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Stanford's Simple New Quantum Computer Design: Photonic Computation in a Synthetic Time Dimension - SciTechDaily
Nov 30, 2021 2 mins, 21 secs

A relatively simple quantum computer design that uses a single atom to manipulate photons could be constructed with currently available components.

Now, Stanford University researchers have proposed a simpler design for photonic quantum computers using readily available components, according to a paper published on November 29, 2021, in Optica.

Their proposed design uses a laser to manipulate a single atom that, in turn, can modify the state of the photons via a phenomenon called “quantum teleportation.” The atom can be reset and reused for many quantum gates, eliminating 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’d 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 PhD candidate in applied physics and lead author of the paper.

An animation of the photonic quantum computer proposed by the researchers.

The spheres at the top, called “Bloch spheres,” depict the mathematical state of the atom and one of the photons.

Because the atom and the photon are entangled, manipulating the atom also affects the state of the photon.

The scientists’ design consists of two main sections: a storage ring and a scattering unit.

The storage ring, which functions similarly to memory in a regular computer, is a fiber optic loop holding multiple photons that travel around the ring.

Analogous to bits that store information in a classical computer, in this system, each photon represents a quantum bit, or “qubit.” The photon’s direction of travel around the storage ring determines the value of the qubit, which like a bit, can be 0 or 1.

Stanford graduate student Ben Bartlett and Shanhui Fan, professor of electrical engineering, have proposed a simpler design for photonic quantum computers using readily available components.

The researchers can manipulate a photon by directing it from the storage ring into the scattering unit, where it travels to a cavity containing a single atom.

The photon then interacts with the atom, causing the two to become “entangled,” a quantum phenomenon whereby two particles can influence one another even across great distances.

Then, the photon returns to the storage ring, and a laser alters the state of the atom.

Because the atom and the photon are entangled, manipulating the atom also influences the state of its paired photon.

Because you can control the way the atom and photons interact, 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.

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