Towards distributing qubit entanglement in open waveguides using entangled microwave radiation

Distributing quantum entanglement over long distances is essential for creating quantum networks. Deterministic entanglement generation is possible via direct exchange of photons that propagate through an open, low loss channel. Yet, these protocols rely on shaped pulses and high temporal control, and require low photon loss in the propagation channel. It has been proposed [1] that using a two – mode squeezed vacuum (TMSV) state to drive two qubits one can stabilize discrete variable entanglement in a way which is more resilient to photon loss, at the expense of more moderate fidelities that could in principle be purified. We present our experimental progress towards realizing this protocol using a Josephson Parametric Converter (JPC) to generate a spatially separated TMSV state that drives two superconducting transmon qubits through two open waveguides. Understanding this entangling mechanism may be relevant for future quantum interconnects, such as links using microwave – optics transduction with limited conversion efficiency. It also provides a means for directly sensing and quantifying a microwave TMSV without the typically required noise subtraction techniques.

[1] Agustí, J. et al. Phys. Rev. A 105, 062454 (2022).