applications.
A scheme to observe direct experimental evidence of Jaynes-Cummings nonlinearities in a strongly dissipative cavity quantum electrodynamics system was devised. In such a system, large losses compete with the strong light-matter interaction. Comparing coherent and incoherent excitations of the system, it was shown that resonant excitation of the detuned emitter makes it possible to evidence few photon quantum nonlinearities in currently available experimental systems.
A system where a Bose-Einstein condensate of exciton-polaritons coexists with a Fermi gas of electrons has been recently proposed as promising for realization of room-temperature superconductivity. In order to find the optimum conditions for exciton and exciton-polariton mediated superconductivity, we studied the attractive mechanism between electrons of a Cooper pair mediated by the exciton and exciton-polariton condensate. We also analyzed the gap equation that follows. We specifically examined microcavities with embedded n-doped quantum wells as well as coupled quantum wells hosting a condensate of spatially indirect excitons, put in contact with a two-dimensional electron gas. An effective potential of interaction between electrons was derived as a function of their exchanged energy ℏω, taking into account the retardation effect that allows two negatively charged carriers to feel an attraction. In the polariton case, the interaction is weakly attractive at long times, followed by a succession of strongly attractive and strongly repulsive windows. Strikingly, this allows high critical temperature solutions of the gap equation. An approximate three-steps potential is used to explain this result that is also obtained numerically. The case of polaritons can be compared with that of excitons, which realize the conventional scenario of high-Tc superconductivity where a large coupling strength accounts straightforwardly for the high critical temperatures. Excitons are less advantageous than polaritons but may be simpler systems to realize experimentally. It is concluded that engineering of the interaction in these peculiar Bose-Fermi mixtures is complex and sometimes counter-intuitive, but leaves much freedom for optimization, thereby promising the realization of high-temperature superconductivity in multilayered semiconductor structures.
An almost ideal thresholdless laser can be realized in the strong-coupling regime of the light-matter interaction,
with Poissonian fluctuations of the field at all pumping powers. Here, we show that this ideal scenario is thwarted
by quantum nonlinearities when crossing from the linear to the stimulated emission regime. A universal jump
in the normalized intensity correlation function is predicted to occur, the measurement of which could be used
to establish a standard fingerprint of the onset of lasing in the strong coupling regime.
We analyze the impact of both an incoherent and a coherent continuous excitation on our proposal to generate a
two-photon state from a quantum dot in a microcavity [New J. Phys. 13, 113014 (2011)]. A comparison between
exact numerical results and analytical formulas provides the conditions to efficiently generate indistinguishable
and simultaneous pairs of photons under both types of excitation.
In 2004 two groups have reported observation of the strong coupling regime in 3D microcavities with single quantum dots (QD). We present the quantum theory of non-linear emission of photons by such structures. We derive the exciton creation operator which coincides with a Fermi one for QDs smaller than the exciton Bohr radius and with Bose one for very large QDs. In intermediate size dots excitonic statistics is in between the Fermi and Bose ones. Consequently, the non-linear optical spectra change from the Mollow triplet in the fermionic case to the Rabi doublet in the bosonic case. We predict appearance of a characteristic multiplet structure of the non-linear emission in the intermediate regime.
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