July 2013
Abstracts of the QSIT Lunch Seminar, July 4, 2013
Non-local excitations of Andreev bound states
Jens Schindele, Nanoelectronics Group, University of Basel
New physics and interesting device possibilities arise when quantum dots (QDs) are coupled to superconducting electrodes (S). The properties of such hybrid devices are governed by the interplay of the superconductor’s paring interaction and the repulsive forces between charges confined on a quantum dot. Two recent breakthroughs in the field have been the direct observation of Andreev bound states by tunnelling spectroscopy [1] and the splitting of Cooper pairs into spatially separated quantum dots [2]. Here we combine these two themes: we use electrons that originate from split Cooper pairs (“half a supercurrent”) to excite Andreev bound states on a QD.
References:
[1] J.-D. Pillet, et al., Nature Physics 6, 965 (2010)
[2] L. Hofstetter, et al., Nature 461, 960 (2009).
Quantum Teleportation from a Propagating Photon to a Solid-State Spin Qubit
Weibo Gao, Quantum Photonics Group, IQE, ETH Zurich
The realization of a quantum interface between a propagating photon used for transmission of quantum information, and a stationary qubit used for storage and manipulation, has long been an outstanding goal in quantum information science. A method for implementing such an interface between dissimilar qubits is quantum teleportation, which has attracted considerable interest not only as a versatile quantum-state-transfer method but also as a quantum computational primitive. Here, we experimentally demonstrate transfer of quantum information carried by a photonic qubit to a quantum dot solid-state spin qubit using quantum teleportation. In our experiment, a single photon in a superposition state of two colors -- a photonic qubit -- is generated using selective resonant excitation of a neutral quantum dot. We achieve an unprecedented degree of indistinguishability of single photons from different quantum dots by using local electric and magnetic field control. To teleport a photonic qubit, we generate an entangled spin-photon state in a second quantum dot located 5 meters away from the first and interfere the photons from the two dots in a Hong-Ou-Mandel set-up. A coincidence detection at the output of the interferometer heralds successful teleportation, which we verify by measuring the resulting spin state after its coherence time is prolonged by an optical spin-echo pulse sequence. The demonstration of successful inter-conversion of photonic and semiconductor spin qubits constitute a major step towards the realization of on-chip quantum networks based on semiconductor nano-structures.