1. T. Smoleński 1, M. Goryca 1,2, T. Kazimierczuk 1, J. A. Gaj 1, P. Płochocka 2, M. Potemski 2,P. Wojnar 3, P. Kossacki 1,2 1. Institute of Experimental Physics, University of Warsaw 2. Grenoble High Magnetic Field Laboratory 3. Institue of Physics, Polish Academy of Sciences

2. Outline Introduction – what a quantum dot (QD) is? Samples – how to observe a single magnetic atom Experiment 1. Optical reading of information on the Mn spin state 2. Optical writing and storage of information Conclusion

3. Quantum dots Nanostructures, made of two semiconductors with different energy gaps 10 nm Inner material, with small energy gap Outer material, with wide energy gap

4. Exciton in QD Two types of carriers: electrons and holes J z = ± 1/2J z = ± 3/2 +e+e -e-e 4 possible spin states of X J z = -1 J z = +1 J z = -2 J z = +2

5. Exciton in QD Two types of carriers: electrons and holes 4 possible spin states of X J z = -1 J z = +1 J z = -2 J z = +2 The way to observe single QDs: photoluminescence measurements !

6. QD with a single Mn ion Single Mn ion: S = 5/2, L = 0 Mn has 6 possible spin states with 6 different S z values Energy

7. Samples How to make QDs? We can do it using MBE method. In an appropriate moment we open the effusive cell with Mn atoms for a short time. Number of Mn ions in a single QD ~ 1 ZnTe CdTe (formation layer)

8. Experimental setup How to observe a single QD? T=1.5K Tunable dye laser Monochromator with CCD camera and avalanche photodiode Criostat with microscope Pol λ/4 Modulators

9. Optical QD excitation How to introduce spin polarized excitons to QD with single Mn ion? Light should be circularly polarized (i.e.  ) We should use … another QD without Mn ion !

10. Photoluminescence spectrum Excitation with unpolarized light = unoriented Mn spin

11. Photoluminescence spectrum (2)  photoluminescence (arb. u.) energy (eV) Excitation with circularly polarized light = we observe Mn spin orientation! energy (eV)

12. What is the storage time? t I σ+ Excitation Steady state

13. What is the storage time? t I σ+ Excitation Steady state σ-

14. What is the storage time? t I σ+ Excitation Steady state I t Signal on APD σ-

15. What is the storage time? t I σ+ Excitation Steady state I t Signal on APD σ-

16. What is the storage time? t I σ+ Excitation Steady state I t Signal on APD σ-

17. Storage time determination Excitation scheme t I σ+σ-

18. Conclusion We demonstrated optical writing and reading of information on the spin state of a single Mn ion embedded in a CdTe/ZnTe QD We shown, that single magnetic atom in a QD is a spin memory with optical writing and readout of information, storage time ~1ms