Microwave Spectroscopy on the radio-frequency Cooper Pair ...

Microwave Spectroscopy on the radio-frequency Cooper Pair ...

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 1. Engineering the properties of superconducting aluminium 2. The single cooper pair transistor (SCPT) 3. Radio frequency operation of the SCPT 4. The superconducting transport processes 5. Microwave spectroscopy Aluminium Devices Superconducting Qubits Y. Nakamura et al Nature 398 786 (1999) I. Chiorescu et al Science 299 1869 (2002)

Single electron (Cooper-pair) transistors Aluminium Materials Science Thin films: dramatic change in superconducting properties Bc Tc, 10 1 Tc (K) B (T) 3 2

0.1 1 0.01 1 0.1 0.3 d (nm ) -1 10 100 d (nm) 1000 Pauli-limited Bc: spin effects in superconducting SETs. A. J. Ferguson et al. on cond-mat soon -1

R. Meservey and P. M. Tedrow J. Appl. Phys. 42, 51 (1971) An alternative approach to O2 doping J. Aumentado et al., PRL 92, 066802 (2004) The thin-film SCPT 7 nm islands used for these devices ~1K of quasiparticle barrier 7 nm ~ 200 V ~ 300 V ~ 200 V 30 nm 30 nm 30 nm 7 nm Films evaporated onto LN2 cooled stage at 0.1 nms-1 Electrically continuous films to 5 nm possible

30nm Single Cooper pair transistor EJ,C1 EJ,C2 In a 2-band model 2 EC ( ng ) H E cos J 2 Cg 2 EC (2 ng ) 2

E J cos EC=e2/(C1+C2+Cg) I sw,m (Q ) dE 2e max m h d Q EJ/EC=0.5 Why do it? QP poisoning Careful filtering required to avoid non-equilibrium qps These qps tunnel on and poison supercurrent 1

2 2 A QP barrier reduces poisoning rate 22 2 2 1/2~exp(2-1/kT) The device itself becomes a qp filter J. Aumentado et al., Phys. Rev. Lett, 92, 066802 (2004) 21 rf-SET Main idea: LC circuit matches high resistance of SET towards 50 Ohms. rf (321MHz)

1 Z j L j C R 1 L / RC 50 a L / RC 50 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 Irf

Irf>Isw: R>0 Resistance is now Reff(Irf, Isw), use to find reflection coefficient in the usual way. Single shot: QP poisoning events Imin Imax J. Aumentado et al., cond-mat\0511026 Device I: Parameters R = 18 k EJ = 43 eV Ec = 77 eV EJ/EC = 0.56 B=0T Diamonds 2e supercurrent enabled by thin-island

0 1 Imin JQP DJQP 21 + 22 = 1.05 meV Ec=180 eV R=71 k EJ=11 eV EJ/EC=0.06 Imax 2e supercurrent Mixer out (a.u.) Device II: Parameters

Resonant CP tunnelling E(n+2)-E(n)=0 E(n+2)-(E(n)-2eV)=0 (ne) 2 ne E(n) (CgVg C1Vds) 2C C @B @A 2 1 3 2 4 3 A 2 0 Resonant

Dissipative Dissipative Resonant V V B V 2 0 Resonant Resonant 2

0 Supercurrent occurs when resonance occurs for a CP on both junctions. DJQP resonance: QPs involved D. B. Haviland et al., PRL 73, 1541 (1994) Microwave Spectroscopy 40GHz No -waves -25 dBm -19 dBm 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 2 1 0 2 2 0 0 2 2 0 0 2 0

2eVrf 1 i ( E Nhf ) i ( E ) J N2 N Nhf 2 0 2 0 P. K. Tien and J. P. Gordon, Phys Rev. 129, 647 (1963) Frequency dependence Linear dependence of sidebands observed. Anti-crossing not observable since Ej=11eV (2.6 GHz)

1: 186 eV 2: 193 eV c.f. 180 eV from transport hf 4 Ec (CgVg ) 2 ( Ej / 4 Ec ) 2 Power dependence 30 GHz EC=180 eV, =300 eV, EJ=11 eV 0 1 2 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 2eperiodicity 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)

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