IBM joins quest to build a qubit

A reader writes:

While it's refreshing to find someone as skeptical of scientific hype as you, I think you have done too far with the claim that "no one has a qubit yet".

So I report progress in efforts to prove me wrong. Today's NY Times reports:

I.B.M. is jumping into an area of computing that has, until now, been primarily the province of academia: the quest to build a quantum computer.

A computer that took advantage of the oddities of quantum physics could solve in seconds certain problems that would occupy present-day computers for billions of years. But for now, it is impossible to build such a computer because the bits of information it would need for the calculations fall apart before a calculation can be completed. The problem is, in essence, like trying to knit a sweater with yarn that unravels before the first purl.

On Tuesday, I.B.M. researchers will present experimental results that they say put them close to solving this problem, both by lengthening the lifetime of the quantum bits of information and by quickening the pace of computation. The presentation will take place at a meeting of the American Physical Society in Boston.

“In the past, people have said, maybe it’s 50 years away, it’s a dream, maybe it’ll happen sometime,” said Mark B. Ketchen, manager of the physics of information group at I.B.M.’s Thomas J. Watson Research Center in Yorktown Heights, N.Y. “I used to think it was 50. Now I’m thinking like it’s 15 or a little more. It’s within reach. It’s within our lifetime. It’s going to happen.”

This acknowledges that they cannot build a quantum computer because no one can make a qubit that is stable enough to be used in a computation.

The IBM method is commercially impractical because it requires a circuit that is a whole lot colder than liquid helium:

When cooled to a hundredth of a degree above absolute zero, the circuits act as qubits.

The problem is that a qubit becomes scrambled in short order, and the information it carries turns into gibberish. ...

Even though that is still not long enough for perfect calculations, it is almost good enough for error correction algorithms to detect and fix any mistakes. “We’re just crossing this threshold,” Dr. Ketchen said, “which is a big morale booster that says, gee, this is becoming doable.”

Below the threshold, generating reliable answers is impossible. “No matter how many qubits you had, you couldn’t even get one effectively good one because of the error rates being too high,” he said.

I read this as saying that IBM is claiming to make progress towards a qubit that is suitable for computation, but that no one has made such a qubit yet.

I get a lot of flack for being a quantum computer skeptic. But when I deny that anyone has made a true qubit, I am just saying that same thing that this NY Times article says, and what the experts quoted in it say. Where I disagree with them is where they express confidence in doing something that has never been done before.

To me, it seems much more likely that quantum computing is impossible. I say this because (1) it is contrary to conventional notions of computability, (2) it is not implied by quantum mechanics, (3) it is relentlessly overhyped, and (4) it has been pursued by a lot of smart men and money for decades, without much to show for the work.

Of course you have no more reason to believe my predictions than those of a big-shot MIT professor. Just ask yourself why you keep reading stories about quantum computers are doing complex computations with dozens of qubits, and yet no one has a convincing demonstration that anyone has even computed anything with a single qubit.

Update: Lubos Motl summarizes quantum computers and adds:

Errors in the calculations and decoherence make all existing prototypes of a quantum computer unusable. So far it is the case. Maybe one of you will help to solve the technological obstacles.

The obstacles may be more than technological; as a comment below points out, the laws of physics may require that calculating with qubits requires exponentially large amounts of energy.

Bohmian mechanics makes no sense

A. S. Sanz writes in a new paper:

At present, there is no doubt that quantum mechanics can be considered the most successful theory ever devised to explain the physical world. Its applicability ranges from very fundamental physical problems to the high-technology applications that are nowadays an important part of our daily life. This theory, though, still constitutes a veiled mystery at a deeper level of understanding, for there is a lack of a clear interpretation of the physics underlying quantum systems. This is somehow connected to its widely accepted interpretation, namely the Copenhagen interpretation [1], which not only does not allow us to think of quantum systems as we do of classical ones, but it just forbids such a thing.

A feasible way to surmount this drawback (although surely not the final one) comes through Bohmian mechanics [2–5].

There are two problems with this. First, Bohmian mechanics has not been able to reproduce the successes of quantum mechanics. Second, Bohmian mechanics is much more bizarre and harder to interpret physically than Copenhagen.

As Wikipedia explains:

The de Broglie–Bohm theory is explicitly non-local: The velocity of any one particle depends on the value of the wavefunction, which depends on the whole configuration of the universe. Because the known laws of physics are all local, and because non-local interactions combined with relativity lead to causal paradoxes, many physicists find this unacceptable.

