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Today's quantum computers are difficult to build and scale up, and need cold temperatures to operate. Researchers are looking into the possibility of building quantum computers that use light. This approach is promising because phons can easily carry information from one place to another and quantum computers can operate at room temperature. It's difficult to build large numbers of gates and connect them in a reliable fashion to perform complex calculations because people have successfully created individual quantum gates.
A paper published in November in Optica states that researchers from the University of California, Berkeley, have proposed a simpler design for quantum computers. Their proposed design uses a laser to manipulate a single atom that in turn can modify the state of the photon. The atom can be used for many quantum gates, eliminating the need to build multiple separate physical gates for a quantum computer.
If you wanted to build a quantum computer, you'd have to take thousands of quantum emitters, make them all indistinguishable, and then integrate them into a giant photonic circuit. 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 only requires a few pieces of equipment, including a fiber cable, a beam splitter, and a pair of optical switches.
These components are commercially available. Since they're currently used in applications other than quantum computing, they're continually being refined. For years, telecommunications companies have been working to improve their products.
The senior author on the paper said that the paper was about building upon the effort and investment that people have put in for improving these components. They are not new components for quantum computation.
A novel design.
The storage ring and scattering unit are the main parts of the scientists' design. The storage ring is similar to a regular computer's memory and is a loop of fibers. Each photon represents a quantum bit, which is similar to bits in a classical computer. The value of the qubit is determined by the direction of travel of the photon around the storage ring. A photon can flow in both directions at the same time if it exists in two states at the same time.
The researchers can manipulate a photon by directing it from the storage ring to the scattering unit. The photon interacts with the atom, causing them to becomeentangled, a quantum phenomenon that can affect one another even across great distances. The photon comes back to the storage ring and the laser changes the state of the atom. The state of the photon is influenced by the atom and the atom being entangled.
By measuring the state of the atom, you can make use of the photon. We can use the atomic qubit as a proxy to manipulate all of the other qubits, because we only need the one controllable atomic qubit.
You can run any quantum program of any size using only one controllable atomic qubit, because any quantum logic gate can be compiled into a sequence of operations performed on the atom. To run a program, the code is translated into a sequence of operations that direct the photons into the scattering unit and manipulate the atomic qubit. The same device can run many different quantum programs because you can control how the atom and photons interact.
"For many quantum computers, the gates are physical structures that the photons pass through, so if you want to change the program that's running, it often involves physically reconfiguring the hardware." You don't need to change the hardware, you just need to give the machine a different set of instructions.
More information is available from Ben Bartlett et al. There is a DOI: 10.368/OPTICA.
The journal has information about Optica.
The researchers propose a simpler design for quantum computers.
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