Generating and verifying entangled itinerant microwave fields with efficient and independent measurements

Understand

By combining a squeezed propagating microwave field and an unsqueezed vacuum field on a hybrid (microwave beam-splitter), we generate entanglement between the two output modes.

• We verify that we have generated entangled states by making independent and efficient single-quadrature measurements of the two output modes.
• We observe the entanglement witness $E_\mathrm{W}=-0.263^{+0.001}_{-0.036}$ and the negativity $N=0.0824^{+0.01}_{-0.0004}$ with measurement efficiencies at least $26\pm{0.1}\%$ and $41\pm{0.2}\%$ for channel~1 and 2 respectively.
• These measurements show that the output two-mode state violates the separability criterion and therefore demonstrate entanglement.