Google’s Quantum Computer Achieves Chemistry Milestone
When researchers at Google announced last fall that they had achieved “quantum superiority”—a point at which a quantum computer can perform a task beyond the reach of regular computers—some people wondered what the big deal was. The program, which checked the output of a random number generator, was of limited practical value and did not prove that the company’s machine could do anything useful, critics said.
Now, however, Google’s quantum computer has achieved something that could have real-world applications: successfully simulating a simple chemical reaction. The feat points the way toward quantum chemistry, which could expand scientists’ understanding of molecular reactions and lead to useful discoveries, such as better batteries, new ways to make fertilizer and improved methods of removing carbon dioxide from the air.
Last year’s quantum superiority experiment was run on a chip dubbed Sycamore, which contained 53 superconducting quantum bits, or qubits. Chilled to near absolute zero, the qubits take on quantum-mechanical properties, allowing scientists to manipulate them in more complicated and useful ways than the simple “on/off” flows of current that make up the bits of classical computers. The hope is that one day, quantum computers will become powerful enough to quickly perform calculations that would take the lifetime of the universe for a classical computer to complete.
This quantum-chemistry experiment, which was described in the August 28 issue of the journal Science, relied on the same basic Sycamore design, though it only used 12 qubits. But it demonstrates the system’s versatility, says Ryan Babbush, the researcher in charge of developing algorithms for the Google project. “It shows that, in fact, this device is a completely programmable digital quantum computer that can be used for really any task you might attempt,” he says.
The team first simulated a simplified version of the energy state of a molecule consisting of 12 hydrogen atoms, with each of the 12 qubits representing one atom’s single electron. They then modeled a chemical reaction in a molecule containing hydrogen and nitrogen atoms and including how that molecule’s electronic structure would change when its hydrogen atoms shifted from one side to the other. Because the energy of electrons dictates how fast a reaction occurs at a given temperature or concentration of different molecules, such simulations could help chemists understand exactly how that reaction works—and how it would change if they altered the temperature or the chemical cocktail.
The simulation the researchers ran, known as the Hartree-Fock procedure, can also be performed on a classical computer, so it did not, by itself, demonstrate the superiority of a quantum computer. And it was run with help from a classical computer, which used machine learning to evaluate each calculation and then refine new rounds of quantum simulation. But the feat validates the project’s underlying methods, which will be integral to future quantum-chemistry simulations, says Nicholas Rubin, a research scientist on the Google quantum team. And it was twice as large as the previous record-holding chemistry calculation made on a quantum computer.
In 2017 IBM performed a quantum-chemistry simulation using six qubits. Rubin says that result described a molecular system with a level of complexity that scientists in the 1920s could calculate by hand.
