A versatile optical chip that produces, measures and controls two important quantum phenomena — mixture and entanglement — has been developed, representing an important step toward developing quantum computers. Artist's impression of the quantum photonic chip, showing the waveguide circuit (in white) and the voltage-controlled phase shifters (metal contacts on the surface). Photon pairs become entangled as they pass through the circuit. (Images: University of Bristol's Centre for Quantum Photonics) Mixture is an undesirable effect caused by interaction with the surroundings, but mixture has now become useful in characterizing quantum circuits, when it is efficiently controlled. Entanglement is the link between two remote particles. Jeremy O’Brien, a professor and the director of the Center for Quantum Photonics at the University of Bristol, stated that the device’s ability to manipulate and measure quantum phenomena is a major step toward the realization of optical quantum computing. Each blue sphere shows a particular quantum state, created and measured using the photonic chip. This visualization illustrates the precision with which arbitrary mixed states can be prepared: 63 states have been used to draw the Greek letter "psi" (symbol looks LIKE A PITCHFORK-MR). The chip, which performs several experiments that ordinarily would each be carried out on an optical bench the size of a large dining table, measures 70 by 3 mm. It consists of a network of tiny channels that guide, manipulate and interact with single photons. By using eight reconfigurable electrodes embedded in the circuit, photon pairs can be manipulated and entangled, producing any possible entangled state of two photons or any mixed state of one photon. Peter Shadbolt, a researcher, said that the team demonstrated a reconfigurable device that is capable of performing several tasks. The device is roughly 10 times more intricate compared to earlier experiments conducted utilizing the technology, he said. The fact that this single reconfigurable chip is capable of performing various experiments directly is exciting, Shadbolt added. The team is now working on expanding the device’s complexity, studying the possibility of using the technology as the basic component for the development of quantum computers. The work is published in Nature Photonics. For more information, visit: www.bristol.ac.uk