Superconducting Qubit Array could be a non-Dwave quantum computer approach that is nearly ready to scale

A new five-qubit array from UCSB’s Martinis Group is on the threshold of making a quantum computer technologically feasible to build

“Even the best state-of-the-art [quantum computer] hardware is unreliable. Our paper shows that for the first time reliability has been reached.”

While the Martinis Group has shown logic operations at the threshold, the array must operate below the threshold to provide an acceptable margin of error. “Qubits are faulty, so error correction is necessary,” said graduate student and co-lead author Julian Kelly who worked on the five-qubit array.

“We need to improve and we would like to scale up to larger systems,” said lead author Rami Barends, a postdoctoral fellow with the group. “The intrinsic physics of control and coupling won’t have to change but the engineering around it is going to be a big challenge.”

a, Optical image of the integrated Josephson quantum processor, consisting of aluminium (dark) on sapphire (light). The five cross-shaped devices (Q0–Q4) are the Xmon variant of the transmon qubits30, placed in a linear array. To the left of the qubits are five meandering coplanar waveguide resonators used for individual state readout. Control wiring is brought in from the contact pads at the edge of the chip, ending at the right of the qubits. b, Circuit diagram. Our architecture uses direct, nearest-neighbour coupling of the qubits (red/orange), made possible by the nodal connectivity of the Xmon qubit. Using a single readout line, each qubit can be measured using frequency-domain multiplexing (blue). Individual qubits are driven through capacitively coupled microwave control lines (XY), and frequency control is achieved through inductively coupled d.c. lines (Z) (violet). c, Schematic representation of an entangling operation using a controlled-phase gate with unitary representation UCZ; (I) qubits at rest, at distinct frequencies with minimal interaction; (II) when brought near resonance, the state-dependent frequency shift brings about a rotation conditional on the qubit states; (III) qubits are returned to their rest frequency.

Nature – Superconducting quantum circuits at the surface code threshold for fault tolerance

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