Some nonlinear radiations such as superfluorescence can be understood as cooperative effects between atoms. We regard the cooperative radiation as a manifested effect secondary to the intrinsic cooperativity among the atoms and propose a time-resolved measure of cooperativity on a cavity-coupled dual-qubit system using multi-partite concurrence measures. We find that the cooperativity features a time delay characterisitic to superfluorescent pulses in its evolution, which coincides with the duration for the qubits to synchronize with each other. Thereafter, the cooperativity monotonically increases to a stationary value while the measure of asynchronicity dives to a steady minimum. Furthermore, the asynchronicity experiences a continuous transition to nonzero values when the coupling strength crosses from the weak to the strong coupling regime.Some nonlinear radiations such as superfluorescence can be understood as cooperative effects between atoms. We regard the cooperative radiation as a manifested effect secondary to the intrinsic cooperativity among the atoms and propose a time-resolved measure of cooperativity on a cavity-coupled dual-qubit system using multi-partite concurrence measures. We find that the cooperativity features a time delay characterisitic to superfluorescent pulses in its evolution, which coincides with the duration for the qubits to synchronize with each other. Thereafter, the cooperativity monotonically increases to a stationary value while the measure of asynchronicity dives to a steady minimum. Furthermore, the asynchronicity experiences a continuous transition to nonzero values when the coupling strength crosses from the weak to the strong coupling regime.

Jun 23, 20160 citations

The pair-coupling model

Huiyao Chen, T. Song, DAVID J. ROWE

Nuclear Physics AJan 1, 199525 citations

Numerical study of energy loss by a nanomechanical oscillator coupled to a Cooper-pair box

Rakesh P. Tiwari, D. Stroud

We calculate the dynamics of a nanomechanical oscillator (NMO) coupled capacitively to a Cooper-pair box (CPB) by solving a stochastic Schr\"odinger equation with two Lindblad operators [Commun. Math. Phys. 48, 119 (1976).]. Both the NMO and the CPB are assumed dissipative, and the coupling is treated within the rotating wave approximation. We show numerically that, if the CPB decay time is smaller than the NMO decay time, the coupled NMO will lose energy faster and the coupled CPB more slowly than the uncoupled NMO and CPB do. The results show that the efficiency of energy loss by an NMO can be substantially increased if the NMO is coupled to a CPB.We calculate the dynamics of a nanomechanical oscillator (NMO) coupled capacitively to a Cooper-pair box (CPB) by solving a stochastic Schr\"odinger equation with two Lindblad operators [Commun. Math. Phys. 48, 119 (1976).]. Both the NMO and the CPB are assumed dissipative, and the coupling is treated within the rotating wave approximation. We show numerically that, if the CPB decay time is smaller than the NMO decay time, the coupled NMO will lose energy faster and the coupled CPB more slowly than the uncoupled NMO and CPB do. The results show that the efficiency of energy loss by an NMO can be substantially increased if the NMO is coupled to a CPB.

arXiv:0805.4401Physical Review BJun 20, 20087 citations

Mutual interaction

Noriaki Horiuchi

Nature PhotonicsNov 28, 20130 citations

Two-Level Couplings

Essential textbooks in physicsJun 16, 20200 citations

Tunneling of Cooper pairs across voltage-biased asymmetric single-Cooper-pair transistors

Juha Leppäkangas, E. V. Thuneberg, Rene K. Lindell +1 more

We analyze tunneling of Cooper pairs across voltage biased asymmetric single-Cooper-pair transistors. Also tunneling of Cooper pairs across two capacitively coupled Cooper-pair boxes is considered, when the capacitive coupling and Cooper pair tunneling are provided by a small Josephson junction between the islands. The theoretical analysis is done at subgap voltages, where the current-voltage characteristics depend strongly on the macroscopic eigenstates of the island(s) and their coupling to the dissipative environment. As the environment we use an impedance which satisfies $\mathrm{Re}[Z(\ensuremath{\omega})]⪡{R}_{Q}$ and a few $LC$ oscillators in series with $Z(\ensuremath{\omega})$. The numerically calculated $I\text{\ensuremath{-}}V$ curves are compared with experiments where the quantum states of mesoscopic SQUIDs are probed with inelastic Cooper pair tunneling. The main features of the observed $I\text{\ensuremath{-}}V$ data are reproduced. Especially, we find traces of band structure in the higher excited states of the Cooper-pair boxes as well as traces of multiphoton processes between two Cooper-pair boxes in the regime of large Josephson coupling ${E}_{J}⪢{E}_{C}$ .We analyze tunneling of Cooper pairs across voltage biased asymmetric single-Cooper-pair transistors. Also tunneling of Cooper pairs across two capacitively coupled Cooper-pair boxes is considered, when the capacitive coupling and Cooper pair tunneling are provided by a small Josephson junction between the islands. The theoretical analysis is done at subgap voltages, where the current-voltage characteristics depend strongly on the macroscopic eigenstates of the island(s) and their coupling to the dissipative environment. As the environment we use an impedance which satisfies $\mathrm{Re}[Z(\ensuremath{\omega})]⪡{R}_{Q}$ and a few $LC$ oscillators in series with $Z(\ensuremath{\omega})$. The numerically calculated $I\text{\ensuremath{-}}V$ curves are compared with experiments where the quantum states of mesoscopic SQUIDs are probed with inelastic Cooper pair tunneling. The main features of the observed $I\text{\ensuremath{-}}V$ data are reproduced. Especially, we find traces of band structure in the higher excited states of the Cooper-pair boxes as well as traces of multiphoton processes between two Cooper-pair boxes in the regime of large Josephson coupling ${E}_{J}⪢{E}_{C}$.

arXiv:cond-mat/0604092Physical Review BAug 7, 200613 citations

LC

oscillators in series with $Z(\ensuremath{\omega})$. The numerically calculated $I\text{\ensuremath{-}}V$ curves are compared with experiments where the quantum states of mesoscopic SQUIDs are probed with inelastic Cooper pair tunneling. The main features of the observed $I\text{\ensuremath{-}}V$ data are reproduced. Especially, we find traces of band structure in the higher excited states of the Cooper-pair boxes as well as traces of multiphoton processes between two Cooper-pair boxes in the regime of large Josephson coupling

{E}_{J}⪢{E}_{C}