PowerPoint-Pr

1
A two-qubit conditional quantum gate with single
spins  
Univ. of Stuttgart
F.Jelezko, J. Wrachtrup I. Popa, T. Gaebel, M.
Domhan, C.Wittmann
2
Outline
Introduction Single spin states Read-out,
manipulation, coherence time CROT gate with
single electron and nuclear spin in a solid
Scaling up Positioning of single N-V defects in
diamond
3
History
Science 275 (1997) 350-365
A pure state (single spin EPR,NMR)
but see e.g. J. Wrachtrup, A. Gruber, L. Fleury,
C. von Borczyskowski Magnetic Resonance on
single nuclei CPL 267 (1997) 179
4
Single spin read-out
2. Electrical detection
Durkan, C. Welland, M. E. Appl. Phys. Lett. 80,
458-460 (2002) - STM
M. Xiao, I. Martin, E. Yablonovitch, H. W. Jiang
Nature 430, 435 - 439 (2004) - FET
J. M. Elzerman, R. Hanson, L. H. Willems van
Beveren, B. Witkamp, L. M. K. Vandersypen, L. P.
Kouwenhoven Nature 430, 431 - 435 (2004)
5
Optical readout
Single defect detection Optical microscopy
m
n
300 nm

0
0
3
The number of scattered photons depends on spin
state Brossel and Bitter (1952) Phys. Rev. 86 308
(mercury vapours) Wrachtrup et al. Nature 363,
244245 (1993) (single molecules)
6
Set-up
Variable temperature microscope Operating
temperature 1,6 300 K Detection yield 1
percent
Magnetic field up to 5 T
7
Nitrogen Vacancy (NV) center in diamond
Diamond -bandgap 6 eV -Tdebay 2000K Long T2 of
defects at RT
Optical detection of single defects Gruber A,
Wrachtrup J et al, SCIENCE 276 2012 (1997)
8
Single N-V centers implantation
App. 2 N iones/ N-V defect
9
Single center signature photon antibunching
Single photon source Weinfurter et al. PRL 85
(2000) Grangier et al. PRL 89 (2003)
10
Observation of single electron spin quantum jump
at T2K
Low temperature optical spectroscopy, bulk D.
Redman J. Opt. Soc. Am. B 9, No. 5, (1992).
Single defects Jelezko F et al. APL 81 , 2160
(2002)
3E
1A
?E3GHz
11
Inhibition of coherent spin state evolution by
measurement ( a watched pot never boils)
T300K
MW pulse
Weak probe
12
How large is T2?Hahn Echo
13
Hahn echo decay
F. Jelezko et al PRL 92 (2004) 076401
Decoherence due to P1 centers ? (P1 - single
substitutional nitrogen, 100 ppm in HPHT Ib
diamond)
first data T2 0.3-0.5 ?s
14
Hahn echo decay of single N-V center in IIa type
diamond

• pulse 8 ns
• T2/Tgate 105

15
Optical single nuclear spin read-out (13C diamond)
13C spins as qubits Wrachtrup Opt. Spectr. 91
429 (2001) optical spectroscopy
Hyperfine splitting A1,2,3 130 MHz
Fine Structure Splittting 3 GHz
Experimental realization using ESR Jelezko et
al. Phys. Rev. Lett. 93, 130501 (2004)   
Ab initio calculations M.Luszczek et al. Physica
B 348, 292 (2004)
16
Gates qubits
1st qubit electron spin of N-V 2nd qubit
nuclear spin of 13C
C130 MHz D10 MHz
A2800 MHz B2940 MHz
ESR
NMR (ENDOR)
17
Rabi nutation of single electron and single 13C
spin single qubit operations
ESR (transition A)
C
ENDOR (transition C)
Averages over 105 Cycles
18
CROT-gatea two qubit gate
flips the nuclear spin dependent on the
orientation of the electron spin with p/2(z)
equivalent to the CNOT-gate
Experimental selective NMR p-pulse
2
p
1
3
4
19
Tomography of state after CROT
p
Ideal result
Initial state
20
Tomography of state after CROT
Theory
Experiment
Parameters for calculation
0.1 0.16 0.04 0
0.16 0.9 0.12 0
0.04 0.12 0 0
0 0 0 0
?ESR 15 ns T2e1.2 ?s ?NMR400 ns T2n3.6
?s
Jelezko et al. quant-ph/0402087
21
Scaling up
13C spin cluster is scalable up to 3-12 qubits
Fully scalable architecture coupled NV defects
Coupling magnetic dipole (short range) Optical
dipole (long range)
N beam
5 nm
Diamond
NV defect
22
Positioning accuracy limitations
N ions
surface of sample
1,1µm
500nm FWHM
target depth
1 nm accuracy for 1 keV ions possible
23
Summary single spin QC

• Single electron and nuclear spin state read-out
• and coherent manipulation

• 1 and 2 Qbit operation
• ( 3. Qbit 14N not used in experiment)

• scaling requires coupling of defects (nm
  positioning)

24
Acknowledgment
3. Institute of Physics University of
Stuttgart J. Wrachtrup I. Popa T. Gaebel, M.
Domhan C.Wittmann A. Gruber currently at
University of Chemnitz
In collaboration with S.Kilin, A. Nizovtsev
(Minsk) J. Twamley (University of Ireland) J.
Buttler (NRL Washington) JD. Suter (Dortmund) J.
Meyer (Bochum) J. Rabeau, S. Prawer
(Melbourne) DFG, EU (QIPDDF ROSES)
Landesstiftung BW