“But, as Deepak Chopra taught us, quantum physics means anything can happen at any time for no reason.” - Professor Farnsworth

Quantum mechanics is the phrase at the center of a host of nonsensical beliefs spread by charlatans like Deepak Chopra. From curing baldness to talking with the dead, no matter what you desire, I guarentee that there is someone who will tell you that quantum mechanics can provide it to you. The only explanations offered are a stream of nonsensical technobabble so egregious that it would make a pulp writer blush. This was inevitable. Quantum mechanics presents a combination of difficult to understand and conterintuitive results that form a breeding ground for such nonsense. Unfortunately, these attitudes have begun to spread to quantum computing.

To the lay person quantum computers seem to be devices that are unimaginably faster than current computers. They promise to shatter encryption and lead us to the singularity. These apperances provide a fertile breeding ground for the same mystical nonsense that surrounds quantum mechanics. I think that we are just at the beginning of the era of quantum computing nonsense. Knowledge of quantum computers has just recently begun to enter the general population. Soon the conmen will begin to emerge from the woodwork with seductive promises of how quantum computers will make you and your buisness rich. Like the quantum charlatans of today, they will have no substance behind their claims. Cryptocurrencies, in particular, are an area that will be ripe targets for quantum computing charlatans. When cryptocurrencies and pareidolia collide

Cryptocurrencies are a natural target for quantum computing scams. It just seems logical. Cryptocurrencies, especially those based on proof of work, rely on various computations to mint coins and carry out transactions. Surely there must be some way to exploit the speed advantages of quantum computers for cryptocurrencies. A recent event in the Bitcoin community already demonstrates that this sort of thinking is already present. A recently mined Bitcoin block has the hash 00000000000000000021e800c1e8df51b22c1588e5a624bea17e9faa34b2dc4a. The 21e800 at the beginning led to an outbreak of wild speculation. Mining bitcoins involves finding a group of transactions and associated bookkeeping data whose SHA-256 hash starts with a certain number of zeros. The exact number depends on the difficultly set by the network and is updated every two weeks. People claimed that this block was mined specifically to start with 21e800 as some sort of message. There were claims it was created by Satoshi Nakamoto, the enigmatic creator of Bitcoin who vanished shortly after the creation of Bitcoin. 21e800 was claimed to be a reference to a certain grand unified theory in physics, a reference to the 21 million total Bitcoins that will ultimately be mined and all other sorts of nonsense. Mining a block so that its hash starts with 21e800, in addition to the required zeros, would indeed be very computationally expensive. This lead to speculation that whoever mined this “message” is either from the future or has access to large computational resources in the form, of course, of a quantum computer. The most disappointing thing about this whole debacle is that hashes starting with 21e800 have happened before. The entire thing was nothing but people trying to find meaning in the meaningless. But it does show the general attitude for quantum computers. Quantum computers won’t help you

This hysteria around this hash showed the reverence that surrounds quantum computers. The only way that this hash could arise is through time travel or with a quantum computer. But how would a quantum computer help? If you were to ask the people involved the answer would undoubtably be along the lines of “quantum computers are like regular computers, but much faster” or that “quantum computers preform their computations in parallel”. These are both wrong, with the latter being a little less wrong. Quantum computers operate in a fundamentally different way than classical computers and the parallelism that they use is limited. It is true that there are quantum algorithms that are better than any known classical algorithm, but the problem for an aspiring quantum Bitcoin miner is that there are only a few (a few dozen at most) known quantum algorithms and none of them would be of use in mining bitcoins. In fact, the best way to mine Bitcoins on a quantum computer given our current knowledge is to use the quantum computer to simulate a classical computer and mine bitcoins with the simulated classical computer.

Just because certain quantum algorithms are better, doesn’t mean that they’re faster. When I say an algorithm is better, I mean it takes fewer steps to complete. Imagine that you are given a function that takes N bits as input and outputs either a zero or a one for each input. The function also has the property that it is either constant (always ouputs zero or always outputs one) or balanced (outputs zero for half its inputs and one for the other half). The challange is to figure out if the function is balanced or constant. The best known classical algorithm requires, in the worst case, 2N−1+1

evaluations of the function, but the Deutsch–Jozsa algorithm is a quantum algorithm which only requires one evaluation. It is exponentially better than the best known classical version. But imagine if that one evaluation on a quantum computer took 10 minutes, while each evaluation on a classical computer took 100 ns. If you’re only working with 32 bits, then the classical computer would always be faster.

Another claim is that quantum computers preform their computations in parallel. This is not true, at least not in the sense that most people would consider. Imagine cashiers at a store, a single one can scan all your items in a certain amount of time and give you your total. Multiple cashiers could scan your items and add up their subtotals at the end to give your overall total, faster than a single cashier. The quantum computing analogy is a cashier putting all your items in a box, shaking it and telling you that your total is an even number. The type of parallelism that quantum computing uses is opaque, most of the information is completely hidden from you and the best you can do is use some clever tricks to extract a small amount of very specific information. This is what happens with the Deutsch–Jozsa algorithm, at one point you have a state that consists of a mixture (the actual term is superposition) of every possible value from your function. But you cannot access that information. If you try to you’ll end up with one specific output (and you can’t even tell which input gave that value). The best you can do is get one bit of information: is the function constant or balanced? Rules for the road

If somebody is trying to sell you on the amazing things that quantum computers can do keep in mind that quantum computers are specialists. Vague explanations like “they’re just faster” or “they operate in parallel” don’t cut it. The former isn’t guarenteed by anything and, for a rule of thumb, the latter is limited to giving yes or no answers. Quantum algorithms are few and far between and will almost certainly have a specific name, usually named after their creator(s). If somebody is trying to sell you something and they can’t give you specifics then they should be treated with as much skepticism as you can muster.