Yesterday, Google made an announcement about a breakthrough in Quantum computing. I don’t know much about this topic but it was being discussed by a number of people I respect, so this is a self-serving learning post.

Some learnings so far:

  • Quantum is a hypothetical model of computation. Compared to classical computing in which memory is represented in “bits” as 1’s and 0’s (a bit is the smallest unit of data in a computer), quantum memory stores a quantum state.
  • Quantum states are represented by qubits, basic unit of quantum information. There are two possible outcomes for the measurement of a qubit—usually taken to have the value “0” and “1”, like a bit or binary digit. However, whereas the state of a bit can only be either 0 or 1, the general state of a qubit according to quantum mechanics can be a coherent superposition of both. Moreover, whereas a measurement of a classical bit would not disturb its state, a measurement of a qubit would destroy its coherence and irrevocably disturb the superposition state. It is possible to fully encode one bit in one qubit.
  • Quantum Supremacy is the concept of a crossover point, at which it becomes impossible to do something without representing and computing with quantum states.
  • If we compute using the rules of quantum mechanics, instead of binary logic, some intractable computational tasks become feasible. An important goal in the pursuit of a universal quantum computer is the determination of the smallest computational task that is prohibitively hard for today’s classical computers.
  • Google announced that it has created a 53-qubit processor. The computational task was to sample the output of a pseudo random quantum circuit and perform some operation on it that is really difficult for a classical computer to do. Each sample is represented by a bit-string (e.g. 1100011, 1010101, etc).

I’ll update this as my understanding of this topic increases.