Gregor Weihs, Institut für Experimentalphysik, Universität Innsbruck
For fundamental tests of quantum physics as well as for quantum communications non-classical states of light are an important tool. In our research we focus on developing semiconductor-based and integrated sources of single photons and entangled photon pairs.
In this talk we will present our work on single InAs/GaAs quantum dots. For the highest degree of quantum control we use resonant two-photon excitation to deterministically trigger a biexciton-exciton cascade. We block the pump light from the detectors by using side excitation through the waveguide mode of a planar microcavity. We demonstrate Rabi oscillations, Ramsey interference and all-optical coherent control of the quantum dot resulting in single and paired photons with a high degree of indistinguishability [1]. Using novel quantum optical assessment tools we are then able to show the non-classical and non-Gaussian characteristics of the emitted photons.
This indistinguishability can further be exploited to obtain time-bin entangled photon pairs through the biexciton-exciton cascade. Time-bin entanglement is a useful variant for long distance communication because it is robust against decoherence in optical fibers. Two successive coherent pulses excite the dot either in the early or in the late pulse. The emitted photons pass imbalanced interferometers for analysis in the energy basis. Through quantum state tomography we are able to demonstrate significant entanglement of the emitted pairs.
This work was supported by the European Research Council (ERC) and Canadian Institute for Advanced Research (CIFAR).
[1] H. Jayakumar, A. Predojević, T. Huber, T. Kauten, G. S. Solomon, and G. Weihs, Deterministic Photon Pairs and Coherent Optical Control of a Single Quantum Dot, Phys. Rev. Lett. 110, 135505 (2013), DOI: 10.1103/PhysRevLett.110.135505
[2] A. Predojević, M. Ježek, T. Huber, H. Jayakumar, T. Kauten, G. Solomon, R. Filip, and G. Weihs, Efficiency vs. multi-photon contribution test for quantum dots, Opt. Express 22, 4789-4798 (2014). DOI: 10.1364/OE.22.004789
[2] H. Jayakumar, A. Predojević, T. Kauten, T. Huber, G. S. Solomon, and G. Weihs, Time-bin entangled photons from a quantum dot, Nature Communications 5, 4251 (2014). DOI: 10.1038/ncomms5251