New Qubit Architecture Enables Easier Manufacturing Without Performance Loss

Scientists at Brookhaven National Laboratory have made a breakthrough in quantum computer manufacturing, demonstrating that a new type of qubit architecture can perform comparably to current leading designs without compromising performance. Led by Mingzhao Liu and Charles Black, the researchers showed that qubits with constriction junctions, which are easier to manufacture, can rival those with traditional SIS junctions.

Constriction junctions consist of two superconducting layers connected by a thin wire, making them more compatible with standard semiconductor manufacturing methods. The team’s analysis revealed that by using specific materials and designing the junction’s size and shape, they could overcome the limitations of constriction junctions, including increased current flow and linearity issues. This development brings us closer to scalable quantum computers, and Brookhaven Lab is working with the Co-design Center for Quantum Advantage to explore new materials and manufacturing techniques.

Constriction Junctions: A Promising Qubit Architecture for Scalable Quantum Computing

The quest for scalable quantum computing has led researchers to explore alternative qubit architectures that can be easily manufactured without compromising performance. Scientists from the U.S. Department of Energy’s Brookhaven National Laboratory have demonstrated that constriction junctions, a type of qubit architecture, can perform comparably to traditional superconducting qubits with SIS (superconductor-insulator-superconductor) junctions.

Overcoming Current Flow and Linearity Challenges

Constriction junctions, which consist of two superconducting layers connected by a thin wire, inherently conduct more current than SIS junctions. However, this increased current flow can be mitigated by using less traditional superconducting metals that do not conduct as well. The researchers found that the constriction wire would need to be impractically thin if they used aluminum, tantalum, or niobium, but other superconductors could allow for practical dimensions.

Moreover, constriction junctions behave differently from SIS counterparts, exhibiting more linearity, which is less ideal for qubit architectures. However, the scientists discovered that the nonlinearity of constriction junctions can be tuned through the selection of a superconducting material and the design of the junction’s size and shape.

Tuning Nonlinearity and Material Properties

The researchers identified specific tradeoffs between a material’s ability to carry electricity (determined by its resistance) and the junction’s nonlinearity. For example, for qubits operating between 5 and 10 gigahertz, which is typical for today’s electronics, certain combinations of material properties are not workable.

However, with materials that meet the criteria outlined by the Brookhaven scientists, qubits with constriction junctions can operate similarly to qubits with SIS junctions. The researchers are currently exploring materials such as superconducting transition metal silicides, which are already used in semiconductor manufacturing and have captured their attention.

Co-Design Principle and Interdisciplinary Collaboration

This work embodies the co-design principle of C2QA (Center for Quantum Computing and Artificial Intelligence), where Liu and Black explored a qubit architecture that could satisfy the demands of quantum computing and align with current electronics manufacturing capabilities. The collaboration between materials scientists, physicists, and engineers is crucial in realizing scalable quantum computers.

As Charles Black noted, “These types of interdisciplinary collaborations will continue bringing us closer to realizing scalable quantum computers.” The Brookhaven National Laboratory’s research demonstrates a promising step towards achieving this goal.