Last time we talked about the weird quantum universe, where particles can be in more than one state at the same time and can be entangled with another particle at great distances. What does this have to do with computers?
Since their beginning in the late 1930s, all digital computers are based on binary digits (bits), which can have a value of zero or one. Early computers might have a few thousand bits in a box the size of a refrigerator. Your smart phone probably has more than 100 billion bits in a box that fits in your pocket. Digital computers work because the computer can tell a particular bit to be a zero or a one, and it will stay in that state until it is explicitly told to change. This is a good thing, and a bad thing. It is good because we can rely on the state of that bit. It is bad because it takes time to set the value of a bit, and later to look at it to see what that state is. Because of that, there are problems that would take computers millions of years to solve.
The quantum world is a little different. Niels Bohr who won the 1922 Nobel Prize in physics for his work in quantum theory famously said, “If quantum mechanics hasn’t profoundly shocked you, you haven’t understood it yet.”
Quantum computers use quantum bits, called qubits. Qubits are very small; they must be to have quantum effects. They can be individual atoms, photons, or electrons. Unlike a digital computer, each qubit can be in multiple states simultaneously. The effect of that is that a quantum computer with a single qubit could solve two simple problems at the same time, one with two qubits could solve four simultaneously, and one with ten qubits could solve over a thousand simple problems simultaneously. This is called parallelism. A 30-qubit quantum computer would be at least a thousand times faster than today’s conventional desktop computer.
To solve very complex problems, the digital world has created computers to take advantage of problems that can be solved using parallelism techniques. Computer companies have created computers with dozens to thousands of separate processors, each doing the same function across a large array of data. IBM’s Blue Gene is one example of a massively parallel supercomputer. SETI@home (Search for Extraterrestrial Intelligence) is an example of a distributed parallelism approach, often called grid computing, where 290,000 computers around the world can work on the same problem across the Internet.
Blue Gene cost $100 million to build. SETI takes advantage of idle time on lots of computers, so it hard to put a dollar cost on it. In ten years, it managed to cover only about 20% of the celestial sphere.
One problem with a qubit is that if you look at it, it assumes a specific state and stays there; superposition disappears. This is where entanglement comes in: you can indirectly look at the value of qubit’s attribute.
Armed with a quantum computer, what could you do? In general, not what you do today on your digital mainframe, desktop, or phone. A quantum computer would be lousy at balancing a checkbook, creating a spreadsheet, or writing a book. (Unless you were trying to prove the infinite monkey theorem: a monkey sitting at a typewriter hitting the keys at random would eventually write the complete works of William Shakespeare.)
Quantum computers will be very good in two areas: search and factoring.
- If you have a lot of data to search (like the SETI problem), a quantum computer could look at all of the data at once.
- While it is easy for a digital computer to multiply two large numbers, even if they each have hundreds of digits. Determining the factors of a very large number, like one with 500 digits in it, is very difficult and can take thousands of years with today’s fastest computers. A quantum computer could factor a 500-digit number in seconds.
OK, a very quick search would be neat but Google is fast enough for me. And I never even want to think about factoring a 500-digit number, so I don’t care about that.
Next time we will explore why you should care.
The last word:
As you probably know, the US is far behind most of the rest of the world in cell phone and credit card technology. Almost every point of sale in Europe takes EMV cards, smart cards that store the card data in integrated circuits embedded in the cards or in RFID chip. If you are wondering what the acronym “EMV” stands for, it is ”Europay, Mastercard and VISA,” the three companies that created the standard.
There are two security concerns you should be aware of:
- The RFID chips in your smart credit card can be read over a distance of up to three feet. Anyone close to you for a second could be a thief stealing your card. Always carry it in an RFID shielded envelope, wallet, or purse.
- Because non-smart cards are a pain for the retailers in Europe, they don’t like to take them and when they do they are not very careful. They won’t bother checking the signature on the card, even if you have signed it with “CHECK ID.” Anyone who steals your physical card will have no problem using it. Your credit card company should cover your costs, but it will be a huge pain. Never carry debit cards – you have very little protection against someone emptying your bank account, and they can do it in a matter of minutes.
Keep your sense of humor.