June 2013

Abstracts of the QSIT Lunch Seminar, June 6, 2013

Engineered nano(hetero)structures for solar energy conversion

Esther Alarcón-Lladó, Laboratory of Semiconductor Materials, EPF Lausanne

Photovoltaics (PV) is one of the most important contributors to next generation renewable green power production. Since the first solar cell, efficiency has been one of the main concerns. In order to achieve high-efficiency PV conversion, new scientist and technological approaches are required. An example is the so-called Intermediate Band Solar Cell (IBSCs), which are multi-energy level systems that are able to scavenge low energy photons and convert them into high voltage electrons. IBSCs are able to absorb light from a broad spectral range, as well as is expected to overcome the thermodynamical limit of 31% in efficiency for single-junction solar cells. So far, IBSCs have only been recently proven, and showed very little efficiencies.

In this talk, we will discuss the limiting factors in third generation PV efficiencies, which theoretically can reach values up to 60% but in practice have not offered an improvement from traditional solar cells. Also, we will see how to tackle such factors by the use of heterostrctures and reducing the device size down to the nanoscale.

Hong-Ou-Mandel Experiments with Microwaves: Correlations, Indistinguishability and Entanglement

Christian Lang, Quantum Device Lab, ETH Zurich
Co-authors: C. Eichler¹, L. Steffen¹, J. M. Fink¹, M. J. Woolley², A. Blais², A. Wallraff¹

1 Department of Physics, ETH Zurich, Switzerland
2 Département de Physique, Université de Sherbrooke, Canada

When two indistinguishable single photons impinge at the two inputs of a beam splitter they coalesce into a pair of photons appearing in either one of its two outputs. This effect is due to the bosonic nature of photons and was first experimentally observed by Hong, Ou and Mandel. Here, we present the observation of the Hong-Ou-Mandel effect with two independent single-photon sources in the microwave frequency domain. We probe the indistinguishability of single photons, created with a controllable delay, in time-resolved second-order cross- and auto-correlation function measurements. Using quadrature amplitude detection we are able to resolve different photon numbers and detect coherence in and between the output arms. This scheme allows us to fully characterize the two-mode entanglement of the spatially separated beam-splitter output modes.

Reference:

C. Lang et al., external page Nat. Phys., 10.1038/nphys2612 (2013).