For the first time, a quantum computer made from photons—particles of light—has outperformed even the fastest classical supercomputers.The article uses "primacy" instead of "supremacy", because of George Floyd. Or maybe Donald Trump or George Washington, I am not sure.
Physicists led by Chao-Yang Lu and Jian-Wei Pan of the University of Science and Technology of China (USTC) in Shanghai performed a technique called Gaussian boson sampling with their quantum computer, named Jiŭzhāng. The result, reported in the journal Science, was 76 detected photons—far above and beyond the previous record of five detected photons and the capabilities of classical supercomputers. ...
This is only the second demonstration of quantum primacy [supremacy], which is a term that describes the point at which a quantum computer exponentially outspeeds any classical one, effectively doing what would otherwise essentially be computationally impossible.
Scott Aaronson brags about it, as they needed to get his approval to call it quantum supremacy. He didn't invent the term, but he owns it now.
Okay, I am going to have to study this. What was really computed?
The setup for boson sampling is analogous to the toy called a bean machine, which is just a peg-studded board covered with a sheet of clear glass. Balls are dropped into the rows of pegs from the top. On their way down, they bounce off of the pegs and each other until they land in slots at the bottom. Simulating the distribution of balls in slots is relatively easy on a classical computer.It appears to me that they didn't compute anything. They just concocted a complicated setup that would be hard to simulate. It is hard for me to see how anything like this could be applied to a useful computation.
Instead of balls, boson sampling uses photons, and it replaces pegs with mirrors and prisms. Photons from the lasers bounce off of mirrors and through prisms until they land in a “slot” to be detected. ...
Even so, she acknowledges that the USTC setup is dauntingly complicated. Jiŭzhāng begins with a laser that is split so it strikes 25 crystals made of potassium titanyl phosphate. After each crystal is hit, it reliably spits out two photons in opposite directions. The photons are then sent through 100 inputs, where they race through a track made of 300 prisms and 75 mirrors. Finally, the photons land in 100 slots where they are detected. Averaging over 200 seconds of runs, the USTC group detected about 43 photons per run. But in one run, they observed 76 photons — more than enough to justify their quantum primacy claim.
It is difficult to estimate just how much time would be needed for a supercomputer to solve a distribution with 76 detected photons—in large part because it is not exactly feasible to spend 2.5 billion years running a supercomputer to directly check it. Instead, the researchers extrapolate from the time it takes to classically calculate for smaller numbers of detected photons. At best, solving for 50 photons, the researchers claim, would take a supercomputer two days, which is far slower than the 200-second run time of Jiŭzhāng.
But I should study this more before jumping to conclusions. I am still trying to figure out what is so impressive about observing 76 photons in one run.