Bohm ironicly called it a "causal interpretation" even tho it violates causality. I think that it is a little strange that Bohmian advocates act as if they are clarifying some quantum mystery, when they replace ordinary quantum mechanics with something that makes no sense.

Universe not so interconnected

Sean Carroll writes on his Cosmic Variane blog:

More recently, though, another excerpt from this lecture has been passed around, this one about ramifications of the Pauli Exclusion Principle. (Headline at io9: “Brian Cox explains the interconnectedness of the universe, explodes your brain.”)

The problem is that, in this video, the proffered mind-bending consequences of quantum mechanics aren’t actually correct.

Lubos Motl agrees:

It's very refreshing to agree with Sean Carroll (and a guy named Tom Swanson) on something.

Brian Cox wanted to use quantum mechanics to defend the Gaia religious proposition that "everything is connected with everything else" (the last sentence of the video above). I am convinced that this main "punch line" he wanted to prove was predetermined by ideological prejudices and goals.

The vague misconception that "everything is connected with everything else" is a pillar of the broader environmentalist movement into which Cox indisputably belongs.

I explained Cox's errors here back in Dec. 2011:

He is talking about a theoretical effect that is not measurable unless the electrons are very close. I think that it is a bizarre and unscientific point. It is like saying that my finger has a graviational effect on Venus. If so, it is negligible and unobservable. ... The idea that everything is connected to everything else seems contrary to causality. If that is what Cox means to say, then he ought to say whether it is contrary to causality.

I was complaining because the Bad Astronomer Phil Plait endorsed this video, in spite of its faults.

A theme of my blog is to attack real scientists who present unscientific conclusions. That is, I attack pseudoscience, but I am really not interested in astrology and other such matters. I prefer to point out pseudoscience in academically respectable channels. There is a lot of it in quantum mechanics.

I just noticed that Carroll and Motl were responding to Cox's defense of his video in the WSJ:

I recently gave a lecture, screened on the BBC, about quantum theory, in which I pointed out that “everything is connected to everything else”. This is literally true if quantum theory as currently understood is not augmented by new physics. This means that the subatomic constituents of your body are constantly shifting, albeit absolutely imperceptibly, in response to events happening an arbitrarily large distance away; for the sake of argument, let’s say on the other side of the Universe.

This statement received some criticism in scientific circles. Not because it’s wrong, because it isn’t; without this behavior, we wouldn’t be able to explain the bonds that hold molecules together. The problem is that it sounds like woo woo, and quantum theory attracts woo-woo merde-merchants like the pronouncements of New Age mystics attract flies – metaphorically speaking.

I guess that I am one of those that Cox is responding to. It is "woo woo" when he claims a scientific truth and then qualifies it with "albeit absolutely imperceptibly".

Double-slit needs no probabilities

I posted below that no probabilities are needed in quantum mechanics. A reader asks whether the Double-slit experiment proves randomness in quantum mechanics.

I don't see how any physical experiment could prove randomness, or directly observe probabilities. The double-slit experiment was performed and understood by Young in 1803, and no one thought then that it implied anything about probability or randomness.

I think that the relation is as follows. If you assume that light is composed of classical (non-quantum) photons, then the photons go thru one slit or the other, with some probability for each. The diffraction pattern can also be interpreted as a probability distribution.

You get similar results if you collect data on coin tosses. It does not say anything about whether the coin tosses are deterministic or probabilistic.

To get the quantum probabilities, we had to assume classical particles, which is clearly an invalid assumption. Quantum mechanics is emphatic that light does not consist of classical particles. Sometimes quantum mechanics textbooks say that light is composed of particles, but then they are funny particles that can be in two places at once. So we cannot say that the light particle goes thru one slit or the other.

One atom transistor

ScienceDaily reports:

The smallest transistor ever built -- in fact, the smallest transistor that can be built -- has been created using a single phosphorus atom by an international team of researchers at the University of New South Wales, Purdue University and the University of Melbourne. ...

"This is a beautiful demonstration of controlling matter at the atomic scale to make a real device," Simmons says. "Fifty years ago when the first transistor was developed, no one could have predicted the role that computers would play in our society today. As we transition to atomic-scale devices, we are now entering a new paradigm where quantum mechanics promises a similar technological disruption. It is the promise of this future technology that makes this present development so exciting." ...

The single-atom transistor does have one serious limitation: It must be kept very cold, at least as cold as liquid nitrogen, or minus 391 degrees Fahrenheit (minus 196 Celsius). ...

