Stanford Scientists Resurrect Niobium for High-Performance Quantum Computing

Scientists led by David Schuster at Stanford University have found a way to engineer high-performing qubits using niobium, a material previously considered underperforming in the field of quantum computing. The team’s design for a niobium-based Josephson junction, the core of a superconducting qubit, has revived niobium as a viable material for quantum technologies. Niobium-based qubits can operate at higher temperatures and across a wider frequency and magnetic field range than their aluminum counterparts. The research, supported by Q-NEXT, a U.S. Department of Energy National Quantum Information Science Research Center, could expand the capabilities of quantum computers, networks, and sensors.

Niobium’s Resurgence in Quantum Science

For a long time, niobium was considered an underperformer in the realm of superconducting qubits. However, recent advancements by scientists supported by Q-NEXT have led to the development of a high-performing niobium-based qubit, leveraging niobium’s superior qualities. This development has reestablished niobium as a viable option for core qubit material.

The Comeback of Niobium in Quantum Technology

Niobium, once a promising candidate for quantum technologies due to its superior superconducting qualities, had been sidelined for the past 15 years due to difficulties in engineering it as a core qubit component. Qubits, the fundamental components of quantum devices, rely on superconductivity to process information. A group led by David Schuster from Stanford University has now demonstrated a method to create niobium-based qubits that rival the state-of-the-art for their class. This development has expanded the possibilities of what can be achieved with qubits.

The Advantages of Niobium in Superconducting Qubits

In the field of superconducting qubits, aluminum has been the dominant material. Aluminum-based superconducting qubits can store information for a relatively long time before the data disintegrates. However, niobium-based qubits have several advantages over their aluminum counterparts. They can operate at higher temperatures, require less cooling, and can operate across a much wider frequency and magnetic field range. Despite these advantages, the short coherence time of niobium-based qubits had been a major drawback.

Overcoming the Limitations of Niobium

The team led by Schuster focused on the niobium Josephson junction, the information-processing heart of the superconducting qubit. They found that the niobium oxide layer in the junction was draining the energy required to sustain quantum states. The team’s breakthrough involved a new junction arrangement and a new fabrication technique that eliminated the energy-draining niobium oxide and reduced energy loss from the junction’s supporting architecture.

The Birth of a New Qubit

The new junction arrangement incorporated aluminum, resulting in a low-loss, trilayer junction. After incorporating their new junction into superconducting qubits, the team achieved a coherence time 150 times longer than its best-performing niobium predecessors. The qubits also exhibited a quality factor, an index of how well a qubit stores energy, that was a 100-fold improvement over previous niobium-based qubits and competitive with aluminum-based qubit quality factors. This development is expected to elevate niobium’s place in the lineup of superconducting qubit materials.