Quantum tomography of polarization-entangled two-photon state generated from a InAs/InP naowire quantum dot

Chiao-Tzu Huang^1,2*, Mohammed K. Alqedra³, Sofiane Haffouz⁴, Philip J. Poole⁴, Ali W. Elshaari³, Val Zwiller³, Wen-Hao Chang^1,2

¹Research Center for Critical Issues, Academia Sinica, Tainan City 711010, Taiwan
²Department of Electrophysics, National Yang Ming Chiao Tung university, Hsinchu City 300093, Taiwan
³Division of Quantum and Nano Physics, Kungliga Tekniska högskolan, Stockholm 11419, Sweden
⁴National Research Council, Ontario K1A 0R6, Canada

* Presenter:Chiao-Tzu Huang, email:chiaotzu.sc11@nycu.edu.tw

An entangled photon source is a critical component for constructing a quantum network. It is also utilized in quantum key distribution, such as the E91 protocol. Among various platforms, indium arsenide (InAs) quantum dots stand out for their ability to generate high-quality single photons from near-infrared to telecom bands. With its excitonic energy levels, polarization-entangled photon pairs can be generated through biexciton-exciton cascaded emission. However, the fidelity is limited by fine-structure splitting (FSS) induced by the asymmetry of the quantum dot. This leads to dramatically degraded of entanglement. Here, we report the reconstruction of the time-evolving density matrix of an optical two-qubit state in the telecom O-band. The sample is an InAs quantum dot grown in an InP shell with a vertical waveguide structure, and the experiments are conducted using photoluminescence spectroscopy and time-correlated single-photon counting at cryogenic temperatures. The results reveal how the entangled state evolves, which is a consequence of FSS in the time domain. We also propose a method to modulate the FSS by applying a magnetic field. The concept is to modulate spin-spin interaction of carriers and eventually cancel FSS via valence-band mixing.

Keywords: Quantum optics, Spectroscopy, Low-dimensional semiconductors