Single spin detection
Maksym Sladkov
Top master nanoscience symposium
June 23, 2005
Outline
Introduction Magnetic Resonance Force Microscopy Quantum Dot detection of single spin Other detection techniques Summary
What is spin?
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
Application: MRI & MD visualizationMRI imaging of human brain
Dynamics of small paramagnetic particles in the cell
Require large number of spins. 105!
Applications: Quantum computing
noayesa ny 1.Initial state:
2.Perform a well defined sequence of quantum operations (Quantum gates):
iHtetU )(
3. Read final state: Single Spin Detection!
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
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
Adiabatic reversal of the spin and cantilever frequency shift detection
Related movie at:
http://www.almaden.ibm.com/st/nanoscale_science/asms/mrfm/
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
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.
Quantum Dot detection of single spin
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
Elzerman JM et al. (2004) Nature
Two-pulse technique
1. Empty the dot2. Injection & waiting –
twait
3. Read-out – tread
IQPC=f(VP+charge on the dot)
Spin-down – detected as charachteristic step durring the tread.
T1 – measurementsFraction of spin-down traces vs. waitng time. 625 traces for each from 15 different waiting times
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
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.
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