Condensation of Cooper pairs and Cooper quartets in fermionic systems with multiple internal degrees of freedom is studied.In this thesis work, I work on two major projects.On the first project I discuss Cooper pair condensation and while on the second I discuss Cooper quartet condensation.Due to the restrictions imposed by Pauli's principle, no two identical fermions can occupy a single quantum state.Therefore for electronic systems with two internal states, the maximum number of electrons that could be bound together is two.However; for a fermionic system having more than two internal states, it is possible that the bound state structure could be quite different.On my thesis I focus on systems that have four internal states.On one hand it is possible that the system will still undergo some types of pairing condensation, but there is also a possibility that the fermions will form a more complex structure where four fermions are bound together which we call a quartet.Physical systems where fermions can have four internal states include a system of spin-3 2 fermionic atoms and a two band electronic system.I look at possible two and four particle bound state structures in such systems.Condensation of Cooper pairs and Cooper quartets in fermionic systems with multiple internal degrees of freedom is studied.In this thesis work, I work on two major projects.On the first project I discuss Cooper pair condensation and while on the second I discuss Cooper quartet condensation.Due to the restrictions imposed by Pauli's principle, no two identical fermions can occupy a single quantum state.Therefore for electronic systems with two internal states, the maximum number of electrons that could be bound together is two.However; for a fermionic system having more than two internal states, it is possible that the bound state structure could be quite different.On my thesis I focus on systems that have four internal states.On one hand it is possible that the system will still undergo some types of pairing condensation, but there is also a possibility that the fermions will form a more complex structure where four fermions are bound together which we call a quartet.Physical systems where fermions can have four internal states include a system of spin-3 2 fermionic atoms and a two band electronic system.I look at possible two and four particle bound state structures in such systems.

Jan 1, 20080 citations

Dissecting Cooper Pairs

ScienceMay 31, 20120 citations

Scalability of supercurrent modulable with single Cooper-pair transistors connected in parallel

Jutarat Tanarom, Yoshinao Mizugaki, Hiroshi Shimada

Abstract A single Cooper-pair transistor (SCPT) can work as a fast supercurrent switch. However, a direct combination of an SCPT with other superconducting-electronics circuits is not easy because of the smallness of the switchable supercurrent with it. In this work, scalability of the supercurrent that can be modulated with an SCPT structure is studied using multiple SCPTs connected in parallel having a common gate electrode. It is found that the magnitude of the maximum supercurrent is scaled up almost linearly with the increase in the number of SCPTs, N , and that it is modulated with the gate voltage as in the case for a single SCPT. The modulability, however, decreases with the increase in N , which is demonstrated to be mostly because of the charge-state fluctuations of either islands of the constituent SCPTs caused by the capacitive coupling among them. A practically possible method of improving the modulability is also discussed.Abstract A single Cooper-pair transistor (SCPT) can work as a fast supercurrent switch. However, a direct combination of an SCPT with other superconducting-electronics circuits is not easy because of the smallness of the switchable supercurrent with it. In this work, scalability of the supercurrent that can be modulated with an SCPT structure is studied using multiple SCPTs connected in parallel having a common gate electrode. It is found that the magnitude of the maximum supercurrent is scaled up almost linearly with the increase in the number of SCPTs, N , and that it is modulated with the gate voltage as in the case for a single SCPT. The modulability, however, decreases with the increase in N , which is demonstrated to be mostly because of the charge-state fluctuations of either islands of the constituent SCPTs caused by the capacitive coupling among them. A practically possible method of improving the modulability is also discussed.

Japanese Journal of Applied PhysicsJun 9, 20211 citation

Stable and resonant Cooper pairs

Valdir C. Aguilera-Navarro, Mauricio Fortes, MANUEL DE LLANO

Solid State CommunicationsDec 11, 200318 citations

Effect of decoherence on resonant Cooper-pair tunneling in a voltage-biased single-Cooper-pair transistor

Juha Leppäkangas, E. V. Thuneberg

We analyze how decoherence appears in the $I\text{\ensuremath{-}}V$ characteristics of a voltage-biased single-Cooper-pair transistor. Especially the effect on resonant single or several Cooper-pair tunneling is studied. We consider both a symmetric and an asymmetric transistor. As a decoherence source we use a small resistive impedance $(\text{Re}[Z(\ensuremath{\omega})]⪡{R}_{Q}=h/4{e}^{2})$ in series with the transistor, which provides both thermal and quantum fluctuations of the voltage. Additional decoherence sources are quasiparticle tunneling across the Josephson junctions and quantum $f$ noise caused by spurious charge fluctuators nearby the island. The analysis is based on a real-time diagrammatic technique which includes Zeno-type effects in the charge transport, where the tunneling is slowed down due to strong decoherence. As compared to the Pauli-master-equation treatment of the problem, the present results are more consistent with experiments where many of the predicted sharp resonant structures are missing or weakened due to decoherence.We analyze how decoherence appears in the $I\text{\ensuremath{-}}V$ characteristics of a voltage-biased single-Cooper-pair transistor. Especially the effect on resonant single or several Cooper-pair tunneling is studied. We consider both a symmetric and an asymmetric transistor. As a decoherence source we use a small resistive impedance $(\text{Re}[Z(\ensuremath{\omega})]⪡{R}_{Q}=h/4{e}^{2})$ in series with the transistor, which provides both thermal and quantum fluctuations of the voltage. Additional decoherence sources are quasiparticle tunneling across the Josephson junctions and quantum $f$ noise caused by spurious charge fluctuators nearby the island. The analysis is based on a real-time diagrammatic technique which includes Zeno-type effects in the charge transport, where the tunneling is slowed down due to strong decoherence. As compared to the Pauli-master-equation treatment of the problem, the present results are more consistent with experiments where many of the predicted sharp resonant structures are missing or weakened due to decoherence.

arXiv:0806.4512Physical Review BOct 28, 200811 citations

f

noise caused by spurious charge fluctuators nearby the island. The analysis is based on a real-time diagrammatic technique which includes Zeno-type effects in the charge transport, where the tunneling is slowed down due to strong decoherence. As compared to the Pauli-master-equation treatment of the problem, the present results are more consistent with experiments where many of the predicted sharp resonant structures are missing or weakened due to decoherence.