Jan Gudat

CNOT and Bell-state analysis in the weak-coupling cavity QED regime

We propose an interface between the spin of a photon and the spin of an electron confined in a quantum dot embedded in a microcavity operating in the weak-coupling regime. This interface, based on spin selective photon reflection from the cavity, can be used to construct a CNOT gate, a multiphoton entangler and a photonic Bell-state analyzer. Finally, we analyze experimental feasibility, concluding that the schemes can be implemented with current technology.

Strong coupling through optical positioning of a quantum dot in a photonic crystal cavity

crystal cavities have relied largely on random chance 5,6 and often required the measurement of many devices before finding a cavity in which a quantum dot is both spectrally and spatially in resonance with the cavity mode. These devices have the additional complication that the photonic crystal cavity typically interacts with many emitters due to the large quantum dot density required to find a strongly coupled device. A deterministic coupling method based on using atomic force microscopy to locate the strain sites of buried quantum dots has previously been demonstrated. 7,8 Here, we present an all-optical method for measuring the positions of individual quantum dots that allows us to deterministically achieve strong coupling between a quantum dot and a photonic crystal cavity. This versatile method can be performed in the measurement setup at a very low quantum dot density and could be applied to many emitter-cavity systems. Our technique relies on the precise determination of the optical

Tuning micropillar cavity birefringence by laser induced surface defects

We demonstrate a technique to tune the optical properties of micropillar cavities by creating small defects on the sample surface near the cavity region with an intense focused laser beam. Such defects modify strain in the structure, changing the birefringence in a controllable way. We apply the technique to make the fundamental cavity mode polarization-degenerate and to fine tune the overall mode frequencies, as needed for applications in quantum information science.

Strain tuning of quantum dot optical transitions via laser-induced surface defects

We discuss the fine-tuning of the optical properties of self-assembled quantum dots by the strain perturbation introduced by laser-induced surface defects. We show experimentally that the quantum dot transition red-shifts, independently of the actual position of the defect, and that such frequency shift is about a factor five larger than the corresponding shift of a micropillar cavity mode resonance. We present a simple model that accounts for these experimental findings.

Permanent tuning of quantum dot transitions to degenerate microcavity resonances

We demonstrate a technique for achieving spectral resonance between a polarization-degenerate micropillar cavity mode and an embedded quantum dot transition. Our approach is based on a combination of isotropic and anisotropic tensile strain effected by laser-induced surface defects, thereby providing permanent tuning. Such a technique is a prerequisite for the implementation of scalable quantum information schemes based on solid-state cavity quantum electrodynamics.

Independent electrical tuning of separated quantum dots in coupled photonic crystal cavities

Systems of photonic crystal cavities coupled to quantum dots are a promising architecture for quantum networking and quantum simulators. The ability to independently tune the frequencies of laterally separated quantum dots is a crucial component of such a scheme. Here, we demonstrate the independent tuning of laterally separated quantum dots in photonic crystal cavities coupled by in-plane waveguides by implanting lines of protons which serve to electrically isolate different sections of a diode structure.

Optical modes in oxide-apertured micropillar cavities.

We present a detailed experimental characterization of the spectral and spatial structure of the confined optical modes for oxide-apertured micropillar cavities, showing good-quality Hermite-Gaussian profiles, easily mode-matched to external fields. We further derive a relation between the frequency splitting of the transverse modes and the expected Purcell factor. Finally, we describe a technique to retrieve the profile of the confining refractive index distribution from the spatial profiles of the modes.

Cavity-QED with quantum dots in oxide-apertured micropillars

We describe quantum information schemes involving photon polarization and the spin of a single electron trapped in a self-assembled quantum dot. Such schemes are based on spin-selective reflection in the weak-coupling regime of cavity quantum electrodynamics. We discuss their practical implementation in oxide-apertured micropillar cavities. We introduce a technique, based on the creation of small surface defects by means of a focused intense laser beam, to permanently tune the optical properties of the microcavity without damaging the cavity quality. This technique allows low-temperature polarization-selective tuning of the frequencies of the cavity modes and the quantum dot optical transitions.

Solid-state cavity-QED in polarization-degenerate micropillar cavities

We describe a technique to entangle a single photon with an electron-spin in a quantum dot. We discuss the implementation in micropillars, showing how dot transitions can be tuned into resonance with polarization-degenerate cavities.