This is not a new paradism. Quantum mechanics has always been used to make transistors. We have no other understanding of them. But the real hype here is not smaller or faster computers, but the holy grail of quantum computers.

The single-atom transistor could lead the way to building a quantum computer that works by controlling the electrons and thereby the quantum information, or qubits. Some scientists, however, have doubts that such a device can ever be built.

"Whilst this result is a major milestone in scalable silicon quantum computing, it does not answer the question of whether quantum computing is possible or not," Simmons says. "The answer to this lies in whether quantum coherence can be controlled over large numbers of qubits. The technique we have developed is potentially scalable, using the same materials as the silicon industry, but more time is needed to realize this goal."

This is where quantum computing research has been stuck for 30 years. Physicists can find more and cleverer ways of demonstrating quantum phenonema, but they cannot show that scalable qubits are possible. I am betting that scalable qubits are impossible.

Wired explains:

This means a quantum computer could do things a classical machine never could, letting you, say, crack today’s most complex encryption algorithms in relatively short order. But physicists still can’t agree on whether a quantum computer can actually be built. The rub is that if you interact with a quantum system, it “decoheres,” collapsing into a single state. In other words, the qubit turns into an ordinary bit. If you want to build a quantum computer, you have to — among other things — isolate its qubits from their surrounding environment.

The new research from Purdue and New South Wales does not demonstrate a quantum bit. But in placing a single-atom transistor on a silicon crystal — and carefully isolating it from the surrounding substrate — it provides a clearer path to a working quantum computer.

Note the admission that no one has a qubit yet, in spite of all the hype.

Quantum computer hype in Vancouver

The Vancouver Sun shows a picture of computer scientist Scott Aaronson and brags about the vast computational advantages of quantum computers:

“If this all works well, this is five years off. ...

“But who knows what will happen in the future. That's how people used to think about regular computers.”

The field has a dramatic mix of views. One company says that it is in commercial production of 100-qubit computers. A qubit is the basic building block of a quantum computer. If we could make qubits that could be chained together, then we could make quantum computers. We cannot make quantum computers, and predictions vary from saying that it will be possible in 5 years, to saying that it is forbidden by the laws of physics.

Aaronson thinks some problems in mathematics will remain beyond the limits of quantum computing and indeed, he thinks a breakthrough in development of a large-scale quantum computer is many decades, rather than a few years, away.

“Even quantum computers would have significant limitations. If you're just looking for a needle in a haystack. . . then not even a quantum computer will give you an exponential speedup for this problem,” Aaronson said.

He said that view is contrary to most popular representations of quantum computers as infinitely capable.

Nonetheless, he rejects skeptics who doubt they will get built – he's offering a $100,000 prize to anyone who can demonstrate that it's impossible to build a large scale quantum computer.

Aaronson says that I was one of the skeptics that pushed him over the edge to offer his prize.

Czech String theorist Lubos Motl has another view:

Many people have said many stupid things about quantum computation. Many but not all anti-quantum zealots of course believe that quantum computation is impossible because the world must be fundamentally classical and a classical computer of a given size can't solve certain problems after a certain number of steps.

That is not my view. I believe that the world is fundamentally quantized and not classical.

Other people believe in quantum computers but they have used them to "prove" bizarre "interpretations" of quantum mechanics. In particular, David Deutsch has said that the likely existence of quantum computers proves the many-worlds interpretation of quantum mechanics.

At least Deutsch does recognize that a true quantum computer would demonstrate a phenomenon that has never been seen before in any experiment. Because if it had, then that would be a proof of many-worlds, and everyone agrees that there is no proof of many-worlds. And I do not believe that there will ever be any proof of many-worlds, as it is a silly and unscientific idea.

Motl goes on with a little rant about the nature of science:

The only way to rule out a hypothesis is to actually find a wrong prediction that the hypothesis makes, one that disagrees with observations. Various anti-quantum zealots love to use some "alternative", non-scientific ways to falsify theories. A theory doesn't agree with their medieval prejudices so they just decide it means that the theory has to be abandoned. But science hasn't worked in this way for 500 years. What a prejudiced bigot a priori thinks is totally irrelevant in science.

That's right. A-priori opinions about how the world works are irrelevant, whether then come from Einstein or anyone else.

My main reason for being skeptical about scalable quantum computing is that decades of research by really smart people and 100s of millions of dollars have gone into this, and no one has even figured out a way to show that it is even possible. If the dramatic and implausible consequences were really possible, then I would expect to see some evidence of it. At this point, it seems more likely that some law of physics is preventing it, such as the laws of thermodynamics that prevent perpetual motion machines.

