A single photon at the end of the tunnel
The 'Experimental generation of distant quantum dot spin entanglement' (QUANTUMDOTS) project used quantum dots to represent stationary particles as well as photons, particles that fly. A propagating photon can be used for the transmission of quantum information and a stationary qubit for storage and manipulation. To connect them, the researchers relied on entanglement between a pair of particles and the properties they share. Broadly speaking, as a pair of particles shares characteristics, altering one changes the other. The QUANTUMDOTS researchers used a very small region of a semiconductor to trap a single electron and create a so-called quantum dot. Considered to be an artificial atom, the dot trapped electrons and possessed a spectrum of discrete energies. Specifically, laser light of wavelengths stimulated the quantum dot to spontaneously emit a photon and return to its lower state. The photon was released as either horizontally or vertically polarised with a wavelength that was demonstrated to be of either a red or blue colour. However, to use the information from a spin qubit, only one of the two properties can exist; the other must be removed. The QUANTUMDOTS researchers' removed the colour by runningthe photon through a crystal that was also shot with a laser beam. The colour smeared enough to consider this property removed from the entangled particles, opening the way for coupling distant qubits. The QUANTUMDOTS researchers described the process and results in papers they have published in the Nature and Nature Communications magazine. It is hoped that the spin-photon entanglement will be key enabling technology for a distributed approach to quantum information processing and new computing devices.
Keywords
Photon, quantum computer, qubits, quantum dot, photons, entanglement, semiconductor, electron, atom, laser, spin, quantum processor
