Google’s Quantum Supremacy Proves Quantum Computing is Merely ‘Really, Really Hard’
Why I Called It ‘Quantum Supremacy’
Excerpts and salient points ~
+ The quantum supremacy milestone allegedly achieved by Google is a pivotal step in the quest for practical quantum computers. I thought it would be useful to have a word for the era that is now dawning, so I recently made one up: NISQ. (It rhymes with risk.) This stands for “noisy intermediate-scale quantum.” Here “intermediate-scale” refers to the size of quantum computers that are now becoming available: potentially large enough to perform certain highly specialized tasks beyond the reach of today’s supercomputers. “Noisy” emphasizes that we have imperfect control over the qubits, resulting in small errors that accumulate over time; if we attempt too long a computation, we’re not likely to get the right answer.
In the 2012 paper that introduced the term “quantum supremacy,” I wondered: “Is controlling large-scale quantum systems merely really, really hard, or is it ridiculously hard? In the former case we might succeed in building large-scale quantum computers after a few decades of very hard work. In the latter case we might not succeed for centuries, if ever.” The recent achievement by the Google team bolsters our confidence that quantum computing is merely really, really hard. If that’s true, a plethora of quantum technologies are likely to blossom in the decades ahead.
+ However, the demonstration is still significant. By checking that the output of their quantum computer agrees with the output of a classical supercomputer (in cases where it doesn’t take thousands of years), the team has verified that they understand their device and that it performs as it should. Now that we know the hardware is working, we can begin the search for more useful applications.
+ Why is it so important to verify the performance of the hardware? It’s because precisely controlling a quantum computer is notoriously difficult. In a sense, merely looking at a quantum system unavoidably disturbs it, a manifestation of Heisenberg’s famous uncertainty principle. So if we want to use such a system to store and reliably process information, we need to keep that system nearly perfectly isolated from the outside world. At the same time, though, we want the qubits to interact with one another so we can process the information; we also need to control the system from the outside and eventually measure the qubits to learn the results of our computations. It is quite challenging to build a quantum system that satisfies all of these desiderata, and it has taken many years of progress in materials, fabrication, design and control to get where we are now.
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