Friday, January 17, 2014

No evidence of quantum speedup

Quantum computing is one of the most overhyped technologies of our day, with nearly all the press stories and experts saying that it is an inevitable consequence of known physics. And yet after maybe $100M of research money over 20 years, it has been a total failure.

MIT quantum computing theorist Scott Aaronson announces:
A few days ago, a group of nine authors (R√łnnow, Wang, Job, Boixo, Isakov, Wecker, Martinis, Lidar, and Troyer) released their long-awaited arXiv preprint Defining and detecting quantum speedup, which contains the most thorough performance analysis of the D-Wave devices to date, and which seems to me to set a new standard of care for any future analyses along these lines.
The paper says:
The development of small-scale digital and analog quantum devices raises the question of how to fairly assess and compare the computational power of classical and quantum devices, and of how to detect quantum speedup. ... we find no evidence of quantum speedup when the entire data set is considered ...
Separately M.I. Dyakonov posts another paper, Prospects for quantum computing: extremely doubtful:
When will we have useful quantum computers? The most optimistic experts say: “In 10 years”, others predict 20 to 30 years, and the most cautious ones say: “Not in my lifetime”. The present author belongs to the meager minority answering “Not in any foreseeable future”, and this paper is devoted to explaining such a point of view.
I agree with him, for reasons stated here, and I have been banned from Aaronson's blog for expressing that view.

(In fairness, it is alleged that Dyakonov does not address this paper from last month.)

I agree with Lumo that Scientific theories need to be falsifiable, and quantum computing has not yet been falsified. But unless someone finds some evidence of a quantum speedup, people are going to stop believing in this nonsense.

In this recent NPR interview, Seth Lloyd and others describe quantum computing as technologically inevitable, but breaking communications in real time might be 5 years away. This is as crazy as saying that we might have a manned space station on Jupiter in 5 years.

The above D-wave device supposedly has 503 qubits. Meanwhile the NSA classifies any research on a mere 3 logical qubits. If the research were showing an increasing number of qubits with a corresponding quantum speedup, then there would be reason to believe that some progress was being made. But whether the device as 1 or 503 qubits, no quantum speedup has been found.


  1. Quantum Computers: The biggest scientific joke of all time.

  2. Roger:

    Is it---I mean QC---too dangerous for the III world [and non-Christian,non-white, non-USA-graduated, non-USA-post-doc, never-taken-a-graduate-course-on-QM-esp.-in-North-America] fellows like me to, say, sneak a peep into?

    If so, say, bad for you all Americans, you know!

    [Roger, pardon me, but just been on the 'net after a loong while, you know.... Just couldn't resist... As they say, old habits die hard....]