Motl concludes:

Quantum computers demonstrate the power of quantum mechanics, the fundamental framework underlying the laws of physics in our Universe, very crisply and if and when they will be produced, the world may substantially change, at least at some level. Let's hope the change won't be catastrophic.

Okay, but that is wishful thinking. If he follows his own advice, then he has to admit that the world may not follow his a-priori prejudices.

Update: Aaronson says he visited D-Wave Systems near Vancouver, and he reiterated his skepticism about their quantum computer:

It remains true, as I’ve reiterated here for years, that we have no direct evidence that quantum coherence is playing a role in the observed speedup, or indeed that entanglement between qubits is ever present in the system. ...

So I hereby retire my notorious comment from 2007, about the 16-bit machine that D-Wave used for its Sudoku demonstration being no more computationally-useful than a roast-beef sandwich. ...

... the fundraising pressure is always for more qubits and more dramatic announcements, not for clearer understanding of its systems. So, let me try to get a message out to the pointy-haired bosses of the world: a single qubit that you understand is better than a thousand qubits that you don’t. There’s a reason why academic quantum computing groups focus on pushing down decoherence and demonstrating entanglement in 2, 3, or 4 qubits: because that way, at least you know that the qubits are qubits! Once you’ve shown that the foundation is solid, then you try to scale up. ...

For the first time, I find myself really, genuinely hoping — with all my heart—that D-Wave will succeed in proving that it can do some (not necessarily universal) form of scalable quantum computation. For, if nothing else, such a success would prove to the world that my $100,000 is safe, and decisively refute the QC skeptics who, right now, are getting even further under my skin than the D-Wave boosters ever did.

In other words, he accused them of being charlatans 5 years ago for over-hyping quantum computing when they cannot even prove that they have one true qubit. But now he hopes that they will make a quantum computer so that he can prove me and the other quantum skeptics wrong! This is pathetic. Aaronson seems to realize that the field is going nowhere.

Sprung from Einstein’s head

Science writer Jeremy Bernstein writes in a new paper:

Periodically I prepare an imaginary lecture the purpose of which is to remind philosophers of physics, and indeed some physicists, that the quantum theory had its origins in experiments. Unlike general relativity which seems to have sprung from Einstein’s head, the quantum theory was a response to experiment. Even de Broglie’s conjecture that particles had also a wave-like nature was influenced by how this notion could be used to explain the quantization of the radii of the Bohr orbits. The experiment driven theoretical developments of the quantum theory began with Planck and have continued ever since.

General relativity sprung from Einstein’s head? One of the persistent myths that I debunk in my book is that Einstein created relativity out of pure thought, with any input from experiment. Einstein himself promoted this myth in his later years, and paradigm shift philosophers have made it the centerpiece of bogus theories about how science works.

Usually the myth is told about the special relativity of 1905, as Einstein's biographers acknowledge that he relied heavily on others for general relativity.

The term general relativity means (special, spacetime, electromagnetic) relativity applied to gravity. It is called general because it is nonlinear. The first breakthru was in 1905, when Poincare discovered the space-time metric, proposed a Lorentz-invariant theory of gravity, and explained how gravity could propagate at the speed of light and still be consistent with solar system observations. A couple of years later he announced that he had figured out how to use relativity to partially explain an anomaly in Mercury's orbit.

Einstein's biggest breakthru was to deduce in 1907 that gravity had an apparent effect on clocks.

We know from Einstein's letters that he spent several years trying (off and on) to extend Poincare's work on Mercury. Others helped him on the problem. He also wanted to explain the deflection of starlight. His next big breakthru was in 1915 when he showed how Grossmann's 1913 relativity equations could be used to explain the Mercury anomaly. When Hilbert gave another derivation of Grossmann's equations in 1915, Einstein became convinced that those equations must be right. Einstein's famous general relativity paper was published in 1916, with an acknowledgement to Grossmann, but no mention of Poincare or Hilbert.

Thus relativity had its origin in experiments, just like quantum mechanics.

Update: A new paper on Einstein the Stubborn: Correspondence between Einstein and Levi-Civita has explained the correspondence between Einstein and Levi-Civita and Hilbert in 1914-16. The letters mostly consisted of Levi-Civita and Hilbert trying to convince Einstein of errors in his general relativity papers. Grossmann had introduced covariant equations in 1913, but Einstein did not accept them, and gave fallacious arguments for non-covariant equations. Einstein finally admitted in 1916 to Hilbert, "The error you found in my paper of 1914 has now become completely clear to me".