Diapositiva 1

1
Investigation of high-temperature grain boundary
junctions as a tool for superconducting quiet
qubit
Istituto di Cibernetica E. Caianiello Consiglio
Nazionale delle Ricerche Pozzuoli (Napoli), Italy
Dept. of Materials Science University of
Cambridge,UK
E. Sarnelli G. Testa E. Esposito D. Perez de
Lara A. Monaco
M. Blamire E. J. Tarte D. J. Kang S. H. Mennema
2
Superconducting flux qu-bit
Flux qu-bit
3
LTS flux qubit bLIc/F0gt1
IC ICo sin j
IC ICo sin j
F0/2
FextF0/2
Fext0
Bocko et al. IEEE TAS7 (1997) J. R. Friedman, V.
Patel, W. Chen, S. K. Tolpygo, and J. E. Lukens,
Nature 406, 43 (2000)
4
LTS phase qubit LIc/F0ltlt1
IC ICo sin j
b ltlt 1
FextF0/2
J. E. Mooij, T. P. Orlando, L. S. Levitov, L.
Tian, C. H. van der Wal, and S. Lloyd, Science
285, 1999. L. B. Ioffe, V. B. Geshkebein, M. V.
Feigelman, A. L. Fauchere, and G. Blatter,
Nature 398, 679 1999
5
Introduction to d-wave Order parameter symmetry
D. J. Van Harlingen, Rev. Mod. Phys.
67, 515 (1995)
6
Schultz et al., Appl. Phys. Lett. 76, 912 (2000)
7
C. C. Tsuei and J. R. Kirtley, Rev. Mod. Phys.
72, 2000
8
HTS flux qu-bit with d-wave superconductors
IC ICo sin j
IC ICo sin (p-j)
0
p
M. Sigrist and T.M. Rice, J. Phys. Soc. Jpn. 61,
4283 (1992)
9
Qu-bit using d-wave superconductors
b ltlt 1
pf1f2f3f4
Ioffe et al. Nature (1999)
Blatter, Geshkenbein, and Ioffe PRB 2001
Current-carrying ground state

• SND p loop
• SD or DD asymmetric junctions
• DD symmetric junctions

I(f)I1sin(f)I2sin(2f)
p/2
p
0
Ip?vD/T
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Asymmetric 45 DD GBJ
SD junction
Why is a DD symmetric junction quiet?
I//sin(f))?0
I?sin(2f))
Symmetric 45 DD GBJ
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Andreev Bound States
S
N
DLR(?) D0 cos2(?LR - aLR)
12
Anomalous temperature dependence of the Josephson
current
Yu.Tanaka and S. Kashiwaya, Phys.Rev.B 56, 892,
1997
13
Experimental procedure for the fabrication
of YBCO p-junctions based on Andreev Midgap
states

• Need a submicron technology compatible
  with HTS
• Appropriate grain boundary configuration
• in order to enhance the effect of MGS
• Appropriate phase sensitive experiment
• (to exclude spurious effect)

14
FIB Microscope
Liquid Metal Source

• 30 keV Ga ion (high ion density),
• lt10 nm beam resolution,
• Rapid implementation of complex nanostructures
• Versatile and unique advantages over other
  similar type of microscopes
• High resolution image
• precision

Extractor Cap
Lense 1
Beam Defining Aperture
Steering Quadrupole
Deflection Octopole
Lense 2
15
Bicrystal grain boundary junction configuration
001 24
001 45
a
b
a -b 12
a -b 22.5
c
b
a
16
5 mm
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Submicron 001 symmetric tilt GBJs
FIB Picture
G Testa, A Monaco, E Sarnelli, A DAgostino,
D-JKang, E J Tarte, S H Mennema, C Bell and M G
Blamire SuST 17, 287 (2004)
18
4 mm
19
001 24
20
001 24
I-V characteristics at T 77 K
21
001 24
Transport properties and magnetic field dependence
G Testa, A Monaco, E Sarnelli, D-JKang, E J
Tarte, S H Mennema, C Bell and M G Blamire SuST
17, 287 (2004)
22
Submicron dc SQUID as a probe of the 0-p
junction transition
a
b
bicrystal line
23
Submicron HTS YBCO dc-SQUID on 001 45
symmetric bicrystal
Junction width 0.3 mm -- hole 3x3 mm2 -- b ??
1
24
Experimental Ic(T) of the submicron dc SQUID
25
Experimental Ic(T) of the submicron dc SQUID
AB
MGS
Josephson
G Testa, A.Monaco, E Sarnelli, D-JKang, E J
Tarte, SHMennema, C Bell and M G Blamire, APL
2004
26
T
27
T
28
T 21.2 K
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Curren-phase relation in 45 001 symmetric tilt
GBJ In the presence of Andreev midgap states
I(f)?sin(f)
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Effect of barrier roughness on the current-phase
relation
With
Without
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Contribution of Andreev bound states to the
Josephson current
Simplified equivalent electrical circuit
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(No Transcript)
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aAR 0.1
aAR 0.1
34
aAR 0.3
35
aAR 0.5
36
aAR 0.7
37
aAR 0.9
38
aAR 1.0
39
aAR 1.1
40
aAR 1.3
41
aAR 1.5
42
aAR 1.7
43
aAR 1.9
44
aAR 2.0
45
aAR 3.0
46
Conclusions

• A study has been done concerning the realization
  of a phase qu-bit based on the properties (midgap
  states) of a non-conventional order parameter
  symmetry in HTS
• High quality submicron bicrystal GBJs have been
  fabricated for the first time by a FIB system
• The effect of Andreev midgap states and a clear
  0-p junction transition in a symmetric 45 001
  tilt dc-SQUID has been observed by two different
  phase sensitive tests
• Anomalous temperature dependence of Ic
• Half flux quantum shift in the Ic(H) dependence

47
Coming experiments

• Fabrication of a large number of such p junctions
• Analysis of the intrinsic noise of single
  junctions and p-loops
• Development of an integrated technology for the
  fabrication of three and/or five junction loop