Dynamic Qubit Coupling

J. R. Johansson, Sahel Ashhab, Alexandre M. Zagoskin +1 more

We study the decoherence dynamics of a superconducting qubit coupled to a quantum two-level system (TLS) in addition to its weak coupling to a background environment [1]. We identify two weak-coupling regimes, which differ by the relation between qubit and TLS decoherence times, and a strong coupling regime. We find expressions for the qubit decoherence rates in the weak-coupling regimes. For a weakly coupled and strongly dissipative TLS we find that the qubit dynamics is markovian, whereas for a weakly dissipative TLS the qubit dynamics shows non-markovian behavior. In the strong-coupling regime we study the driven qubit dynamics and we analyze the differences from standard Rabi-oscillations due to the coupling to the quantum TLS [2]. In doing so we identify signatures in the qubit dynamics that can be used to characterize the TLS. We also investigate the possibility of using environmental TLSs with long coherence times for quantum information processing [3]. By using the Josephson junction as a bus and the TLSs in the environment as qubits, we demonstrate that initialization, a universal set of quantum gates, and read-out of the TLSs can be implemented, even though the TLSs themselves cannot be directly accessed.

Wei-Chen Chien, C. T. Lin, Tse-Yu Lai +3 more

The iSWAP operation between two qubits serves as a means to quantify the inter-qubit coupling strength. We examine the inter-qubit coupling strength when the qubit frequency is modulated at 80 MHz. The coupling strength between qubits, mediated by various sidebands generated from the frequency modulation, can be dynamically tuned, following the Bessel dependencies. This dynamically tunable coupling between qubits provides a straightforward approach to create a testing ground for versatile quantum models.

Michel Le Bellac

李磊, 邹健, 徐宝明 +1 more

We consider a composite system:an anisotropic two-qubit Heisenberg XY Z chain coupled independently to their own environments.We take one of the qubit as the subsystem and the other qubit as an auxiliary qubit,and then the subsystem we concern can be considered to be coupled to a structured bath(auxiliary qubit + environments).Based on this,we study the non-Markovianity of the subsystem dynamics and show how the subsystem dynamics can be changed by manipulating the intensity of the qubit-qubit couplings or the anisotropy parameter.Moreover,we show how entanglement between the subsystem and the structured bath can be affected by the properties of the structured bath and the magnetic field.