Manipulating photons for microseconds tops 9,000 years on a supercomputer

Chris Lee is a big fan of photon-based quantum computing because he has been playing with lasers for a long time. He gushed about an optical quantum computer put together by a Canadian startup called Xanadu even as various forms of physical hardware made progress. In the year since Xanadu described its hardware, companies using that other technology continued to make progress by cutting down error rates, exploring new technologies, and increasing the qubit count.

Xanadu is back with a reminder that the advantage of optical quantum computing is still there. Xanadu is now able to perform operations with more than 200 qubits thanks to some changes it made a year ago. It was shown that it would take 9000 years for the behavior of just one of those operations to be mimicked, while the optical quantum computer could do them in a few dozen milliseconds.

The quantum computer is just being itself while the supercomputer is trying to mimic it. The potential of Xanadu's hardware to scale is the news here.

Remain in light

There are many advantages to optical-based quantum computing. Improvements in optical hardware have the chance to be applied to quantum computing hardware. Hardware that is small enough to fit on a chip can be etch onto it. The hardware can be kept at room temperature, avoiding some of the challenges of getting signals into or out of equipment that sits near absolute zero.

Xanadu thinks that building a company around these advantages makes sense. The hardware described by Lee last year relies on a single chip to put photon in a specific quantum state and force photon pairs to interact in ways that entangle them. The basis of qubit manipulation can be found in these interactions. The answer to the calculation is provided by the number of photons in each state.

There are challenges in scaling this technology. Adding another photon means you have to include hardware features for the necessary interactions. scaling all of the hardware on the chip is required to get the processor to a higher qubit count. It is not a problem now, but it could easily be one as things scale through the hundreds to the thousands.

Choose your own adventure

Xanadu's new system, called Borealis, involves a significant revision to the architecture. The earlier machine used a bunch of identical photons that all entered the chip in parallel and traveled through it simultaneously. In Borealis, the photons enter the system and follow a path that is similar to a game.

A beam splitter is the first piece of hardware hit by the photons. Two photons can become entangled if they arrive at it at the same time. Depending on the state of the beam splitter, it can take the photon out of the main path and into a loop of optical fiber. Traveling around that loop adds a delay to the photon's travel, allowing it to exit the fiber at the same time as a new photon is arriving at the beam splitter, allowing it to become entangled with a later photon.

The longer loop of optical fiber introduces a longer delay to any photons sent down it. Then on to a third with a longer loop. The optional delays allow forentanglement with other photons that arrived at the hardware after they did. As Xanadu shows it, each of the three beam splitters in Borealis adds an additionaldimension to the entanglement matrix, taking it up from no entanglement to three dimensions of potential entanglement.

The photons are sorted by their properties and sent to a series of detectors. The detectors keep track of how many photons arrive and when, which will give an answer to any calculations it is performing. As configured, it could handle more than 200 individual photons.