New two-dimensional design of a quantum computer

Standard circuit architecture and our proposed architecture for surface codes with 5 × 5 qubit array. (a) Standard system utilizing global multi-layer structures, a separated qubit layer (top figure), and a control/readout layer (clear layer in bottom figure). Qubits are divided into data qubits (orange circles) and X (blue circles) and Z (green circles) syndrome qubits, and all nearest-neighbor qubits are connected by inter-qubit wiring. Vertical arrows indicate input/output wiring. (b) Folding operation of proposed architecture. In the horizontal direction, interconnections of the 2D qubit array are stretched out while maintaining the resonator frequency. At each qubit column, the interconnection is folded. (c) Proposed planar architecture for surface code. After process (b), the proposed architecture has completely planar external wiring (no arrow intersect any wiring, external lines, and inter-qubit connections) with the help of pseudo-2D interconnections.

Scientists from Tokyo University of Science, RIKEN Centre for Emergent Matter Science, Japan, and University of Technology, Sydney, have collaborated and proposed a novel two-dimensional design that can be constructed using existing integrated circuit technology. This design solves typical problems facing the current three-dimensional packaging for scaled-up quantum computers, bringing the future one step closer.

The theoretical requirement for quantum computers is that these are arranged in two-dimensional (2-D) arrays, where each qubit is both coupled with its nearest neighbor and connected to the necessary external control lines and devices. When the number of qubits in an array is increased, it becomes difficult to reach qubits in the interior of the array from the edge. The need to solve this problem has so far resulted in complex three-dimensional (3-D) wiring systems across multiple planes in which many wires intersect, making their construction a significant engineering challenge.

The team has solved this problem and presented a modified superconducting micro-architecture that does not require any 3-D external line technology and reverts to a completely planar design.

The scientists began with a qubit square lattice array and stretched out each column in the 2-D plane. They then folded each successive column on top of each other, forming a dual one-dimensional array called a bilinear array. This put all qubits on the edge and simplified the arrangement of the required wiring system. The system is 2-D. In this new architecture, some of the inter-qubit wiring – each qubit is also connected to all adjacent qubits in an array – does overlap, but because these are the only overlaps in the wiring, simple local 3-D systems such as airbridges at the point of overlap are enough and the system overall remains in 2-D. As you can imagine, this simplifies its construction considerably. (

The study has been published in the New Journal of Physics.

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