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