microwave spectroscopy of the radio-frequency cooper pair transistor
DESCRIPTION
Microwave Spectroscopy of the radio-frequency Cooper Pair Transistor. A. J. Ferguson, N. A. Court & R. G. Clark. Centre for Quantum Computer Technology, University of New South Wales, Sydney. Summary. Engineering the properties of superconducting aluminium - PowerPoint PPT PresentationTRANSCRIPT
Microwave Spectroscopy of the radio-frequency Cooper Pair
TransistorA. J. Ferguson, N. A. Court & R. G.
Clark
Centre for Quantum Computer Technology, University of New South Wales, Sydney
Summary
1. Engineering the properties of superconducting aluminium
2. The single cooper pair transistor (SCPT)3. Radio frequency operation of the SCPT4. The superconducting transport processes5. Microwave spectroscopy
Aluminium Devices
Y. Nakamura et al Nature 398 786 (1999) I. Chiorescu et al Science 299 1869 (2002)
Superconducting Qubits
Single electron (Cooper-pair) transistors
Aluminium Materials Science
Thin films: dramatic change in superconducting properties
R. Meservey and P. M. Tedrow J. Appl. Phys. 42, 51 (1971)
J. Aumentado et al., PRL 92, 066802 (2004)
An alternative approach to O2 doping
Tc, Bc
d (nm)10 1001 1000
1
0.1
10
B (
T)
d-1 (nm-1)0.30.10.01
2
3
1
Tc
(K)
Pauli-limited Bc: spin effects in superconducting SETs.A. J. Ferguson et al. on cond-mat soon
The thin-film SCPT
7 nm30 nm 30nm
~ 200 V ~ 300 V ~ 200 V
~1K of quasiparticle barrier
Films evaporated onto LN2 cooled stage at 0.1 nms-1
Electrically continuous films to 5 nm possible
7 nm
30 nm 30 nm
7 nm islands used for these devices
Single Cooper pair transistor
2
2
)2(2
cos
2cos)(
gCJ
JgC
nEE
EnEH
In a 2-band model
EJ/EC=0.5
EJ,C1 EJ,C2
Cg
EC=e2/(C1+C2+Cg)
Q
mmsw d
dEeQI
max
2)(, h
Why do it? QP poisoning
Careful filtering required to avoid non-equilibrium qpsThese qps tunnel on and ‘poison’ supercurrent
2
1/2~exp(2-1/kT)A QP barrier reduces poisoning rate
1
The device itself becomes a qp filter
2122
2
22
J. Aumentado et al., Phys. Rev. Lett, 92, 066802 (2004)
rf-SET
1
1
RCj
LjZ
Main idea: LC circuit matches high resistance of SET towards 50 Ohms.
50/
50/
RCL
RCLa
Amplitude of reflected signal (S11), related to resistance (R) of SET.
R. J. Schoelkopf et al., Science 280 1238 (1998)
rf (321MHz)
Reflected signal either diode or mixer detected.
rf-SCPT
Lj
V~I rf
rf
Irf<Isw: R~0
Irf>Isw: R>0
Single shot: QP poisoning events
J. Aumentado et al., cond-mat\0511026
Resistance is now Reff(Irf, Isw), use to find reflection coefficient in the usual way.
Device I: Parameters R = 18 k EJ = 43 eVEc = 77 eVEJ/EC = 0.56
Ima
x
Imin
B=0T Diamonds
Ec=180 eVR=71 kEJ=11 eVEJ/EC=0.06
2e supercurrent enabled by thin-island
21 + 22 = 1.05 meV
2e ‘supercurrent’
JQP DJQP
Mix
er
out
(a.
u.)
Device II: Parameters
0
1
Ima
x
Imin
Resonant CP tunnelling
D. B. Haviland et al., PRL 73, 1541 (1994)
V
E(n+2)-E(n)=0E(n+2)-(E(n)-2eV)=0
Supercurrent occurs when resonance occurs for a CP on both junctions.
ResonantDissipative
V 02
@ A21 3
B
2 3 4
A
Vds)C(CgVgC
ne
2C
(ne)E(n) 1
ΣΣ
2
DJQP resonance: QPs involved
Resonant Dissipative
V02
@ B
Resonant Resonant
02
Microwave Spectroscopy
D. J. Flees et al., Phys. Rev. Lett., 78, 4817 (1997)Y. Nakamura et al., Czech. J. Phys., 46, 2301 (1996) Y. Nakamura et al., Phys. Rev. Lett., 12, 799 (1997)
40GHz
-25 dBm -19 dBm
Suppression of supercurrent
Frequency dependent sidebands on supercurrent
Frequency dependent sidebands on resonant CPT
No -waves
PAT + resonant CPT
0
2
012
N
irf
Ni NhfENhf
eVJE )(
2)( 12
0
2
0
2
0
2
0
2
0
2
P. K. Tien and J. P. Gordon, Phys Rev. 129, 647 (1963)
0
2
Frequency dependence
Linear dependence of sidebands observed.
Anti-crossing not observable since Ej=11eV (2.6 GHz)
22 )4/()(4 EcEjCgVgEchf
1: 186 eV
2: 193 eVc.f. 180 eV from transport
Power dependence30 GHz
0 1 2
EC=180 eV, =300 eV, EJ=11 eV
Multiple events occur
Possibly QP states excited too
J. M. Hergenrother et al., Physica B 203, 327 (1994)
Conclusions
• ~100 eV of QP barrier possible with thin film
• Reduced QP poisoning allows 2e-periodicity
• rf-measurement of 2e supercurrent shown • Observe individual QP poisoning events• Combination of PAT and CP resonant
tunneling observed
Future
• Experimental: investigate charge noise of thin film
• Experimental: further study individual QP poisoning events
• Theoretical: look at rf-supercurrent measurement as electrometer (ultimate sensitivity etc)