

Google quantum computer test shows breakthrough is within reach  
Google has come up with a strategy for demonstrating quantum supremacy,
the claim that quantum computers can perform tasks that no current
computers can.
Their plan is based on simulating coin flips. An ordinary computer does this by storing two numbers and choosing one of them at random each time. To simulate 50 coin tosses, it just selects 50 times in a row. This is simple with regular coins, but if the coins behave like particles obeying the laws of quantum mechanics, things get more complicated. In that case, we cannot know whether any individual coin turned up heads or tails without knowing about all the other coins, a phenomenon known as quantum entanglement. The problem of simulating coin tosses with quantum entanglement is called quantum sampling. Computers work sequentially, so choosing 50 numbers at the same time is not something they can do. For this reason, the Google group argues, quantum sampling would require storing all possible configurations of all 50 coin tosses, so that all of the coins can be thrown simultaneously. Since one bit can only store one of two states, heads or tails, covering all possible configurations for 50 coins takes thousands of terabytes of data storage. This is where quantum computers come in. They’re based on qubits, which can be in two states at the same time. This makes it possible to store the probability distribution of all the configurations at once using a single qubit for each coin. For this reason, the Google group argues, quantum sampling would be easy for a quantum computer. The team demonstrates quantum sampling up to nine coins with high accuracy using their 9qubit quantum computer. 'If similar error rates are achievable in future devices with around 50 qubits, we will be able to explore quantum dynamics that are inaccessible otherwise,' Google's proposal states. This way, quantum computers of the near future can be used to study physics, a huge stepup from their infancy when they couldn’t do anything practical. 


