Quantum-nanomechanical switch for quantum communication facilitated by the charge qubit

Journal article, 2025

We suggest a nanoelectromechanical setup for designing a quantum-nanomechanical motion of a charge qubit in two-dimensional space. The quantum character of such motion comes through the fact that states of the qubit are entangled with nanomechanical cat states. The setup is based on mesoscopic terminal utilizing the ac Josephson effect between voltage-biased superconducting electrodes and mesoscopic superconducting grain — the charge qubit, vibrating in plane fixed on a nanomechanical cantilever. Required functionality is achieved by operating two external parameters: bias voltage between superconducting electrodes and controlling voltage applied over the gate electrodes. While the resonant tunneling of Cooper pairs between the superconductors and charge qubit builds nanomechanical coherent states comprising the cat state, gate voltage has a specific role of tuning their two-dimensional character in the form of the in-plane linear motion under the voltage-controlled direction. Controlling the spatial motion of a charge qubit opens a possibility of quantum communication between different terminals located in space. Directional control of nanomechanical motion entangled with charge qubit states we call the “quantum switch”.