Classical computer (the ones we use on a daily basis) encode all the information we need in bits, that is, in “zeroes” and “ones”. This type of computer performs calculations in a similar way to how it would be done by hand. It does have more patience than most of us to solve such problems, but the problems it can solve efficiently are, essentially, the same that we would be able to solve efficiently by hand (if we were patient enough). By solving a problem efficiently, we mean that the time it would take to solve the problem doesn’t grow too quickly as the size of the input grows.
Figure 1. Quantum computers can, in principle, be much faster than classical computers. But they can accumulate errors due to the fragility of the quantum states.
Quantum computers, on the other hand, stores information in quantum bits (q-bit). These can be states labelled as “zeros” (|0>) or “ones” (|1>), as is done in classical computing. Now, however, quantum mechanics brings a novelty: it is possible to have a q-bit in a state “zero”, “one”, or in any superposition of the two states. That is, you can find any mixture of these states in a q-bit. This is a situation similar to the (in)famous Shroedinger cat, in which the cat can be thought of as being simultaneously dead and alive. These superpositions states should, at least in principle, allow a quantum computer to test several possibilities at the same time. This could lead to a significant increase in the velocity with which a computer solves a problem. And that is one of the reasons why scientists are so interested in quantum computers.
But a quantum computer also has its downsides. One of the problems it faces regards the durability and dependability of the information it stores. The problem is, due to it’s quantum nature, quantum bits are a bit fragile and they can’t store information for a long time. This leads to errors that can seriously compromise the dependability in the information stored. And, needless to say, that is not a great feature for any type of computer, be it quantum or classical.
Figure 2. Researchers found a way to detect and correct errors in quantum bits. The figure above illustrates the process.
Now, a team of researchers from the University of Yale seem to have taken a huge step towards making quantum computers a reality. They developed an algorithm that allows for an efficient correction of the errors that appear in the information stored in a quantum computer.
The quantum error correction (QEC) system encodes the information from the q-bit in a higher dimensional space, that is, a space with a larger number of quantum bits. This allows the information to be stored in a redundant way, that is, the same information can be written in several ways in this higher dimensional space. The team used a superconductor inside an aluminum box with a chamber in each side. One of the chambers was filled with photons that were linked to the superconductor. All these elements encode a single quantum bit of information. The other chamber reads from the quantum bit, and writes data in it. The system is able to encode, spot errors in a quantum bit and correct them.
This was the first error correction system that was developed to detect and correct naturally occurring errors. It may just be the breakthrough quantum computing needed and, hopefully, we should soon be able to see a fully working, efficient and reliable quantum computer.
By Kellen Manoela Siqueira.
The full work (“Extending the lifetime of a quantum bit with error correction in superconducting circuits”) can be found in the August, 2016 edition of Nature.