Hexbyte – Tech News – Ars Technica |
Rotating wheel of whips —
Microwaves plus clever tricks make qubits more immune to noise.
Companies like IBM and Google have leapt at the opportunity to build toy quantum computers. They’ve produced nice interfaces so you can play quantum computing games. The access frameworks they’ve provided makes me feel like we are about to break out in useful quantum computers.
The public interface, however, hides the relatively slow progress in solving hardware problems. In particular, qubits don’t live very long, so not much computation can be done. Now, in a very nice bit of work, a team of researchers from China have put together qubits that last about 10-15 times longer.
Hexbyte – Tech News – Ars Technica | The case of the vanishing qubits
To get your head around this result, we need to understand three key features of how information is stored and processed in quantum computing. Information is stored in qubits, but a qubit does not just hold a one or a zero; it is really a probability of being a one or a zero. Computations are performed by modifying the probability of a qubit being a one or a zero when it’s measured.
A second important point is that during a computation, the qubit probabilities are all linked to each other—measuring one qubit restricts (or even reveals) the value of the linked qubits.
A third feature is that between computational operations, the probabilities do not stay constant. Instead, they are like swings, oscillating between unity (you will always measure the qubit to be one) and zero (you will always measure the qubit to be zero). Computation depends on measuring at the right time.
Since the qubits are all linked—so they can’t swing back and forth in isolation—they have to swing together, otherwise the linked probabilities between qubits will break. Once they break, you can’t compute anything anymore.
Noise also plays a role. Noise pushes the swings, randomly speeding or slowing them. Each qubit slowly (or not so slowly) moves out of sync with its neighbors. I cannot, based on the amount of time the qubit has been left to swing, predict the probability of a single qubit anymore. Effectively, the quantumness of the qubit has gone.
As a result of these issues, the sort of qubit that the researchers in this work u