In the race for quantum supremacy, IBM has just beaten Google, with a step researchers previously thought to be impossible. The company has come up with a way to simulate quantum computers with 56 quantum bits, or qubits on a classical computer.
Simulating anything more than 49 qubits on a classical computer was thought impossible because of the memory limitations. Classical computers have limited memory compared to their quantum counterparts. Because of this memory difference, the memory required for simulations increases exponentially with each additional qubit, in the classical simulation. The closest anyone had come to putting the 49-qubit limit to a test was a 45-qubit simulation which needed 500 terabytes of memory, by the Swiss Federal Institute of Technology in Zurich. However, IBM’s new 56-qubit simulation needs just 4.5 terabytes of memory, dramatically reducing the amount of memory used in the previous efforts.
“IBM pushed the envelope. It’s going to be much harder for quantum-device people to exhibit [quantum] supremacy,” Itay Hen at the University of Southern California said.
It’s also worth noting that earlier this year in April, Google revealed its plans to achieve quantum supremacy by the end of 2017 with a new 50 qubit chip. However, that will no longer win them the achievement of quantum supremacy. Bob Wisneiff, the principal investigator of the IBM study, says that their current simulation runs about “a billion times slower” than an actual 56-qubit quantum computer.
This milestone by IBM was achieved by dividing the simulation task into parallel chunks, which allowed the IBM researchers to use multiple processors of a supercomputer simultaneously.
The tech giant wishes to build a quantum computer that can “explore practical problems” like quantum chemistry. The company also hopes to verify the accuracy of quantum computers against their simulations before putting real quantum computers to the test.