If a quantum processor is to run algorithms beyond the scope of classical simulations, a large number of qubits are required, along with low error rates on readout and logical operations, such as single and two-qubit gates.
By employing a technique called scanning tunnelling microscopy lithography, the scientists are able to directly measure each atom’s wavefunction, thereby determining its exact location in the chip. “We are the only group in the world who can actually see where our qubits are,”
Every Bristlecone chip features 72 qubits. The general assumption in the industry is that it will take 49 qubits to achieve quantum supremacy, but Google also cautions that a quantum computer isn’t just about qubits. “Operating a device such as Bristlecone at low system error requires harmony between a full stack of technology ranging from software and control electronics to the processor itself,” the team writes today.
The world clearly needs more powerful processors, as demand explodes for artificial intelligence workloads that require faster and more efficient chips than what’s currently available from Nvidia NVDA and AMD . But there’s a healthy amount of debate among researchers and scientists about whether quantum computers are useful for practical real-world applications
A paper published this month by Flavio Del Santo, Borivoje Dakić, and Philip Walther in Physical Review Letters, and a follow up demonstration posted on arXiv.org explains how. The technique relies on quantum superposition—the idea that unobserved quantum particles can be in more than one place at once.
And the goalposts are shifting. “When it comes to saying where the supremacy threshold is, it depends on how good the best classical algorithms are,” said John Preskill, a theoretical physicist at the California Institute of Technology. “As they get better, we have to move that boundary.”