Whispering galleries and the control of artificial atoms.

Derek Michael Forrester,Feodor V Kusmartsev

doi:10.1038/srep25084

Abstract

Quantum computation using artificial-atoms, such as novel superconducting circuits, can be sensitively controlled by external electromagnetic fields. These fields and the self-fields attributable to the coupled artificial-atoms influence the amount of quantum correlation in the system. However, control elements that can operate without complete destruction of the entanglement of the quantum-bits are difficult to engineer. Here we investigate the possibility of using closely-spaced-linear arrays of metallic-elliptical discs as whispering gallery waveguides to control artificial-atoms. The discs confine and guide radiation through the array with small notches etched into their sides that act as scatterers. We focus on π-ring artificial-atoms, which can generate their own spontaneous fluxes. We find that the micro-discs of the waveguides can be excited by terahertz frequency fields to exhibit whispering-modes and that a quantum-phase-gate composed of π-rings can be operated under their influence. Furthermore, we gauge the level of entanglement through the concurrence measure and show that under certain magnetic conditions a series of entanglement sudden-deaths and revivals occur between the two qubits. This is important for understanding the stability and life-time of qubit operations using, for example, a phase gate in a hybrid of quantum technologies composed of control elements and artificial-atoms.

Highlights

Quantum computation using artificial-atoms, such as novel superconducting circuits, can be sensitively controlled by external electromagnetic fields
Using the principles behind concurrence Yu and Eberly[12] discovered that entanglement may be born out of a bipartite system only to endure a series of deaths interspersed by revivals. This phenomenon was named entanglement sudden death (ESD)[13]. We find that this occurs for certain parameters in a system of two coupled flux qubits that are controlled by a plasmonic waveguide
The two superconducting π-rings can be thought of as two artificial atoms, interacting with mutual inductance if close enough to one another and manipulated by the magnetic field generated from the plasmonic array

Summary

OPEN Whispering galleries and the control of artificial atoms

We gauge the level of entanglement through the concurrence measure and show that under certain magnetic conditions a series of entanglement sudden-deaths and revivals occur between the two qubits This is important for understanding the stability and life-time of qubit operations using, for example, a phase gate in a hybrid of quantum technologies composed of control elements and artificialatoms. The control is performed through the plasmonic waveguide that is composed of two lines of elliptical disks as shown schematically in Fig. 1 (other architectures are shown schematically in the supporting information) Artificial atoms, such as superconducting qubits are solid-state analogues of optical beam splitters and interferometers and have been discussed in the context of tight–binding networks too[16]. The two inductively coupled flux qubits, with two-state pseudo-spins that are related to the phase differences over the Josephson junctions, are highly sensitive detectors of magnetic field changes

Results

Discussion and Conclusions

Additional Information