Supercurrent method could read a qubit's full state without destroying it

[Matt77]

Physicists in Brazil and China have proposed a gentler way to read quantum information. Interesting Engineering reports on a method from José Carlos Egues at the University of São Paulo and Yugui Yao at the Beijing Institute of Technology that reads a qubit's state without extra helper qubits or resets

The idea uses an Andreev qubit, a quantum dot in an indium arsenide nanowire placed between two superconductors. The qubit sits in a closed superconducting loop, with a sensitive magnetometer called a SQUID nearby to detect tiny magnetic fields

The qubit's own supercurrent has a constant part and an oscillating part, and it flows without any applied voltage. Measuring both parts reveals the proportions of 0 and 1 in the superposition and the phase between them, which is everything needed to describe the state

In simulations, the method reconstructed qubit states with accuracies of 99.52, 99.81 and 99.85 percent, depending on how many measurements were taken. The authors say that meets common error correction thresholds. Egues stressed that the method does not remove the fundamental problem of quantum measurement, but because the coupling is very weak, the instrument disturbs the qubit only slightly. The work is published in Physical Review B

Gentle measurement is a big deal for quantum computing, because measuring usually destroys the state you care about. This is purely theoretical for now, and the device has not been built. If it works in practice, it could simplify readout for superconducting qubits

Could weak measurement methods like this change how qubits are read? And how long before someone builds the device?

Supercurrent could reveal quantum information without destroying itinterestingengineering.com