What is quantum error correction? (part 1)
Earlier this week, Google published cutting-edge research on reducing error rates in their experimental quantum systems. With this breakthrough in error correction, they have reached a milestone on the road to a fully functional, error corrected quantum computer with thousands of qubits. What is quantum error correction, and why is it so important to the foundations of quantum computing?
Before we explain error correction, it would be helpful to review what qubits are. And before that, it would be helpful to review what regular bits are.
Classical computers (like your laptop) talk in the language of bits, or units of information that can either be of value 0 or 1. Quantum computers talk in qubits. Qubits are similar, but instead of being restricted to being only 0 or 1, they can be 0 and 1 at the same time! This is a cool and strange phenomenon of quantum systems called superposition. To learn more about qubits, we recommend playing some quantum chess.
In a classical computer, bits travel back and forth at the speed of light. It’s very important that the bits don’t become corrupted; that is, a bit with value 0 doesn’t inadvertently change to 1, or vice versa. Since bits are very sensitive, this can happen through the slightest interference, such as by a passing ray of light or an imperfect cable for the bits to travel through. Nevertheless, no system is perfect, and so we need to be able to know when bits erroneously change. The solution is quite straightforward; make copies of the bit so if one changes, it’s obvious that there was an error.
With qubits, however, it’s much more difficult. Since a qubit has an infinite number of potential states, it is prone to an infinite number of errors. Furthermore, qubits can’t just be copied, because simply trying to read a qubit causes it to lose its state (a phenomenon called wavefunction collapse). How, then, do we solve this problem of quantum error correction (QEC)?
In part 2, we’ll discover the answer to this question and learn more about Google’s recent advances. See you then!
~ Sanjay