quantum computing using light.
Photonics system is a promising platform for implementing universal quantum information processing. The primary challenge is precise control of massive circuits of linear optical components along with sustained connection entangling operations on photons. It means, it is hard to do gates on them. Researchers, using large-scale silicon photonic circuits implemented an extension of the linear combination of quantum operators scheme, demonstrating, although only 2 qubits, a fully programmable two-qubit quantum processor, enabling universal two-qubit quantum information processing in optics. They have proved the concept.
The quantum processor equipped with Photonic circuits fabricated with mature CMOS-compatible processing comprises more than 200 photonic components. 98 different two-qubit unitary operations* (with an average quantum process fidelity of 93.2 ± 4.5%) demonstrated using a two-qubit quantum approximate optimization algorithm, and efficient simulation of Szegedy directed quantum walks.
A major advantage in using Szegedy's formalism over discrete-time and continuous-time quantum walks based on its ability to define a unitary quantum walk on directed and weighted graphs. Therefore, future photonic quantum processors are realizable. There is a path to scale it up.
That research paper published a couple of years ago. Since then, there are many groups trying to scale up and develop a NISQ device with road to scale. Below, see a few remarks from Chris Lee, a writer and also a physicist talking about Photonics.
"Photons, as far as I’m concerned, still make the best quantum bits (qubits). This is because photons mostly pass through the world unhindered. A photon, in a super-special quantum state, can go from air to an optical fiber to air, through a silicon chip, back into air, and into a fiber again, all without destroying its quantum state. About all you need to ensure is that your photon detector is in the dark so that only the qubit photons hit it.
Superconducting qubits are made up of electrons, which are sensitive to everything. It takes real experimental skill and good engineering to ensure that superconducting qubits maintain their quantum state.
You should be wondering why, if light is so good, light-based quantum computers lag so far behind. It is for exactly the same reason: photons don’t notice each other, but electrons do. Imagine you want to switch the state of one qubit based on the state of another qubit. For electrons, that’s simple because they have an electric and magnetic field through which they can manipulate each other. Photons, however, just pass right through each other without noticing. The simple way to implement quantum operations is actually very, very hard using photons."
Below see a short list of Photonic Quantum Computing companies. I will update this list as I keep my ears to the ground, watch out for new information or trends.
"ILLUMINATING THE QUANTUM REVOLUTION
Ground-breaking single-photon components to enable the next generation of commercially- viable photonic quantum technologies."
Parityqc, a software, algorithm, and hardware company working with photonics.
Extra long-distance quantum secure QKD telecommunications with minimal operational and infrastructure costs
* Free to download: Entangling power of two-qubit unitary operations.
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