**(MirageNews)** Yasunobu Nakamura, Team Leader, Superconducting Quantum Electronics Research Team has written this extensive explanation as to why he believes a new circuit-wiring scheme developed over the last three years by RIKEN, in collaboration with other institutes, opens the door to scaling up to 100 or more qubits within the next decade

Challenge one: Scalability

The challenge of scalability arises from the fact that each qubit then needs wiring and connections that produce controls and readouts with minimal crosstalk. As we moved past tiny two-by-two or four-by-four arrays of qubits, we have realized just how densely the associated wiring can be packed, and we’ve had to create better systems and fabrication methods to avoid getting our wires crossed, literally.

Challenge two: Stability

In theory, one way we could deal with instability is to use quantum error correction, where we exploit several physical qubits to encode a single ‘logical qubit’, and apply an error correction protocol that can diagnose and fix errors to protect the logical qubit. But realizing this is still far off for many reasons, not the least of which is the problem of scalability.

Challenge Three: Quantum Circuits

We at Riken eventually came up with the idea of using a superconducting circuit. The superconducting state is free of all electrical resistance and losses, and so it is streamlined to respond to small quantum-mechanical effects.

Hybrid Systems:

We use our superconducting quantum-circuit platform in combination with other quantum-mechanical systems. This hybrid quantum system allows us to measure a single quantum reaction within collective excitations-be it precessions of electron spins in a magnet, crystal lattice vibrations in a substrate, or electromagnetic fields in a circuit-with unprecedented sensitivity.

Quantum internet

Interfacing a superconducting quantum computer to an optical quantum communication network is another future challenge for our hybrid system.