March 2013

Abstracts of the QSIT Lunch Seminar, March 7, 2013

Intrinsic Charge Fluctuations in a few electron GaAs double quantum dot

Daniel Biesinger, Quantum Coherence Lab, University of Basel

We present real-time charge sensing experiments on a lateral GaAs double quantum dot in the few electron regime. In absence of inter-dot tunneling, a clear diamond-shaped region centered between the (0,0) and (1,1) triple points appears in the charge stability diagram, exhibiting metastable charge-state switching between (0,1) and (1,0) as a function of time. This persists at very small sensor bias and larger electron numbers, but disappears when inter-dot tunneling is turned on, ruling out extrinsic processes such as charge traps, sensor back-action or absorption of phonons or photons.
We present a model of thermally-excited sequential-tunneling electron exchange with the reservoirs, and find very good agreement with the data. Within the model, such charge fluctuations are an intrinsic, fundamental double dot effect. Though potentially limiting spin-qubit coherence for typical loading rates and temperatures, the fluctuations are otherwise not easily visible in charge sensing in presence of small but finite inter-dot tunneling. However, decreasing temperature and reducing dot-reservoir tunneling rates will reduce the fluctuation rate.

A microfabricated segmented linear Paul trap for precision control of mixed-species ion chains

Daniel Kienzler,Trapped Ion Quantum Information Group, ETH Zurich

Ion trap experiments are leading systems for investigations of quantum information [1,2], and have been used to realize the highest precision atomic clocks [3]. One important experimental technique is co-trapping of multiple ion species. For quantum information studies, this allows the motion of the ion string to be cooled while quantum information is stored in the ions' internal states (an important element for large-scale processing). In atomic clock work, it has opened up new types of spectroscopy.
We are focused on co-trapping of calcium and beryllium ions, with the aim of realizing simulations of open quantum systems and dissipative entanglement, along with scalable quantum computation. I will describe the design, fabrication and first trapping results from a new multi-zone ion trap which I have built for this purpose, which was specifically designed for the use of multiple ion species.