Coherent Quantum Phase Slip Oleg Astafiev NEC Smart Energy Research Laboratories, Japan and The Institute of Physical and Chemical Research (RIKEN), Japan RIKEN/NEC: O. V. Astafiev, S. Kafanov, Yu. A. Pashkin, J. S. Tsai Rutgers: L. B. Ioffe Jyväskylä: K. Yu. Arutyunov Weizmann: D. Shahar, O. Cohen herent quantum phase slip, Nature, 484, 355 (2012)
Coherent quantum phase slip, Nature, 484, 355 (2012). RIKEN/NEC: O. V. Astafiev, S. Kafanov, Yu. A. Pashkin, J. S. Tsai Rutgers: L. B. Ioffe Jyv ä skyl ä : K. Yu. Arutyunov Weizmann: D. Shahar, O. Cohen. Coherent Quantum Phase Slip. Oleg Astafiev - PowerPoint PPT Presentation
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Coherent Quantum Phase Slip
Oleg Astafiev
NEC Smart Energy Research Laboratories, Japanand
The Institute of Physical and Chemical Research (RIKEN), Japan
RIKEN/NEC: O. V. Astafiev, S. Kafanov, Yu. A. Pashkin, J. S. TsaiRutgers: L. B. Ioffe Jyväskylä: K. Yu. ArutyunovWeizmann: D. Shahar, O. Cohen
= Phase across junction = Phase across junction nq = normalized charge alongthe wire
nq = normalized charge alongthe wire
Mooij, Nazarov. Nature Physics 2, 169-172 (2006)
IICC
VVCC
Shapiro Step
Shapiro Step
[nq,] = -i
Supercurrent CQPS voltage
NNNNE
NNEH SN 11
2
Flux is quantized: N0
A loop with a nano-wire
Hamiltonian:
L
NE extN 2
20
The loop with phase-slip wire is dual to the charge qubit
BSext
(PS qubit proposed by Mooij J. E. and Harmans C.J.P.M )
Magnrtic energy:
Phase-slip energy: ECQPS
E
Degeneracy
>> kT
0 2 31 4
The Phase-Slip Qubit
ext
EL
>> ECQPS
ELCQPS qubit:
0
1 0
1
L
NE extN 2
20
NNNNE
NNE
H JN 1122
Charge is quantized: 2eN
Duality to the charge qubit
Hamiltonian:
C
qeNE extN 2
2 2
The loop with phase-slip wire is dual to the charge qubit
EJ
Reservoir
BoxC
Cg
Vg
ggext CVq
Cg
L C 0 2e extqext
Loops of usual (BCS) superconductors (Al, Ti) did not show qubit behavior BCS superconductors become normal metals, when superconductivity is suppressed Special class of superconductors turn to insulators, when superconductivity is suppressed Superconductor-insulator transition (SIT) High resistive films in normal state high kinetic inductance
Choice of materials
R
RaE Q
S exp
Superconductor-insulator transition
(SIT)
InOx, TiN, NbN
Requirements: high sheet resistance > 1 k
n
k
RL
High resistance high kinetic inductance
107
106
105
104
103
102
101
0 5 10 15
T (K)
Sh
ee
t re
sist
an
ce R
□ (
)
The materials demonstratingSIT transition are the most promising for CQPS
40 nm
Es
N0 (N+1)0
E
ext(N+1/2)0
Gold ground-planes InOx
5 m
0.5 mmInOx
MW in MW out
Amorphous InOx film:R□ = 1.7 k
The device
Step-impedance resonator:High kinetic inductance
Measurement circuit
NetworkAnalyzer
-20 dB
-20 dB
Isolator
Isolator
resonator
Phase-slip qubit Coil
Low
pas
s fil
ters
output
input4.2 K
1 K
40 mK
Transmission through the step-impedance resonator
1st
2nd
Z0 Z1
Z0
Current field the resonator
Current amplitudes: maximal for evenzero for odd modes
6 7 8 9 10 11 120.0
0.5
1.0
t (a.
u.)
f (GHz)
34
5250 MHz
-0.10 -0.05 0.00 0.05 0.100.7
0.8
0.9
1.0
0.0
0.1
0.2
t
Bext
(mT)
arg
(t)
B
Z1 >> Z0
Transmission at 4th peak
5.0 5.5 6.0-6
-4
-2
0
arg
(t)
(m
rad
)
f (GHz)
f = 260 MHz
0
-5
arg
(t)
(mra
d)
Two-tone spectroscopy
We measure transmission through the resonator at fixed frequency fres
Another frequency fprobe is swept
The fitting curve: Ip = 24 nA, ES/h = 4.9 GHz
Current driven loop with CQPS
Transitions can happen only when ES 0
M
Ip
I0
|1
|0
tacosa
tIMIE
H axpxS
z cos
22 0
a
Sp
EIMI
0
zH 2int
RWA:
22sa E
tH axza
cos22
ES
The result is well reproducibleThree identical samples show similar behaviorwith energies 4.9, 5.8 and 9.5 GHz
After “annealing” at room temperature InOx becomes more superconducting.The samples were loaded three times with intervals about 1 months. Es is decreased with time.
00.0 0.5 1.0
0
20
40
60
80
E/h
(G
Hz)
ext
/
fprobe
2 fprobe + fres
(3-photons)
h
EI
hE
sp22
2
/
fprobe + fres
(2 photons)
Wide range spectroscopy
Linear inductance!
Decoherence
5.0 5.5 6.0-6
-4
-2
0
arg
(t)
(m
rad
)
f (GHz)
f = 260 MHz
Gaussian peak low frequency noise
k
kSkS e
qiEE
2
2exp
Total PS energy:
Potential fluctuations along the chain of Josephson junctions leads to fluctuations of energy and decoherence
Potential equilibration (screening) in the wire? Mechanism of decoherence?
L 1.6 nH/sq
NbN thin filmsR 2 kIn MW measurements Tc 5 K
Many qubits can be identified
20 different loops with wires of 20-50 nm width
General tendency: the higher resistance, the higher ES
NbN qubitsf (
GH
z)
Tra
nsm
issi
on a
mp
litud
e
Conclusion
We have experimentally demonstrated Coherent Quantum Phase Slip
Phase-slip qubit has been realized in thin highly resistive films of InOx and NbN
Mechanism of decoherence in nano-wires is an open question