t. smoleński 1, m. goryca 1,2, t. kazimierczuk 1, j. a. gaj 1, p. płochocka 2, m. potemski 2,p....
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Single Mn atom in CdTe/ZnTe quantum dot as an optical quantum memory
T. Smoleński1, M. Goryca1,2, T. Kazimierczuk1 , J. A. Gaj1,
P. Płochocka2, M. Potemski2,P. Wojnar3, P. Kossacki1,2
1. Institute of Experimental Physics, University of Warsaw2. Grenoble High Magnetic Field Laboratory3. Institue of Physics, Polish Academy of Sciences
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OutlineIntroduction – what a quantum dot (QD) is?
Samples – how to observe a single magnetic atom
Experiment 1. Optical reading of information on the Mn
spin state 2. Optical writing and storage of information
Conclusion
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Quantum dotsNanostructures, made of two semiconductors
with different energy gaps
10 nm
CdTeZnTe
Inner material, with small energy gap
Outer material, with wide energy gap
ECdTe EZnTe
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Exciton in QDTwo types of carriers:
electrons and holes
Jz = ±1/2 Jz = ±3/2+e
-e
Exciton X4 possible spin states of X
Jz = -1
Jz = +1 Jz = -2
Jz = +2
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Exciton in QDTwo types of carriers:
electrons and holes4 possible spin states of X
Jz = -1
Jz = +1 Jz = -2
Jz = +2
The way to observe single QDs: photoluminescence measurements !
1.922 1.923
energy (eV)
phot
olum
ines
cenc
e (a
rb.
u.)
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QD with a single Mn ionSingle Mn ion: S = 5/2, L = 0Mn has 6 possible spin states
with 6 different Sz values
Mn
En
erg
y
exchange interaction between Mn and X
1.906 1.907 1.908 1.909
energy (eV)
ph
oto
lum
ine
sce
nce
(a
rb.
u.)
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SamplesHow to make QDs? We can
do it using MBE method.
GaAs (substrate)
CdTe(buffer)
ZnTeIn an appropriate moment
we open the effusive cell with Mn atoms for a short time.
Number of Mn ions in a single QD ~ 1
ZnTe
CdTe(formation layer)
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Experimental setupHow to observe a single QD?
T=1.5K
Tunable dye laser
Monochromator with CCD camera and avalanche photodiode
Criostat with microscope
Pol λ/4
Modulators
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Optical QD excitationHow to introduce spin polarized excitons to QD
with single Mn ion?
Light should be circularly polarized (i.e. -s )
We should use … another QD without Mn ion!
Mn
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Photoluminescence spectrum
Excitation with unpolarized light = unoriented Mn spin
1.906 1.907 1.908 1.909
energy (eV)
phot
olum
ines
cenc
e (a
rb. u
.)
Mn
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Photoluminescence spectrum (2)+
s
ph
oto
lum
inesc
en
ce (
arb
. u
.)
energy (eV)
Excitation with circularly polarized light = we observe Mn spin orientation!
energy (eV)
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What is the storage time?
t
Iσ+Excitation
Steady state
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What is the storage time?
t
Iσ+Excitation
Steady state
σ-
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What is the storage time?
t
Iσ+Excitation
Steady state
I
t
Signal on APD
σ-
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What is the storage time?
t
Iσ+Excitation
Steady state
I
t
Signal on APD
σ-
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What is the storage time?
t
Iσ+Excitation
Steady state
I
t
Signal on APD
σ-
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Storage time determinationExcitation scheme
0
0.5
1.0
0 500 1000 1500 2000
exc 2.5W
time (ns)
PL
inte
nsi
ty (
arb
.u.)
T=1.5K, B=1T
0.8
0.9
1.0
0 100 200
= 0.4 ms
Dark Period (s)
Nor
mal
ized
Pea
k A
mpl
iude
t
Iσ+ σ-
Storage time~ 0.4 ms
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Conclusion
We demonstrated optical writing and reading of information on the spin state of a single Mn ion embedded in a CdTe/ZnTe QD
• We shown, that single magnetic atom in a QD is a spin memory with optical writing and readout of information, storage time ~1ms