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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

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Microwave spectroscopy of the radio frequency cooper pair transistor l.jpg

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 l.jpg
Summary Transistor

  • Engineering the properties of superconducting aluminium

  • The single cooper pair transistor (SCPT)

  • Radio frequency operation of the SCPT

  • The superconducting transport processes

  • Microwave spectroscopy


Aluminium devices l.jpg
Aluminium Devices Transistor

Superconducting Qubits

I. Chiorescu et al Science 299 1869 (2002)

Y. Nakamura et al Nature 398 786 (1999)

Single electron (Cooper-pair) transistors


Aluminium materials science l.jpg

10 Transistor

3

1

Tc (K)

B (T)

2

0.1

1

0.3

0.1

0.01

d-1 (nm-1)

1

10

100

1000

An alternative approach to O2 doping

J. Aumentado et al., PRL 92, 066802 (2004)

Aluminium Materials Science

Thin films: dramatic change in superconducting properties

Bc

Tc, D

R. Meservey and P. M. Tedrow J. Appl. Phys. 42, 51 (1971)

d (nm)

Pauli-limited Bc: spin effects in superconducting SETs.

A. J. Ferguson et al. on cond-mat soon


The thin film scpt l.jpg
The thin-film SCPT Transistor

7 nm islands used for these devices

~1K of quasiparticle barrier

7 nm

D ~ 300 mV

D ~ 200 mV

D ~ 200 mV

30 nm

30 nm

30nm

30 nm

7 nm

Films evaporated onto LN2 cooled stage at 0.1 nms-1

Electrically continuous films to 5 nm possible


Single cooper pair transistor l.jpg

h Transistor

Single Cooper pair transistor

EJ,C2

EJ,C1

In a 2-band model

Cg

EC=e2/(C1+C2+Cg)

EJ/EC=0.5


Why do it qp poisoning l.jpg

G Transistor2

2D2

2D2

2D1

Why do it? QP poisoning

Careful filtering required to avoid non-equilibrium qps

These qps tunnel on and ‘poison’ supercurrent

G1

2D

A QP barrier reduces poisoning rate

G1/G2~exp(D2-D1/kT)

The device itself becomes a qp filter

J. Aumentado et al., Phys. Rev. Lett, 92, 066802 (2004)


Rf set l.jpg
rf-SET Transistor

Main idea: LC circuit matches high resistance of SET towards 50 Ohms.

rf (321MHz)

Amplitude of reflected signal (S11), related to resistance (R) of SET.

Reflected signal either diode or mixer detected.

R. J. Schoelkopf et al., Science 280 1238 (1998)


Rf scpt l.jpg

Device I: Parameters Transistor

R = 18 kW

EJ = 43 meV

Ec = 77 meV

EJ/EC = 0.56

Imin

Imax

rf-SCPT

Irf<Isw: R~0 W

Irf>Isw: R>0 W

Resistance is now Reff(Irf, Isw), use to find reflection coefficient in the usual way.

Single shot: QP poisoning events

J. Aumentado et al., cond-mat\0511026


B 0t diamonds l.jpg

Imin Transistor

Imax

B=0T Diamonds

2e supercurrent enabled by thin-island

Device II: Parameters

0

Ec=180 meV

RS=71 kW

EJ=11 meV

EJ/EC=0.06

Mixer out (a.u.)

1

2e ‘supercurrent’

DJQP

JQP

2D1 + 2D2 = 1.05 meV


Resonant cp tunnelling l.jpg

V Transistor

2

3

4

1

2

3

A

B

@ A

@ B

Resonant

Dissipative

Dissipative

Resonant

Resonant

Resonant

2

V

0

2

2

V

0

0

Resonant CP tunnelling

E(n+2)-E(n)=0

E(n+2)-(E(n)-2eV)=0

DJQP resonance: QPs involved

Supercurrent occurs when resonance occurs for a CP on both junctions.

D. B. Haviland et al., PRL 73, 1541 (1994)


Microwave spectroscopy l.jpg

-19 dBm Transistor

-25 dBm

Microwave Spectroscopy

40GHz

No m-waves

Suppression of supercurrent

Frequency dependent sidebands on supercurrent

Frequency dependent sidebands on resonant CPT

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)


Pat resonant cpt l.jpg

2 Transistor

2

0

0

2

2

0

0

2

2

2

0

0

0

PAT + resonant CPT

2g

1g

0g

P. K. Tien and J. P. Gordon, Phys Rev. 129, 647 (1963)


Frequency dependence l.jpg
Frequency dependence Transistor

Linear dependence of sidebands observed.

Anti-crossing not observable since Ej=11meV (2.6 GHz)

1g: 186 meV

2g: 193 meV

c.f. 180 meV from transport


Power dependence l.jpg

30 GHz Transistor

1

0

2

Power dependence

EC=180 meV, D=300 meV, EJ=11 meV

Multiple g events occur

Possibly QP states excited too

J. M. Hergenrother et al., Physica B 203, 327 (1994)


Conclusions l.jpg
Conclusions Transistor

  • ~100 meV 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 l.jpg
Future Transistor

  • 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)


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