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Communications in Theoretical Physics

Statistical Properties of a System Consisting of a Superconducting Qubit Coupled to an Optical Field Inside a Transmission Line

Clodoaldo Valverde, Gabriela Rodrigues Vaz, Vitor Teles de Oliveira, B. Baseia

Published Jun 1, 2018• 0 citations
Publisher

Abstract

Abstract The present work investigates the entropy and the excitation inversion of a coupled system that consists of a qubit represented by a Cooper pair box (CPB) interacting with a transmission line working as a circuit quantum electrodynamics (CQED). The proposed scheme uses the Buck-Sukumar model with a time dependent frequency in the presence of losses to study the evolution of the entropy and the excitation inversion of the system. We have shown that the CQED is much more sensitive to the presence of losses than the CPB. The results also show that it is possible to monitor properties of the subsystems through appropriate choices of the time-dependent parameters.

DOI
10.1088/0253-6102/69/6/727

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Abstract The present work investigates the entropy and the excitation inversion of a coupled system that consists of a qubit represented by a Cooper pair box (CPB) interacting with a transmission line working as a circuit quantum electrodynamics (CQED). The proposed scheme uses the Buck-Sukumar model with a time dependent frequency in the presence of losses to study the evolution of the entropy and the excitation inversion of the system. We have shown that the CQED is much more sensitive to the presence of losses than the CPB. The results also show that it is possible to monitor properties of the subsystems through appropriate choices of the time-dependent parameters.
We propose an experimental procedure to directly measure the state of an electromagnetic field inside a resonator, corresponding to a superconducting transmission line, coupled to a Cooper-pair box (CPB). The measurement protocol is based on the use of a dispersive interaction between the field and the CPB, and the coupling to an external classical field that is tuned to resonance with either the field or the CPB. We present a numerical simulation that demonstrates the feasibility of this protocol, which is within reach of present technology.
We show a scheme to generate entangled coherent states in a circuit quantum electrodynamics system, which consists of a nanomechanical resonator, a superconducting Cooper-pair box (CPB), and a superconducting transmission line resonator. In the system, the CPB plays the role of a nonlinear medium and can be conveniently controlled by a gate voltage including direct-current and alternating-current components. The scheme provides a powerful tool for preparing the multipartite mesoscopic entangled coherent states.
We propose a scheme to implement quantum information transfer between Cooper-pair boxes (CPBs) in a circuit quantum electrodynamic (QED) system with Landau—Zener tunneling. The system consists of two CPB qubits and a one-dimensional transmission line resonator (TLR). By analytically solving the eigenequation and numerically calculating the transition probability, the results show the quantum state transfer from one qubit to another via a fast adiabatic passage. The coupling mechanism is robust against decoherence effects.
Sideband transitions are spectroscopically probed in a system consisting of a Cooper pair box strongly but nonresonantly coupled to a superconducting transmission line resonator. When the Cooper pair box is operated at the optimal charge bias point, the symmetry of the Hamiltonian requires a two-photon process to access sidebands. The observed large dispersive ac-Stark shifts in the sideband transitions induced by the strong nonresonant drives agree well with our theoretical predictions. Sideband transitions are important in realizing qubit-photon and qubit-qubit entanglement in the circuit quantum electrodynamics architecture for quantum information processing.
A Hamiltonian which represents the interaction between a single Cooper-pair box and two quantized electromagnetic fields is considered in order to find new ways for quantum information. The wave function in Schrdinger picture is obtained. The evolution of the entropy of the box as a function of the scaled time is ploted to measure the entanglement between the box and the fields. It is found that the entanglement is sensitive to the detuning between the Josephson energy and the fields frequency, increasing the detuning can decrease the entanglement.