Throughout human history we have discovered many different ways of organizing, processing and using information, with the greatest step forward being the computer. With each advancement this technology has become more efficient, though recently we have been posed with a problem: we are reaching the physical limits of how small computers can be. Luckily, science has found the solution in quantum physics, where scientists are now developing quantum computers. But what are these super machines, their uses, and how will they impact the modern world?
We must first have an understanding of regular computers in order to comprehend how the aforementioned quantum computer works. There are three stages in the composition of a computer: transistors, logic gates, and modules, each one consisting of several of the previous parts (e.g a module is composed of many logic gates, they themselves being made of many transistors). A transistor is essentially a switch that prevents or allows current to flow (1). In modern computers, these devices are a small fraction of the diameter of the HIV virus (very small!). Several of these transistors can be arranged into logic gates, which transforms inputs from the transistors into one useful output (a 1 or a 0, also known as binary). There are many types of logic gates, each of them serving different functions, as seen on the left. Finally, the module, or the computer itself, is a combination of logic gates. Keep in mind that this is a very “in a nutshell” explanation which will help us later. The moral of the story is that if computers get smaller and more powerful, they will reach their physical limit of “smallness”. This is where quantum computing comes into place.
Everyone has probably heard the term “binary” before. A binary code consists of a series of 1’s and 0’s arranged in a specific order. Depending on the order, the output may be a letter, number, symbol, command, etc. The individual 1’s and 0’s are called bits, and they are the most fundamental unit of information in computing. Quantum computers, on the other hand, have qubits as their fundamental units. Then things start getting funky, since qubits can take on quantum properties like superposition and entanglement.
Qubits, much like bits, can be in one of two states: 1 or 0. However, their quantum properties allow them to be in a third state, which is 1 and 0. This is called superposition: a state in which a particle can be in any proportion of each state at once (until it is observed). This property is monumental and defines the world of quantum computing. Let’s say there are three regular bits: there are a total of 23 = 8 combinations of 1’s and 0’s that can be formed, out of which only one can be used. Three qubits in superposition, on the other hand, can be in all of the 8 combinations at once. This is super useful because with each extra qubit the number of combinations grows exponentially.
Another property that qubits can have is entanglement. This is rather counterintuitive because when qubits are entangled, no matter the distance between them, a change in one of them will cause the other to undergo the same change instantaneously, meaning that when measuring one qubit, one can determine the state of the other immediately. We can see how these two properties fit each other perfectly: upon being measured, an entangled qubit will assume a state, which will cause another to do so as well. Hence, we can observe two qubits only by looking at one of them.
Quantum computing also revolutionizes logic gates. While the latter will only produce one output from a set of inputs, a quantum gate (a logic gate for a quantum computer) will take a superposition and produce, as an output, another superposition. Theoretically, these gates would be responsible for entangling particles and measuring their probabilities, only for the computer itself to eventually collapse the outputs into actual 1’s and 0’s. What this means is that millions of calculations, depending on the number of inputs, can all be done at the same time with quantum computers. This will prove to be extremely useful when dealing with large amounts of data; while regular computers will go through every combination individually, quantum computers will obtain the wanted result much quicker, which in turn saves a lot of time.
Several applications for these machines arise based on the explanations above. One of the most prominent uses is database searching. While regular computers are capable of completing this task, quantum computers are far superior at it, only taking a square root of the time regular computers would need. This would make a colossal difference to companies with large databases such as IBM and Google. Another interesting use for these tools has been found in simulations of the quantum world. While standard computers are technically able to run these simulations, they are often inaccurate and require a lot of power. Though with quantum computers scientists are able to create more reliable and error-free simulations; by studying these replications scientists could become more comprehensive of proteins that could potentially revolutionize modern medicine as an example.
Quantum computers probably won’t replace commercial computers, but this doesn’t mean that they won’t impact our day to day lives in the future. They have applications in other areas where they can prove to be massively superior to regular computers. They will provide a new outlook on IT security and the development of quantum physics as a whole.