Controlling and swapping quantum information in a quantum coherent way between the microwave and optical regimes is essential for building long-range superconducting quantum networksbut extremely challenging. We propose a hybrid quantum interface between the microwave and optical domains where the propagation of a single-photon pulse along a nanowaveguide is controlled in a coherent way by tuning electromagnetically induced transparency window with the quantum state of a flux qubit. The qubit can route a single-photon pulse with a single spin in nanodiamond into a quantum superposition of paths without the aid of an optical cavity – simplifying the setup. By preparing the flux qubit in a superposition state our cavity-less scheme creates a hybrid state-path entanglement between a flying single optical photon and a static superconducting qubit, and can conduct heralded quantum state transfer via measurement.
We propose a design for a quantum interface exploiting the electron spins in crystals to swap the quantum states between the optical and microwave. Using sideband driving of a superconductingflux qubit and a combined cavity/solid-state spin ensemble Raman transition, we demonstrate how a stimulated Raman adiabatic passage (STIRAP)-type operation can swap the quantum state between a superconducting flux qubit and an optical cavity mode with a fidelity higher than 90%. We further consider two distant superconducting qubits with their respective interfaces joined by an optical fiber and show a quantum transfer fidelity exceeding 90% between the two distant qubits.
A quantum internet, where widely separated quantum devices are coherently connected, is a fundamental vision for local and global quantum information networks and processing. Superconductingquantum devices can now perform sophisticated quantum engineering locally on chip and a detailed method to achieve coherent optical quantum interconnection between distant superconducting devices is a vital, but highly challenging, goal. We describe a concrete opto-magneto-mechanical system that can interconvert microwave-to-optical quantum information with high fidelity. In one such node we utilise the magnetic fields generated by the supercurrent of a flux qubit to coherently modulate a mechanical oscillator that is part of a high-Q optical cavity to achieve high fidelity microwave-to-optical quantum information exchange. We analyze the transfer between two spatially distant nodes connected by an optical fibre and using currently accessible parameters we predict that the fidelity of transfer could be as high as ∼80%, even with significant loss.
We study the slowing, storing and releasing of microwave pulses in a superconducting circuits composed of two coplanar waveguide resonators and a superconducting transmon-type qubit.The quantum interference analogy to electromagnetically induced transparency is created in two coupled resonators. By tuning the resonance frequency of the transmon, we dynamically tune the effective coupling between the resonators. Via the modulation of the coupling, we show the tunable true time delay of microwave pulses at the single-photon level. We also store the microwave field in a high-Q resonator and release the signal from it to the output port. Our scheme promises applications in both quantum information processing and classical wireless communications.