Two different types of Cooper pair transistors, with Al and Nb islands, have been investigated in a tunable electromagnetic environment. The device with an Al island demonstrates gate charge modulation with 2e periodicity in a wide range of environmental impedances at bath temperatures below 340 mK. Contrary to the results of the Al sample, the authors were not able to detect 2e periodicity under any conditions on similar samples with Nb island. The authors attribute this to the material properties of Nb.Two different types of Cooper pair transistors, with Al and Nb islands, have been investigated in a tunable electromagnetic environment. The device with an Al island demonstrates gate charge modulation with 2e periodicity in a wide range of environmental impedances at bath temperatures below 340 mK. Contrary to the results of the Al sample, the authors were not able to detect 2e periodicity under any conditions on similar samples with Nb island. The authors attribute this to the material properties of Nb.

Aug 1, 20077 citations

Coulomb blockade of Cooper pair tunneling and parity effects in the Cooper pair transistor

S. Corlevi, Wiebke Guichard, F. W. J. Hekking +1 more

We have measured the Cooper pair transistor (CPT) in a tunable electromagnetic environment consisting of four one-dimensional superconducting quantum interference device arrays. The transport properties of the CPT in the high impedance limit, ${Z}_{\mathrm{env}}⪢{R}_{Q}\ensuremath{\simeq}6.45\phantom{\rule{0.3em}{0ex}}\mathrm{k}\ensuremath{\Omega}$, are studied for different ratios of the Josephson coupling energy to the charging energy. As the impedance of the environment is increased, the current-voltage characteristic (IVC) of the CPT develops a Coulomb blockade of Cooper pair tunneling and the measured IVCs agree qualitatively with a theory based on quasicharge dynamics for a CPT. Increasing the impedance of the environment induces a transition in the modulation of the IVC with the gate charge from $e$ -periodic to $2e$ -periodic.We have measured the Cooper pair transistor (CPT) in a tunable electromagnetic environment consisting of four one-dimensional superconducting quantum interference device arrays. The transport properties of the CPT in the high impedance limit, ${Z}_{\mathrm{env}}⪢{R}_{Q}\ensuremath{\simeq}6.45\phantom{\rule{0.3em}{0ex}}\mathrm{k}\ensuremath{\Omega}$, are studied for different ratios of the Josephson coupling energy to the charging energy. As the impedance of the environment is increased, the current-voltage characteristic (IVC) of the CPT develops a Coulomb blockade of Cooper pair tunneling and the measured IVCs agree qualitatively with a theory based on quasicharge dynamics for a CPT. Increasing the impedance of the environment induces a transition in the modulation of the IVC with the gate charge from $e$-periodic to $2e$-periodic.

arXiv:cond-mat/0606407Physical Review BDec 13, 200621 citations

Parity effect in a superconducting island in a tunable dissipative environment

Watson Kuo, Cen-Shawn Wu, Jia-Hong Shyu +1 more

We have experimentally studied Coulomb oscillation in a superconducting single-electron transistor, where electromagnetic-environment impedance was controlled using a one-dimensional array of superconducting quantum interference devices. By decreasing environment impedance, the Coulomb oscillation exhibited a crossover from $2e$ to $1e$ periodicity. In addition, the $1e$ component was enhanced when additional noise was introduced by connecting a potential meter to the central island of the transistor. We propose a theoretical analysis for this parity effect that includes the effect of fluctuations arising from the finite noise temperature of the electromagnetic environment.We have experimentally studied Coulomb oscillation in a superconducting single-electron transistor, where electromagnetic-environment impedance was controlled using a one-dimensional array of superconducting quantum interference devices. By decreasing environment impedance, the Coulomb oscillation exhibited a crossover from $2e$ to $1e$ periodicity. In addition, the $1e$ component was enhanced when additional noise was introduced by connecting a potential meter to the central island of the transistor. We propose a theoretical analysis for this parity effect that includes the effect of fluctuations arising from the finite noise temperature of the electromagnetic environment.

