July 2015

Abstracts of the QSIT Lunch Seminar, Thursday, July 2, 2015

Impedance and noise measurements of clean CNT quantum dots using GHz superconducting matching circuits

Vishal Ranjan, Nanoelectronics group, University of Basel

Coulomb charging and 3D-confinement in Q-dots provide us with tailored-artificial-atom systems with discreet energies. Coherent manipulation and readout of such systems are however challenging because of large mismatches in their impedance with the standard Z0. Here, we design and characterize low-loss matching circuits to efficiently couple microwaves into and from Q-dots confined in carbon nanotubes.  We employ stamping of nanotubes to retain their pristine transport characteristics such as the control over formation of, and coupling strengths between, the quantum dots. Matching capability more importantly enables quantitative parameter extraction of conductance, susceptance and electronic shot noise at gigahertz frequency with improved signal to noise ratio.

Generation of heralded entanglement between distant quantum dot hole spins

Zhe Sun, Quantum Photonics Group, ETH Zurich

co-authors: Aymeric Delteil, Wei-bo Gao , Emre Togan, Stefan Faelt, Atac Imamoglu

In the seminar, we will present the realization of heralded quantum entanglement between two heavy hole spins in semiconductor quantum dots separated by more than five meters. Our results extend the previous demonstrations of distant spin entanglement in single trapped ions or neutral atoms, in atom ensembles and nitrogen vacancy centers to the domain of artificial atoms in semiconductor nanostructures that allow for on-chip integration of electronic and photonic elements. Moreover the efficient spin-photon interface provided by self-assembled quantum dots allows us to reach an unprecedented rate of 2300 entangled spin pairs per second, which represents an improvement of three orders of magnitude as compared to prior experiments.
Our results lay the groundwork for the realization of quantum networks in semiconductor nanostructures. Combined with schemes for transferring quantum information to a long-lived memory qubit, fast entanglement generation we demonstrate could also impact quantum repeater architectures.