I. Sagnes

Ultrabright source of entangled photon pairs

A source of triggered entangled photon pairs is a key component in quantum information science; it is needed to implement functions such as linear quantum computation, entanglement swapping and quantum teleportation. Generation of polarization entangled photon pairs can be obtained through parametric conversion in nonlinear optical media or by making use of the radiative decay of two electron–hole pairs trapped in a semiconductor quantum dot. Today, these sources operate at a very low rate, below 0.01 photon pairs per excitation pulse, which strongly limits their applications. For systems based on parametric conversion, this low rate is intrinsically due to the Poissonian statistics of the source. Conversely, a quantum dot can emit a single pair of entangled photons with a probability near unity but suffers from a naturally very low extraction efficiency. Here we show that this drawback can be overcome by coupling an optical cavity in the form of a ‘photonic molecule’ to a single quantum dot. Two coupled identical pillars—the photonic molecule—were etched in a semiconductor planar microcavity, using an optical lithography method that ensures a deterministic coupling to the biexciton and exciton energy states of a pre-selected quantum dot. The Purcell effect ensures that most entangled photon pairs are emitted into two cavity modes, while improving the indistinguishability of the two optical recombination paths. A polarization entangled photon pair rate of 0.12 per excitation pulse (with a concurrence of 0.34) is collected in the first lens. Our results open the way towards the fabrication of solid state triggered sources of entangled photon pairs, with an overall (creation and collection) efficiency of 80%.

Near-optimal single-photon sources in the solid state

A single photon with near-unity indistinguishability is generated from quantum dots in electrically controlled cavity structures. The cavity allows for efficient photon collection while application of an electrical bias cancels charge noise effects.

Spontaneous formation and optical manipulation of extended polariton condensates

Long-lived polariton condensates can propagate well beyond the area of their initial excitation while still maintaining spatial coherence. This enables direct and controllable manipulation of the condensate wavefunction.

Polariton Laser Using Single Micropillar GaAs − GaAlAs Semiconductor Cavities

Polariton lasing is demonstrated on the zero-dimensional states of single GaAs/GaAlAs micropillar cavities. Under nonresonant excitation, the measured polariton ground-state occupancy is found as large as 10(4). Changing the spatial excitation conditions, competition between several polariton lasing modes is observed, ruling out Bose-Einstein condensation. When the polariton state occupancy increases, the emission blueshift is the signature of self-interaction within the half-light half-matter polariton lasing mode.

Sub-500-fs soliton-like pulse in a passively mode-locked broadband surface-emitting laser with 100 mW average power

We report on femtosecond operation of a broadband diode-pumped external-cavity surface-emitting semiconductor laser, passively mode locked with a fast quantum–well Semiconductor Saturable Absorber Mirror grown at 735 °C. We obtained 477 fs pulses at 1.21 GHz. The average output power is 100 mW at 1040 nm, the pulse peak power 152 W, with ∼1 W of 830 nm pump. The rf spectrum shows a linewidth <50 kHz at the noise level (−65 dB). We believe that the group-delay dispersion is compensated by the negative self-phase modulation in the absorber structure, leading to soliton-like mode locking. This system requires no additional technological step after the growth of the structures.

Controlled light-matter coupling for a single quantum dot embedded in a pillar microcavity using far-field optical lithography.

Using far-field optical lithography, a single quantum dot is positioned within a pillar microcavity with a 50 nm accuracy. The lithography is performed in situ at 10 K while measuring the quantum dot emission. Deterministic spectral and spatial matching of the cavity-dot system is achieved in a single step process and evidenced by the observation of strong Purcell effect. Deterministic coupling of two quantum dots to the same optical mode is achieved, a milestone for quantum computing.

Bright solid-state sources of indistinguishable single photons

Bright sources of indistinguishable single photons are strongly needed for the scalability of quantum information processing. Semiconductor quantum dots are promising systems to build such sources. Several works demonstrated emission of indistinguishable photons while others proposed various approaches to efficiently collect them. Here we combine both properties and report on the fabrication of ultrabright sources of indistinguishable single photons, thanks to deterministic positioning of single quantum dots in well-designed pillar cavities. Brightness as high as 0.79±0.08 collected photon per pulse is demonstrated. The indistinguishability of the photons is investigated as a function of the source brightness and the excitation conditions. We show that a two-laser excitation scheme allows reducing the fluctuations of the quantum dot electrostatic environment under high pumping conditions. With this method, we obtain 82±10% indistinguishability for a brightness as large as 0.65±0.06 collected photon per pulse.

Enhancement of second-harmonic generation in a one-dimensional semiconductor photonic band gap

We demonstrate significant enhancement of second-order nonlinear interactions in a one-dimensional semiconductor Bragg mirror operating as a photonic band gap structure. The enhancement comes from a simultaneous availability of a high density of states, thanks to high field localization, and the improvement of effective coherent length near the photonic band edge.

Optical absorption evidence of a quantum size effect in porous silicon

This study presents optical transmission measurements performed on free‐standing homogeneous porous silicon (PS) films of different porosities and substrate doping levels. The absorption coefficient curves deduced from these measurements, taking into account the total quantity of matter in the PS film, exhibit significant blue shift (up to 500 meV). These shifts, well correlated with the crystallite size variations with porosity and substrate doping observed by electron microscopy and gas adsorption experiments, are attributed to quantum size effects in the silicon microcrystallites.

Temporal solitons and pulse compression in photonic crystal waveguides

We demonstrate soliton-effect pulse compression in mm-long photonic crystal waveguides resulting from strong anomalous dispersion and self-phase modulation. Compression from 3ps to 580fs, at low pulse energies(~10pJ), is measured via autocorrelation.