Physical Review BNov 16, 20069 citations

Periodicity in Al/Ti superconducting single electron transistors

Sarah J. MacLeod, Sergey G. Kafanov, Jukka P Pekola

We present experiments on single Cooper-pair transistors made of two different superconducting materials. We chose Ti and Al to create an energy gap profile such that the island has a higher gap than the leads, thereby acting as a barrier to quasiparticle tunneling. Our transport measurements demonstrate that quasiparticle poisoning is suppressed in all our TiAlTi structures (higher gap for the island) with clear 2e periodicity observed, whereas full quasiparticle poisoning is observed in all AlTiAl devices (higher gap for the leads) with e periodicity.We present experiments on single Cooper-pair transistors made of two different superconducting materials. We chose Ti and Al to create an energy gap profile such that the island has a higher gap than the leads, thereby acting as a barrier to quasiparticle tunneling. Our transport measurements demonstrate that quasiparticle poisoning is suppressed in all our TiAlTi structures (higher gap for the island) with clear 2e periodicity observed, whereas full quasiparticle poisoning is observed in all AlTiAl devices (higher gap for the leads) with e periodicity.

arXiv:0906.0715Applied Physics LettersAug 3, 20098 citations

Suppression of Cooper-pair tunneling in superconducting charge boxes in tunable electromagnetic environments

Watson Kuo, Cen-Shawn Wu, Jia-Hong Shyu +1 more

The Cooper-pair tunneling in superconducting charge boxes in tunable electromagnetic environments is experimentally studied using a single-electron-transistor electrometer and via current-voltage characteristics measurement with small excitations. In the low-impedance regime, the environmental effect is quantified with an effective Josephson coupling energy, which is found to decrease as the environment impedance increases. In the high-impedance regime, the Cooper-pair tunneling is blockaded. For impedance above $250\phantom{\rule{0.3em}{0ex}}\mathrm{M}\ensuremath{\Omega}$, Coulomb oscillation of the zero-bias conductance suggests that Cooper-pair tunneling is completely suppressed and subgap quasiparticle tunneling becomes dominant.The Cooper-pair tunneling in superconducting charge boxes in tunable electromagnetic environments is experimentally studied using a single-electron-transistor electrometer and via current-voltage characteristics measurement with small excitations. In the low-impedance regime, the environmental effect is quantified with an effective Josephson coupling energy, which is found to decrease as the environment impedance increases. In the high-impedance regime, the Cooper-pair tunneling is blockaded. For impedance above $250\phantom{\rule{0.3em}{0ex}}\mathrm{M}\ensuremath{\Omega}$, Coulomb oscillation of the zero-bias conductance suggests that Cooper-pair tunneling is completely suppressed and subgap quasiparticle tunneling becomes dominant.

Physical Review BJan 11, 20072 citations

The single Cooper pair transistor: a macroscopic quantum system

P. Joyez

In a system where two small-area (100 nm x 100 nm) superconducting tunnel junctions are connected in series, the Josephson effect which tends to impose the phase competes with the charging effects in the central electrode (the of the device) which tend to set the charge of the island. By applying a voltage on an electrode capacitively coupled to the island (the electrode) one can arbitrate this competition in favour of either effect. This is can be seen in particular on the supercurrent which can flow through the junctions : it is modulated periodically by the gate voltage (hence the name of given to the system). This modulation shows sharp peaks when two charge states of the island are degenerate with respect to the electrostatic energy. The system is then in a state which has no classical description : it is in a coherent superposition of states. In this thesis we demonstrate experimentally the behaviour of this transistor and we analyse the theoretical and practical problems which can prevent the observation of the coherent superposition of states through the modulation of the supercurrent. In particular we show that the parity of the electron number in the island must be rigorously controlled and that the impedance connected to the circuit plays a crucial role in setting the magnitude of the measured supercurrent.In a system where two small-area (100 nm x 100 nm) superconducting tunnel junctions are connected in series, the Josephson effect which tends to impose the phase competes with the charging effects in the central electrode (the of the device) which tend to set the charge of the island. By applying a voltage on an electrode capacitively coupled to the island (the electrode) one can arbitrate this competition in favour of either effect. This is can be seen in particular on the supercurrent which can flow through the junctions : it is modulated periodically by the gate voltage (hence the name of given to the system). This modulation shows sharp peaks when two charge states of the island are degenerate with respect to the electrostatic energy. The system is then in a state which has no classical description : it is in a coherent superposition of states. In this thesis we demonstrate experimentally the behaviour of this transistor and we analyse the theoretical and practical problems which can prevent the observation of the coherent superposition of states through the modulation of the supercurrent. In particular we show that the parity of the electron number in the island must be rigorously controlled and that the impedance connected to the circuit plays a crucial role in setting the magnitude of the measured supercurrent.

Mar 6, 19956 citations

e

-periodic to

2e

-periodic.

2e

1e

periodicity. In addition, the

1e

component was enhanced when additional noise was introduced by connecting a potential meter to the central island of the transistor. We propose a theoretical analysis for this parity effect that includes the effect of fluctuations arising from the finite noise temperature of the electromagnetic environment.