A laser on a lithium niobate crystal comes to life with a current of 40 milliamps. Its light splits into two streams, each passing through a six-millimeter waveguide, where twin photon pairs are born. One stream rotates the polarization of its twins, after which both flows merge into a common channel. At the output is a quantum factory in the palm of your hand: 45 billion entangled pairs per second at a power of just 18.8 microwatts.

Entangled photons are the workhorses of quantum technologies: they are needed for computation, secure communication, and ultra-sensitive measurements. Most current sources require a bulky external laser for optical pumping, which hinders scaling. Here, the laser and the nonlinear material live on the same crystal, and the polarization rotator-combiner is fabricated with the same process as the waveguides. Before this work, electrically pumped on-chip sources were either dim, narrowband, or did not produce polarization entanglement.

Now entanglement can be obtained without external optics: just apply a current. This is a step toward fully autonomous quantum systems on a chip. The next frontier is full monolithic integration: transferring the laser onto the same chip via wafer bonding or micro-transfer to eliminate the coupling and improve light injection efficiency. Further, modulators, filters, and detectors can be integrated on the same lithium niobate platform, creating an all-in-one quantum chip. Wavelength multiplexing will open the path to multi-channel sources for quantum networks.

A quantum factory in the palm of your hand can already produce entangled pairs for wavelength-multiplexed quantum key distribution and satellite-based quantum communication. The remaining challenge is to package detectors and control electronics onto the same crystal, and then quantum communications will become truly portable.