
Corporate tussles in the quantum realm - who’ll reign 'Supreme’?
On the 23rd of this month, in a major milestone for the field of quantum computing, Google claimed to have achieved quantum supremacy in a paper released on the Nature magazine. Using their programmable superconducting processor, Sycamore, Google claimed to have sampled one instance of a quantum circuit one million times in about 200 seconds. According to Google, the equivalent figures on a state of the art classical supercomputer would be about 10,000 years approximately, for the same task.
Dubbed Sycamore, Google's very own quantum processor with 53 qubits was pitted against the world's most powerful supercomputer: ORNL’s Summit, housed at the Oak Ridge Leadership Computing Facility (OLCF). The task they had to perform: Random Circuit Sampling or RCA, devised specifically to rate the computational prowess of quantum processors like Sycamore. Not only was Sycamore faster than its classical counterpart, but it was also approximately 10 million times more energy efficient.
But what is this hullabaloo all about?
Google's results should not be seen in isolation to the past discoveries made in the field. Infact, it is the latest milestone in an already ripening field of research where contributions have come from researchers and corporations all over the world. Quantum Supremacy was already around the corner.
However, the term "Quantum Supremacy" should be treated with utmost care. The term means refers to the ushering of an era where Quantum computers can solve only a certain class of problems better and faster than their best known classical counterparts. However, this does not in any way imply that all of today's tasks can be solved in a quantum computer at a rate exponentially faster than a classical computer - only some can. This also means that we are still quite far away from fully realising a commercially available quantum computer for all our needs.
So why is Quantum Supremacy important?
Quantum Supremacy is not the end goal of quantum computing, it is an experimental and real time affirmation of theoretical advances done in the field long before, and serves as a message that we are on the correct technological path to making quantum computing a reality for all. The transformation from pen and paper mathematics to reality comes with the tedious task of keeping a particular set of qubits entangled to keep up the operations by removing noise and decoherence in quantum systems. Unwanted noise is where most Quantum Processors lose their game, and the real challenge is, in layman terms, to minimize the noise and to be able to use all of the n qubits, that is, all of the 2^n states in the computational space.
Random Circuit Sampling does so in a 'random' manner where the randomness of the process ensures that there are no nice properties that could be exploited by a classical simulation.
So the task of simulating arbitrary random circuits will require a full simulation of the n qubits, the required classical resources for which scale exponentially with n. And at the juncture where the quantum processor is performing exponentially better than its classical counterpart at a certain task (here, RCS), Quantum Supremacy can be safely declared for the task (again, RCS here). It is very important to note that quantum supremacy for one task does not extend to other tasks as well.
The competitive edge:
Along with Google, IBM has also been working on its own Quantum Computing program (read more about their endeavours here). Google's announcement about the quantum breakthrough didn't come without a tinge of controversy. Reacting to the announcement, IBM published a blog post in which it said that Google might have overstated its achievements.
"We argue that an ideal simulation of the same task can be performed on a classical system in 2.5 days and with far greater fidelity. This is in fact a conservative, worst-case estimate, and we expect that with additional refinements the classical cost of the simulation can be further reduced,"
IBM's Edwin Pednault, John Gunnels and Jay Gambetta wrote in the blog post. They have also released a paper justifying their claims.
"Because the original meaning of the term "quantum supremacy," as proposed by John Preskill in 2012, was to describe the point where quantum computers can do things that classical computers can't, this threshold has not been met," they added.
