A Coherent Spin-Photon Interface in Silicon

Electron spins in silicon quantum dots are attractive systems for quantum computing due to their long coherence times and the promise of rapid scaling using semiconductor fabrication techniques. While nearest neighbor exchange coupling of two spins has been demonstrated, the interaction of spins via microwave frequency photons could enable long distance spin-spin coupling and "all-to-all" qubit connectivity. Here we demonstrate strong-coupling between a single spin in silicon and a microwave frequency photon with spin-photon coupling rates g_s/(2\pi) > 10 MHz. The mechanism enabling coherent spin-photon interactions is based on spin-charge hybridization in the presence of a magnetic field gradient. In addition to spin-photon coupling, we demonstrate coherent control of a single spin in the device and quantum non-demolition spin state readout using cavity photons. These results open a direct path toward entangling single spins using microwave frequency photons

Investigation of Mobility Limiting Mechanisms in Undoped Si/SiGe Heterostructures

We perform detailed magnetotransport studies on two-dimensional electron gases (2DEGs) formed in undoped Si/SiGe heterostructures in order to identify the electron mobility limiting mechanisms in this increasingly important materials system. By analyzing data from 26 wafers with different heterostructure growth profiles we observe a strong correlation between the background oxygen concentration in the Si quantum well and the maximum mobility. The highest quality wafer supports a 2DEG with a mobility of 160,000 cm^2/Vs at a density 2.17 x 10^11/cm^2 and exhibits a metal-to-insulator transition at a critical density 0.46 x 10^11/cm^2. We extract a valley splitting of approximately 150 microeV at a magnetic field of 1.8 T. These results provide evidence that undoped Si/SiGe heterostructures are suitable for the fabrication of few-electron quantum dots.Comment: Related papers at http://pettagroup.princeton.ed

Walsh - Hadamard Transformation of a Convolution

A convolution is mathematical operation used in signal processing, in the homomorphous signal processing and digital image processing (e.g. image interpolation). In regard of computational complexity of the convolution in the time domain, it used to calculate in the other domain. Exp. x(n) * h(n) R X(W) × H(W), resp. X(W) × H(W), shows that a convolution in the time domain corresponds to multiplication in the Z domain, respectively frequency domain. This paper shows utilization of Walsh-Hadamard orthogonal transformations for convolution

Role of product characteristics for the adoption of fruit and fruit product innovations

The aim of this study was the identification of those product characteristics that are important for the adoption of fruit and fruit product innovations by consumers. Sixteen focus group discussions were held in four European countries (Greece, The Netherlands, Poland, and Spain). Different aspects of six innovative fruit products were discussed, revealing those characteristics that were important for the adoption of each of them. It was observed that the participants did not perceive fruit innovations as a homogenous group, but assigned them to different groups, which led to a number of categories of fruit innovation. Three categories concerned the level of preparation of fruit. These were fresh, prepared, and processed fruit product innovations. Another two categories, radical and evolutionary innovations, related to the level of novelty of the fruit innovation. Characteristics important for the adoption of each of these categories are given.The results will be used for further, more quantitative, research

Screening nuclear field fluctuations in quantum dots for indistinguishable photon generation

A semiconductor quantum dot can generate highly coherent and indistinguishable single photons. However, intrinsic semiconductor dephasing mechanisms can reduce the visibility of two-photon interference. For an electron in a quantum dot, a fundamental dephasing process is the hyperfine interaction with the nuclear spin bath. Here we directly probe the consequence of the fluctuating nuclear spins on the elastic and inelastic scattered photon spectra from a resident electron in a single dot. We find the nuclear spin fluctuations lead to detuned Raman scattered photons which are distinguishable from both the elastic and incoherent components of the resonance fluorescence. This significantly reduces two-photon interference visibility. However, we demonstrate successful screening of the nuclear spin noise which enables the generation of coherent single photons that exhibit high visibility two-photon interference.Comment: 5 pages, 4 figures + Supplementary Informatio

Effect of cyclic freezing and thawing on the microstructure of composite cements

Mixed performance of composite cements exposed to freeze-thaw has been reported. A detailed understanding of the degradation mechanism is also lacking. This study investigates the microstructure of composite slag cements with and without limestone subjected to cyclic freezing and thawing. Freeze-thaw was assessed on concrete samples in accordance with CEN/TR 15177 but with a modified temperature profile. Microstructure was characterized by SEM and thermogravimetric analysis. The results indicate decalcification through carbonation and then leaching as dominant degradation mechanisms. This has implications on the pore structure and hence the water suction capacity and progression of the ice-front in concrete