In quantum physics, entangled photons are the cornerstone of much cutting-edge technology research, including quantum communications, computing, and encryption. Now an international team of researchers claims to have incorporated a range of quantum technologies on a single integrated chip that is compatible with existing fiber and semiconductor applications, and may soon provide the means to build quantum circuits directly into laptops and cell phones.

In quantum physics, entangled photons are the cornerstone of much cutting-edge technology research, including quantum communications, computing, and encryption. Now an international team of researchers claims to have incorporated a range of quantum technologies on a single integrated chip that is compatible with existing fiber and semiconductor applications, and may soon provide the means to build quantum circuits directly into laptops and cell phones.

Using a bevy of quantum electronic components tested and proven in recent research (including a type of micro-ring resonator and a version of a quantum frequency comb necessary for hyperentanglement and the generation of multiphoton entangled quantum bit, or qubit, states), the team of researchers has achieved a new record in the complexity and amount of entangled photons generated on a single chip.

"This represents an unprecedented level of sophistication in generating entangled photons on a chip," said Professor David Moss, Director of the Centre for Micro-Photonics at Swinburne University of Technology. "Not only can we generate entangled photon pairs over hundreds of channels simultaneously, but for the first time we've succeeded in generating four-photon entangled states on a chip."

The generation of qubits (the quantum equivalent of classical computing's data bit) can rely on several different approaches, including electron spins, atomic energy levels, and photon quantum states. And, unlike conventional computers, quantum computers do not use binary data storage (ones and zeroes), where a bit can be one of two states. Instead, quantum computers use what is known as "superpositioning," where the data contained in a qubit can also be simultaneously both one or zero, and may exist at any and all possible positions simultaneously, and in various dimensions.

To achieve this state of superpositioned, entangled qubits, the new integrated chip firstly uses a laser-pumped, micro-ring resonator to generate a large number of entangled photons, which are then fed via a spectrum filter into an optical integrated Kerr frequency comb (that is, a system where a single frequency of light is made to generate a pair of other evenly-spaced frequencies as a result of the refractive index, the Kerr effect, of the resonator material). This frequency comb then generates entangled multi-photon qubit states over several hundred frequencies which are then capable of being transmitted by optical fiber.

According to the researchers, the chip meets numerous criteria for its ready incorporation into existing technologies such as quantum information processing, imaging, and microscopy. This, they say, is because it is compact, cheap to make, scalable, compatible with ordinary electronic components, and it uses standard telecommunication frequencies.

"By achieving this on a chip that was fabricated with processes compatible with the computer chip industry we have opened the door to the possibility of bringing powerful optical quantum computers for everyday use closer than ever before," said Professor Morandotti of the Institut National de la Recherche Scientifique (INRS).

The combined effort of the City University of Hong Kong, the University of Sussex and Herriot Wat University in the UK, Yale University, the Xi'an Institute in China, and the INRS in Montreal, Canada, this ground-breaking research is the result of a decade of collaborative research on complementary metal–oxide–semiconductor (CMOS) compatible chips for nonlinear optics in classical and quantum physics.