Photonic quantum computer changes operations without changing hardware

(Photonics) Stanford University researchers have proposed a design for photonic quantum computer that uses readily available components and a laser to manipulate a single atom that can modify the state of the photons in the system via the phenomenon of quantum teleportation.
The researchers said their photonic design is simpler than today’s quantum computers that are difficult to scale up and that require temperatures colder than interstellar space to operate. Though scientists have previously created photonic quantum computers that operate at room temperature, which makes them a promising approach to quantum computing, it is challenging to construct large numbers of logic gates for photons that connect in a reliable fashion to enable complex calculations.
In the Stanford design, the atom can be reset and reused for many quantum gates. This eliminates the need to build multiple distinct physical gates, vastly reducing the complexity of building a quantum computer.
“Normally, if you wanted to build this type of quantum computer, you would have to take potentially thousands of quantum emitters, make them all perfectly indistinguishable, and then integrate them into a giant photonic circuit,” said Ben Bartlett, a Ph.D. candidate in applied physics and lead author of the paper. “Whereas with this design, we only need a handful of relatively simple components, and the size of the machine doesn’t increase with the size of the quantum program you want to run.”
The design requires only a fiber optic cable, a beamsplitter, a pair of optical switches, and an optical cavity. In addition to their commercial availability, the researchers said that each of these components are continually being refined since they are currently used in applications other than quantum computing. For example, telecommunications companies have been working to improve fiber optic cables and optical switches for years.
“What we are proposing here is building upon the effort and the investment that people have put in for improving these components,” said Shanhui Fan, the Joseph and Hon Mai Goodman Professor of the School of Engineering and senior author of the paper. “They are not new components specifically for quantum computation.
Control of the way the atom and photons interact means the same device can run many different quantum programs.
“For many photonic quantum computers, the gates are physical structures that photons pass through, so if you want to change the program that’s running, it often involves physically reconfiguring the hardware,” Bartlett said. “Whereas in this case, you don’t need to change the hardware — you just need to give the machine a different set of instructions.”