Speaker: Dr. Zeng-Zhao Li, Beijing Computational Science Research Center    

Abstract: The very recent observation of the coherent quantum phase slips based on highly disordered $\ce{InO_{x}}$ [O. V. Astafiev et al, Nature 484, 355 (2012)] may prompt the Mooij-Harmans qubit (also known as phase-slip flux qubit) to be a more promising candidate for realizing novel applications such as scalable quantum computation and quantum metrology. However, theory for such highly disordered materials goes beyond the standard BCS framework. Thus, questions how to realize coherent quantum phase slips within the BCS theory and to what extent the disorder could be for observing the phenomena arise. In this work, we attempt to answer these questions via a proposed super phase-slip flux qubit involving $m$ phase-slip junctions connected by $m − 1$ superconducting islands with a capacitively coupled gate in between in the superconducting loop. We theoretically show that an effective phase-slip flux tunneling rate resulting from collective behaviors of all paseslip junctions and obtained as a periodic function of the product of the gate voltages and the number of the junctions, can be more pronounced to fight against flux noise. Besides more tunability provided by gate voltages, this super phase-slip flux qubit could be used for demonstrating the possibly experimental observation of the coherent quantum phase slips even with less disordered materials for which the BCS theory applies. To implement two-qubit operations, we further construct an Hamiltonian of two coupled such qubits through a directive mutual inductive interaction and show that this mutual inductance could not only give rise to the interaction Hamiltonian but also shift and enhance the kinetic energies of the qubits.

Date&Time: July 12, 2013 (Friday), 14:30 – 15:30
Location: 606 Conference Room