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Single Spin Detection

Single Spin Detection. J. Fernández-Rossier IUMA, Universidad de Alicante, Spain. Manipulation and Measurement of the Quantum State of a single spin in a solid state environment. 10 23 atoms, 10 25 spins Signal for only 1. Needle in a Hay Stack.

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Single Spin Detection

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  1. Single Spin Detection J. Fernández-Rossier IUMA, Universidad de Alicante, Spain Manipulation and Measurementof the Quantum State of a single spin in a solid state environment 1023 atoms, 1025 spins Signal for only 1 Needle in a Hay Stack Talk available in: www.ua.es/jfrossier/personal

  2. PL S=5/2 2S+1=6 L. Besombes et al., PRL 93, 207403, (2004) Single Spin Detection CdTe nanocrystal + 1Mn

  3. The institute of Complex Adaptative Matter encourages (forces) scientist to explain their work to other scientist in pedestrian terms. I have learned more science through workshops organized by this institute and the personal contacts they generated than I have from all other professional activities combined. R. Laughlin, A Different Universe, (2005) Outline • Motivation • II.Basic Stuff • III. Quantum Simulations • IV. Conclusions

  4. Single Spin Detection • RELATED WORK • J. Fernández-Rossier, C. Piermarocchi, P.C. Chen, L. J. Sham, and A. H. MacDonald, • Theory of Laser induced ferromagnetism • Phys. Rev. Lett. 93, 127201 (2004) • J. Fernández-Rossier, L. BreyFerromagnetism mediated by few electrons in semimagnetic quantum dots Phys. Rev. Lett. 93, 1172001 (2004) • G. Chiappe, J. Fernández-Rossier, E. Anda, E. LouisSingle-photon exchange interaction in a semiconductor microcavityCond-mat/0407639 Talk available in: www.ua.es/jfrossier/personal

  5. Motivation • II.Basic Concepts • III. Quantum Simulations • IV. Results and Conclusions

  6. Motivation I.Understanding QM from small... =

  7. .....to big

  8. 104-106 Atoms Not only a philosophycal question 1 Atom “Shut up and calculate”. -- R. Feynman "I think it is safe to say that no one understands quantum mechanics." -- R. Feynman 1023 Atoms: BULK

  9. Going Nano Motivation II. The limits of miniaturization ‘Single electron’ transistor

  10. Miniaturization: The limits Going Nano ‘Single atom’ magnet

  11. Going around THE LIMITS • New Questions: • Smallest wire? • Smallest magnet? • Smallest diode? • Smallest transistor? • New challenges: • Single spin control • Single molecule transport • Nanocrystal formation • Different Materials: • Molecular Electronics • Oxides • Different Ideas: • Spintronics • DNA • Quantum Computing Electronics: we ain´t seen nothing yet

  12. Motivation • II.Basic Concepts • III. Quantum Simulations • IV. Conclusions

  13. Basic Concepts • Quantum computing for absolute beginners: • Quantum bit vs classical bit • Spin S=1/2 as a qbit • Quantum software and hardware • Diluted Magnetic Semiconductors • Quantum Dots

  14. Quantum information Classical information What is a qbit? Will you marry me?

  15. What is a qbit (II)? A qbit is like a spin ½

  16. What is a quantum computation? I. Prepare initial state • Perform a well defined sequence ofquantum operations (Quantum gates) “Engineering” Hamiltonian. Universal Gates III. Read final state(single spin detection)

  17. Can something useful be done? Quantum factorization Algorithm (Shor ’90) Classical factorization algorithm Number of bits: N=2n Number of steps: n2 Example n=10 Qsteps: 100 Csteps: 10.000 QUANTUM SOFTWARE: A few algorithms and ideas Number of steps: n 2n

  18. Quantum Hardware: Proposals Not in yet

  19. Diluted Magnetic Semiconductors

  20. Metal N- ZnTe (Zn,Ga)Te Charge doping of Semiconductors Pure ZnTe p- ZnTe Zn (Te,N) CHARGE DOPING

  21. (Zn,Mn)Te Spin doping: diluted Magnetic Semiconductors (DMS) Zn: Ar: 3d10 4s2 Mn: Ar: 3d5 4s2 Conduction Band Mainly s orbitals of Zn Valence Band Mainly p orbitals of Te Mn d levels SPIN DOPING

  22. Why S=5/2 ? Ground State S=5/2 S=3/2 Excited States Mn SPIN ROTATIONAL INVARIANCE S=5/2. 2S+1=6 DEGENARATE STATES S=1/2 Real Space Cartoon S=5/2. LOWEST Coulomb Repulsion (Hunds Rule) Magnetic Moment SPIN S=5/2 3/2 1/2 5/2

  23. How to manipulate the spins ?

  24. Electrons, holes, Mn and their interactions SPIN attraction SPIN repulsion SPIN FLIP Spin of the CB electron and VB hole SPIN ORBIT MATTERS A LOT CARRIER WAVE FUNCTION ENGINEERING

  25. Single quantum spectroscopy? CdSe nanocrystal: TEM CONFINEMENT Absorption Emission 5nm

  26. Motivation • II.Basic Concepts • III. Quantum Simulations • IV. Conclusions

  27. PL S=5/2 2S+1=6 L. Besombes et al., PRL 93, 207403, (2004) S=5/2 qbits in semiconductor nanocrystals? dummy dummy Spin evolution Absorption Emission 1 SPIN 5/2 = 2 QBITS

  28. 4 -1 -1 +1 +2 1 4x6N Exciton States Manifold (XSM) 6N Ground State Manifold (GSM) • Method : • Calculation of one-body wave functions (for a given dot) • Evaluation of many body exciton-Mn spin Hamiltonian • Exact diagonalization of GSM • Exact diagonalization of XSM • Linear reponse theory

  29. HAMILTONIAN Ground State Manifold (GSM) 6N Exciton States Manifold (XSM) e Heisenberg 4 6N Ising h SPIN ORBIT INTERACTION

  30. 4 -1 -1 +1 +2 1 Absorption Spin orbit and OPTICAL SELECTION RULES How can light affect spin?

  31. Valence band Spin orbit: Ising coupling SHAPE MATTERS: Quenching the Hole-Mn spin flip

  32. GSM and XSM spectrum Magnetic Field (0,0,5) 1 Mn NG=6 NX=24 2 Mn NG=36 NX=244 3Mn NG=216 NX=864 E(meV) E(meV)

  33. PL: results Photoluminescence(PL)Theory PL, theory PL, experiment Spontaneous Emission from X to G Energy conservation Optical Selection rules SPIN BLOCKADE PL SPECTRUM Energy (meV) Occupation of excited state Thermal like occupation

  34. Standardoptical selection rule OPTICAL SPIN BLOCKADE Franck Condon= Spin Blockade GSM Photon QUANTUM MEASUREMENT XSM

  35. N=3. Narrowing and shift PL, experiment 0T 2T 4T 6T 8T 10T P. S. Dorozhkin, Phys. Rev. B 68, 195313 (2003)

  36. Bell States in DMS? HIGLY ENTANGLED Lowest energy state Of XSM GSM Intriguing question: can the detection of a linearly polarized photon yield a Bell state?

  37. CONCLUSIONS (and future work) • Single spin detection possible due to • Chemical Engineering (nanocrystals) • Advanced material processing and electronics (multilayers, photodetectors) • Laser technology, low temperatures • DEEP UNDERSTANDING of the ELECTRONIC STRUCTURE (Solid state physics and chemistry) • S=5/2 qbits. • Detection ok (at least N=2) • Time resolved control ok • 2 qbit operations ok

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