Single Spin Detection

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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
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Single Spin Detection
CdTe nanocrystal 1Mn
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Outline
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)

• Motivation
• II. Basic Stuff
• III. Quantum Simulations
• IV. Conclusions

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

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Motivation I.Understanding QM from small...

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.....to big
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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
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Motivation II. The limits of miniaturization
Single electron transistor
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Miniaturization The limits
Going Nano
Single atom magnet
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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 aint seen nothing yet
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• Motivation
• II. Basic Concepts
• III. Quantum Simulations
• IV. Conclusions

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Basic Concepts

• Quantum computing for absolute beginners
• Quantum bit vs classical bit
• Spin S1/2 as a qbit
• Quantum software and hardware
• Diluted Magnetic Semiconductors
• Quantum Dots

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What is a qbit?
Will you marry me?
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What is a qbit (II)?
A qbit is like a spin ½
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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)
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Can something useful be done?
Quantum factorization Algorithm (Shor 90)
Classical factorization algorithm
Number of bits N2n Number of steps n2
Example n10 Qsteps 100 Csteps 10.000
QUANTUM SOFTWARE A few algorithms and ideas
Number of steps n 2n
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Quantum Hardware Proposals
Not in
yet
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Diluted Magnetic Semiconductors
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Charge doping of Semiconductors
Pure ZnTe
p- ZnTe Zn (Te,N)
CHARGE DOPING
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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
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Why S5/2 ?
S5/2
Ground State
S3/2
Excited States
Mn SPIN ROTATIONAL INVARIANCE S5/2. 2S16
DEGENARATE STATES
S1/2
Real Space Cartoon
S5/2. LOWEST Coulomb Repulsion (Hunds
Rule) Magnetic Moment SPIN S5/2
?3/2
?5/2
?1/2
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How to manipulate the spins ?
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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
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Single quantum spectroscopy?
CdSe nanocrystal TEM
CONFINEMENT
Absorption
Emission
5nm
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• Motivation
• II. Basic Concepts
• III. Quantum Simulations
• IV. Conclusions

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S5/2 qbits in semiconductor nanocrystals?
dummy
dummy
Spin evolution
Absorption
Emission
1 SPIN 5/2 2 QBITS
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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

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HAMILTONIAN
Ground State Manifold (GSM)
6N
Exciton States Manifold (XSM)
e
Heisenberg
4? 6N
Ising
h
SPIN ORBIT INTERACTION
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Spin orbit and OPTICAL SELECTION RULES
How can light affect spin?
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Valence band Spin orbit Ising coupling
SHAPE MATTERS Quenching the Hole-Mn spin flip
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GSM and XSM spectrum
Magnetic Field (0,0,5)
1 Mn NG6 NX24
2 Mn NG36 NX244
3Mn NG216 NX864
E(meV)
E(meV)
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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
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Standardoptical selection rule
OPTICAL SPIN BLOCKADE
Franck Condon Spin Blockade
GSM
Photon QUANTUM MEASUREMENT
XSM
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N3. Narrowing and shift
PL, experiment
0T
2T
4T
6T
8T
10T
P. S. Dorozhkin, Phys. Rev. B 68, 195313 (2003)
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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?
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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)
• S5/2 qbits.
• Detection ok (at least N2)
• Time resolved control ok
• 2 qbit operations ok