Oiwa Laboratory

Photon-spin quantum interface

　In quantum cryptography, photons, which has a long coherence time, have been used for long distant communications. In contrast, in quantum computing, various candidates like atoms, ions and superconductor junctions are individually investigated as a qubit. Recent years, it becomes popular for basic physics and its application to quantum information processing to create novel quantum mechanical functionalities by hybridizing two different quantum systems having different properties. We pursue the coherent quantum state transfer from polarization states of single photons to single spin states in quantum dots. Such a photon-spin quantum interface is indispensable technology for quantum repeaters to realize long distance quantum information communications.


　For the electron spins in a semiconductor QDs as spin qubits, several basic quantum gate operations have been demonstrated and the multi-qubit systems are under development. If the quantum interface which can coherently couple the photons and spins, the ability of the spin qubit is wildly extended. Until now we use the QDs formed in GaAs/AlGaAs 2 dimensional electron gas systems. A nearby point contact can be used as a sensitive change sensor with a sensitivity less than single electron change. Using the QD and charge sensor, we have succeeded to detect the single photoelectrons trapped in the QD [1]. Recently, we have developed the non-destructive and robust single photoelectron detection by utilizing resonant inter-dot tunneling [2,3] and the spin of the single photoelectrons in a real time manner. Moreover, it has confirmed the detected spin direction depends on the incident photon polarization and the angular momentum conversion from single photons to single electron spin has been verified. We are At present we are studying the coherent quantum state transfer from single photons to single electron spin. For future we aim at realizing the non-local entanglement between photon and spin and also between distant two spins for studying novel quantum effects.
　Extending this photon-spin interface, we will work the quantum state transfer and the resultant new quantum effects emerging in the hybrid system consisting of more than two physical systems with different coherence and different controllability of the quantum states.
References

1. "Single-Shot Detection of Electrons Generated by Individual Photons in a Tunable Lateral Quantum Dot", A. Pioda, E. Totoki, H. Kiyama, T. Fujita, G. Allison, T. Asayama, A. Oiwa, and S. Tarucha, Phys. Rev. Lett. 106, 146804 (2011).
2. "Non-destructive Measurement of Single Photo-electrons by Inter-dot Tunneling in a Double Quantum Dot", T. Fujita, H. Kiyama, K. Morimoto, S. Teraoka, G. Allison, A.Ludwig, A. D. Wieck, A. Oiwa, and S. Tarucha, Phys. Rev. Lett. 110, 226803 (2013).
   
3. "Single photoelectron detection after selective excitation of electron heavy-hole and electron light-hole pairs in double quantum dots", K. Morimoto, T. Fujita, G. Allison, S. Teraoka, M. Larsson, H. Kiyama, S. Haffouz, D. G. Austing, A. Ludwig, A. D. Wieck, A. Oiwa, and S. Tarucha, Phys. Rev. B 90, 085306 (2014)