A scheme is proposed for the generation of branch-entangled pairs of microcavity polaritons through spontaneous interbranch parametric scattering. Branch entanglement is achievable when there are two twin processes, where the role of signal and idler can be exchanged between two different polariton branches. Branch entanglement of polariton pairs can lead to the emission of frequency-entangled photon pairs out of the microcavity. In planar microcavities, the necessary phase-matching conditions are fulfilled for pumping of the upper polariton branch at an arbitrary in-plane wave vector. The important role of nonlinear losses due to pair scattering into high-momentum exciton states is evaluated. The results show that the lack of protection of the pump polaritons in the upper branch is critical. In photonic wires, branch entanglement of one-dimensional polaritons is achievable when the pump excites a lower polariton sub-branch at normal incidence, providing protection from the exciton reservoir.
A scheme is proposed for the generation of branch-entangled pairs of microcavity polaritons through spontaneous interbranch parametric scattering. Branch entanglement is achievable when there are two twin processes, where the role of signal and idler can be exchanged between two different polariton branches. Branch entanglement of polariton pairs can lead to the emission of frequency-entangled photon pairs out of the microcavity. In planar microcavities, the necessary phase-matching conditions are fulfilled for pumping of the upper polariton branch at an arbitrary in-plane wave vector. The important role of nonlinear losses due to pair scattering into high-momentum exciton states is evaluated. The results show that the lack of protection of the pump polaritons in the upper branch is critical. In photonic wires, branch entanglement of one-dimensional polaritons is achievable when the pump excites a lower polariton sub-branch at normal incidence, providing protection from the exciton reservoir.
Summary form only given. Several theoretical studies have recently suggested that the scattering of microcavity polaritons can be a source of non-classical photon correlations, producing photon pairs that are entangled in either the energy (branch index) [1], or the polarization degree of freedom [2]. Even cluster states can be generated [3]. Motivated by the above-mentioned proposals for the creation of entangled photon pairs, we studied parametric polariton scattering in 2D coupled planar and ID micro-cavities grown by molecular beam epitaxy (Fig. 1, left hand side). The advantage of these structures is that the polariton branches involved in the parametric scattering are located energetically below the exciton reservoir, thus the particles are protected from excitonic losses, as shown in Fig. 1.In this paper, we are going to experimentally explore entanglement schemes similar to that in Fig. 1. These measurements are carried out using time-correlated photon counting and utilizing the flexible excitation scheme developed in our group [4]. We also compare the experimental results to numerical calculations which are based on the extension of the microscopic theory of Portolan et al. [5]. Our model allows us to optimize the samples for particular scattering schemes.
A scheme is proposed for the generation of polarization- and frequency-entangled photons in a semiconductor planar microcavity. Photon entanglement can be achieved by converting two lower polariton branches with symmetric in-plane momenta into lower and upper polariton branches with zero in-plane momentum via a biexciton state. The phase-matching condition is satisfied for a microcavity with cavity detuning equal to the biexciton binding energy. The generation efficiency and energy control of the entangled photons are demonstrated for a CuCl microcavity as an example.
The recent development of interbranch optical parametric oscillation (OPO) in 2D vertical coupled microcavities [1] or 1D microcavities [2] opens new path towards the realization of monolithic micro-OPOs and for the generation of twin photon beams useful in quantum optics applications. It is now well established that very large Chi(3) polaritonic non-linearities in semiconductor microcavities operating in the strong-coupling regime [3] can be used to achieve low-threshold OPO. In conventional planar microcavities, the required phase-matching is obtained thanks to the strong coupling of excitons and photons. Nevertheless, single planar microcavities suffer from several drawbacks that prevent its use as a convenient device: (i) the required strong light-matter coupling regime is achieved only at low temperature, (ii) the pump laser must be adjusted to a specific angle, (iii) signal and idler beams are intrinsically strongly un-balanced, thus precluding practical applications. Alternatively, it has been demonstrated that interbranch parametric scattering in coupled microcavities allows to relax the requirement for a strong-coupling regime, thus leading to higher operating temperature [1]. In the present work, we show that interbranch parametric scattering in 1D microcavities also allows to relax this constraint as well as to generate efficient signal and idler beams with balanced intensities. The OPO regime is achieved and studied both at 4K in the strong-coupling regime, as well as above 100K in the weak-coupling regime. [1] C. Diederichs, et al., Nature 440, 904 (2006). [2] G. Dasbach et al., Phys. Rev. B 71, 161308R (2005) [3] P. G. Savvidis et al., Phys. Rev. Lett. 84, 1547 (2000)
We propose and theoretically analyze a new scheme for generating hyperentangled photon pairs (EPPs) in a system of polaritons in coupled planar microcavities.Starting from a microscopic model, we evaluate the relevant parametric scattering processes and numerically simulate the phonon-induced noise background under continuous-wave excitation.Our results show that, compared to other polariton entanglement proposals, our scheme enables the generation of photon pairs that are entangled in both the path and polarization degrees of freedom, and simultaneously leads to a strong reduction in the photoluminescence noise background.This can significantly improve the fidelity of the EPPs under realistic experimental conditions.
Summary form only given. Semiconductor microcavities can be engineered to produce strong coupling between photons and quantum well excitons leading to the formation of new eigenstates called polaritons. Due to their peculiar dispersion, enabling non-equilibrium Bose-Einstein condensation [1], and their straightforward experimental accessibility, microcavity polaritons have gained considerable interest in recent years. Polariton states can be selectively populated by choosing the excitation angle and the wavelength of the excitation laser. After a lifetime of a few picoseconds the polariton decays and a photon is emitted from the cavity, carrying the complete information on the underlying polariton state. Several theoretical works [2-3] suggest that polariton-polariton interactions can be a source of non-classical photon correlations, producing photon pairs that are entangled in either the energy, the polarization, or the momentum degree of freedom. One appeal of such a system is that many parameters such as the polariton-polariton interaction strength are tunable [4] and multipartite entangled states can be created in a single device [5]. However, due to the lack of high-quality samples, experimental realisations of these schemes have been elusive so far. In this contribution, we will discuss some of our experimental work on the statistics of polariton-polariton parametric scattering. Excited polaritons can scatter in a four-wave mixing process into signal and idler states lying on a figure-eight shaped curve in k-space, where phase-matching is fulfilled. We make use of a sample with ultra narrow exciton resonances, which allows for the generation and detection of correlated light. We present our measurements of the second order correlation functions using time-correlated photon counting. We discuss in detail, how polariton quantum correlations depend on a number of experimental parameters, such as phase space location and excitation density and find that the results can be understood in the framework of the well known Bogoliubov theory for 2D Bose gases utilised for microcavity polaritons [6]. We find bunching below the parametric threshold and a slow buildup of coherence above the threshold similar to the quantum statistics of a non-degenerate optical parametric oscillator, which is well known for its nonclassical properties [7]. We discuss in particular the influence of strong background processes on the observed photon statistics.
The quantum correlations between the beams generated by polariton pair scattering in a semiconductor microcavity above the parametric oscillation threshold are computed analytically. The influence of various parameters, including the cavity-exciton detuning, the intensity mismatch between the signal and idler beams, and the amount of spurious noise, is analyzed. We show that very strong quantum correlations between the signal and idler polaritons can be achieved. However, the quantum effects in the outgoing light fields are strongly reduced due to the large mismatch in the coupling of the signal and idler polaritons to the external photons.