1. Single spin detection Maksym Sladkov Top master nanoscience symposium June 23, 2005

2. Outline • Introduction • Magnetic Resonance Force Microscopy • Quantum Dot detection of single spin • Other detection techniques • Summary

3. Fundamental property of elementary particles “Intrinsic angular moment” Purely QM nature Only either “up” or “down” orientation can be measured Precess around direction of static magnetic field Leads to the Zeeman splitting Has tendency to resonance in presence of periodic MF Obey Pauli exclusion principle What is spin?

4. Application: MRI & MD visualization MRI imaging of human brain Dynamics of small paramagnetic particles in the cell Require large number of spins. 105!

5. 3. Read final state: Single Spin Detection! Applications: Quantum computing 1.Initial state: 2.Perform a well defined sequence of quantum operations (Quantum gates):

6. Magnetic Resonance Force Microscopy • Mass-loaded high sensitive cantilever (10-15 N) • Changing in resonant frequency of cantilever is the detectedion parameter • Presence of resonance slice • Spin adiabatic motion Rugar D. et al. (2004) Nature

7. Spin-tip interaction • Spin-tip interaction changing the resonant frequency of cantilever • Sign of the frequency shift depends on the relative orientation of spin with respect to magnetic field

8. Adiabatic reversal of the spin and cantilever frequency shift detection Related movie at: http://www.almaden.ibm.com/st/nanoscale_science/asms/mrfm/

9. Single spin observation • Signal/noise ~ 0.06 • <[Signal][Noise]> = 0 • Time averaging of energy allows extract signal from noise: <(x+dx)2>=<x2>+<dx2> • Averaging time 13 h per point

10. The future of MRFM • Not only electron spin, but any magnetic moment can be detected • Sensitivity (for nuclei spin detection) and read-out time can be improved by increasing of field gradient and by lowering the temperature • Read-out of single-spin quantun state would be possible • MRFM also holds the potential to map 3-D images of molecules (e.g. proteins) in situ with high resolution and atomic scale characterization of nanodevices.

11. Quantum Dot detection of single spin Elzerman JM et al. (2004) Nature • QD is created in 2DEG by applying negative voltage to T,M & R electrodes. • VP changes relative position of dot energy levels with respect to EF • Depending on the spin orientation and potential on the dot electron can tunnel off or on the dot • IQPC senses the charge on QD

12. Two-pulse technique • Empty the dot • Injection & waiting – twait • Read-out – tread IQPC=f(VP+charge on the dot) Spin-down – detected as charachteristic step durring the tread.

13. T1 – measurements Fraction of spin-down traces vs. waitng time. 625 traces for each from 15 different waiting times

14. Future of QD single spin detection • Principal electrical detection • Can be used in quantum computing • Shows possibility of studying spin relaxation processess on the single-spin scale

15. Other detection techniques • FET Detection of single spin: Xiao M et al. (2004) Nature. • STM: Durkan C. (2004) Contemp. Phys. • Optical quantum dot detection, nano-SQUID…etc.

16. Summary • Detection of single electron spin is possible • It opens a possibility of creation of spin-based quantum computer • Can lead to the prominent new 3-D imaging techniques • It allows to get deeper understanding of spin-relaxation processes in solids