Shigemasa Matsuo

Order Parameter Mixing Effectin the Fulde-Ferrell State

It is shown that when the triplet pairing interaction is finite in the singlet pairing superconductor, the Fulde-Ferrell (FF) state is significantly enhanced by the mixing effect which is inherent to nonuniform superconducting states in a strong magnetic field. The mixed FF state can exist at higher temperatures than the pure singlet FF state. This may explain the behavior of the recently observed high-field phase of the heavy fermion superconductor UPd 2 Al 3 . The phase diagram of the second-order phase transition is given for a simple model of s -wave- p -wave mixing state.

Phase Diagram of the Fulde-Ferrell-Larkin-Ovchinnikov State in a Three-Dimensional Superconductor

The phase diagram of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in a 3-dimensional superconductor is discussed. We use the quasi-classical Greens function to calculate the free energy. It is shown that the phase transition from the normal state is of first order at high temperatures but is of second order near T =0. To describe the phase transition in the Ginzburg-Landau theory, one has to take into account up to eighth order term with respect to the order parameter. The phase transition from the FFLO state to the uniform superconducting state is of second order in all the temperature range T <0.561 T c in accordance with Burkhardt and Rainers result in a 2-dimensional system.

Odd-frequency Cooper pairs and zero-energy surface bound states in superfluid 3He

He. The odd-frequency pair amplitude is closely related to the local density of states in the low energy limit. Wederive a formula relating explicitly the two quantities. This formula holds for arbitrary boundarycondition at the surface. We also present some numerical results on the surface odd-frequency pairamplitude in superfluid

A Nonuniform State in a d-Wave Superconductor under Magnetic Field

We consider a model d-wave superconductor in which the Y 2±2 states have the highest transition temperature and the Y 2±1 states have a slightly lower transition temperature and show that this model has a nonuniform phase just below the upper critical field in a wide temperature range. The nonuniform state is due to the mixing between the Y 2,±2 state and the Y 2,±1 state under magnetic field and has a spatially oscillating order parameter like the Fulde-Ferrell state but has a different character from the Fulde-Ferrell state because this nonuniform state is induced by the orbital magnetic effect. The relevance of the model to a heavy Fermion superconductor UPd 2 Al 3 is mentioned.

Generation of Macroscopic Entangled States in Coupled Superconducting Phase Qubits

We consider the possibility of generating macroscopic entangled states in capacitively coupled phase qubits. First we discuss the operation of phase qubits and the implementation of the basic gate ...

Generalized switchable coupling for superconducting qubits using double resonance

We propose a method for switchable coupling between superconducting qubits using double resonance. The interqubit coupling is achieved by applying near-resonant oscillating fields to the two qubits. The deviation from resonance relaxes the criterion of strong driving fields while still allowing for a fully entangling two-qubit gate. This method avoids some of the shortcomings of previous proposals for switchable coupling. We discuss the possible application of our proposal to a pair of inductively coupled flux qubits, and we consider the extension to phase qubits.

Squeezing of a quantum flux in a double rf-SQUID system

We investigate the nonstationary boundary effect for a quantum flux in a double rf-SQUID system. In a superconducting ring interrupted by a dc-SQUID (so-called double rf-SQUID), the Josephson potential can be controlled by the magnetic flux through the dc-SQUID ring. This system is equivalent to an anharmonic oscillator with a time-dependent frequency. A rapid change of the magnetic flux in the dc-SQUID leads to the nonadiabatic mixing of the quantum states for a quantum flux in a double rf-SQUID. Therefore, this becomes a circuit analogue of the dynamical Casimir effect in quantum field theory. We perform numerical calculations for the quantum state evolution of the quantum flux within a harmonic approximation, taking account of the nonadiabatic effect. We found that the resulting state distribution has a super-Poissonian character that reflects flux squeezing caused by the Bogoliubov transformation between eigenstates at different times.

Fluxon-based gate controls of capacitively coupled flux-based-phase qubits

The authors propose a scheme for controlling the gate operation for qubit-qubit interactions in superconducting flux-based phase qubits using a moving fluxon. The basic unit is composed of three capacitively coupled flux-based phase qubits. One of the qubits acts as a switch connecting the other two (two logical qubits) with an identical energy separation. The fluxon controls the energy separation of the switch qubit via its inductive coupling, leading to the resonance among qubits appropriately adjusting the fluxon velocity. As a result, the resonance is capable of performing a gate operation between two logical qubits.

Theory of Photocurrent in BCS Excitons

We derive a photocurrent formula for a hybrid semiconductor junction with an excitonic Bardeen‐Cooper‐Schrieffer (BCS) state. The formula provides a new approach to confirm the excitonic BCS state as well as its potential for applications like solar cells.

Crowd Behavior in Alternative@ - Conflicts in the Decision-making between an Individual and the Group

Crowd behavior depends on social interaction among group members. In particular, there has been considerable interest in the decision-making of such a group on their movement during travel. Here we discuss the decision-making processes in choice selection between two things, i. .e., alternative, by means of numerical simulations based on social force model developed by Helbing et al. This allows us to introduce an individual decision-making process into the decision-making of the whole group through psychological parameter, the so-called dependence p, equivalent to panic parameter in an emergency evacuation. We demonstrate the conflict that arises in the decision-making between an individual and the group in alternative. In addition, we reconfirmed a similar stochastic collective behavior in the decision-making processes observed by Couzin et al. in traveling animals at the large p regimes even if there are no leaders in the group. On the other hand, individualistic behavior is pronounced in smaller p regimes. This feature prevents the formation of group, leading to no collective decision-making anymore. Therefore, the parameter p is a key to consider in the decision-making of both the individual and the group.